1 WAN Basics

2 Agenda WAN Basics Point-to-Point Protocol (PPP) Integrated Services Digital Network (ISDN) Frame Relay

3 WAN Basics

4 A network that serves users across a broad geographic area Often uses transmission devices provided by public carriers (Pacific Bell, AT&T, etc.) This service is commonly referred to as “plain old telephone service” (POTS) WANs function at the lower three layers of the OSI reference model Physical layer, data link layer, and network layer What Is a WAN?

5 WAN Devices WAN SwitchSwitches traffic such as Frame Relay, X.25, and SMDS, and operates at the data link layer ModemInterprets digital and analog signals, enabling data transmission over telephone lines Access ServerA concentration point for dial-in and dial-out connections CSU/DSUAdapts a terminal physical interface to a switch interface in a switched-carrier network ISDN TerminalConnects ISDN Basic Rate Interface (BRI) to other interfaces, such as EIA/TIA-232

6 WAN Terms Customer premises equipment (CPE) Demarcation point Local loop Central office (CO) Toll network

7 WAN Terminating Equipment Modem Data Terminal Equipment DTE Data Circuit-Terminating Equipment The Service Providers Equipment DCE EIA/TIA-232 V.35 X.21 HSSI To Corporate Network The Customer’s Equipment WAN Provider (Carrier) Network Physical Cable Types Usually on the Customer’s Premises Router

8 Wan Connection Types Leased line Circuit switching Packet switching

9 Leased Line One connection per physical interface Bandwidth: 56 kbps–1.544 Mbps T1/E1 and fractional T1/E1 Cost effective at 4–6 hours daily usage Dedicated connections with predictable throughput Permanent Cost varies by distance

10 Dedicated physical circuit established, maintained, and terminated through a carrier network for each communication session Datagram and data stream transmissions Operates like a normal telephone call Example: ISDN WAN Modem Circuit Switching

11 Network devices share a point-to-point link to transport packets from a source to a destination across a carrier network Statistical multiplexing is used to enable devices to share these circuits Examples: ATM, Frame Relay, SMDS, X.25 WAN Modem Multiplexing Demultiplexing Packet Switching

12 A logical circuit ensuring reliable communication between two devices Switched virtual circuits (SVCs) Dynamically established on demand Torn down when transmission is complete Used when data transmission is sporadic Permanent virtual circuits (PVCs) Permanently established Save bandwidth for cases where certain virtual circuits must exist all the time Used in Frame Relay, X.25, and ATM WAN Virtual Circuits

13 OSI Reference Model Physical Layer Data Link Layer Network Layer LLC Sublayer MAC Sublayer SMDS X.21bis EIA/TIA-232 EIA/TIA-449 V.24 V.35 HSSI G.703 EIA-530 HDLCPPP WAN Protocols LAPB X.25 PLP Frame RelaySDLC WAN Protocols

14 SDLCIBM’s SNA data link layer communications protocol HDLCBit-oriented synchronous data link layer protocol LAPBData link layer protocol in the X.25 protocol stack PPPProvides router-to-router and host-to-network connections over sync and async circuits X.25 Defines connections for remote terminal access and computer communications in PDNs ISDNPermits telephone networks to carry data, voice, and other source traffic Frame Relay Switched data link layer protocol that handles multiple virtual circuits using HDLC; replacing X.25 due to higher efficiency WAN Protocols

15 Point-to-Point Protocol (PPP)

16 HDLC

17 Point-to-Point Protocol (PPP)

18 LCP Configuration Option Authentication  PAP (Password Authentication Protocol)  CHAP (Challenge Handshake Authentication Protocol) Compression Error detection Multilink PPP callback

19 PPP Session Establishment Link-establishment phase Authentication phase Network layer protocol phase

20 Integrated Services Digital Network (ISDN)

21 Integrated Services Digital Network (ISDN) High bandwidth Up to 128 Kbps per basic rate interface Dial on demand Multiple channels Fast connection time Monthly rate plus cost-effective, usage-based billing Strictly digital LAN Server Company Network Telecommuter/After- Hours, Work-at-Home BRI 2B+D BRI/PRI 23B+D 30B+D (Europe) ISDN

22 ISDN Terminals and Reference Points

23 ISDN Protocols Defined by ITU-T There are several series:  E  ISDN on the existing telephone network.  I  concepts, aspects, and services.  Q  switching and signaling Q.921  layer 2 Q.931  layer 3

24 ISDN Switch Types

25 ISDN One physical connection to the ISDN network 23 logical connections (U.S./Canada) 30 logical connections (Europe) Used at central site Primary Rate Interface (PRI) Mbps 23B 30B D 64 Kbps } One physical connection to the ISDN network Two logical connections Used at remote telecommuter site 64 Kbps 16 Kbps 144 Kbps 2B D } { Basic Rate Interface (BRI)

26 Bandwidth-on-Demand Adds bandwidth when needed Configurable thresholds Controls usage costs Start File Transfer Remote Site Main Office PSTN

27 Dial Backup If a primary link goes down or is too busy Load balancing Completely customizable Secondary Primary Autodial X

28 Dial-on-Demand Routing Dials connection only when needed Ideal for low-volume, periodic traffic Controls usage costs InterestingTraffic Remote Site Main Office PSTN

29 Configuring DDR 1) Define static routes 2) Specify the interesting traffic 3) Configure the dialer information

30 Configuration Example (1)

31 Configuration Example (2)

32 Configuration Example (3)

33 Frame Relay

34 X.25 Very robust protocol for low-quality lines Packet-switched Bandwidth: 9.6 kbps–64 kbps Well-established technology; large installed base Worldwide availability X.25 DCE DTE DCE

35 Frame Relay Permanent, not dialup Multiple connections per physical interface (permanent virtual circuits) Efficient handling of bursty (peak performance period) data Guaranteed bandwidth (typical speeds are 56/64 Kbps, 256 Kbps, and Mbps)— committed information rate (CIR) Cost varies greatly by region Permanent Virtual Circuit (PVC)

36 Committed Information Rate (CIR) Access rate  the maximum speed at which the Frame Relay interface can transmit. CIR  the maximum bandwidth of data guaranteed to be delivered.

37 Free If Available Traffic Time Peak CIR What You Pay For { { Frame Relay Connecting Offices with Frame Relay

38 Data Link Connection Identifier (DLCI) Used to identify virtual circuits. Locally significant.

39 Local Management Interface (LMI) Signaling standard between router and the first Frame Relay switch. It communicates information about:  Keepalives  Multicasting  Global addressing  Status of virtual circuits Virtual circuit status:  Active state  Inactive state  Deleted state

40 Frame Relay Congestion Control Discard Eligibility (DE) Forward Explicit Congestion Notification (FECN) Backward Explicit Congestion Notification (BECN)

41 Operate beyond the local LAN’s control Customers pay telephone service providers for WAN connections such as ISDN, xDSL, Frame Relay, leased line, X.25, etc. Switching methods include point-to-point, circuit switching, packet switching, dialup, and WAN virtual circuits Key devices include WAN switches, access servers, modems, and CSU/DSUs Bandwidth optimization features are essential for controlling WAN costs WAN Summary