5. When an ISUP Address Complete message is received from the
terminating switch in the PSTN, the TPS sends a SIP 180
RINGING provisional response, which includes:
• encapsulated ISUP Address Complete Message, and
• the same SIP Allow and Require headers as the 183
SESSION PROGRESS.
6. Audible ringing is provided by the terminating switch in the
PSTN.
7. When the TPS receives an ISUP Answer message, it sends a SIP
200 OK INVITE response, which includes the encapsulated ISUP
ANM.
8. When the called party goes on-hook first, the TPS receives an
ISUP Suspend message, which it sends in a SIP INFO message
with the ISUP SUS message.
Note: When the calling party goes on hook, the OPS receives an
ISUP Release and sends a SIP BYE message with the
encapsulated ISUP REL Message. The call resources are then
released.
Message Flow 2
In this message flow, the 5ESS
®
switch is acting as a PSTN Gateway,
handling a call that originates from subscriber on a TAS in the IP
network and terminates to a subscriber on another switch in the
PSTN. The 5ESS
®
switch is the TPS in this scenario, and the TAS is
the OPS. It is presumed in this scenario that the TAS has a directly
provisioned route to the 5ESS
®
switch PSTN Gateway, so there are no
proxies or other intermediate nodes between the 5ESS
®
switch PSTN
Gateway and the TAS. Refer to Figure 3-7, “ 5ESS
®
Switch PSTN
Gateway TPS and TAS OPS Message Flow” (3-21).
The provisioning at the 5ESS
®
switch PSTN Gateway which affects
the message flow and message content is as follows:
• Transport Layer: UDP (RC/V 5.71 UDP PATH provisioned),
• Preconditions: No (RC/V 5.71 SIP-T PRECOND=N),
• Encapsulated ISUP: No (RC/V 5.82 ISUP
ENCAPSULATION=N),
• PRACK procedures: Yes (RC/V 5.82 PRACK ENABLED=Y),
and
Message Flows
Call Flow
....................................................................................................................................................................................................................................
235-200-118
Issue 3.02B, March 2007
Lucent Technologies
3-19
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