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  • 1. IPV6 PDF generated using the open source mwlib toolkit. See for more information. PDF generated at: Mon, 29 Aug 2011 16:36:25 UTC
  • 2. ContentsArticlesint 1 Portable Document Format 1 IPv6 20References Article Sources and Contributors 34 Image Sources, Licenses and Contributors 35Article Licenses License 36
  • 3. 1 intPortable Document Format Portable Document Format Adobe Reader icon Filename extension .pdf Internet media type application/pdf application/x-pdf application/x-bzpdf application/x-gzpdf Type code PDF (including a single space) Uniform Type Identifier com.adobe.pdf Magic number %PDF Developed by Adobe Systems Initial release 1993 Latest release 1.7 Standard(s) [1] ISO 32000-1:2008 Website [2] Adobe PDF Reference ArchivesPortable Document Format (PDF) is an open standard for document exchange. This file format created by AdobeSystems in 1993 is used for representing documents in a manner independent of application software, hardware, andoperating systems.[3] Each PDF file encapsulates a complete description of a fixed-layout flat document, includingthe text, fonts, graphics, and other information needed to display it.In 1991 Adobe Systems co-founder John Warnock outlined a system called "Camelot"[4] that evolved into thePortable Document Format (PDF).While the PDF specification was available for free since at least 2001,[5] PDF was originally a proprietary formatcontrolled by Adobe, and was officially released as an open standard on July 1, 2008, and published by theInternational Organization for Standardization as ISO 32000-1:2008.[1] [6] In 2008, Adobe published a Public PatentLicense to ISO 32000-1 granting a royalty-free rights for all patents owned by Adobe that are necessary to make,use, sell and distribute PDF compliant implementations.[7]HistoryPDFs adoption in the early days of the formats history was slow.[8] Adobe Acrobat, Adobes suite for reading andcreating PDF files, was not freely available; early versions of PDF had no support for external hyperlinks, reducingits usefulness on the Internet; the larger size of a PDF document compared to plain text required longer downloadtimes over the slower modems common at the time; and rendering PDF files was slow on the less powerful machinesof the day.Additionally, there were competing formats such as DjVu (still developing), Envoy, Common Ground Digital Paper,Farallon Replica and even Adobes own PostScript format (.ps); in those early years, PDF was popular mainly in
  • 4. Portable Document Format 2 desktop publishing workflows. Adobe soon started distributing its Acrobat Reader (now Adobe Reader) program at no cost, and continued supporting the original PDF, which eventually became the de facto standard for printable documents on the web (a standard web document). Adobes PDF specifications Adobe changed the PDF specification several times and continues to develop new specifications with new versions of Adobe Acrobat. There have been nine versions of PDF with corresponding Acrobat releases:[9] • 1993 – PDF 1.0 / Acrobat 1.0 • 1994 – PDF 1.1 / Acrobat 2.0 • 1996 – PDF 1.2 / Acrobat 3.0 • 1999 – PDF 1.3 / Acrobat 4.0 • 2001 – PDF 1.4 / Acrobat 5.0 • 2003 – PDF 1.5 / Acrobat 6.0 • 2005 – PDF 1.6 / Acrobat 7.0 • 2006 – PDF 1.7 / Acrobat 8.0 • 2008 – PDF 1.7, Adobe Extension Level 3 / Acrobat 9.0 • 2009 – PDF 1.7, Adobe Extension Level 5 / Acrobat 9.1 The ISO standard ISO 32000-1:2008 and Adobe PDF 1.7 are technically consistent[10] . Adobe declared that it is not producing a PDF 1.8 Reference. The future versions of the PDF Specification will be produced by ISO technical committees. However, Adobe published documents specifying what extended features for PDF, beyond ISO 32000-1 (PDF 1.7), are supported in its newly released products. This makes use of the extensibility features of PDF as documented in ISO 32000-1 in Annex E. Adobe declared all extended features in Adobe Extension Level 3 and 5 have been accepted for a new proposal of ISO 32000-2 (a.k.a. PDF 2.0).[11] The specifications for PDF are backward inclusive. The PDF 1.7 specification includes all of the functionality previously documented in the Adobe PDF Specifications for versions 1.0 through 1.6. Where Adobe removed certain features of PDF from their standard, they too are not contained in ISO 32000-1.[1] PDF documents conforming to ISO 32000-1 carry the PDF version number 1.7. Documents containing Adobe extended features still carry the PDF base version number 1.7 but also contain an indication of which extension was followed during document creation.[11] Adobes versions Version [1] Year of New features Acrobat Edition publication Reader version support 1.0 First 1993 Carousel 1.1 First, 1996 [12] 2.0 Passwords, encryption (MD5, RC4 40bit), device-independent color, threads and links revised 1.2 First, 1996 3.0 Interactive page elements (radio buttons, checkboxes &c); interactive, fill-in forms revised (AcroForm); Forms Data Format (FDF) for interactive form data that can be imported, exported, transmitted and received from the Web; mouse events; external movie reproduction; external or embedded sound reproduction; zlib/deflate compression of text or [12] binary data; Unicode; advanced color features and image proxying
  • 5. Portable Document Format 3 1.3 Second 2000 4.0 Digital signatures; ICC and DeviceN color spaces; JavaScript actions; embedded file streams of any type (e.g. used for attachments); new annotation types; new features of the Adobe PostScript Language Level 3 imaging model; masked images; alternate representations for images; smooth shading; enhanced page numbering; Web capture — a facility for capturing information from World Wide Web and converting it to PDF; representation of logical structure independently of graphical structure; additional support for CIDFonts; data structures for mapping strings and numbers to PDF objects; information for prepress production workflows support; new functions for several function object types [13] [14] that represent parameterized classes of functions 1.4 Third 2001 5.0 JBIG2; transparency; RC4 encryption key lengths greater than 40 bits (40–128 bits); enhancements to interactive forms and Forms Data Format (FDF), XML form submissions, embedded FDF files, Unicode specification of field export values, remote collaboration and digital signatures in FDF files; accessibility to disabled users; metadata streams using XML — Extensible Metadata Platform (XMP); tagged PDF; inclusion of printer’s marks; display and preview of production-related page boundaries; new predefined CMaps; alternate presentations; importing content from one PDF document into another; EmbeddedFiles entry in the PDF document’s name dictionary — a standard location for the embedded [14] [15] data; OCR text layer 1.5 Fourth 2003 JPEG 2000; enhanced support for embedding and playback of multimedia; object streams; 6.0 cross reference streams; XML Forms Data Format (XFDF) for interactive form submission (replaced the XML format in PDF 1.4); support for forms, rich text elements and attributes based on Adobe’s XML Forms Architecture (XFA) 2.02; public-key security handlers using PKCS#7 (introduced in PDF 1.3 but not documented in the Reference until 1.5), public-key encryption, permissions — usage rights (UR) signatures (does not require document encryption), PKCS#7 with SHA-1, RSA up to 4096-bits; security handler can use its own encryption and decryption algorithms; document sections selectively viewed or hidden by authors or readers — for items such as CAD drawings, layered artwork, maps, and multi-language documents; Alternate Presentations — the only type is slideshow — [14] [16] invoked by means of JavaScript actions (Adobe Reader supports only SVG 1.0) [17] ; support for MS Windows 98 dropped. To view and print newer version PDFs, such [18] as those at the IRS , with older versions of Reader requires downloading in Google Docs "Quick View" simplified PDF format. 1.6 Fifth 2004 3D artwork, e.g. support for Universal 3D file format; OpenType font embedding; support 7.0 for XFA 2.2 rich text elements and attributes; AES encryption; PKCS#7 with SHA256, DSA up to 4096-bits; NChannel color spaces; additional support for embedded file attachments, including cross-document linking to and from embedded files; enhancements and clarifications to digital signatures related to usage rights and modification detection and [14] prevention signatures Sixth (ISO 2006 Increased presentation of 3D artwork; XFA 2.4 rich text elements and attributes; multiple 8 1.7 first) file attachments (portable collections); document requirements for a PDF consumer (ISO application; new string types: PDFDocEncoded string, ASCII string, byte string; PKCS#7 32000-1:2008 [1] [11] with SHA384, SHA512 and RIPEMD160 ) 1.7 Extension 2008 256-bit AES encryption; incorporation of XFA Datasets into a file conforming PDF/A-2; 9 Level 3 improved attachment of Flash applications, video (including Flash video with H.264), audio, and other multimedia, two-way scripting bridge between Flash and conforming applications; XFA 2.5 and 2.6 rich text conventions 1.7 Extension 2009 XFA 3.0 9.1 Level 5 2011 [11] X (10) 1.7 Extension Specification not published as of May 2011 [19] Level 8
  • 6. Portable Document Format 4 Standardization Specialized subsets of PDF The following specialized subsets of PDF specification has been standardized as ISO standards (or are in standardization process):[1] [20] [21] [22] • PDF/X (since 2001 - series of ISO 15929 and ISO 15930 standards) - a.k.a. "PDF for Exchange" - for the Graphic technology - Prepress digital data exchange - (working in ISO Technical committee 130), based on PDF 1.3, PDF 1.4 and later also PDF 1.6 • PDF/A (since 2005 - series of ISO 19005 standards) - a.k.a. "PDF for Archive" - Document management - Electronic document file format for long-term preservation (working in ISO Technical committee 171), based on PDF 1.4 and later also ISO 32000-1 - PDF 1.7 • PDF/E (since 2008 - ISO 24517) - a.k.a. "PDF for Engineering" - Document management - Engineering document format using PDF (working in ISO Technical committee 171), based on PDF 1.6 • PDF/VT (since 2010 - ISO 16612-2) - a.k.a "PDF for exchange of variable data and transactional (VT) printing" - Graphic technology - Variable data exchange (working in ISO Technical committee 130), based on PDF 1.6 as restricted by PDF/X-4 and PDF/X-5[23] • PDF/UA (under development in 2011 - ISO/DIS 14289-1) - a.k.a. "PDF for Universal Access" - Document management applications - Electronic document file format enhancement for accessibility (working in ISO Technical committee 171), based on ISO 32000-1 - PDF 1.7 There is also the PDF/H, a.k.a. "PDF Healthcare", a Best Practices Guide (BPG), supplemented by an Implementation Guide (IG), published in 2008. PDF Healthcare is not a standard or proposed standard, but only a guide for use with existing standards and other technologies. It is supported by the standards development organizations ASTM and AIIM. PDF/H BPG is based on PDF 1.6.[24] [25] [26] Full function PDF PDF 1.7 The final revised documentation for PDF 1.7 was approved by ISO Technical Committee 171 in January 2008 and published as ISO 32000-1:2008 on July 1, 2008. PDF is now a published ISO standard, titled Document management—Portable document format—Part 1: PDF 1.7. ISO 32000-1:2008 is the first ISO standard for the full function PDF. The previous ISO PDF standards (PDF/A, PDF/X, etc.) are for more specialized uses. The ISO 32000-1 includes all of the functionality previously documented in the Adobe PDF Specifications for versions 1.0 through 1.6. Adobe removed certain features of PDF from previous versions; these features are not contained in PDF 1.7 either.[1] ISO 32000 document was prepared by Adobe Systems Incorporated based upon PDF Reference, sixth edition, Adobe Portable Document Format version 1.7, November 2006. It was reviewed, edited and adopted, under a special fast-track procedure, by ISO Technical Committee 171 (ISO/TC 171), Document management application, Subcommittee SC 2, Application issues, in parallel with its approval by the ISO member bodies. According to the ISO PDF standard abstract:[27] ISO 32000-1:2008 specifies a digital form for representing electronic documents to enable users to exchange and view electronic documents independent of the environment in which they were created or the environment in which they are viewed or printed. It is intended for the developer of software that creates PDF files (conforming writers), software that reads existing PDF files and interprets their contents for display and interaction (conforming readers) and PDF products that read and/or write PDF files for a variety of other purposes (conforming products).
