Once upon a time Jim Robertson shaped the electrons to say... > cautioning me that although FAX over VOIP worked for him, it was with a high > bandwidth Satellite internet connection, and that with 1.5 mb/sec download > aDSL (have to emphasize the ?a? there), the max upload rate was too slow
Well, most home DSL services are ADSL. Upstream speeds will vary - I've seen anything from 128Kbps to 768Kbps on standard home lines. I have 6Mbps/768Kbps ADSL through Speakeasy.net. Even 128Kbps is more than enough for VOIP - but not if lots of other services are competing for the bandwidth so the VOIP gets choked out. There are ways around that - some VOIP gateways will do traffic shaping, reserving a minimum bandwidth for VOIP and throttle all other traffic of the total volume exceeds the capacity of the line. This basically prioritizes the VOIP traffic higher than all the other traffic, ensuring it always has enough of the pipe. Keep in mind that the telco backbone is digital and the standard circuit is only 56Kbps (64Kbps DS0 with 8Kbps used for in-band signalling), or 64Kbps at best (clear DS0). And that 'analog' line you have is only analog to the CO, where it hits a codec and is digitized. (This is why modems maxed out at 56Kbps - I can explain how that works in more detail than anyone wants due to a past job...) In many areas, where population growth has exceeded line capacity the telco MUXes lines so two POTS lines share one DS0, effectively giving each line a max of 32Kbps for voice. But you never notice it - the human voice compresses very well. But that's why FAXes and modems have problems (on such a MUXed line modems generally can't break 21.6Kbps) - the compression. And VOIP systems are 'worse' than the telco codecs, because they're optimized *just* for voice, while the telco's encoding is designed to handle voice, modems, fax, etc. One of the first things a VOIP box does is throw away most of the signal. The human voice is limited to a narrow frequency range. So the first thing the box does is toss any sound above or below this range. This actually improves sound quality, because it chops out a lot of background noise, but that also throws away most of the signal spectrum a modem would use. Then it takes the remaining data and uses aggressive encoding to reduce the signal to as little data as possible. It is generally tuned to be a lot more aggressive than the average MP3 rip - any 'masked' sounds are just tossed. (Those are sounds that the human ear generally wouldn't perceived because some other, simultaneous, sound would drown it out.) In the end you generally get a pretty clear voice on the line - but it just trashes a modem's signal completely. Generally they can't connect at all, and if they can connect then they're limited to very slow speeds - the smaller the available signal spectrum, the lower the speed. VOIP services that offer FAX or modem support do so by using a different encoding - they don't toss as much signal and they use encoding designed to preserve more of the data, more like the telco switch codec, but that results in a much larger data stream, which is then more likely to have issues with a slower pipe. Since few people use modems these days, most VOIP services just don't bother with the hassle and have optimized their systems very well for voice only. > And is it the case that I cannot use the internet for updating the TV > schedule if my DVR is a DirecTiVo? I think I?ve read previously that the USB > ports are turned off by DirecTV on the series 2 units (such as I have). By default DirecTV has disabled all networking on the DirecTiVo units. You can use hacks to enable them to use the network instead of the phone, but that's about it. I think the newer non-TiVo DVRs may allow the use of the network. -MZ -- megazone-at-megazone.org http://www.MegaZone.org/ Gweep, Geek, Human, me. http://www.TiVoLovers.com/ http://www.Eyrie-Productions.com/ -><- Hail Eris "A little nonsense now and then, is relished by the wisest men" 508-852-2171
