SIP Call to Certain BCMs fail

[TelSpt]

I have multiple BCM50s, and 450s in our business along with 6 CS1000.
BCMs are all 6.0, and CS1000s are all 7.5.
We recently implemented Session Manager
We are starting to migrate some traffic to SIP from and to our Lync 2010 server using Session Manager to Proxy.
Traffic to the Lync server from all endpoints works fine.
Traffic from the Lync server to the CS1000s, and "MOST" BCMs is working correctly with normal 2-way call path.
Calls from Lync to certain BCM50s, and 450s, is failing to actually ring the phone, or even activate the lights on the phone.
I can see the inbound call in Line Monitor of the BCM Monitor, with what appears to be the correct call setup.
RTP sessions does not show any signalling path setup.
The BCM450 and 50s that are having issues have (for the most part) the same patch levels.
I did a STARE AND COMPARE between a BCM450 r6.0 that is receiving SIP calls correctly, as well as a BCM450 R6.0 that does not work, and all SIP trunk settings, patch levels, as well as all other settings are same-same.
I am starting to think that we may have router or firewall issues.

 

[SupportDude]

If the phone is not ringing, you have a signaling problem.
There cannot be any RTP without the signaling completing the Call Setup.

I would start looking at the signaling through the firewall.
If memory serves me, it should be port 5060.

-SD-

http://www.mysupportguy.net

 

[TelSpt]

Network Engineers are saying that NO ports are being blocked.

 

[ucxguy]

Are the BCMs that have these problems by any chance behind routers that implement SIP ALG and have this feature enabled? Some SIP ALG implementations can modify or even block some SIP messages. If your routers have this feature, try turning SIP ALG off.