Question about propagation and queuing delays

Mon Aug 22 15:41:31 UTC 2005

On Aug 22, 2005, at 11:32 AM, Eric A. Hall wrote:

> On 8/22/2005 11:14 AM, David Hagel wrote:
>
>> This is interesting. This may sound like a naive question. But if
>> queuing delays are so insignificant in comparison to other fixed  
>> delay
>> components then what does it say about the usefulness of all the
>> extensive techniques for queue management and congestion control
>> (including TCP congestion control, RED and so forth) in the  
>> context of
>> today's backbone networks?
>
> Latency is cumulative. Knocking a little time off Part A will still  
> act to
> shorten total time, regardless of the time occupied by Part B
>
> Queuing behaviors are also significant when you are suffering  
> congestion,
> apart from the delay factors

I think the key here is "when you are suffering congestion".

RS said that queueing delay is irrelevant when the link was between  
60% and > 97% full, depending on the speed of the link.  If you have  
a link which is more full than that, queueing techniques matter.

Put another way, queueing techniques are irrelevant when the queue  
size is almost always <= 1.

-- 
TTFN,
patrick