Re: [RPRWG] More comments on preemption
Leon,
Simulation may or may not catch the worst case situation. There are 128
nodes in your simulation model, the sheer number of nodes which makes
it look like the "toughest" you can get. While I believe it is good to
evaluate
the delay, but it make the jitter evaluation more difficult. Why ? because
the
the probability of getting minimum delay (packet pass through 127 nodes
without being blocked by Jumbo frame insertion) and the probability of
getting maximum delay (packet pass through 127 nodes and being blocked
by Jumbo frame insertion at every node) diminish quickly as the number of
nodes increases.
Secondly, assume we're comparing a 100Mbps traffic flow going through
1G ring vs. 10G ring with the same number of nodes and same traffic
generation models, AND on the other end of the anti-jitter buffer, traffic
will be extracted out at 100Mbps for the same flow. In theory, the size
of the anti-jitter buffer and the delay caused by the anti-buffer should be
the SAME. It should not be a surprise because 10G ring is only 10 times
wider than 1G ring, not 10 times faster for the 100Mbps traffic flow.
I'm not a simulation believer (although I used to be in that field), but I
do
respect those people who is doing that. It is just a tool used by PEOPLE.
Best regards
William Dai
----- Original Message -----
From: "Leon Bruckman" <leonb@xxxxxxxxxxxxx>
To: "'William Dai'" <wdai@xxxxxxxxxxxx>; <stds-802-17@xxxxxxxx>
Sent: Thursday, April 19, 2001 4:54 AM
Subject: RE: [RPRWG] More comments on preemption
> William,
> Actually we are concerned about jitter. We even presented some results
> during the January meeting (Gal Mor), you can see in the slides the
general
> assumptions made.
> Further simulations that we did indicate that for 128 nodes rings
operating
> at 1G with jumbo frames, the added delay caused by the jitter absorption
> buffer is bounded to 6 msec. For 10G rings it is bounded to 1 msec. It is
> not ignorable, but it is still low. Note that the ring tested was 128
nodes,
> I believe that jitter and delay sensitive services will be provided over
> rings with much less nodes (SONET limits the number of nodes to 20).
> You could argue that for lower rates the impact will be more significant,
I
> agree, but again I don't think that jitter and delay sensitive services
will
> be provided in low rate rings with many nodes.
>
> Leon
>
> -----Original Message-----
> From: William Dai [mailto:wdai@xxxxxxxxxxxx]
> Sent: Wednesday, April 18, 2001 11:03 PM
> To: stds-802-17@xxxxxxxx
> Subject: Re: [RPRWG] More comments on preemption
>
>
>
> For those who only concern about current market reality,
> please ignore the following. Otherwise, please read on.
>
> During the preemption discussion, the most dominating
> factor people use againt preemption is that "under high
> speed condition, the worst case delay increase due to
> Jumbo frame is ignorable".
>
> However, does anybody concern about JITTER and the
> size requirement of the anti-jitter buffer at the receiving
> end terminal of the RPR (although the anti-jiiter buffer may
> not be required on the RPR node). For those who care,
> let me remind you the fact that the size of the anti-jitter
> buffer will increase along with JITTER, which results in
> further more delay. By looking at the percentage of increase,
> I'm not sure whether the word "ignorable" can be easily used
> here.
>
> One more point, I'm a cut-through advocate, not just for the
> gain on the delay factor, but mainly for the gain on the jitter
> factor. But for those cut-through advocates who are STRONGLY
> against preemption, I would ask the question: How can we
> justify the sacrifice of the hop-by-hop error checking capability
> in favor of "ignorable" gains on the delay and jitter by supporting
> the cut-through capability?
>
>
> Best Regards
>
> William Dai
>
>
>
>