  • 7. Portable Document Format 5 PDF 2.0 A new version of PDF standard is under development under the name ISO/CD 32000-2 - Document management—Portable document format—Part 2: PDF 2.0 (as of July 2011).[28] PDF 2.0 was accepted by ISO as a new proposal in 2009 (ISO/NP 32000-2). Adobe has submitted the Adobe Extension Level 5 and Adobe Extension Level 3 specifications to ISO for inclusion into the next version of the ISO 32000 specification. Adobe declared they have all been accepted for part 2 of ISO 32000.[11] Technical foundations Anyone may create applications that can read and write PDF files without having to pay royalties to Adobe Systems; Adobe holds patents to PDF, but licenses them for royalty-free use in developing software complying with its PDF specification.[29] The PDF combines three technologies: • A subset of the PostScript page description programming language, for generating the layout and graphics. • A font-embedding/replacement system to allow fonts to travel with the documents. • A structured storage system to bundle these elements and any associated content into a single file, with data compression where appropriate. PostScript PostScript is a page description language run in an interpreter to generate an image, a process requiring many resources. It can handle not just graphics, but standard features of programming languages such as if and loop commands. PDF is largely based on PostScript but simplified to remove flow control features like these, while graphics commands such as lineto remain. Often, the PostScript-like PDF code is generated from a source PostScript file. The graphics commands that are output by the PostScript code are collected and tokenized; any files, graphics, or fonts to which the document refers also are collected; then, everything is compressed to a single file. Therefore, the entire PostScript world (fonts, layout, measurements) remains intact. As a document format, PDF has several advantages over PostScript: • PDF contains tokenized and interpreted results of the PostScript source code, for direct correspondence between changes to items in the PDF page description and changes to the resulting page appearance. • PDF (from version 1.4) supports true graphic transparency; PostScript does not. • PostScript is an interpretive programming language with an implicit global state, so instructions accompanying the description of one page can affect the appearance of any following page. Therefore, all preceding pages in a PostScript document must be processed in order to determine the correct appearance of a given page, whereas each page in a PDF document is unaffected by the others. As a result, PDF viewers allow the user to quickly jump to the final pages of a long document, whereas a Postscript viewer needs to process all pages sequentially before being able to display the destination page (unless the optional PostScript Document Structuring Conventions have been carefully complied with).
  • 8. Portable Document Format 6 Technical overview File structure A PDF file consists primarily of objects, of which there are eight types:[30] • Boolean values, representing true or false • Numbers • Strings • Names • Arrays, ordered collections of objects • Dictionaries, collections of objects indexed by Names • Streams, usually containing large amounts of data • The null object Objects may be either direct (embedded in another object) or indirect. Indirect objects are numbered with an object number and a generation number. An index table called the xref table gives the byte offset of each indirect object from the start of the file.[31] This design allows for efficient random access to the objects in the file, and also allows for small changes to be made without rewriting the entire file (incremental update). Beginning with PDF version 1.5, indirect objects may also be located in special streams known as object streams. This technique reduces the size of files that have large numbers of small indirect objects and is especially useful for Tagged PDF. There are two layouts to the PDF files—non-linear (not "optimized") and linear ("optimized"). Non-linear PDF files consume less disk space than their linear counterparts, though they are slower to access because portions of the data required to assemble pages of the document are scattered throughout the PDF file. Linear PDF files (also called "optimized" or "web optimized" PDF files) are constructed in a manner that enables them to be read in a Web browser plugin without waiting for the entire file to download, since they are written to disk in a linear (as in page order) fashion.[11] PDF files may be optimized using Adobe Acrobat software or QPDF. Imaging model The basic design of how graphics are represented in PDF is very similar to that of PostScript, except for the use of transparency, which was added in PDF 1.4. PDF graphics use a device independent Cartesian coordinate system to describe the surface of a page. A PDF page description can use a matrix to scale, rotate, or skew graphical elements. A key concept in PDF is that of the graphics state, which is a collection of graphical parameters that may be changed, saved, and restored by a page description. PDF has (as of version 1.6) 24 graphics state properties, of which some of the most important are: • The current transformation matrix (CTM), which determines the coordinate system • The clipping path • The color space • The alpha constant, which is a key component of transparency
  • 9. Portable Document Format 7 Vector graphics Vector graphics in PDF, as in PostScript, are constructed with paths. Paths are usually composed of lines and cubic Bézier curves, but can also be constructed from the outlines of text. Unlike PostScript, PDF does not allow a single path to mix text outlines with lines and curves. Paths can be stroked, filled, or used for clipping. Strokes and fills can use any color set in the graphics state, including patterns. PDF supports several types of patterns. The simplest is the tiling pattern in which a piece of artwork is specified to be drawn repeatedly. This may be a colored tiling pattern, with the colors specified in the pattern object, or an uncolored tiling pattern, which defers color specification to the time the pattern is drawn. Beginning with PDF 1.3 there is also a shading pattern, which draws continuously varying colors. There are seven types of shading pattern of which the simplest are the axial shade (Type 2) and radial shade (Type 3). Raster images Raster images in PDF (called Image XObjects) are represented by dictionaries with an associated stream. The dictionary describes properties of the image, and the stream contains the image data. (Less commonly, a raster image may be embedded directly in a page description as an inline image.) Images are typically filtered for compression purposes. Image filters supported in PDF include the general purpose filters • ASCII85Decode a deprecated filter used to put the stream into 7-bit ASCII • ASCIIHexDecode similar to ASCII85Decode but less compact • FlateDecode a commonly used filter based on the zlib/deflate algorithm (a.k.a. gzip, but not zip) defined in RFC 1950 and RFC 1951; introduced in PDF 1.2; it can use one of two groups of predictor functions for more compact zlib/deflate compression: Predictor 2 from the TIFF 6.0 specification and predictors (filters) from the PNG specification (RFC 2083) • LZWDecode a deprecated filter based on LZW Compression; it can use one of two groups of predictor functions for more compact LZW compression: Predictor 2 from the TIFF 6.0 specification and predictors (filters) from the PNG specification • RunLengthDecode a simple compression method for streams with repetitive data using the Run-length encoding algorithm and the image-specific filters • DCTDecode a lossy filter based on the JPEG standard • CCITTFaxDecode a lossless bi-level (black/white) filter based on the Group 3 or Group 4 CCITT (ITU-T) fax compression standard defined in ITU-T T.4 and T.6 • JBIG2Decode a lossy or lossless bi-level (black/white) filter based on the JBIG2 standard, introduced in PDF 1.4 • JPXDecode a lossy or lossless filter based on the JPEG 2000 standard, introduced in PDF 1.5 Normally all image content in a PDF is embedded in the file. But PDF allows image data to be stored in external files by the use of external streams or Alternate Images. Standardized subsets of PDF, including PDF/A and PDF/X, prohibit these techniques. Text Text in PDF is represented by text elements in page content streams. A text element specifies that characters should be drawn at certain positions. The characters are specified using the encoding of a selected font resource. Fonts A font object in PDF is a description of a digital typeface. It may either describe the characteristics of a typeface, or it may include an embedded font file. The latter case is called an embedded font while the former is called an unembedded font. The font files that may be embedded are based on widely used standard digital font formats: Type 1 (and its compressed variant CFF), TrueType, and (beginning with PDF 1.6) OpenType. Additionally PDF supports the Type 3 variant in which the components of the font are described by PDF graphic operators.
  • 10. Portable Document Format 8 Standard Type 1 Fonts (Standard 14 Fonts) There are fourteen typefaces known as standard 14 fonts that have a special significance to PDF documents: • Times (v3) (in regular, italic, bold, and bold italic) • Courier (in regular, oblique, bold and bold oblique) • Helvetica (v3) (in regular, oblique, bold and bold oblique) • Symbol • Zapf Dingbats These fonts are sometimes also referred to as the "base fourteen fonts".[32] These fonts, or suitable substitute fonts with the same metrics, must always be available in all PDF readers and so need not be embedded in a PDF.[33] PDF viewers must know about the metrics of these fonts. Other fonts may be substituted if they are not embedded in a PDF. Encodings Within text strings, characters are shown using character codes (integers) that map to glyphs in the current font using an encoding. There are a number of predefined encodings, including WinAnsi, MacRoman, and a large number of encodings for East Asian languages, and a font can have its own built-in encoding. (Although the WinAnsi and MacRoman encodings are derived from the historical properties of the Windows and Macintosh operating systems, fonts using these encodings work equally well on any platform.) PDF can specify a predefined encoding to use, the fonts built-in encoding or provide a lookup table of differences to a predefined or built-in encoding (not recommended with TrueType fonts).[34] The encoding mechanisms in PDF were designed for Type 1 fonts, and the rules for applying them to TrueType fonts are complex. For large fonts or fonts with non-standard glyphs, the special encodings Identity-H (for horizontal writing) and Identity-V (for vertical) are used. With such fonts it is necessary to provide a ToUnicode table if semantic information about the characters is to be preserved. Transparency The original imaging model of PDF was, like PostScripts, opaque: each object drawn on the page completely replaced anything previously marked in the same location. In PDF 1.4 the imaging model was extended to allow transparency. When transparency is used, new objects interact with previously marked objects to produce blending effects. The addition of transparency to PDF was done by means of new extensions that were designed to be ignored in products written to the PDF 1.3 and earlier specifications. As a result, files that use a small amount of transparency might view acceptably in older viewers, but files making extensive use of transparency could view completely wrongly in an older viewer without warning. The transparency extensions are based on the key concepts of transparency groups, blending modes, shape, and alpha. The model is closely aligned with the features of Adobe Illustrator version 9. The blend modes were based on those used by Adobe Photoshop at the time. When the PDF 1.4 specification was published the formulas for calculating blend modes were kept secret by Adobe. They have since been published.[35] The concept of a transparency group in PDF specification is independent of existing notions of "group" or "layer" in applications such as Adobe Illustrator. Those groupings reflect logical relationships among objects that are meaningful when editing those objects, but they are not part of the imaging model.
  • 11. Portable Document Format 9 Interactive elements PDF files may contain interactive elements such as annotations and form fields. Interactive Forms is a mechanism to add forms to the PDF file format. PDF currently supports two different methods for integrating data and PDF forms. Both formats today coexist in PDF specification:[36] [37] [38] [39] • AcroForms (also known as Acrobat forms), introduced in the PDF 1.2 format specification and included in all later PDF specifications. • Adobe XML Forms Architecture (XFA) forms, introduced in the PDF 1.5 format specification. The XFA specification is not included in the PDF specification, it is only referenced as an optional feature. Adobe XFA Forms are not compatible with AcroForms.[40] AcroForms AcroForms were introduced in the PDF 1.2 format. AcroForms permit using objects (text boxes, Radiobuttons, etc.) and some code (JavaScript). Alongside the standard PDF action types, interactive forms (AcroForms) support submitting, resetting, and importing data. The "submit" action transmits the names and values of selected interactive form fields to a specified uniform resource locator (URL). Interactive form field names and values may be submitted in any of the following formats, (depending on the settings of the action’s ExportFormat, SubmitPDF, and XFDF flags):[36] • HTML Form format (HTML 4.01 Specification since PDF 1.5; HTML 2.0 since 1.2) • Forms Data Format (FDF) • XML Forms Data Format (XFDF) (external XML Forms Data Format Specification, Version 2.0; supported since PDF 1.5; it replaced the "XML" form submission format defined in PDF 1.4.) • PDF (the entire document can be submitted rather than individual fields and values). (defined in PDF 1.4) AcroForms can keep form field values in external stand-alone files containing key:value pairs. The external files may use Forms Data Format (FDF) and XML Forms Data Format (XFDF) files.[41] [42] [43] The usage rights (UR) signatures define rights for import form data files in FDF, XFDF and text (CSV/TSV) formats, and export form data files in FDF and XFDF formats.[36] Forms Data Format (FDF) Forms Data Format (FDF) Filename extension .fdf Internet media type application/vnd.fdf[44] Type code FDF Developed by Adobe Systems Initial release 1996 (PDF 1.2) Extended from PDF Extended to XFDF Standard(s) ISO 32000-1:2008 The Forms Data Format (FDF) is based on PDF, it uses the same syntax and has essentially the same file structure, but is much simpler than PDF, since the body of an FDF document consists of only one required object. Forms Data Format is defined in the PDF format specification (since PDF 1.2). The Forms Data Format can be used when submitting form data to a server, receiving the response, and incorporating into the interactive form. It can also be
  • 12. Portable Document Format 10 used to export form data to stand-alone files that can be imported back into the corresponding PDF interactive form. Beginning in PDF 1.3, FDF can be used to define a container for annotations that are separate from the PDF document to which they apply. FDF is typically used to encapsulate information such as X.509 certificates, requests for certificates, directory settings, timestamp server settings, and embedded PDF files for network transmission.[43] The FDF uses the MIME content type application/vnd.fdf, filename extension .fdf and on Mac OS it uses file type FDF .[36] Support for importing and exporting FDF stand-alone files is not widely implemented in free or freeware PDF software. For example, there is no support in Evince, Okular, KPDF or Sumatra PDF. Import support for stand-alone FDF files is implemented in Adobe Reader; export and import support (including saving of FDF data in PDF) is for example implemented in Foxit Reader and PDF-XChange Viewer Free; saving of FDF data in a PDF file is also supported in pdftk. XML Forms Data Format (XFDF) XML Forms Data Format (XFDF) Filename extension .xfdf Internet media type application/vnd.adobe.xfdf[45] Type code XFDF Developed by Adobe Systems Latest release 2.0 Extended from PDF, FDF, XML Website [46] XFDF 2.0 specification XML Forms Data Format (XFDF) is the XML version of Forms Data Format, but the XFDF implements only a subset of FDF containing forms and annotations. There are not XFDF equivalents for some entries in the FDF dictionary - such as the Status, Encoding, JavaScript, Pages keys, EmbeddedFDFs, Differences and Target. In addition, XFDF does not allow the spawning, or addition, of new pages based on the given data; as can be done when using an FDF file. The XFDF specification is referenced (but not included) in PDF 1.5 specification (and in later versions). It is described separately in XML Forms Data Format Specification.[42] The PDF 1.4 specification allowed form submissions in XML format, but this was replaced by submissions in XFDF format in the PDF 1.5 specification. XFDF conforms to the XML standard. XFDF can be used the same way as FDF - e.g. form data is submitted to a server, modifications are made, then sent back and the new form data is imported in an interactive form. It can also be used to export form data to stand-alone files that can be imported back into the corresponding PDF interactive form. A support for importing and exporting FDF stand-alone files is not widely implemented in free or freeware PDF software. Import of XFDF is implemented in Adobe Reader 5 and later versions; import and export is implemented in PDF-XChange Viewer Free; embedding of XFDF data in PDF form is implemented in pdftk (pdf toolkit). Adobe XML Forms Architecture (XFA) In the PDF 1.5 format, Adobe Systems introduced a new, proprietary format for forms, namely Adobe XML Forms Architecture (XFA) forms. The XFA 2.02 is referenced in the PDF 1.5 specification (and also in later versions) but is described separately in Adobe XML Forms Architecture (XFA) Specification, which has several versions.[47] Adobe XFA Forms are not compatible with AcroForms. Adobe Reader contains "disabled features" for use of XFA Forms, that will activate only when opening a PDF document that was created using enabling technology available only from Adobe.[48] [49] The XFA Forms are not compatible with Adobe Reader prior to version 6.
