Quote:
Originally Posted by Womble
Yes the very same Bill. Reasons for my statements are, I have friend who was an SDH planner/manager for BT. He was privvy to meetings between NTL and BT about 21C. "We" are a BT partner in the 21c program, thats why I "believe" BT own/payed for it, plenty of their circuits running over it!!
---------- Post added at 09:32 ---------- Previous post was at 09:30 ----------
I was talking the other day and was led to believe there are two schools of thought, each has their own "Big Boy"
supporting it. The director that came from cable in the states whats HFC, the one that didn't whants Telco
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I made a couple of calls today to see what I could find out, it seems the HFC plan is the way they are going to go because of the cost imlications and the fact that they have a large customer base on that technology allready.
I was interested to hear again that there appears to be money to spend on the core national network but nothing at regional level even for maintenance, they are saying the regional people will be having further budget cuts. It certainly sounds like figures are being massaged and what little they can afford is being spent on the national network. I cannot see any investors putting money in and take a risk on ntl/TW, but I can see the either selling off the whole thing or perhaps offloading the poorly maintained cash starved regional networks to some unsuspecting company with less commercial/technical intelligence than ntl. (If such a company exiscts)
Anyway, it looks like they are committing to HFC because of the cost implications, the current plan is to use 4 off 8MHz 256 QAM Docsis downstreams per laser from a Dual Docsis MC28, and 4 off 1.6MHz 16 QAM upstreams.
The injection and combining sounds like a nightmare, apparently they haven't yet sorted out how the modem aquires the correct downstream, and how they are going to technically implement the proposal. The proposal has apparently been put forward by one of my favourite 'good old red neck college boy' (That may give you a clue) Unfortunately this guy is one of the survivors, in the position because his other job became redundant. (Another clue is none of the trials he was involved with running were either successful or implemented)
I had a laugh because apparently the highly qualified degree level doctor types are still unable to know how to measure the power in a digital channel, and one of the highly qualified fools seems to think 4 digital channels running 10dB down on the analogue launch levels is comparable to one analogue channel. They have managed to get closer to the answer by visiting one of the TW labs, unfortunately the characteristics of both the amplitude modulated analogue TV signal and the QAM signal means they cannot be reliably measure with a power meter without a peak reading sensor as a peak signal averaged over x number of measurement points to gain an average peak reading.
Clue ntl university boys with fancy degrees.... The 'A' in QAM stands for Amplitide, and the 'M' stands for Modulation. (No I dont know all the answers Mr 'B' but I dont ever claim to be clever)
There is of course concern from people who do have some practical experience and in depth knowledge of the HFC network, like are they going to re-align the return path to cope with all these extra signals that are now 16QAM instead of QPSK, or perhaps they are just going to let the lasers clip and run into distortion? If they are going to re-align is there enough headroom for the increased demand on signal to nopise required by 16QAM over the existing QPSK?
Also what about the 256QAM downstream signal to noise, this will require extra headroom to maintain the signal to noise performance, or perhaps you are saying the levels will be running higher than a 10dB delta on the analogues, and thats why the figure of 4 QAM256's per Analogue crept in.
I wonder what the cost will be for this lot, it sounds like a practical nightmare in many hubsites. I wonder if they have really thought about all the cabling and combining for the forward and return path this will require.
Chatting today about the plans and some of the people involved made it sound very much like a Heath Robinson set-up, run by a guy with a reputation for dropping a project and setting someone else up to take the blame just as it all goes wrong.
call me cynical, go on I'm asking for it!