FTTC – what exactly is it?

FTTC exchange rollout posts have attracted a huge amount of interest on this blog. More so in fact than any other subject I have posted on. There is clearly a demand out there for the faster speeds.

There isn’t that much info out there on what the proposition actually is so I am happy to remedy this. The following spiel has been pinched from the BT Wholesale FTTC Handbook (thanks to BT for letting me do this) .  This is normally only provided to ISPs who are reselling the technology/solution.

As is the nature of these things I have had to simplify the wording but if you see some complex technospeak it is probable left over from the original text. I’m afraid there is no getting away from the acronyms. The diags are BT (Wholesale & Openreach) originals.

FTTC Intro

Fibre To The Cabinet (FTTC) utilises BT’s 21st Century Network.  If an ISP already offers ADSL2+ services based on BT’s 21st Century Network  then it is relatively easy for them to extend this to also offering FTTC.  They use the same eCo Plus provisioning system for both.  For the ISP FTTC is just another ordering option in a drop down box.

FTTC, whilst using the same network from the exchange does have significant differences when compared with ADSL2+ not least of those being faster speeds.

FTTC does not, at launch, have the same geographic coverage as ADSL2+.  This is because the roll out to cabinets has only just started and will take some time to reach the same market penetration.  This also assumes BT will make the investment which is of course based on a business case for each exchange.

FTTC – General Overview

The BT 21st Century Network (known in this case as Wholesale Broadband Connect or WBC) provides Broadband services from the End User to one of 20 WBC interconnect points around the UK. ISPs, like Timico, connect to BT’s 21st Century Network at these interconnect points.

FTTC uses the same WBC infrastructure but offers an End User Access based on VDSL 2 technology (rather than ADSL 1 and ADSL 2+ on WBC). This End User Access provides a higher line rate of up to 40Mbit/s downstream and optionally up to 10Mbit/s upstream.

The main difference between the FTTC service and ADSL2+ Service is that the DSLAM (Digital Subscriber Line Access Module) is situated in an exchange building for ADSL2+ but for FTTC the DSLAM is situated in a cabinet in the street (the “Street DSLAM”). The Street DSLAM is served with a fibre back to the exchange to carry the Broadband signals.

The Street DSLAM is connected to the Street Cabinet using tie pair cables. VDSL 2 is used to carry the Broadband over the copper pair from the Street Cabinet to the End Users’ premises. See diagram 1 below.

Diag1 - FTTC architectural overview

Just like standard ADSL a single ISP buys the FTTC connection on the copper pair. This is necessary to ensure that the available bandwidth over FTTC is allocated for delivery of the best broadband speed technically possible to that premises. More than one copper pair connection can be provided to the premises if the end user requires additional FTTC services.

The baseband voice service can be provided by either the same ISP or a different Communications Provider.  The baseband voice service runs over the existing copper network using Wholesale Line Rental on the same copper pair as used by FTTC. This replicates the WLR + Single Metallic Path Facility model where FTTC replaces SMPF.

Note SMPF is the basis of the whole Local Loop Unbundling market.

FTTC local access network

diag 2 FTTC local access network

Note also BT does not yet offer voice services over FTTC (as opposed to the baseband voice service running over copper) but there is nothing to stop the ISP doing so.

FTTC Available Line Speeds

FTTC offers the following VDSL2 line rates:

- Up to 40Mbit/s downstream, with up to 2Mbit/s upstream

- Up to 40Mbit/s downstream, with an optional up to 10Mbit/s upstream.

BT guarantees a minimum 15Mbps downstream provided the connection passes certain tests (enhanced Managed Line Characteristics (eMLC)) and provided issues are reported within 28 days.

The actual rates that can be supported on any individual line are influenced by two main factors. Firstly the distance of the copper connection from the End User’s premises to the Street Cabinet and secondly the number of End Users signed-up and using the common cable which will determine cross-talk noise impact. Either of these two factors may result in the End User experiencing a drop in the speed from what was originally achieved.

The table below sets out the initial WBC FTTC End User Access options  (ie speed options) for the FTTC Service.

FTTC access options

Table 1 - FTTC access speed options

 

 

 

 

 

 

 

 

FTTC Installation

The installation must currently be performed by BT Openreach who contact the End User before the booked appointment to discuss the proposed installation and confirm the appointment slot.

The engineer will call the End User on the day of appointment prior to starting work at the Street Cabinet but will not commence work unless the End User has confirmed their or their agent’s availability.

Openreach engineers only fit the Openreach Active Network Termination Equipment and Openreach VDSL modem. ISPs will typically supply their own routers which simply plug into the Ethernet port of the VDSL modem.

At the End User premises there are two aspects to the Openreach installation.

During the installation of the FTTC service the Openreach engineer will fit a Service Specific Front Plate to the existing NTE5. Where no NTE5 exists, Openreach will install an NTE5 within 3 metres of the entrance to the End User premises. Where an external NTE exists  Openreach will install an NTE5 with service specific front plate internally immediately adjacent to the external NTE.

A service specific front plate splits the delivery of telephony and DSL signals at the NTE5, delivering each service to a separate port on the socket. This terminates the DSL signal at this point, meaning the signal is not received on any telephone extension sockets that may exist.

Fig 1 Service Specific Front plate for FTTC

Fig 1 Service Specific Front plate for FTTC

 

A VDSL2 modem will be supplied and connected to the data port of the service specific front plate. This is an active NTE which allows BT to monitor and test the service provided. The active NTE must be within reach of a power supply, and must remain connected to the power and data port of the service specific front plate at all times.

Picture 2 FTTC VDSL2 modem

Openreach VDSL2 modem – plugs into the SSFP

This installation does not need ADSL filters. The modem provided may be different to the one in the photo.

FTTC setup at End User premises

FTTC setup at End User premises

The active Ethernet EU port on the VDSL2 Active NTE supports:

  • • 10/100Base-Tx with RJ-45 connectivity
  • • Auto-negotiation and MDI/MDIX auto-sensing.
  • • Data transfer at wire-speed for all packet sizes.
  • • Built-in layer-2 switch

 

Power Supply

The power supply to the VDSL2 Active NTE is a single, low voltage power interface and is and plugs into a standard domestic UK 240V (ac) socket.  The power consumption is <9 W.

Openreach will install a line extension of up to 30m at the premises if required although it is worth noting that all installations will be subject to survey. In other words if an engineer turns up and it is physically impossible or too difficult to do the installation all bets are off.

An End User’s service will be subject to its ISP’s own broadband offerings and applicable terms and conditions. So read the small print!

Anyone wanting the service or looking at preregistering their interest can email to fttc@trefor.net and I’ll get someone to either sort it or put you on the waiting list for when the exchange is ready (actually when the cabinet is ready!). If you have any questions you can either leave them as comments on this blog post or email to the same address.

Link to more FTTC stuff and exchange availability information here.

Trefor Davies

This article was written by Trefor Davies
on Thursday, 18 March, 2010

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