Cisco Semester 4 Chapter 2

1. Cisco Semester 4 Chapter 2 WANS

2. Technologies Not Coveredin Semester 4 • DSL • Cable Modem • ATM • SONET • SMDS

3. WAN Services • Layer 1 • CSU/DSU connects to WAN to CSU/DSU to other route • Service Providers • POTS, X.25/Frame Relay, TDM or T1/E1, Call setup, e.g. SS7 • Frame Relay LMI • Allows DLCI to become unique network addresses • DLCI value placed in frame header

4. DCE/DTE • CPE – customer premises equipment • On customer premises – owned and leased • Demaraction – point where CPE ends and local loop service begins, e.g. POP • Local Loop – last mile – CAT 5 – goes from demarc to WAN provider central office • CO – nearest point of presence for provider’s WAN • Toll Network – inside WAN provider cloud • DTE – typically router DCE – converts user data into WAN acceptable format

5. Virtual Circuits • Pathway through a packet-switched network that appears to be dedicated physical circuit • Can be connection-oriented (like TCP) • PVC - Customer and carrier negotiate end points and characteristics of virtual circuit • Constantly available • SVC – virtual circuit availably only on demand

6. WAN Line Types and Bandwidth • 56 DSO 56b kbps • 64 DSO 64 kbps • T1 DS1 1.544 Mbps • E1 ZM 2.048 Mbps • E3 M3 34.068 Mbps • J1 Yi 2.048 Mbps • T3 DS3 44.736 Mbps • OC 1-48 Sonet 51.84 to 2488.32 Mbps

7. WAN Devices • Router – both LAN and WAN • WAN Switches – connect to WAN bandwidth • Layer 2 (but distinct); mostly in WAN cloud • Frame Relay, X.25, SMDS • Modems - CSU/DSU and TA/NT1 devices that interface ISDN services • Communication servers to concentrate dial-in and dial-out communications

8. Modems • Interprets digital and analog signals • Enable data to be transmitted over voice-grade telephone lines

9. Leased Lines • Router Port • CSU/DSU • Service Provider Circuit

10. ISDN • TA - device used to connect ISDN BRI connection to other interfaces

11. WAN and OSI Model • WANS focus on physical and data link layers • Standards describe physical-layer delivery methods and data-link layer requirements • Addressing, flow control, encapsulation • Agencies • ITU-T, ISO, IETF, EIA, TIA

12. WAN Physical Layer Protocols • EIA/TIA 232 - common standard • Supports up to 64 kbps; resembles V.24; was RS-232 • V.35 and X.21 • HSSI • DTE-DCE • Modem • Standards • EIA/TIA 449 up to 2 Mbps • EIA/TIA 612-3 HSSI • ITU-T V.24 and .35 • X.21 – used in Europe and Japan

13. WAN Data Link Layer • Encapsulation Protocols • HDLC high-level data link control • Cisco has its own proprietary version • PPP point to point – standard • Supports several router protocols • Replaced SLIP • WAN Technologies • Frame Relay - simplified HDLC • Packet Switched • ISDN – data-link signal • Circuit Switched

14. WAN Data Link Layer • Dedicated Point to Point • Cisco HDLC, PPP, and LAPB (ISDN) • Packet Switched • Frame Relay (IETF) • X.25, Frame Relay • Circuit Switched • ISDN D channel LAPD • ISDN B channel

15. WAN Data Link Detail • Frame Relay – simple encapsulation, no error correction, rapid data transmission • PPP (RFC 1661) developed by IETF – contains field to identify network layer protocol • ISDN – digital; uses existing telephone lines • LAPB- used to encapsulate packets in the X.25 stack; provides reliability and flow control • Cisco/IETF – encapsulates Frame Relay traffic • HDLC – implemented differently by vendors

16. WAN FORMATS • Common Fields • Flag, Address, Control, Data, FCS , Flag • Different Fields • PPP uses Protocol field; HDLC has proprietary field

17. PPP • Described in RFC 1661 • Specifies Layer 3 protocol type • Is a link control protocol • Provides Authentication • PAP Password Authentication Protocol • CHAP Challenge Handshake Authentication Protocol

18. HDLC • Derived from SDLC encapsulation (Synchronous Data Link Control) • Cisco default for serial lines • No windowing or flow control • Allows only point to point connections • Address field set to 1s • 20byte type code – not interoperable • NOTE: Use PPP with devices not running Cisco IOS software

19. Dedicated/Switched Lines • Dedicated • Leased Lines • Fractional T1/E1 • T1/E1 • T3/E3 • Switched • Circuit • POTS, ISDN, Switched 56 • Packet/Cell Switched • X.25, Frame Relay, SMDS, ATM

20. Packet Switched Connections • Network devices share PVC – permanent virtual circuit • Like a point-to-point link • Frame Relay, SMDS, and X.25

21. Frame Relay • Types of Service • DLCI (Data-Link Connections Identifier) • CIR (Committed Information Rate) • Access Rate 56, 65 kbps or 1.544 Mbps • Two topologies • Fully meshed – every device has PVD to every other device • Partially meshed – star topology • LMI global addressing allows DLCIs to become unique address for DTE device

22. Circuit Switched Connections • Connection on Demand • Relatively low bandwidth • Uses • Remote users • Mobile users • Backup lines

23. DDR –Dial on Demand Routing • Router can dynamically initiate and close circuit-switched sessions • Used as backup link when primary fails • Source of extra bandwidth when traffic on primary link reaches a threshhold • Substitute for dedicated lines when full-time circuit availability is not required

24. ISDN • Three channels – 2 64 kbps B (bearer) and 1 16 kbps D (signaling • Connections • TE1 connects to NT (Type 1 or 2 • TE2 designates device not compatible • TA converts standard signal to ISDN • NT1 Connects 4-wire ISDN wiring • NT2 Directs traffic to and from difference subscriber devices and NT1 • S/T defines TE1 and NT; R is TE2 and TA U is NT and ISDN cloud