Frame Relay Notes – LMI, Headers, and Encapsulation

Local Management Interface
  • Manages link between the router and frame relay switch
  • Routers send Status Enquiry to the switch
  • The switch responds with a Status message informing the router of the DLCIs available
  • Serves as a keepalive
  • Default keepalive is 10 seconds, 3 misses is failed
  • Three types
    • cisco <- default
    • ansi (Annex D)
    • q933a

Headers and Encapsulation
  • Link Access Procedure for Frame-mode Bearer Services (LAPF) is the first header
    • Includes DLCI, DE, FECN, BECN
    • To be read by the frame relay switch
  • Frame relay encapsulation header is next
    • To be read by the router on the other end of the VC
  • Two types
    • cisco : proprietary <- default
    • ietf : IETF RFC 2427

Aaron Conaway

I shake my head around sometimes and see what falls out. That's what lands on these pages. If you have any questions, the best way to contact me is through Twitter at @aconaway.

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