Protocol
A protocol is basically a set of rules and regulations that govern how data is to be transmitted across a network. It defines the regulations regarding software as well as hardware. To enable two/more devices to communicate, they must follow the same protocol - an agreed format for transmission of data between devices. The protocol determines things such as: Type of error checking to be used, data compression methods, etc.
Packet
A network packet is the fundamental component of transmitting data over a network. All data being transferred is in packets. It is a unit of data that has the ability to be routed over network(s). It usually has 3 parts: the header, the body or payload and the footer/trailer. The header contains details such as the destination IP, the host IP & host MAC address. The body contains the actual data or part of the data to be transferred and lastly the footer signifies the end of the packet and also contains the packet number.
Why can the data transmission rate across a network vary?
Data transmission rate across a network can vary for several reasons. Some are given below:
1) The transmission media: The transmission media used to transmit the data across a network is an important factor that can limit the transmission rate. If a fast medium such as fiber optic cables are used then the transmission will be faster. However if a slower medium such as telephone cables are used then obviously the transmission will be slower.
2) The level of activity on the network is also a important factor. The network is limited by the amount of data it can transmit at a point in time. This is called the bandwidth. Thus if the level of activity on the network is very high or exceeding the allowed bandwidth, then any further data to be transmitted will have to wait/ be queued.
3) Collisions on the network can also determine the rate of data transfer. Whenever a data collision occurs, a