NTL - how far from fibre?
 

NTL cable provides both TV and broadband. This is carried over fibre and coax. Where does the changeover from fibre to caox take place and what hardware is used to make this transition? What is the maximum length of coax that can be used and is this maximum the same for TV and broadband?

Re: NTL - how far from fibre?
 

AKAIK its fibre up until the street cab, this is where the change over happens. Not sure abt the rest, soz!

Re: NTL - how far from fibre?
 

There are different types of street cabs though, I doubt if they all have fibre to them.

Re: NTL - how far from fibre?
 

i was under the impression and i could be wrong its only the last little bit, ie from cab to house that isn't fibre :shrug: could be wrong though :)

Re: NTL - how far from fibre?
 

:shrug: I think it is fiber to the big three door cabs, from then out it is coax. I didn't see any fiber in the two door one at the end of my drive and the smaller flip top ones don't have any in them.

Re: NTL - how far from fibre?
 

A simple answer to your question is the fibre ends at the Nodal cabinet, the nodal cabinet usually feeds an area passing an average of 500 Homes. The Nodal cabinet then uses coax in both direction (forward and return path) to feed Distribution Amplifier cabinets and Distribution points.

The nodal amplifier contains an optical receiver that converts the optical signal back to an RF electrical signal that is the same as the one leaving the headend, it also contains an optical transmitter to take the return path RF from your set-top or cable modem and convert it into an optical signal to send back to the ubr.

One area thats probably not realised by many is between the headend and the node, is a hubsite. This is a building containing racks of equipment, and the optical forward signal in the case of TV is converted from optical to RF, and then back to optical to feed the nodes. The return path signals are also converted back to RF at the hubsite and split to various equipment for processing. (ubr, intersect etc) some frequencies/services are fed to another optical transmitter to be yet again converted and sent back to the headend.

So to put it into context the RF Television signals, both analogue and digital leaving the headend modulators undergo the following before they reach to customer.

RF fed to headend optical transmitter, down a bibre to the hubsite. Fed to an optical receiver for conversion back to RF, this signal is then fed to an optical transmitter and fed via splitters to individual nodes. The node then converts this optical signal back to RF to be distributed via DA/DP cabinets.

The return path/US is just the reverse process.................. :Yikes:

Re: NTL - how far from fibre?
 

Thanks for that Escapee. How long can the coax be after it leaves the nodal cabs?

Re: NTL - how far from fibre?
 

Interesting to see that to get Fibre to the Home the additional runs needed are not long (by comparison to say BT).

Re: NTL - how far from fibre?
 

A nodal cab is those big ones you see about 5 foot tall round and about with the doors on the front and side.

Re: NTL - how far from fibre?
 

Depends on what size of coax is used.

Re: NTL - how far from fibre?
 

There's a description with pictures here:
http://homepage.ntlworld.com/draig.goch/

Note: this site is Firefox unfriendly!

Re: NTL - how far from fibre?
 

Forgot about that site. Thanks for the Firefox warning, good job there is an option to open in IE in the right click menu.

Like that bit in the "connection from the home to the headend" page which talks about allowing future fibre to the home upgradability. Will it ever?

Could extra fibre be run from the nodal cabinet back to the hub and headend to allow VSDL over the NTL network?

Re: NTL - how far from fibre?
 

Spot on, also there are 2 seperate issues here. The coax between node and DA/DP and the coax from DA/DP to the customer.

Most of us are now aware that distance from the home to the cabinet and level available at the tap port affect what coax is used for the drop cable to the customer. Also remember that attenuation at higher frequencies will also affect the choice of cable, to put it into simple terms a customer with x amount of level with a cabinet outside his front door compared to a customer with x amount of level and a far away cabinet would need different cable. The customer with the cabinet directly outside would not be affected as much with slope attenuation as frequency increases.
(The type of cable used has very little affect on attenuation at the return path/US frequencies because the frequencies are low)

