CCNA Guide to Cisco Networking

1. CCNA Guide to Cisco Networking Chapter 5: WAN Concepts

2. Objectives Describe WAN standards Explain the WAN connection methods Discuss WAN data link protocols Understand the WAN Physical layer Recognize the various WAN physical topologies Emerging WAN connection methods

3. WAN Standardization Organizations that create standards International Organization for Standards (ISO) American National Standards Institute (ANSI) Electronic Industries Alliance (EIA) Internet Engineering Task Force (IETF) International Telecommunications Union-telecommunication (ITU-T)

4. WAN Connection Methods Four connection methods Dedicated point-to-point Also known as a leased line Point-to-multipoint Time division multiplexing Circuit-switched Packet-switched Standards organizations define several types of Data Link protocols used on WAN connections

5. WAN Connection Methods (continued)

6. WAN Connection Methods (continued)

7. WAN Connection Methods (continued)

8. WAN Data Link Protocols Three categories of Data Link protocols used for WAN Interface to IBM enterprise data centers Synchronous Data Link Control (SDLC) WAN connections using peer devices High-level Data Link Control (HDLC) Point-to-Point Protocol (PPP) Switched or relay services X.25/Link Access Procedure Balanced (LAPB) Frame Relay

9. WAN Data Link Protocols (continued) Three categories of Data Link protocols used for WAN (continued) Switched or relay services (continued) Integrated Services Digital Network (ISDN)/Link Access Procedure D-channel (LAPD) Asynchronous Transfer Mode (ATM)

10. WAN Data Link Protocols (continued) SDLC IBM hosts system communication over WAN links Point-to-point Point-to-multipoint Connections between Remote devices Central mainframe Synchronous communication

11. WAN Data Link Protocols (continued) HDLC Default protocol on WAN links Also known as Advanced Data Communications Control Procedure (ADCCP) Superset of the SDLC protocol Point-to-point Point-to-multipoint Supports full-duplex and half-duplex

12. WAN Data Link Protocols (continued) HDLC (continued) Synchronous and asynchronous Default HDLC does not support multiple protocols Cisco HDLC allows for multiple protocols

13. WAN Data Link Protocols (continued) PPP SLIP Further extends default HDLC by providing a protocol field Dial-up Leased lines Network Control Protocols (NPCs) Can transfer IP, IPX, AppleTalk and other network layer protocols

14. WAN Data Link Protocols (continued) PPP (continued) PPP provides the following connections Router-to-router Host-to-router Host-to-host Physical interfaces for PPP Asynchronous serial ISDN/synchronous serial High-speed Serial Interface (HSSI)

15. WAN Data Link Protocols (continued)

16. WAN Data Link Protocols (continued) X.25/LAPD Packet-switching Widely implemented for international communications Connections over virtual circuits Create to function over existing unreliable analog telecommunication lines Errors correction and flow control Older than OSI, does not directly translate

17. WAN Data Link Protocols (continued)

18. WAN Data Link Protocols (continued) Frame Relay A Data Link protocol A service Improved upon X.25 standard Operates between 56 Kbps and 45 Mbps Higher layer protocols provide error checking and flow control Packet-switching Shared bandwidth with other frame relay subscribers

19. WAN Data Link Protocols (continued) Frame Relay (continued) Defines the connection between Customer premise equipment (CPE) Service provider’s local access switching equipment Operates on almost any Physical layer interface Two types of virtual circuits Switched virtual circuits (SVC) Permanent virtual circuits (PVC) Uses statistical multiplexing to allocate bandwidth

20. WAN Data Link Protocols (continued) Frame Relay (continued) Congestion control Forward explicit congestion notification (FECN) Backward explicit congestion notification (BECN) Configuration considerations Local access rate Committed information rate (CIR) Committed burst size (CBS) Excess burst size (EBS)

21. WAN Data Link Protocols (continued) Frame Relay (continued) Configuration considerations (continued) Data link connection identifier (DLCI) Local Management interface (LMI) Discard eligible (DE)

22. WAN Data Link Protocols (continued) ISDN/LAPD Circuit-switched technology Dedicated circuit for the length of the transmission Two types of ISDN Basic rate interface (BRI) Primary rate interface (PRI) Bandwidth BRI 128 kbps PRI 1.544 mbps

23. WAN Data Link Protocols (continued) ISDN/LAPD (continued) B-channels (bearer channels) 64-kbps D-channel (delta or data channel) BRI 16 kbps PRI 64 kbps BRI Two B channels One D channel PRI 23 B channels One D channel

