Massive jump in speed

I was previously with Virgin Media but after so many years of erratic speeds; sometimes good, sometimes appalling, I decided to go with BT as I had a BT business line and they made an offer of 3 months free. Signed up with BT Business Broadband and the speed on my existing 3-com modem went from 3.6 to 4.6Mb overnight.

The other week I manage to pick up a BT Business Hub3 cheaply on ebay and installed it today; the speed jumped from 4.6 to 8.4Mb! How on earth can a different modem make this much difference? Has me truly puzzled?

Mike.

The Hub3 supports ADSL2+

Thanks for the reply Batboy.

I always thought that my 3com one supported ADSL2+ too.
Model No. 3CRWE754G72A?

Perhaps I was wrong, it worked OK and the lights on the front changed when ADSL2+ came on line here?

Perhaps I was mislead by the lights. The modem was getting on in years.

Just waiting for FTTC to come on line. Promised by end of 2014 but promises have been broken before.

Mike.

In reply to a post by RepairExpert:

Thanks for the reply Batboy.

I always thought that my 3com one supported ADSL2+ too.
Model No. 3CRWE754G72A?

Perhaps I was wrong, it worked OK and the lights on the front changed when ADSL2+ came on line here?

Perhaps I was mislead by the lights. The modem was getting on in years.

Just waiting for FTTC to come on line. Promised by end of 2014 but promises have been broken before.

Mike.

Information on that Modem is very vague but it appears to support ADSL2+.

Did you change the RJ11 Cable or Microfilter when changing the Modem? The 3Com may have been on its last legs as-well if you've had it for a while. The 3com should tell you on its interface when synced whether it's connected via ADSL (ITU G.992.1) or ADSL2+ (ITU G.992.5) if you are curious.

Post deleted by RepairExpert

Hi Chris; no didn't change anything, cable, filters, etc. just plugged the new one in. Worked straight away.

With regard to the 3Com, it was very old, I had it second hand at least 5 years ago. I did try and find out at the changeover time of ADSL2+ whether it was suitable and there wasn't a lot of agreement from various people on this site as to whether it was or wasn't compatible. I think the answer in the end was try it, and that it would probably work, and it did, but not necessarily at the maximum speed; that seems to be the case.

I wonder how many others out there are using an old router on ADSL2+ and getting poorer speeds than they could? I bet I'm not the only one.

Of course BT give Home BT users a free hub, but Business users have to pay nearly £90 for them. Hence me buying one off ebay for around a fiver including postage.

Whether there is any difference between the Home Hub3 and the Business Hub3 I have no idea; perhaps it's a more rugged version inside? Anyone know?

Mike.

The quality of the device, noise from the power supply or internal circuitry, the actual modem front end - quality and impedance, the modem's internal high pass filters ...

Any of those can have an effect on the attenuation, or noise levels and thus speed. I have seen it many times - changing hubs with internal modems giving large incresses or decreases in speeds.

Can you try to get the Attenuation, SNR and Sync Speeds for both?

Hi MHC; I have got the two sets of data as requested.

3Com router
Interleaved Channel Data Rate
Down 5248kbps, Up 928kbps,
Noise Margin 5.5dB down, 7dB up
Attenuation 41dB down, 24.5dB up
Output power 20dBm down, 12dBm up

BT Business Hub3
Downstream 9.128Mpps, Upstream 888.9kbps
VPI/VCI 0/38
Noise margin 3.4dB Down, 11.6dB up
Attenuation 38.9dB Down, 23.7dB up
Output power 20.4dBm Down, 12.1dBm up

Only major differences appear to be the noise figures.

Mike.

I doubt the business version is any more rugged at all, rugged electronics costs a lot more and I don't see businesses taking their hub with them around building sites.

From my reading there are two immediately obvious differences and one which can be gleaned from understanding what the figures mean. Attenuation is the first and SNR the second - however then looking at teh SNR figures in conjunction with sync gives teh thrid factor.

2dB difference in attenuation - could be down to the termination impedance and certainly the cause is within the device.

5.5 dB noise on 3com - would have been set at 6dB on sync and the 3.4dB from the HH3 would have been 3dB. A 3 dB difference would normally give a speed difference of around 500kbps to 1Mbps assuming that the actual noise level was similar. This suggests that there is a lot more noise present with the 3com which could emanate from the power supply or the device itself or that the circuit design and layout is more susceptible to noise.