[SIPForum-techwg] TCP vs. UDP (SP adoption of TCP?)

Wed May 21 04:24:28 EDT 2008

Within a UK context the 21st Century Network programme is intending to build a national next generation network.  The primary transport that will be used in this network is SCTP.  SCTP was chosen because the network architects want PSTN replication and need not just a reliable, but a resilient transport, that duplicates the features provided by MTP.

At one point, and I am not sure what the state of play today is, the situation in the UK (for inter-working between networks and enterprise access) was going to be:
* RECOMMEND (and in some contexts MUST) use SCTP
* MAY use UDP (if you really have to)
* but, MUST NOT use TCP (under any circumstances)

I am not sure how or why this particular situation arose, but on a national scale UDP was seen as acceptable (though not preferred) and TCP was out of the question.

I would not be surprised if this mindset exists elsewhere to a greater or lesser extent.

Regards,

Peter

-----Original Message-----
From: techwg-bounces at sipforum.org [mailto:techwg-bounces at sipforum.org]On
Behalf Of Elwell, John
Sent: 20 May 2008 20:15
To: Hiers, David; Russell Bennett; Zweig, Greg; techwg at sipforum.org
Subject: Re: [SIPForum-techwg] TCP vs. UDP (SP adoption of TCP?)

Yes, this has always been the thing that puzzled me. A lot of vendors
and service providers have tried to reproduce PSTN capabilities with
SIP. Yet PSTN signalling protocols always ran over a reliable transport,
so the obsession with UDP seems to be a contradiction.

John 

> -----Original Message-----
> From: techwg-bounces at sipforum.org 
> [mailto:techwg-bounces at sipforum.org] On Behalf Of Hiers, David
> Sent: 20 May 2008 18:28
> To: Russell Bennett; Zweig, Greg; techwg at sipforum.org
> Subject: Re: [SIPForum-techwg] TCP vs. UDP (SP adoption of TCP?)
> 
> All,
> As a service provider using an expensive mix of best-of-breed SIP
> implementations that service a fair number of endpoints and minutes, I
> see the ability to use UDP as one of SIP's primary weaknesses.  
> 
> The attempt to supplant the TDM PSTN five-nines reliability is not
> particularly well facilitated by running the entire show over an
> unreliable transport protocol whose primary benefit is reduced HW
> resource requirements.
> 
> When shopping for future peering partners, I would tend to prefer one
> who's engineering philosophy happily embraces the 
> deterministic control
> of TCP rather than the fire-and-forget nature of UDP.
> 
> Best regards,
> 
> 
> David Hiers
> 
> CCIE (R/S, V), CISSP
> ADP Dealer Services
> 2525 SW 1st Ave.
> Suite 300W
> Portland, OR 97201
> o: 503-205-4467
> f: 503-402-3277 
> 
> 
> 
> -----Original Message-----
> From: techwg-bounces at sipforum.org [mailto:techwg-bounces at sipforum.org]
> On Behalf Of Russell Bennett
> Sent: Tuesday, May 20, 2008 9:21 AM
> To: Zweig, Greg; techwg at sipforum.org
> Subject: Re: [SIPForum-techwg] TCP vs. UDP (SP adoption of TCP?)
> 
> Greg et al.
> 
> I have already agreed that we have to accommodate the past, 
> but we also
> have to drive the future.  If we "make it OK to just offer UDP" then
> that is what people will think that it is acceptable to do.
> 
> I have been actively engaged with a number of service providers for
> quite some time now and, without naming names or providing 
> timelines, I
> can assure you that TCP is being deployed by service providers.
> 
> As for encouraging quick adoption - the issue is not one of which SIP
> Transport is best/cheapest/already there; the issue is one of simple
> economics: SIP Trunks cannibalize Service Provider revenues under
> existing pricing models.  The SPs who offer "UDP only" are 
> seeing little
> demand for SIP Trunking - what they don't realize is that it is a
> "chicken and egg" problem.
> 
> We must move SP SIP connectivity capability forward such that SPs can
> start to deploy revenue generating services and applications 
> to replace
> revenue lost by decrementing PRI trunks.  We can only get to a service
> federation model by moving rapidly beyond SIP Voice.  If we 
> can't *even*
> get to more broadly deployed SIP Voice, then (some) SPs will remain
> where they are - stuck in the 20th century.
> 
> Forward looking SPs that I work with have heard this loud and clear.
> 
> UDP should be a 'MUST' to support older architectures.  TCP MUST be a
> 'MUST' to support newer architectures.  I don't see how we accommodate
> the past and drive the future any other way.
> 
> 
> Russell
> 
> -----Original Message-----
> From: techwg-bounces at sipforum.org [mailto:techwg-bounces at sipforum.org]
> On Behalf Of Zweig, Greg
> Sent: Monday, May 19, 2008 11:39 AM
> To: Peter Dunkley; techwg at sipforum.org
> Subject: Re: [SIPForum-techwg] TCP vs. UDP (SP adoption of TCP?)
> 
> Agreed -- We also have to consider the capabilities at the customer
> premise.  I wouldn't want to advocate a solution that drives end
> customers into a position where their existing equipment is made
> obsolete.  There are many products in-use that could be upgraded to
> other facets of a SIPconnect 1.1 implementation but will never cost
> effectively support TCP.  I want to embrace them, not disenfranchise
> them.
> 
> We need to accommodate the past while we drive the future.
> 
> Greg Zweig
> Sonus Networks. Inc
> (978) 614-8027
> 
> 
> -----Original Message-----
> From: techwg-bounces at sipforum.org [mailto:techwg-bounces at sipforum.org]
> On Behalf Of Peter Dunkley
> Sent: Monday, May 19, 2008 2:23 PM
> To: techwg at sipforum.org
> Subject: Re: [SIPForum-techwg] TCP vs. UDP (SP adoption of TCP?)
> 
> The danger with this approach is that you will may end up with a
> wonderful SIPconnect 1.1 recommendation that the writers/purists love
> but is unpalatable to the industry.
> 
> There needs to be a pragmatic approach taken that illustrates what SIP
> trunking should be, while still encouraging quick adoption.
> 
> Making SPs have to choose between changing their architecture or
> becomming compliant will not encourage them to adopt 
> SIPconnect (quickly
> 
> or otherwise).
> 
> Russell Bennett wrote:
> > All,
> >
> > I know from trying to work with the SPs on SIP Trunking that *some*
> SPs are going to take a firm position on the support of UDP 
> only.   The
> question that Janne poses is:
> >
> >         1) Are we going to define SC1.1 to be what a SIP 
> Trunk service
> should be (e.g. UDP *and* TCP, among many other things)?
> >         OR
> >         2) Write SC1.1 to be what we think will enroll more 
> SPs in the
> SC compliance program?
> >
> > I argue strongly against 2 - this would not be a step forward on
> SC1.0.  3261 is very clear on TCP support.  If SIP Forum was a
> commercial entity, then we would go for 2 to maximize revenue.
> >
> > However, SF is a standards body and it is incumbent upon us 
> to develop
> SC1.1 as a *correct*, albeit pragmatic, document.  The key is the
> balance between pragmatism and correctness and I, for one, think that
> accommodating SPs that are mired in the 20th century is the wrong side
> of that balance.
> >
> > Russell
> >
> >
> 
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