  • 13. Portable Document Format 11 XFA forms can be created and used as PDF files or as XDP (XML Data Package) files. The format of an XFA resource in PDF is described by the XML Data Package Specification.[36] The XDP may be a standalone document or it may in turn be carried inside a PDF document. XDP provides a mechanism for packaging form components within a surrounding XML container. An XDP can also package a PDF file, along with XML form and template data.[47] PDF may contain XFA (in XDP format), but also XFA may contain PDF.[47] When the XFA (XML Forms Architecture) grammars used for an XFA form are moved from one application to another, they must be packaged as an XML Data Package.[50] When the PDF and XFA are combined, the result is a form in which each page of the XFA form overlays a PDF background. This architecture is sometimes referred to as XFAF (XFA Foreground). The alternative is to express all of the form, including boilerplate, directly in XFA. It is sometimes called full XFA.[50] Starting with PDF 1.5, the text contents of variable text form fields, as well as markup annotations may include formatting information (style information). These rich text strings are XML documents that conform to the rich text conventions specified for the XML Forms Architecture specification 2.02, which is itself a subset of the XHTML 1.0 specification, augmented with a restricted set of CSS2 style attributes.[36] In PDF 1.6, PDF supports the rich text elements and attributes specified in the XML Forms Architecture (XFA) Specification, 2.2. In PDF 1.7, PDF supports the rich text elements and attributes specified in the XML Forms Architecture (XFA) Specification, 2.4[36] Logical structure and accessibility A PDF may contain structure information to enable better text extraction and accessibility. When published, PDF/UA, now ISO/AWI 14289 [51], will provide definitive information on how the contents of PDF files are to be tagged with accurate structure information. Tagged PDFs also allow a page-limited reflow of documents for smaller devices, sometimes called "reflowable PDFs".[52] Security and signatures A PDF file may be encrypted for security, or digitally signed for authentication. The standard security provided by Acrobat PDF consists of two different methods and two different passwords, "user password" and "owner password". A PDF document may be protected by password to open (user password) and the document may also specify operations that should be restricted even when the document is decrypted: printing, copying text and graphics out of the document, modifying the document, or adding or modifying text notes and AcroForm fields (using owner password). However, all operations (except the document open password protection, if applicable) which are restricted by "owner" or "user" passwords are trivially circumvented by many commonly available "PDF cracking" software and even freely online,[53] and if circumvented these restrictions no longer let the author control what can and cannot be done with the pdf file once distributed. This warning is also displayed when applying such restrictions using Adobe Acrobat software to create or edit PDF files. Even without removing the password, most freeware or open source PDF readers will ignore the permission "protections" and will allow the user to print or make copy of excerpts of the text as if the document were not limited by password protection. Some solutions, like Adobes LiveCycle Rights Management , are more robust means of information rights management, which can both restrict who can open documents, but also reliably enforce permissions in ways that the standard security handler does not.
  • 14. Portable Document Format 12 Usage rights Beginning with PDF 1.5, Usage rights (UR) signatures are used to enable additional interactive features that are not available by default in a particular PDF viewer application. The signature is used to validate that the permissions have been granted by a bonafide granting authority. For example, it can be used to allow a user:[36] • to save the PDF document along with modified form and/or annotation data • import form data files in FDF, XFDF and text (CSV/TSV) formats • export form data files in FDF and XFDF formats • submit form data • instantiate new pages from named page templates • apply a digital signature to existing digital signature form field • create, delete, modify, copy, import, export annotations For example, Adobe Systems grants permissions to enable additional features in Adobe Reader, using public-key cryptography. Adobe Reader will verify that the signature uses a certificate from an Adobe-authorized certificate authority. The PDF 1.5 specification declares that other PDF viewer applications are free to use this same mechanism for their own purposes.[36] File attachments PDF files can have document-level and page-level file attachments, which the reader can access and open or save to their local filesystem. PDF attachments can be added to existing PDF files for example using pdftk [54]. Adobe Reader provides support for attachments, and poppler based readers like Evince or Okular also have some support for document-level attachments. Metadata PDF files can contain two types of metadata.[55] The first is the Document Information Dictionary, a set of key/value fields such as author, title, subject, creation and update dates. This is stored in the optional Info trailer of the file. A small set of fields is defined, and can be extended with additional text values if required. Later, in PDF 1.4, support was added for the Metadata Streams, using the Extensible Metadata Platform (XMP) to add XML standards-based extensible metadata as used in other file formats. This allows metadata to be attached to any stream in the document, such as information about embedded illustrations, as well as the whole document (attaching to the document catalog), using an extensible schema. Subsets Proper subsets of PDF have been, or are being, standardized under ISO for several constituencies: • PDF/X for the printing and graphic arts as ISO 15930 (working in ISO TC130) • PDF/A for archiving in corporate/government/library/etc environments as ISO 19005 (work done in ISO TC171) • PDF/E for exchange of engineering drawings (work done in ISO TC171) • PDF/UA for universally accessible PDF files A PDF/H variant (PDF for Healthcare) is being developed.[56] However, it may consist more of a set of "best practices" than of a specific format or subset.
  • 15. Portable Document Format 13 Mars Adobe is exploring an XML-based next-generation PDF code named Mars.[57] Information about the Mars file format is published by Adobe at http:/ / www. adobe. com/ go/ mars and also http:/ / labs. adobe. com/ wiki/ index. php/Mars [58]. The format of graphic elements of Mars is sometimes described simply as "SVG", but according to the version 0.8 draft specification of November 2007 (§3 Mars SVG Support) the format is actually merely similar to SVG: it contains both additions to and subtractions from SVG, so it is in general neither viewable by nor creatable with standard SVG tools: some things will look noticeably different between SVG viewers and Mars viewers. The Mars format was effectively dropped in 2008.[59] Technical issues Accessibility PDF files can be created specifically to be accessible for disabled people.[60] [61] [62] [63] [64] Current PDF file formats can include tags (XML), text equivalents, captions, audio descriptions, et cetera. Some software can automatically produce tagged PDFs, however this feature is not always enabled by default. Leading screen readers, including JAWS, Window-Eyes, Hal, and Kurzweil 1000 and 3000 can read tagged PDFs; current versions of the Acrobat and Acrobat Reader programs can also read PDFs aloud.[65] [66] [67] Moreover, tagged PDFs can be re-flowed and magnified for readers with visual impairments. Problems remain with adding tags to older PDFs and those that are generated from scanned documents. In these cases, accessibility tags and re-flowing are unavailable, and must be created either manually or with OCR techniques. These processes are inaccessible to some disabled people. PDF/UA, the PDF/Universal Accessibility Committee, an activity of AIIM, is working on a specification for PDF accessibility based on ISO 32000. One of the significant challenges with PDF accessibility is that PDF documents have three distinct views, which, depending on the documents creation, can be inconsistent with each other. The three views are (i) the physical view, (ii) the tags view, and (iii) the content view. The physical view is displayed and printed (what most people consider a PDF document). The tags view is what screen readers read (useful for people with poor eyesight). The content view is displayed when the document is re-flowed to Acrobat (useful for people with mobility disability). For a PDF document to be accessible, the three views must be consistent with each other.[68] Viruses and exploits PDF attachments carrying viruses were first discovered in 2001. The virus, named "OUTLOOK.PDFWorm" or "Peachy", uses Microsoft Outlook to send itself as an attachment to an Adobe PDF file. It was activated with Adobe Acrobat, but not with Acrobat Reader.[69] From time to time, new vulnerabilities are discovered[70] in various versions of Adobe Reader, prompting the company to issue security fixes. Other PDF readers are also susceptible. One aggravating factor is that a PDF reader can be configured to start automatically if a web page has an embedded PDF file, providing a vector for attack. If a malicious web page contains an infected PDF file that takes advantage of a vulnerability in the PDF reader, the system may be compromised even if the browser is secure. Some of these vulnerabilities are a result of the PDF standard allowing PDF documents to be scripted with JavaScript. Disabling JavaScript execution in the PDF reader can help mitigate such future exploits, although it will not provide protection against exploits in other parts of the PDF viewing software. Security experts say that JavaScript is not essential for a PDF reader, and that the security benefit that comes from disabling JavaScript outweighs any compatibility issues caused.[71] One way of avoiding PDF file exploits is to have a local or web service convert files to another format before viewing.[72]
  • 16. Portable Document Format 14 On March 30, 2010 security researcher Didier Stevens reported an Adobe Reader and Foxit Reader exploit which runs a malicious executable if the user allows it to launch when asked.[73] Usage restrictions and monitoring PDFs may be encrypted so that a password is needed to view or edit the contents. The PDF Reference defines both 40-bit and 128-bit encryption, both making use of a complex system of RC4 and MD5. The PDF Reference also defines ways in which third parties can define their own encryption systems for use in PDF. PDF files may also contain embedded DRM restrictions that provide further controls that limit copying, editing or printing. The restrictions on copying, editing, or printing depend on the reader software to obey them, so the security they provide is limited. The PDF Reference has technical details or see [74] for an end-user overview. Like HTML files, PDF files may submit information to a web server. This could be used to track the IP address of the client PC, a process known as phoning home. After update 7.0.5 to Acrobat Reader, the user will be notified "via a dialogue box that the author of the file is auditing usage of the file, and be offered the option of continuing."[75] Through its LiveCycle Policy Server product, Adobe provides a method to set security policies on specific documents. This can include requiring a user to authenticate and limiting the timeframe a document can be accessed or amount of time a document can be opened while offline. Once a PDF document is tied to a policy server and a specific policy, that policy can be changed or revoked by the owner. This controls documents that are otherwise "in the wild." Each document open and close event can also be tracked by the policy server. Policy servers can be set up privately or Adobe offers a public service through Adobe Online Services. As with other forms of DRM, adherence to these policies and restrictions may or may not be enforced by the reader software being used. Default display settings PDF documents can contain display settings, including the page display layout and zoom level. Adobe Reader will use these settings to override the users default settings when opening the document.[76] The free Adobe Reader cannot remove these settings. Content A PDF file is often a combination of vector graphics, text, and bitmap graphics. The basic types of content in a PDF are: • text stored as content streams (i.e., not text) • vector graphics for illustrations and designs that consist of shapes and lines • raster graphics for photographs and other types of image In later PDF revisions, a PDF document can also support links (inside document or web page), forms, JavaScript (initially available as plugin for Acrobat 3.0), or any other types of embedded contents that can be handled using plug-ins. PDF 1.6 supports interactive 3D documents embedded in the PDF - 3D drawings can be embedded using U3D or PRC and various other data formats.[77] [78] Two PDF files that look similar on a computer screen may be of very different sizes. For example, a high resolution raster image takes more space than a low resolution one. Typically higher resolution is needed for printing documents than for displaying them on screen. Other things that may increase the size of a file is embedding full fonts, especially for Asiatic scripts, and storing text as graphics.
