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Author Topic: FTTC - Distance from the Cabinet - Realistic speed estimate  (Read 253947 times)

les-70

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Re: FTTC - Distance from the Cabinet - Realistic speed estimate
« Reply #525 on: April 10, 2012, 09:14:05 AM »

  I assume you do mean the big feature at the end. I meant the end of the VDSL cable segment and should have been more precise.  I would guess that it must be at the FTTC DSLAM but don't know how they configure the DSLAM end of the cable for the test.  Do they use the TDR with the CAB DSLAM connected? or do they fully disconnect the  cable in  DSLAM CAB for the test?  I notice that at least some TDR test equipment advice is for a open end.
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waltergmw

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Re: FTTC - Distance from the Cabinet - Realistic speed estimate
« Reply #526 on: April 10, 2012, 09:54:31 AM »

@ les 70,

I hope BS will correct me if I'm wrong, but it's my understanding that "ordinary" BT O staff do not have access to FTTC cabinets (Unless they have been issued with the secure key) as I believe any VDSL modifications are only carried out in the associated PCP (or possibly on the associated cable joints if necessary).

Also FTTC cabinets around Guildford (and I believe other earlier version cabinets) have additional star shaped keys rather than the standard triangle ones. Later cabinets have reverted to the triangle ones.
(There's a nice easy overtime job for BS to go round swapping out the star keys !)

Kind regards,
Walter
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Bald_Eagle1

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Re: FTTC - Distance from the Cabinet - Realistic speed estimate
« Reply #527 on: April 10, 2012, 10:28:56 AM »

  I assume you do mean the big feature at the end. I meant the end of the VDSL cable segment and should have been more precise.  I would guess that it must be at the FTTC DSLAM but don't know how they configure the DSLAM end of the cable for the test.  Do they use the TDR with the CAB DSLAM connected? or do they fully disconnect the  cable in  DSLAM CAB for the test?  I notice that at least some TDR test equipment advice is for a open end.

Yes, the big feature was indeed the cabinet. I should have written it on my sketch.

The engineer firstly TDR tested from the PCP cabinet, with my modem still connected.

After carrying out his work at my home, he TDR tested from my home back to the cabinet, the D-side was still connected at the cabinet (as per the sketch).

These tests were conducted using an 'Exfo' tester.

I THINK a 'Hawk' tester requires an open end or an impulse generator to be attached.
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Black Sheep

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Re: FTTC - Distance from the Cabinet - Realistic speed estimate
« Reply #528 on: April 10, 2012, 11:28:33 AM »

@ les 70,

I hope BS will correct me if I'm wrong, but it's my understanding that "ordinary" BT O staff do not have access to FTTC cabinets (Unless they have been issued with the secure key) as I believe any VDSL modifications are only carried out in the associated PCP (or possibly on the associated cable joints if necessary).

Also FTTC cabinets around Guildford (and I believe other earlier version cabinets) have additional star shaped keys rather than the standard triangle ones. Later cabinets have reverted to the triangle ones.
(There's a nice easy overtime job for BS to go round swapping out the star keys !)

Kind regards,
Walter

Ha ha, yes us mere mortals, AKA 'Ordinary BT O staff'  ;) ;D are not allowed in the FTTC Cabinets. Obviously as the 'Build' is taking place we can, as the link cables have to be installed, but after that it's over to the PCR lads (Private Circuit Repair) to maintain. Also, with the presence of 240V power, I believe (but can't confirm) that our Power Maintenace Engineers may be tasked to enter them at times ??

The best form of TDR trace is when it's taken against applied voltage, so the best method would be to TDR back from the premises towards the PCP with all connections intact. The other beneficial test would be to perform a 'Leg balance' test from the PCP to the premises, in other words on a 'dead pair'. With JDSU/EXFO or HAWK we can measure each leg's resistance and capacitance. If there's a +/- 5% difference between legs, I would probably investigate further.

BE, I may be at cross-purposes with you but the HAWK has most of the same functions as the JDSU and EXFO in relation to copper pair testing. The only 'impulse generator' I can think you mean is what's called a 'Remote Unit' that has to be physically connected up at one end of the circuit ?? This is exactly the same for the other 2 testers. These would only be fitted for testing at 300Khz or any other inputted frequency.
Instead , we use a 'Remote Unit Emulation' which is activated by dialling in from our mobiles and mimicks fitting an actual unit. Again, this RUE test (usually used for PQT testing), can be used on all 3 testers. At present, it tests at 1.6Khz then applies an algorithm to calculate the results at 300Khz.

In a nutshell, HAWK/JDSU/EXFO are very very similar when it comes down to Copper pair testing.  :)
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Bald_Eagle1

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Re: FTTC - Distance from the Cabinet - Realistic speed estimate
« Reply #529 on: April 10, 2012, 01:21:02 PM »


BE, I may be at cross-purposes with you but the HAWK has most of the same functions as the JDSU and EXFO in relation to copper pair testing. The only 'impulse generator' I can think you mean is what's called a 'Remote Unit' that has to be physically connected up at one end of the circuit ?? This is exactly the same for the other 2 testers. These would only be fitted for testing at 300Khz or any other inputted frequency.
Instead , we use a 'Remote Unit Emulation' which is activated by dialling in from our mobiles and mimicks fitting an actual unit. Again, this RUE test (usually used for PQT testing), can be used on all 3 testers. At present, it tests at 1.6Khz then applies an algorithm to calculate the results at 300Khz.

