Call Control Signals

These signals consist of octets a through 1 of Fig. 9.1-1.

Continuity Signals. These forward signals report the success or failure of a continuity check on a trunk.

Signal Meaning HI HO

COT Continuity check success 0011 0010 CCF Continuity check failure 0100 0010

Unsuccessful Backward Signals. These signals are sent backwards by the exchange that determines that the call set-up cannot be completed, and indicate the reason for the set-up failure (subscriber busy, address incomplete, etc.). The signal acronyms and heading codes are listed in Table 9.2-1.

Call Supervision Signals. This group consists of forward and backward that are sent on the occurrence of events in a connection that has been set up (answer, clear-forward, etc.). The signals and their heading codes are listed in Table 9.2-2.

Table 9.2-1 Unsuccessful backward set-up signals (HO = 0101).
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