QOS - VOIP traffic: payload and signalling

Question

Two questions For VOIP traffic,
Q.1. should the payload and signalling be assigned the same COS ?? to avoid losing Signalling traffic.
Q.2. flash upgrades to the phone sets are tftp. Should this traffic be assigned COS=0 or the same cos as the signalling traffic ? Phone flash gets corrupted if some of these packets are lost ?
thanks for your help,

Answer 1

Hello,
best practice puts signaling into another class than voip "payload" as you named it.
The reason is that the qos requirements are different. Signaling needs guaranteed bandwidth, voip needs low delay and guaranteed bandwidth.
TFTP can be placed into signaling class or in a separate class.
An example config could look like this:
ip cef
class-map match-any VoIP
match ip dscp ef cs5
match protocol rtp audio
class-map match-any VoIPsignal
match ip dscp cs3
class-map match-all TFTP
match protocol tftp
policy-map VoIPprio
class VoIP
priority percent 10
class VoIPsignal
bandwidth remaining percent 5
class TFTP
bandwidth remaining percent 5
class class-default
fair-queue
random-detect
interface Serial0
ip address ...
service-policy output VoIPprio
You would have to adjust the bandwith ratios for your needs and the interface naming to your environment.
The policy will give 10% of the link to voip traffic with lowest possible delay, 5% of the rest for voip signaling, 5% to TFTP and the rest for the other data present.
Hope this helps