RE: [RPRWG] MAC Question
Hi Adisak,
No one can say that higher latency is a virtue and so if it came at no or
little
price every one will welcome low latency. But, in my experience it has a
significant
cost which someone has to pay for. Let us take a few latency crtical
examples:
1. Ring control packets
2. Voice packets
In case (1) we talk of the time of the order of millisecond (if I am correct
our
objective is 50 ms for restoration). The control packets are expected to be
fairly small ones. At Gigabit rate (the system speed is going to be much
faster than
this) it takes about 1 us (For 128 byte packet) per node. We can use a
system with 500 nodes under .5 ms time.
For voice packets the turn around time is of the order of 50 ms. The packet
sizes are
likely going to be 64 -128 bytes in this case too. Thus similar calculations
apply.
Having said this, I would support cut through for priority packets.
Regards,
Devendra Tripathi
VidyaWeb, Inc
90 Great Oaks Blvd #206
San Jose, Ca 95119
Tel: (408)226-6800,
Direct: (408)363-2375
Fax: (408)226-6862
> -----Original Message-----
> From: owner-stds-802-17@xxxxxxxx [mailto:owner-stds-802-17@xxxxxxxx]On
> Behalf Of Adisak Mekkittikul
> Sent: Thursday, March 22, 2001 9:37 AM
> To: stds-802-17@xxxxxxxx
> Subject: RE: [RPRWG] MAC Question
>
>
>
>
> Latency is definitely an issue, especially when it is accumulated
> end to end
> to a very
> high valve, affecting applications. From my own experience, I have yet to
> see any
> switch vendor proudly announce that their switches are capable of adding
> "high
> delay" as a feature.
>
> Adisak
> Lantern Communications
>
> -----Original Message-----
> From: Devendra Tripathi [mailto:tripathi@xxxxxxxxxxxx]
> Sent: Thursday, March 22, 2001 9:04 AM
> To: Ajay Sahai; Ray Zeisz
> Cc: stds-802-17@xxxxxxxx
> Subject: RE: [RPRWG] MAC Question
>
>
>
> Going by experience in switches, latency is not a real issue.
>
> Regards,
>
> Devendra Tripathi
> VidyaWeb, Inc
> 90 Great Oaks Blvd #206
> San Jose, Ca 95119
> Tel: (408)226-6800,
> Direct: (408)363-2375
> Fax: (408)226-6862
>
> > -----Original Message-----
> > From: owner-stds-802-17@xxxxxxxx [mailto:owner-stds-802-17@xxxxxxxx]On
> > Behalf Of Ajay Sahai
> > Sent: Thursday, March 22, 2001 6:34 AM
> > To: Ray Zeisz
> > Cc: stds-802-17@xxxxxxxx
> > Subject: Re: [RPRWG] MAC Question
> >
> >
> > Ray:
> >
> > I guess the answer is that the group is still debating this issue. Some
> > vendors prefer to have a largish transit buffer where transit frames
> > are stored. Others are proposing "cut through" transit functionality.
> >
> > I personally feel that latency will be larger in the first approach.
> >
> > On another note I do not believe that the similarity with 802.5 is
> > on the lines of claiming a token etc. etc. The MAC mechanism
> > is going to be different.
> >
> > Hope this helps.
> >
> > Ajay Sahai
> >
> > Ray Zeisz wrote:
> >
> > > I am following the .17 group from afar, but I have a question:
> > >
> > > Is it acceptable for each node in the ring to buffer up an
> entire packet
> > > before forwarding it to its neighbor? Would the latency be to
> > great if this
> > > were done? Or is the .17 direction more along the lines of
> > 802.5 where only
> > > a few bits in each ring node are buffered...just enough to
> > detect a token
> > > and set a bit to claim it.
> > >
> > > Ray
> > >
> > > Ray Zeisz
> > > Technology Advisor
> > > LVL7 Systems
> > > http://www.LVL7.com
> > > (919) 865-2735
> >
>