Stephen, that was some excellent reporting on ADSL. I also enjoyed reading Martin's thoughts on the topic. I would add several points here, if I may.
Concerning some previous statements on the thread relating to xDSL's inability to support VON services... it is becoming clear that generalizations and many common notions will no longer hold any water in this regard.
First, the upstream (loiwer-speed) side of the ADSL channel at its absolute worst is 64 kbps. Downstream it is usually anywhere from 384 kbps to 8 Mbps. The upstream is where the point of contention lies, I surmise.
The reasons cited for ADSL's not supporting VoIP are really not pertinent for the most part, in a mild kind of way, of course <s>, akin to apples and oranges, but let's assume for discussion's sake that this was a valid concern. If the upstream is, at worst, 64 kbps, then it is still probably faster than many users are accustomed to today using traditional 28.8 and 56 kbps devices. In fact, the 64 kbps rate is exactly the same rate that defines high quality POTS voice today on the PSTN.
More to the point, however, most deployments of DSL that are actually making it to the marketplace are either symmetrical or have higher upstreams (128, 384, etc.) than the 64 kbps cited (or implied... I don't have too much time on my hands otherwise I would revisit that posting), and many are dynamically set per line conditions such as loop length and signal to noise ratios.
In either case, the foregoing doesn't really address the more intriguing issue of VoIP over xDSL. In some vendors' remote access concentration devices, such as those you dial into for Internet access, they are incorporating ADSL chips today which are being provisioned with VoIP compliant software.
Once these are fired up and we see some uptake, you wont have to "dial" your ISP, since you will have permanent web tone, or call it what you like... And they will support H.323 VON services, although these will differ in the way that first- and second- generation gateways operate.
This does not minimize the role of gateways, rather, it extends the VoIP paradigm to yet another means of deployment: One that I feel will be more in line with the capabilities of the IP world in the future. But we ain't there yet.
Therefore, in addition to the "splitter" component inherent in ADSL - which allows simultaneous voice and data over different parts of the spectrum on the twisted pair copper line - the user will then have yet another choice in how to do voice over IP: Through the TCP/IP session into the cloud _without_ the need for entering a POTS switch. That's what Web Tone will be all about.
While there are a handful of vendors poised to announce these features in their remote access services devices in a couple of months, this sort of thing is still very new, and it lacks a lot of the assistance from the PSTN that is still needed at this time (but gateways are now being built to handle this needed POTS signalling emulation, I like to call it). Conversely, VoIP gateways get this assistance "now" from the directory lookups in POTS switching centers, via telco subscriber Line Information Data Bases (LIDBs) and the universal Signalling System Number 7. SS7 is responsible for call setups, routings and teardowns, to name just a few of its functions. While the latter processes do not necessary take place in the IP cloud in quite the same way, they most assuredly are needed to reach endpoints on the local sides of the connections. For now, anyway, and going into the next five or so years. Maybe longer.
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I usually maintain a low profile in these fora for various reasons, preferring to lurk, but your coverage was a welcome and refreshing sign, in stark contrast to some of the nonsense that otherwise characterized the past several weeks here. I simply wanted to acknowledge and corroborate your work, and suggest that there be more of the same, going forward.
Best Regards, Frank |
