Call Control and Voice traffic in same priority queue?

Answered Question
Jun 5th, 2007

Avaya recommends marking call control traffic the same as voice traffic, COS=5 and DSCP=46, and therefore putting call control traffic in the same priority queue with voice during congestion.

The rational is that call control and inter-IPSI traffic is as crucial as voice and should be treated as such.

This is different than Cisco's recommendation as described in the Enterprise QoS SRND, where call control is marked as COS=3/DSCP=24 and treated via bandwidth quarantees.

Is Avaya's approach a sound approach and are there advantages to their approach? We will be deploying Avaya IP phones along with Cisco 3750's and 6509's as access-layer switches.

Any and all comments are appreciated.

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Correct Answer by thisisshanky about 9 years 7 months ago

Cisco voice control packets are mostly TCP/IP so TCP will take care of retransmissions if any required. While RTP stream is UDP and has no built in mechanism for retransmissions. This is one big reason why RTP stream is mission critical compared to control packets. Again the same reason I would think why Cisco recommends to classify both with different DSCP values so that you can treat them different. Not sure how Avaya does their voice signalling (TCP or UDP).

HTH

Sankar

PS: please remember to rate posts!

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Correct Answer
thisisshanky Tue, 06/05/2007 - 06:28

Cisco voice control packets are mostly TCP/IP so TCP will take care of retransmissions if any required. While RTP stream is UDP and has no built in mechanism for retransmissions. This is one big reason why RTP stream is mission critical compared to control packets. Again the same reason I would think why Cisco recommends to classify both with different DSCP values so that you can treat them different. Not sure how Avaya does their voice signalling (TCP or UDP).

HTH

Sankar

PS: please remember to rate posts!

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