Chapter07 -- wa ns and remote connectivity


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Chapter07 -- wa ns and remote connectivity

  1. 1. Chapter 7: WANs and Remote Connectivity Network+ Guide to Networks
  2. 2. Objectives <ul><li>Identify network applications that require WAN technology </li></ul><ul><li>Explain various WAN topologies, including their advantages and disadvantages </li></ul><ul><li>Describe a variety of WAN transmission and connection methods, including PSTN, ISDN, T-carriers, DSL, broadband cable, and SONET </li></ul>
  3. 3. Objectives (continued) <ul><li>Assess WAN implementation options based on speed, security, and reliability </li></ul><ul><li>Understand the hardware and software requirements for remotely connecting to a network </li></ul>
  4. 4. WANs and Remote Connectivity <ul><ul><li>A WAN is a network that connects two or more geographically distinct LANs </li></ul></ul><ul><ul><li>Remote connectivity and WANs are significant concerns for organizations attempting to meet the needs of telecommuting workers, global business partners, and Internet-based commerce </li></ul></ul>
  5. 5. WAN Essentials <ul><ul><li>A WAN is a network that traverses some distance and usually connects LANs, whether across the city or across the nation </li></ul></ul><ul><ul><li>The internet is the largest WAN in existence today7 </li></ul></ul><ul><ul><li>LANs use a building’s internal cabling, such as twisted-pair, that runs from work area to the wall, through plenum areas and to a telecommunications closet </li></ul></ul>
  6. 6. WAN Essentials (continued) <ul><ul><li>WANs typically send data over publicly available communications networks, which are owned by local and long-distance telecommunications carriers </li></ul></ul><ul><ul><ul><li>Such carriers, which are privately owned corporations, are also known as network service providers (NSPs) </li></ul></ul></ul>
  7. 7. WAN Essentials (continued) <ul><ul><li>For better throughput, an organization might lease a dedicated line, or a continuously available communications channel, from a telecommunications provider, such as a local telephone company or ISP </li></ul></ul><ul><ul><li>A WAN link is a connection between one WAN site (or point) and another site (or point) </li></ul></ul>
  8. 8. WAN Topologies <ul><li>Bus </li></ul><ul><ul><li>A WAN in which each site is directly connected to no more than two other sites in a serial fashion is known as a bus topology WAN </li></ul></ul><ul><ul><ul><li>A bus topology WAN is similar to a bus topology LAN in that each site depends on every other site in the network to transmit and receive its traffic </li></ul></ul></ul><ul><ul><ul><li>The WAN bus topology uses different locations, each one connected to another one through point-to-point links </li></ul></ul></ul>
  9. 9. WAN Topologies (continued) <ul><ul><ul><li>A bus topology WAN is often the best option for organizations with only a few sites and the capability to use dedicated circuits </li></ul></ul></ul><ul><ul><ul><li>Bus WAN topologies are suitable for only small WANs </li></ul></ul></ul><ul><ul><ul><li>A single failure on a bus topology WAN can take down communications between all sites </li></ul></ul></ul>
  10. 10. WAN Topologies (continued) <ul><li>Ring </li></ul><ul><ul><li>In a ring topology WAN, each site is connected to two other sites so that the entire WAN forms a ring pattern </li></ul></ul><ul><ul><li>This architecture is similar to the simple ring topology used on a LAN, except that a WAN ring topology connects locations rather than local nodes and in most WANs, a ring topology uses two parallel paths for data </li></ul></ul>
  11. 11. WAN Topologies (continued) <ul><ul><li>A ring topology WAN cannot not be taken down by the loss of one site; instead, if one site fails, data can be rerouted around the WAN in a different direction </li></ul></ul><ul><ul><li>WANs that use the ring topology are only practical for connecting fewer than four or five locations </li></ul></ul>
  12. 12. WAN Topologies (continued) <ul><li>Star </li></ul><ul><ul><li>The star topology WAN mimics the arrangement of a star topology LAN </li></ul></ul><ul><ul><li>A single site acts as the central connection point for several other points </li></ul></ul>
