NTL Broadband

#1
I'm moving offices and thinking of getting ntl:telewest business to provide my broadband conection (they're still separate from Virgin). They claim they give 10Mb already, and are moving to 20Mb for £40 a month.

I had a few questions...
- does anyone have any experience of ntl business? (I know ntl consumer were terrible)
- when the say 10Mb what am I likely to get? (I know on ADSL there are contention issues and distance from the exchange, does the same apply to cable?)
- does a cable modem just connect with the rest of my ethernet network like a adsl mode does?

Thanks for any help anyone can provide

Justin

#2
I'd previously used ntl consumer, and while their customer service was dreadful, the line was actually much more reliable than ADSL. That was some time ago though ...

ISPs usually quote the downstream bandwidth only. The same applied to cable - because NRL/Telewest/Virgin's network was originally designed for getting signals to the home (ie TV) and not back again, they too are asymmetric.

VoIP needs downstream *and* upstream bandwidth. How much depends on what codec your phone is using. If you're using the default g.711 codec, you'll need about 100Kb/s per concurrent call. If you're using the GSM codec, you'll only need about 40Kb/s per concurrent call. You don't lose much in quality if most of your calls are to or from the PSTN, as that works on only slightly better than GSM quality.

So let's say that your connection is 10Mb/s downstream and 256Kb/s upstream. That would give you 2 concurrent calls using g.711 with a bit spare for other traffic, or 5-6 concurrent calls using GSM.

If you doubled your downstream bandwidth to 20Mb/s but the upstream stayed the same - you'll get no more concurrent calls for your money.

You do also get contention issues with cable, just like ADSL. The lower the contention ratio, the better. I'd want at least 10:1, and ideally 5:1. There's no distance from exchange issue though.

A cable modem connects to your network like any other 100Base-T network device. It will have an RJ-45 port and you connect this to your network switch.

#4
For those of you interested....

The contention ratio is 20:1
The up speed is 768

Which seems like a reasonable deal - a 10Mb connection, soon to be 20Mb, for £40 a month. £40 sounds high, but it is less than £12 for the BT line plus £30-odd for a not-really-8Mb business broadband.

But, no, I haven't got the convictons in my own analysis to go for it. I'm driftng back to BT on the basis of fear and uncertainty, just the sort of thing that upsets me in other people!

#5
I am using the NTL/ Virgin Media 20 Mb/s service for £ 35/ £ 37 a month. The cable modem is set by them at 20.480 MB/s one way and 768 KB/s the other way.

Most days I get better than 18 MB/s and 680 KB/s but occasionally the nominal 20 MB/s service drops to 2 MB/s in the evening.

I am using the S 450 DECT phone which is set to use the G711 codecs at about 100 KB/s each way. The S450 supports two simultaneous connection and I have not experienced any VOIP problems - apart from the published outages.

Brian

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