Is cos 6 = DSCP 48? 1

[Rod25]

Hi Guys,

I am trying to implement QOS of IP Phones across the WAN. I am using 2950 switches and 1700 routers. I have programmed the routers with class maps. I would like to configure the fast ethernet ports on the switches for QOS.

I ran a sniffer on the IP Phone and found that sigaling was class selector 6 110000 and UDP or voice packets was Expedited Forwarding EF 101110

Does this mean cos 6 = DSCP 48 and cos 5 = DSCP 46?

Thanks

Rod

 

[KiscoKid]

CoS and DSCP are not essentially the same. CoS is layer 2 marking and involves manipulating the 802.1p tag. CoS uses 3 bits and therefore values can be anything from 0 to 7.

DSCP involves manipulating the IP header info (specifically the ToS field). DSCP uses 6 bits and value range from 0 to 63.

Cisco IP phones typically do mark their packets with DSCP 46 and 48 - this is normal.

On your 2950, you could trust the IP Phones (I usually do) and map the CoS to a DSCP value or forward the existing CoS values without modifying the DSCP value (called passthrough).

Hope this helps.

 

[KiscoKid]

Forgot to mention, consider using AutoQoS on the 2950. It really simplifies getting a switch configured for voip service.

Take a look at the following doc for more information about AutoQoS and how to configure it.

 

[Rod25]

Hi Kiscokid,

I have being asked to configure QOS on the 1700 routers. The IP PBX uses cos 6 for layer 2 signaling and DSCP 46 for Voice packets.
When I trace the IP Phone I see that UDP is set to EF and TCP is set to class selector 6

I have been told that the 2950 switches will automatically prioritize these packets and all I have to do is prioritize these packets on both 2950s.

I was going to use the following:

class-map match-any VoiceTraffic
match ip dscp ef
class-map match-any VoiceSignaling
match ip dscp cs6
!
policy-map Voip
class VoiceTraffic
priority 180 (6 calls at 8k plus overhead)
policy-map Voip
class VoiceSignaling
priority 30
class class-default
fair-queue



Hope I am on the right track

Rod

 

[Rod25]

Hi Kiscokid,

Could you send me a sample config for trusting ip phones on 2950...

Thanks again,

Rod

 

[ADB100]

Wrong, wrong wrong.......


Pay for someone.....

Sorry but QoS isn't a subject you can expect to handle on a forum.....

Andy (i get paid for this and it isn't worth trying to 'bodge it')

Andy

 

[Rod25]

Hi ADB100,

I dont understand your post?? I thought the whole idea of this site was to gain and share knowledge from experts like you. I am from a telephony background and would galdly asist you if needed. As for paying someone... this project has landed on my lap hence

http://www.tek-tips.com

If anyone could point me in the right direction, very much appreciated.

Rod

 

[plshlpme]

if your phones are marking the packets then i wouldn't worry about doing any policy maps on the 2950s i would just set the policy outbound on your 1700 routers wan interface

youve got the right idea setting the voice class to priority that will help the voice out in times of congestion. (you don't want your voice queuing)

just make sure you apply the policy to an interface
service-policy output xxxx

and then check to see that its working as intended..

 

[ADB100]

My point is that this is how bad networks get installed. Do it right the first time, otherwise you will upset users and make yourself look bad.
I have seen people replace perfectly good switches and routers simply because they were installed badly.

Design it, test it and implement it........

Apologies if I sounded a bit harsh but I see more and more bad networks and it is generally down to people 'thinking' they can do the work without actually knowing they can.

Andy

 

[Rod25]

Hi Guys,

Thanks for the advice... I have a month to get this working and I have the routing working between sites.

These are the steps that I took:

I wanted to keep the voice and data seperate and thanks to Guys like you on this site I learnt how to create a voice vlan for my IP Phones and trunk a fastethernet port to the router. The router has two sub-interfaces setup for the data 10.x.x.x and one for voice 192.168.1.x I believe this is called inter-vlan routing.

I have IP Telephony working between site but it is not going live until next month. I was sending large files across the WAN and notice that my QOS was not working.

When I trace the IP Phone I see that UDP is set to EF and TCP is set to class selector 6

I will enable QOS on the switches...i think it's one command.

I was going to use the following:

class-map match-any VoiceTraffic
match ip dscp ef
class-map match-any VoiceSignaling
match ip dscp cs6
!
policy-map Voip
class VoiceTraffic
priority 180 (6 calls at 8k plus overhead)
policy-map Voip
class VoiceSignaling
priority 30
class class-default
fair-queue
!
int s0/0
service-policy output Voip
!

Unforunately, I cant get to test this config until next week...Does it look ok...


Andy, I agree about planning jbos but I am learning and have the luxury of having time on my side.

Rod

 

[Rod25]

time on my side......for this job

 

[plshlpme]

i don't think you want to mark the signalling "priority" and should use the bandwidth statement instead.. your voice-traffic is our priority queue

 

[Rod25]

Hi Plshpme,

Thanks for your reply... I will try this next week...

policy-map Voip
class VoiceTraffic
priority 180
policy-map Voip
class VoiceSignaling
bandwidth 30
class class-default
fair-queue

 

[plshlpme]

that should be a good start.
im not sure if you realize but your stating the policy map statement twice there... it will look like this in the router

policy-map Voip
class VoiceTraffic
priority 180
class VoiceSignaling
bandwidth 30
class class-default
fair-queue

and if your applying to the s0/0 you can run

sh pol int s0/0
to see some stats to make sure its seeing your traffic properly.. it will also tell you if you are exceeding etc.

 

[Rod25]

Hi plshlpme,

Thanks for that...Thanks was a cut and paste error on my part.

Thanks again,

Rod