There are two basic component to a backbone network:
1. The network cable
2. Devices that connect to the backbone network
The cable is essentially the same as that used on a LAN except that it is higher in quality providing higher data rates eg fibre optic or Cat5 shielded twisted pair (STP).

Devices
Hubs
1. They are repeaters/amplifiers that increase the strength of a signal in the circuit to enable the circuit to run longer distances than cable alone.
2. Operate at the physical layer
3. Pass all traffic bidirectionally across any link
4. Forward every message to other LAN sections needlessly
5. Used within one LAN

Bridges
1. Operate at data link layer
2. Connect two lan segments that use the same data link and network protocol
3. May connect same or different cable types
4. Forward only those messages that need to go other network segments
5. On recieving a packet it reads its source address comparing it with its own routing table, if it is not in the table, it adds it to the table.If the destination address is not in its routing table it forwards the packets to other network segments except the originating one.
6. Its a combination of hardware,processor and memory, and software. It can also be a normal PC with two or more network interface cards (NICs) and a special bridging software.

Switches
1. Operate at the data link layer
2. Connect more than two lan segments that use the smae data link and network protocol.enable all ports to be in use simultaneously and thus faster than bridges
3. May connect several low speed lan segments into a faster backbone network
There are two types:
(i)Cut through switches
Examine destination of incoming packets and immediately connect the port with the incoming message to the correct outgoing port
(ii) . Store and forward switches
4. Copy the incoming packets into memory before processing the destination address.
5. If the outgoing port is available the packet are forwarded immediately otherwise they are stored till the port is free
6. Slower and more expensive than cut throughs but rapid changes in cost and speed are eliminating these differences.