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