Is length the real issue or cable quality?

Radiation · 23 Mar 2010 at 14:16

I've wondered about this before, what would happen if BT as a test decided to replace all the cable and connections between an exchange and a house with only the best quality shielded cables, if the connection only managed a few meg before would the improved cable increase speeds?

I would have thought so but im unsure if its a physical limitation from cable length, what if it also had small powered repeaters, or even if it was superconducting?

paradigm · 23 Mar 2010 at 16:27

Length never has been the limitation/problem, although usually the root cause of signal degradation/line noise goes hand in hand with length.

It is however entirely possible to have a short run to the exchange completely ruined by line noise (although rare).

alex24 · 23 Mar 2010 at 16:30

Place where I worked had up to 8mbit ADSL, they were literally next door to the exchange and couldn't get more than 5mbit, so I think quality is definitely important. Here I am about 2 miles away and I can get 7.2 on up to 8. The line here was refitted a few years back as it wouldn't hold an ADSL connection at all then.

Sp00n · 23 Mar 2010 at 16:31

It is also entirely possible for you to be right next to the exchange (as the crow flies) but your actual connection to the exchange goes off elsewhere then comes back, we had a client with this issue very recently whereby they were 500 yards from the exchange but the line length was something stupid like 1km.

derfderfley · 23 Mar 2010 at 18:41

Shielded UG cable is only shielded for the entire cable, not each individual pair of wires. So no shielded cable would make little if any difference (unless the cable was run next to HV electricity cables).

What would make a difference is a increase in the diameter of each pair in the cable, that can have a fairly drastic (positive) effect on long cable runs, when customers have xdsl problems.
That however would cost a telco a huge amount of money, money that would be better spent putting fibre in the ground.

Interestingly testing xdsl modems/routers/wic cards, can have strange results on very short cable lengths. For example testing some consumer xdsl kit;
12mpbs directly connected to the exchange frame (effectively as close as you are going to get to 0 meters of cable)
14mbps with a added 250 meters of cable added
20mbps with 1000 meters of cable added
Much scratching of heads ensued...

No idea why this happens, but some of the very clever bods on here can probably give a useful explanation.

ncjok · 25 Mar 2010 at 00:15

Echoing earlier comments with regard to cable dimensions, an Openreach engineer told me about an out-of-town village which was distant from their parent exchange having a "hefty" weight of cable installed because the voice quality was poor. This had a dramatically positive effect on broadband speeds to the point it would outdo users from other areas which had shorter runs.

Radiation · 25 Mar 2010 at 12:24

Interesting, let's just hope we don't have to wait too long for fibre then, it should be the last cable we'll ever need as they can keep increasing bandwidth with advances in transceiver technology until it hits some physical limit of light and fibre capacity, which is huge i suspect?