Tag Archives: WAN

CCDA Notes – WAN

Additions/subtractions needed? Let me know.

WAN Categories

  1. Circuit Switched – created only when needed. i.e. ISDN and dial-up.
  2. Leased Lines – dedicated connection. TDM based.
  3. Packet switched – shared bandwidth using virtual circuits. i.e. Frame Relay.
  4. Cell Switched – ATM
  5. Broadband – xDSL, Cable, Wireless

Time Division Multiplexing (TDM)

  1.  Multiple channels such as voice, video, and data can be combined
  2. DS1 or T1 provides 24 time slots of 64kbps each and one 8 kbps control time slot

Frame Relay

  1. NBMA
  2. DLCI = L2 addressing
  3. LMI reports VC status.
  4. LMI has 3 types. Cisco, ANSI, Q.933A. Auto tries all three.
  5. Multipoint interfaces require L2-to-L3 address resolution. Done via inverse-ARP or static “frame-relay map”.
  6. Physical interface is multipoint by default. i.e Serial0/1
  7. Static L2-to-L3 mappings override dynamic mappings.
  8. “frame-relay interface-dlci <dlci #>” on point-to-point subifs. LMI does not communicate DLCI number on subifs.


  1.  Enabled automatically when a supported protocol is cfgd. i.e. “ip address”
  2. Requests are sent out all circuits assigned to the interface for all supported protocols.
  3. Requests can be disabled via “no frame-relay inverse-arp”. Replies can not be disabled.
  4. Automatically supports multicast/broadcast via a replicated unicast.


  1. Circuit-based ring topology.
  2. Optical
  3. ATM or Packet Over SONET(POS)
  4. Optical carrier rates. i.e. OC-1 =51.85 Mbps  OC-255=13.21 Gbps