Hi, the title says it all! I have a customer with a 7200s V4.91 that has a number of 3rd party SIP softphones and 4 Polycom SIP conference units. A couple of months ago they decided to expand their network and split it into Voice/Data using VLAN's. I went to site to work with their IT guy's and after the network implementation all IP phones registered and have worked fine ever since. All the SIP devices, both Soft and Real registered and worked fine, for about 2 weeks. I logged onto the system and all devices were registered. If I exited any of them, they deregistered immediately and when turned back on they register straight away. The issue is that none of them can dial internally/ externally or be called, you just get busy. After a bit of experimenting I found that if I changed the Session Expire Time in 5.2.12 (MMC 837) from 1800 seconds to anything else (even 1799) then the SIP phones start working immediately. Since discovering this the problem has reoccurred a couple of times, although there seems to be no pattern to when it stops.

These are the things I know;

1. The Softphones are on laptops that connect to the Data VLAN, although there is inter-VLAN routing and they use DHCP to get an address.
2. The Conference phones have static addresses on the Voice VLAN, the reason being that the customer can log into them easily if needed.
3. The problem effects both sets of devices at the same time so I think I can rule out a VLAN issue.
4. The system was upgraded prior to the VLAN implementation (I know it is only to 4.91 and I can't remember why it was decided to take it there).
5. Samsung Support do not recognise this as a fault and wanted a load of stuff I cannot get easily.

I don't know why the SIP Expire Time brings the calling ability back, I only tried it because I have had to reduce it in the past to get WeVoip to work.

Any help or ideas would be appreciated as this has me stumped.