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

Wed May 21 04:35:18 EDT 2008

I agree.

The resilient transport (MTP) was required there because ISUP did not have any retransmission capability.  SS7 user parts are designed to assume that messages are delivered reliably, in order - and to allow MTP to take care of re-routing on failure and loadsharing.

With SIP able to retransmit the reliability part of this isn't quite as vital.

I suppose it depends what people want from PSTN replication.  Do they want a replacement PSTN that functions in the same way (or as closely as possible) at each layer of the stack, or do they want a replacement network that is identical from the end users point-of-view but may behave completely differently internally (because after all, the end user really doesn't care)?

Regards,

Peter

-----Original Message-----
From: techwg-bounces at sipforum.org [mailto:techwg-bounces at sipforum.org]On
Behalf Of Kaushik V Shah
Sent: 21 May 2008 08:24
To: Elwell, John
Cc: techwg at sipforum.org; Russell Bennett; Hiers, David
Subject: Re: [SIPForum-techwg] TCP vs. UDP (SP adoption of TCP?)

In context of 3261, UDP is as reliable as TCP due to retransmissions 
over UDP.

TCP has clear efficiency issues compared with UDP and that is fundamentally
because, reliability - which is application level issue, is being 
enforced irrespective.

For e.g. in context of SIP, response to request (1xx, 2xx, ...) is 
itself an indication
of request having reached the remote (or the proxy who in turn takes on 
responsibility
of sending further up/down). Now if TCP is used, we are introducing  two 
levels of ACK
(one at TCP level due to reliable transfer and other at SIP level in the 
form of response).

There are practical issues of UDP fragmentation, but imho, we will be 
better off fixing
these UDP issues, if possible.

Regards,
Kaushik

Elwell, John wrote:
> 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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