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Asynchronous and Synchronous

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Introduction

Ricki Lambert Communications Technology Task 4 Bits and Bytes A bit is a singular digit represented by a binary number. A character is represented in computing terms but a code called ASCII There are 7 bits to an ASCII number With parity bit added there are 8 bits, parity is added to aid in error detection. 8 bits is equal to a byte. 1 1 0 This diagram represents an 8 bit binary number (1byte). The step represents a 1 and the flat part represents nothing. This number would then look like this, 100000001. In ASCII this represents the character A. Packet Structure Instead of sending singular characters it is possible to send many in one go, this is called a packet. For example we use the ASCII code to represent a sentence and this may take up to 50 characters. When sent in the form of a packet we must split the packet up, this is done by using control characters. The control characters are; SYN = Synchronise STX = Start of text ETX = End of text Above is an example of a packet structure used with Asynchronous sending. ...read more.

Middle

It can be used for connecting Printer, Terminal, Modem and home connections to the internet. Asynchronous protocol was one of the first around and was popular with the early invention of the tele typewriters. It requires the use of start and stop bits as previously said and this provides byte timing and overhead. No clocks are needed and a parity bit is also sent to help with error detection. Asynchronous transmission will send single bits of data at a time. There is a standard for this form and it is called RSC323C. Asynchronous represents negative voltage as 1 and positive voltage as 0. Information is sent in a packet with the start and stop bit plus parity for error detection. This method of transmission is suitable for low speed. This is because for every character that is sent a further 2 bits (start and stop) must be added. For example, 1000 characters are to be sent, there are 8 bits per character plus a start and stop for each that's a total of 10000 bits. ...read more.

Conclusion

It's the lack of timing information sent with the data which restricts it so greatly. Synchronous Transmission Packet of data Effect Of Bandwidth Limitation And Noise Bandwidth is the sum amount of data being sent to a recipient in a given time through a form of communicational media. This sum is normally represented on bit per second. Bandwidth also has an alternative meaning and can represent the differing frequency ranges. All media types have their own forms of bandwidth limitation; this means we cannot transmit the same things on the differing types of media at the same speeds. If sending something with 10bits it will be sent at 10bits a second. This should apply for the bandwidth also (10 bits a second) however; it can be affected by something that is known as cross talk. This is interference on the line, also known as noise. Noise can occur in many forms and this will always affect speed. The only method of transmitting data without any electrical noise affecting it is by using a fibre optic cable. Fibre optic cables uses the use of light and mirrors, this is why it can not be affected. However it is also very expensive. ...read more.

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