Your SlideShare is downloading. ×
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Week 2   chapter 2
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

Week 2 chapter 2

396

Published on

Published in: Technology
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
396
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
36
Comments
0
Likes
0
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. 10/09/2012 Computer Communications & Networking Week 2 ISO/OSI Model 5th September 2012 OSI/ISO Seven Layers Model  To address the problem of networks being incompatible and unable to communicate with each other, the International Organization for Standardization (ISO) researched network schemes like TCP/IP in order to find a set of rules.  As a result of this research, the ISO created a network model that would help vendors create networks that would be compatible with, and operate with, other networks.  Rather than developing protocols, they identified which networking functions had related uses and collected those functions into discrete groups that became the layer 1
  • 2. 10/09/2012 The OSI reference model  The OSI reference model, released in 1984, was the descriptive scheme they created. It provided vendors with a set of standards that ensured greater compatibility and interoperability between the various types of network technologies that were produced by the many companies around the world.  In the OSI reference model, there are seven numbered layers, each of which illustrates a particular network function. This separation of networking functions is called layering. Each layer defines a family of functions distinct from those of the other layers 2
  • 3. 10/09/2012 Advantage of seven layers model  Dividing the network into these seven layers provides the following advantages:  It standardizes network components to allow multiple-vendor development and support.  It allows different types of network hardware and software to communicate with each other.  It prevents changes in one layer from affecting the other layers, so that they can develop more quickly.  It breaks network communication into smaller simpler parts to make learning it easier to understand. Encapsulation  The data portion of a packet at layer (n-1) carries whole packet (including data and headers) from layer n  A packet at layer 7 is encapsulated in a packet at layer 6, the whole packet of layer 6 is encapsulated into a packet at layer 5 and so on 3
  • 4. 10/09/2012 Application layer The application layer is responsible for providing services to the user. Layer 7: The Application Layer  It provides network services to the user’s applications.  It differs from the other layers in that it does not provide services to any other OSI layer, but rather, only to applications outside the OSI model.  Example browsers (http protocol), e-mail client like outlook express (pop3 protocol, smtp protocol), file transfer (ftp protocol), remote access (telnet) and NFS etc. 4
  • 5. 10/09/2012 Layer 7: The Application Layer  Remote login  ftp  Mail services Presentation layer The presentation layer is responsible for translation, compression, and encryption. 5
  • 6. 10/09/2012 Layer 6: The Presentation Layer  The presentation layer ensures that the information that the application layer of one system sends out is readable by the application layer of another system.  If necessary, the presentation layer translates between multiple data formats by using a common format.  If you want to think of Layer 6 in as few words as possible, think of a common data format.  Provides platform independence Layer 6: The Presentation Layer  Code Conversion  ASCII to EBCDIC  Encryption  For secure messages encryption at sender end and decryption at recipient end  Compression  To improve performance by reducing size of the message. 6
  • 7. 10/09/2012 Session layer The session layer is responsible for dialog control and synchronization Layer 5: The Session Layer  As its name implies, the session layer establishes, manages, and terminates sessions between two communicating hosts.  The session layer provides its services to the presentation layer.  It also synchronizes dialogue between the two hosts' presentation layers and manages their data exchange.  In addition to session regulation, the session layer offers provisions for efficient data transfer, class of service, and exception reporting of session layer, presentation layer, and application layer problems. 7
  • 8. 10/09/2012 Layer 5: The Session Layer  Dialog control  It allows communication between two processes to take place  Synchronization   Allows a process to add check points or synchronization points e.g. if transferring a file of 1000 pages, a checpoint may be inserted after every 10 page unit to ensure received acknowledgement In case of disconnection, the transferred pages should not be re-transmitted. Layer 4: The Transport Layer  The transport layer segments data from the sending host's system and reassembles the data into a data stream on the receiving host's system. The boundary between the session layer and the transport layer  Whereas the application, presentation, and session layers are concerned with application issues, the lower three layers are concerned with data transport issues  The transport layer attempts to provide a data transport service that shields the upper layers from transport implementation details. 8
  • 9. 10/09/2012 Source-to-destination delivery Transport layer The transport layer is responsible for the delivery of a message from one process to another 9
