Subject: RE: draft-ietf-mmusic-sip-session-timer-00.txt

From: Francois Menard Distribution List Management Account <[email-masked]>
Date: Thu, 11 Feb 1999 20:04:36 -0500

There is no way to properyly time the session unless the end-point is a
controlled network element.  A gatekeeper and/or SIP server cant do anything
unless the media stream gets through it ... of course, a SIP server, and or
H.323 gatekeeper can talk to routers, which control an IP media stream, and
affect the media stream.

Even worse, a sip server / gatekeeper that wishes to track the end of a call
so that it can bill by the second needs to worry about end points that just
go out and die and never send an end of conversation ... this mechanism is
not yet specified ...

-=Francois=-

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Thursday, February 11, 1999 6:22 PM
To: Donovan, Steven R. (MCI); [email-masked]';
[email-masked]'; [email-masked]'
Subject: RE: draft-ietf-mmusic-sip-session-timer-00.txt

>
>
>> -----Original Message-----
>> From:	[email-masked] [SMTP:[email-masked]]
>> Sent:	Thursday, February 11, 1999 1:02 PM
>> To:	Donovan, Steven R. (MCI); [email-masked]';
>> [email-masked]'
>> Subject:	RE: draft-ietf-mmusic-sip-session-timer-00.txt
>> 
>> Pardon the perhaps very naive question, but I suppose I am not as versant
>> in 
>> SIP as I would like to be.
>> 
>> My understanding is that a SIP Client issues an Invite message to a SIP
>> Server,
>> which in turn forwards the request to a target SIP Client (or some GW or
>> some
>> sort). Once the ACK has returned to the originating client, I was under
>> the
>> impression that both SIP Clients send RTP packets directly to each other,
>> bypassing the SIP Server (this is where I am unclear).
>> 
>	This depends on the implementation of the SIP Server.  There are
>valid reasons to have the SIP Server proxy the IP packets.  But in general,
>you are correct.  There will be SIP Servers that do not have a view of the
>RTP flow.
>
>> So if this is true, how will a SIP Server (stateful, or stateless)
enforce
>> any
>> session timeouts? A malicious SIP Client can simply keep the session
>> active
>> for as long as it wishes, ignoring any messages from the SIP Server that
>> may
>> tell it to disconnect.
>> 
>> This, as far as I can see, could cause some serious problems if one
wishes
>> to
>> deploy a service and still maintain some control over the sessions.
>> 
>> Again, perhaps I am way off here. Any clarifications would certainly be 
>> appreciated.
>> 
>	You are correct and I personally would not rely on reporting from
>the SIP Server to do reliable billing.  However, if a stateful SIP Proxy
>server is built, for whatever reason, the current SIP specification does
not
>have a mechanism for the SIP server to know which of the sessions for which
>it has state are valid.  This draft gives the SIP Server a mechanism to
>remove those sessions that it feels are no longer valid.
>
>	The amount of control that a SIP server exerts over sessions is a
>separate issue.  As John Hearty accurately points out in a separate email,
>the user of the SIP device can choose to bypass the SIP server entirely.
>The challenge for service providers will be to implement services that make
>user's want to access the service provider's SIP server.

This is not actually true. It is quite simple for service providers to
install
a set of filters in their systems that require that all RTP traffic be
directed
to one of their local SIP Servers.

Note that I am not advocating such an idea. I like free service, but one
must
realize that free services are rarely every deployed by the services 
providers :(

PatC
>
>> PatC
>> 
>> >This time with the draft attached.  Sorry for the extra mail.
>> >
>> >Steve
>> >
>> > <<draft-ietf-mmusic-sip-session-timer-00.txt>> 
>> >
>> >> -----Original Message-----
>> >> From:	Donovan, Steven R. (MCI) 
>> >> Sent:	Thursday, February 11, 1999 10:17 AM
>> >> To:	[email-masked]'; [email-masked]'
>> >> Subject:	draft-ietf-mmusic-sip-session-timer-00.txt
>> >> 
>> >> This message is notification of the following Internet Draft which has
>> >> been submitted to the IETF for posting.
>> >> 
>> >> <draft-ietf-mmusic-sip-session-timer-00.txt> 
>> >> 
>> >> Abstract: 
>> >> 
>> >> This document proposes an extension to the SIP specification.  This
>> >> extension adds a new message header that is used to specify the 
>> >> duration of a requested session.
>> >> 
>> >> The session timer can be used to limit the total duration of a session
>> >> if, for instance, one of the participants in the session wants to
>> >> limit the cost of the session.  It can also be used by stateful SIP
>> >> Proxy Servers to track the status of sessions for which session state
>> >> exists on the servers. Currently a stateful SIP Proxy Server that is 
>> >> not handling the media stream(s) for the session has no mechanism to 
>> >> definitively determine the state of all sessions for which it has
>> state.
>> >> While the SIP Specification does provide the BYE method for
terminating
>> >> the session, there is no mechanism for a SIP Proxy Server to detect
the
>> >> end of a session when the BYE message is not sent or is lost due to 
>> >> network problems.
>> >> 
>> >> The internet draft is attached.
>> >> 
>> >> Steve Donovan
>> >> MCIWorldcom
>> 

---------
This message came from the IETF IPTEL Working Group Mailing List.

---

From: Douglas Clowes <[email-masked]>
Date: Fri, 12 Feb 1999 13:01:40 +1100

Bonjour Francois, Ca va?

It's about the services that you provide, and the services that you like to
charge for.

If you sell the users Mediatrix gateways, then it is their capital
investment, they would like to be in control, and amortize their
investments. They don't want to pay you for each second they use them, no
matter how much you would like them to.

If they are your gateways, that you connect to the PSTN, and provide an
egress service, then you should be in control, and you can control charging
for the service.

At 20:04 1999-02-11 -0500, Francois Menard Distribution List Management
>H.323 gatekeeper can talk to routers, which control an IP media stream, and

If it's your gateway (you bought it) and you need it to obey your
controller (SIP server or gatekeeper) and it doesn't, then send it back and
get one that will. If it's your gateway (you bought it) and you don't want
it to obey someone elses controller and it does, send it back and get one
that does what you want it to.

>go out and die and never send an end of conversation ... this mechanism is

And if it wishes to bill by the byte, it needs endpoints that will report
resource usage. It needs endpoints that will report periodically, or store
records in non-volatile storage to report when they come up.

Work is in progress, in both ITU SG-16, and ETSI EP-TIPHON.