Appendix E. ITU-T Q.931 Messages
The table in this appendix summarizes Q.931 messages and the purpose of each. Q.931 is the layer 3 protocol of the subscriber signaling system used for ISDN and is known as Digital Subscriber Signaling System No. 1 (DSS 1). It employs a message set that is made for interworking with SS7's ISDN User Part (ISUP). As such, the message set maps to the ISUP message set.
Table E-1. Q.931 Messages
Binary Code | Message Name | Purpose |
|---|---|---|
Call Establishment Messages | ||
0 0 0 0 0 0 0 1 | Alerting | Direction: Called User → Network and Network → Calling User The called user is being alerted; that is, “the 'B' party's phone is ringing.” |
0 0 0 0 0 0 1 0 | Call Proceeding | Direction: Called User → Network or Network → Calling User Call establishment is ... |
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