1. Chap 2 WANs and Routers Andres, Wen-Yuan Liao Department of Computer Science and Engineering De Lin Institute of Technology andres@dlit.edu.tw http://www.cse.dlit.edu.tw/~andres

3. Overview WAN devices, technologies, and standards The function of a router in a WAN

4. WANs WANs and devices WAN standards WAN technologies

5. WANs and devices Operates at the physical layer and the data link layer Interconnects LANs that are usually separated by large geographic areas

6. WANs and devices Provide for the exchange of data packets/frames between routers/bridges and the LANs they support

9. WAN Devices Routers -- offer many services, including internetworking and WAN interface ports Switches -- connect to WAN bandwidth for voice, data, and video communication

10. WAN Devices Channel service units/digital service units (CSU/DSUs) that interface T1/E1 services Terminal Adapters/Network Termination 1 (TA/NT1s) that interface ISDN services

11. WAN Devices Communication servers -- concentrate dial-in and dial-out user communication Modems -- interface voice-grade services

12. WAN Standards

13. WAN physical layer protocols describe how to provide electrical, mechanical, operational, and functional connections for WAN services

14. WAN Standards WAN data link protocols describe how frames are carried between systems on a single data link

15. WAN physical layer Describes the interface between the data terminal equipment (DTE) and the data circuit- terminating equipment (DCE)

16. WAN physical layer DCE: service provider – modem or a CSU/DSU DTE: the attached device

18. Physical layer standards EIA/TIA-232 EIA/TIA-449 V.24 V.35 X.21 G.703 EIA-530

20. Data link encapsulations HDLC -- IEEE standard – May not be compatible with different vendors – Supports both point-to-point and multipoint configurations with minimal overhead

21. Data link encapsulations Frame Relay -- uses high-quality digital facilities – Uses simplified framing with no error correction mechanisms – Send Layer 2 information much more rapidly than other WAN protocols

22. Data link encapsulations PPP -- described by RFC 1661 – Contains a protocol field to identify the network layer protocol

23. Data link encapsulations Simple Data Link Control Protocol (SDLC) – An IBM-designed WAN DL protocol for SNA – Being replaced by the more versatile HDLC Serial Line Interface Protocol (SLIP) – Popular WAN DL protocol (IP packets) – Being replaced by the more versatile PPP

24. Data link encapsulations Link Access Procedure Balanced (LAPB) – A data link protocol used by X.25 – Has extensive error checking capabilities Link Access Procedure D-channel (LAPD) – The WAN DL protocol used for signaling and call setup on an ISDN D-channel – Data transmissions take place on the ISDN B channels

25. Data link encapsulations Link Access Procedure Frame (LAPF) – For Frame-Mode Bearer Services – A WAN DL protocol, similar to LAPD, used with frame relay technologies

26. WAN technologies Circuit-switched Cell-switched Dedicated digital Analog services

27. Circuit-Switched Services POTS (Plain Old Telephone Service) – Not a computer data service, but included Narrowband ISDN – The first all-digital dial-up service – 128 kbps (BRI) – 3 Mbps (PRI)

28. Packet-Switched Services X.25 – An older technology, but still widely used – Has extensive error-checking capabilities – Make it reliable but limits its bandwidth – 2 Mbps (maximum)

29. Frame Relay A packet-switched version of Narrowband ISDN More efficient than X.25, but with similar services Maximum bandwidth is 44.736 Mbps 56kbps and 384kbps are extremely popular

30. Cell-Switched Services ATM (Asynchronous Transfer Mode) – Closely related to broadband ISDN – An increasingly important WAN/LAN – Small, fixed length (53 byte) frames – Maximum bandwidth is 622 Mbps

31. Cell-Switched Services SMDS (Switched Multimegabit Data Service) – Closely related to ATM – Typically used in MANs – Maximum bandwidth is 44.736 Mbps – Usage not very widespread; cost is relatively high

32. Dedicated Digital Services T series of services in the U.S E series of services in Europe T1 -- 1.544 Mbps T3 -- 44.736 Mbps E1 -- 2.048 Mbps E3 -- 34.368 Mbps

33. Dedicated Digital Services xDSL – DSL: Digital Subscriber Line – x: a family of technologies – A new and developing WAN technology (home use)

34. Dedicated Digital Services xDSL – Bandwidth decreases with increasing distance from the phone companies equipment – Top speeds of 51.84 Mbps (near a phone company office) – From 100s of kbps to several Mbps)

35. Dedicated Digital Services HDSL -- high-bit-rate DSL SDSL -- single-line DSL ADSL -- asymmetric DSL VDSL -- very-high-bit-rate DSL RADSL -- rate adaptive DSL

36. Dedicated Digital Services  SONET (Synchronous Optical Network)  A family of very high-speed physical layer technologies  For optical fiber, also for copper cables

37. Dedicated Digital Services  SONET  OC (optical carrier) levels: 51.84 Mbps (OC-1) to 9,952 Mbps (OC-192)  Wavelength division multiplexing (WDM)  Usage is widespread among Internet backbone entities

38. Other WAN Services Dial-up modems (switched analog) – Maximum bandwidth approx. 56 kbps Cable modems (shared analog) – Put data signals on the same cable as television signals

39. Other WAN Services – Increase in popularity in regions that have large amounts of existing cable TV coaxial cable (90% of homes in U.S.) – Maximum bandwidth can be 10 Mbps – Degrades as more users

40. Other WAN Services Wireless – The signals are electromagnetic waves Terrestrial – Bandwidths typically in the 11 Mbps range (e.g. microwave) – Cost is relatively low; line-of-sight is usually required

41. Other WAN Services Satellite – Serve mobile users and remote users – Usage is widespread; cost is high

43. WANs and Routers Router basics The function of a router in a WAN

44. Router basics Routers need the Internetworking Operating Software (IOS) to run configuration files Selects the best paths and manages the switching of packets Network layer

45. Internal configuration components RAM/DRAM – Stores routing tables, ARP cache, fast-switching cache, packet buffering (shared RAM), and packet hold queues – Provides temporary and/or running memory – Be lost when you power down or restart

46. Internal configuration components NVRAM -- nonvolatile RAM – Stores a router’s backup/startup configuration file – Content remains when you power down or restart

47. Internal configuration components  Flash -- Erasable, reprogrammable ROM  Hold the operating system image and microcode  Update software without removing and replacing chips on the processor  Content remains when you power down  Store multiple versions of IOS software

48. Internal configuration components ROM – Contains power-on diagnostics, a bootstrap program, and operating system software – Software upgrades: replacing pluggable chips

49. Internal configuration components Interface – Network connection through which packets enter and exit a router – It can be on the motherboard or on a separate interface module

50. The function of a router in a WAN While routers can be used to segment LAN devices, their major use is as WAN devices Routers have both LAN and WAN interfaces

51. The function of a router in a WAN WAN technologies are frequently used to connect routers – Communicate with each other by WAN connections – Make up autonomous systems and the backbone of the Internet

53. The function of a router in a WAN Two main functions of routers – The selection of best paths (Logical Address) – The switching of packets to the proper outgoing interface

56. The function of a router in a WAN Any internetwork includes: – Consistent end-to-end addressing – Addresses that represent network topologies – Best path selection – Dynamic routing – Switching