VOIP and Qos?

Question

I have Comcast internet service using a Motorola modem SB5120 which connects to a Linksys WRT54G wireless G router. I have VOIP service using a Linksys SPA2102-R connected to port 1 on the Linksys router. The router has Qos settings that can be changed for better distribution of packets. I have the VOIP device's MAC address set to have highest priority and upstream bandwidth is set to auto. However, I still seem to get low Qos % when I run VOIP tests, and I get choppy audio at times too. Can anyone help me with this ongoing saga? Any help is much appreciated.

Answer 1

You sound like you know what you are doing so I am going to assume that your WRT54G is setup correctly to give top priority to your VOIP device. I bet I have used almost the exact same equipment as you. I would work the problem like this.
1. Make sure you have the bandwidth to do VoIP. Go find a speed test and follow their instrutions and look at the numbers. (take the SPA2102-R out of the picture). You may want to run it at different times during the day to see if something is happening out there and your bandwidth isn't what you think it is.
1.1 If you are not getting the speeds your cable company advertises then you could take this issue up to them.

2. Make sure nothing else is using your bandwidth. This could be computers, TiVo, etc. hogging your bandwidth. The WRT54G is wireless so make nobody else is on your network using your bandwidth. Yes, I know you turned on packet prioritizing but these devices cost $100 and the routers companies purchase cost many thousands of dollars...I'm sure there are some differences.
2.1 Take everything off your network (including turning wireless off) except the three devices up there and make a few phone calls to see if it improves.

3. Try to packet prioritize on the port and not the Mac...plug the SPA2102-R into the fast port.

If you have the bandwidth and you still have problems then I have these suggestions.

1. Work this through you VoIP provider (chance of success probably very low)
2. You could switch to Comcast VoIP. They have a cable modem that includes the VoIP (and an 8 hour lithium battery for phone service when the power goes out). I garuntee that packet prioritizing is MUCH better when done here with this device.
3. You might can upgrade your speed. Cable and twisted-pair (a.k.a. phone company) offer different levels of high-speed access...you might need to upgrade from fast access to super fast access (I'm sure prices will vary)

Any of the above testing might give you a clue to replace a component above. I would suspect the WRT54G or the SPA2102-R before the cable modem.

Answer 2

Are there QoS settings for the WRT54G? If so, those need to be configured as well. Unless the VoIP is offered by Comcast, then their network will not honor the QoS markings on the VoIP packets (most likely).

The way QoS with VoIP works is that the IP header has a "tag" applied to it to differentiate a voice packet from a non-voice packet. All the devices in the network need to honor the tag or it becomes meaningless. The technical name for this tagging is called Diffserv (Differentiated Services), the markings are standardized - being that Linksys is owned by Cisco I'm reasonably sure they support the standard markings.

I'd call Linksys tech support with your issue, they should be able to tell you how to configure each device for optimal use. They may even have a white paper or something on their web site to guide you.

The motorola modem won't care one way or the other about the QoS marking - it doesn't "route" packets.