Re: Kamailio /3CX

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Hi Asma

> More specifically, can Kamailio be used as a SIP proxy/SBC in front
> of a 3CX PBX? I would be interested in hearing about any real-world
> deployments, best practices, or challenges you encountered.

Sure, we are a Swiss Voice Service Provider (VSP) for (single
SIP account) residential and (SIP Trunking) business customers. The core
and registrar parts of our services is using Kamailio but we still
have commercial SBC in between kamailio and our customers and IC for
topology hiding and media handling and to get a different CallID on
each leg of a call.

Also looping forwarded calls via an SBC to get a different CallID and
therefore a different dialogues and CDR for correct billing of all legs
involved in a call (imagine parallel forking a call to a customer's sip
device, to his holiday home phone abroad and to his mobile phone, I
need to know which one picked up the call for correct billing)
Kamailio not being an SBC therefore using the same CallID on all
branched legs sometimes is a bit of an extreme challenge.

We have many, especially small business customers using 3CX. Our
office telephony with customer hotline, hunt-groups, IVR, time based
announcements and forwarding, and call queueing is running on a 3CX.

Of course, it is up to you, how you configure trunking, what headers
you use etc.
Attached our 3CX template file we supply to our customers which works
for our set-up and with the way we use the different SIP headers,
especially when using clip-no-screening to use the original callerID
on a forwarded outbound leg (for which we use the PPI header).

Challenges:

* 3CX has very bad support, especially for voice service
  provider - if you are not a paying customer - you don't get support -
  not even if you are a VSP with hundreds of connected 3CX customers.

Known Issues (possibly a rant :-) )

* Issue reported 2021: 3CX generates ringback tone to the caller
  BEFORE the call is indeed being alerted by a device ringing - from a
  technical point of view this causes a lot of confusion as the caller
  (especially the technical knowing one) assumes the call has reached
  the destination.
  https://www.3cx.de/forum/threads/ringback-tone-obwohl-kein-180-von-remote=
.125251/

* There is either an generic issue handling method UPDATE or something
  broken when two nested transactions use the same sequence number:
  https://www.3cx.de/forum/threads/suspected-bug-with-sequence-cseq-numbers=
.126242/

  Only Solution known for the later issue: Use Kamailio to inspect
  User-Agent.
  If INVITE from 3CX: Remove UPDATE from Method list and set dialog
  variable to keep that setting during all requests and replies in the
  complete dialog (or smuggle a flag in record-route so you only have to
  remember in each transaction).
  When looking up location information of a registered PBX consult
  'User-Agent' and repeat.
  Or make this configurable per customer so you can disable 'update'
  support for a specific customer.

Except of all this - 3CX seems to be a very versatile PBX solution with
good mobile / web / native client and support for many different sip
phones.

Mit freundlichen Gr=C3=BCssen

-Beno=C3=AEt Panizzon-
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I m p r o W a r e   A G    -    Leiter Commerce Kunden
______________________________________________________

Zurlindenstrasse 29             Tel  +41 61 826 93 00
CH-4133 Pratteln                Fax  +41 61 826 93 01
Schweiz                         Web  http://www.imp.ch
______________________________________________________

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