Subject: RE: [PWE3] CW sequence number (was length)

From: [email-masked]
Date: Fri, 6 May 2005 12:09:00 -0500

Stewart,

My preference  is that there will be only one option: Use the entire sequence number set without skipping zero. The skip zero is a wrong design choice. It should be defined that if sequence numbers are not used, the sequence number must be set to zero. Otherwise all sequence numbers must be used. Apart from the fact that some might have implemented this, what is the benefit of skipping zero?

I would at least first ask who has strong objections to the above. Only if compromise must be taken I would choose (a). 

Best
Ron

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From: "Andrew G. Malis" <[email-masked]>
Date: Fri, 06 May 2005 13:35:06 -0400

Ron,

I strongly object! :-)  There are a whole bunch (at least 20?) of 
interoperating implementations that skip 0.  I know we all implement 
pre-standard at our peril, but this has been shown to work fine, all of the 
existing implementations that would have to change (or most probably need 
to add a per-pseudowire configuration time as to whether to skip zero or 
not), and skipping zero is an error-checkable confirmation of whether or 
not sequence numbers are being used on a pseudowire.  Adding a 
configuration item means that we need to add another object to the PW MIB 
as well, and this is all additional complexity that would need to be 
tested.  Also remember that we don't have a version number in the CW, so 
you can't figure out by looking at the wire if this is a header from the 
current drafts, or from the eventual RFC that would require not skipping 
zero.  It's much easier to leave the sequence number the way it is.

If we were starting from a blank slate right now, then consistency for its 
own sake might be a good idea, but the time to make a decision of that 
magnitude is long behind us.

Thanks,
Andy

--------

At 5/6/2005 12:09 -0500, [email-masked] wrote:
>Stewart,
>
>My preference  is that there will be only one option: Use the entire 
>sequence number set without skipping zero. The skip zero is a wrong design 
>choice. It should be defined that if sequence numbers are not used, the 
>sequence number must be set to zero. Otherwise all sequence numbers must 
>be used. Apart from the fact that some might have implemented this, what 
>is the benefit of skipping zero?
>
>I would at least first ask who has strong objections to the above. Only if 
>compromise must be taken I would choose (a).
>
>Best
>Ron

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From: Stewart Bryant <[email-masked]>
Date: Sun, 08 May 2005 19:42:45 +0100

Andrew G. Malis wrote:

> pre-standard at our peril, but this has been shown to work fine, all of 
> the existing implementations that would have to change (or most probably 
> need to add a per-pseudowire configuration time as to whether to skip 
> zero or not), and skipping zero is an error-checkable confirmation of 
> whether or not sequence numbers are being used on a pseudowire.  Adding 
> a configuration item means that we need to add another object to the PW 
> MIB as well, and this is all additional complexity that would need to be 
> If we were starting from a blank slate right now, then consistency for 
> its own sake might be a good idea, but the time to make a decision of 
> that magnitude is long behind us.
> 

I agree with Andy.

It is far too late to make this change.

Stewart

>> sequence number set without skipping zero. The skip zero is a wrong 
>> design choice. It should be defined that if sequence numbers are not 
>> used, the sequence number must be set to zero. Otherwise all sequence 
>> numbers must be used. Apart from the fact that some might have 
>> implemented this, what is the benefit of skipping zero?
>>
>> I would at least first ask who has strong objections to the above. 
>> Only if compromise must be taken I would choose (a).
>>
>> Best
>> Ron
> 
> 
>