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.