General : Virgin Media Network Quality

[thenry]

Why does the network (which can deliver a lot) lack quality? Why does the network have limitation on upload? In simple terms please. Theres so many whys as to why! the network isn't running as well as it could, may be?

[Sephiroth]

TH

I think you need to define the term "quality" as you see it for the purpose of the question.

I can certainly answer the question as regards upload limitations. In simple terms (I can explain it in much greater depth), the upstream operates in a noisy-ish (susceptible to noise) part of the frequency spectrum. Accordingly the packing density of upstream data is lower than downstream so that the potholes created by noise can be corrected at the CMTS. The frequency range is prescribed by international bodies.

The only way of increasing upload speed within these limitations is to bond upstream channels.

[thenry]

The sort of quality on openreach fibre. would DOCSIS 3.1, on a new spectrum be the only answer? or can DOCSIS 3 be worked on. Bonding aside, could VM do other things?

[qasdfdsaq]

Originally Posted by Sephiroth

I can certainly answer the question as regards upload limitations. In simple terms (I can explain it in much greater depth), the upstream operates in a noisy-ish (susceptible to noise) part of the frequency spectrum. Accordingly the packing density of upstream data is lower than downstream so that the potholes created by noise can be corrected at the CMTS. The frequency range is prescribed by international bodies.

There's also a lot less of it.

---------- Post added at 12:04 ---------- Previous post was at 12:02 ----------

Originally Posted by thenry

The sort of quality on openreach fibre. would DOCSIS 3.1, on a new spectrum be the only answer? or can DOCSIS 3 be worked on. Bonding aside, could VM do other things?

1) It's a shared, CSMA-TDMA network. Openreach fibre is not. Every modem has to guess and randomly try to send data requests on VM. On Openreach fibre anyone or any step wanting to send data can always just send immediately.

2) It's a RF hack over a coaxial network. You're basically shoving a ton of wifi signals down a copper cable instead of an antenna. Fibre is, well, fibre using purpose-made Ethernet protocols.

[Qtx]

Originally Posted by qasdfdsaq

There's also a lot less of it.[COLOR="Silver"]

The width of the spectrum is small?

[ferretuk]

Originally Posted by qasdfdsaq

2) It's a RF hack over a coaxial network. You're basically shoving a ton of wifi signals down a copper cable instead of an antenna.

Akin to the house<>cabinet link in FTTC, albeit with a reduced bandwidth, except the copper pair is less suitable for this application than coax...

I think the differences are more to do with the fundamental architecture rather than the technology used for the 'last mile'.

[Qtx]

Just to help me understand too, all these limitations are with VM's actual fibre structure and nothing to do with the coax part? Does the Coax part also add issues on top in a similar way as a copper line to the property?

[Sephiroth]

Openreach's solution for the upstream uses a totally different frequency plan. Someone can correct me but the upstream and downstream are in the same frequency zone somewhere like DOCSIS downstream. So upstream isn't as susceptible to RF noise.

For VM to improve upstream/downstream symmetry, and given that they cannot leave the specturm they're using on DOCSIS 3.0, bonding is the only uplift solution.

I'm not privy to VM's DOCSIS 3.1 plans. But a layman's description of what needs to be done fore the upstream can be found here:
http://www.lightreading.com/blog.asp...27176&site=cdn

This would put the upstream into half the space currently occupied by downstream, which would move further up the frequency spectrum. However, this would still not provide the same number of total channels for the upstream as there are for downstream. So bonding would be lower; QAM would be higher than at present and upstream speeds will remain asymmetric with downstream but will be higher than at present.

[Qtx]

Looks like you partly answered my question as I was typing it ferretuk

[Sephiroth]

Originally Posted by Qtx

Just to help me understand too, all these limitations are with VM's actual fibre structure and nothing to do with the coax part? Does the Coax part also add issues on top in a similar way as a copper line to the property?

The coax part, to my mind, is where the RF noise ingress occurs. Of course that does include the RF/Optical conversion node.

[babis3g]

Hi one question maybe out of all these
To my cabinet is going fibre cable, then from cabinet going to the property coax cable at the SH
Will SH operate normal (and give better quality to line) if this coax will replaced with fibre going to the property & so to SH?
Thanks

[qasdfdsaq]

Originally Posted by Qtx

Just to help me understand too, all these limitations are with VM's actual fibre structure and nothing to do with the coax part? Does the Coax part also add issues on top in a similar way as a copper line to the property?

Kind of both. VM's network uses the same protocols (with the same limitations) over both the fibre and copper part to the CMTS.

Openreach FTTC uses different protocols, both specific to each interface. In other words DOCSIS cable uses the same (RF) protocols over fibre whereas FTTC uses Ethernet on the fibre part.

---------- Post added at 13:03 ---------- Previous post was at 13:01 ----------

Originally Posted by ferretuk

Akin to the house<>cabinet link in FTTC, albeit with a reduced bandwidth, except the copper pair is less suitable for this application than coax...

I think the differences are more to do with the fundamental architecture rather than the technology used for the 'last mile'.

Agreed. Though technology used is inextricably linked to the architecture and vice versa.

[babis3g]

Quote:
Originally Posted by Qtx
Just to help me understand too, all these limitations are with VM's actual fibre structure and nothing to do with the coax part? Does the Coax part also add issues on top in a similar way as a copper line to the property?
Kind of both. VM's network uses the same protocols (with the same limitations) over both the fibre and copper part to the CMTS.

qasdfdsaq
Openreach FTTC uses different protocols, both specific to each interface. In other words DOCSIS cable uses the same (RF) protocols over fibre whereas FTTC uses Ethernet on the fibre part.

so to my query at post 11 will not make difference pure fibre instead of coax from cabinet to home unless it will be faster transmitted due to the advance of the fibre

[Sephiroth]

Originally Posted by babis3g

Hi one question maybe out of all these
To my cabinet is going fibre cable, then from cabinet going to the property coax cable at the SH
Will SH operate normal (and give better quality to line) if this coax will replaced with fibre going to the property & so to SH?
Thanks

To your cabinet is going coax from another cabinet which has the coax to fibre conversion.

So VM FTTH in coax areas is prolly not in prospect owing to the infrasytructure costs involved. They are piloting FTTH but I believe that it is pole strung fibre.

[babis3g]

thank you