VoIP over wireless links

[jaregalado]

Hi

We have a client using VoIP between locations served by wireless bridges (Enterasys Romabout bridges).

The available bandwidth is enough for day to day operations incuding VoIP calls but ocasionally the voice quality degrades, the obvious culprit for us is someone downloading a big file across the wireless link so we're planning using Quality of Service on the Catalyst switches connected to the wireless bridges (Catalyst 6513 on main site and Catalyst 3548XL on remote side).

Voice Gw (1751) <--> Cat3548XL <--- Wireless Link --> Cat6513 <----> Voice Gw (AS5300)

I wonder if any one of you has worked with this type of network setup and what your recommendations would be. What would you use in this case ? CAR, LLQ, etc.

Thanks very much.

[sjhern]

Configuring QOS between sites will make a substantial difference. If the routers have an AUTO-QOS for Voice package on them already I would suggest trying the base config to see where you get. If you still have issues you can tweak those settings to help improve quality but if those a Critical calls and needs absolute priority, I would combine QOS with a Gatekeeper in the mix to also assure that there is enough bandwidth to even attempt a call. If the phones are on the same cluster the CCM should know well enough through QOS that the call can be attempted. However, wireless will always have its issues with call quality. Sorry if this info wasnt useful.

[thisisshanky]

Are the 1751 and 5300 doing the data routing between the two sites ? Then doing qos on the 1751 and 5300 will be a good option. If there are separate routers for data, then you will have to set qos parameters on the catalyst lan switches.

I dont know if Enterasys bridges supports qos. Cisco wireless bridges do support one way qos (from bridge to the wireless media). Qos on wireless is achieved by adjusting the random time for which a particular class of traffic waits before transmitting into the media. (utilizing the wait time for CSMA/CA)

[jaregalado]

Hello, I appreciate your responses.

The routers are only used for making VoIP calls and data is just bridged from the Catalyst 3548 and across the wireless link to the Catalyst 6500 where it is terminated on an SVI interface so PCs connected to the Catalyst 3548 see the Cat 6500 IP address on the SVI interface as their default gateway. From there data is routed to the rest of the network included the AS5300. Do you think we should be routing from the remote site (using the 1751 router or the Catalyst 3548 multilayer capabilities) to the the core Cat 6500 ?

We´re going to perform some tests with AutoQoS and then manually tweak QoS and see what happens.

Regards.