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Contributor

voice

hi all,

 

in the 450 / 450i SM, what is the correct QoS for VoIP? i know that i need to turn on the hi priority channel and set the diffserv..is there anything else i need to turn on or provision in the radio?

4 REPLIES
Moderator

Re: voice

If your VoIP equipment properly tags VoIP traffic (nearly all of them do), the traffic will be marked with a DiffServ codepoint of 46 typically.

 

This traffic will then flow via the High Priority channel once you have enabled this on the SM.

 

There is some discussion on this here.

 

Another thread also discussed this here.

 

Please post if there are further questions... thanks.

Contributor

Re: voice

hi all,

 

so, customers keep calling saying their calls are broken. we have high priority turned on, but at 0 kbps. 

Frequent Contributor

Re: voice

You do need to provision some cir to high priority channel, dont leave it at zero.

 

We generally d 200kbits high priority up/down for one call session and extra 100 per call after that. It's a bit overkill but we would rather air on the higher / safer side.

 

As a side effect make sure you have enough contention slots for number of subs you have. High priority channel adds another vc so can increase contention slots needed for ap's with a lot ot users.

 

I would also recommend 15.1 software as 14.x and 13.x had some odd combination of speeds neede due to the refill buckets not being granular enough.

 

Tim

 

 

 

Super Contributor

Re: voice

I also do 200 Kbps CIR standard, adding 100 Kbps if they buy more lines. G.711 voice is a 64 Kbps payload, and winds up being just shy of 100 Kbps packet size after all the various headers, etc.

 

If you still have call quality issues check the VC statistics tab on both the AP and the SM. You are looking for packets that are matched into the HP VC.

If you see those then your problem lies elsewhere. You need to make sure that backhauls perform similar classification, and any switches or routers you have are not resetting the DSCP values. Because of variations in tagging behaviour, I always make sure all of my equipment acts on DSCP - NOT 802.1p (where applicable... some of my ancient backhauls are L2 only).

 

If you don't see packets matched into those VCs you need to check out the source. Some ATAs or software may not set the DSCP flag properly and require some configuration, or a router could be overwriting them.