  • 10. 10/09/2012 Reliable process-to-process delivery of a message Layer 4: The Transport Layer  Specifically, issues such as how reliable transport between two hosts is accomplished is the concern of the transport layer.  In providing communication service, the transport layer establishes, maintains, and properly terminates virtual circuits.  In providing reliable service, transport error detection-and-recovery and information flow control are used.  If you want to remember Layer 4 in as few words as possible, think of quality of service, and reliability. 10
  • 11. 10/09/2012 Layer 4: The Transport Layer  Program Addressing  Segmentation and Reassembly  Connection control  Connection oriented transport protocol establishes connection with the recipient machine’s transport layer before exchange of message  Flow control  Flow control is performed end-to-end rather than across a single link  Error control  Error control from process to process rather than across a single link Hop-to-hop delivery The network layer is responsible for the delivery of individual packets from the source host to the destination host. 11
  • 12. 10/09/2012 Network layer Layer 3: The Network Layer  The network layer is a complex layer that provides connectivity and path selection between two host systems that may be located on geographically separated networks.  If you want to remember Layer 3 in as few words as possible, think of path selection, routing, and addressing.  Logical Addressing  Physical addresses can be used for data transmission within the same network and if a packet passes boundaries of the network, then we need another addressing scheme  Routing  In internetwork routers are used to route packets from source to destination 12
  • 13. 10/09/2012 Data link layer The data link layer is responsible for moving frames from one hop (node) to the next. Layer 2: The Data Link Layer  The data link layer provides reliable transit of data across a physical link.  In so doing, the data link layer is concerned with physical (as opposed to logical) addressing, network access, error notification, ordered delivery of frames, and flow control.  If you want to remember Layer 2 in as few words as possible, think of frames and media access control. 13
  • 14. 10/09/2012 Layer 2: The Data Link Layer  Framing  Converts network layer packets into frame  Physical Addressing  Flow Control  Sender and receiver should communicate at mutually accepted data rate  Error Control  Error detection mechanism  Access Control  When two or more devices are connected to the same link, then which device should have control over shared medium Layer 1: The Physical Layer  The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems.  Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors, and other, similar, attributes are defined by physical layer specifications.  If you want to remember Layer 1 in as few words as possible, think of signals and media. 14
  • 15. 10/09/2012 Physical Layer  Physical characteristics of medium  Representation of bits  Data rate  Synchronization of bits  Line configuration  Connection of devices to the media – point to point (dedicated) or multipoint – shared  Physical topology  Transmission mode    Simplex Half duplex Full duplex Physical layer The physical layer is responsible for Movements of individual bits from one hop (node) to the next. 15
  • 16. 10/09/2012 Summary of layers 16
  • 17. 10/09/2012 2-4 TCP/IP PROTOCOL SUITE The layers in the TCP/IP protocol suite do not exactly match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application. Topics discussed in this section: Physical and Data Link Layers Network Layer Transport Layer Application Layer TCP/IP and OSI model 17
  • 18. 10/09/2012 2-5 ADDRESSING Four levels of addresses are used in an internet employing the TCP/IP protocols: physical, logical, port, and specific. Topics discussed in this section: Physical Addresses Logical Addresses Port Addresses Specific Addresses Addresses in TCP/IP 18
  • 19. 10/09/2012 Relationship of layers and addresses in TCP/IP Example 2.1 In Figure 2.19 a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link (bus topology LAN). As the figure shows, the computer with physical address 10 is the sender, and the computer with physical address 87 is the receiver. 19
  • 20. 10/09/2012 Physical addresses Example 2.2 As we will see in Chapter 13, most local-area networks use a 48-bit (6-byte) physical address written as 12 hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon, as shown below: 07:01:02:01:2C:4B A 6-byte (12 hexadecimal digits) physical address. 20
  • 21. 10/09/2012 Example 2.3 Figure 2.20 shows a part of an internet with two routers connecting three LANs. Each device (computer or router) has a pair of addresses (logical and physical) for each connection. In this case, each computer is connected to only one link and therefore has only one pair of addresses. Each router, however, is connected to three networks (only two are shown in the figure). So each router has three pairs of addresses, one for each connection. IP addresses 21
  • 22. 10/09/2012 Example 2.4 Figure 2.21 shows two computers communicating via the Internet. The sending computer is running three processes at this time with port addresses a, b, and c. The receiving computer is running two processes at this time with port addresses j and k. Process a in the sending computer needs to communicate with process j in the receiving computer. Note that although physical addresses change from hop to hop, logical and port addresses remain the same from the source to destination. Port addresses 22
  • 23. 10/09/2012 Note The physical addresses will change from hop to hop, but the logical addresses usually remain the same. Example 2.5 As we will see in Chapter 23, a port address is a 16-bit address represented by one decimal number as shown. 753 A 16-bit port address represented as one single number. 23
  • 24. 10/09/2012 Note The physical addresses change from hop to hop, but the logical and port addresses usually remain the same. 24

×