  • 17. Portable Document Format 15 Implementations PDF-viewing software is generally provided free of charge, and many versions are available from a variety of sources (List of PDF software). There are many software options for creating PDFs, including the PDF printing capabilities built in to Mac OS X and most Linux distributions, the multi-platform, Microsoft Office 2007 (if updated to SP2),[79] WordPerfect since version 9, Free PDF XP[80] and numerous PDF print drivers for Microsoft Windows, the pdfTeX typesetting system, the DocBook PDF tools, applications developed around Ghostscript and Adobe Acrobat itself. Googles online office suite Google Docs also allows for uploading, and saving to the Portable Document Format. Raster image processors (RIPs) are used to convert PDF files into a raster format suitable for imaging onto paper and other media in printers, digital production presses and prepress in a process known as rasterisation. RIPs capable of processing PDF directly include the Adobe PDF Print Engine[81] from Adobe Systems and Jaws[82] and the Harlequin RIP from Global Graphics. Editing PDFs (structure) There is also specialized software for editing PDF files, though the choices are much more limited and often expensive. As of version 0.46, Inkscape also allows PDF editing through an intermediate translation step involving Poppler. Enfocus PitStop Pro, a plugin for Acrobat, allows manual and automatic editing of PDF files,[83] while the free Enfocus Browser makes it possible to edit the low-level structure of a PDF.[84] See List of PDF software for a more complete list of PDF editors. Annotating PDFs Adobe Acrobat is one example of proprietary software that allows the user to annotate, highlight, and add notes to already created PDF files. One UNIX application available as free software (under the GNU General Public License) is PDFedit. Another GPL-licensed application native to the unix environment is Xournal. Xournal allows for annotating in different fonts and colours, as well as a rule for quickly underlining and highlighting lines of text or paragraphs. Xournal also has a shape recognition tool for squares, rectangles and circles. In Xournal annotations may be moved, copied and pasted. The freeware Foxit Reader allows annotating but adds a watermark on each annotated page. The commercial version of the package does not have this limitation. Tracker Softwares PDF-XChange Viewer allows annotations and markups without restrictions in its freeware alternative. Apples Mac OS Xs integrated PDF viewer, Preview, does also enable annotations. For mobile annotation, iAnnotate PDF for the iPad and Aji Annotate for the iPhone, both produced by Aji, allow annotation of PDFs as well as exporting summaries of the annotations. There are also web annotation systems which allow to annotate pdf and other documents formats, e.g. A.nnotate, crocodoc, WebNotes. In cases where PDFs are expected to have all of the functionality of paper documents, ink annotation is required. Many programs which accept ink input from the mouse are not responsive enough for handwriting using an input tablet or tablet PC. Existing solutions on the PC include Bluebeam PDF Revu, and PDF Annotator.
  • 18. Portable Document Format 16 Other applications and functionalities Several applications embracing the PDF standard are now available as an online service including Scribd for viewing and storing, Pdfvue for online editing, and Zamzar for PDF Conversion. In 1993 the Jaws RIP from Global Graphics became the first shipping prepress RIP that interpreted PDF natively without conversion to another format. The company released an upgrade to their Harlequin RIP with the same capability in 1997. Agfa-Gevaert introduced and shipped Apogee, the first prepress workflow system based on PDF, in 1997. Many commercial offset printers have accepted the submission of press-ready PDF files as a print source, specifically the PDF/X-1a subset and variations of the same.[85] The submission of press-ready PDF files are a replacement for the problematic need for receiving collected native working files. PDF was selected as the "native" metafile format for Mac OS X, replacing the PICT format of the earlier Mac OS. The imaging model of the Quartz graphics layer is based on the model common to Display PostScript and PDF, leading to the nickname "Display PDF". The Preview application can display PDF files, as can version 2.0 and later of the Safari web browser. System-level support for PDF allows Mac OS X applications to create PDF documents automatically, provided they support the Print command. The files are then exported in PDF 1.3 format according to the file header. When taking a screenshot under Mac OS X versions 10.0 through 10.3, the image was also captured as a PDF; in 10.4 and 10.5 the default behaviour is set to capture as a PNG file, though this behaviour can be set back to PDF if required. Some desktop printers also support direct PDF printing, which can interpret PDF data without external help. Currently, all PDF capable printers also support PostScript, but most PostScript printers do not support direct PDF printing. The Free Software Foundation considers one of their high priority projects to be "developing a free, high-quality and fully functional set of libraries and programs that implement the PDF file format and associated technologies to the ISO 32000 standard."[86] [87] The GNUpdf library has, however, not been released yet, while Poppler has enjoyed wider use in applications such as Evince, which comes with the GNOME desktop environment, at the expense of relying on the GPLv2-licensed Xpdf[88] [89] code base that cant be used by GPLv3 programs. There are also commercial development libraries available as listed in List of PDF software. The Apache PDFBox project of the Apache Software Foundation is an open source Java library for working with PDF documents. PDFBox is licensed under the Apache License.[90] References [1] "ISO 32000-1:2008 - Document management — Portable document format — Part 1: PDF 1.7" (http:/ / www. iso. org/ iso/ iso_catalogue/ catalogue_tc/ catalogue_detail. htm?csnumber=51502). 2008-07-01. . Retrieved 2010-02-21. [2] http:/ / www. adobe. com/ devnet/ pdf/ pdf_reference_archive. html [3] Adobe Systems Incorporated, PDF Reference, Sixth edition, version 1.23 (30 MB) (http:/ / www. adobe. com/ devnet/ acrobat/ pdfs/ pdf_reference_1-7. pdf), Nov 2006, p. 33. [4] Warnock, J. (1991). "The Camelot Project" (http:/ / www. planetpdf. com/ planetpdf/ pdfs/ warnock_camelot. pdf) (PDF). PlanetPDF. . "This document describes the base technology and ideas behind the project named “Camelot.” This project’s goal is to solve a fundamental problem [...] there is no universal way to communicate and view ... printed information electronically." [5] PDF Reference, third edition, http:/ / partners. adobe. com/ public/ developer/ en/ pdf/ PDFReference. pdf [6] Orion, Egan (2007-12-05). "PDF 1.7 is approved as ISO 32000" (http:/ / www. theinquirer. net/ gb/ inquirer/ news/ 2007/ 12/ 05/ pdf-approved-iso-32000). The Inquirer. The Inquirer. . Retrieved 2007-12-05.; "Adobe wins backing for PDF 1.7" (http:/ / www. vnunet. com/ vnunet/ news/ 2205065/ pdf-takes-first-step-towards). . [7] Adobe Systems Incorporated (2008), Public Patent License, ISO 32000-1: 2008 – PDF 1.7 (http:/ / www. adobe. com/ pdf/ pdfs/ ISO32000-1PublicPatentLicense. pdf), , retrieved 2011-07-06 [8] Laurens Leurs. "The history of PDF" (http:/ / www. prepressure. com/ pdf/ basics/ history). . Retrieved 2007-09-19. [9] R, Leonard, History of PDF Openness (http:/ / web. archive. org/ web/ 20071014010805/ http:/ / www. acrobatusers. com/ blogs/ leonardr/ history-of-pdf-openness/ ), Acrobat users, archived from the original (http:/ / www. acrobatusers. com/ blogs/ leonardr/
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  • 20. Portable Document Format 18 [47] Adobe Systems Incorporated. "Adobe XML Forms Architecture (XFA)" (http:/ / partners. adobe. com/ public/ developer/ xml/ index_arch. html). . Retrieved 2010-02-19. [48] (PDF) Adobe Reader - Software license agreement (http:/ / www. adobe. com/ products/ eulas/ pdfs/ Reader_Player_AIR_WWEULA-Combined-20080204_1313. pdf), , retrieved 2010-02-19 [49] "LiveCycle Reader Extensions ES features and benefits" (http:/ / www. adobe. com/ go/ readerextensions). . Retrieved 2010-02-19. [50] (PDF) XML Forms Architecture (XFA) Specification Version 2.5 (http:/ / partners. adobe. com/ public/ developer/ en/ xml/ xfa_spec_2_5. pdf), 2007-06-08, , retrieved 2010-02-19 [51] http:/ / www. iso. org/ iso/ iso_catalogue/ catalogue_ics/ catalogue_detail_ics. htm?ics1=35& ics2=240& ics3=30& csnumber=54564 [52] http:/ / books. google. com/ books?id=dlJ94KZqwqcC& pg=PA379 [53] FreeMyPDF - A website that removes PDF "user password" restrictions (http:/ / freemypdf. com/ ) [54] http:/ / www. pdfhacks. com/ pdftk/ [55] Adobe PDF reference version 1.7 (http:/ / www. adobe. com/ devnet/ acrobat/ pdfs/ pdf_reference_1-7. pdf), section 10.2 [56] AIIM (2006-10-20). "New Best Practices Guide Addresses Exchange of Healthcare Information" (http:/ / www. aiim. org/ ResourceCenter/ AIIMNews/ PressReleases/ article. aspx?ID=34318). . Retrieved 2007-03-09. [57] Jackson, Joab (2006-12-07). "Adobe plunges PDF into XML" (http:/ / www. gcn. com/ blogs/ tech/ 42740. html). Government Computer News. . Retrieved 2008-01-12. [58] http:/ / labs. adobe. com/ wiki/ index. php/ Mars [59] http:/ / labs. adobe. com/ technologies/ mars/ [60] "PDF Accessibility" (http:/ / www. webaim. org/ techniques/ acrobat/ ). WebAIM. . Retrieved 2010-04-24. [61] Joe Clark (2005-08-22). "Facts and Opinions About PDF Accessibility" (http:/ / www. alistapart. com/ articles/ pdf_accessibility). . Retrieved 2010-04-24. [62] "Accessibility and PDF documents" (http:/ / wac. osu. edu/ pdf/ ). Web Accessibility Center. . Retrieved 2010-04-24. [63] "PDF Accessibility Standards v1.2" (http:/ / www. bbc. co. uk/ guidelines/ futuremedia/ accessibility/ accessible_pdf. shtml). . Retrieved 2010-04-24. [64] (PDF) PDF Accessibility (http:/ / www. csus. edu/ training/ handouts/ workshops/ creating_accessible_pdfs. pdf), California State University, , retrieved 2010-04-24 [65] "Adobe Reader 8 - Read a PDF with Read Out Loud" (http:/ / help. adobe. com/ en_US/ Reader/ 8. 0/ help. html?content=WS58a04a822e3e50102bd615109794195ff-7d15. html). . Retrieved 2010-04-24. [66] "Tip of the Week: Adobe Reader’s ‘Read Aloud’ Feature" (http:/ / gadgetwise. blogs. nytimes. com/ 2009/ 04/ 10/ tip-of-the-week-adobe-readers-read-aloud-feature/ ). The New York Times. 2009-04-10. . Retrieved 2010-04-24. [67] (PDF) Accessing PDF documents with assistive technology: A screen reader users guide (http:/ / www. adobe. com/ accessibility/ pdfs/ accessing-pdf-sr. pdf), Adobe, , retrieved 2010-04-24 [68] Chris Rusbridge (2008-04-29). "Why PDF is a Hamburger" (http:/ / wwmm. ch. cam. ac. uk/ blogs/ murrayrust/ ?p=1056). . Retrieved 2010-04-24. [69] Adobe Forums, Announcement: PDF Attachment Virus "Peachy" (http:/ / www. adobeforums. com/ webx/ . ef39082), 15 August 2001. [70] "Security bulletins and advisories" (http:/ / www. adobe. com/ support/ security/ #readerwin). Adobe. . Retrieved 2010-02-21. [71] Steve Gibson - SecurityNow Podcast (http:/ / www. grc. com/ sn/ sn-187. txt) [72] PDFCleaner - PDF Exploit Sanitizer (http:/ / pdfcleaner. ossbox. com/ ) [73] blogs (http:/ / blogs. pcmag. com/ securitywatch/ 2010/ 03/ malicious_pdfs_execute_code_wi. php) [74] "Create Adobe PDF Online - Security Settings Help" (http:/ / createpdf. adobe. com/ cgi-feeder. pl/ help_security?BP=& LOC=en_US). . Retrieved 2010-02-21. [75] New features and issues addressed in the Acrobat 7.0.5 Update (Acrobat and Adobe Reader for Windows and Mac OS) (http:/ / kb. adobe. com/ selfservice/ viewContent. do?externalId=332208& sliceId=2) [76] "Getting Familiar with Adobe Reader > Understanding Preferences" (http:/ / www. adobepress. com/ articles/ article. asp?p=412914). . Retrieved 2009-04-22. [77] "3D supported formats" (http:/ / www. adobe. com/ manufacturing/ resources/ 3dformats/ ). Adobe. 2009-07-14. . Retrieved 2010-02-21. [78] "Acrobat 3D Developer Center" (http:/ / www. adobe. com/ devnet/ acrobat3d/ ). Adobe. . Retrieved 2010-02-21. [79] "Description of 2007 Microsoft Office Suite Service Pack 2 (SP2)" (http:/ / support. microsoft. com/ kb/ 953195). Microsoft. . Retrieved 2009-05-09. [80] "Free PDF XP" (http:/ / freepdf-xp. en. softonic. com/ ). . Retrieved 2010-07-27. [81] (http:/ / www. adobe. com/ products/ pdfprintengine/ overview. html) [82] (http:/ / www. globalgraphics. com/ products/ jaws_rip/ ) [83] (http:/ / www. enfocus. com/ product. php?id=855) [84] http:/ / www. enfocus. com/ product. php?id=4530 [85] Press-Ready PDF Files (http:/ / www. prepressx. com) "For anyone interested in having their graphic project commercially printed directly from digital files or PDFs." (last checked on 2009-02-10). [86] Current FSF High Priority Free Software Projects (http:/ / www. fsf. org/ campaigns/ priority. html) (last checked on 2009-02-10) [87] Goals and Motivations - GNUpdf (http:/ / gnupdf. org/ Goals_and_Motivations)
