Appendix A. MTP Messages (ANSI/ETSI/ITU)

The table in this appendix summarizes Message Transfer Part (MTP) messages and the purpose of each. The signaling network management (SNM) procedures of MTP3 generate MTP messages. For an introduction to MTP3, refer to Chapter 7, "Message Transfer Part 3 (MTP3)."

Table A-1. MTP Message Explanation and Codings

H1/H0 Code	MESSAGE NAME	PURPOSE
0 0 0 1 0 0 0 1	COO Changeover Order	Indicates that traffic is being changed over from a primary link to an alternate link.
0 0 1 0 0 0 0 1	COA Changeover Acknowledgement	Acknowledgement sent in response to a COO.
0 1 0 1 0 0 0 1	CBD Changeback Declaration	Indicates that traffic is being changed back to a primary link from an alternate link.
0 1 1 0 0 0 0 1	CBA Changeback Acknowledgement	Acknowledgement sent in response to a CBD.
0 0 0 1 0 0 1 0	ECO Emergency Changeover Order	Indicates that traffic is being changed over from a primary link to an alternative link. This differs from a COO in that the last accepted FSN cannot be determined, resulting in possible message loss.
0 0 1 0 0 0 1 0	ECA Emergency Changeover Acknowledgement	Acknowledgement sent in response to an ECO.
0 0 0 1 0 0 1 1	RCT Routeset Congestion Test	Sent after receiving a TFC in order to test whether a routeset is at the congestion level specified by the priority of the RCT message.
0 0 1 0 0 0 1 1	TFC Transfer Controlled	Indicates routeset congestion for a destination. The level of congestion is indicated in the message to prevent messages of a lower priority from being sent.
0 0 0 1 0 1 0 0	TFP Transfer Prohibited	Sent by an STP to indicate that messages to a particular destination must be sent via another route because of a total loss of routing capability to that destination.
0 0 1 0 0 1 0 0	TCP Transfer Cluster Prohibited (A)	Sent by an STP to indicate that messages to a particular cluster must be sent via another route because of a total loss of routing capability to that cluster.
0 0 1 1 0 1 0 0	TFR Transfer Restricted	Sent by an STP to indicate that messages to a particular destination should be sent via another route, if possible, because of diminished routing capability to that destination.
0 1 0 0 0 1 0 0	TCR Transfer Cluster Restricted (A)	Sent by an STP to indicate that messages to a particular cluster should be sent via another route, if possible, because of diminished routing capability to that cluster.
0 1 0 1 0 1 0 0	TFA Transfer Allowed	Sent by an STP to indicate that messages to a particular destination can be routed normally.
0 1 1 0 0 1 0 0	TCA Transfer Cluster Allowed (A)	Sent by an STP to indicate that messages to a particular cluster can be routed normally.
0 0 0 1 0 1 0 1	RST (ITU) RSP (ANSI) Routeset Prohibited Test	Sent periodically after receiving a TFP to test whether the routeset state is still prohibited.
0 0 1 0 0 1 0 1	RSR Routeset Restricted Test	Sent periodically after receiving a TFR to test whether the routeset state is still restricted.
0 0 1 1 0 1 0 1	RCP (A) Routeset Cluster Prohibited Test	Sent periodically after receiving a TCP to test whether the routeset state for a cluster is still prohibited.
0 1 0 0 0 1 0 1	RCR (A) Routeset Cluster Restricted Test	Sent periodically after receiving a TCR to test whether the routeset state for a cluster is still restricted.
0 0 0 1 0 1 1 0	LIN Link Inhibit	A request to place a link in the inhibited state. An inhibited link cannot transmit user traffic from level 4.
0 0 1 0 0 1 1 0	LUN Link Uninhibit	A request to uninhibit a link that has been placed in the inhibited state.
0 0 1 1 0 1 1 0	LIA Link Inhibit Acknowledge	Acknowledgement sent in response to a LIN, allowing a link to be inhibited.
0 1 0 0 0 1 1 0	LUA Link Uninhibit Acknowledgement	Acknowledgment sent in response to a LUN.
0 1 0 1 0 1 1 0	LID Link Inhibit Denied	Sent in response to an LIN, denying the request to inhibit a link.
0 1 1 0 0 1 1 0	LFU Link Forced Uninhibit	Sent to request that a previously inhibited link be uninhibited. Used when the inhibited link is the only available route to a destination.
0 1 1 1 0 1 1 0	LLT (ITU) LLI (ANSI) Link Local Inhibit Test	Sent for a link in the locally inhibited state to test that the far-end link state is marked as remotely inhibited.
1 0 0 0 0 1 1 0	LRT (ITU) LRI (ANSI) Link Remote Inhibit Test	Sent for a link in the remote inhibited state to test that the far-end link state is marked as locally inhibited.
0 0 0 1 0 1 1 1	TRA Traffic Restart Allowed	Sent as part of the MTP restart procedure to indicate that traffic may be restarted.
0 0 1 0 0 1 1 1	TRW Traffic Restart Waiting (A)	Sent as part of the MTP restart procedure to indicate that the sending of traffic should be delayed because of an MTP restart in progress.
0 0 0 1 1 0 0 0	DLC Data Link Connection [*]	No specification.
0 0 1 0 1 0 0 0	CSS Connection Successful[*]	No specification.
0 0 1 1 1 0 0 0	CNS Connection Not Successful[*]	No specification.
0 1 0 0 1 0 0 0	CNP Connection Not Possible[*]	No specification.
0 0 0 1 1 0 1 0	UPU User Part Unavailable	Sent to the originating signaling point when MTP cannot deliver a message to an MTP3 User.
KEY: (A) Messages supported in ANSI only (ANSI T1.111-2000). All others supported by ANSI and ITU (Q.704–1996). Note: ETSI MTP [9] uses exactly the same message set and codings as ITU-T.

^[*] These messages are defined by the ITU and ANSI standards, but no specifications are stated as to their use. The authors are not aware of their actual use in existing networks.