  13. 13. WAN Topologies (continued) <ul><ul><li>If a single connection fails, only one location loses WAN access </li></ul></ul><ul><ul><li>When all of its dedicated circuits are functioning, a star WAN provides shorter data paths between any two sites </li></ul></ul>
  14. 14. WAN Topologies (continued) <ul><li>Mesh </li></ul><ul><ul><li>A mesh topology WAN incorporates many directly interconnected sites </li></ul></ul><ul><ul><li>Because every site is interconnected, data can travel directly from its origin to its destination </li></ul></ul><ul><ul><li>Mesh WANs are the most fault-tolerant type of WAN because they provide multiple routes for data to follow between any two points </li></ul></ul>
  15. 15. WAN Topologies (continued) <ul><ul><li>The type of mesh topology in which every WAN site is directly connected to every other site is called a full mesh WAN </li></ul></ul><ul><ul><li>Partial mesh WAN are used when only critical WAN sites are directly interconnected and secondary sites are connected through star or ring topologies </li></ul></ul><ul><ul><li>Partial mesh WANs are more common in today’s business world than full mesh WANs because they are more economical </li></ul></ul>
  16. 16. WAN Topologies (continued) <ul><li>Tiered </li></ul><ul><ul><li>In a tiered topology WAN, sites connected in star or ring formations are interconnected at different levels, with the interconnection points being organized into layers to form hierarchical groupings </li></ul></ul>
  17. 17. WAN Topologies (continued) <ul><ul><li>Tiered systems allow for easy expansion and inclusion of redundant links to support growth </li></ul></ul><ul><ul><li>Their enormous flexibility means that creation of tiered WANs requires careful consideration of geography, usage patterns, and growth potential </li></ul></ul>
  18. 18. PSTN <ul><ul><li>Stands for Public Switched Telephone Network </li></ul></ul><ul><ul><li>Refers to the network of typical telephone lines and carrier equipment that service most homes </li></ul></ul><ul><ul><li>PSTN may also be called plain old telephone service (POTS) </li></ul></ul><ul><ul><li>The PSTN comprises the entire telephone system, from the lines that connect homes and businesses to the network centers that connect different regions of a country </li></ul></ul>
  19. 19. PSTN (continued) <ul><ul><li>The PSTN is often used by individuals connecting to a WAN (such as the Internet) via a dial-up connection </li></ul></ul><ul><ul><li>A dial-up connection is one in which a user connects, via a modem, to a distant network from a computer and stays connected for a finite period of time </li></ul></ul>
  20. 20. PSTN (continued) <ul><ul><li>A central office is the place where a telephone company terminates lines and switches calls between different locations </li></ul></ul><ul><ul><li>The portion of the PSTN that connects your house to the nearest central office is known as the local loop, or the last mile </li></ul></ul>
  21. 21. X.25 <ul><ul><li>X.25 is an analog, packet-switched technology designed for long-distance data transmission </li></ul></ul><ul><ul><li>The X.25 standard specifies protocols at the Physical, Data Link, and Network layers of the OSI Model </li></ul></ul><ul><ul><li>The X.25 provides excellent flow control and ensures data reliability over long distances by verifying the transmission at every node </li></ul></ul><ul><ul><li>X.25 checks for errors and, in the case of an error, either corrects the damaged data or retransmits the original data </li></ul></ul>
  22. 22. Frame Relay <ul><ul><li>An updated, digital version of X.25 that also relies on packet switching </li></ul></ul><ul><ul><li>Frame Relay protocols operate at the Data Link layer of the OSI Model and can support multiple different Network and Transport layer protocols </li></ul></ul><ul><ul><li>The name is derived from the fact that data is separated into frames, which are then relayed from one node to another without any verification or processing </li></ul></ul><ul><ul><li>Frame Relay does not guarantee reliable delivery of data </li></ul></ul>
