SIP ext to SIP ext calls

[lyson123]

Hi,
I'm new here, but need help.
Here's the scenario:
NCP500 with approx 10 DT343 phones, NT343's couple of PS (5 I guess) and off site 5 SIP exts ( Grandstream GXV3140 )
got it setup to handle SIP calls through NAT and firewall, I can dial out through all SIP trunks and POTS lines from all exts in the system ( including remote SIP ones ). For some weird reason I can't dial SIP ext to SIP ext ( both off site ),
I get forbidden or no response. To make things even more interesting if I dial from SIP softphone to SIP hardphone ( both off site ) call goes through, it doesn't if i do it vice versa ( hardphone -> softphone ).
I know Panasonic officially does not support anything outside of the same network or VPN ( at least tech support doesn't ), they told me my configuration will not work ( already proved wrong ) now I need to find out why I can't call between extensions.

Anyone with any ideas, please help

thanks.

 

[Shieldsy]

Hi there,

the off site sip phones have to have a VPN between them also as i think the call is handled as peer to peer.

 

[obtsystems]

it could bee your windows firewall on the pc with the softphone.
are the off site phones in the same location or different dsl connections.

 

[lyson123]

hi guys

@Shieldsy,
this isn't entirely true. as long as you open correct ports on your firewall, and find a way to handle NAT traversal on from the SIP phone side, SIP phone will work off site without VPN, that's basic networking.
Besides, issue applies to phones both onsite and off site.
SIP calls cannot be handled as p2p - Panasonic does not support ip dialing, so it has to go through the PBX.

@obtsystems

thanks, that i figured, but since the issue does not apply to the soft phone, i think it has something to do with the way 3CX ( softphone in question ) handles NAT on it's side.
phones off site are spread between different ISP ( cable, DSL, Fios, T1 ).

Still need a solution, Panasonic tech support has no idea what I'm talking about.