Subject: [SIP] Proxy replies to BYE

From: Dvir Oren <[email-masked]>
Date: Thu, 6 Jul 2000 19:13:58 +0300 (IDT)

Should a Proxy reply to a BYE?  

If it doesn't reply to the BYE, then everybody along the path will
keep retrnasmitting the BYE until the OK reaches from the other end.
This does not seem like proper behavior to me.

-- 
Dvir Oren               <[email-masked]>
Lucid VON Ltd.     <http://www.lucidvon.com>
9 Saloniki St.,        Tel-Aviv       Israel
Tel:  +972 3 644 3038  Fax:  +972 3 644 3039

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From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 06 Jul 2000 12:37:22 -0400

> Should a Proxy reply to a BYE?

Absolutely NOT. The only response a proxy would send is a 100 Trying.

Proxies do not send final responses to requests, INVITE, BYE or
otherwise.

> This does not seem like proper behavior to me.

No, this is correct in the end to end model, which is what we have here.
As BYE responses are generally automatic, you won't usually see even a
single BYE retransmission, since the response will come within 4 seconds
(the 100 Trying from each proxy will cause the BYE retransmission rate
to increase to 4 seconds).

-Jonathan R.

-- 
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
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From: Dvir Oren <[email-masked]>
Date: Fri, 7 Jul 2000 16:56:40 +0300 (IDT)

> to increase to 4 seconds).

Even if the responses are automatic, if the request has to travel a long
distance (whether it is many proxies, or many routers, or both), the
response might take some time.  It also might take some time if one
of the servers along the way is a bit busy.

As far as I understand it, 4 seconds is a lot of time.  If the second bye
is sent after 30sec, and then after 1sec, and then after 2sec, then 4 
BYEs will be sent at the end client.  Each proxy along the way will
send less and less as the OK will reach it sooner.

It seems to me like the protocol assumes, or expects the call to 
stop going through a proxy after the OK.  This might be good
in many cases, but it limits certain applications.  This is why
the Record-Route header was 'invented'.  However, the behavior
of the proxy does not suit, IMHO, the situation above.

I don't understand why BYE has to be end-to-end.  If I hang
up my telephone, as much as I want the other end to hang up
his telephone, I really couldn't care less if there was some
problem along the way.

Perhaps the solution is simply for the proxy to send a
100 'Trying' response to quiet down the client.

---

From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 07 Jul 2000 11:10:47 -0400

> send less and less as the OK will reach it sooner.

You have missed my point. Each proxy receiving the BYE will send a 100
Trying. This causes the BYE retransmissions to immediately become 4
seconds. Thus, so long as you get a final response to the request within
4 seconds (a long time by your own reckoning) there will be no extra
retransmissions. The spec is clear on this one:

Section 7.1:

> Informational responses indicate that the server or proxy contacted
>    is performing some further action and does not yet have a definitive
>    response. The client SHOULD wait for a further response from the
>    server, and the server SHOULD send such a response without further
>    prompting. A server SHOULD send a 1xx response if it expects to take
>    more than 200 ms to obtain a final response.

Note the last sentence.

> stop going through a proxy after the OK.  

Umm, no.

> This might be good

That is because you have misunderstood the reliability mechanism.

> his telephone, I really couldn't care less if there was some

What your UI presents to the user, and reliability mechanisms in the
protocol,
are separate issues.

> 100 'Trying' response to quiet down the client.

It will. Thats what I am saying.

-Jonathan R.