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April 30, 2008



I was prepared to write a comment taking you to task for being so conservative about QoS network upgrades when you ended the piece with an excellent incremental proposal: let the ISPs use QoS tech to ease the last-mile bottleneck. In fact, this is what most of them do now (http://www.pbs.org/cringely/pulpit/2007/pulpit_20070412_001931.html), they just don't let you tag arbitrary traffic as privileged. They sell you a VoIP service with their own proprietary hardware and you can get decent VoIP QoS just as long as you only buy it from them. Given the historic prices of phone service, they have no real incentive to offer general-purpose privileged traffic. The only way that I can see to force them to offer that is to drive down the prices of phone service so low that they can then make more money by offering a low-latency traffic option than by offering phone service. That is in fact what I'm doing right now by buying VoIP service very cheaply, from a service that offers a free call-in number and outgoing calls at less than 2 cents/minute. I spent $20 on phone service last year, though the main reason for that is that I barely use the phone. The quality is not always so great but it's usually decent. I think some form of internet QoS is inevitable and I'd be happy if last-mile QoS is all it takes to solve the problem.

Brough Turner

Ajay, sorry for the long delay in responding but I'm back now. :)

I read the Cringely article you pinted out but I think Cringely is making some mistakes. If Vonage (or any similar service) has best efforts and their customer premises device is upstream of everything else in the home network, then they should be able to provide acceptable voice quality. I gather that is what Cringely gets, but you don't always get. The key here is the best efforts speed test. Cringely says he's getting 6.7 Mbps down and 1.4 Mbps up. That's more than enough head room for VoIP to work. Of course, if the broadband service provider (Comcast or otherwise) is actively identifying and discriminating against VoIP packets, i.e. giving them less than best efforts service, or if the available best efforts bandwidth (in either direction) falls below a few hundred kbps, then the voice quality will suffer.

Fax is another story. Fax only needs 9600 bps but it sends these bits via analog modem technology, i.e. it turns the 9600 bps of information into audio signals exactly matched to a 64 kbps G.711 voice channel. Unfortunately, many VoIP service providers compress the voice signal using an algorithm like G.729. G.729 is a speech coder that can pass acceptable speech using 8 kbps, but it can't encode music or other audio information acceptable. In particular G.729 speech coding will not pass Fax modem audio. This is the most likely reason that Cringely's fax doesn't work. His problem is with Vonage, not with Comcast.


Hello Brough, I don't think the Vonage device is upstream of everything else. It's just a linksys router that is plugged into your home network just like any other network device, so I doubt Vonage is able to provide better QoS. As for fax, you're right that it just shows Cringely's ignorance but that issue is irrelevant: who uses fax nowadays anyway? I only referred to Cringely for evidence that the major ISPs have already installed multi-tiered packet tagging. They just don't let the consumer tag their packets themselves. I personally think net neutrality is a crock and that some level of tiered services at the network level is inevitable. I hope you're right and that QoS tiers will only be necessary for the last mile, but I would support it throughout the network if it were found to be technically necessary to guarantee QoS.

Brough Turner

Ajay, I'm not a Vonage customer but when last I looked the Linksys router they provide was supposed to be plugged into you DSL modem or cable modem directly. Everything else in your home is supposed to be connected to the Linksys router. The Linksys device Vonage uses has two telephony ports on it. Internally, that Linksys router gives packets from the two telephony ports absolute priority in access to upstream bandwidth.


My only knowledge of Vonage is because I had a roommate who was an early Vonage customer and his linksys router was only useful for phone service: the network ports didn't work so you couldn't use it as an upstream router as you describe. I supposed it's possible that Vonage has sold both configurations, possibly moving to the upstream configuration you describe more recently. Getting back to the original QoS issue, I realized when thinking about it just now that video conferencing may be what is going to push QoS into the network. A 480p H.264 video stream takes around 2.5 Mbits/s, more than 60X the typical 40 kbits/s of an audio stream. The only way you'll get a decent video stream at that bitrate is if it's tagged as higher-priority, though I suppose video may be more forgiving of drops than audio. You'd certainly have to make sure the audio was pristine though.

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