  • 21. Portable Document Format 19 [88] Poppler homepage (http:/ / poppler. freedesktop. org/ ) "Poppler is a PDF rendering library based on the xpdf-3.0 code base." (last checked on 2009-02-10) [89] Xpdf license (http:/ / www. foolabs. com/ xpdf/ about. html) "Xpdf is licensed under the GNU General Public License (GPL), version 2." (last checked on 2009-02-10). [90] The Apache PDFBox project (http:/ / incubator. apache. org/ pdfbox/ ) . Retrieved 2009-09-19. Further reading • Hardy, M. R. B.; Brailsford, D. F. (2002). "Mapping and displaying structural transformations between XML and PDF" ( Proceedings of the 2002 ACM symposium on Document engineering - DocEng 02. Proceedings of the 2002 ACM symposium on Document engineering. pp. 95–102. doi:10.1145/585058.585077. ISBN 1-58113-594-7. External links • Adobe PDF 101: Quick overview of PDF ( • Adobe: PostScript vs. PDF ( – Official introductory comparison of PS, EPS vs. PDF. • PDF Standards....transitioning the PDF specification from a de facto standard to a de jure standard (http:// – Information about PDF/E and PDF/UA specification for accessible documents file format • ISO 19005-1:2005 ( htm?csnumber=38920) Document of the PDF/A-1 Standard at the International Organization for Standardization (chargeable) • PDF Reference • Latest PDF version specification (including free version of the ISO standard) ( devnet/pdf/pdf_reference.html) • Books: PDF 1.6 (ISBN 0-321-30474-8), PDF 1.4 (ISBN 0-201-75839-3), PDF 1.3 (ISBN 0-201-61588-6) • Portable Document Format: An Introduction for Programmers ( Vol.15/15.09/PDFIntro/) – Quick one-page intro to PDF vs. PostScript and PDF internals (up to v1.3) • The Camelot Paper ( – the paper in which John Warnock outlined the project that created PDF • Everything you wanted to know about PDF but were afraid to ask ( everything-you-wanted-to-know-about-pdf-but-were-afraid-to-ask/) - recording of talk by Leonard Rosenthol (Adobe Systems) at TUG 2007
  • 22. IPv6 20 IPv6 Internet Protocol version 6 (IPv6) is a version of the Internet Protocol (IP). It is designed to succeed the Internet Protocol version 4 (IPv4). The Internet operates by transferring data between hosts in small packets that are independently routed across networks as specified by an international communications protocol known as the Internet Protocol. Each host or computer on the Internet requires an IP address in order to communicate. The growth of the Internet has created a need for more addresses than are possible with IPv4. IPv6 was developed by the Internet Engineering Task Force (IETF) to deal with this long-anticipated IPv4 address exhaustion, and is described in Internet standard document RFC 2460, published in December 1998.[1] Like IPv4, IPv6 is an Internet Layer protocol for packet-switched internetworking and provides end-to-end datagram transmission across multiple IP networks. While IPv4 allows 32 bits for an Internet Protocol address, and can therefore support 232 (4,294,967,296) addresses, IPv6 uses 128-bit addresses, so the new address space supports 2128 (approximately 340 undecillion or 3.4 × 1038) addresses. This expansion allows for many more devices and users on the internet as well as extra flexibility in allocating addresses and efficiency for routing traffic. It also eliminates the primary need for network address translation (NAT), which gained widespread deployment as an effort to alleviate IPv4 address exhaustion. IPv6 also implements additional features not present in IPv4. It simplifies aspects of address assignment (stateless address autoconfiguration), network renumbering and router announcements when changing Internet connectivity providers. The IPv6 subnet size has been standardized by fixing the size of the host identifier portion of an address to 64 bits to facilitate an automatic mechanism for forming the host identifier from link layer media addressing information (MAC address). Network security is also integrated into the design of the IPv6 architecture, and the IPv6 specification mandates support for IPsec as a fundamental interoperability requirement. The last top level (/8) block of free IPv4 addresses was assigned in February 2011 by IANA to the 5 RIRs, although many free addresses still remain in most assigned blocks and each RIR will continue with standard policy until it is at its last /8. After that, only 1024 addresses (a /22) are made available from the RIR for each LIR – currently, only APNIC has already reached this stage.[2] While IPv6 is supported on all major operating systems in use in commercial, business, and home consumer environments,[3] IPv6 does not implement interoperability features with IPv4, and creates essentially a parallel, independent network. Exchanging traffic between the two networks requires special translator gateways, but modern computer operating systems implement dual-protocol software for transparent access to both networks either natively or using a tunneling protocol such as 6to4, 6in4, or Teredo. In December 2010, despite marking its 12th anniversary as a Standards Track protocol, IPv6 was only in its infancy in terms of general worldwide deployment. A 2008 study[4] by Google Inc. indicated that penetration was still less than one percent of Internet-enabled hosts in any country at that time. Motivation and origins IPv4 The first publicly used version of the Internet Protocol, Version 4 (IPv4), provides an addressing capability of 232 or approximately 4.3 billion addresses. This was deemed sufficient in the early design stages of the Internet when the explosive growth and worldwide proliferation of networks connected to the internet and the internet itself was not anticipated. During the first decade of operation of the Internet (by the late 1980s), it became apparent that methods had to be developed to conserve address space. In the early 1990s, even after the redesign of the addressing system using a classless network model, it became clear that this would not suffice to prevent IPv4 address exhaustion, and that further changes to the Internet infrastructure were needed.[5]
  • 23. IPv6 21 Working group proposal By the beginning of 1992, several proposals appeared and by the end of 1992, the IETF announced a call for white papers[6] . In September 1993, the IETF created a temporary, ad-hoc IP Next Generation (IPng) area to deal with specifically with IPng issues. The new area was led by Allison Mankin and Scott Bradner, and had a directorate with 15 engineers from diverse backgrounds for direction-setting and preliminary document review.[5] [7] The Internet Engineering Task Force adopted the IPng model on July 25, 1994, with the formation of several IPng working groups.[5] By 1996, a series of RFCs was released defining Internet Protocol version 6 (IPv6), starting with RFC 1883. (Version 5 was used by the experimental Internet Stream Protocol.) It is widely expected that IPv4 will be supported alongside IPv6 for the foreseeable future. IPv4-only and IPv6-only nodes cannot communicate directly, and need assistance from an intermediary gateway or must use other transition mechanisms. Exhaustion of IPv4 addresses On February 3, 2011, in a ceremony in Miami, the Internet Assigned Numbers Authority (IANA) assigned the last batch of 5 /8 address blocks to the Regional Internet Registries.,[8] officially depleting the global pool of completely fresh blocks of addresses.[9] Each of the address blocks represents approximately 16.7 million possible addresses, or over 80 million combined potential addresses. These addresses could well be fully consumed within three to six months of that time at current rates of allocation.[10] APNIC was the first RIR to exhaust its regional pool on 15 April 2011, except for a small amount of address space reserved for the transition to IPv6, which will be allocated in a much more restricted way.[11] In 2003, the director of Asia-Pacific Network Information Centre (APNIC), Paul Wilson, stated that, based on then-current rates of deployment, the available space would last for one or two decades.[12] In September 2005, a report by Cisco Systems suggested that the pool of available addresses would exhaust in as little as 4 to 5 years.[13] In 2008, a policy process started for the end-game and post-exhaustion era.[14] In 2010, a daily updated report projected the global address pool exhaustion by the first quarter of 2011, and depletion at the five regional Internet registries before the end of 2011.[15] Comparison to IPv4 IPv6 specifies a new packet format, designed to minimize packet header processing by routers.[1] [16] Because the headers of IPv4 packets and IPv6 packets are significantly different, the two protocols are not interoperable. However, in most respects, IPv6 is a conservative extension of IPv4. Most transport and application-layer protocols need little or no change to operate over IPv6; exceptions are application protocols that embed internet-layer addresses, such as FTP and NTPv3.
  • 24. IPv6 22 Larger address space The most important feature of IPv6 is a much larger address space than in IPv4. The length of an IPv6 address is 128 bits, compared to 32 bits in IPv4.[1] The address space therefore supports 2128 or 38 approximately 3.4 × 10 addresses. By comparison, this amounts to approximately 5 × 1028 addresses for each of the 6.8 billion people alive in 2010.[17] In addition, the IPv4 address space is poorly allocated, with approximately 14% of all available addresses utilized.[18] While these numbers Decomposition of an IPv6 address into its binary form are large, it was not the intent of the designers of the IPv6 address space to assure geographical saturation with usable addresses. Rather, the longer addresses simplify allocation of addresses, enable efficient route aggregation, and allow implementation of special addressing features. In IPv4, complex Classless Inter-Domain Routing (CIDR) methods were developed to make the best use of the small address space. The standard size of a subnet in IPv6 is 264 addresses, the square of the size of the entire IPv4 address space. Thus, actual address space utilization rates will be small in IPv6, but network management and routing efficiency is improved by the large subnet space and hierarchical route aggregation. Renumbering an existing network for a new connectivity provider with different routing prefixes is a major effort with IPv4.[19] [20] With IPv6, however, changing the prefix announced by a few routers can in principle renumber an entire network since the host identifiers (the least-significant 64 bits of an address) can be independently self-configured by a host. Multicasting Multicasting, the transmission of a packet to multiple destinations in a single send operation, is part of the base specification in IPv6. In IPv4 this is an optional although commonly implemented feature.[21] IPv6 multicast addressing shares common features and protocols with IPv4 multicast, but also provides changes and improvements by eliminating the need for certain protocols. IPv6 does not implement traditional IP broadcast, i.e. the transmission of a packet to all hosts on the attached link using a special broadcast address, and therefore does not define broadcast addresses. In IPv6, the same result can be achieved by sending a packet to the link-local all nodes multicast group at address ff02::1, which is analogous to IPv4 multicast to address IPv6 also supports new multicast solutions, including embedding rendezvous point addresses in an IPv6 multicast group address which simplifies the deployment of inter-domain solutions.[22] In IPv4 it was very difficult for an organization to get even one globally routable multicast group assignment and the implementation of inter-domain solutions was very arcane.[23] Unicast address assignments by a local Internet registry for IPv6 have at least a 64-bit routing prefix, yielding the smallest subnet size available in IPv6 (also 64 bits). With such an assignment it is possible to embed the unicast address prefix into the IPv6 multicast address format, while still providing a 32-bit block, the least significant bits of the address, or approximately 4.2 billion multicast group identifiers. Thus each user of an IPv6 subnet automatically has available a set of globally routable source-specific multicast groups for multicast applications.[24]