The choice of cable between cabinets is a similar situation, the original ntl areas can generally use around 2 or 3 different sizes, and the choice is more to do with distance between cabinets than levels. The Distribution amplifier not only has to amplify the signal but also has to compensate for the slope by amplifying more at higher frequencies. The amplifiers have a device known as an "cable equaliser" plugged in to compensate for the cable loss. The frequency response of the equaliser would be exactly the opposite of the cable it is compensating for. Another point to consider is how many times they are splitting the signal from the Node/DA cabinet to feed other cabinets, every time you split in the real world you will lose aalmost 4dB. Sometimes the split is not equal as one cabinet may be much closer than the other to be fed, in this case they could use a directional coupler. If it was say an 8dB directional coupler there would be about 1.5dB loss in the through leg and 8dB on the tap leg. All of this would depend on the planning and topology of the area, but generally cabinets further away would have larger hardline coax (750 or 860 series) to keep the slope attenuation within a manageable figure, and cabinets closer would use smaller hardline (500 series) for cost efficiency.

The HFC network is far more complex to understand than first appears, there are lots of other consideratiuons for derating amplifiers in cascade, cascade noise figures, and thats without even thinking about all the return path headaches. :D

Re: NTL - how far from fibre?
 

The 750/860 are absolute *******s to pull in arghh!

Re: NTL - how far from fibre?
 

I wonder if anyone has got hardline as their drop cable because they are so far from the cab.

Re: NTL - how far from fibre?
 

Ignore the jargon and bull****. Simplified; If you are in an ntl area you are rarely more than a couple of hundred metres away from a nodal cab.

You are not always fed from a hub site, in fact Kirklees only has one hub site, In fact if you are near a hub site - good for you.

from a nodal cab (ex cabletelarea) there is a DA cab which you may be fed from.failing that it will be a DP cab. But its no great shakes. Like I say it's never more that a few hundres metres. Can't speak for other franchises but they're never that different.

Re: NTL - how far from fibre?
 

I wonder if you have ever seen 860 used overhead strung between telegraph poles! Thats what we used on the broadband system in the Rhondda valleys. They never used flexible tails either, and the amplifiers didn't have seperate modules. When the amp went faulty you had to remove the 860 cable and replace the complete amplifier housing :Yikes:

It was quite often that we used to find customers fed from the wrong cabinet, the install crew would install to the nearest cabinet and that was possibly not the one on their install sheet. That always makes me laugh when people refer to records and figures!

We also found quite a few wrongly labelled Node to DA cables, it was never noticed until the return path became more of an issue. I heard they had a problem getting a nodal cabinet to work in Swansea earlier last year, they spent 3 days loooking at a return path fault, only to realise they had connected it up to the wrong card and were looking at the US/return signal from a different node.
I laughed when the guy started telling me about the 3 engineers working on it and what problem they had because it was quite obvious in about 5 minutes what was wrong, he was giving me the story to see if I could guess!

That was after a resegmentation. :D

Re: NTL - how far from fibre?
 

I dread to think, scary...

Re: NTL - how far from fibre?
 

Just can't get the staff these days eh mate ;)

We've a couple in Leicester, mainly where someone has sold half of their back garden and a new house has been built on it.

Re: NTL - how far from fibre?
 

Very interesting point made "Fibre to 500 home level allows future upgrade to fibre to the home" - did the original poster see this? (sounds like he was leaning towards it)

Re: NTL - how far from fibre?
 

I've been an advocate of fibre direct to home for a long time but realistically I don't see it coming for a long time.

A "drop fibre" would have to be armoured to the hilt. If someone was to dig up and damage the fibre running through their garden the first thing they're going to do is a have good nose at it. Imagine the fun that claims direct, the accident group or any of the other lot would have with the blindness that could result. That armouring would make the cables difficult to work with weight and flexibility wise, not to mention could end up making it physically larger than the existing cables which means less cables in a duct so more duct needed.

There would have to be some form of optical splitters in the street cabinets. That causes a whole new range of problems, splitting light generally causes alot more loss of signal than splitting RF this would mean that the lasers firing into the fibre would have to be a lot more powerful so more expensive, also the folks working in the cabinets currently have difficulty in putting covers back onto unused RF ports, theres no reason to believe that they'd be anymore conscientious with fibre splitters so again we have laser energy bouncing around ready to blind the unwary.

