----- Original Message ----- From: "Andrew Kohlsmith" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Tuesday, August 03, 2004 5:06 PM Subject: Re: [Asterisk-Users] VoIP experiences with Cable and DSL
> On Tuesday 03 August 2004 19:44, Chris Shaw wrote: > > > QoS isn't going to help you get to talk in a crowded CSMA/CD network. > > > > I might be misunderstanding you about QoS, but I know for a fact that it > > does help greatly because whether you use DSL or Cable, your bridge device > > (it's not a modem no matter how much people want to call it that, it's a > > bridge!) uses large buffered queues to achieve sustained transfer rates... > > this is awesome for bulk downloads but makes your VoIP conversation sound > > like you're on a cellphone under a bridge in a windstorm... Also if the ISP > > is using QoS and they classify users by the MAC address of your bridge > > device, they can create something similar to ATM PVCs, allowing traffic to > > flow more orderly and evenly across THEIR network... > > What I am saying is that you are shaping your ethernet to your cable modem > (and yes I call it a cable MODEM -- you're still modulating and demodulating > -- it's just DMT or some superhypermega modulation method) -- once it hits > your cable modem you're playing the CSMA/CD game and if you collide you're > SOL, there goes your timely packet. > > And yes I know all about huge queues... The cure for that (at least with DSL) > is to get a Sangoma S518 -- it's a PCI ADSL modem with drivers for > everything... I just prioritise packets now (no rate limiting) and get my > full 4M/800kbit without any nonsense. I can flood the link in both > directions and my VOIP sounds perfect. > > You just can't do that with an external modem -- tested 3 different ones > (Speedstream one that comes with Bell HSE, an "industrial" grade one that > comes with commercial DSL and also an old FP2100 -- the Bell one was by far > the worst -- I had to rate limit to 400kbps or it would start queueing up the > packets like crazy. > > > Bear in mind that when you're using QoS you're shaping YOUR traffic as it > > goes out YOUR link... you can do nothing about what happens to it once it > > crosses your ISP's router into the rest of the InterNet. > > Exactly -- you're shaping your upstream and with a busy CSMA/CD or CA network > you won't have much luck since your prioritised packets are getting delayed > on their way to the head unit. > > -A. > Not really familiar with DOCSIS specs but I'm not sure cable IS actually CSMA/CD, it may be ATM or FDMA or even TDMA... I guess it depends on the provider? _______________________________________________ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users