SIP with Cisco PIX 506e

[dean]

We have just started using voice over IP using SIP. Users complaints are:

• That on occasions they experience poor sound quality.

• Although they are able to hear the person at the other end of the phone clearly, the person at the other end is unable to hear them. I must point out that this does not happen all the time, approximately 10% of the time, but this is 10% too much.

My question is should I configure a SIP policy on the PIX and if so why?

[Patrick Laidlaw]

Hello,

Can you describe how your setup is. Are you using SIP to people on the internet. I'm assumeing yes if your going through the PIX.

Your most likely suspect if you connecting to the internet using voip is your experiencing congestion somewhere on your lan or interenet connection. There really isn't much you can do about the internet but you can try to configure QOS on your lan. The pix isn't very good at doing this with 6.3 hopefully they'll come out with a slimmed down version of 7.x for the 501's and 506's that include some sort of QOS for the pix.

Patrick

[dean]

We have roughly 20 users using SIP over the internet, using SDSL. The SDSL link is in a different building, the two buildings are connecting via fibre which is terminated at both ends with 100Mbps converters connecting to managed switches.

I am in the process of reducing the traffic on the network. I am removing any hubs, and also changing the converters to 1000Mbps. Do you have any ideas of what else I could do to remove unnecessary traffic from the network?

Regards,

Dean

[Patrick Laidlaw]

Dean,

I can already tell you just from the sounds of your network that I'm surprised that you haven't had more problems with your sip phones.

Hubs, converters are bad for streaming applications. These 1000mbps converters your going to be using are they plugging straight into your switch's or are they truly converters that will then plug into a Gig E port or is it a Gig E fiber port in a switch.

Also to help if your using Cisco switches you can setup queuing on them and setup vlans to segment your sip VOIP traffic from you everyday data.

If you are using Cisco switches let us know which types of switches. Post there configs I'm sure we can help you come up with a configuration for QOS on them.

Patrick

[dean]

Patrick,

unfortunately we are using Netgear switches that has Gig eth ports. I hoping the converters will improve things quite a bit.

I am not sure if it would be possible to setup vlans since all traffic will come across the fibre and enter one port on the switch.

Regards,

Dean