Re: [Sip] Impossible to use real persistent connection with sip

["Vijay K. Gurbani" <vkg@lucent.com>]

Cullen Jennings wrote:
> Just to get a little more precise about this ... what does persistence 
> mean?  For the length of the transaction? For the dialog? As long as
> the registration is valid? Until some box crashes? Until the world moves 
> to IPv6.
Hi Cullen:

Yes, we've grappled with that as well.  Clearly, to get most bang for
the buck, the persistent connection lives beyond the dialog that
established it; i.e. it spans transactions.  One place where such
persistent connections may be used is between a UAC and its default
outbound proxy, or between two proxies that may have a trusted peering
relationship between them for traffic between their domains.

Exactly how to quantify this length of time is tricky.  As you point
out, sometime a peer may go down for administrative reasons, other times
it may simply crash.  Depending on how we specify and implement it,
there may be an expiry time for this connection -- I don't know what the
correct answer is right now.

> I would be very happy to see some good thought on when devices should 
> close a TCP socket - I think that figuring out a good algorithm and 
> understanding the large scale consequences is going to be surprisingly 
> complicated.
We're working on an I-D that extends the connect-reuse ID to outline
some of these issues.  I will post it to the list as soon as I can.  It
contains a lot of what Sarit also outlines below:

Sarit Galanos Mekler (Sarit@radvision.com) writes:
> First I would like to say that I think that the pc=1 is a good choice.
> To my opinion adding the pc=1 to the via header is only a recommendation 
> to the server to keep the connection open.
Unfortunately, this is just a hint to the server, and as you point out
below:

> Servers that don't understand pc or don't want to keep the connection 
> open are more then welcome to close it.
But that may be all we need to do.  I don't yet know if it is worthwhile
to go through some negotiation mechanism (i.e. register Require and
Proxy-Require tokens with IANA).  Even it we do go the "pc=1" parameter
route, we should register the "pc" token with IANA.

> A server can also decide that it wishes to keep the connection open only 
> if it is actually being used.  An implementation can for example, set a 
> timer on server connections.   When ever a message is received/sent on
> the connection the timer is reset. when the timer expires the server 
> closes  the connection.
All this presumes that clients and servers are well-behaved.  In the
extreme case, I think that we may rely on I/O failing on a now
unconnected socket because one of the peers crashed or got brought down
for adminstrative reasons.  That is, we proscribe behavior for well-
behaved peers, taking in account extreme cases where one of them
suddenly disappears.

> The persistency level (dialog / transaction) if for the specific 
> application to decide. For dialog persistency the application will have 
> to keep the connection open for the duration of the call.  Using the 
> pc=1 parameter will give a good chance for using connections for more 
> then one transaction. An option that today (almost) does not exist.
Right.

Cheers,

- vijay
--
Vijay K. Gurbani  vkg@{lucent.com,research.bell-labs.com,acm.org}
Wireless Networks Group/Internet Software and Services
Lucent Technologies/Bell Labs Innovations, 2000 Lucent Lane, Rm 6G-440
Naperville, Illinois 60566     Voice: +1 630 224 0216

_______________________________________________
Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol
Use sip-implementors@cs.columbia.edu for questions on current sip
Use sipping@ietf.org for new developments on the application of sip