Virgin Media - how does it all work then?

[browney]

So what are those green boxes that are only about 20inches tall what are those?

also there is a building 1.6miles from me that has virgin media written all over it and it has about 6 satellite dishes (big ones) outside.

What is that building?

[Sephiroth]

Originally Posted by digitalspace

Downstream / nodes / etc, they're all terms I understand but not in the context that Broadbandings is providing.

A nice simple diagram showing actual cables used between distribution / conversion points would be awesome. Take this for example, if the green cab is a simple RF amplifier and nothing intelligent, and all the fancy stuff lies in the UBR in some building somewhere, then why is it seemingly so difficult to upgrade an analogue cabled area to a digital service? Surely all it takes is to pull the fibre cable from analogue UBR and plug it in to a digital one?

Originally Posted by Broadbandings

Rather than using additional fibre to produce new nodal areas one can also use WDM / wave division multiplexing and digitise the analogue signals at for transport down the WDM'd fibre and decode back to analogue when they reach their destination for delivery to CPE or CMTS depending if downstream or upstream.....

You made me re-read Broadbandings' helpful update to the NTLWorld diagram and I came up with the above quote.

What's this about "analogue" in the broadband transport chain? Where is it analogue? Which equipments are analogue devices?

[Impz2002]

Originally Posted by browney

So what are those green boxes that are only about 20inches tall what are those?

also there is a building 1.6miles from me that has virgin media written all over it and it has about 6 satellite dishes (big ones) outside.

What is that building?

The tiny green boxes are BT AFAIK or are Telco cabinets of some sort.


The building you are refering to is a Franchise head end. This is where the UBR's are all connected to and where you will find the equipment that provides all the TV / VOD / Connection to VM's Backhaul for broadband connections. These regional centres are then either fed from Bromley or Langley Super-headends where all the content for TV comes from.


This is as far as i understand it and without any too technical terms

Impz

---------- Post added at 12:31 ---------- Previous post was at 12:29 ----------

I am sure Broadbandings will correct me if i am wrong as he is the man with the real technical knowledge

Impz

[Ignitionnet]

Originally Posted by Sephiroth

You made me re-read Broadbandings' helpful update to the NTLWorld diagram and I came up with the above quote.

What's this about "analogue" in the broadband transport chain? Where is it analogue? Which equipments are analogue devices?

The cable side of the CMTS / uBR outputs analogue signals, these are combined with the analogue outputs from the TV multiplexers and used to modulate the downstream laser.

Digital information is encoded in analogue signals using QAM these outputs are then used to modulate the downstream laser's output.

Lasers don't just have to be on or off

---------- Post added at 13:31 ---------- Previous post was at 13:24 ----------

Originally Posted by digitalspace

Take this for example, if the green cab is a simple RF amplifier and nothing intelligent, and all the fancy stuff lies in the UBR in some building somewhere, then why is it seemingly so difficult to upgrade an analogue cabled area to a digital service? Surely all it takes is to pull the fibre cable from analogue UBR and plug it in to a digital one?

The RF amplifiers have certain specifications.

For example, this kind of thing may well be what's used in analogue areas. If all that 550MHz is used up there's no space to put the digital signals.

Yes a straight switching over, unplug one input and plug in the other would be ideal but the people who receive analogue cable in the area might get a tad upset at their TV just going off like that

The upgrades in areas with restrictions on amplifiers usually consist of replacing the amplifiers with higher rated ones that go to 750 or 860MHz, and depending on the quality of the coax in the network this may necessitate replacing that as well as higher frequency signals don't travel as well as lower frequency ones.

[Sephiroth]

Originally Posted by Broadbandings

The cable side of the CMTS / uBR outputs analogue signals, these are combined with the analogue outputs from the TV multiplexers and used to modulate the downstream laser.

Digital information is encoded in analogue signals using QAM these outputs are then used to modulate the downstream laser's output.

Lasers don't just have to be on or off .

Not being clued up on the insides of VM cable, I was surprised to see the word "analogue" there. Now, you're rarely wrong at this level of discussion. So any further knowledge tap from you would be appreciated.

Since analogue bandwidth is several times larger than digital channels and I'm told that RG (where I'm served by VM) is a digital solution, I would have expected to see digital bit streams (especially because of HDTV) modulated by QAM.

So what's this analogue stuff?

[altis]

All digital signals are analogue really if you look at them close enough.

[Ignitionnet]

Originally Posted by Sephiroth

Not being clued up on the insides of VM cable, I was surprised to see the word "analogue" there. Now, you're rarely wrong at this level of discussion. So any further knowledge tap from you would be appreciated.

Since analogue bandwidth is several times larger than digital channels and I'm told that RG (where I'm served by VM) is a digital solution, I would have expected to see digital bit streams (especially because of HDTV) modulated by QAM.

