Re: [Sipping] Re: draft-rosenberg-sipping-overload-reqs recovery

[[e-mail]]

Stability is an implicit requirement of every load control and overload
protection mechanism (for network elements and networks targeting high
system and/or service availability).

The rational behind is the fact that any overload control may be modeled (&
realized) as open or closed control loop. Any control arround signalling
protocols is typically realized as closed loop (e.g. due to realtime
background).
A well designed closed control requires a proof of stability for the
intended range of operation; stability is an implicit requirement from
control theory, particularly for load control with stochastic components as
in our case here.

- Albrecht



                                                                                                                                        
                      Volker Hilt                                                                                                       
                      <volkerh@bell-la         To:      Cullen Jennings <[e-mail]>                                              
                      bs.com>                  cc:      sipping <[e-mail]>                                                      
                                               Subject: Re: [Sipping] Re: draft-rosenberg-sipping-overload-reqs recovery                
                      08.11.2006 17:18                                                                                                  
                                                                                                                                        




I think that stability of overload control is an important requirement.
We certainly want to avoid building something that starts to oscillate
once it reaches overload state. It may be somehow implicit to REQ 1
since an unstable system will hardly be able to maintain the overall
useful throughput at a high level.

Volker



Cullen Jennings wrote:
> Clearly this was a long way from the text for a requirement but, yes, I
> was proposing that this be added as one of the requirements. I don't
> feel strongly about this and if we can't figure out how to express this
> as a requirement that is useful, I can certainly live with not adding it.
>
> The reason I think it is a requirement is I can easily imagine that the
> mechanism for doing overload push-back causes the systems to fail in the
> way I described below (i.e. never recover back to steady state).
>
>
> On Nov 6, 2006, at 11:17 AM, Jonathan Rosenberg wrote:
>
>>
>>
>> Cullen Jennings wrote:
>>
>>> A possible additional requirement....
>>> Imagine a system (perhaps a single proxy) that could do 100cps. It
>>> is  in steady state doing 80cps with very few retransmission. Then
>>> for 5  minutes the incoming requests goes to 500cps then drops back
>>> to an  incoming call rate of 80cps. The question is, how long before
>>> the  system gets back to the state where it if is successfully
>>> processing  all the 80cps?
>>
>> As soon as it can. Are you suggesting a requirement here? Seems like
>> this is an implementation thing and wouldn't impact any protocol
>> mechanisms.
>>
>>> I have seen systems that never recover - that is bad. I think one of
>>> the design goals is that it is at least possible to build to systems
>>> that recover back to steady state relatively quickly after an
>>> overload impulse.
>>
>> Sure; but I'm not sure I see the protocol requirement.
>>
>> -Jonathan R.
>>
>>
>>
>> --Jonathan D. Rosenberg, Ph.D.                   600 Lanidex Plaza
>> Cisco Fellow                                   Parsippany, NJ 07054-2711
>> Cisco Systems
>> [e-mail]                              FAX:   [phone]
>> http://www.jdrosen.net                         PHONE: [phone]
>> http://www.cisco.com
>
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_______________________________________________
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This list is for NEW development of the application of SIP
Use [e-mail] for questions on current sip
Use [e-mail] for new developments of core SIP