Spring 2000John Kristoff1 Wide Area Networks Computer Networks

Spring 2000John Kristoff2 Motivation zConnect multiple sites zSpan geographic distances zCross public right-of-way ystreets ybuildings yrailroads

Spring 2000John Kristoff3 Building blocks zPoint-to-point long distance connections yleased circuits yprovided by telecommunications companies zPacket switches yIP routers yATM switches ymany types...

Spring 2000John Kristoff4 Long-Distance Transmission Technology zLease transmission facilities from telecommunications companies yGenerally point-to-point yNOT part of the conventional telephone system yCopper, fiber, microwave or satellite yAnalog or digital

Spring 2000John Kristoff5 WAN Transmission Equipment zAnalog yMODEM required at each end zDigital yCSU/DSU required at each end

Spring 2000John Kristoff6 CSU/DSUs zPerforms two functions, usually in a single box zNeeded because telecommunications digital encoding differs from computer industry digital encoding zDSU ytranslates between the two encodings zCSU yterminates line yallows for maintenance

Spring 2000John Kristoff7 CSU/DSU Illustrated

Spring 2000John Kristoff8 Standards for WAN Circuits zSpecified by telephony industry in each region zCan differ around the world zNorth America and Japan examples yDS0, DS1, DS3, T1, T3, Fractional T1 yOC1, OC3, OC12, OC48, SONET zRest of the world examples yE1, E2, E3 ySDH

Spring 2000John Kristoff9 Inverse Multiplexing zRecall multiplexing zInstead of intertwining, you combine zCombines two or more circuits zProduces intermediate capacity circuit zSpecial hardware required

Spring 2000John Kristoff10 Inverse Multiplexing Illustrated

Spring 2000John Kristoff11 Early WAN Technologies zARPANET yhistorically important in packet switching yfast when invented, slow by current standards yprecursor to today’s Internet zX.25 protocol suite yearly commercial service ystill used ymore popular in Europe yservice by telecommunications companies

Spring 2000John Kristoff12 Recent WAN Technologies zSMDS yoffered by telecommunications companies ynot as popular as frame relay zFrame relay ywidely used commercial service yoffered by telecommunications companies zATM yoffered by telecommunications companies ydesigned for both WAN and LAN

Spring 2000John Kristoff13 Future WAN Technologies zPacket over SONET yprovided by telecommunications companies yremoves intermediate complexity zPacket over DWDM yprovided by telecommunications companies and long haul fiber optic providers zEthernet?

Spring 2000John Kristoff14 Asynchronous Transfer Mode (ATM) zConnection oriented using virtual circuits zUse of fixed sized packets called cells zDefines service categories for QoS networking zOperates on LANs using LAN Emulation (LANE) zUsually used for high-speed WAN connectivity

Spring 2000John Kristoff15 Virtual Circuits zCircuit ID instead of full host address pairs zSwitches swap IDs using translation tables zSwitch stores connection state for hosts

Spring 2000John Kristoff16 Cell Format

Spring 2000John Kristoff17 Service Types zCBR constant bit rate zVBR-NRT variable bit rate - non real time zVBR-RT variable bit rate - real time zABR available bit rate zUBR unspecified bit rate

Spring 2000John Kristoff18 LANE and MPOA zOverview yBackwards compatibility of ATM nodes with LANs such as Token Ring and Ethernet. Must support the broadcast nature of LANs with the virtual circuit nature of ATM. zLAN Emulation Client (LEC) yProvides abstraction for LAN protocols to ATM network zLAN Emulation Server (LES) yManages and supports LECs zLAN Emulation Configuration Server (LECS) yMaintains emulated LANs (ELANs) and supports LECs zBroadcast and Unknown Server (BUS) yDistributes broadcasts/multicasts

Spring 2000John Kristoff19 How ATM is Used in a LAN z1. LEC - Implemented at each client (bridge listens to all) z2. LEC contacts LECS to going a ELAN via a pre-configured SVC or discovered dynamically via integrated local management interface (ILMI) z3. LECS assign LEC to a ELAN and direct them to a LES z4. LEC setups up connection to LES and registers addresses z5. LES assigns a BUS to the LEC z6. LEC queries LES for a MAC address to ATM address translation z7. LECS responds directly or forwards query to another LEC z8. MAC broadcasts are sent to BUS so that an associated ATM broadcast can be sent to all stations in the ELAN.

Spring 2000John Kristoff20 ATM Summary The aim was to combine the flexibility of packet data networks (e.g. Internet) with the per-user quality of service guarantees of a circuit switched network (e.g. telephone network). A monumental task! Although an important technology, it may follow the path of similar technologies (e.g. Token Ring) Stay tuned.

Spring 2000John Kristoff21 Final Thoughts zLocal loop zISDN zDigital Subscriber Line (DSL) zCable modems zCellular zCIR/CAR zEverything over packets