Chapter 8


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Chapter 8

  1. 1. WAN Protocols CMC Limited
  2. 2. Objectives • Understand advantages of WAN. • Understand the different ways to connect computer within a WAN. • Understand different protocols used in WAN. CMC Limited
  3. 3. Introduction • A Wide Area Network (WAN) spans a large physical distance. • A network device called a router connects LANs to a WAN. • In IP networking, the router maintains both a LAN address and a WAN address. CMC Limited
  4. 4. Importance and Advantages of WANsTwo great advantages of WAN are allowing secure and fastdata transmission between the different nodes in thenetwork.WAN Connection Types• Point-to-Point Connection or Dedicated Connection• Circuit Switching• Packet Switching CMC Limited
  5. 5. WAN Connection Types contd..Point-to-Point Connection or DedicatedConnection Dedicated connections are point-to-point serial connections that offer fixed, permanent connections to remote networks. Data can be transmitted through the connection in two different ways:• Datagram transmission: Data is transmitted packet by packet.• Data stream transmission: Data is transmitted byte by byte. CMC Limited
  6. 6. WAN Connection Types contd..Circuit SwitchingThe circuit switching method occupies phone lines onlyduring communication.ISDN is one of the protocols used in this method.Packet SwitchingPacket switching is considered the foundation of mosttelecommunications networks.Packet switching links together all the nodes in a WAN withthe use of a physical link. CMC Limited
  7. 7. Devices Used in WANA router is commonly used in the frame relay of T1-basedWANs.Routers are also beneficial when linking WANs to theInternet, as they can monitor security policies within a WAN.When two routers are far apart, a multiport device, calleda WAN switch can link them together within the network. CMC Limited
  8. 8. WAN ProtocolsIn this section we introduces various protocols and used inWide Area Network (WAN) environments. These are asfollows:Frame Relay: A packet-switched technology that emergedin the early 1990s, Frame Relay is a Data Link andPhysical layer specification that provides high performance.Integrated Services Digital Network (ISDN): It is a set ofdigital services that transmit voice and data over existingphone lines. CMC Limited
  9. 9. WAN Protocols contd..Link Access Procedure, Balanced (LAPB): It was createdto be used as a connection-oriented protocol at the Data Linklayer for use with X.25. It can also be used as a simple DataLink transport.High-Level Data Link Control (HDLC): It was derived fromSynchronous Data Link Control (SDLC), which was createdby IBM as a Data Link connection protocol.Point-to-Point Protocol (PPP): It is an industry-standardprotocol. CMC Limited
  10. 10. Frame RelayFrame Relay is a high-performance WAN protocol thatoperates at the physical and data link layers of the OSIreference model.Frame Relay originally was designed for use acrossIntegrated Services Digital Network (ISDN) interfaces.Frame Relay Devices Devices attached to a Frame Relay WAN fall into the two general categories: CMC Limited
  11. 11. Frame Relay contd..Data terminal equipment (DTE): DTEs generally areconsidered to be terminating equipment for a specificnetwork and typically are located on the premises of acustomerData circuit-terminating equipment (DCE): DCEs arecarrier-owned internetworking devices.The link layer component defines the protocol thatestablishes the connection between the DTE device, such asa router, and the DCE device, such as a switch. CMC Limited
  12. 12. Frame Relay contd..Frame Relay Terminology To understand the terminology used in Frame Relay networks, first you need to know how the technology works. The users network device sends a frame out on the local network. The router picks up the frame, extracts the packet, and discards the frame. The router then forwards the data out the interface that it thinks can find the remote network. The CO receives the frame and sends it through the Frame Relay "cloud to its destination. CMC Limited
  13. 13. Frame Relay contd..Frame Relay Frame Formats To understand much of the functionality of Frame Relay, it is helpful to understand the structure of the Frame Relay frame. Three primary components make up the Frame Relay frame: the header and address area, the user-data portion, and the frame check sequence (FCS). This identifier commonly is referred to as the data-link connection identifier (DLCI). CMC Limited
  14. 14. Frame Relay contd..Local Management Interface (LMI) FrameFormat LMI was developed in 1990 by Cisco Systems, StrataCom, Northern Telecom and Digital Equipment Corporation and became known as the Gang-of-Four LMI or Cisco LMI. LMI DLCI – Identifies the frame as an LMI frame instead of a basic Frame Relay frame. The LMI-specific DLCI value defined in the LMI consortium specification is DLCI = 1023. CMC Limited
  15. 15. Local Management Interface (LMI) Frame Format contd..Protocol Discriminator – Always contains a valueindicating that the frame is an LMI frame.Frame Check Sequence (FCS) – Ensures the integrityof transmitted data. CMC Limited
  16. 16. Local Management Interface (LMI) Frame Format contd..Frame Relay EncapsulationWhen configuring Frame Relay on Cisco routers, you needto specify it as an encapsulation on serial interfaces.Youd opt for the IETF-type encapsulation if you needed toconnect a Cisco device to a non- Cisco device with FrameRelay.Data Link Connection Identifiers (DLCIs)DLCI numbers, used to identify a PVC, are typicallyassigned by the provider and start at 16. CMC Limited
