Kitz ADSL Broadband Information
adsl spacer  
Support this site
Home Broadband ISPs Tech Routers Wiki Forum
 
     
   Compare ISP   Rate your ISP
   Glossary   Glossary
 
Please login or register.

Login with username, password and session length
Advanced search  

News:

Author Topic: Speed estimate for length (full crosstalk, no GINP, no vectoring, 6db)  (Read 1616 times)

ktz392837

  • Reg Member
  • ***
  • Posts: 559

Does anyone have speed estimates for length of line assuming full crosstalk and no GINP and no vectoring enabled targeting 6db? (ie ECI cabs)

I am at over 40% sync speed loss compared to when there was only me on the cabinet.  This seems quite high.

BT have tested line they say it is fine.  I persuaded the engineer to to a reset that gave me a 20% speed boost but he didn't think it would last and over the past few months it has gradually gone down to even worse than what is has ever been.

I am approx 400m from the cabinet with a line attenuation of 15.9db what should a fair sync speed be for my line?
Logged

Chrysalis

  • Content Team
  • Addicted Kitizen
  • *
  • Posts: 7382
  • VM Gig1 - AAISP L2TP

There is no static full crosstalk value.

Key metrics you have ommited from your post are.

Estimate provided by isp at signup.
Current estimates on the BT wholesale checker.
Current sync speed and line profile.

The closest thing I would consider to a "full crosstalk" value would be when a cabinet is fully populated which will be variable from cabinet to cabinet and from pair to pair on each cabinet.

For reference I am actually slightly over 40% loss currently based on when I first had FTTC, and my lowest in % terms was about 55% (at which point I had a pair swap).
Logged

WWWombat

  • Kitizen
  • ****
  • Posts: 1674

Here's one I prepared earlier...

I need to add some explanation, but I'm about to go out. More later...
Logged

WWWombat

  • Kitizen
  • ****
  • Posts: 1674

OK, some explanation...

The basic graph dates back to the early days of vectoring, and is found in a "Brodband Forum" document: MR-257, though that link is to a newer "issue 2" of the document.

The graph applies to the UK to some extent, because it depicts profile 17a, with the theoretical top speed of 170Mbps.

However, it isn't fully appropriate...
- It is for 0.4mm cable, whereas the UK tends to be 0.5mm - at least in the D-side. As the footnotes in issue 2 say: the range of a particular speed can be increased by perhaps 4/3.
- It is for Annex A (US), not Annex B (EU).
- It almost certainly doesn't include any PSD masks for ADSL. That could maybe knock up to 8Mbps off the speeds.
- It makes no allowance for any of the bandwidth being used for FEC protection. The old DLM intervention settings would steal 10-15% of your speed for this.
- It makes no allowance for G.INP either.

As you can see, the gap between "perfect" and "almost absolute worst case" (the two triangles) is *huge*. Your line could be anywhere inbetween. However, the majority will be somewhere in the region of the blue crosses.

I used to have a line that was just over 16dB attenuation, with length around 375m. The current "A range" estimate is 59-78Mbps.

Using that "4/3" factor on the distance, I should be comparing with the set of results for 300m on that graph. It suggests a "single user" or "perfect vectoring" speed of  140Mbps, and a likely range "with crosstalk" of 60-100Mbps. If you lost 8Mbps (PSD mask) and 10% (DLM) from that, you could be somewhere under 50Mbps.
Logged

ktz392837

  • Reg Member
  • ***
  • Posts: 559

Thanks very interesting, I am just about in the range.  I guess still well above the worse case so could be much worse. 

I wish it was possible to see how busy a cabinet was and therefore the likelyhood of further losses.
Logged

Chrysalis

  • Content Team
  • Addicted Kitizen
  • *
  • Posts: 7382
  • VM Gig1 - AAISP L2TP

If that graph is for 0.4 then it suggests my cable is worse quality (of course I Already know it is, its a mixture of 0.3 copper and 0.5 ali D side, E side is 0.2 copper).

e.g. that graph for my line length has a projected speed range of between 130-140mbit when no crosstalk is present, yet me first on the cabinet had 110mbit.  Factor in 15-20mbit lost for adsl power back off, I was under by 10-15mbit.

The bulk of the time on my first pair was in the lower region of the blue X bar, mid to high 60s sync speed.

When my line was low enough to trigger a pair swap it was around where the downward triangle is.

I dont know how much of the UK is 0.5 copper but whenever I mentioned it to friendly engineers they tend to laugh and one even said "I wish".  However I expect their responses are related to the state of Leics openreach network rather than what it is elsewhere around the UK.  My gut thinking is that urban areas probably have the worst quality cabling (MK aside) and villages at end of long runs of cable tend to have the better stuff to try and mitigate the long lengths.
Logged