  23. 23. X.25 and Frame Relay <ul><ul><li>Both X.25 and Frame Relay may be configured as switched virtual circuits (SVCs) or permanent virtual circuits (PVCs) </li></ul></ul><ul><ul><li>SVCs are connections that are established when parties need to transmit, then terminated once the transmission is complete </li></ul></ul><ul><ul><li>PVCs are connections that are established before data needs to be transmitted and maintained after the transmission is complete and they are not dedicated, individual links </li></ul></ul><ul><ul><li>The service provider guarantees a minimum amount of bandwidth, called the committed information rate (CIR) </li></ul></ul>
  24. 24. ISDN <ul><ul><li>Integrated Services Digital Network is an international standard for transmitting digital data over the PSTN </li></ul></ul><ul><ul><li>ISDN specifies protocols at the Physical, Data Link, and Transport layers of the OSI Model </li></ul></ul><ul><ul><li>ISDN relies on the PSTN for its transmission medium </li></ul></ul><ul><ul><li>ISDN is distinguished because it can simultaneously carry as many as two voice calls and one data connection on a single line </li></ul></ul>
  25. 25. ISDN (continued) <ul><ul><li>All ISDN connections are based on two types of channels: B channels and D channels </li></ul></ul><ul><ul><li>The B channel is the “bearer” channel, employing circuit-switching techniques to carry voice, video, audio, and other types of data over the ISDN connection </li></ul></ul><ul><ul><li>The D channel is the “data” channel, employing packet-switching techniques to carry information about the call, such as session initiation and termination signals, caller identity, call forwarding, and conference calling signals </li></ul></ul>
  26. 26. ISDN (continued) <ul><ul><li>In North America, two types of ISDN connections are commonly used: Basic Rate Interface (BRI) and Primary Rate Interface (PRI) </li></ul></ul><ul><ul><li>BRI (Basic Rate Interface) uses two B channels and one D channel </li></ul></ul><ul><ul><li>In a process called bonding, these two 64-Kbps B channels can be combined to achieve an effective throughput of 128 Kbps </li></ul></ul>
  27. 27. ISDN (continued) <ul><ul><li>PRI (Primary Rate Interface) uses 23 B channels and one 64-Kbps D channel </li></ul></ul><ul><ul><li>PRI is less commonly used by individual subscribers than BRI is, but it may be selected by businesses and other organizations that need more throughput </li></ul></ul><ul><ul><li>PRI link can carry voice and data, independently of each other or bonded together </li></ul></ul>
  28. 28. T-Carriers <ul><ul><li>T-carrier standards specify a method of signaling, which means they belong to the Physical layer of the OSI Model </li></ul></ul><ul><ul><li>A T-carrier uses time division multiplexing (TDM) over two wire pairs (one for transmitting and one for receiving) to divide a single channel into multiple channels </li></ul></ul><ul><ul><li>Each channel may carry data, voice, or video signals </li></ul></ul><ul><ul><li>The medium used for T-carrier signaling can be ordinary telephone wire, fiber-optic cable, or wireless links </li></ul></ul>
  29. 29. T-Carriers (continued) <ul><li>Types of T-Carriers </li></ul><ul><ul><li>T1 circuit can carry the equivalent of 24 voice or data channels, giving a maximum data throughput of 1.544 Mbps </li></ul></ul><ul><ul><li>A T3 circuit can carry the equivalent of 672 voice or data channels, giving a maximum data throughput of 44.736 Mbps </li></ul></ul>
  30. 30. T-Carriers (continued) <ul><ul><li>A fractional T1 lease allows organizations to use only some of the channels on a T1 line and be charged according to the number of channels they use </li></ul></ul><ul><ul><li>The signal level refers to the T-carrier’s Physical layer electrical signaling characteristics </li></ul></ul><ul><ul><li>DS0 (digital signal, level 0) is the equivalent of one data or voice channel </li></ul></ul>
  31. 31. T-Carriers (continued) <ul><li>T-Carrier Connectivity </li></ul><ul><ul><li>Every T-carrier line requires connectivity hardware at both the customer site and the local telecommunications provider’s switching facility </li></ul></ul><ul><ul><li>T-carrier lines require specialized connectivity hardware that cannot be used with other WAN transmission methods </li></ul></ul><ul><ul><li>T-carrier lines require different media depending on their throughput </li></ul></ul><ul><ul><li>Wiring </li></ul></ul><ul><ul><ul><li>T1 technology can use unshielded or shielded twisted-pair (UTP or STP) copper wiring </li></ul></ul></ul><ul><ul><ul><li>STP is preferable to UTP </li></ul></ul></ul>
