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Wide Area Networks

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Wide Area Networks Computer Networks Motivation Connect multiple sites Span geographic distances Cross public right-of-way streets buildings railroads Building blocks ... – PowerPoint PPT presentation

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Date added: 28 July 2019
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Title: Wide Area Networks


1
Wide Area Networks
Computer Networks
2
Motivation
  • Connect multiple sites
  • Span geographic distances
  • Cross public right-of-way
  • streets
  • buildings
  • railroads

3
Building blocks
  • Point-to-point long distance connections
  • leased circuits
  • provided by telecommunications companies
  • Packet switches
  • IP routers
  • ATM switches
  • many types...

4
Long-Distance Transmission Technology
  • Lease transmission facilities from
    telecommunications companies
  • Generally point-to-point
  • NOT part of the conventional telephone system
  • Copper, fiber, microwave or satellite
  • Analog or digital

5
WAN Transmission Equipment
  • Analog
  • MODEM required at each end
  • Digital
  • CSU/DSU required at each end

6
CSU/DSUs
  • Performs two functions, usually in a single box
  • Needed because telecommunications digital
    encoding differs from computer industry digital
    encoding
  • DSU
  • translates between the two encodings
  • CSU
  • terminates line
  • allows for maintenance

7
CSU/DSU Illustrated
8
Standards for WAN Circuits
  • Specified by telephony industry in each region
  • Can differ around the world
  • North America and Japan examples
  • DS0, DS1, DS3, T1, T3, Fractional T1
  • OC1, OC3, OC12, OC48, SONET
  • Rest of the world examples
  • E1, E2, E3
  • SDH

9
Inverse Multiplexing
  • Recall multiplexing
  • Instead of intertwining, you combine
  • Combines two or more circuits
  • Produces intermediate capacity circuit
  • Special hardware required

10
Inverse Multiplexing Illustrated
11
Early WAN Technologies
  • ARPANET
  • historically important in packet switching
  • fast when invented, slow by current standards
  • precursor to today?s Internet
  • X.25 protocol suite
  • early commercial service
  • still used
  • more popular in Europe
  • service by telecommunications companies

12
Recent WAN Technologies
  • SMDS
  • offered by telecommunications companies
  • not as popular as frame relay
  • Frame relay
  • widely used commercial service
  • offered by telecommunications companies
  • ATM
  • offered by telecommunications companies
  • designed for both WAN and LAN

13
Future WAN Technologies
  • Packet over SONET
  • provided by telecommunications companies
  • removes intermediate complexity
  • Packet over DWDM
  • provided by telecommunications companies and long
    haul fiber optic providers
  • Ethernet?

14
Asynchronous Transfer Mode (ATM)
  • Connection oriented using virtual circuits
  • Use of fixed sized packets called cells
  • Defines service categories for QoS networking
  • Operates on LANs using LAN Emulation (LANE)
  • Usually used for high-speed WAN connectivity

15
Virtual Circuits
  • Circuit ID instead of full host address pairs
  • Switches swap IDs using translation tables
  • Switch stores connection state for hosts

16
Cell Format
17
Service Types
  • CBR constant bit rate
  • VBR-NRT variable bit rate - non real time
  • VBR-RT variable bit rate - real time
  • ABR available bit rate
  • UBR unspecified bit rate

18
LANE and MPOA
  • Overview
  • 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.
  • LAN Emulation Client (LEC)
  • Provides abstraction for LAN protocols to ATM
    network
  • LAN Emulation Server (LES)
  • Manages and supports LECs
  • LAN Emulation Configuration Server (LECS)
  • Maintains emulated LANs (ELANs) and supports LECs
  • Broadcast and Unknown Server (BUS)
  • Distributes broadcasts/multicasts

19
How ATM is Used in a LAN
  • 1. LEC - Implemented at each client (bridge
    listens to all)
  • 2. LEC contacts LECS to going a ELAN via a
    pre-configured SVC or discovered dynamically via
    integrated local management interface (ILMI)
  • 3. LECS assign LEC to a ELAN and direct them to a
    LES
  • 4. LEC setups up connection to LES and registers
    addresses
  • 5. LES assigns a BUS to the LEC
  • 6. LEC queries LES for a MAC address to ATM
    address translation
  • 7. LECS responds directly or forwards query to
    another LEC
  • 8. MAC broadcasts are sent to BUS so that an
    associated ATM broadcast can be sent to all
    stations in the ELAN.

20
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.

21
Final Thoughts
  • Local loop
  • ISDN
  • Digital Subscriber Line (DSL)
  • Cable modems
  • Cellular
  • CIR/CAR
  • Everything over IP
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