120M How does Virgin's Fiber network work?

lewisp8 · 31-12-2015, 22:39

Hi there, i am wondering exactly how virgin's fiber network actually works, I understand that the delivery of services to the property is provided via a coaxial feed, and i'm assuming that this then goes to a fiber enabled cabinet, similar to BT's FTTC network. However there are two types of VM cabinets in my area the small ones which are spaced about every 100M apart which i believe are just distribution cabs and the large cabinets. Which ones does the fiber actually go to? I ask this because i live in a rural location, that has VM on the street, but the large cabinet which i'm assuming is the Fiber cabinet is about 0.6 miles away from me and i'm worried that this distance may effect the speed i may be able to obtain. I'm currently not a customer as my house doesn't actually reach their network (only house in the whole village

), and thus their network will need to be extended by approximately 50M. Which apparently they are willing to do.

pip08456 · 01-01-2016, 00:45

You are pretty much correct in what you have posted but, the speeds delivered via coax cable don't drop the same as twisted pair (Openreach).

That is why VM have consitantly delivered higher speeds than other ISP's using the Openreach network.

Add to that the effects of crosstalk on Openreach cabinets and in the ideal world VM will be miles better.

Now the bad side.

VM are very slow when upgrades are necessary to solve capacity issues in certain areas but not others, it's very much hit and miss.

Stephen · 01-01-2016, 10:35

VMs full network is fibre, apart from the short length of coax to customer premises.

Unlike the Openreach network VMs BB speeds aren't affected by distance from any of the cabs. 99% of the time you will get the advertised speed, unless you are in a heavily congested area, for example near student accomodation or somewhere with a lot of customers.

jb66 · 01-01-2016, 10:56

Quote:

Originally Posted by Stephen

VMs full network is fibre, apart from the short length of coax to customer premises.

Unlike the Openreach network VMs BB speeds aren't affected by distance from any of the cabs. 99% of the time you will get the advertised speed, unless you are in a heavily congested area, for example near student accomodation or somewhere with a lot of customers.

So its full network isnt fibre then....

tweedle · 01-01-2016, 11:08

Quote:

Originally Posted by Stephen

VMs full network is fibre, apart from the short length of coax to customer premises.

Unlike the Openreach network VMs BB speeds aren't affected by distance from any of the cabs. 99% of the time you will get the advertised speed, unless you are in a heavily congested area, for example near student accomodation or somewhere with a lot of customers.

Yeah...... That short length of coax is not always short, infact it's some times very long.

vm_tech · 01-01-2016, 11:19

Quote:

Originally Posted by tweedle

Yeah...... That short length of coax is not always short, infact it's some times very long.

What do you define as long?

tweedle · 01-01-2016, 11:21

Quote:

Originally Posted by vm_tech

What do you define as long?

500 meters plus...

vm_tech · 01-01-2016, 11:23

from a network side of things anything on that run will have amplifiers. And drop cables won't be anywhere near that long

roughbeast · 01-01-2016, 11:31

It has been said here that even if the link between the larger boxes you identified and the smaller boxes was fibre we wouldn't get a better service. As it stands Virgin architecture is fibre to the node, coax to the street box and then a shared coax to the premises. This is FTTN. Only if fibre is within 300m from the premises can it be referred to as FTTC.

The potential bottle neck with VM is the shared coax from the small street box to the premises. It only works because it depends upon most people on the coax not needing full capacity most of the time. Some people in congested well-subscribed areas notice a small drop in speed during peak times. As has been pointed out, those areas with oversubscribed street boxes do suffer less than the advertised speed quite a lot and get a lot of jitter.

vm_tech · 01-01-2016, 11:42

The drop cable from, let's call it the DP because some are underground, to the premises shouldn't be shared. It does happen though. Any "bottle neck" won't be due to the coax. The difference between the different coax that vm use are purely distance related not capacity related. The way to overcome utilisation issues are as some people on the forum call it "splitting the node". Which is kind of correct. Basically the more UBR ports that a node can use the more capacity. There are many ways of doing that, and I'm aware of a few different ways. But as a business VM will be looking at the cheapest and most efficient way of doing that. Without going into too much detail, I imagine fibre will be going deeper into the network. As I'm not sure what is and isn't open knowledge I'll leave it there

Eeeps · 01-01-2016, 17:23

Just looking at the downstream; for a cable modem running with eight bonded 256QAM channels it will always receive data at ~400mb/s. Unfortunately, those bits are shared amongst many modems.

