One for the BT guys, curious about FTTC and phone service.

[plugwash]

With FTTC services AIUI your broadband is delivered though a VDSL connection that goes from your property, via the existing patch cabinet to the new FTTC cabinet. It then goes via fiber to the phone exchange.

What i'm curious about is what happens with the phone line. Does it get split out at the cabinet and sent down a traditional phone cable to the exchange or does it go down the fiber along with the data?

 

[SimonH2]

What happens is that your existing copper pair to the exchange still provides your phone service. But instead of the ADSL signal being added on at the exchange, they re-route things a bit.

With ADSL, the cable to your house ends up back at the "green box"* where it terminates on a terminal strip (a Krone 237 disconnect strip if you want the gory details). Also in the cabinet are a load of pairs back to the exchange. Within the cabinet, there will be a jumper wire (just a bit of single pair wire) that links your connection to a connection back to the exchange.
At the exchange end, all these pairs also terminate on huge patch bays - long ago they used wire wrap pins, now they also use Krone IDC punchdowns. I believe the circuit is routed to the ADSL equipment, and the ADSL equipment is then connected to the POTS** port of the exchange.

When you get your FTTC upgrade, they remove the jumper in the green cabinet. There will be a 'kin large multipair cable or two from the green cabinet to the new FTTC cabinet. Your phone line is patched out to the FTTC cabinet where it is connected to the subscriber port of the VDSL equipment. The POTS port of the VDSL equipment comes back down another pair where it is patched to your phone service from the exchange.

So the data service is : fibre form the exchange -> FTTC cab -> green cab -> your house
And the phone service is : copper from the exchange -> green cab -> FTTC cab -> green cab -> your house.

* They aren't all "green boxes", I believe some are underground and use different connections.
** POTS - plain old telephone service.

 

[SimonH2]

Oh yes, another difference between ADSL and FTTC.

With ADSL, it's normal for the end user to provide the ADSL modem/router - although it may well be provided by the ISP as part of the package.

With VDSL, I believe it's normal for OpenReach to provide the VDSL modem. You then need to connect via Ethernet and use PPPoE to sign into the service (normally using a router). I don't know if it's "permitted" to use your own VDSL modem.

Also, OpenReach will install a filter plate at your master socket - so you don't need any filters of your own. If you don't want to have the modem next to the master socket, there is a punchdown pair on the back of the filter plate to allow the signal to be piped elsewhere.

I've now done two of these for customers at work, and one of my colleagues. I'm "a bit jealous"
On the upside, at the moment we are down to have it available on our cab by the end of the year
I won't be hesitating to upgrade.

 

[Lectrician]

I have seen several VDSL modems appearing, so assume you're not tied to the supplied one.

All the old cabs I see in our area are full of the IDC jellies hanging in front of the krone strips. Looks like they do longer use the krone strips and prefer the jellies.

 

[Monkeh]

You're not tied to the supplied VDSL2 modem, but there have been challenges in getting replacements to work. There really is little point in changing it, though, because the supplied units (whether ECI or Huawei) work fine.

Love the back and forth stupidity with the POTS. It's about time they just ran VoIP out instead.

 

[bernardgreen]

Love the back and forth stupidity with the POTS. It's about time they just ran VoIP out instead.

POTS is the only phone service that will continue to work during a prolonged loss of power as it is powered entirely from the "battery" at the telephone exchange. VoIP requires power to be available at various locations along the route.

A POTS conversation has a fixed routing for the duration of the conversation, That is not he case for VIP the route and hence delay and speech quality will vary during a conversation carried by VoIP.

 

[SimonH2]

Ah yes, the cab full of jellies. I can imagine that, I've often wondered how the disconnect modules fare in an outdoor environment. The IDC termination itself is supposed to be gas tight, but there's a pair of contacts with fairly light pressure in each wire.

The back and forth for POTS isn't really stupid - seems to me it's a reasonable solution to the problem of merging the two services.

As for VoIP ... I work with it at work, and I don't think you want to go there en-masse. Perhaps as a closed infrastructure (as BT would like - BT to the house, BT hub, etc), but even then it would cause a lot of support issues. At the moment, it's all nicely concentrated at the exchange where it's easy and relatively cheap (bulk effects) to manage stuff. Move that management point to people's homes and it'll get harder and more expensive to manage - "is it plugged in ? Is the power light on ? ..."

 

[plugwash]

The back and forth for POTS isn't really stupid - seems to me it's a reasonable solution to the problem of merging the two services.

It's an expedient solution in the sense that it minimises the ammount of network changes needed but it also means that they are stuck with maintaining a copper infrastructure in parallel with the fibre infrastructure.

They are clearly doing voice over the fiber for the FTTH services, I wonder why they didn't do the same fo the FTTC service. Maybe it was because the FTTC service was introduced sooner and they were concerned about making it work reliably.

 

[SimonH2]

I'm not familiar with FTTH, but I strongly suspect that the voice is not VoIP. I suspect it could be something related to ISDN which (over simplifying things somewhat) merely moves the A/D conversion point from the line card in the exchange to the NTE.

Hmm, just had a very quick look and found this. It looks like voice over the fibre is optional (with mny providers sticking with copper for the phone service), and it also looks like it provides two channels. I would not be at all surprised to find it based on ISDN technology I was working with 20 years ago.

 

[Monkeh]

ISDN, properly controlled VoIP (note: Just because it's VoIP, doesn't mean they have to expose that to the customer).. doesn't matter, it's a far superior solution to maintaining miles of copper when there's already fibre in place.

 

[plugwash]

Doing some searching it looks like the voice over fiber service is VOIP based. Of course it's VOIP over a controlled network, not VOIP over the open internet.

AIUI BT 21CN is an entirely IP based network that is gradually replacing the older (ATM based AIUI) 20CN

I get the impression that many people have a negative impression of VOIP because of experience with VOIP on the open internet which is a cheap solution in more than one sense of the word.

 

[bernardgreen]

it's a far superior solution to maintaining miles of copper when there's already fibre in place.

Is it. Miles of copper cable can be maintained by a man with simple tools and a reel of cable. Introduce complex electronics and the maintainance requires specialist equipment and training to locate and repair or more often replace faulty equipment. ( a router is a fairly complex lump of electronics ).

Doing some searching it looks like the voice over fiber service is VOIP based. Of course it's VOIP over a controlled network, not VOIP over the open internet.

Voice over fibre has to use the data equipment connected to the fibre so the voice has to be encoded in a compatible format and has a full audio bandwith up to ( from memory ) 20 kHz. Telephone quality speech need not go above 3.4 kHz so 16 kHz is wasted.

The encoding system used in telephone systems limits speach to 3.4 kHz and can carry 900 conversations on a single pair of copper wires.

This link has a layman's explanation of how this is achieved.

http://www.portsdown-tunnels.org.uk/cold_war/repeater_station_info.html

 

[SimonH2]

Of course, another consideration is that with FTTC it should be possible to have a "data only" service and not use any copper back to the exchange (only to the local box). With the voice over <whatever>, this should in theory allow a significant saving in copper and exchange space.

What's the odds on this not being an option !

 

[Bodgeitandleggit]

There is a small exchange Deddington which has gone FTTP for the whole exchange and getting up to 300meg... wonder how the costs/payback is standing

http://www.thinkbroadband.com/news/5126-deddington-to-be-first-fibre-only-exchange-in-uk.html

 

[SimonH2]

There is a small exchange Deddington which has gone FTTP for the whole exchange ...

There just isn't an emoticon to express how jealous I am of that On the upside, the new cabs have started to appear in my town and we're down to have FTTC available by the end of the year