WAN Technologies

What Is WAN?

  • Wide area network.
  • Communication between LANs which are in distant areas like different cities, different countries. (geographically far from each other)
  • Service provider network is the transit area in WAN.
  • Customer need to pay money to the service provider.
  • Amount depends on speed and distance of the WAN link.
  • LANs and WANs are different at the data link layer and physical layer.
  • Standards:
    1. American standard
      • E1 : 2 Mbps.
    2. European standard
      • T1 : 1.5 Mbps
      • T3 : 45 Mbps

WAN connection types:

  • Leased lines
    1. A pre-established, private connection from one site to another through a service provider’s network.
    2. Also called as a dedicated circuit or dedicated connection.
    3. Always a point to point connection between two end points.
    4. Used when there is a constant flow of data, or when a dedicated amount of bandwidth is required.
    5. Leased line is secured reliable, always up, dedicated connection.
    6. Billing is done on 24/7 basis.
    7. PPP and HDLC are used as WAN protocols.

HDLC and PPP:    (HDLC & PPP are WAN link encapsulation protocols)

  • HDLC:
    1. High level data link control
    2. Cisco proprietary protocol
    3. Provides error detection
    4. Doesn’t support authentication
    5. No data compression
    6. HDLC is the default encapsulation on serial interfaces
  • PPP
    1. Point to point protocol
    2. Open standard
    3. Supports authentication
    4. Data compression
    5. PPP has three main components
      • Frame format (encapsulation)
      • Link control protocol
      • Network control protocol
    6. Multilink
    7. LCP and NCP are responsible for establishing, configuring, authenticating and testing PPP connection.
    8. LCP:
      • To send and receive keep alive messages through the leased line to know if the other end is available.
      • LCP also helps PPP to find that which features both sides are using, and if they don’t use the same features then the link will not come up.
    9. NCP:
      • The routers negotiate with each other that which layer 3 protocols data they will be sharing through the PPP link.
  • PPP authentication:
  • PPP uses two methods to support authentication:   PAP and   CHAP.
    1. PAP  –  password authentication protocol
      • Simplest but less secure
      • Two way hand shake process
      • Source send its username and password in clear text to destination.
      • Destination compares username and password with its data base.
      • If it matches then sends accepts message otherwise sends reject message.
    2. CHAP – challenge handshake authentication protocol
      • Three way hand shake process & secure than PPP.
      • Source sends its username to destination.
      • Destination looks at username/password in its database and generates a challenge value using MD5 and sends that value to source.
      • Source uses that challenge and generates a hash value and send it to the destination.
      • Destination verify this hash value and sends accept or reject message
      • Password is never sent on that link to provide security.
  • Circuit switching:
    • A dialup connection through a provider’s voice-grade connection.
    • Either uses an analog modem or an ISDN connection
    • Used when a slow speed connection is needed, or there is no need to transfer a lot of data.
    • One call establishes a circuit to one destination site
    • Establishes logical circuits between source and destination (circuit switching)
    • PPP, HDLC and SLIP are the protocols used in circuit switching
    • Example:
      • PSTN – Public switched telephone network
      • ISDN – Integrated service digital network
  • Packet switching:    (Frame Relay)
    • Contains all features of leased line and ISDN
    • Virtual circuits (VCs) reduced no of leased lines significantly
    • PVC and SVC offers flexibility
    • Very economical
    • Billing can be done on any basis
    • Suitable for all scenarios (high bandwidth)
    • Availability is an issue
    • No frame relay technology in India.

Frame Relay Terminology:

  1. FRS – Frame relay switch
    • The switch used at service provider end in frame relay network.
  2. VC – Virtual circuit (a logical circuit establish between FRS)
    • Logical connection between two FRS
  3. PVC – Permanent virtual circuit
    • The VC that is always available. Similar to dedicated line.
  4. SVC – switched virtual circuit
    • The VC that established when needed. Similar to ISDN
  5. DLCI – Data link connection identifier (tag attached to VC for identification)
    • It is identification for VC. Range is 16 – 1007
    • The DLCI no’s are assigned by the service provider’s.
  6. CIR – committed information rate
    • The bandwidth committed by Service provider
    • The max allowable bandwidth through the PVC from one to another
    • Each PVC can have a unique CIR.
  7. LMI – local management interface (keep alive messages)
    • Signals checks the keep alive status: DTE to DCE
    • Signalling between routers and frame relay switches
    • LMI does not travel across the entire PVC from one end to another
    • LMI types: q933a, cisco, ANSI…
  8. FECI – Forward explicit congestion notification
    • Messages to FRS and source if congestion occurs between FRS and destination
  9. BECI – Backward explicit congestion notification
    • Messages to FRS and destination if congestion occurs between FRS and source
  10. BE – burst excessive (boosting bandwidth)
    • Frame relay boosts the bandwidth of VC if network is free.

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