[alcatel-nsp] Question about Service QoS Policies on 7750SR

Kila Hsu hsukila at yahoo.com
Thu Feb 19 17:44:26 EST 2009

Thanks a lot, Diego!

I still have several question though. Assume that we don't have a port scheduler defined, and we do get congestion. As you mentioned, now queues are transmitted at the physical level using round robin, with expedited queues being served first.

1. By "queues" do you mean the queue-to-be-transmitted for each SAP? If there are multiple tier 1 schedulers, or orphaned queues in a SAP, which one will get transmitted? (or will these queues now become the candidates for the physical level round-robin?)

2. How are the weights assigned for all these queues? Or is this just an plain old round-robin with every queue equally weighted?

3. If under each SAP I have hierarchical scheduler, it is possible that for one SAP, the next packet to be sent comes from an best-effort queue but the next-next one comes from an expedited queue (although this is a bad design). In this case, will this SAP have to wait in the physical level until the expedite queues from other SAPs are transmitted?

I hope I state the problems clearly. Thanks again for all who kindly answer!

Best Regards,
Kila Hsu

--- On Mon, 2/16/09, GARCIA DEL RIO Diego <Diego.Garcia_Del_Rio at alcatel-lucent.be> wrote:
From: GARCIA DEL RIO Diego <Diego.Garcia_Del_Rio at alcatel-lucent.be>
Subject: Re: [alcatel-nsp] Question about Service QoS Policies on 7750SR
To: alcatel-nsp at puck.nether.net
Date: Monday, February 16, 2009, 1:15 PM




Hi Hsu, 


If your version of TiMOS allows it, you could run a “port-parent”
scheduler, which allows you to map the parent scheduler of the queues in the
SAPs to a port-level scheduler that will distribute bandwidth between all
it’s children according to the configured prioritied. 


If you don’t have the port-schduler function (it appeared in TiMOS 5.0r4
and onwards), sap-queues and schedulers behave “as expected” when
there is no congestion at the port level, that is, all egressing traffic is
less than the port’s egress rate. 


If there is congestion though, and no port-scheduler is configured, queues are indeed
served in round-robin fashion with the “expedited” queues (in
in-profile state) being served exhaustively, then “best-effort”
(in-profile) and finally all out-of-profile queues. 


So.. in short, if using TiMOS 5.0 or newer, take a look at port-level
schedulers ;-) 




Diego Garcia
 del Rio

New Product
Introduction - Network Design Engineer 

IP Division

- Antwerpen

Mobile: +32 4734 30 245

OnNET 2 605 3871

Phone (+32) 3 2403871 

diego.garcia_del_rio at alcatel-lucent.com  


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alcatel-nsp-bounces at puck.nether.net
[mailto:alcatel-nsp-bounces at puck.nether.net] On
Behalf Of Kila Hsu

Sent: 16 February 2009 16:46

To: alcatel-nsp at puck.nether.net

Subject: Re: [alcatel-nsp]
Question about Service QoS Policies on 7750SR 



  Thanks a lot to Mark for the information about the ways to share a port among

  However, my boss seems to like the idea that each SAP can have its own queues
  and schedulers though..

  So say if I still need to deploy QoS on a per-SAP base, anyone know how the
  packets from different SAPs defined on a common port would be scheduled, if
  each has its own queue/scheduler?

  From the config guide I do see the "expedite" setting have
  something to do with "hardware scheduler", but it is not clear if
  the setting is used in cases like this.

  Any idea would be appreciated.



  Kila Hsu 



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