I have a setup where we have CISCO IPT setup running independently and Separate AVAYA setup. Both are working fine.
Now we have a plan to integrate both so that both the existing setup will be as it is and both cisco & Avaya users can communicate.
So as per my knowledge we can do it by having QSIG/SIP/H323 any trunk.
So please confirm is it the only thing we have to do or we need to do something more.
Also want to know that what is will the Latency MAX & MIN recommenced by Cisco for Voice calls over WAN.
Assuming the Avaya is also IP then yes, you can do SIP or H323 between CUCM and the Avaya. Or, if the Avaya isn't SIP, then you can terminate a Qsig trunk on a Cisco GW which then communicates with CUCM via whatever IP protocol you want to use.
Of course, other than the trunk you use, you need to set up the dial-plans on the Cisco side and the Avaya side so that each knows what calls to route to each other.
ITU states that max latency for voip shouldn't exceed 150 ms one way, and no packet loss.
Then yeah, you'd need to terminate the Avaya to a cisco voice gateway in some manner. Since this isn't integrating voice-mail or anything, you can just set up a normal T1 CAS, T1 PRI, Qsig trunk, FXS etc...some sort of analog or TDM connection, it all depends on what the Avaya supports. You then terminate this to an interface on the cisco router, then route calls to CUCM from the cisco gateway via dial-peer routing. On the GW and CUCM you can use SIP, H323 or MGCP, it's really up to you and your preference.
To add to what David posted, you'll find examples on the different types of integrations at the Cisco Interop site.
The documents may not fix with the exact versions of IOS or PBX software but they are a good reference when deciding how best to proceed.