In a nutshell, HAWK/JDSU/EXFO are very very similar when it comes down to Copper pair testing.  :)

Ah, thanks for clarifying that BS - my misunderstanding.
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les-70

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Re: FTTC - Distance from the Cabinet - Realistic speed estimate
« Reply #530 on: April 10, 2012, 03:55:26 PM »

  I wondered if BS could comment on the realism of the examples in the EXFO application note given above in my first post here?  and also in relation to the "The hump in your sketch look bit like a weak HR point in the cable??." remark I made  based on the EXFO examples

 ps I thought all the FTTC DSLAM cabling for every port in the DSLAM went to the ordinary CAB where it joined the main copper pairs as required.  I am thus not sure why any disconnection would need FTTC access. Sounds like I am wrong?
« Last Edit: April 10, 2012, 04:12:18 PM by les-70 »
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burakkucat

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Re: FTTC - Distance from the Cabinet - Realistic speed estimate
« Reply #531 on: April 10, 2012, 06:02:54 PM »

Quote
ps I thought all the FTTC DSLAM cabling for every port in the DSLAM went to the ordinary CAB where it joined the main copper pairs as required.

Correct. The tie-pairs are connected to the DSLAM, within the FTTC, at build time and are run into the supporting PCP, where they are left "hanging" until a service provision require a port.

Quote
I am thus not sure why any disconnection would need FTTC access. Sounds like I am wrong?

It doesn't and you're not!  ;D
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waltergmw

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Re: FTTC - Distance from the Cabinet - Realistic speed estimate
« Reply #532 on: April 10, 2012, 06:51:07 PM »

@ les 70,

Just to add that all connections, disconnections and maintenance is normally done by our good BT Openreach friends (even in the middle of winter with the rain hissing down) within the PCP leaving the FTTC alone.
Even if there was a question about the integrity of the inter-cabinet tie cables or the actual DSLAM ports, I suspect the standard solution would be to select a different pair circuit and leave the FTTC completely out of the investigation.
Were that to occur I suspect some DSLAM re-configuration would also be required.

Below is a link to a low res picture of a PCP cabinet I took last summer, during the lunch break, just as the cables were being terminated in the FTTC.
If you carefully count all the wires you will see that the E side (on the LHS) and the D side (RHS) tie cables have 100 twisted pairs in bunches of 10 pairs.
As there are no FTTC connections yet, all the original E to D jumpers are still intact mostly running along the top of the cabinet.

When a new FTTC service is required the corresponding pairs from the same bunch in both tie cables have new jumper pairs crimped and then punched down into the IDC blocks to connect the service to the appropriate E side and D side pairs.
In these parts, this type of IDC cabinet is in a minority with most using the loose pairs construction as illustrated in the second picture link (Before this particular cabinet was re-sleeved to accommodate the tie cables); in which case a new jumper pair is just crimped to the pairs in the bunch at one end and to the appropriate E side and D side pairs at the other. Finally here we also have yet another construction where the tie cables are made off onto new blocks of IDCs with the twin jumper pairs now having punched down connections at both ends. Ergo our long-suffering friends can be confronted with at least three different configurations of connections whether its pitch black or otherwise. What astonishes me is that, with the exception of BE's case, BT O staff get it right first time for the vast majority !

Some of us might have wry smiles when we observe Mr Livingstone saying quite earnestly that BT are investing vast amounts of money in this 20 year solution.

http://www.scribd.com/doc/66247741/BT-IDC-PCP

http://www.scribd.com/doc/42050356/Typical-BT-PCP-Section

Kind regards,
Walter

PS I'm fully expecting (and hope) BS will contribute to my little essay !

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Black Sheep

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Re: FTTC - Distance from the Cabinet - Realistic speed estimate
« Reply #533 on: April 10, 2012, 06:55:36 PM »

  I wondered if BS could comment on the realism of the examples in the EXFO application note given above in my first post here?  and also in relation to the "The hump in your sketch look bit like a weak HR point in the cable??." remark I made  based on the EXFO examples

 ps I thought all the FTTC DSLAM cabling for every port in the DSLAM went to the ordinary CAB where it joined the main copper pairs as required.  I am thus not sure why any disconnection would need FTTC access. Sounds like I am wrong?

Hi les

Yes, I read that linky with interest, and TBH, have saved it as well. 'Tis a good link sir, and I personally can't fault it.

Regarding your other point (the 'hump'), I've already PM'd Mr Bald_Eagle about this, but for clarification it could be a High Resistance (HR) fault developing, or a cable poundage change. As I've mentioned previously, I personally would have TDR'd the circuit whilst still 'juiced up' and measured the distance to the 'hump' on the trace, by way of moving the cursor to its position on the trace screen. It then gives a distance in metres as to how fat this is. I could then cross-reference this measurement against the plant 'Network Records' to ascertain if there is a cable change at approximately this distance. This is a bit 'hit and miss' as the NR's aren't particularly kept up to date as they are stored on our hard-drive and any plant renewal that was carried out, we would be unaware of via these records. Obviously, the NR data-base would be updated with the new details.