24. WAN Data Link Protocols (continued) ATM Used within and between LAN connections Based on Frame Relay technology Cell-switched technology Circuit-oriented in the sense that ATM cells follow the same path for the duration of the connection Cell are fixed length of 53 bytes

25. WAN Data Link Protocols (continued) ATM (continued) Provides high-speed data transmission No error correction like X.25 Bandwidth up to 10 gbps

26. WAN Physical Layer

27. WAN Connections Provide connections between two LANs Connections between Channels service unit/ data service unit CSU/DSU Router Routers now include internal CSU/DSU Data terminal equipment (DTE) Data-circuit terminating equipment (DCE)

28. WAN Connections (continued) Demarcation or demarc Point of presence (POP) Local loop or last mile Central office switch (CO) Toll network

29. WAN Physical Standards Physical WAN serial interface standards EIA/TIA-232 EIA/TIA-449 EIA-530 High-Speed Serial Interface (HSSI) V.24 V.35 X.25

30. WAN Physical Standards (continued) Physical WAN serial interface standards (continued) X.21 G.703

31. WAN Topologies WAN topologies Peer Star Partial mesh Mesh

32. WAN Topologies (continued)

33. WAN Topologies (continued) Peer topology Daisy-chained Simplest WAN topology Least expensive Easy to configure No redundancy

34. WAN Topologies (continued) Star topology Most implemented design Also know as the “hub-and-spoke” topology Simple hierarchical design One central router acting as the hub Several edge routers connect to hub

35. WAN Topologies (continued) Full mesh Most expensive topology Most fault-tolerant design Each router has a connection to every other router Partial mesh Compromise between star and full mesh Connection are made according to need and traffic flow

36. Emerging WAN Connection Methods Broadband access Two new WAN connection methods Digital subscriber lines (DSL) Cable access with cable modem DSL Two types of DSL Asynchronous DSL Symmetric DSL

37. Emerging WAN Connection Methods (continued) DSL (continued) Modulates voice and data over existing copper phone lines Download speeds vary 256 kbps to faster than T1 (1.544 mbps) Upload speeds are typically slower than download speeds Speed and cost are attractive Distance limitations to CO

38. Emerging WAN Connection Methods (continued) Cable access and cable modems Uses existing cable TV infrastructure Shared bandwidth Distance limitation not an issue like DSL Need VPN!

39. Summary WANs connect LANs in geographically separate areas WAN connections typically function at the Physical and Data Link layers of the OSI reference model, and are made over serial connections WAN connections operate at a lower speed than LAN connections, and can be made as point-to-point, point-to-multipoint, and switched WAN connections You can use several different data link protocols for WAN connections

40. Summary (continued) The different types of WAN connections are: (1) interfaces to IBM mainframes provided by SDLC; (2) WAN connections using peer devices with HDLC and PPP; and (3) switched or relayed services including X.25, Frame Relay, ATM, and ISDN X.25 is the oldest of the switched or relayed services and provides the least efficient service because of its excessive error checking Frame Relay is an enhancement over X.25 because it is faster and does not provide redundant error checking

41. Summary (continued) ATM is similar to Frame Relay, except that it uses fixed-length cells instead of variable-length packets In addition, the ATM protocol can be used on LANs as well as WANs ISDN is a leased digital line that can support X.25 and Frame Relay connections, among others ISDN comes in PRI and BRI levels

42. Summary (continued) BRI only provides 128-Kbps throughput over two B-channels, and 16 Kbps over one D-channel that is used for controlling the connection PRI provides 23 B-channels of 64 Kbps each and one 64-Kbps D-channel for controlling the connection This allows PRI to offer 1.544-Mbps throughput The Physical layer WAN connections concern the interface between the DTE and DCE

43. Summary (continued) The DTE is the endpoint of the user’s network, which connects to the WAN interface This is typically a router, computer, or terminal of some type The WAN service provider usually provides the DCE, which is often a CSU/DSU, modem, or terminal adapter The DCE is then connected to a demarc, which is a communications facility owned by the WAN service provider The local loop is the connection (usually copper cable) that links the demarcation to the WAN service provider’s CO switch, which is actually part of the toll network or PSTN

44. Summary (continued) The physical WAN topologies are Peer, which is simply customer facilities connected in a daisy-chained fashion Star, which involves connecting remote customer facilities to a central facility Full mesh, which connects every location to every other location Partial mesh, which provides redundancy only where necessary