  • 25. IPv6 23 Stateless address autoconfiguration (SLAAC) IPv6 hosts can configure themselves automatically when connected to a routed IPv6 network using Internet Control Message Protocol version 6 (ICMPv6) router discovery messages. When first connected to a network, a host sends a link-local router solicitation multicast request for its configuration parameters; if configured suitably, routers respond to such a request with a router advertisement packet that contains network-layer configuration parameters.[25] If IPv6 stateless address autoconfiguration is unsuitable for an application, a network may use stateful configuration with the Dynamic Host Configuration Protocol version 6 (DHCPv6) or hosts may be configured statically. Routers present a special case of requirements for address configuration, as they often are sources for autoconfiguration information, such as router and prefix advertisements. Stateless configuration for routers can be achieved with a special router renumbering protocol.[26] Mandatory support for network layer security Internet Protocol Security (IPsec) was originally developed for IPv6, but found widespread deployment first in IPv4, into which it was back-engineered. IPsec is an integral part of the base protocol suite in IPv6.[1] IPsec support is mandatory in IPv6 but optional for IPv4. Simplified processing by routers In IPv6, the packet header and the process of packet forwarding have been simplified. Although IPv6 packet headers are at least twice the size of IPv4 packet headers, packet processing by routers is generally more efficient,[1] [16] thereby extending the end-to-end principle of Internet design. Specifically: • The packet header in IPv6 is simpler than that used in IPv4, with many rarely used fields moved to separate optional header extensions. • IPv6 routers do not perform fragmentation. IPv6 hosts are required to either perform path MTU discovery, perform end-to-end fragmentation, or to send packets no larger than the IPv6 default minimum MTU size of 1280 octets. • The IPv6 header is not protected by a checksum; integrity protection is assumed to be assured by both link layer and higher layer (TCP, UDP, etc.) error detection.[27] Therefore, IPv6 routers do not need to recompute a checksum when header fields (such as the time to live (TTL) or hop count) change.[28] • The TTL field of IPv4 has been renamed to Hop Limit, reflecting the fact that routers are no longer expected to compute the time a packet has spent in a queue. Mobility Unlike mobile IPv4, mobile IPv6 avoids triangular routing and is therefore as efficient as native IPv6. IPv6 routers may also support network mobility which allows entire subnets to move to a new router connection point without renumbering.[29] Options extensibility The IPv6 protocol header has a fixed size (40 octets). Options are implemented as additional extension headers after the IPv6 header, which limits their size only by the size of an entire packet. The extension header mechanism provides extensibility to support future services for quality of service, security, mobility, and others, without redesign of the basic protocol.[1]
  • 26. IPv6 24 Jumbograms IPv4 limits packets to 65535 (216 – 1) octets of payload. IPv6 has optional support for packets over this limit, referred to as jumbograms, which can be as large as 4294967295 (232 – 1) octets. The use of jumbograms may improve performance over high-MTU links. The use of jumbograms is indicated by the Jumbo Payload Option header.[30] Packet format The IPv6 packet is composed of two parts: the packet header and the payload. The header consists of a fixed portion with minimal functionality required for all packets and may contain optional extension to implement special features. The fixed header occupies the first 40 octets (320 bits) of the IPv6 packet. It contains the source and destination addresses, traffic classification options, a hop counter, and a pointer for extension headers if any. The Next Header field, present in each extension as well, points to the next element in the chain of extensions. The last field points to the upper-layer protocol that is carried in the packets IPv6 packet header. payload. Extension headers carry options that are used for special treatment of a packet in the network, e.g., for routing, fragmentation, and for security using the IPsec framework. The payload can have a size of up to 64KB without special options, or larger with a jumbo payload option in a Hop-By-Hop Options extension header. Unlike in IPv4, fragmentation is handled only in the end points of a communication session; routers never fragment a packet, and hosts are expected to use Path MTU Discovery to select a packet size that can traverse the entire communications path. Addressing The most important feature of IPv6 is a much larger address space than in IPv4. IPv6 addresses are 128 bits long, compared to only 32 bits previously.[31] While the IPv4 address space contains only about 4.3 × 109 (4.3 billion) addresses, IPv6 supports approximately 3.4 × 1038 (340 undecillion) unique addresses, deemed enough for the foreseeable future.[32] IPv6 addresses are written in eight groups of four hexadecimal digits separated by colons, for example, 2001:0db8:85a3:0000:0000:8a2e:0370:7334. IPv6 unicast addresses other than those that start with binary 000 are logically divided into two parts: a 64-bit (sub-)network prefix, and a 64-bit interface identifier.[33] For stateless address autoconfiguration (SLAAC) to work, subnets require a /64 address block as defined in RFC 4291 section 2.5.1. Local Internet registries get assigned at least /32 blocks, which they divide among ISPs.[34] The obsolete RFC 3177 recommended the assignment of a /48 to end consumer sites. This was replaced by RFC 6177, which "recommends giving home sites significantly more than a single /64, but does not recommend that every home site be given a /48 either." /56s are specifically considered. It remains to be seen if ISPs will honor this recommendation; for example, during initial trials Comcast customers have been given a single /64 network.[35] IPv6 addresses are classified by three types of networking methodologies: unicast addresses identify each network interface, anycast addresses identify a group of interfaces, usually at different locations of which the nearest one is automatically selected, and multicast addresses are used to deliver one packet to many interfaces. The broadcast method is not implemented in IPv6. Each IPv6 address has a scope, which specifies in which part of the network it is
  • 27. IPv6 25 valid and unique. Some addresses are unique only on the local (sub-)network; Others are globally unique. Some IPv6 addresses are reserved for special purposes, such as the address for loopback, 6to4 tunneling, Teredo tunneling and several more. See RFC 5156. Also, some address ranges are considered special, such as link-local addresses for use on the local link only, Unique Local addresses (ULA) as described in RFC 4193 and solicited-node multicast addresses used in the Neighbor Discovery Protocol. IPv6 in the Domain Name System In the Domain Name System, hostnames are mapped to IPv6 addresses by AAAA resource records, so-called quad-A records. For reverse resolution, the IETF reserved the domain, where the name space is hierarchically divided by the 1-digit hexadecimal representation of nibble units (4 bits) of the IPv6 address. This scheme is defined in RFC 3596. Address Format IPv6 addresses have two logical parts: a 64-bit network prefix, and a 64-bit host address part. (The host address is often automatically generated from the interface MAC address.[36] ) An IPv6 address is represented by 8 groups of 16-bit hexadecimal values separated by colons (:) shown as follows: A typical example of an IPv6 address is 2001:0db8:85a3:0000:0000:8a2e:0370:7334 The hexadecimal digits are case-insensitive. The 128-bit IPv6 address can be abbreviated with the following rules: • Rule one: Leading zeroes within a 16-bit value may be omitted. For example, the address fe80:0000:0000:0000:0202:b3ff:fe1e:8329 may be written as fe80:0:0:0:202:b3ff:fe1e:8329 • Rule two: One group of consecutive zeroes within an address may be replaced by a double colon. For example, fe80:0:0:0:202:b3ff:fe1e:8329 becomes fe80::202:b3ff:fe1e:8329 A single IPv6 address can be represented in several different ways, such as 2001:db8::1:0:0:1 and 2001:0DB8:0:0:1::1. RFC 5952 recommends a canonical textual representation. Transition mechanisms Until IPv6 completely supplants IPv4, a number of transition mechanisms[37] are needed to enable IPv6-only hosts to reach IPv4 services and to allow isolated IPv6 hosts and networks to reach the IPv6 Internet over the IPv4 infrastructure. For the period while IPv6 hosts and routers co-exist with IPv4 systems various proposals have been made: • RFC 4213, Basic Transition Mechanisms for IPv6 Hosts and Routers • RFC 2766, Network Address Translation — Protocol Translation NAT-PT, obsoleted as explained in RFC 4966 Reasons to Move the Network Address Translator — Protocol Translator NAT-PT to Historic Status • RFC 2185, Routing Aspects of IPv6 Transition • RFC 3056, 6to4. Connection of IPv6 Domains via IPv4 Clouds • RFC 4380, Teredo: Tunneling IPv6 over UDP through Network Address Translations NATs • RFC 4798, Connecting IPv6 Islands over IPv4 MPLS Using IPv6 Provider Edge Routers (6PE) • RFC 5214, Intra-Site Automatic Tunnel Addressing Protocol ISATAP • RFC 3053, IPv6 Tunnel Broker • RFC 3142, An IPv6-to-IPv4 Transport Relay Translator • RFC 5569, IPv6 Rapid Deployment on IPv4 Infrastructures (6rd)
  • 28. IPv6 26 • RFC 5572, IPv6 Tunnel Broker with the Tunnel Setup Protocol (TSP) • RFC 6180, Guidelines for Using IPv6 Transition Mechanisms during IPv6 Deployment • RFC 6343, Advisory Guidelines for 6to4 Deployment Dual IP stack implementation The dual-stack protocol implementation in an operating system is a fundamental IPv4-to-IPv6 transition technology. It implements IPv4 and IPv6 protocol stacks either independently or in a hybrid form. The hybrid form is commonly implemented in modern operating systems supporting IPv6. Dual-stack hosts are described in RFC 4213. Modern hybrid dual-stack implementations of IPv4 and IPv6 allow programmers to write networking code that works transparently on IPv4 or IPv6. The software may use hybrid sockets designed to accept both IPv4 and IPv6 packets. When used in IPv4 communications, hybrid stacks use an IPv6 application programming interface and represent IPv4 addresses in a special address format, the IPv4-mapped IPv6 address. IPv4-mapped IPv6 addresses Hybrid dual-stack IPv6/IPv4 implementations support a special class of addresses, the IPv4-mapped IPv6 addresses. This address type has its first 80 bits set to zero and the next 16 set to one, while its last 32 bits are filled with the IPv4 address. These addresses are commonly represented in the standard IPv6 format, but having the last 32 bits written in the customary dot-decimal notation of IPv4; for example, ::ffff: represents the IPv4 address It substitutes the old and deprecated IPv4-compatible IPv6 address formed by ::[38] Because of the significant internal differences between IPv4 and IPv6, some of the lower level functionality available to programmers in the IPv6 stack do not work identically with IPv4 mapped addresses. Some common IPv6 stacks do not support the IPv4-mapped address feature, either because the IPv6 and IPv4 stacks are separate implementations (e.g., Microsoft Windows 2000, XP, and Server 2003), or because of security concerns (OpenBSD) .[39] On these operating systems, it is necessary to open a separate socket for each IP protocol that is to be supported. On some systems, e.g., the Linux kernel, NetBSD, and FreeBSD, this feature is controlled by the socket option IPV6_V6ONLY as specified in RFC 3493.[40] Tunneling In order to reach the IPv6 Internet, an isolated host or network must use the existing IPv4 infrastructure to carry IPv6 packets. This is done using a technique known as tunneling which consists of encapsulating IPv6 packets within IPv4, in effect using IPv4 as a link layer for IPv6. The direct encapsulation of IPv6 datagrams within IPv4 packets is indicated by IP protocol number 41. IPv6 can also be encapsulated within UDP packets e.g. in order to cross a router or NAT device that blocks protocol 41 traffic. Other encapsulation schemes, such as used in AYIYA or GRE, are also popular. Conversely, on IPv6-only internet links, when access to IPv4 network facilities are needed, tunneling of IPv4 over IPv6 protocol occurs, using the IPv6 as a link layer for IPv4. Automatic tunneling Automatic tunneling refers to a technique where the routing infrastructure automatically determines the tunnel endpoints. 6to4 is recommended by RFC 3056 tunneling method for automatic tunneling, which uses protocol 41 encapsulation.[41] Tunnel endpoints are determined by using a well-known IPv4 anycast address on the remote side, and embedding IPv4 address information within IPv6 addresses on the local side. 6to4 is widely deployed today. Teredo is an automatic tunneling technique that uses UDP encapsulation and can allegedly cross multiple NAT boxes.[42] IPv6, including 6to4 and Teredo tunneling, are enabled by default in Windows Vista[43] and Windows 7.