Fibre splicers tend to be experienced, qualified and in short supply, unfortunately many of the current crop of installers are the the opposite, so you've got to train a whole bunch of folks on something that no disrespect meant to any installers on the forum many of them wont be able to grasp.

I could add to the list of problems indefinitely, non of them are individually insurmountable but it comes down to one thing, cost.

Despite the continuing reduction in the price and physical size of the electronics and the fibres its still a huge cost. Which with the rate that data encryption/encapsulation technology is evolving isn't yet warranted. In the last few years on a pair of copper cable we've gone from 56K through ISDN, DSL, ADSL who's to say what will be out in the public domain in the next few.

Re: NTL - how far from fibre?
 

The 500 home level was always original ntl ie: cableTel architecture dating back to the mid 90's.

They started building nodes at the 500 home level, and then later as money was short (long before chapter 11) they increased new build to 1000 homes. They did some other strange things in Wales to save cost, like having no mains installed at one node but using Line power down the coax (like a DA is fed) from another node. We all shook our head at the cost saving and we were proved right when they had to revisit and rebuild some of these areas/nodes because they were too large for targetted services like Cable Modems, Interactive and proposed VOD.

There was talk many years ago, that fibre to the home would be a long way off because of many of the problems that stu038 mentioned above, and they would probably move the fibre out closer to the customer by making the distribution amplifiers nodes. That would take nodal homes passed to somewhere nearer the 150 home level (average guess). this would however mean using more fibre that's a short supply commodity in the nodal rings, or using DWDM from hubsite to the existing node then diplex each wavelength to the corresponding nodes. This would mean very little change to the existing architecture compared with FTTH, but would effectively increase the bandwith because the services could be targetted at a 150 home leven instead of the 500 home level.

If you do enough digging, I would bet my pension the 500 home figure was being suggested by the equipment vendors at the time. I remember seeing schematics in vendors leafets and ntl/cabletel planning/architecture would of taken advice from these people, as they were supplying equipment for build all across the world.

If you really got to the bottom of the 500 home figure

Re: NTL - how far from fibre?
 

You could do the last 100m in CAT5e and still get 1Gbps in each direction. I'm sure that would keep everyone happy for quite a while. ;)

That would mean everything running over IP mind - just a minor detail! But you wouldn't need much in each cab - just a relatively cheap ethernet switch.

Re: NTL - how far from fibre?
 

Yes I did, mentioned it in post#12.

I realise that fibre to the home is problematic and won't happen for some time, if at all. I was more thinking along the lines of VDSL which can give up to 55Mbps download over shortish lengths of copper connected to fibre.

Some of the thoughts going through my head are:

VDSL via cablecos.

Duplicating fibre all the way to the nodes to provide double the capacity for TV and broadband.

Moving UBRs to Nodes.

Continuing fibre from nodes to cabs.

Having STBs that fetch TV from servers at the Hub (BOD) similar to VOD so that not all TV channels are sent to all customers, freeing up bandwidth for other purposes.

In a way it is a pity that there are competing platforms providing services. Just think of using satellite for most of the download for TV and broadband and cable or DSL for upload and return path.

There is a lot of talk around various forums of how far Britain is behind other parts of the World and I was wondering about the feasability of various methods of catching up.

There are two issues though, feasability and cost. Don't know which are feasable but all would be very costly.

Re: NTL - how far from fibre?
 

I disagree with your point about there being no hubsite!

Cardiff CA area has no seperate hubsite as it's located in the same building as the headend. I was aware that Kirklees had only the one hub, but will you agree/disagree with me that the hub contains DFB racks to feed the nodes. (ie: a hubsite in the headend)
This is because of the topology of the build, but is the exception to the rule as are the ex-cwc areas using EDFA's.

I have never visited Kirklees, but I understand they saved on building hubsites and YAG/DFB feeds forward/DFB return. One trade off is the increase in DFB's to feed nodes because the long lengths of fibre to some of the nodes means they are not able to split as many times.

Re: ian's post (#24)
 

Indeedy. You could have up to 20 small cabinets connected by a 10Gbps fibre ring to the hub. In each cabinet would be a switch like this to connect to up to 48 homes with 10/100/1000 Mbps CAT5e. The ring would provide redundancy in case of a switch or fibre failure. Each of the 1000 homes could be watching a different TV channel and there'd still be bandwidth to spare.