So what's this analogue stuff?

QAM is analogue, and the bit streams are encoded into QAM channels. Pure digital / baseband has a spectral efficiency of 1 bit per Hz, 256QAM has an efficiency of 8 bits per Hz. No real competition.

Analogue TV is 8MHz per channel, digital TV is digital streams encoded into analogue for transport. Once the QAM has been decoded it will produce 1s and 0s.

http://en.wikipedia.org/wiki/Quadrat...ude_modulation

This is a nice image.



Each grouping in the lower right indicates 8 bits of data, there are 256 possible points in the constellation, 2 ^ 8 = 256. The signal that arrives at the decoder is actually 2 signals 90 degrees apart in phase, the decode splits them and decodes them, one into the horizontal axis on the constellation, one into the vertical axis, 16 possible values for each signal, that produces the 8 bits per Hz.

[digitalspace]

Confused again.... Does anyone have a pretty diagram of how VM supply my house with broadband?

[Sephiroth]

Originally Posted by digitalspace

Confused again.... Does anyone have a pretty diagram of how VM supply my house with broadband?

You're right. I've taken this off to a separate thread.

I think, for now, we have a picture from the earlier parts of this thread as to how VM supply your house.

When Broadbandings and I have sorted out this crazy detail, I might get onto Visio and update what's been posted in this thread.

From my perspective (and I suspect yours) we really want to get to the bottom o whether or not the transport path from modem to centre is as efficient as possible (i.e. handles optimum bandwidth).

[digitalspace]

That Visio would be great

I'm looking at my green box outside, and wondering where that connects to, and how. Hmmm. I live in Southampton, if that helps.

[Dave9946]

Hmm, interesting reading (dont blame me for this I never dug the thread up lol). But in theory should'nt virgin now be able to know down to a single street how much potential bandwidth capacity that street has based on houses in street, current customers in that street and potential customers in that street based on the size of the street?.

So if our street has reached a potential limit bandwidth capacity wise for both tv & broadband services and any current customers start to upgrade internet speeds or make more use of on demand\catch up services to go above capacity then is'nt it very wrong to singup new customers that they know there is no free capacity for knowing there is a potential risk of disruption to services to current and all customers on our street if they did?. There only options would therefor be to invest to freeup capacity (to expensive) or to restrict services dramatically to current customers but dont tell them there services are being restricted.

[Sephiroth]

Well, of course, they do know - exactly. Region, Area & Locality. I've said in many places what Dave9946 has said - before you buy, VM can tell you exactly what you can expect.

Now that would be honest!

What's more, they have the data necessary to tell each person who receives the dreaded letter what the usage parameters for the area should be.

They don't make apply the information they have in the interests of their customers and I find this questionable.

BTW, I've done Visio diagrams but I'm not satisfied that I've struck the right balance between detail and digestability. It needs something more than the Wikipedia diagram but lI'm struggling with where to draw the line. I might bbreak it up and put it into a PDF.

[pip08456]

Originally Posted by Sephiroth

Well, of course, they do know - exactly. Region, Area & Locality. I've said in many places what Dave9946 has said - before you buy, VM can tell you exactly what you can expect.

Now that would be honest!

What's more, they have the data necessary to tell each person who receives the dreaded letter what the usage parameters for the area should be.

They don't make apply the information they have in the interests of their customers and I find this questionable.

BTW, I've done Visio diagrams but I'm not satisfied that I've struck the right balance between detail and digestability. It needs something more than the Wikipedia diagram but lI'm struggling with where to draw the line. I might bbreak it up and put it into a PDF.

You've had over a year to refine it Seph!!!!!

[Dave9946]

So if there are issues with the tv services, freezing channels and even the on-demand services not working at all is'nt that another indication of an over stretched capacity for a given area?. And do the tv & broadband use the exact same strand (for use of a better word lol) of fibre optic or cable?. If not I'd sure love to know how 1 affects the other in that it's always the broadband thats gets the blame for problems and never the tv or phone services that virgin complain is getting used to much even though I'll bet more people have issues with the tv and phone than the net.

[pip08456]

Originally Posted by Dave9946

So if there are issues with the tv services, freezing channels and even the on-demand services not working at all is'nt that another indication of an over stretched capacity for a given area?. And do the tv & broadband use the exact same strand (for use of a better word lol) of fibre optic or cable?. If not I'd sure love to know how 1 affects the other in that it's always the broadband thats gets the blame for problems and never the tv or phone services that virgin complain is getting used to much even though I'll bet more people have issues with the tv and phone than the net.

In simple terms yes the same strand is used just as everything comes into your home (except phone) through the same piece of coax cable. Your STB receives exactly the same signals your Modem (hub) does but can only accept the TV signal it contains and vice versa.