Virgins Infrastructure
 

For no other reason other than curiosity I came across this link re Distribution of cable services.

http://en.wikipedia.org/wiki/File:HF...rk_Diagram.svg

The thing I would like to know is the limitations, in distance, from the Headend to the Distribution Hubs and what the connection cabling is, i.e. Cable or Optical??
Also, if I undestand this correctly, the 'Optical Nodes' in the diag. are in the VM Street Cabs.?

Sorry for being 'nerdy;, but that's just me :angel:

Re: Virgins Infrastructure
 

My Sticky Post in the VM Forums (Power Levels & SNR) explains a lot of this.

It works like this (but can vary in different parts of the country according to who was the original cable supplier):

1/
A small street cabinet connects either 16 or 32 customers. A larger street cabinet connects 48. It is passive equipment.

2/
The cable from a cabinet passes along to another cabinet configured as above.

3/
5 or 6 cabinets go to an optical node (with 240V labelled) and it's fibre from there. This cabinet is active.
or 96
4/
In high density population areas, you might get 20 coax cabinets feeding the optical node.

5/
The optical node originally would have supported only 2 upstream channels and these might have been split between two nodes at the VM end line card. So that's a heck of a lot of users who think they're getting, say 5 meg upstream sharing just 40 meg upstream capacity.

6/
A downstream bonding group currently has 4 downstream channels with c. 200 meg capacity to share across one or two optical nodes. VM intend that this should rise to 8 downstream channels. VM are also introducing bonded upstream channels.

That explains how over utilisation can occur.

The current infrastructure upgrade programme should double all the capacities I've mentioned. For high contention areas, VM should be adding more optical nodes and line cards and CMTS devices at their end to cope with the additional channels allocated. That's what they say they're doing.

7/
The optical node connects via fibre to a line card on a UBR/CMTS at the local hub. Many optical nodes terminate on a single line card. An individual's downstream and upstream (both shared with other users) terminate on the same line card and (AFAIK) in the same Service Group.

Re: Virgins Infrastructure
 

That doesn't quite answer his question - your description only covers between the home and the distribution hub (CMTS) and not beyond, which is what the OP was asking.

There is no real distance limitation between the headend and the distribution hub(s), it could theoretically be hundreds or thousands of miles. The cabling is all fibre, though in some special cases can be satellite. On modern networks your data connection gets split off at the CMTS anyway so the rest is primarily only used for TV these days.

Re: Virgins Infrastructure
 

I answered his final question properly knowing you'd fill in the rest.

The CMTS connections are cable.

Re: Virgins Infrastructure
 

Somewhat ambiguous/misleading or even incorrect I'm afraid. :(
Because being a "time based" slotted algorithm DOCSIS standard imposes an overall maximum "delay" limit of 0.8ms between CableModem and CMTS. As the velocity profiles/progation delays vary between Fibre and Coax and also the ratio between these may be different in the actual deployed HFC network then this for practical purposes limits the length to typically no more than 100 miles.

Re: Virgins Infrastructure
 

Perhaps the OP might find the diagram in the attachment useful.

Nice to see someone wanting to take a deep dive.

Let us know what you think.

Re: Virgins Infrastructure
 

Completely misleading or even incorrect I'm afraid.

The OP is asking about the bit beyond the CMTS. For modern data services it is routed via an IP network. It has nothing to do with DOCSIS or coax. There is no DOCSIS or coax involved.

Re: Virgins Infrastructure
 

I think Horse's info has indeed been helpful. For example, there are some very long fibre backhauls in Devon going into Newton Abbott. It helps complete the picture and the OP was clearly interested in the whole thing.

Re: Virgins Infrastructure
 

Well guys, many thanks for the information. It's a lot to take in at my age ....
I'll re-read some of the above several times and maybe, just maybe, some of it will stick :)

I always like to know these things, but that's not to say I'll ever fully understand it !!

P.S. Very nice diagram Seph, did you do this yourself ??

Re: Virgins Infrastructure
 

Audduxi - I did draw it in Visio myself, but it originates elsewhere (but can''t remember where). I've originated quite a few myself, but this one needed knowledge I didn't have a couple of years ago.

Re: Virgins Infrastructure
 

Yep definitely my bad, I to was reading more into the OP's question than he specifically asked! But I did say it was ambiguous. ;)
The Wiki diag possibly could have been more useful if it had included
(Master) Headend and (Regional/Mini/Local Headend, including CMTS's) Distribution Hubs hence covered by your answer. The spanner-in-the-works was the ancillary question regarding the O/E node & street cabs! :(

Clearly an opportunity for Seph to elaborate/extend his Visio diag perhaps? ;)

Re: Virgins Infrastructure
 

what I find dubious is seph's info on how many conenctions per cabinet? didnt you admit a while back seph some cabinets may have way more than your quoted figures?

my cabinet serves 100s of houses, whilst its true they may not all be connected, I find it hard to believe less than 100 would be connected as each cabinet around here serves many long roads.

Re: Virgins Infrastructure
 

Chrys

I thought ll that had been cleared up about the cabinets. The highest I've seen is 96 but I've seen photos of cabinets with splitters on the tap points. So in that respect Chrys is right - my list needs updating.

Maybe I'm mistaken, but aren't groups of 96 the way to allocate fibre spectrum?

Also, my uin depth survey of RG41 5 showed that there was one cabinet per 200 metres (approximately) on a long road. Also there was a similar distribution on homes passed for side streets and so on. No side street didn't have a VM box.

Re: Virgins Infrastructure
 

I think the amount of cabinets per streets I expect is dependent on when cable services were rolled and who did the rollout. My city had cable services very early, I have read in multiple places that early cable rollouts were bodge jobs not done properly. I have been driven around the streets round here and there is definitly not a cable box on every road, the one serving me appears to serve at least half a dozen streets including 2 long roads with over 300 houses on. Some of those houses also converted to flats and bedsits. My cabinet also is bigger than the pictures posted. Up until half a year ago the doors couldnt even close due to the sheer amount of cables and splitters inside.

On my road the only other cabinet is a BT cabinet, there is a VM cabinet right at the other end but this is a 2 mile road.

seph you have links to info's on street cabinet density?

Re: Virgins Infrastructure
 

Chrys

The best I can do is to attach the map I mad of my area. I now think that there are only three optical nodes - becasue I suspect that the ones I've marked at such are in fact powered launch cabinets.

You can see the number of houses per street, so the density is easily calculated!

Cheers