  • 29. IPv6 27 Most Unix systems only implement native support for 6to4, but Teredo can be provided by third-party software such as Miredo. ISATAP[44] treats the IPv4 network as a virtual IPv6 local link, with mappings from each IPv4 address to a link-local IPv6 address. Unlike 6to4 and Teredo, which are inter-site tunnelling mechanisms, ISATAP is an intra-site mechanism, meaning that it is designed to provide IPv6 connectivity between nodes within a single organisation. Configured and automated tunneling (6in4) In configured tunneling, the tunnel endpoints are explicitly configured, either by an administrator manually or the operating systems configuration mechanisms, or by an automatic service known as a tunnel broker;[45] this is also referred to as automated tunneling. Configured tunneling is usually more deterministic and easier to debug than automatic tunneling, and is therefore recommended for large, well-administered networks. Automated tunneling provides a compromise between the ease of use of automatic tunneling and the deterministic behaviour of configured tunneling. Raw encapsulation of IPv6 packets using IPv4 protocol number 41 is recommended for configured tunneling; this is sometimes known as 6in4 tunneling. As with automatic tunneling, encapsulation within UDP may be used in order to cross NAT boxes and firewalls. Proxying and translation for IPv6-only hosts After the regional Internet registries have exhausted their pools of available IPv4 addresses, it is likely that hosts newly added to the Internet might only have IPv6 connectivity. For these clients to have backward-compatible connectivity to existing IPv4-only resources, suitable IPv6 transition mechanisms must be deployed. One form of address translation is the use of a dual-stack application layer proxy server, for example a web proxy. NAT-like techniques for application-agnostic translation at the lower layers in routers and gateways have been proposed. The NAT-PT standard was dropped due to a number of criticisms,[46] however more recently the continued low adoption of IPv6 has prompted a new standardization effort under the name NAT64. Application transition RFC 4038, Application Aspects of IPv6 Transition, is an informational RFC that covers the topic of IPv4 to IPv6 application transition mechanisms. Other RFCs that pertain IPv6 at the application level are: • RFC 3493, Basic Socket Interface Extensions for IPv6 • RFC 3542, Advanced Sockets Application Program Interface (API) for IPv6 Similar to the OS-level WAN stack, applications can be: • IPv4 only • IPv6 only • dual set of IPv4 and IPv6 only • hybrid IPv4 and IPv6
  • 30. IPv6 28 IPv6 readiness Compatibility with IPv6 networking is mainly a software or firmware issue. However, much of the older hardware that could in principle be upgraded is likely to be replaced instead. The American Registry for Internet Numbers (ARIN) suggests that all Internet servers be prepared to serve IPv6-only clients by January 2012.[47] [48] Software Most personal computers running recent operating system versions are IPv6-ready. Most popular applications with network capabilities are ready, and most others could be easily upgraded with support from the developers. Java applications adhering to Java 1.4 (February 2002) standards have support for IPv6.[49] Hardware and embedded systems Low-level equipment like network adapters and network switches may not be affected by the change, since they transmit link layer frames without inspecting the contents. Networking devices that obtain IP addresses or perform routing based on IP address do need IPv6 support. Most equipment would be IPv6 capable with a software or firmware update if the device has sufficient storage and memory space for the new IPv6 stack. However, manufacturers may be reluctant to spend on software development costs for hardware they have already sold when they are poised for new sales from IPv6-ready equipment. In some cases, non-compliant equipment needs to be replaced because the manufacturer no longer exists or software updates are not possible, for example, because the network stack is implemented in permanent read-only memory. Consumers view networking devices as household appliances that do not need maintenance. Little effort has been made to educate consumers about the need to upgrade. The CableLabs consortium published the 160 Mbit/s DOCSIS 3.0 IPv6-ready specification for cable modems in August 2006. The widely used DOCSIS 2.0 does not support IPv6. The new DOCSIS 2.0 + IPv6 standard also supports IPv6, which may on the cable modem side only require a firmware upgrade.[50] [51] It is expected that only 60% of cable modems servers and 40% of cable modems will be DOCSIS 3.0 by 2011.[52] Other equipment which is typically not IPv6-ready ranges from Voice over Internet Protocol devices to laboratory equipment and printers. Deployment The introduction of Classless Inter-Domain Routing (CIDR) in the Internet routing and IP address allocation methods in 1993 and the extensive use of network address translation (NAT) delayed the inevitable IPv4 address exhaustion. The final phase of exhaustion started on February 3, 2011.[15] In 2008, IPv6 accounted for a minuscule fraction of the used addresses and the traffic in the publicly-accessible Internet which is still dominated by IPv4.[53] In October 2010, 243 (83%) of the 294 top-level domains (TLDs) in the Internet supported IPv6 to access their domain name servers, and 203 (69%) zones contained IPv6 glue records, and approximately 1.4 million domains (1%) had IPv6 address records in their zones.[54] Of all networks in the global BGP routing table, 7.2% have IPv6 protocol support. The 2008 Summer Olympic Games were a notable event in terms of IPv6 deployment, being the first time a major world event has had a presence on the IPv6 Internet at http:/ / ipv6. beijing2008. cn/ en and all network operations of the Games were conducted using IPv6.[55] At the time of the event, it was believed that the Olympics provided the largest showcase of IPv6 technology since the inception of IPv6.[56] Since that time, major providers of Internet services, such as Google, have begun to implement IPv6 access into their products.[57] Cellular telephone systems present a large deployment field for Internet Protocol devices as mobile telephone service is being transitioned from 3G systems to next generation (4G) technologies in which voice is provisioned as a Voice
  • 31. IPv6 29 over Internet Protocol (VoIP) service. This mandates the use of IPv6 for such networks. In the U.S., cellular operator Verizon has released technical specifications for devices operating on its future networks.[58] The specification mandates IPv6 operation according to the 3GPP Release 8 Specifications (March 2009) and deprecates IPv4 as an optional capability. Some implementations of the BitTorrent peer-to-peer file transfer protocol make use of IPv6 to avoid NAT issues common for IPv4 private networks.[59] All major operating systems in use as of 2010 on personal computers and server systems have production quality IPv6 implementations.[60] Microsoft Windows has supported IPv6 since Windows 2000, and in production ready state beginning with Windows XP. Windows Vista and later have improved IPv6 support.[61] Mac OS X Panther (10.3), Linux 2.6, FreeBSD, and Solaris also have mature production implementations. Controversy Privacy extensions are, except for the Windows platform, not enabled by default. That the unique MAC address is exposed to the internet and therefore makes devices trackable caused criticism of data privacy responsibles in various countries. Two actions are necessary to guarantee the same level as with todays IPv4 networks: the client device has the privacy extensions enabled, and the provider dynamically assigns a varying address block to the client device. [62] [63] [64] [65] [66] Major milestones Year Major development and availability milestones 1996 Alpha quality IPv6 support in Linux kernel development version 2.1.8.[67] 6bone (an IPv6 virtual network for testing) is started. 1997 By the end of 1997 IBMs AIX 4.3 is the first commercial platform supporting IPv6.[68] [69] [70] Also in 1997, Early Adopter Kits for DECs operating systems, Tru64 and OpenVMS, are made available. 1998 Microsoft Research[71] releases its first experimental IPv6 stack. This support is not intended for use in a production environment. 2000 Production-quality BSD support for IPv6 becomes generally available in early to mid-2000 in FreeBSD, OpenBSD, and NetBSD via the [72] KAME project. [71] Microsoft releases an IPv6 technology preview version for Windows 2000 in March 2000. [73] Sun Solaris supports IPv6 in Solaris 8 in February. [70] Compaq ships IPv6 with Tru64. 2001 In January, Compaq ships IPv6 with OpenVMS.[70] [74] Cisco Systems introduces IPv6 support on Cisco IOS routers and L3 switches. [75] HP introduces IPv6 with HP-UX 11i v1. [76] On April 23, 2001, the European Commission launches the European IPv6 Task Force 2002 Microsoft Windows NT 4.0 and Windows 2000 SP1 have limited IPv6 support for research and testing since at least 2002. Microsoft Windows XP (2001) supports IPv6 for developmental purposes. In Windows XP SP1 (2002) and Windows Server 2003, IPv6 is [77] included as a core networking technology, suitable for commercial deployment. [78] IBM z/OS supports IPv6 since version 1.4 (generally availability in September 2002).
  • 32. IPv6 30 2003 Apple Mac OS X v10.3 "Panther" (2003) supports IPv6 which is enabled by default.[79] 2004 In July, ICANN announces that IPv6 address records for the Japan (jp) and Korea (kr) country code top-level domain nameservers are visible in the DNS root server zone files with serial number 2004072000. The IPv6 records for France (fr) are added later. This makes IPv6 DNS publicly operational. 2005 Linux 2.6.12 removes experimental status from its IPv6 implementation.[80] 2007 Microsoft Windows Vista (2007) supports IPv6 which is enabled by default.[77] Apples AirPort Extreme 802.11n base station includes an IPv6 gateway in its default configuration. It uses 6to4 tunneling and manually [81] configured static tunnels. (Note: 6to4 was disabled by default in later firmware revisions.) 2008 On February 4, 2008, IANA adds AAAA records for the IPv6 addresses of six root name servers.[82] [83] With this transition, it is now possible to resolve domain names using only IPv6. [84] [57] On March 12, 2008, Google launches a public IPv6 web interface to its popular search engine at the URL http:/ / ipv6. google. com . On March 12, 2008, IETF does an hour long IPv4 blackout at its meeting as an opportunity to capture informal experience data to inform [85] protocol design work going forward; this led to many fixes in operating systems and applications. On May 27, 2008, the European Commission publish their Action Plan for the deployment of Internet Protocol version 6 (IPv6) in Europe [86] [87] , with the aim of making IPv6 available to 25% of European users by 2010. 2009 In January 2009, Google extends its IPv6 initiative with Google over IPv6 [88], which offers IPv6 support for Google services to compatible networks. 2011 On June 8, 2011 the Internet Society together with several other big companies and organizations held World IPv6 Day, a global 24 hour test [89] [90] of IPv6. Notes [1] RFC 2460, Internet Protocol, Version 6 (IPv6) Specification, S. Deering, R. Hinden (December 1998) [2] (http:/ / www. eweek. com/ c/ a/ IT-Infrastructure/ IPv4-Address-Exhaustion-Not-Instant-Cause-for-Concern-with-IPv6-in-Wings-287643/ ) [3] Google: more Macs mean higher IPv6 usage in US (http:/ / arstechnica. com/ news. ars/ post/ 20081113-google-more-macs-mean-higher-ipv6-usage-in-us. html) [4] Global IPv6 Statistics – Measuring the current state of IPv6 for ordinary users, S. H. Gunderson (Google), RIPE 57 (Dubai, Oct 2008) (http:/ / www. ripe. net/ ripe/ meetings/ ripe-57/ presentations/ Colitti-Global_IPv6_statistics_-_Measuring_the_current_state_of_IPv6_for_ordinary_users_. 7gzD. pdf) [5] RFC 1752 The Recommendation for the IP Next Generation Protocol, S. Bradner, A. Mankin, January 1995. [6] RFC 1550, IP: Next Generation (IPng) White Paper Solicitation, S. Bradner, A. Mankin (December 1993) [7] History of the IPng Effort (http:/ / playground. sun. com/ ipv6/ doc/ history. html) [8] http:/ / arstechnica. com/ tech-policy/ news/ 2011/ 02/ river-of-ipv4-addresses-officially-runs-dry,ars [9] Rashid, Fahmida Y. (February 3, 2011). "IPv4 Address Depletion Adds Momentum to IPv6 Transition" (http:/ / www. eweek. com/ c/ a/ IT-Infrastructure/ IPv4-Address-Depletion-Adds-Momentum-to-IPv6-Transition-875751/ ). . Retrieved February 3, 2011. [10] "Two /8s allocated to APNIC from IANA" (http:/ / www. apnic. net/ publications/ news/ 2011/ delegation). APNIC. 2010-01-01. . Retrieved 2011-02-03. [11] Asia-Pacific Network Information Centre (15 April 2011). "APNIC IPv4 Address Pool Reaches Final /8" (http:/ / www. apnic. net/ publications/ news/ 2011/ final-8). . Retrieved 15 April 2011. [12] Exec: No shortage of Net addresses (http:/ / news. zdnet. com/ 2100-1009_22-1020653. html) By John Lui, CNETAsia [13] A Pragmatic Report on IPv4 Address Space Consumption (http:/ / www. cisco. com/ web/ about/ ac123/ ac147/ archived_issues/ ipj_8-3/ ipv4. html) by Tony Hain, Cisco Systems [14] Proposed Global Policy for the Allocation of the Remaining IPv4 Address Space (http:/ / www. ripe. net/ ripe/ policies/ proposals/ 2008-03. html) [15] IPv4 Address Report (http:/ / www. potaroo. net/ tools/ ipv4/ ) [16] RFC 1726, Technical Criteria for Choosing IP The Next Generation (IPng), Partridge C., Kastenholz F. (December 1994) [17] U.S. Census Bureau (http:/ / www. census. gov/ main/ www/ popclock. html) [18] "Moving to IPv6: Now for the hard part (FAQ) | Deep Tech – CNET News" (http:/ / news. cnet. com/ 8301-30685_3-20030482-264. html). . Retrieved 2011-02-03. [19] RFC 2071, Network Renumbering Overview: Why would I want it and what is it anyway?, P. Ferguson, H. Berkowitz (January 1997)
