atcomsystems.ca/forum Forums TDM Business Telephone Systems Samsung Telephones & Systems Very strange problem with remote IP phones on OS 7200-S

I've got an issue going on with a client that has the following setup -

Main Office -

OS 7200-S w/ OAS card,
SIP Trunks, Digital Keysets inhouse
Sits behind Linksys BEFSX41 with 6000-6001 & 9000-9001 forwarded to the MP20S, and 30000-30031 forwarded to the OAS

Remote office -

3 SMT IP Phones behind AT&T 2Wire router with no ports forwarded.

The issue is this, the remote office seems to be able to place and receive calls via the SIP Trunk without an issue, however, about 50% of the time, when an employee in the main office initiates an intercom call to any of the remote phones, there is no audio, they client discovered, quite by accident, that if you hit CONF, then hit CONF again, bingo, you have your audio working. I placed a few calls from our office here using a remote phone registered to the main office, via intercom feature, and found the problem occurs in the opposite direction as well, ie. intercom FROM the remote phone to the main office. I've gone over this with Samsung tech support, and they have sworn up and down it is a firewall issue, but I come from an IT/Networking background in addition to my telecom experience, so had the forethought enough to try putting the OAS in the DMZ on the router at the main office, same result, and although I didn't think this would work, just for the heck of it I tried it also with the MP20S in the DMZ, same. (I knew the MP20S in the DMZ wouldn't do it since it does not handle the RTP voice data, but figured what the hell, why not!) I am at a loss as to what could be causing this issue.

Have you tried disabling the MPS channels or port forwarding the MPS channel ports? Also make sure the ports you have forwarded are the ones for the OAS card and not the onboard MGI channels. I believe the onboard ports use 30000-30011 by default and the OAS card would use 30012-30043.

I actually now have 30000-30064 forwarded just to be on the safe side, and as far as I can tell, MPS is disabled. I'm fairly new to the officeserv systems, but not to VoIP, I come from and Asterisk background, which operates in a similar fashion. (both systems support SIP, just on different ports for the RTP streaming media) I have not had a chance to test it since the change in the port forwarding, as the client is too busy to do so right now, but tomorrow I plan on taking an IP phone to the site and connecting it on the LAN INSIDE the firewall and testing it from there, if I cannot reproduce the problem INSIDE the LAN, I will know for sure it is a firewall issue. Thanks for the speedy response, btw!! Feel free to shoot any pointers my way on anything else I should check while I have access to the local LAN....

-Andy

But different devices are using a different range. IE MP-20S onboard MGI channels by default use 30000-30011 so ports 30000-30011 would forward to the IP address of the MP-20S. Then the OAS would use ports 30012-30043 which would forward to the IP address of the OAS card. Also check check your MGI USE GROUP and make sure you only have the MGI ports being used in the group.

I think you just might be onto something there! I hadn't thought of that! What MMC's/IT Tool sections can I check as far as what IP's goto what, ports, etc?

-Andy

Its the same one you assign the IP address to the OAS card.(We are not allowed to post tech MMC's and the PM feature is down right now).

Also dont forget that if you are using OAS with MPS enabled, you will need to port forward the 40,000 range too.