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Return path problems?
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Old 09-08-2006, 15:36   #1
MrDuck
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Return path problems?

Hi,

I've had BB disconnects happening continuously for approx. 6 months.

So far:

1. New external cable pull - RG11 - ~90m
2. New internal cabling - RG6 (i think)
3. Ambit (NTL 250) modem (same as original) replacement - same problems

I have to connect directly to the incoming coax, without a splitter (to STB) to get some sort of BB service. It will stay up for undetermined periods with usually one or two disconnects per day - sometimes down for hours at a time.

I have tried 3 types of NTL splitter: 3.5 dB (red writing on label), 3 dB (blue writing - from memory - engineer took this one back, so can't confirm) and an isolated 2 way (green label, chunky). I also now have a 6dB forward path attenuator, square type, FLD5W (not currently used). Any splitter in the signal path kills my BB. The FP attenuator does not seem to greatly affect the uptime of the modem, when used.

Here are stats from modem - note upstream power level:

Downstream Lock : Locked
Downstream Channel Id : 2
Downstream Frequency : 586750000 Hz
Downstream Modulation : QAM64
Downstream Symbol Rate : 6952 Ksym/sec
Downstream Interleave Depth : taps12Increment17
Downstream Receive Power Level : 5.4 dBmV
Downstream SNR : 33.4 dB

Upstream Lock : Locked
Upstream Channel ID : 6
Upstream Frequency : 22000000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 2560 Ksym/sec
Upstream transmit Power Level : 61.0 dBmV
Upstream Mini-Slot Size : 2

It looks like a return path issue to me. We also have no return path on the STB when connected. My immediate neighbour noticed that his return path has not been available since a local TV and BB outage a few weeks ago. We have updated STBs for interactive services and are serviced by Bromley.

I have also been told by TS (UK) that the UBR has low utilisation (~13%).

I have an engineer coming out on Saturday and would like to make sure that he checks the cabinet equipment. Should I ask him to check the 'Return Path Modulator and Amplifier' as per:

http://www.cableforum.co.uk/board/sh...hlight=cabinet

?

Not sure if the 'normal' engineers have the ability to repair cabinet equipment so would like to check. Will the engineer have to make a request back to NTL to get another (network) engineer out to fix cabinet equipment? I have not got any reasonable info back from TS (UK or India) on this question.

Any help would be greatly appreciated as this is now driving me nuts! The last engineer said that he did not know what the problem was when the modem failed to come up - should he have tried to diagnose the problem from the cabinet? or is that left up to somebody else?

Thanks
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Old 09-08-2006, 19:07   #2
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Re: Return path problems?

Whenever I've had an engineer, they've seemed to spend more time at the cabinet than at my house. Since most signal issue eminate from cabinet settings, and that is the crux of most faults other than simple modem / STB dying, engineers who can't touch cabinets would be rather silly.
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Old 09-08-2006, 20:00   #3
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Re: Return path problems?

Quote:
Originally Posted by MrDuck
Hi,

I've had BB disconnects happening continuously for approx. 6 months.

So far:

1. New external cable pull - RG11 - ~90m
2. New internal cabling - RG6 (i think)
3. Ambit (NTL 250) modem (same as original) replacement - same problems

I have to connect directly to the incoming coax, without a splitter (to STB) to get some sort of BB service. It will stay up for undetermined periods with usually one or two disconnects per day - sometimes down for hours at a time.

I have tried 3 types of NTL splitter: 3.5 dB (red writing on label), 3 dB (blue writing - from memory - engineer took this one back, so can't confirm) and an isolated 2 way (green label, chunky). I also now have a 6dB forward path attenuator, square type, FLD5W (not currently used). Any splitter in the signal path kills my BB. The FP attenuator does not seem to greatly affect the uptime of the modem, when used.

