[cisco-voip] [OSL | CCIE_Voice] SIlly QoS Question

[Peter Smale]

I think there are only 3 drop thresholds on 3550 very primitive RED
C1 is better than CS2 which is better than CS3 etc.   But within a class as
for as RED or WRED the opposite is true.
AD31 is dropped before AF32  etc.   Traffic in CS3 should not be eligible
for drop at all.
Been a long time since I have taught QoS but that's how I remember it.

I made the argument sometime ago that control traffic SKINNY RS323 SIP etc.
is so negligible that it could just be classified with the RTP stream itself
CS2.

But I guess that would make things too easy.

By the way if you are dropping packets on a 100 or even 10 meg link in a
short Range campus i.e. 10 millisecond range something has gone very wrong.
Broadcast storm, virus etc.  in any event you've got a problem to fix.
Peter.  :-)

-----Original Message-----
From: cisco-voip-bounces at puck.nether.net
[mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Jonathan Charles
Sent: Saturday, April 05, 2008 5:46 PM
To: Pulos, Greg
Cc: CCIE Maillist; cisco-voip at puck.nether.net
Subject: Re: [cisco-voip] [OSL | CCIE_Voice] SIlly QoS Question

So, if CS3 has a higher drop probability than AF31, why change the CS3?

It seems to me that it would be good to get dial-tone when I pick up
the receiver, even if there is congestion.

This seems like a bad idea...



Jonathan

On Sat, Apr 5, 2008 at 6:47 PM, Pulos, Greg <GPulos at doc.gov> wrote:
> I think it sounds a bit confusing too but the concept of rfc2474 defining
the CSx as 'not subject to dropping' is correct. (although in fact the
taildrops can/will drop cs3 if absolutely required by the qos design and
traffic requirements.)
>
>  I think the bigger point that is being made by the migration is to allow
for MissionCriticalData to be assigned af31....period. (therefore allowing
greater drop preference scalability, ie: AFx(1-3), depending on the qos
design and exact traffic type)
>
>  Gregory T. Pulos II
>  Sr. VoIP Engineer
>  U.S. Department of Commerce
>  Office of the Secretary
>  OCIO/ONTO/NOC
>  202.482.5010
>
> gpulos at doc.gov
>
>  -----Original Message-----
>  From: ccie_voice-bounces at onlinestudylist.com
[mailto:ccie_voice-bounces at onlinestudylist.com] On Behalf Of Jonathan
Charles
>  Sent: Saturday, April 05, 2008 6:11 PM
>  To: CCIE Maillist; cisco-voip at puck.nether.net
>  Subject: [OSL | CCIE_Voice] SIlly QoS Question
>
>
>
> [cross-posting to Puck and the CCIE Online Study List...if you guys
>  aren't familiar with each other, you should be...]
>
>
>  Ok, so Cisco is migrating control traffic from AF31 to CS3...
>
>  I am curious as to why... the QoS SRND says they are moving to CS3
>  "because Class Selector code points, as defined in RFC 2474, were not
>  subject to markdown/aggressive dropping"
>
>  OK, I guess...
>
>  But.
>
>  WRED is enabled on each non-priority queue on the Cisco 3550 (queues
>  1,2 and 3)...
>
>  Doesn't the lack of any drop thresholds (low, medium and high) in the
>  CSX PHB levels, cause this traffic to be potentially dumped in the
>  case of congestion?
>
>  In other words, since AF31 has a binary value of 011010 and CS3 has a
>  binary value of 011000, that means that CS3 has nothing set for Delay,
>  Throughput or Reliability; whereas AF31 had high throughput set.
>
>  How is CS3 better?
>
>
>
>  Jonathan
>
>
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