SIP INVITE MTU size / defragmentation

[Jclausen]

I'am trying to configure an SIP-trunk from the danish provider TDC.

I got the following information fra TDC:

PBX server IP - ok
TDC SBC SIP/RTP IP: ok
SIP trunk groupID: *******
SIP url Domain vk******.hvoip.dk
SIP trunk VPN VRF*****

How do i configure SIP trunk groupID, url domain and SIP trunk VPN in 3cx?

And the following information regarding defragmentation: (question: does 3cx handle defragmentation corretly?)

Important! An SIP INVITE can be larger than standard MTU size on TDC Managed CPE and can therefore be sent
fragmentet. Therefore, you need to make sure that your equipment supports defragmentation.

Examples of SIP signaling in connection with TDC SIP Trunk:

Example of SIP OPTIONS sent from TDC SBC:
OPTIONS sip:[email protected]:5060;transport=tcp SIP/2.0
…
To: sip:[email protected]
From:<sip:[email protected]>;tag=0cc…
Eksempel på SIP OPTIONS sendt til TDC SBC:
OPTIONS sip:128.77.191.7 SIP/2.0
…
FROM: <sip:lyncsbc01.blah.net:5060;...
TO: sip:128.77.191.7
Eksempel på SIP INVITE sendt fra TDC SBC:
INVITE sip:+ 458752****@VK155602.hvoip.dk:5060 SIP/2.0
…
To: "Ole Olsen"<sip:+458752****@VK155602.hvoip.dk>;cscf
From: <sip:+4570909090@***.243.25.***:5060;user=phone>;tag=41…-
…
Contact: sip:128.77.191.7:5060;transport=tcp
Eksempel på SIP INVITE sendt fra kunde mod TDC SBC:
INVITE sip:[email protected];user=phone SIP/2.0
…
FROM: "Olsen, Ole"<sip:+4458752****@blah1.blah.blah.net;user=phone>;…
TO: sip:[email protected];user=phone

 

[YiannisH_3CX]

Hi @Jclausen

And the following information regarding defragmentation: (question: does 3cx handle defragmentation corretly?)

Yes 3CX does handle it correctly but since your provider knows that their SIP Invites could be larger than the standard MTU then they should really switch to TCP. If they can already handle TCP then its best you switch your trunk to use TCP instead of UDP.

How do i configure SIP trunk groupID, url domain and SIP trunk VPN in 3cx?

The SIP url domain should go in the registrar value of the PBX and the SBC SIP/RTP IP should go in the proxy field in 3CX.

SIP Trunk GroupID: Not sure what they mean by that. That could be a caller ID or the Auth id of the trunk used to identify the group ID your trunk belongs to and should be sent to a specific sip header to help the provider identify where the call needs to be routed.

SIP trunk VPN VRF: This is something we have never tested so we cannot guarantee it will work. Also this is something that needs to be set up in the OS hosting the 3CX PBX and not in the 3CX software. Again since we have never tested this we cannot guarantee it will work properly.

My advice would be to use a 3CX supported provider to avoid the guess work.