What I would also have done whilst the trace was running, is to ring the EU's landline and watch to see if the 'hump' increased in height, a sure-fire sign of a HR fault.

Thanks again for that linky.  :)
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Black Sheep

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Re: FTTC - Distance from the Cabinet - Realistic speed estimate
« Reply #534 on: April 10, 2012, 07:10:01 PM »

Hi Walter

Another comprehensive and insightful guide to our FTTC cabinets. Some of you guys should come and work with us, you have the same, and often more knowledge than we do .......  :-[ ;D

As pointed out, we dont enter the actual DSLAM Cab. If there's a port fault that we identify using our testers in the original-sited Cabinet. We then ring our NGA Helpdesk for co-op. This can either be the usual port reset, DLM reset or a 'Lift & Shift'. What I can say is, the timescales involved in performing a VDSL 'L&S', are far in advance of the ADSL 'L&S'. I've been at Cabinets for up to 3 hrs whilst we tried 2 different 'L&S'. The job then had to go back to PCR as it was apparent the DSLAM had gone faulty. Meanwhile back at the ranch, my boss was heating up his 'Poor Performer' branding iron !!! Only jesting, but a few of them a week and it could quite easily become the truth. :lol:

Thanks Walter for the understanding of OR lads and lasses, having to work in all weathers. It's not quite time just yet to get the smallest violin in the world out, and play a sad tune for us. But, cold, wet weather can be a small hindrance when working outside in it. Especially when you lose feeling in your fingers, and you are getting constant electric shocks due to the body resistance being damn near 0 ohms !!!  :'( ;D. Sod it, get that violin out after all !!!! ;)
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waltergmw

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Re: FTTC - Distance from the Cabinet - Realistic speed estimate
« Reply #535 on: April 10, 2012, 08:51:38 PM »

@ BS,

I do really sympathise. Many many moons ago I have done some winter work 30 ft up (and without a hard hat !) with conductors up to about 1 Inch in diamater. You begin to get worried when your legs refuse to go down the ladder !

However I digress. Whilst I realise you are in no position to question the lord high executioner, sooner of probably later, somebody somewhere has to think about raising a white flag regarding FTTC deployments, or at the very least give you, or your office staff, some tools to discover what is going wrong with a DSLAM ! I suspect that a part of that design is in place at a crude level using the telemetry services which are installed in the FTTC. As a tool of last resort there must be a way of rebooting the DSLAM locally. There should also be a watchdog healthy signal transmitted periodically with an alarm attached so your control centre can take appropriate action upon a failure. These should be hard wired through the 5 pr twisted pair cable along with many other more complex functions available through ethernet control messages down the fibre channel.

Let us close this particular conversation as I expect that nobody around has sufficient knowledge yet to discuss these matters properly.


Kind regards,
Walter
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JoshShep

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Re: FTTC - Distance from the Cabinet - Realistic speed estimate
« Reply #536 on: April 11, 2012, 04:50:47 PM »

Just found something interesting, look like we now have the option to disable interleaving, thank god!

Take a look guys - http://www.openreach.co.uk/orpg/home/products/super-fastfibreaccess/fibretothecabinet/fttc/downloads/GEA_FTTC_2%2063350%20111108.pdf

Black Sheep

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Re: FTTC - Distance from the Cabinet - Realistic speed estimate
« Reply #537 on: April 11, 2012, 06:58:40 PM »

Not sure if I'm missing a trick here Josh ?? That link doesn't mention in as many words about switching off interleaving, it just alludes to the fact you can choose between stability or speed. Is this what you mean ?? :)
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JoshShep

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Re: FTTC - Distance from the Cabinet - Realistic speed estimate
« Reply #538 on: April 11, 2012, 09:33:58 PM »

Not sure if I'm missing a trick here Josh ?? That link doesn't mention in as many words about switching off interleaving, it just alludes to the fact you can choose between stability or speed. Is this what you mean ?? :)

Yeah BS,

Standard - Auto, what we are all currently on.

Stable- Interleaving

Fast - Fastpath, lower ping for gamers.

You can now choose one of those options. Unless I'm missing something here?

Black Sheep

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Re: FTTC - Distance from the Cabinet - Realistic speed estimate
« Reply #539 on: April 12, 2012, 07:23:10 AM »

Not sure if I'm missing a trick here Josh ?? That link doesn't mention in as many words about switching off interleaving, it just alludes to the fact you can choose between stability or speed. Is this what you mean ?? :)

Yeah BS,

Standard - Auto, what we are all currently on.

Stable- Interleaving

Fast - Fastpath, lower ping for gamers.

You can now choose one of those options. Unless I'm missing something here?

Thanks Josh. However, the EU has always had personal control of that situation. See ..... https://www.btwholesale.com/shared/document/Products/Broadband/IPStream/dsl_max_myths_legends_issue1.pdf ........ section 12.
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