Re: [RPRWG] control TTL (the 255-station and 2000-km issue)
Anoop,
For a protection hierarchy to work all nodes
need to know about all failures.
I agree with your comment that this needs to be
clearly documented as part of the standard.
Futhermore, if the WG decides to accept this
TTL decrement algorithm it must be documented
properly.
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.
cheers,
mike
Anoop Ghanwani wrote:
>
>
> Mike,
>
> I was trying to say that when a node "unwraps" due
> to the ring healing, it can't throw away packets
> forever because the ring might wrap at some other
> place making it valid for this node to see packets
> with the wrap bit set. Therefore a node would have
> to set some kind of timer (on the order of RTT) and
> only throw away packets for that duration.
>
> The above discussion was trying to solve the problem
> where all nodes do not know about protection events;
> only those adjacent to the fault do. If all nodes do
> know about protection events, the solution you mention
> should work, but it does need to be documented in the
> spec.
>
> [Off topic discussion]
> To me, it seemed like the main argument for doing wrapping
> is that only nodes adjacent to the fault need to know about
> it and react to it. If all nodes do need to know about
> a protection event, then it it probably more efficient
> for them to use steering.
>
> -Anoop
>
> -----Original Message-----
> From: Mike Takefman
> To: Anoop Ghanwani
> Cc: djz@xxxxxxxxxxx; stds-802-17@xxxxxxxx
> Sent: 6/24/02 12:07 AM
> Subject: Re: [RPRWG] control TTL (the 255-station and 2000-km issue)
>
> Anoop,
>
> wrapping nodes always communicate with every other
> node anyway. This is necessary for protection
> heirarchy to work. Also, given the broadcast
> nature of messages to make steering work in under
> 50 ms, I have no concern over all nodes knowing
> that all protection events are done and the ringlets
> are healed.
>
> If one waits for the ringlets to be healed
> and then killing the packet life is fine. Or
> maybe I did not understand your comment.
>
> mike
>
> Anoop Ghanwani wrote:
> >
> > > > The problem with (3), which you seem to advocate,
> > > > is the time gap between the wrap action and the
> > > > the distribution/settling of the wrap state information
> > > > in other stations. During this time difference, any
> > > > and all TTL-strip based frames will be discarded.
> > >
> > > A good point david, in response please consider the following
> > >
> > > Never decrement when on the wrong ring. Once the wrap
> > > state is left, kill the packet if the ring id
> > > is wrong. THus going into wrap does not cause the
> > > packets to be prematurely lost. When leaving wrap
> > > the packets will be killed once everyone knows
> > > the wrap is over.
> >
> > Mike,
> >
> > Does everyone on the ring know when a wrap has occured
> > and when it heals? I thought wrapping was a local issue
> > and only nodes adjacent to the fault know about it.
> > In that case, if the node at which wrapping occurs
> > detects a heal, and for some reason doesn't pull a wrap
> > packet off, it will continue to circulate forever.
> > The node can't be dropping wrapped packets forever
> > because the wrap could occur somewhere else at
> > which time it would be a legal packet for pass-through.
> >
> > -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
--
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