Your firewall is clearly blocking the return path. Rather than explain how to fix this in a lengthy email, I will forward you a whitepaper that explains overcming firewalls and video conferencing...
Video "jerkiness" not associated with b/w issues usually results from excess jitter in the which may overrun jitter buffers that may exist in video endpoints. Source could be serialization delay in your topology - Cisco recommends running video on F...
If I understand your question properly, you are trying to invite an ISDN only connected endpoint by using the IP "invite" dialsting on an H.323 into a multipoint conference on the Polycom. If I'm misreading this, please correct. If this is the case...
This is a complex question that requires more than BB post to answer. I suggest looking at the following link that explains QoS Strategy and configs for video in depth. http://www.cisco.com/en/US/tech/tk543/tk544/technologies_tech_note09186a0080094...
Note that the embedded GK in the MCU is not recommended for enterprise deployments. Cisco design guides and best practices re: enterprise video deployments recommend using the MCM/GK on IOS as the proper solution.