Although the physical coax from the DP may not be shared, logically the data it provides is. This is why you can take your Super Hub next door (or even to the next street) and it will still work.

Coax cable (and the associated amps) have a limited bandwidth. Only about 120 channels are available on each cable segment. Unfortunately, most of these are used for TV so only about 20 are available to Broadband. This relates to about 1Gb/s of bandwidth available per cable segment. It is this limit that causes end user congestion (as it gets shared between more and more users).
If a cable segment is congested and all available channels are used, then the only fix is to physically split the segment in two (or more), thus reducing the number of users per segment.

MUD_Wizard · 01-01-2016, 17:51

Something like this..

Signal levels are adjusted on route to ensure you get a connection and inside the home if necessary.

Speeds are not affected by distance from the cabinet/node.

The speed you get will mostly be determined by the load on the downstream/upstream channels you share with other subscribers on the same node.

Cable uses a Docsis architecture, rather than BT's ADSL/VDSL system.

ADSL/VDSL is affected by cross-talk, which reduces speeds over distance on separate users telephone lines. Whereas VM users on the Docsis system share the same VM cable by use of "channel bonding".

Cross-talk explained:
https://www.youtube.com/watch?v=zkVmej4urx4

Channel bonding explained:
https://www.youtube.com/watch?v=X4-9ZtThZHs

VM supply a minimum of 8x2 channels on the Superhub 1/2/2ac cable routers (those cable routers are capable of 8x4 max) and usually anywhere from 10 to 16 downstream channels with a Superhub 3 (capable of 24x8), depending on the CMTS used in your area (Motorola, Cisco, Arris) and the number of fibres they've connected to that node.

Each 256 QAM downstream channel has 50 Mbps of useable bandwidth, shared between users on that cable. At a quiet time you should get your full tier speed. At peak times it depends on the utilisation levels in your area.

Upstream channels usually come in the form of two 16 QAM or 64 QAM channels, providing 17 or 27 Mbps respectively per channel, but since the upstream is shared between all users on a node (and possibly across nodes), the upstream is still traffic managed:
https://my.virginmedia.com/traffic-m...or-higher.html

vm_tech · 01-01-2016, 18:23

Fibre nodes only have 2 fibres connected. 1 forward 1 return. The segmentable nodes sometimes used can allow more fibres to be connected but I haven't seen this used in my franchise. Those nodes are no longer used as a solution for resegs.

DJSADERS · 01-01-2016, 18:33

Quote:

Originally Posted by Eeeps

Although the physical coax from the DP may not be shared, logically the data it provides is. This is why you can take your Super Hub next door (or even to the next street) and it will still work.

Kinda right however as long as your on the same area reference it will work most places.

i.e. when i lived in Aldershot that is area 26, and then when i moved to Guildford this is also area 26 so my kit worked even though it's a different head end

same principle in thames valley Bracknell is area 31 and i have seen customers who moved from Swindon which is also area 31 and they used their old kit until the account was closed.

lewisp8 · 01-01-2016, 20:06

Thanks for all the replies, so I'm assuming from what I've heard the larger cabinet is referred to as a node and basically the connection speed is limited by this and not the coax link. I also assume from what I've heard that this varies from place to place as some places are so what over subscribed, and the node can not supply the bandwidth required. Our node supplies a semi-rural village so I don't think the demand will be to bad, I don't know what the network is like in my area area code 31, and specifically Abingdon? It would appear that the network was originally built by a company called Comtel, which was then taken over by NTL.