T1: A Survival Guide

Frame Relay

Frame relay standardization work was carried out in parallel by the ITU and ANSI. Standards documents often refer to frame relay services as frame mode bearer services. Here is a list of standards:

ITU Recommendation X.25

“Interface between Data Terminal Equipment (DTE) and Data Circuit-terminating Equipment (DCE) for terminals operating in the packet mode and connected to public data networks by dedicated circuit”

X.25 was one of the first specifications for public data networks. It incorporated hop-by-hop flow control and error correction, which contributed to the high latency of packets through X.25 networks. X.25 is still widely used for low-data-rate connectivity for point-of-sale terminals and similar applications.

ITU Recommendation Q.921

“ISDN user-network interface—Data link layer specification”

Frame relay shares several features with ISDN. The frame relay data link layer incorporates several features from the ISDN data link layer specification.

ITU Recommendation Q.922

“ISDN data link layer specification for frame mode bearer services”

Q.922 specifies the frame format used for frame relay services. It incorporates several features from Q.921 by reference, which is why it is helpful to have a copy of each.

ANSI T1.618

“Digital Subscriber Signaling System No. 1 (DSS1)—Core Aspects of Frame Protocol for Use with Frame Relay Bearer Service”

ITU Recommendation Q.933

“Integrated services digital network (ISDN) digital subscriber signaling system No. 1 (DSS 1)—Signaling ...