Subject: [SIP] Media after INVITE

From: Christer Holmberg <[email-masked]>
Date: Tue, 16 Jan 2001 08:57:39 +0200

Hi,

I was reading the thread about Early media replacement. My question,
however, has not so much to do with the 183-to-be-or-not-to-be, but
rather with the requirement that a UA should be able to receive media
after the first INVITE is sent. This mean that the remote user wouldn't
have to send any response at all - instead he could start sending media
and would never be charged for it. Yes, the re-transmission timer for
the INVITE will expire, and the call will be dropped, but until that the
remote party have plenty of time to send media to the caller (even if
it's only one-way, it can be a news service/weather service/ voice mail/
whatever, where two-way direction is not needed).

My opinion is that SOME response (183, 200, or whatever will be decided
upon) should be received before the UA is required to start receiving
media. I know that we then can get some other issues, ie. if it takes a
long time for the 200 response to reach the caller the first RTP media
packets will be lost. But, again, at least the caller (or a possible
intermediate proxy handling charging) will know that the media can be
sent.

This doesn't solve the issue about getting media streams from different
locations, but at least we would know when we should expect to receive
media in the first place.

This issue may have been discussed before, so I appologise if I'm
bringing it up again...

Regards,

Christer Holmberg
Ericsson Finland

---

From: Rick Dean <[email-masked]>
Date: Tue, 16 Jan 2001 11:12:57 -0600

> whatever, where two-way direction is not needed).

200 OK need not be tied to billing.  In typical phone systems each
device creates a call detail record (CDR) which contains more 
information and is used for billing.  For this example the gateway
CDR would probably be relied upon.

Some systems like AT&T cell phones charge for ringback.  Maybe
SIP gateway service will write their contracts similarly.  The
ringback need not be sent as RTP.

Yes, some interactive voice response (IVR) servers use this
technique to "steal" service.

--
Rick
[email-masked]

> This issue may have been discussed before, so I appologise if I'm
Content-Description: Card for Christer Holmberg

_______________________________________________
"This list is for continuing development of the SIP protocol.
The sip-implementer's list is the place to discuss implementation,
and to receive advice on understanding existing sip
to subscribe to it, send mail to [email-masked] with
"subscribe sip-implementors" in the body"

---

From: Michael Thomas <[email-masked]>
Date: Tue, 16 Jan 2001 09:08:35 -0800 (PST)

> whatever, where two-way direction is not needed).

I believe that this is an appeal to put the best
effort genie back in the bottle. Namely, unless
there is some way to prevent two cooperating
parties from sending traffic to one another
(firewall, elevated qos), early media is the least
of your worries. I could just as easily send you a
mail message with an SDP announcement and
circumvent your biller, after all.

 > intermediate proxy handling charging) will know that the media can be

It seems to me that the UAC can do whatever it
feels like to the media stream, including
dropping it on the floor, so is this really
a protocol issue?

		Mike

---

From: Christer Holmberg <[email-masked]>
Date: Wed, 17 Jan 2001 16:51:15 +0200

Hi,

>circumvent your biller, after all.

Well, I assumed that you are somehow dependent of your service
provider/operator. Otherwise you and your friend can get a couple of SIP
phones and talk to each other directly for free...

Also, sending the SDP in a mail doesn't help very much if you are making
a PSTN-to-SIP call.
 
Regards,

Christer (lmfchh)

---

From: Christer Holmberg <[email-masked]>
Date: Wed, 17 Jan 2001 16:55:38 +0200

Hi,

>CDR would probably be relied upon.

Yes, but the gateway must also know when to start the billing.
 
>ringback need not be sent as RTP.

No, the gateway can also e.g. generate a local ringback tone, or play
some message, but then the gateway will control this and can charge if
needed.

Regards,

Christer Holmberg
Ericsson Finland