Re: [MEDIACTRL] MRB seqnumber

Simon Pietro Romano <spromano@unina.it> Thu, 14 February 2013 10:37 UTC

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From: Simon Pietro Romano <spromano@unina.it>
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Date: Thu, 14 Feb 2013 11:37:20 +0100
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References: <4C39824D-E014-4893-B6F9-6DE10C2F0557@standardstrack.com> <511B8D9D.6070506@ns-technologies.com> <20130214111141.1be4b19a@rainpc>
To: Lorenzo Miniero <lorenzo@meetecho.com>
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Subject: Re: [MEDIACTRL] MRB seqnumber
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+1 from here.

Simon

Il giorno 14/feb/2013, alle ore 11:11, Lorenzo Miniero ha scritto:

> On Wed, 13 Feb 2013 12:57:01 +0000
> Chris Boulton <chris-standards@ns-technologies.com>; wrote:
> 
>> All,
>> 
>> After some discussion we have agreed that the text needs to change 
>> slightly to address the comment submitted and other queries we have 
>> received.  The change would result in subscription reading something like:
>> 
>>  seqnumber:  indicates a sequence number to be used in conjunction
>>       with the subscription session id to identify a specific
>>       subscription command.  The first subscription MUST contain a 
>> non-zero number
>>       'seqnumber', and following subscriptions MUST contain a higher 
>> number that the
>>       previous 'seqnumber' value.  If a subsequent 'seqnumber' is not 
>> higher, a XXX response code is generated
>> as per section 5.1.4.  The attribute MUST be present.
>> 
>> This also applies to the notification text in section 5.1.5 and the 
>> following text is proposed:
>> 
>> seqnumber:  indicates a sequence number to be used in conjunction
>>       with the subscription session id to identify a specific
>>       notification update.  The first notification update MUST contain 
>> a non-zero number
>>       'seqnumber', and following notification updates MUST contain a 
>> higher number that the
>>       previous 'seqnumber' value.  If a subsequent 'seqnumber' is not 
>> higher the situation should
>>       be considered an error by the entity receiving the notification 
>> update.  It is implementation
>>      specific how the receiving entity deals with this situation. The 
>> attribute MUST be present.
>> 
>> Please let me know if you are OK with these changes.
>> 
> 
> 
> Of course I support them all: +1 from me as well.
> 
> L.
> 
>> Thanks.
>> 
>> Chris.
>> 
>> 
>> On 12/02/2013 23:02, Eric Burger wrote:
>>> The MRB document talks about a seqnumber in a subscription request and notification response. For your laziness, I have included the entirety of the text defining both uses:
>>> 
>>> 5.1.3.1.  <subscription>
>>> [...]
>>>    seqnumber:  indicates a sequence number to be used in conjunction
>>>       with the subscription session id to identify a specific
>>>       subscription command.  The first subscription MUST have 1 as
>>>       'seqnumber', and following subscriptions MUST increment by 1 the
>>>       previous 'seqnumber' value.  The attribute MUST be present.
>>> 
>>> [...]
>>> 
>>> 5.1.5.  <mrbnotification>
>>> [...]
>>>    seqnumber:  indicates a sequence number to be used in conjunction
>>>       with the subscription session id to identify a specific
>>>       notification update.  The first notification MUST have 1 as
>>>       'seqnumber', and following notifications MUST increment by 1 the
>>>       previous 'seqnumber' value.  The attribute MUST be present.
>>> 
>>>    It's important to point out that the 'seqnumber' that appears in a
>>>    <mrbnotification> is not related to the 'seqnumber' appearing in a
>>>    <mrbsubscription>.  In fact, the latter is associated with
>>>    subscriptions and would increase at every command issued by the MRB,
>>>    while the former is associated with the asynchronous notifications
>>>    the Media Server would trigger according to the subscription, and as
>>>    such would increase at every notification message to enable the MRB
>>>    keep track of them.
>>> [...]
>>> 
>>> 
>>> The AD's are having trouble wrapping their heads around the use of seqnumber. Upon closer inspection, this chair has trouble wrapping his head around the utility of seqnumber.
>>> 
>>> On the subscribe side, what does it mean in a TCP/DTLS environment, where there is no issue of out-of-sequence request delivery, for there to be an out-of-sequence request? Can anyone tell me the value of seqnumber in this environment? In particular, what does a server do if it gets an out of order request (which cannot happen) or a request gets lost (which cannot happen)?
>>> 
>>> On the notification side, I *think* I *might* see a value of having monotonically increasing response sequence numbers. If for some reason the server loses a request, the client might figure out that, for a given id, no response ever came. However, in a TCP/DTLS environment, where there is no issue of out-of-sequence notification delivery, what does it mean for the client to receive an out-of-order response (which cannot happen) or a request gets lost (which cannot happen)?
>>> 
>>> <chair hat off>
>>> Unless there is a reason to keep seqnumber, my vote is to take it out altogether.
>>> 
>>> If there is a reason to keep seqnumber, then we need to describe what a server does if it gets a request "out of sequence" and what a client does if it gets a response "out of sequence."
>>> 
>>> Also, if we keep it, I would offer having two attributes that are unrelated having the same name is confusing at best, and will lead to implementation errors at worst. Thus, I would propose we give them different names, like reqseq and respseq.
>>> 
>>> 
>>> <chair hat on>
>>> This is the LAST issue holding up publication.  Prompt discussion and resolution is strongly desired.
>>> 
>>> 
>>> _______________________________________________
>>> MEDIACTRL mailing list
>>> MEDIACTRL@ietf.org
>>> https://www.ietf.org/mailman/listinfo/mediactrl
>>> Supplemental Web Site:
>>> http://www.standardstrack.com/ietf/mediactrl
>> 
>> 
>> -- 
>> Chris Boulton
>> CTO & Co-founder
>> NS-Technologies <http://www.ns-technologies.com>
>> m: +44.7876.476681
> 
> 
> -- 
> Lorenzo Miniero, COB
> 
> Meetecho s.r.l.
> Web Conferencing and Collaboration Tools
> http://www.meetecho.com
> _______________________________________________
> MEDIACTRL mailing list
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> http://www.standardstrack.com/ietf/mediactrl
> 

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                    				Simon Pietro Romano
             				 Universita' di Napoli Federico II
                		     Computer Engineering Department 
	             Phone: +39 081 7683823 -- Fax: +39 081 7683816
                                           e-mail: spromano@unina.it

		    <<Molti mi dicono che lo scoraggiamento Ë l'alibi degli 
		    idioti. Ci rifletto un istante; e mi scoraggio>>. Magritte.
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