  32. 32. T-Carriers (continued) <ul><li>CSU/DSU (Channel Service Unit/Data Service Unit) </li></ul><ul><ul><li>The CSU/DSU is the connection point for a T1 line at the customer’s site </li></ul></ul><ul><ul><li>The CSU provides termination for the digital signal and ensures connection integrity through error correction and line monitoring </li></ul></ul><ul><ul><li>The DSU converts the T-carrier frames into frames the LAN can interpret and vice versa </li></ul></ul><ul><ul><li>After being demultiplexed, an incoming T-carrier signal passes on to devices collectively known as terminal equipment </li></ul></ul>
  33. 33. T-Carriers (continued) <ul><li>Terminal Equipment </li></ul><ul><ul><li>On a typical T1-connected data network, the terminal equipment will consist of switches, routers, or bridges </li></ul></ul><ul><ul><li>Usually, a router or Layer 3 or higher switch is the best option, because these devices can translate between different Layer 3 protocols that might be used on the WAN and LAN </li></ul></ul><ul><ul><li>On some implementations, the CSU/DSU is not a separate device, but is integrated with the router or switch as an expansion card </li></ul></ul>
  34. 34. DSL <ul><ul><li>Digital subscriber line (DSL) is a WAN connection method introduced by researchers at Bell Laboratories in the mid-1990s </li></ul></ul><ul><ul><li>DSL can span only limited distances without the help of repeaters and is therefore best suited to the local loop portion of a WAN link </li></ul></ul><ul><ul><li>DSL can support multiple data and voice channels over a single line </li></ul></ul><ul><ul><li>DSL uses advanced data modulation techniques </li></ul></ul>
  35. 35. DSL (continued) <ul><li>Types of DSL </li></ul><ul><ul><li>The term xDSL refers to all DSL varieties, of which at least eight currently exist </li></ul></ul><ul><ul><li>DSL types can be divided into two categories: asymmetrical and symmetrical </li></ul></ul><ul><ul><li>The term downstream refers to data traveling from the carrier’s switching facility to the customer </li></ul></ul><ul><ul><li>Upstream refers to data traveling from the customer to the carrier’s switching facility </li></ul></ul>
  36. 36. DSL (continued) <ul><ul><li>A technology that offers more throughput in one direction than in the other is considered asymmetrical </li></ul></ul><ul><ul><ul><li>In asymmetrical communications, downstream throughput is higher than upstream throughput </li></ul></ul></ul><ul><ul><li>Symmetrical technology provides equal capacity for data traveling both upstream and downstream </li></ul></ul><ul><ul><ul><li>Symmetrical transmission is suited to users who both upload and download significant amounts of data </li></ul></ul></ul>
  37. 37. DSL (continued) <ul><li>DSL Connectivity </li></ul><ul><li>A DSL modem is a device that modulates outgoing signals and demodulates incoming DSL signals </li></ul><ul><ul><li>The DSL modem may be external to the computer and connect to a computer’s Ethernet NIC via an RJ-45,USB, or wireless interface </li></ul></ul><ul><ul><li>DSL access multiplexer (DSLAM) aggregates multiple DSL subscriber lines and connects them to a larger carrier or to the Internet backbone </li></ul></ul><ul><ul><li>DSL is not available in all areas of the United States </li></ul></ul>
  38. 38. Cable <ul><ul><li>Cable connections require that the customer use a special cable modem, a device that modulates and demodulates signals for transmission and reception via cable wiring </li></ul></ul><ul><ul><li>Cable modems operate at the Physical and Data Link layer of the OSI Model, and therefore do not manipulate higher-layer protocols such as IP or IPX </li></ul></ul><ul><ul><li>To provide Internet access through its network, the cable company must upgrade its existing equipment to support bidirectional, digital communications </li></ul></ul><ul><ul><li>The cable company’s network wiring must be replaced with hybrid fiber-coax (HFC), an expensive fiber-optic link that can support high frequencies </li></ul></ul>
