QoS and SIP on a WS-C3750G-24TS

ece344609_2 · ‎02-25-2009

I am trying to troubleshoot an issue with a VoIP unit called Aastralink PRO 160. I seem to be having repeated issues with this unit and according to the vendor it seems to be a Cisco issue.

I only have access to the switch at the access layer and I need to know if there is any QoS policies being distributed and/or any sort of implementation of Cisco's SIP that may interfere with the functioning of this unit. I know this is general but what can I do to ensure that QoS and SIP on this Cisco switch are not interfering with the functioning of this VoIP unit.

Thanks all.

bmcginn · ‎02-25-2009

Hi there,

Your explanation is a bit general, so I can only offer some suggestions.

Does the device (PRO 160) mark the TOS byte for the SIP packets? If it does, you may have to configure a trust command on the 3750 port that it connects to (something like mls qos trust cos).

Secondly, is that switch already set up for voice? ie does it have the qos commands on it? If not, the easiest way would be to run autoqos. Here's a link about autoqos: http://www.cisco.com/en/US/technologies/tk543/tk879/technologies_white_paper0900aecd803228e0.html

Bear in mind that your device (if it marks packets) may mark them differently to what the autoqos is expecting. If the device doesn't mark the packets at all, you may need to get them marked on the 3750.

If you only have access to the switch at the access layer, you may need to have a chat to the administrators of the core to ensure that the device or your switch is marking the packets to the right TOS value.

Having said that, it may not be a qos issue anyway, have you checked spanning-tree, port speeds and duplexing (for the device and all uplinks etc), have you checked the cable etc.

Good luck with it!