RE: [RPRWG] control TTL (the 255-station and 2000-km issue)
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