  39. 39. Cable (continued) <ul><ul><ul><li>Either fiber-optic or coaxial cable may connect the node to the customer’s business or residence via a connection known as a cable drop </li></ul></ul></ul><ul><ul><ul><li>These nodes then connect to the cable company’s central office, which is known as its head-end </li></ul></ul></ul>
  40. 40. SONET <ul><ul><li>SONET (Synchronous Optical Network) is a high-bandwidth WAN signaling technique </li></ul></ul><ul><ul><li>SONET specifies framing and multiplexing techniques at the Physical layer of the OSI Model </li></ul></ul>
  41. 41. SONET (continued) <ul><ul><li>Its four key strengths are that it: can integrate many other WAN technologies; offers fast data transfer rates; allows for simple link additions and removals; and provides a high degree of fault tolerance </li></ul></ul><ul><ul><li>The word synchronous means that data being transmitted and received by nodes must conform to a timing scheme </li></ul></ul>
  42. 42. SONET (continued) <ul><ul><li>SONET provides interoperability </li></ul></ul><ul><ul><li>SONET is often used to aggregate multiple T1s, T3s, or ISDN lines </li></ul></ul><ul><ul><li>SONET is also used as the underlying technology for ATM transmission </li></ul></ul><ul><ul><li>Internationally, SONET is known as SDH (Synchronous Digital Hierarchy) </li></ul></ul><ul><ul><li>SONET’s extraordinary fault tolerance results from its use of a double-ring topology over fiber-optic cable </li></ul></ul><ul><ul><li>Self-healing is a characteristic of dual-ring topologies that allows them to automatically reroute traffic along the backup ring if the primary ring becomes severed </li></ul></ul>
  43. 43. SONET (continued) <ul><ul><li>Most SONET multiplexers allow for easy additions or removals of connections to the SONET ring, which makes this technology easily adaptable to growing and changing networks </li></ul></ul><ul><ul><li>The data rate of a particular SONET ring is indicated by its Optical Carrier (OC) level </li></ul></ul>
  44. 44. WAN Implementation <ul><li>Reliability </li></ul><ul><li>A WAN’s reliability depends partly on the transmission medium it uses and partly on its topology and transmission methods </li></ul><ul><ul><li>Not very reliable, suited to individual or unimportant transmissions: PSTN dial-up </li></ul></ul><ul><ul><ul><li>Sufficiently reliable, suited for day-to-day transmissions: ISDN,T1, fractional T1, T3, DSL, cable, X.25, and Frame Relay </li></ul></ul></ul><ul><ul><ul><li>Very reliable, suited to mission-critical applications: SONET </li></ul></ul></ul>
  45. 45. WAN Implementation (continued) <ul><li>Security </li></ul><ul><ul><li>Fiber optic media are the most secure transmission media </li></ul></ul><ul><ul><li>WAN security depends in part on the encryption measures each carrier provides for its lines </li></ul></ul><ul><ul><li>Enforce password-based authorization for LAN and WAN access and teach users how to choose difficult-to-decrypt passwords </li></ul></ul><ul><ul><li>Take the time to develop, publish, and enforce a security policy for users in your organization </li></ul></ul><ul><ul><li>Maintain restricted access to network equipment rooms and data centers </li></ul></ul>
  46. 46. Remote Connectivity <ul><li>As a remote user, you must connect to a LAN via remote access, which can be accomplished in one of several ways: dial-up networking, remote control, terminal services, Web portals, or a virtual private network (VPN) </li></ul>
  47. 47. Remote Connectivity (continued) <ul><li>Dial-up Networking </li></ul><ul><ul><li>Dial-up networking refers to dialing into a private network’s or ISP’s remote access server to log on to a network </li></ul></ul><ul><ul><li>The remote access server (a server designed to accept incoming client connections) is attached to a group of modems, all of which are associated with one phone number </li></ul></ul><ul><ul><li>An advantage to using this remote access option are that the technology is well-understood and its software comes with virtually every operating system </li></ul></ul><ul><ul><li>Dialing into a remote access server can be slow because it relies on the PSTN </li></ul></ul>
