Subject: [sipcore] SIP Session setup

From: Adnan Aziz <[email-masked]>
Date: Wed, 19 Oct 2016 00:28:42 +0200

Hi Everyone,
I have couple of basic questions regarding SIP session setup

1) is it compulsory for UAC to REGISTER to SIP server before session setup?
2) does SIP server checks if the UAC is REGISTERED to the SIP server if it
has received an INVITE request from a UAC? If yes then how SIP server
handle to the INVITE requests from unregistered UAC?

Regards,
Adnan Aziz

---

From: Paul Kyzivat <[email-masked]>
Date: Tue, 18 Oct 2016 20:33:37 -0400

On 10/18/16 6:28 PM, Adnan Aziz wrote:
> 2) does SIP server checks if the UAC is REGISTERED to the SIP server if
> it has received an INVITE request from a UAC? If yes then how SIP server

There is no simple answer to your question - it "depends".

As far as the core sip specs envisioned things there is no need to 
register to send or receive calls. The primary reason for registering is 
so that a device that only has an ephemeral address can receive calls 
directed to a server with a nice public URL.

BUT, the way SIP-based systems have evolved, the expectations are 
different. Access to the telephone network is gated by providers who 
have rules. It is quite often a requirement that you first register with 
a provider, then route outgoing calls through that provider, and it will 
then deliver incoming calls to you.

The bottom line is that you need to do whatever is required by the 
ecosystem into which you are connecting.

BTW, this sort of question is more properly addressed to: 
[email-masked]

	Thanks,
	Paul

---

From: "Drage, Keith (Nokia - GB)" <[email-masked]>
Date: Wed, 19 Oct 2016 16:03:36 +0000

It is worth noting that many providers require registration because they combine the registration step with authentication and estabalishment of any security association, rather than for any direct need of registration itself (which at its simplest merely creates bindings in the RFC 3261 location server). Other procedures may also be linked to the registration step, e.g. initiation of SigComp, creation of a chain of proxies for both incoming and outgoing calls, and so on.

Keith

-----Original Message-----
From: sipcore [mailto:[email-masked]] On Behalf Of Paul Kyzivat
Sent: 19 October 2016 01:34
To: [email-masked]
Subject: Re: [sipcore] SIP Session setup

On 10/18/16 6:28 PM, Adnan Aziz wrote:
> 2) does SIP server checks if the UAC is REGISTERED to the SIP server 
> if it has received an INVITE request from a UAC? If yes then how SIP 
> server handle to the INVITE requests from unregistered UAC?

As far as the core sip specs envisioned things there is no need to register to send or receive calls. The primary reason for registering is so that a device that only has an ephemeral address can receive calls directed to a server with a nice public URL.

BUT, the way SIP-based systems have evolved, the expectations are different. Access to the telephone network is gated by providers who have rules. It is quite often a requirement that you first register with a provider, then route outgoing calls through that provider, and it will then deliver incoming calls to you.

The bottom line is that you need to do whatever is required by the ecosystem into which you are connecting.

	Thanks,
	Paul

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