QoS DSCP priority for critical business application

mbroberson1 · ‎09-24-2008

Hey guy's just curious for suggestions on this.

We have remote sites connected by point-to-point full T-1's. We are running voice (IPT) over the T-1's and have prioritzed the traffic as ef as expected. Now heres the question. We have a critical business application that needs high priority almost as much as the voice traffic, but I don't want it interferring with the voice traffic. What would be a good DSCP value to mark the applications traffic?

Thanks

francisco_1 · ‎09-24-2008

normally your voice is given DSCP 46 (ef)= ip precedence 5 and your business app dscp 16 = IP precedence 2.

Francisco

patrickvanham · ‎09-24-2008

Depending on what class you have defined for voice signalling you could use af21 or af31. You would like the application lower than signalling since you wouldn't want the application to interfere with voice signalling either. If this is the only application which needs to be preferred af21 would suffice, but if you really consider the application to be close to voip af31 would be more suitable unless af31 is already used for voice signalling.

mbroberson1 · ‎09-24-2008

Currently we do have signaling as af31. If we more to af21 for the application will this hurt signaling?

Thanks

mbroberson1 · ‎09-24-2008

If we have signaling at af31 and desire to leave it would af41 for the application proiritize it enough?

Thanks

francisco_1 · ‎09-24-2008

based on the dscp values i gave above AF31 is is fine for singaling and AF21 for your apps.

mbroberson1 · ‎09-24-2008

So if we currently have signaling at af31 we should leave it and give apps af21? Or are you saying to change the signaling value?

Thanks

francisco_1 · ‎09-24-2008

Brandon,

no need to change the values. leave singal as AF31 and you apps as AF21.

francisco

mbroberson1 · ‎09-24-2008

Great! I'll try that.

Thanks

mbroberson1 · ‎09-24-2008

francisco,

Would this config work for governing my voice and critical application?

class-map match-any Voice-Calls

description Voice-Calls

match ip dscp ef

class-map match-any Voice-Call-Control

description Call-Control

match dscp af31

class-map match-any Critial-Application

description Critical-Application-Traffic

match access-group name Critical-Application

class-map match-any Telnet-Traffic

description Telnet-SSH

match protocol telnet

match protocol ssh

!

policy-map QOS

description Traffic-QoS

class Voice-Calls

priority 282

class Critical-Application

bandwidth 600

set dscp af21

class Telnet-Traffic

bandwidth 64

class Voice-Call-Control

priority 64

class class-default

fair-queue

random-detect

Thanks

Joseph W. Doherty · ‎09-24-2008

See http://www.cisco.com/en/US/technologies/tk543/tk759/technologies_white_paper0900aecd80295a9b.pdf

PS:

Just marking doesn't always guarantee the traffic actually obtains higher priority. Conversely, on a p-2-p T-1, you really don't need to mark to deliver different service priorities.