voicie signalling priority question

Answered Question

Hi !

I'm currently prepare my ONT certification Exam.

In all document I seen where QoS configuration is explain, they set voice signalling trafic just below voice and video trafic classes. In practice exam was for which 2 types of trafic we need QoS in converge network ? in the response choice : voice, voice signaling and mission critical misson data and some others with definete lower importance.

The answer was the pratice test was waiting for is voice and mission critical data.

I would like to know if voice signalling was'nt a good answer, why we provide priority higher of the most of other data trafic. Even if the exam was OK or not, I would like to know we have to provide higher priority for voice signalling then interactive data or web data trafic.

Thanks a lot for your help !

I have this problem too.
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Correct Answer by Jaime Valencia about 8 years 2 weeks ago

VoIP signaling is definitely also an answer that would need to be considered, in almost any situation where you're going to apply QoS to a system when it comes to VoIP you always allocate X BW for the RTP and also a minimum Y BW for signaling.

the reason is that without signaling you cannot establish a call, if you drop a packet that had a DTMF call will fail, you can get delay on softkey response, delay on dial tone, etc. also since the keepalives are also SCCP the drop of this packets can make a phone to lose the connection to CUCM.

the recommendation is always to provide BW on priority Q for RTP with EF PHB and allocate a minimum guaranteed BW for signaling which has CS3 PHB.

signaling can definitely support a little more delay than RTP or any other critical data within a company. at least from a VoIP perspective there should be QoS also for signaling.

HTH

java

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Correct Answer
Jaime Valencia Fri, 01/09/2009 - 11:34

VoIP signaling is definitely also an answer that would need to be considered, in almost any situation where you're going to apply QoS to a system when it comes to VoIP you always allocate X BW for the RTP and also a minimum Y BW for signaling.

the reason is that without signaling you cannot establish a call, if you drop a packet that had a DTMF call will fail, you can get delay on softkey response, delay on dial tone, etc. also since the keepalives are also SCCP the drop of this packets can make a phone to lose the connection to CUCM.

the recommendation is always to provide BW on priority Q for RTP with EF PHB and allocate a minimum guaranteed BW for signaling which has CS3 PHB.

signaling can definitely support a little more delay than RTP or any other critical data within a company. at least from a VoIP perspective there should be QoS also for signaling.

HTH

java

if this helps, please rate

CHRIS CHARLEBOIS Fri, 01/09/2009 - 12:09

I agree that Voice Signaling should get the highest priority for all the reasons java mentioned and one more.

Voice Signaling is low-bandwidth. Unless you have horribly overloaded your network, voice signaling should never be more that a small percentage of available traffic. Priority is only important when there is congestion, so the difference in priority between voice signaling, voice data, and mission critical data should only matter if those three combined cause contention. On a well designed network (with CAC and policing), contention between those streams should not happen.

iptuser55 Mon, 01/12/2009 - 09:24

The recommended approach is 5% for signalling e.g for 100 phones you could get away with 32K bandwidth in remote locations back to the central call Manager

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