Here are stats from modem - note upstream power level:

Downstream Lock : Locked
Downstream Channel Id : 2
Downstream Frequency : 586750000 Hz
Downstream Modulation : QAM64
Downstream Symbol Rate : 6952 Ksym/sec
Downstream Interleave Depth : taps12Increment17
Downstream Receive Power Level : 5.4 dBmV
Downstream SNR : 33.4 dB

Upstream Lock : Locked
Upstream Channel ID : 6
Upstream Frequency : 22000000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 2560 Ksym/sec
Upstream transmit Power Level : 61.0 dBmV
Upstream Mini-Slot Size : 2

It looks like a return path issue to me. We also have no return path on the STB when connected. My immediate neighbour noticed that his return path has not been available since a local TV and BB outage a few weeks ago. We have updated STBs for interactive services and are serviced by Bromley.

I have also been told by TS (UK) that the UBR has low utilisation (~13%).

I have an engineer coming out on Saturday and would like to make sure that he checks the cabinet equipment. Should I ask him to check the 'Return Path Modulator and Amplifier' as per:

http://www.cableforum.co.uk/board/sh...hlight=cabinet

?

Not sure if the 'normal' engineers have the ability to repair cabinet equipment so would like to check. Will the engineer have to make a request back to NTL to get another (network) engineer out to fix cabinet equipment? I have not got any reasonable info back from TS (UK or India) on this question.

Any help would be greatly appreciated as this is now driving me nuts! The last engineer said that he did not know what the problem was when the modem failed to come up - should he have tried to diagnose the problem from the cabinet? or is that left up to somebody else?

Thanks
Yes it is a return path issue/problem. Your transmitting at 61dB this is to high ideally you should be no more than 55dB at the very most. Your connection is dropping out because of this. Why they haven't seen this on previous visit's i don't know. I know they do not have the correct test equipment but a quick look on the STB engineering screens or log into the modem would have flagged this problem before now. They need to come back test to see if it is a network fault and get it passed over oto the network guys if it is, pronto!
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Old 09-08-2006, 20:53   #4
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Re: Return path problems?

Thanks for your encouraging words.

It's hard to know what the engineers should be doing from this end. The last one just looked puzzled and told me that he wasn't sure what the problem was! He did have a T-shaped, yellow test meter in a grey case and did test the signal levels with that. I have thought since then that even if the meter shows 'good' readings that the modem might still be having problems as the electronics might not be up to the same standard as the test equipment. Do the meters actually simulate modem negotiation upstream as the DOCSIS standard requires? If the modem shows 61dBmV then that is the level the modem requires to make a connection, so it's maxed out and on the edge of a nervous breakdown - much like myself as far as BB goes. 'Scuse me if I'm talking gibberish as I'm not NTL compliant.

Thing is they might have realised but thought that it could be cabling etc. and have left the worst (most expensive fix?) till last. Although, I have not heard them mention the return path specifically, so will highlight it this time.

I did notice that the connection uptime improved today as the sunlight moved off the cabinet. It is in shadow for 2/3 of the day. Somebody else mentioned that heat can cause problems with some (failing?) equipment. Could just be coincidence.

One last thing - nobody in TS or CS seems to know whether 'network engineers' exist or not. I have asked for confirmation and they have said that they don't actually know the answer or that there is only one type of engineer. I did then ask who fixes the UBRs and network equipment etc. and they just went quiet on me ... lol. So as a customer, I feel that I'm hitting a brick wall. Is it possible to be transferred through to a person who is specifically technical as opposed to being baseline support?

Thanks again.
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Old 11-08-2006, 21:22   #5
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Re: Return path problems?

Quote:
Originally Posted by MrDuck
Thanks for your encouraging words.

It's hard to know what the engineers should be doing from this end. The last one just looked puzzled and told me that he wasn't sure what the problem was! He did have a T-shaped, yellow test meter in a grey case and did test the signal levels with that. I have thought since then that even if the meter shows 'good' readings that the modem might still be having problems as the electronics might not be up to the same standard as the test equipment. Do the meters actually simulate modem negotiation upstream as the DOCSIS standard requires? If the modem shows 61dBmV then that is the level the modem requires to make a connection, so it's maxed out and on the edge of a nervous breakdown - much like myself as far as BB goes. 'Scuse me if I'm talking gibberish as I'm not NTL compliant.

