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Enabling the R2 Protocol
November 2009 355
R2 Call Control
This section presents an overview of R2 outbound and inbound call
setup and tear down. LEC protocols and ISDN use a similar
mechanism.
Once the trunk is configured, a particular channel that is enabled is
ready to dial an outbound call or process an inbound call from the
network. The R2 protocol stack automatically selects a DSP channel
(Boston channel) to perform the tone detection/generation
operations. The first B-channel on the first line uses the first DSP
channel, then each subsequent B-channel selects the next DSP
channel.
The first B-channel on the next line selects the DSP channel
immediately following the DSP channel selected for the last
B-channel of the previous line, thus ensuring there are no gaps in
the DSP channel usage caused by different number of timeslots in T1
and E1 lines.
During call setup - either inbound or outbound - the application
must not issue any commands to the Tone Generation and Tone
Detection facilities, as these would interfere with the R2 signaling
and cause the call to be abnormally terminated. If the application
connecting DSP channels and B-channels through the Telephony
Bus (H.100), it must ensure the appropriate DSP channel is free and
connected to the corresponding B-channel when it is ready to
receive/place calls. Once the call is connected, the DSP and
B-channels are remapped.