[X4U] ISPs, DSL, dhcp vs. PPPoE, and VOIP

[Stroller]

On 6 Dec 2007, at 00:50, Jim Robertson wrote:
> ... One carries the DSL signal, and
> my dim recollection when I set things up was that I couldn't use  
> that line
> for DirecTV's middle of the night phone calls that update the  
> schedule on my
> TiVo.

I believe this is incorrect, but it is often cited (for fax machines  
& restaurant credit-card machines here in the UK), so distance from  
the exchange / line noise may be a factor.

Fax & the Tivo data phonecalls are designed to go over a regular  
voice telephone line, and you have splitters which allow you to talk  
at the same time as your DSL is active - I have yet to be convinced  
of any reason why modem-fax-data calls should not work over the voice  
section. Indeed, I have many customers here in the UK using their Sky  
satellite subscription boxes on the same line as their ADSL.

> ..Another concern here is that the max download rate I
> can get at this address via DSL is 3 mbits/sec because of my linear  
> distance
> from the nearest fiber closet. Anyone able to hazard a guess  
> whether that's
> enough bandwidth for one line VOIP (it wouldn't be the primary  
> voice line)
> as well as general internet access for 2-5 Macs (typical  
> residential use,
> although my son does some bittorrent downloads - no hosting - when  
> he thinks
> I'm not looking).

3megs is LOADS for VoIP - in fact, 512/256 is quite adequate for a  
VoIP line or two - and the chief-limiting factor is upload speed  
(since speech has to go both ways), which you don't mention. I think,  
in fact, that a voice channel is c 100kbps, so you can get two  
channels over a traditional 512/256 ADSL service, but that is a  
little tight if you're putting any more data over it. Think of it  
this way, tho' - your DSL connection is fat enough for voice over  
Skpe - why shouldn't it be adequate for any other VoIP service?

In fact, your son IS hosting when he downloads via BitTorrent, or  
should be, as it is a distributed protocol - clients are configured  
to share the parts of the file they've already got and give  
preference to other clients who have shared most with them (i.e.  
discriminating against those who don't share).
http://en.wikipedia.org/wiki/BitTorrent_Protocol
http://cognitiveatrophy.blogspot.com/2005_02_01_archive.html (3rd  
diagram)

 From your point of view there are two principle problems with  
BitTorrent:
- it can easily saturate your connection with fast downloads leaving  
no width for anything else.
- it tends to generate a particularly high number of connections.

Both of these can cause VoIP connections to drop or break up, but:
- the first is resolved with traffic prioritising, probably provided  
by any router intended for VoIP use,
- the second can fill up the router's NAT table. This used to be a  
problem - 3 years ago? - with routers with 4meg / 8meg RAM. I see,  
however, that many now have 32meg or 64meg, so you should be ok.
Neveertheless, you should be aware of BitTorrent's potential to cause  
problems with VoIP and be prepared to experiement with shutting BT  
down if you experience problems with phonecalls breaking up (reboot  
the router & the problem should resolve itself within a few minutes).

I don't know anything about the VoIP services supplied by telephone  
companies, so can't answer your AT&T questions.

Stroller.