Thing is they might have realised but thought that it could be cabling etc. and have left the worst (most expensive fix?) till last. Although, I have not heard them mention the return path specifically, so will highlight it this time.

I did notice that the connection uptime improved today as the sunlight moved off the cabinet. It is in shadow for 2/3 of the day. Somebody else mentioned that heat can cause problems with some (failing?) equipment. Could just be coincidence.

One last thing - nobody in TS or CS seems to know whether 'network engineers' exist or not. I have asked for confirmation and they have said that they don't actually know the answer or that there is only one type of engineer. I did then ask who fixes the UBRs and network equipment etc. and they just went quiet on me ... lol. So as a customer, I feel that I'm hitting a brick wall. Is it possible to be transferred through to a person who is specifically technical as opposed to being baseline support?

Thanks again.
Well your question about there being any network engineers to the CS and the response or lack of it does not surprise me at all. Without wanting any sympathy this is about the whole attitude of most people in NTL, they haven't a clue what we are, who we are, what we do ect.

Anyway back to your problem, yes the meter that the service technician will have will only measure the forward downstream levels in a very basic way,(these meters were recently purchased and would have been excellent when CATV service started with analogue about 15years ago, but thats another story) they cannot measure the upstream frquencies or test the power levels as they haven't the equipment to do this,(again certain service technicians in some areas did have the ability to do this but when these new meters, as previously mentioned were purchased they decided to take this test equipment off of those Tech's who had them so that all Tech's accross the country had the same basic test equipment regardless of wheather the what they had previous was far superior but maybe older,again that is another story).

So what they have to rely on is the diagnostics on the STB or modem to tell them what the device is connecting at back at the UBR or intersect, unfortunately some STB's and modems might be faulty and not give a true reading so can be misleading,(obviously NTL have got rid of test equipment or buying any more in favour of the service Tech using the diagnostics on the STB or modem to fault find or give them a clue as to what it is connecting at?).

Until it is recognised that you have a problem with the return path you will still have a problem. So unfortunately you need to ring again and try and convince them that there is a problem still.
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Old 11-08-2006, 23:42   #6
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Re: Return path problems?

Unfortunatly the service techs were screwed over in both training and test equipment so some of them have as little grasp of the intricacies of the upstream path as my 6 year old son. When the poor sod arrives tomorrow explain in simple terms what is happening and lead him by the nose so that he makes the conclusion that its an upstream problem hence he should put in a network referral for the network folks to come out and investigate properly, if needs be they'll then pass it through the proper departments until hopefully we can get a resolution for you.
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Old 12-08-2006, 07:54   #7
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Smile Re: Return path problems?

Hi i recentley been to a job where the return path was not great .All the levels were fine and my test meter said the same (i dont use the rubbish grey thin we were given) this time i found out it was the power supply changed the power supply and the upstream went back to 45dbmv Get the tech to change the power supply .If that does not work he will have to get networks out
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Old 12-08-2006, 12:37   #8
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Re: Return path problems?

Quote:
Originally Posted by Nedkelly
Hi i recentley been to a job where the return path was not great .All the levels were fine and my test meter said the same (i dont use the rubbish grey thin we were given) this time i found out it was the power supply changed the power supply and the upstream went back to 45dbmv Get the tech to change the power supply .If that does not work he will have to get networks out
Hi, was this a power supply in the local cab - or just the brick that goes with the modem?
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Old 12-08-2006, 14:28   #9
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Smile Re: Return path problems?

It was the modem power supply The customer had a modem change from a Ntl home 100 to a 250 the power supply was faulty causing return path prob Me and the network tech could not belive it
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