I have an issue between a site to site VPN using a PIX 506 & PIX 501. The tunnel has been very reliable and I installed an Nortel IP phone to connect to a Nortel BCM at the main office site over the VPN. This workswell but after approximately 4 minutes of a voice call the connection between the phone and the BCM drops then reconnects. I have connected the phone directly to the BCM bypassing the VPN and there are no issues. Any ideas? Thanks John