[SIPForum-discussion] Does SIP support SSL, new protocols, early media, etc?

[Paul Kyzivat]

On 6/9/15 8:41 AM, Rodrigo Pimenta Carvalho wrote:
>
> Hi.
>
> I'm starting with SIP and with a software project in my company. Today I have some beginner doubts:

It sounds like you haven't yet mastered sip basics. So you have a lot of 
homework to do.

> 1 - In my project a SIP client will call others SIP clients at same time, i.e., several SIP clients will receive SIP INVITE, like calling for a conference. But, when one callee answer the call, all the others must stop ringing immediate. The objective is let just one SIP client answer the call. it will be the first that will reply. Can the SIP protocol help me with this idea? Is SIP protocol prepared for such idea, in terms of its messages?

This is pretty basic. When the first answers you can immediately send 
CANCEL to the others. This will work most of the time, unless more than 
one "auto answer". But there is no *guarantee* that you won't have more 
than one answer. If you and up in that situation, you need to deal with 
it - either keep them both active (works if you are establishing a 
conference), or else send a BYE to one of them. (Of course when you send 
a BYE the user experience isn't ideal - it means the UAS alerted, 
answered, and then immediately saw a disconnect.)

> 2 - In my project, a callee must receive and view the video from the caller, even before answering the call (early media). Can SIP help me with this requirement? How?

SIP certainly supports this. You will need for the UAS to send an SDP 
answer in a provisional response - ideally using a reliable provisional 
response - so that the UAC knows where to send the media.

However, it may depend on the environment in which you deploy. Some 
carrier networks may block this.

> 3 - I know that SIP can be used together SDP. And I guess that SIP can be used with any another protocol. So, let's suppose that I have created an new protocol based on Json. This protocol will carry information about some IP devices, like IP addresses and port. Can I send SIP messages with a new Json based protocol together? How can SIP help me with this idea?

Can you explain more about what you have in mind?
It is *possible* to replace the use of SDP with some other format for 
offer/answer. But I'm not aware of anybody doing that in practice. 
(There was once a proposal to migrate from SDP to SDPng, but it failed 
because the migrations was too difficult to deploy.)

Or, it is possible to carry other protocols in a variety of ways. The 
cleanest way to do that is with the INFO method (RFC6086). It is 
possible to do this before the call is answered.

> 4 - I need send/receive SIP messages encrypted, to provide secure to my SIP clients. In this case, what should I do to provide secure SIP messages using SSL or TLS? Does SIP protocol support this idea in some way? How?

Yes, SIP over TLS is defined and used.

Are you intending to build a closed system, where you build all the 
components to a common spec? Or are you planning to deploy this over an 
existing VoIP system. The answer to that will strongly impact what you 
can do.

	Thanks,
	Paul

> Any hint will be very helpful!
>
> Thanks a lot!
>
> Best regards.
>
>
> RODRIGO PIMENTA CARVALHO
> Inatel Competence Center
> Software
> Ph: +55 35 3471 9200 RAMAL 979
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