QOS on the Motorola VT1000

Posts: 3 · New Forum Member Joined: Apr 08, 2004 Posts: 3

Could one of the Vonage gurus on this site be so kind as to explain how the Motorola box manages to do QOS? I'm interested in a technical explanation of how the Motorola is able to prioritize the voice traffic over the data traffic.

Posts: 67 · Full Forum Member Joined: Mar 22, 2004 Posts: 67

I'm going to guess.

The MTA may or may not actually do what is really called QoS. But it doesn't matter because the chances your ISP supports QoS is nearly nil. With QoS, an application can reserve bandwidth, but everyone has to support it.

The MTA may or may not do QoS on the LAN side. If you have computers on the LAN that can do QoS (XP does if you don't turn it off) then that might work.

But my guess is that it is simpler than that. I'd be willing to bet that the MTA simply throttles the bandwidth available to the LAN port while in a call. This isn't perfect because you can't control how much data is going to come barrelling down from the outside no matter what you do (without real QoS). But, most people have way more download then upload. So if you just slow down the LAN to Internet connection, you can conserve upload and that will probably be enough.

This is all guess work.

Many people have said that putting the MTA in front of the router slows them down all the time, even if not on a call. Can't say about that myself.

Posts: 104 · Vonage Forum Senior Joined: Jan 31, 2004 Posts: 104

Indeed correct, the Motorola MTA is doing simple bandwidth throttling.

Frankly, it's not even that sophisticated -- it's doing basic queuing. As most residential broadband links are asymmetrical (the downlink is generally much faster than the uplink). The MTA simply worries about the uplink.

Remember the MTA is actually a simple router. As the router 'spins' along it has two outgoing data queues to look out, queue 1 is from the voice side (and has the voice packets), queue 2 is from the data side (your computer or hub or whatever).

The MTA simply gives priority to 'pushing' out packets from queue 1 over those from queue 2.

The way TCP works, if packets from queue 2 timeout or simply fail to get sent -- no problem you're computer will retransmit and for the most part you won't notice any measureable delay.

So as not to totally shut down the 2nd queue (however unlikely as most conversations have plenty of pauses). My guess is the router might interrupt to take a few 2nd queue packets ocassionally (e.g. take 100 Q1 packets, then take at last 10 Q2 packets) or something similar.

In any event, it's not that sophisticated but for a single or dual telephone line and basic home network - works fine, last a long time Very Happy

Posts: 50 · Full Forum Member Joined: Mar 10, 2004 Posts: 50

The MTA only does QOS to the internet once the data hits the internet it is best effort.