Re: [RE] Latencies through RE links (was cables)
The heading of the item was misleading. Buffer and conflict delays (I'm not sure what you mean by conflict delay as different from buffer - I assume you are differentiating between the delay through buffers when there is no other traffic and the delay when there is other traffic in front of you) are in no way part of "cable" delay. Cable is just the physical media. Link delay might include the delay in physical layer devices. I don't think it includes the delays of items above the link layer such as switch queues or switch relay delays. Hop delay might be a title fof something more inclusive. Getting terminology correct can help in having useful discussion.
Regards,
Pat
-----Original Message-----
From: owner-stds-802-3-re@IEEE.ORG
[mailto:owner-stds-802-3-re@IEEE.ORG]On Behalf Of David V James
Sent: Wednesday, 27 April, 2005 10:50 AM
To: STDS-802-3-RE@LISTSERV.IEEE.ORG
Subject: Re: [RE] Latencies through RE cables
Geoff,
Thanks for the detailed numbers.
I guess it doesn't hurt to use actual numbers, to validate
the following statement.
>> (This number is much more than the speed of light, ...
I suppose an illustration of conflicting traffic, which
can oftentimes be the cause of conflicts, would also
be helpful. I believe Pioneer had a slide presentation
on this topic, and that had been overlooked in the
writeup.
Thanks again,
DVJ
David V. James
>> -----Original Message-----
>> From: Geoff Thompson [mailto:gthompso@nortel.com]
>> Sent: Tuesday, April 26, 2005 1:45 PM
>> To: David V James
>> Cc: STDS-802-3-RE@LISTSERV.IEEE.ORG
>> Subject: Re: [RE] Latencies through RE cables
>>
>>
>> David-
>>
>> The cable latency is less than or equal to 570 ns/100 meter link
>> (one way).
>> This is a well established number within 802.3 and cabling standards.
>>
>> This is based on the 5.7 ns/m figure that is in 10BASE-T (ref: 14.4.2.4)
>> The higher speed links are slightly faster.
>>
>> Geoff
>>
>>
>> At 12:14 PM 4/26/2005 -0800, David V James wrote:
>> >All,
>> >
>> >Things seem to have been quiet for the last week.
>> >Perhaps I could stimulate some discussions on
>> >cable latencies?
>> >
>> >I believe Alexei's presentations have claimed that
>> >interactive latencies of 15ms are nearly audible.
>> >
>> >Since the link delays are only part of the delay
>> >equation, this has led some of us to believe that
>> >(worst case) per-hop latencies should not exceed
>> >0.5ms. (This number is much more than the speed
>> >of light, since it includes buffer and conflict
>> >delays.)
>> >
>> >Is there any controversy with using this as a
>> >working per-hop maximum delay number?
>> >
>> >For background material on this topic, please
>> >reference pages 15-17 of the following
>> >working paper:
>> >
>> > http://groups.yahoo.com/group/REInterestGroup/files/
>> > The paper is listed as dvjRePaper2005Apr26.pdf
>> >
>> >I have spent the last week accumulating content
>> >of various slide presentations into the above
>> >listed working paper. Hopefully this will be helpful
>> >when considering this and other issues.
>> >
>> >DVJ
>> >David V. James
>> >
>>
>>