ICND2 – Chapter 15 – Frame Relay Concepts

I have a good amount of experience with Frame Relay so I do not have highlighting or notes in this chapter that a lot of other people would have. For example, I am familiar with VCs, PVCs, DLCIs, etc. so I did not highlight those topics. I mainly focused on the things I thought I needed to know that I did not already feel strong in. Here are the notes:

Frame Relay networks are called nonbroadcast multiaccess (NBMA)

Frame Relay sends keepalive messages along with other messages defined by Local Management Interface (LMI)

Routers are DTE and the Frame Switch is DCE.

ITU Q.922 and Q.933 documents frame relay standards. ANSI uses T1.617 and T1.618.

LMI is NOT encapsulation. LMI is messaging.

LMI Status messages perform 2 keys functions:

1. Keepalives
2. Active/Inactive VC

Cisco IOS defaults to LMI autosense.

It can be manually set to cisco, ansi, or q933a.

Link Access Frame Bearer Services (LAPF) define the frame relay header and trailer. It contains a protocol field. This is the default Cisco encapsulation.

RFC1490 (later superseded by RFC 2427) was created to overcome the lack of a protocol field in frame relay headers.This is the ietf encapsulation method.

Traffic shaping uses FECNs and BECNs to decrease the sending rate in the event of congestion.


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