The computer works with binary digits only. Therefore, all data , numeric or non – numeric, must be converted into binary digits before the computer can understand it, Computers transmit data in the form of binary codes. Both sender and receiver of the data should have same standard rules for both to understand it
A coding scheme for communications is a binary system, that is used in the computer systems. The system consists of groups of bits (0 or 1) that represent characters. Some codes use different number of bits such as 5, 7, 8, or 9 to represent that during data communication. The following are some coding scheme to represent data.
BCD: ( Binary Codes Decimal) is 4 bits code. A few early computer is processed BCD numbers but were slower and more complicated than a modern computer, which are able to process alphanumeric ( alphabet letters, numbers and other symbols).
- EBCDIC Code : Extended Binary Coded Decimal Interchange Code is an 8-bit code primarily used by international Business Machine (IBM) . This type is intended for efficient transfer between hosts, which use EBCDIC for their internal character representation . For transmission, the data are represented as 8-bit EBCDIC characters. The character code is the only difference between the functional specifications of EBCDIC and ASC11 types.
- ASC11 Code : ASC11 ( American Standard Code for Information Interchange) is a 7-bit code and makes 128 character combinations, whereas an 8-bit can make 256 combinations. It was developed by American National Standards Institute (ANSI) and can handle alphanumeric data. It is intended primarily for the transfer of text files, except when both hosts would find the EBCDIC type more convenient.
Unicode: Universal Code is a 16- bit code and can represent up to 65,536 symbols. Unicode has started to replace ASC11 at all levels. It supports a comprehensive set of mathematical and technical symbols to simplify scientific information With the UTF-8 ( Unicode Transformation Format-8) encoding Unicode can be used in a convenient and backwards compatible way in environments that were designed entirely around ASC!!
Modes of Data Communication
When a person is giving a lecture or speech , information is primarily conveyed in one direction. During a conversation spoken message(information) are usually exchanged in both directions. These messages are normally exchanged alternately but, can of course, are exchanged simultaneously! Similarly, when data is transmitted between two pieces of equipment,three types of data transmission modes can be used .
- Simplex: Simplex is a mode in which data flows in one direction only(Figure 3.3). Because most modern communication systems require a two-way interchange of data ,this mode of transmission is not as popular as it once was. However, one current usage of simplex communications in business involves certain point-of –sale terminals in which sales data is entered without a corresponding reply other examples include radio and T.V transmissions.
- Half- duplex: In half-duplex transmission, data can be sent and received n both directions, but not at the same time. It’s like a one-lane bridge where two-way traffic must give way in order to cross (see figure 3.4). Only one end transmits at a time, the other end receives. In addition, it is possible to perform error detection and request the sender to re-transmit information that arrived corrupted. In some aspects, you can think of Internet surfing as being half-duplex, as a user issues a request a for a web document, then that document is downloaded and displayed before the user issues another request e.g. walkies talkie etc.
- Full Duplex: The directional mode of communication is full-duplex. Here, data is transmitted In both directions simultaneously on the same channel(see figure 3.5). Thus , this type of communication can be thought of as similar to automobile traffic on a two-lane road. Full-duplex communication is made possible by devices called multiplexers. Full-duplex communication is primarily limited to mainframe computers because of the expensive hardware required to support this bi-directional mode e.g. telephone system.