ADTRAN 550 Committed Information Rate CIR, Table B-2. LMI Group of Four Dlci Assignments, Use

Appendix B. OSI Model and Frame Relay Technology Overview

Systems, DEC, Nortel, and StrataCom, is commonly referred to as the Group of Four.

Table B-2. LMI (Group of Four) DLCI Assignments

DLCI	Use
0	Call control signaling channel.
1-15	Reserved for future use.
16-1007	Available for customer data.
1008-1022	Reserved for future use.
1023	LMI channel.

Annex A and Annex D

The International Telecommunications Union Telecommunication Stan- dardization Sector (ITU-T) adopted Annex A as the interface standard for in- ternational frame relay applications. The American National Standards Institute (ANSI) modified the Frame Relay Consortium’s interface specifica- tion and ratified it as Annex D—an interface standard for the United States.

Table B-3. Annex A and Annex D DLCI Assignments

DLCI	Use
0	Carries frame relay signaling (LMI channel).
1-15	Reserved for future use.
16-991	Available for customer data.
992-1007	Management DLCIs for layer 2.
1008-1022	Reserved for future use.
1023	Higher layer protocol communication channel.

Committed Information Rate (CIR)

Customers can order a circuit with a guaranteed amount of bandwidth for their virtual connections. This amount is called the Committed Information Rate (CIR), and it defines how much bandwidth the customer is guaranteed during normal network operation. Any data transmitted above this pur- chased rate is discard eligible (DE) by the network. That is, this data can be discarded in the event of network congestion.

The CIR can be thought of as the size of the virtual connection from end to end. The CIR can be purchased in different increments up to the wire speed of the slowest link. For example, if the circuit in Figure B-3 had T1 access from site A to the frame relay network and a 56-kbps DDS line from site B to

B-6 ATLAS 550 User Manual 61200305L1-1