  17. 17. Local Management Interface (LMI) Frame Format contd..Dynamic or Static Address Mapping Dynamic address mapping uses Frame Relay Inverse ARP to request the next-hop protocol address for a specific connection, given its known DLCI. Inverse ARP is enabled by default for all protocols it supports, but can be disabled for specific protocol-DLCI pairs.Configure LMI Our Frame Relay software supports the industry-accepted standards for addressing the Local Management Interface (LMI), including the Cisco specification. CMC Limited
  18. 18. Local Management Interface (LMI) Frame Format contd..Frame Relay Subinterfaces Frame Relay subinterfaces provide a mechanism for supporting partially meshed Frame Relay networks. By configuring Frame Relay subinterfaces, a single physical interface is treated as multiple virtual interfaces. Subinterfaces address these limitations by providing a way to subdivide a partially meshed Frame Relay network into a number of smaller, fully meshed (or point-to-point) subnetworks CMC Limited
  19. 19. Local Management Interface (LMI) Frame Format contd..Configure Frame Relay SubinterfaceTo configure subinterfaces on a Frame Relay network,perform the following task: CMC Limited
  20. 20. Local Management Interface (LMI) Frame Format contd..Mapping Frame Relay For IP devices at the ends of virtual circuits to communicate, their addresses must be mapped to the DLCIs. There are two ways to make this mapping happen: • Use the frame-relay map command. • Use the inverse-arp function. CMC Limited
  21. 21. Local Management Interface (LMI) Frame Format contd..Monitoring Frame Relay The show frame relay lmi command will give you the LMI traffic statistics exchanged between the local router and the Frame Relay switch.Integrated Services Digital Network (ISDN) ISDN is comprised of digital telephony and data-transport services offered by regional telephone carriers. The emergence of ISDN represents an effort to standardize subscriber services, user/network interfaces, and network and internetwork capabilities. CMC Limited
  22. 22. Local Management Interface (LMI) Frame Format contd..ISDN DevicesISDN devices include terminals, terminal adapters (TAs),network-termination devices, line-termination equipment,and exchange-termination equipment.ISDN TerminalsDevices connecting to the ISDN network are known asterminal equipment (TE) and network terminator (NT)equipment.ISDN Channel There are several types of ISDN channels, the two main being the 64 Kilobits per second B-channel for data, and the D-channel for control information. CMC Limited
  23. 23. Local Management Interface (LMI) Frame Format contd..ISDN ServicesThere are two types of services associated with ISDN: 1. Basic Rate Interface (BRI) 2. Primary Rate Interface (PRI)ISDN ProtocolsISDN protocols are defined in ITU protocols that operates onthe Physical, Data Link and Network layer of the OSI model.Configure ISDN and BRI InterfacesHere you will configure routers 804A and 804B to dial ISDNbetween the networks and, usingnetwork on the ISDN BRI interfaces. CMC Limited
  24. 24. High-Level Data Link Control (HDLC) The HDLC is a popular ISO-standard, bit-oriented Data Link Layer protocol. HDLC specifies an encapsulation method for data on synchronous serial data links using frame characters and checksum.HDLC Operation Modes Normal Response Mode (NRM): This mode is used in unbalanced configurations. In this mode, slave stations (or secondary) can only transmit when specially instructed by the master (primary station). CMC Limited
  25. 25. High-Level Data Link Control (HDLC) contd..Frame ClassesIn the HDLC protocol, three classes of frames are used. • Unnumbered frames • Information frames • Supervisory frames CMC Limited
  26. 26. Point-to-Point Protocol (PPP) PPP is a protocol for communication between two computers using a serial interface, typically a personal computer connected by phone line to a server. PPP uses the Internet protocol (IP). CMC Limited
  27. 27. Point-to-Point Protocol (PPP) contd.. PPP Frame Format The PPP frame format appears in the following figure.Fieldlength, inbytes 1 1 1 2 Variable 2 or 4 Flag Address Control Protocol Data FCS CMC Limited
  28. 28. Point-to-Point Protocol (PPP) contd..PPP ComponentsPPP provides a method for transmitting datagrams overserial point-to-point links.Configure PPP on Cisco RoutersPPP encapsulation must be enabled on both interfacesconnected to a serial line to work, and there are severaladditional configuration options available by using the helpcommand. CMC Limited
  29. 29. Point-to-Point Protocol (PPP) contd..Authentication Types (CHAP/PAP) onPPP LinksAuthentication is an optional phase, but it is highlyrecommended on all dial connections.Configuring PPP Encapsulation andAuthenticationBy default, Cisco routers use High-Level Data Link Control(HDLC) as a point-to-point encapsulation method on seriallinks. CMC Limited
  30. 30. Dial-on-Demand Routing (DDR)DDR is used to allow two or more Cisco routers to dial anISDN dial-up connection on an as-needed basis.Configuring DDRTo forward traffic across the ISDN link, you configure staticroutes in each of the routers. You certainly can configuredynamic routing protocols to run on your ISDN link, but thenthe link will never drop. CMC Limited