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.

Hi,

The link between the ISP and the ONT at the customer's end (certainly for Openreach) is a point to point VLAN, effectively a (more or less) transparent point to point ethernet connection.

That VLAN will pass through all kinds of equipment but the key point is that it is ethernet and it is (more or less) transparent so that equipment is invisible to the traffic passing over the link which only sees the endpoints at the ONT and ISP.

In theory an ISP could simply link all the VLANS from Openreach customers together with an internet connection and add a DHCP service. This would be a completely flat ethernet network, very similar to a LAN, but that has obvious scalability, security and manageability issues.

With respect to "more or less transparent" the link will pass anything encapsulated over ethernet (PPP, IP, IPv6 NETBIOS, IPX, ARP, etc.) but in practise there is equipment on the link that will fiddle with the contents of some PPPoE, DHCPoIPoE and DHCPv6oIPv6oE frames to provide some data identifying the link to the ISP. This prevents things like running a DHCP service at the ONT end of the link serving addresses to an ISP (not that most people would want to do that). I also wouldn't rely on the link being fully transparent to anything other than IP, IPv6 and PPPoE and ARP as other protocols won't necessarily have been well tested.

As implied by the above, anything above the ethernet level, like IP addresses isn't used by Openreach.

In reply to a post by candlerb:

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.

One would hope that anything passing across this point is end-to-end encrypted, because then it puts the onus for interception back onto people deciding which traffic needs to be intercepted and what within that traffic is of interest instead of just being able to hoover up everything.

Full secrecy against anyone with the resources of a government requires equivalent resources. Protecting your financial activity means making it difficult for criminals, not governments.

Generally it isn't. The traffic between ONTs and headends is due to the downstream traffic being sent to all ONTs in each PON so visible to other customers, but beyond that it isn't - extra hardware to handle encryption at each end of each link would be needed, key management and distribution would be a headache to mange as each end of a link are not necessarily managed by the same organisations.

In reply to a post by rippedcotton:

One would hope that anything passing across this point is end-to-end encrypted

It's not - unless you encrypt it yourself.

"End to end" by definition means between the two endpoint devices that are communicating, e.g. your phone and someone else's phone. Hence the phones must perform their own encryption and decryption and key management.

All the devices in between them carry traffic that has already been encrypted - including your home router, the ONT and OLT, the service provider's network and the rest of the Internet.

savamac

You could simplify the whole thing to say that the FTTP and backhaul to the ISP is the equivalent to the copper network.

Your Router is equivalent to the phone and the ISPs device (BRAs / Router etc) is the equivalent of the telephone exchange.

All the Ethernet frames/packets go all the way to the ISP (who allocates your IP) before being looked at for where in the Internet they want to go and any returning to you come from your ISP.

If you use a VPN you connect through the ISP for every packet to be routed to another 'ISP' who routes all your traffic hiding where the original info came from. Encryption hides the info in the packets from your ISP. ( Envelope within an envelope basically)

The ISP is the only legal point of connection without a Judges order ( Parental content controls etc are applied here).

If you are worried about security..

Most personal info is leaked by search engines, end websites, cookie trackers.

Illegal ones are ;- Other people on your PON who could clone the ONT identity to watch all your Frames. ( Same as a man up a pole/cabinet/exchange for copper). Deep packet inspection by duplicating/splitting the stream at the PON/Edge router/ any other router and 'watching' the duplicated frames. Only possible by the network operator and usually done with a court order (GCHQ type)

Looking at your info by your ISP comes as above.