Autumn 2000John Kristoff1 Wide Area Networks Computer Networks

Autumn 2000John Kristoff2 Motivation ÑConnect multiple sites ÑSpan geographic distances ÑCross public right-of-way Ñstreets Ñbuildings Ñrailroads

Autumn 2000John Kristoff3 Building blocks ÑPoint-to-point long distance connections Ñleased circuits Ñprovided by telecommunications companies ÑPacket switches ÑIP routers ÑATM switches Ñmany types...

Autumn 2000John Kristoff4 Long-Distance Transmission Technology ÑLease transmission facilities from telecommunications companies ÑGenerally point-to-point ÑNOT part of the conventional telephone system ÑCopper, fiber, microwave or satellite ÑAnalog or digital

Autumn 2000John Kristoff5 WAN Transmission Equipment ÑAnalog ÑMODEM required at each end ÑDigital ÑCSU/DSU required at each end

Autumn 2000John Kristoff6 CSU/DSUs Ñ Performs two functions, usually in a single box Ñ Needed because telecommunications digital encoding differs from computer industry digital encoding Ñ DSU Ñ translates between the two encodings Ñ CSU Ñ terminates line Ñ allows for maintenance

Autumn 2000John Kristoff7 CSU/DSU Illustrated

Autumn 2000John Kristoff8 Standards for WAN Circuits Ñ Specified by telephony industry in each region Ñ Can differ around the world Ñ North America and Japan examples Ñ DS0, DS1, DS3, T1, T3, Fractional T1 Ñ OC1, OC3, OC12, OC48, SONET Ñ Rest of the world examples Ñ E1, E2, E3 Ñ SDH

Autumn 2000John Kristoff9 Inverse Multiplexing ÑRecall multiplexing ÑInstead of intertwining, you combine ÑCombines two or more circuits ÑProduces intermediate capacity circuit ÑSpecial hardware required

Autumn 2000John Kristoff10 Inverse Multiplexing Illustrated

Autumn 2000John Kristoff11 Early WAN Technologies ÑARPANET Ñ historically important in packet switching Ñ fast when invented, slow by current standards  precursor to today ’ s Internet ÑX.25 protocol suite Ñ early commercial service Ñ still used Ñ more popular in Europe Ñ service by telecommunications companies

Autumn 2000John Kristoff12 Recent WAN Technologies ÑSMDS Ñ offered by telecommunications companies Ñ not as popular as frame relay ÑFrame relay Ñ widely used commercial service Ñ offered by telecommunications companies ÑATM Ñ offered by telecommunications companies Ñ designed for both WAN and LAN

Autumn 2000John Kristoff13 Future WAN Technologies ÑPacket over SONET Ñprovided by telecommunications companies Ñremoves intermediate complexity ÑPacket over DWDM Ñprovided by telecommunications companies and long haul fiber optic providers ÑEthernet?

Autumn 2000John Kristoff14 Asynchronous Transfer Mode (ATM) ÑConnection oriented using virtual circuits ÑUse of fixed sized packets called cells ÑDefines service categories for QoS networking ÑOperates on LANs using LAN Emulation (LANE) ÑUsually used for high-speed WAN connectivity

Autumn 2000John Kristoff15 Virtual Circuits Ñ Circuit ID instead of full host address pairs Ñ Switches swap IDs using translation tables Ñ Switch stores connection state for hosts

Autumn 2000John Kristoff16 Cell Format

Autumn 2000John Kristoff17 Service Types ÑCBRconstant bit rate ÑVBR-NRTvariable bit rate - non real time ÑVBR-RTvariable bit rate - real time ÑABRavailable bit rate ÑUBRunspecified bit rate

Autumn 2000John Kristoff18 LANE and MPOA ÑOverview Ñ Backwards 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. ÑLAN Emulation Client (LEC) Ñ Provides abstraction for LAN protocols to ATM network ÑLAN Emulation Server (LES) Ñ Manages and supports LECs ÑLAN Emulation Configuration Server (LECS) Ñ Maintains emulated LANs (ELANs) and supports LECs ÑBroadcast and Unknown Server (BUS) Ñ Distributes broadcasts/multicasts

Autumn 2000John Kristoff19 How ATM is Used in a LAN Ñ 1. LEC - Implemented at each client (bridge listens to all) Ñ 2. LEC contacts LECS to going a ELAN via a pre-configured SVC or discovered dynamically via integrated local management interface (ILMI) Ñ 3. LECS assign LEC to a ELAN and direct them to a LES Ñ 4. LEC setups up connection to LES and registers addresses Ñ 5. LES assigns a BUS to the LEC Ñ 6. LEC queries LES for a MAC address to ATM address translation Ñ 7. LECS responds directly or forwards query to another LEC Ñ 8. MAC broadcasts are sent to BUS so that an associated ATM broadcast can be sent to all stations in the ELAN.

Autumn 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.

Autumn 2000John Kristoff21 Final Thoughts ÑLocal loop ÑISDN ÑDigital Subscriber Line (DSL) ÑCable modems ÑCellular ÑCIR/CAR ÑEverything over IP