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Data Transmission

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Data Transmission


The purpose of this report is to describe some common data transmission terminology.

Scope of Work:

This paper will discuss various data transmission (communication) protocols and how they are used in data communication.

Synchronous and Asynchronous:

Asynchronous serial transmission is a technique used in serial RS232 communication. The data is framed by a series of control bits known as the start bit, stop bit(s), parity bits and error checking bits. A transmit clock signal is used to clock the data over the transmission line to the receiving end. At the receiver, a clock signal, known as the receive clock, which corresponds to the transmit clock is used to decode the transmitted data back to the original by stripping off the control bits.

Synchronous transmission sends data packets, in contrast to Asynchronous transmission, which sends data one bit at a time. The data is surrounded by start and end frames. The start frame tells the receiver to synchronize its internal clock and to expect the incoming packets. The end frame marks the end of the packet.

Low speed data transmission uses asynchronous transmission. Because asynchronous transmission does not include error checking, it is not very efficient. Synchronous transmission, on the other hand is very efficient. Data is transmitted in blocks. Synchronous communication is well suited for high speed data transmission. The protocol has error checking capabilities.

Analog and Digital:

Analog signals represent continuously changing signal such as sound wave emitted from a speaker or an alternating current (sine wave) traveling on a wire. Digital signal, on the other hand is a digital representation of an analog signal, it is either off or on.

AM - Amplitude modulation and FM - Frequency modulations are means by which use to transmit analog signal. DM - Digital modulation is used to transmit digital signal (Analog vs Digital Transmission, 2005)

X on and X off:

X on / X off is a handshaking control signal used to control the flow of data communication. It works like this. A printer connect locally to computer use the X off control signal to notify the computer that the print buffer is full and should stop sending data. When the printer is ready for more data, the X on signal is send to signal the computer to resume data transfer.

Simplex and Duplex:

Simplex transmission is used transmit data in one direction only. It is like a one-way street for data.

Duplex transmission means that data is transmitted in both directions. There are two type of duplex transmission, there is half duplex in which data travels in both directions but not at the same time. An analogy of half-duplex transmission is two persons communicating using a walkie-talkie.

The protocol for this type of communications, is only one person can talk at one time. If both persons tries to talk at the same time, the conservation will become unintelligent and neither one will be able to understand the other one.

The other type of duplex transmission is the full-duplex transmission. In this type of communication, data transmission can travel in both directions at the same time.

Serial and Parallel transmission:

Serial transmission is a technique in which data is serialized into bits of information and is sent sequentially on a single communication channel or wire, rather than simultaneously as in parallel transmission. Serial transmission is the normal mode for data communication over the telephone lines using a modem. The RS232 serial communication was a popular interface between the computer and the modem. Data is transmitted one character at a time. Each character is encoded with a series start, stop and parity bits which formats the data so that it can be easily decoded at the receiving device. The format 7N1 means that 7 bit of data will be transmitted along 1 stop bit and no parity bit.

Parallel transmission is a technique in which data is transmitted on 2 or more bits simultaneous. Parallel transmission is faster than serial transmission because data is transmitted at the same time on all the available bits as apposed to one bit at a time. A popular parallel interface was the printer port on older computers; nowadays, the USB serial interface has replaced the parallel port.

Baseband and Broadband:

In Baseband Transmission, the entire bandwidth of the transmission medium is used by one signal. In Baseband signaling, only one signal can be transmitted on a time using one cable (or strand of wire); therefore, half duplex transmission is the only mode of transmission capable with baseband, meaning,



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