MAC Based QoS

Unanswered Question
Mar 17th, 2008

Is it possible to implement a MAC Based QoS for IP Phones?


I have this problem too.
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rsabapathee Mon, 03/17/2008 - 10:25

Im using some IAX phones which need to connect to internet (ADSL) to register with a PABX. The registration process is done every x seconds.

The communication to PABX is on port 4569. However on the PABX it shows that the phones are logging on different ports with every registration.

Each phone connects to cisco 29xx switches and to a cisco router 2801, then forwarded to adsl router.

I need to make sure that the phones has top priority and since it is changing ports, i can only do it via MAC QoS.

Secondly how do I monitor the traffic originating from a device as it goes through a network to the adsl router. similary the other way round?



Paolo Bevilacqua Mon, 03/17/2008 - 10:38

Hi, the reason the phones are changing address can be due to NAT and not QoS. Even if the phones had topmost priority that would not change.

For monitoring you can use user prtg (search google) that is free for a single router.

Hope this helps, please rate post if it does!

rsabapathee Mon, 03/17/2008 - 21:41

If one sets an ip phone to connect to a WAN IP Address on a specific port, how come the server on the WAN side shows that the ip phone is registering on a different port?? How does NAT affect this?

Secondly what are the difference (adv/disadv) of MAC QoS over port/application QoS wrt to OSI level?

Does it make a difference to use MAC Qos in a network of 5 PCs and a network of 150 PCs?


Paolo Bevilacqua Tue, 03/18/2008 - 01:49

Hi, you said you're working on the internet so I assume there's is NAT/PAT, correct? If there is, NAT/PAT can change the source port in packets going from inside to outside.

Secondly, cisco really doesn;t use mac-based QoS. If you need something like that, make so you assign Ip in a range to the devices you want WQoS for, anfd and then configure QoS with an IP ACL. The result is the same.


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