The idea
Fibre carries far more than copper, so the ideal is fibre all the way to the user. That is expensive, so providers run fibre as close as they can afford and reuse copper or coaxial cable for the rest. FTTx is the name for that whole family. The X says where the fibre stops.
How it works
FTTx technologies
FTTx is a mix of copper, coaxial and fibre cables used to deliver internet. The architectures are FTTX (Node, Curb, Building, Home) and they vary with the distance between the optical fibre and the end user.
The lecture’s points about the family:
- The central office carries internet traffic to multiple end users within the building.
- The metallic cables are twisted copper wires (Cat 5) or coaxial cables.
- Fibre terminates at X, and the optical signal is converted to an electrical signal there.
- The technologies listed are xDSL, HFC and GPON.
- The examples given are NBN and Vodafone Vision.
How it works
DSLAM
The Digital Subscriber Line Access Multiplexer (DSLAM) goes with an active fibre network. It is mainly used for FTTN or FTTB, where it facilitates the use of xDSL at the premises.
A “powered” DSLAM provides electrical and optical conversion and communicates with the modems in the apartments over WiFi or Ethernet. The lecture summarises this as Ethernet over fibre. See DSL for the copper side.
How it works
Gigabit-capable passive optical network (GPON)
GPON is optical fibre all the way, with unpowered splitters and shorter coax or copper cables at the end.
- The OLT (optical line termination) sits at the central office.
- The ONTs (optical network terminals) sit at the end-user side.
- OLT and ONT carry Ethernet traffic using TDMA at a Gbps rate.
- OLT and ONT provide the conversion between electrical and fibre signals towards the copper-wire Ethernet.
Aside
The lecture’s final WAN topic, MPLS, is described as a WAN at the network layer for FTTx backbone networks, with IP routers connected to OLTs, DSLAMs or cable heads. The slide has no further detail, so none is given here.
In the exam
- Expand FTTx: Node, Curb, Building, Home. The architectures differ by the fibre-to-user distance.
- Place the DSLAM: FTTN and FTTB, to enable xDSL at the premises.
- GPON vocabulary: passive (unpowered splitters), OLT at the central office, ONT at the user, TDMA at Gbps rates, Ethernet traffic.
- Technologies listed under FTTx: xDSL, HFC, GPON.
Check yourself
- FTTx puts fibre as close to the user as practical. X is Node, Curb, Building or Home.
- Fibre ends at X, where light becomes an electrical signal, and the rest runs on copper or coax.
- A DSLAM brings xDSL to the premises in FTTN and FTTB.
- GPON is passive fibre with OLT and ONT carrying Ethernet by TDMA at Gbps.