A question for all the Voice people

in CCIE
Does anyone know anything about qsig and sip? We're about to run this experiment involving Nortel PBX to Cisco SIP gateways. What we're curious about is qsig path replacement.
Here's a sweet ascii diagram:
[NortelPBX]
qsig
[3945]
sip
[3845]
qsig
[astratelecomPBX]
What our switch vendors are telling us is that the qsig D channel remains intact across the sip trunk, and back to the astratelecom PBX. If this is the case then theoretically path replacement should work fine.
However, if the D channel is not intact, then how do the SIP gateways translate the qsig messages into SIP messages?
Here's a sweet ascii diagram:
[NortelPBX]
qsig
[3945]
sip
[3845]
qsig
[astratelecomPBX]
What our switch vendors are telling us is that the qsig D channel remains intact across the sip trunk, and back to the astratelecom PBX. If this is the case then theoretically path replacement should work fine.
However, if the D channel is not intact, then how do the SIP gateways translate the qsig messages into SIP messages?
Comments
ISDN Q-Interface Signaling Protocol Q.931 Tunneling over the IP Network [Empowered Branch Solution] - Cisco Systems
Since you have the PRI hand off to the gateway it takes the q931 and encaps it into the SIP trunk and then de-encaps it at the other end when it hands it back off PRI
Also, if anyone stumbles upon this thread in the future I'll link to the doc that tells you exactly how to do it.
http://www.cisco.com/en/US/docs/voice_ip_comm/cucme/pbx/interop/notes/681800.pdf
Turns out this voice stuff isn't so bad after all.