Call Tear Down at
Originating Packet Switch
(ISUP to SIP)
This section takes a closer look at the processing and messaging
completed by the OPS when acting as a gateway between the PSTN
and an IP network .
1. An ISUP REL message arrives at the OPS on a signaling data
link (SDL). The message is sent from the trunk peripheral
terminating the SDL to the ST PH in the SS7 GSM via nailed up
timeslots.
2. The ST PH examine the message and forward it to the ISUP
terminal process. The message is then forwarded to the SIP
terminal process.
3. Peripheral control in the IP bearer switching module detects
discontinuity and informs the SIP terminal process of the change
of state.
4. The SIP terminal process formulates a BYE message and
forwards it to the SIP PH in the SIP GSM. This message is in a
compact, internal SIP format. This message informs the TPS to
tear down the call.
5. The SIP PH expands the BYE message to standard, external SIP
format, adds the appropriate SCTP and IP headers, and forwards
it to TPS via the IP signaling network.
Detailed Call Scenarios - SIP Base
Call Flow
....................................................................................................................................................................................................................................
235-200-118
Issue 3.02B, March 2007
Lucent Technologies
3-37
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