END TO END QOS FOR L2 AND L3 ON LARGE N/W

ABDUL MAJID KHAN · ‎05-15-2010

Dear All,

I am plannig to apply End to End QOS (L2 and L3) on a Large Network Path that is having many hops. I am new in the QOS field. Please find the attached diagram for your information. I have the following strategy;

1: Identify all the Voice traffic via Access-list and Class Map

2: Tag/Mark the voice traffic with dscp value 46 and prioritise this traffic inside Policy map.

3: Now on each uplink, get the traffic which has dscp value 46, and prioritise it.

Please find the attached sample configuration in note pad.

I have the below confussions;

1: Some devices on the path suppose 3750 is not supporting the priority command inside policy map.

What should i do with it?

2: Should i apply the service policy on outbound direction or inbound direction.

3: Do i need to apply the QOS policy on all the links(uplink, downlink) which is mentioned in the diagram.

4: Is the Voice traffic uni directional or bi-directional. I mean to say, do i only need to apply QOS on links from IP Phone to IPT server or also from IPT Server to IP Phone?

Waiting for your suggestion;

Abu Hadee · ‎05-16-2010

Hi

I'm attaching the QoS SRND ( i can't seem to find the web link)

1: Some devices on the path suppose 3750 is not supporting the priority command inside policy map.

What should i do with it?

[Abu] - Are you using those 3750 as Layer3 too? If not, you can use regular L2 QoS

2: Should i apply the service policy on outbound direction or inbound direction.

[Abu] - On switching you should apply both inbound and outbound QoS. For WAN router, you can only use outbound QoS. But if you suspect that Provider may change the DSCP values, you may want to check and rewrite the DSCP Values

3: Do i need to apply the QOS policy on all the links(uplink, downlink) which is mentioned in the diagram.

[Abu] - See above

4: Is the Voice traffic uni directional or bi-directional. I mean to say, do i only need to apply QOS on links from IP Phone to IPT server or also from IPT Server to IP Phone?

[Abu] - Yes, voice is both direction. But in some case,it may be one direction like Moh. When you are playing Music On Hold, Audio is only from MoH Server to Gateway to Phone. Same as to IVR unless there is a need to DTMF. But any other Voice communication is bidirectional.

The configuration that you've attached, you put Voice Signalling in priority Queue also. Which may not be a good idea. Priority Queue works as Policing. So if goes beyond the limit, packet will be dropped. Which is ok for real time traffic since it is worthless to send it later. But it is not same for Signalling. End device wouldn't mind getting packet 1/2 sec later then completely dropped it. It is ask it agian any way.

Please read through the QoS SRND, there are few exampls. Hope this helps.

Thank you

- abu

ABDUL MAJID KHAN · ‎05-17-2010

@asadee,

Thanks for your reply. Please find below;

1: 3750 switch is used as Layer 3 as you can see from the attached network diagram. so wat u sugest accordingly.

2: On router suppose R1 s0/0, i can expect the voice traffic suppose in both direction (outgoing and incoming), and i can only apply the policy on one direction at at time, so i think outgoing will be the correct choice?????

4: Voice traffic is in both direction so it mean i will consider the above point 2, to apply with one choice (on outgoing direction only)

5: Regarding signalling traffic, as per my knowledge, if we priotize the traffic (voice + signalling), it should not be dropped. It may be dropped in policing but not in priority???????(please double check)

6: As you can see on the diagram, I have big MPLS Cloud between my network devices, so do i need to change any configuration in it as well?????

THIS SEEMS TO BE VERY CHALLENGING OR MAY BE I AM NEW IN THE QOS. I ALSO INVITE OTHER CSC EXPERTS VIEWS AS WELL.