RE: [RPRWG] control TTL (the 255-station and 2000-km issue)
Mike,
With respect to:
> an advantage of wrapping over steering is
> that since the decision is local it can be
> done quicker and there is a much lower
> degree of packet loss...
This is only true if the wrapped frames are not discarded
before the distribution of new topology information,
which is the case with the selective-no-decrement TTL
rules being proposed by some(:>).
DVJ
David V. James, PhD
Chief Architect
Network Processing Solutions
Data Communications Division
Cypress Semiconductor, Bldg #3
3901 North First Street
San Jose, CA 95134-1599
Work: +1.408.545.7560
Cell: +1.650.954.6906
Fax: +1.408.456.1962
Work: djz@xxxxxxxxxxx
Base: dvj@xxxxxxxxxxxx
> -----Original Message-----
> From: owner-stds-802-17@xxxxxxxxxxxxxxxxxx
> [mailto:owner-stds-802-17@xxxxxxxxxxxxxxxxxx]On Behalf Of Mike Takefman
> Sent: Monday, June 24, 2002 6:51 PM
> To: Anoop Ghanwani
> Cc: 'djz@xxxxxxxxxxx '; 'stds-802-17@xxxxxxxx '
> Subject: Re: [RPRWG] control TTL (the 255-station and 2000-km issue)
>
>
>
> Anoop,
>
> an advantage of wrapping over steering is
> that since the decision is local it can be
> done quicker and there is a much lower
> degree of packet loss, as all of the
> packets in flight towards the failed
> span can be wrapped.
>
> Service providers have presented to the WG
> that the lower level of packet loss in wrap
> was a key requirement for them. The question
> is what SLAs are relevant to service providers.
>
> Based on all of the input received at the WG,
> both steer and wrap were accomdated to allow
> vendors to meet the needs of their customers.
>
> cheers,
>
> mike
>
> Anoop Ghanwani wrote:
> >
> > > With regard to your last question / comment.
> > > In wrapping, the adjacent nodes can react immediately if
> > > they have the highest priority failure. Thereby
> > > wrapping will have quicker reaction times to
> > > steering. The need to broadcast in the wrapping
> > > case is to support the hierarchy. If no hierarchy
> > > was supported, then the decision could be completely
> > > local. In this case I would still argue that a
> > > broadcast of the event was useful for 2 reasons.
> > > 1) The same algorithm supports steering which is
> > > the default mode
> > > 2) The packets that are trapped on the wrong ring
> > > will get killed.
> >
> > Mike,
> >
> > This tells me why all nodes need to know about a
> > failure even when wrapping. But now that all nodes
> > need to know about the failure, why do I need
> > wrapping?
> >
> > This is a serious question. In the past, I've
> > always answered it by saying that with wrapping,
> > only nodes local to the fault need to know about
> > it. But if that's not the case, then I'll be
> > stumped every time this question comes up.
> > If steering can be done within 50 msec, is
> > doing it any faster with wrapping worth the
> > bandwidth overhead?
> >
> > -Anoop
>
> --
> Michael Takefman tak@xxxxxxxxx
> Manager of Engineering, Cisco Systems
> Chair IEEE 802.17 Stds WG
> 2000 Innovation Dr, Ottawa, Canada, K2K 3E8
> voice: 613-254-3399 fax: 613-254-4867
>