  48. 48. Remote Connectivity (continued) <ul><ul><li>One well known program used to provide remote access is the Microsoft Routing and Remote Access Service (RRAS), which is available with the Windows Server 2003 network operating system </li></ul></ul><ul><ul><li>The Serial Line Internet Protocol (SLIP) and Point-to-Point Protocol (PPP) are two protocols that enable a workstation to connect to another computer using a serial connection </li></ul></ul>
  49. 49. Remote Connectivity (continued) <ul><li>Remote Control </li></ul><ul><ul><li>Remote control allows the remote user to “take over” a computer that’s directly connected to the LAN </li></ul></ul><ul><ul><li>Remote control is not difficult to configure, but suffers from the same slow throughput as dialing into a remote access server </li></ul></ul><ul><ul><li>Another disadvantage to this solution is that it allows only one connection to the LAN at any given time </li></ul></ul>
  50. 50. Remote Connectivity (continued) <ul><li>Terminal Services </li></ul><ul><ul><li>In terminal services, multiple remote computers can connect to a terminal server on the LAN </li></ul></ul><ul><ul><li>A terminal server is a computer that runs specialized software that allows it to act as a host and supply applications and resource sharing to remote clients </li></ul></ul>
  51. 51. Remote Connectivity (continued) <ul><ul><li>Many companies have created software to supply terminal services </li></ul></ul><ul><ul><ul><li>Microsoft’s version of this solution is called Terminal Services </li></ul></ul></ul><ul><ul><ul><li>Citrix System, Inc.’s version is Metaframe and remote workstations rely on software known as an ICA (Independent Computing Architecture) client </li></ul></ul></ul>
  52. 52. <ul><li>Web Portals </li></ul><ul><ul><li>A Web portal is simply a secure, Web-based interface to an application </li></ul></ul><ul><ul><li>Any type of Internet connection is sufficient for using Web portals </li></ul></ul><ul><ul><li>On the host side, a Web server supplies the application to multiple users upon request </li></ul></ul><ul><ul><li>The use of Web portals calls for secure transmission protocols </li></ul></ul>Remote Connectivity (continued)
  53. 53. <ul><ul><li>Virtual private networks (VPNs) are wide area networks logically defined over public transmission systems </li></ul></ul><ul><ul><li>To allow access to only authorized users, traffic on a VPN is isolated from other traffic on the same public lines </li></ul></ul><ul><ul><li>The software required to establish VPNs is usually inexpensive, and in some cases is being included with other widely used software </li></ul></ul><ul><ul><li>RRAS allows you to create a simple VPN by turning a Windows server into an access server and allowing clients to dial into it </li></ul></ul>Virtual Private Networks (VPN)
  54. 54. <ul><ul><li>Two important considerations when designing a VPN are interoperability and security </li></ul></ul><ul><ul><li>To make sure a VPN can carry all types of data in a private manner over any kind of connection, special VPN protocols encapsulate higher-layer protocols in a process known as tunneling </li></ul></ul><ul><ul><li>A VPN tunneling protocol operates at the Data Link layer and encapsulates Network layer packets </li></ul></ul>Virtual Private Networks (VPN) (continued)
  55. 55. <ul><ul><li>Two major types of tunneling protocols are used on contemporary VPNs: PPTP or L2TP </li></ul></ul><ul><ul><li>PPTP (Point-to-Point Tunneling Protocol) is a protocol developed by Microsoft that expands on PPP by encapsulating it so that any type of PPP data can traverse the Internet masked as an IP or IPX transmission </li></ul></ul><ul><ul><li>Another VPN tunneling protocol is L2TP (Layer 2 Tunneling Protocol), based on technology developed by Cisco and standardized by the IETF </li></ul></ul>Virtual Private Networks (VPN) (continued)
  56. 56. Summary <ul><li>Network applications that require WAN technology </li></ul><ul><li>WAN topologies, including their advantages and disadvantages </li></ul><ul><li>WAN transmission and connection methods, including PSTN, ISDN, T-carriers, DSL, broadband cable, and SONET </li></ul>
  57. 57. Summary (continued) <ul><li>WAN implementation options based on speed, security, and reliability </li></ul><ul><li>Hardware and software requirements for remotely connecting to a network </li></ul>