Network devices:

HUB - This is cheaper than a switch. It does not learn where each device is so it sends a message to every device connected to it so it is slower since it takes up the network bandwidth. This is an example of a broadcast device.



Switch - This device is similar to a HUB however this device learns where each device is connected to it so after each message it stores where the device is. This means that it is quicker since there is less network traffic and only the device you want to send the message to receives it. This are examples of a uni and multi cast devices.



Router - This forwards data packets between computer networks. This creates an overlay inter network. It has 2 or more data lines connecting to different networks. Routers have different types of ports (RJ45, RJ11, Serial and Wi-Fi)




A broadcast is when data is sent to all devices on the network.
A multicast is when data is sent to some, specific devices on the network.
A unicast is when data is sent to one device on a network.

Physical connections

A cable or wire
Can be touched
Limited

Logical connections

Virtual connection
Can't be touched
Multiple connections for different things simultaneously using one physical connection

DTE/DCE:
DTE - Data transmitting equipment
- Usually an end device
- Receives clock signal
- Usually "our" stuff
DCE - Data communications equipment
- Usually a comms device
- Creates clock signal
- Usually "their" stuff