Transmission mode refers to the direction of flow of information between communicating devices. It could be simplex, half duplex, full duplex

• Simplex mode: in this mode, signals are transmitted in only one direction. Example television broad casting, radio emission
• - half duplex: in half duplex mode, signals can be transmitted in both direction but only one way at a time e.g. the police radio (walkie-talkie)
• Full duplex: in full duplex mode, signals can be transmitted in both directions simultaneously e.g. the telephone network

I. PARALLEL TRANSMISSION

This is a method of transfer several bits at the same time over separate channels e.gg. 8 separate channels will be required if a block of 8 bits is to be transmitted in parallels. Its mainly used for connections within the computer and for connecting the computer to the printer

• Advantages of parallel transmission

• High speed: since it can send n-bits simultaneously the parallel interface can operate n-times faster than the serial interface
• Match to underlying hardware: internally, computer and communication hardware uses parallel circuitry thus parallel mission matches this hardware.

II.  SERIAL TRANSMISSION

Serial transmission is the method of transferring data one bit at a time through the same channel. If a block of 8 bits is to be transmitted in series, the bits will be transmitted one after the other on the same channel. Serial transmission is slower than parallel transmission but it is suited for long distance.

• Advantages of serial transmission

• it is cheaper as only one transmission line is required
• Serial can extend over long distances at much less cost due to fewer physical wire needed
• Using a single wire avoid tiny problem that can be cost by one wire slightly longer than another.

Serial transmission can be asynchronous or synchronous:

1. Asynchronous serial transmission

This is when transmitted data is encated with start and stop bit specifying respectively the beginning and end of each character. Data is sent character by character with each character resided by a start bit and a stop bit is added to the end

        2.Synchronous serial transmission

This describes a continuous and consisted time transfer of data blocks. Data is send as one long bit stream or block of data without start or stop bits and with no gaps upon reception, the receiver counts a bit and reconstruct bytes.