Re: [RPRWG] More comments on preemption
Preemption does NOT drop packets.
William Dai (minority member)
----- Original Message -----
From: "Kanaiya Vasani" <kanaiya@xxxxxxxxxxxxxx>
To: <stds-802-17@xxxxxxxx>
Sent: Tuesday, May 01, 2001 1:40 PM
Subject: RE: [RPRWG] More comments on preemption
>
> There has been some good discussion around the subject of preemption.
Looks
> like a majority of the active members on the reflector would prefer to
leave
> it out.
>
> I too believe that there shouldn't be any preemption within the MAC for
the
> following reasons:
>
> 1. The RPR MAC shall be defined with a set of transmission performance
> specifications - worst case packet delay, packet jitter tolerance, packet
> loss, etc. - similar to other transmission and transport technologies. In
> this context, the MAC packet loss shall be zero under normal conditions.
> Pre-emption results in dropping of frames, and therefore should not be a
> function of the MAC.
>
> 2. Packet loss is also an important component of a service level
agreement.
> Service providers obviously want packet loss to be as close to zero as
> possible, and the MAC must do its part to help the overall system achieve
> this objective. Dropping packets or causing CRC errors to support
> pre-emption is not desirable.
>
> Regards,
>
> - Kanaiya
>
> -----Original Message-----
> From: Leon Bruckman [mailto:leonb@xxxxxxxxxxxxx]
> Sent: Sunday, April 22, 2001 10:15 AM
> To: 'William Dai'; stds-802-17@xxxxxxxx
> Subject: RE: [RPRWG] More comments on preemption
>
>
>
> William,
> You are right that the additional delay variation added by each additional
> node becomes lower as the number of nodes already taken into consideration
> increases. But the maximum delay variation will not decrease as the number
> of nodes increases.
> So the simulation shows the limit to the delay variation, under the noted
> assumptions.
> You already corrected your second observation, so I understand it is OK.
> Leon
>
> -----Original Message-----
> From: William Dai [mailto:wdai@xxxxxxxxxxxx]
> Sent: Thursday, April 19, 2001 9:18 PM
> To: stds-802-17@xxxxxxxx
> Subject: 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
>