  • 33. IPv6 31 [20] RFC 2072, Router Renumbering Guide, H. Berkowitz (January 1997) [21] RFC 1112, Host extensions for IP multicasting, S. Deering (August 1989) [22] RFC 3956, Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address, P. Savola, B. Haberman (November 2004) [23] RFC 2908, The Internet Multicast Address Allocation Architecture, D. Thaler, M. Handley, D. Estrin (September 2000) [24] RFC 3306 [25] RFC 4862, IPv6 Stateless Address Autoconfiguration, S. Thomson, T. Narten, T. Jinmei (September 2007) [26] RFC 2894, Router Renumbering for IPv6, M. Crawford, August 2000. [27] UDP/IPv4 may actually have a checksum of 0, indicating no checksum; IPv6 requires UDP to have its own checksum. [28] This improvement may have been made less necessary by the development of routers that perform checksum computation at link speed using dedicated hardware, but it is still relevant for software based routers. [29] RFC 3963, Network Mobility (NEMO) Basic Protocol Support, V. Devarapalli, R. Wakikawa, A. Petrescu, P. Thubert (January 2005) [30] RFC 2675, IPv6 Jumbograms, D. Borman, S. Deering, R. Hinden (August 1999) [31] RFC 4291 IP Version 6 Addressing Architecture, R. Hinden, S. Deering (February 2006) [32] The sheer size of IPv6 (http:/ / pthree. org/ 2009/ 03/ 08/ the-sheer-size-of-ipv6/ ) [33] RFC 4291 p. 9 [34] "IPv6 Address Allocation and Assignment Policy" (http:/ / www. ripe. net/ ripe/ docs/ ripe-512). RIPE NCC. 8 February 2011. . Retrieved 27 March 2011. [35] "Comcast Activates First Users With IPv6 Native Dual Stack Over DOCSIS" (http:/ / blog. comcast. com/ 2011/ 01/ comcast-activates-first-users-with-ipv6-native-dual-stack-over-docsis. html). Comcast. 31 January 2011. . [36] To convert a 48-bit MAC address to IPv6 EUI-64 format host address, first the 7th bit (scope bit) is flipped (so, for instance, 00 becomes 02 and vice-versa). Then 2 bytes with the value 0xFFFE are inserted between the vendor portion (the first 3 bytes) and the host portion (the last 3 bytes) of the MAC address. This pads the 48-bit address to 64 bits. "Recipe 25.1. Automatically Generating IPv6 Addresses for an Interface" (http:/ / fengnet. com/ book/ Cisco. IOS. Cookbook. 2nd/ I_0596527225_CHP_25_SECT_2. html). . Retrieved 14 March 2011. [37] IPv6 Transition Mechanism / Tunneling Comparison (http:/ / www. sixxs. net/ faq/ connectivity/ ?faq=comparison) [38] RFC4291 (http:/ / tools. ietf. org/ html/ rfc4291) [39] OpenBSD inet6(4) manual page (http:/ / www. openbsd. org/ cgi-bin/ man. cgi?query=inet6& apropos=0& sektion=0& manpath=OpenBSD+ Current& arch=i386& format=html#PROTOCOLS) [40] RFC 3493 - Basic Socket Interface Extensions for IPv6 (http:/ / tools. ietf. org/ html/ rfc3493#page-22) [41] RFC 3056 Connection of IPv6 Domains via IPv4 Clouds, B. Carpenter, Februari 2001. [42] RFC 4380 Teredo: Tunneling IPv6 over UDP through Network Address Translations (NATs), C. Huitema, Februari 2006 [43] The Windows Vista Developer Story: Application Compatibility Cookbook (http:/ / msdn2. microsoft. com/ en-us/ library/ aa480152. aspx) [44] RFC 5214 Intra-Site Automatic Tunnel Addressing Protocol (ISATAP), F. Templin, T. Gleeson, D. Thaler, March 2008. [45] RFC 3053, IPv6 Tunnel Broker, A. Durand, P. Fasano, I. Guardini, D. Lento (January 2001) [46] RFC 4966 Reasons to Move the Network Address Translator – Protocol Translator (NAT-PT) to Historic Status [47] Web sites must support IPv6 by 2012, expert warns (http:/ / www. networkworld. com/ news/ 2010/ 012110-ipv6-warning. html), Network World, 21 January 2010, , retrieved 2010-09-30 [48] RFC 5211 [49] "Networking IPv6 User Guide for JDK/JRE 5.0" (http:/ / java. sun. com/ j2se/ 1. 5. 0/ docs/ guide/ net/ ipv6_guide/ index. html). . Retrieved 2007-09-30. [50] "DOCSIS 2.0 Interface" (http:/ / www. cablemodem. com/ specifications/ specifications20. html). 2007-10-29. . Retrieved 2009-08-31. [51] (http:/ / rmv6tf. org/ 2008-IPv6-Summit-Presentations/ Dan Torbet - IPv6andCablev2. pdf) [52] ABI Research (2007-08-23). "DOCSIS 3.0 Network Equipment Penetration to Reach 60% by 2011" (http:/ / www. abiresearch. com/ abiprdisplay. jsp?pressid=710). Press release. . Retrieved 2007-09-30. [53] Geoff Huston – An Update on IPv6 Deployment (RIPE 56) (http:/ / www. ripe. net/ ripe/ meetings/ ripe-56/ presentations/ Huston-Measuring_IPv6_Deployment. pdf) [54] Mike Leber (2010-10-02). "Global IPv6 Deployment Progress Report" (http:/ / bgp. he. net/ ipv6-progress-report. cgi). Hurricane Electric. . Retrieved 2010-10-02. [55] The Beijing Organizing Committee for the Games of the XXIX Olympiad (2008-05-30). " leaps to next-generation Net" (http:/ / en. beijing2008. cn/ news/ official/ preparation/ n214384681. shtml). Press release. . [56] Das, Kaushik (2008). "IPv6 and the 2008 Beijing Olympics" (http:/ / ipv6. com/ articles/ general/ IPv6-Olympics-2008. htm). . Retrieved 2008-08-15. "As thousands of engineers, technologists have worked for a significant time to perfect this (IPv6) technology, there is no doubt, this technology brings considerable promises but this is for the first time that it will showcase its strength when in use for such a mega-event." [57] Official Google Blog (http:/ / googleblog. blogspot. com/ 2008/ 05/ looking-towards-ipv6. html) announcing IPv6 support [58] Derek Morr (2009-06-09). "Verizon Mandates IPv6 Support for Next-Gen Cell Phones" (http:/ / www. circleid. com/ posts/ 20090609_verizon_mandates_ipv6_support_for_next_gen_cell_phones/ ). CircleID. . [59] Rob Issac (2008), Welcome to your IPv6 enabled transit network. Whether you like it, or not (http:/ / www. ausnog. net/ files/ ausnog-03/ presentations/ ausnog03-ward-IPv6_enabled_network. pdf),
  • 34. IPv6 32 [60] Comparison of IPv6 support in operating systems Comparison of IPv6 support in operating systems [61] Vista: How PPPv6 support works? (http:/ / blogs. technet. com/ b/ rrasblog/ archive/ 2006/ 12/ 15/ vista-how-pppv6-support-works. aspx) [62] (http:/ / www. ietf. org/ rfc/ rfc3041. txt), Privacy Extensions for Stateless Address Autoconfiguration in IPv6, T. Narten, R. Draves, 2001-01. [63] Statement on IPv6 Address Privacy (http:/ / playground. sun. com/ ipv6/ specs/ ipv6-address-privacy. html), Steve Deering & Bob Hinden, Co-Chairs of the IETFs IP Next Generation Working Group , 1999-11-06. [64] IPv6: Privacy Extensions einschalten (http:/ / www. heise. de/ netze/ artikel/ IPv6-Privacy-Extensions-einschalten-1204783. html), Reiko Kaps, 2011-04-13 [65] Privacy Extensions (IPv6) (http:/ / www. elektronik-kompendium. de/ sites/ net/ 1601271. htm), Elektronik Kompendium. [66] Neues Internet-Protokoll erschwert anonymes Surfen (http:/ / www. spiegel. de/ netzwelt/ web/ 0,1518,729340,00. html), Konrad Lischka, Spiegel Online, 2010-11-18. [67] Linux IPv6 Development Project (http:/ / linux-ipv6. org/ stable-6-ann. html) [68] IPv6 support shipping in AIX 3.3 (http:/ / dict. regex. info/ ipv6/ 6bone/ 6bone. mail-1998-01/ 0022. html) [69] Its AIX 4.3. (http:/ / dict. regex. info/ ipv6/ 6bone/ 6bone. mail-1998-01/ 0024. html) [70] DEC/Compaq IPv6 history (http:/ / www. ipv6-es. com/ 02/ docs/ yanick_pouffary_2. pdf) [71] Internet Protocol Version 6 (old Microsoft Research IPv6 release) (http:/ / research. microsoft. com/ msripv6/ ) [72] KAME project (http:/ / www. kame. net/ ) [73] Sun Solaris 8 changes from Solaris 7 (http:/ / www. ocf. berkeley. edu/ solaris/ versions/ solaris/ 8. html) [74] Cisco main IPv6 site (http:/ / www. cisco. com/ en/ US/ products/ ps6553/ products_ios_technology_home. html) [75] HP main IPv6 site (http:/ / www. hp. com/ network/ ipv6) [76] IPv6 and Broadband (http:/ / www. ipv6tf. org/ pdf/ ISTClusterbooklet2005. pdf) ISBN 3-00-013801, published 2005, accessed 2011-01-12 [77] Microsofts main IPv6 site (http:/ / www. microsoft. com/ ipv6) [78] "IBM: z/OS operating system" (http:/ / www-03. ibm. com/ servers/ eserver/ zseries/ announce/ zos_r4/ ). . Retrieved 2009-08-31. [79] Mac OS X 10.3 Using IPv6 (http:/ / docs. info. apple. com/ article. html?artnum=152309) *** Document not found error message *** 2008-11-14 [80] Linux 2.6.12 changelog (http:/ / kernelnewbies. org/ Linux_2_6_12) [81] Apple AirPort Extreme technical specifications. (http:/ / www. apple. com/ airportextreme/ specs. html) [82] IPv6: coming to a root server near you (http:/ / arstechnica. com/ news. ars/ post/ 20080102-icann-to-add-ipv6-addresses-for-root-dns-servers. html) [83] IANA – IPv6 Addresses for the Root Servers (http:/ / www. iana. org/ reports/ root-aaaa-announcement. html) [84] http:/ / ipv6. google. com [85] IETF 71 IPv4 Outage (https:/ / wiki. tools. isoc. org/ IETF71_IPv4_Outage) [86] http:/ / ec. europa. eu/ information_society/ policy/ ipv6/ docs/ european_day/ communication_final_27052008_en. pdf [87] Action Plan for the deployment of Internet Protocol version 6 (IPv6) in Europe (http:/ / www. ipv6tf. org/ index. php?id=3882& lan=en& page=news/ newsroom) The IPv6 Portal, published 2008-05-27, accessed 2011-01-12 [88] http:/ / www. google. com/ intl/ en/ ipv6/ [89] World IPv6 Day (http:/ / isoc. org/ wp/ worldipv6day/ ) Internet Society, accessed 2011-05-25 [90] ISOC Monthly Newsletter – Major Websites Commit to 24-Hour Test Flight for IPv6 (http:/ / isoc. org/ wp/ newsletter/ ?p=2902) Internet Society, published 2011-01-12, accessed 2011-05-25 References External links • IPv6 ( at the Open Directory Project • IPv6 News – Daily Updated and IPv6 Portal + IPv6 Task Forces ( • IPv6 Backbone Network Topology ( • IPv4 Exhaustion Counter ( • ( Technical information on IPv6 deployment from ARIN • 6DEPLOY ( – IPv6 deployment support action within the European 7th Framework Programme, featuring an extensive list of tutorials ( • List of product, services and applications with IPv6 support ( • Why IPv6 matters to radio stations ( • Security implications of implementing IPv6 ( EstudiosInformes/cert_inf_security_implications_ipv6.pdf)
  • 35. IPv6 33 • Free Pool of IPv4 Address Space Depleted (
  • 36. Article Sources and Contributors 34 Article Sources and Contributors Portable Document Format  Source:  Contributors: 5gXhlp2fd, 7H4 6U713RR3Z, ?alabio, A bit iffy, ABF, ACBest, AThing, AVRS, Aarchiba, Abelardia, Acrobatfiles, Adam7davies, Addicted, Aerotee965, Ahoerstemeier, Aidnieci, Aido2002, Akhristov, Albert.meronyo, Alex43223, AlexTheHorrible, Alexjohnc3, AlistairMcMillan, Allstarecho, Amelio Vázquez, Amitpagarwal, AnOddName, Andrevan, AndrewJD, AndrewKepert, Andrewa, Anna Lincoln, Anne226, AnonMoos, Anonymous101, Ansiansiansi, Apatterno, Armando, Art LaPella, AshishKulkarni, Aubrey Jaffer, Ayeroxor, B9 hummingbird hovering, Barneca, Behlal, Beinsane, Beland, Belegdal, Benc, Bender235, Bennose, Bentleyd, Bfinn, BladeHamilton, Blakkandekka, Bobblehead, Bobcat hokie, Bogdan.nemteanu, Boombaard, Boredzo, Boris Alexeev, Bortek, BrandonCsSanders, Brazil4Linux, Brentbucci, Brianeversole, Brianyoumans, Bridgeway04, Buchs, CDV, Callidior, Cant sleep, clown will eat me, Canageek, Carrasco, CesarB, Chensiyuan, Chiborg, Chocolateboy, Chovain, Cliffb, Cochonfou, Coldacid, Colm.mcmullan, Colonel Warden, Conversion script, Coolhawks88, Copeland.James.H, Cornlad, Corti, Crissov, Ctxppc, CyberSkull, D-Day, D. 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  • 37. Image Sources, Licenses and Contributors 35 Image Sources, Licenses and Contributors Image:PDF.png  Source:  License: Fair Use  Contributors: 7H4 6U713RR3Z, Bkell, Kahlil88, Kingturtle, Koman90, Logan, MBisanz, Nyttend, Opertinicy, Scarecroe, Sdrtirs, Shahzad121, Silvergoat, Tuanese, VMS Mosaic, We hope, 百家姓之四, 19 anonymous edits Image:Ipv6 address leading zeros.svg  Source:  License: Public Domain  Contributors: Ipv6_address.svg: Indeterminate derivative work: BobbyPeru (talk) File:Ipv6 header.svg  Source:  License: Creative Commons Attribution-Sharealike 3.0,2.5,2.0,1.0  Contributors: Mro
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