FTTP - what's the "id" for the "exchange" end of the Fibre ?

In the old days of landlines and dial-up internet access, there would be a piece of copper cable which at one end (in my home) had a telephone with a number like 020 8123 4567, and at the other end (in the exchange) a "slot" in a cabinet. I assume the "slot" had a number like 123 and somewhere there was a record that 123 corrresponded to (was linked to) telephone 020 8123 4567 . In the brave new world of fibre (and no landline, as we all now use mobiles), there must still be a fibre "slot" numbered 123 in a cabinet. What is 123 linked to ??

No cabinet, but in the fibre exchange the ‘similar’ kinda thing is called a head end

The Openreach FTTP fibre from your premises

1. first goes to a Connectorised Block Terminal (CBT) either on a nearby pole or footway chamber.

2. From there it travels to a splitter node where the separate fibre strands feeding up to 30 premises (with another 2 spare typically) are optically combined to a single fibre.

3. Further up the chain it goes to an Aggregation Node.

4. From the Agg Node it runs to the Head End / Parent exchange where it ends up on an optical distribution frame or Optical Consolidation Rack (OCR).

5. From here it is cross connected / patched to an optical port, on a card, in a chassis known as the Optical Line Terminal (OLT) / Layer 2 Switch (L2S). From here your ISP makes their backhaul connection to take your traffic onto their network, either through their own provision or with the help of a wholesale backhaul provider like BT Wholesale, TalkTalk, Sky, Vodafone etc.

In the openreach network the headend will have an ID of 6 letters beginning with B. The port will be on a card identified by it's position (slot) in the headend chassis and the port number .
To find the headend though, you need to know the exchange building it's in, the floor, suite and rack also.

Edited by witchunt (Mon 27-Mar-23 21:39:01)

In reply to a post by witchunt:

In the openreach network the headend will have an ID of 6 letters beginning with B. The port will be on a card identified by it's position (slot) in the headend chassis and the port number .
To find the headend though, you need to know the exchange building it's in, the floor, suite and rack also.

So, does the headend know my ip address ??

In reply to a post by savamac:

So, does the headend know my ip address ??

No, because the device at the headend (called an OLT) is a layer 2 device only: it passes frames, which could be IPoE, PPPoE, or other protocols. Your IP address is assigned by your ISP, which also routes your traffic to the Internet.

However, it would be a possible point of interception of traffic. When and where and under what conditions this happens is a matter for speculation - anyone who knows isn't allowed to talk about it.

" Your IP address is assigned by your ISP, which also routes your traffic to the Internet."

So, when traffic comes back from the internet, how does it know where it's going ?? (Remember , my query was prompted by the disappearance of copper cable, which has a telephone number at the end of it. In the absence of copper cable and phone number, what's the "target" for data coming to me ?)

The Serial Number of the ONT installed in your property is the "ID" that identifies your property on the network.

In reply to a post by savamac:

So, when traffic comes back from the internet, how does it know where it's going ??

Your home router/wifi box is provided a TCP/IP address, this address is known as "routable" and when you connect to say Thinkbroadband the replies from the Thinkbroadband server are sent back to your router. The router then works out which of your internal devices in your home actually requested.

TCP/IP is the protocol used for this, nothing to do with the physical cabling or telephone numbers etc.

In reply to a post by savamac:

" Your IP address is assigned by your ISP, which also routes your traffic to the Internet."

So, when traffic comes back from the internet, how does it know where it's going ?? (Remember , my query was prompted by the disappearance of copper cable, which has a telephone number at the end of it. In the absence of copper cable and phone number, what's the "target" for data coming to me ?)

The analogue telephone number (and the associated routing etc for calls) is quite a bit different to the architecture used in modern FFTP networks and IP-based internet routing.

So its quite difficult to give you a simple direct analogy for a "phone number" as that information for call routing is held in the switch at the exchange and was mapped to a physical pair on the MDF copper frame.

In the FTTP equivalent, as noted above - the logical structure of the network is based on the PON (passive optical network) which is the physical connection of up to 30/32 properties to one physical port on the headend ONT at the exchange. This is effectively a transparent "pipe" which carries encapsulated ethernet traffic. Your ONT is uniquely identified (and authorised) on the PON using a combination of it serial number (and often password...depending on the network)

The traffic within the PON is carried using standard GPON frames. Your traffic is uniquely identified by the VLAN identifiers that are tagged on the ethernet frames carried within these frames. It's the job of the OLT in the headend to strip out the ethernet frames from the PON and based on the VLAN identifiers to present this to the ISP connection on the OLT (the Layer 2 switch part).

The IP address information for routing across networks is at a higher (deeper?) level in the OSI network model - again this is carried within the Ethernet frames that have been passed onto the ISP own networking equipment, for onward traversal.

Hope that makes sense. Its a bit difficult to summarise in a few paragraphs. It's a reasonably complex subject and I've glossed over lots of detail.