But look at the price of the switches :eek:

Re: NTL - how far from fibre?
 

The term bandwidth can be used for several different things, so to explain it in easy to understand but not quite accurate ;) terms for those who don't know anything about it.

In this instance there are two types of bandwidth;

The first is the frequency bandwidth also called the frequency or RF spectrum this is restricted to a set number of frequencies by physics, in a network such as ntls and Telewests this is termed a Carrier as it carries the TV signal or the data for the modems etc. and is measured in Hertz, MHz KHz etc

The second bandwidth is the data bandwidth which is about the amount of data that can be carried within each carrier measured in the good old bits and bytes Mbs MBs etc

The restriction in the HFC networks isn't on the physical coax but the frequency range of the amplifiers themselves many of which only go up to 750MHz, this means that the majority of the frequencies available are already being used by the cablecos, as well as stuff already in the home such as VCRs, DVDs, STBs etc.

To take Ianathuths suggestions one at time;

tbh I don't know enough about it to comment.

again the restriction isn't the capacity of the fibres to handle the traffic but the electronics that feed into the lasers, if you had two fibres going into a single node you would still only be able to use the same frequencies once unless you doubled up the optical receivers amps etc and redesigned/rebuilt the network, which would be extremely expensive.

No real benefit gained on this one, we've already said that bandwidth isn't the issue on the fibre, the continuing work to resegment is increasingly resulting on a single 500 home area having its own uBR in the hubsite moving it into a street cabinet makes an extremely expensive bit of kit vulnerable to the vandalism etc that all the cabs are subjected to.

This is currently happening, a lot of the 500 home areas are being broken down to smaller groups, this is being driven by BB but will in the future hopefully be driven by VOD.

Very good idea, one that I'm sure is being investigated possibly in line with Altis' suggestion about CAT5e but again the existing coax is a lot more robust for the ducting and gardens and iirc is capable of a better response over longer distances than CAT5

Again a good idea but I'm not convinced that the monopoly and mergers commission would agree :(

Re: NTL - how far from fibre?
 

Lets not fall out here but Escapee is correct, most Headends have a hubsite that was built into them as part of the original DTV project because at the time they had legacy areas that were not capable of carrying DTV.

Re: NTL - how far from fibre?
 

NTL now use 2 different grades of cable from DP to property these are RG6 and RG11, they uses to use RG7 but not anymore.

RG6 is good to about a distance of 100m from the dp to the house, so long as there is only 1 piece of equipment running at the property, but this distance can be reduced by many things such as, age of cable, type and quality of connectors used, any sharp bends in cable etc etc. If more than one device is been used than RG11 would really need to be pulled, but it all depends on signal reading at the time, what is good in one area is not always going to be good in another area a lot depends on the network.

RG11 can be pulled up to about 150-200m depending on how many deviced are going to be used on the pull, and how many splitters etc etc are going to be used, there is a 3.5db loss through each leg of a splitter so this has to be taken into account, but there shouldn't really be a need to have a cable pull that long anyway.

Once the cable is pulled, then there are seval taps that the cable can be connected to in the DP's all transmitting a different level, the installer will have available to them a choice of various atteniators/simulators and equalisers to put on the line to get the signal levels right and they should have a jelly bean chart to tell them what to use.

Re: NTL - how far from fibre?
 

Acropolis sorry mate but i will have to correct you before ntl get millions of people ringing them saying they want another cable putting in (ie rg11).

You can use RG6 upto 170M with 1 device and upto 4 devices within 130M of the node. On RG11 you can go to 250M with 1 device and to 200M with 4 devices.;)

NB devices are SACM or CATV not telco.

Re: NTL - how far from fibre?
 

i would agree with Acropolis 130m would be the max for one device ie modem would be out of spec for digi anything over 130 needs rg11 to keep within ntl spec

Re: NTL - how far from fibre?
 

fair enough, but you try getting four devices to work at 130m and i will take ya word for it, on paper may be, but in the street you aint got a chance of that happening, i have had cables repulled for rg11 at 90m.