[rbridge] Fwd: In-order delivery not an issue?

[Donald Eastlake]

See below

On Mon, Oct 6, 2008 at 12:59 PM, G.Venkatasubramaniyan
<g.venkatasubramaniyan at ieee.org> wrote:
>
> resending my previous mail ...
> Thanks,
> venkatg
> ---------- Forwarded message ----------
> From: Venkatsubramaniyan G, TLS-Chennai <venkatg at hcl.in>
> Date: Mon, Oct 6, 2008 at 7:21 PM
> Subject: RE: [rbridge] In-order delivery not an issue?
> To: rbridge at postel.org, Radia Perlman <Radia.Perlman at sun.com>
> Cc: gvsm <g.venkatasubramaniyan at gmail.com>
>
>
>
> Radia,
>
> Assuming a traffic flow (of given SRC, DST and QoS) happens through
> multiple equal cost paths in Rbridge cloud, I think TRILL cannot not
> offer guarantees that the frames at egress are in the same order as in
> ingress in Layer-2.  The individual paths can have different traffic
> conditions and reaction mechanisms which may not give in-order behavior,
> which could largely vary.

TRILL does not define what a flow is. If you believe that frames with
the same source and destination MAC address and priority should be
delivered in order, then you would use that as the definition of a
flow and send all the frames in that flow over the same equal cost
path in an RBridge campus just as you would send them all over the
same link in the case of link aggregation. Although TRILL supports
equal cost multipath, it does not fully specify it and the granularity
of flows is one aspect left to the implementer.

> At present it is assumed this is left for ES ('s higher layer) to handle
> out-of-order packets.
>
> If this needs to be handled inside TRILL, there may be a need for
> seq-numbering the packets for each flow inside the TRILL cloud. Is it
> not?
> It may also need an elaborate session management and control protocols
> between ingress R-Bridge and egress R-Brdge, so that in-order is
> guaranteed.

I do not see any need for this to be "handled inside TRILL".

> BTW, do not 802 solutions in *steady state* give in-order delivery for a
> given flow?

Yes, as does TRILL.

> Thanks a lot,
> Venkatg

Donald

> -----Original Message-----
> From: Radia Perlman [mailto:Radia.Perlman at sun.com]
> Sent: Monday, October 06, 2008 1:10 PM
> To: gvsm
> Cc: rbridge at postel.org; Venkatsubramaniyan G, TLS-Chennai
> Subject: Re: [rbridge] In-order delivery not an issue?
>
> TRILL ought to do in-order delivery, except with an occasional out of
> order packet in very rare cases. The 802 solutions also, with low
> probability, will occasionally reorder packets. Perhaps one could argue
> that the probability
> might be slightly larger with TRILL, but in either case it will be "very
>
> rare".
>
> Certainly we took the desire for in-order delivery into account in the
> design of TRILL.
>
> Radia
>
>
> gvsm wrote:
> > Hi,
> >
> > Does not present Ethernet by STP families give inorder delivery of
> > frames for a flow?
> > Will not this be compromised with this(TRILL) solution or is it
> > assumed implementation would take care of it?
> >
> > Thanks,
> > venkatg
--
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Donald E. Eastlake 3rd   +1-508-634-2066 (home)
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