“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.

“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.

“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.

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

“Integrated services digital network (ISDN) digital subscriber signaling system No. 1 (DSS 1)—Signaling specifications for frame mode switched and permanent virtual connection control and status monitoring”

The title is a bit wordy, but Q.933 is just the ITU’s LMI specification. Sections of Q.933 refer to ISO/IEC TR 9577.

“Digital Subscriber System No. 1 (DSS1) Signaling Specification for Frame Relay Bearer Service”

T1.617, and its later follow-up, T1.617a, describe a similar but slightly different version of the LMI.

“PVC User-to-Network Interface (UNI) Implementation Agreement”

Q.933 and T1.617 are both complex standards. To make deployment easier, FRF.1 specified a streamlined set of options so that frame relay could be deployed faster.

“Information technology—Protocol Identification in the network layer”

This technical report is available at no charge from the ISO. It describes how to identify both ITU-standardized and ISO-standardized protocols in a number of other protocols. It was adopted by the IETF for use with RFC-1490 encapsulation. Unlike most other ISO and ITU standards, TR 9577 is available at no charge.

“Information technology—Protocol identification in the Network Layer”

This ITU recommendation contains the same text as the ISO/IEC TR 9577.

“Multiprotocol Interconnect over Frame Relay”

RFC 1490 was the first IETF standard for multiprotocol encapsulation over frame relay links. It defines the multiprotocol encapsulation header for different network protocols, plus the encapsulation format for bridged packets. RFC 2427 was an evolutionary update that clarified some minor points and removed the specification of Inverse ARP, among other things. A complete list of changes from RFC 1490 is present in the final section of the RFC.

“Inverse Address Resolution Protocol”

frame relay networks may bring new DLCIs into existence dynamically. New DLCIs are reported in the LMI PVC status message with the “new” bit set. These announcements, however, do not include any higher-layer information. Inverse ARP allows a frame relay device to request the IP address associated with a given DLCI.

“Recommendation T.50 (09/92)—Information technology—7-bit coded character set for information interchange”

T.50 describes character sets used by other standards. Parts of it are used by both LMI Annex A and LMI Annex D.

“Recommendation V.4 (11/88)—General structure of signals of International alphabet No. 5 code for character oriented data transmission over public telephone networks”

International Alphabet 5 is used by the LMI Annex A. This recommendation specifies IA5.