Communications

Communication systems allow people to stay in touch and help to link up the world. A modem is a type of communication device. I used a direct connect modem which is the most common type and fits directly into the telephone socket. Other types of modems include null modem cables and acoustic coupler modems. My modem has features such as auto-answer, auto-disconnect, error correction and data compression.

My modem uses full duplex which allows data to travel in both directions. This has an advantage over simplex modems which are unidirectional and half-duplex which can either send or receive. Parallel transmission involves each bit travelling along its own wire such as used to connect my printer to the computer. A serial transmission involves bits moving down one at a time and is used for my modem.

Asynchronous transmission, where characters are sent one at a time with start and stop bits, was used with my modem as it is inexpensive though slow. The other choice was synchronous transmission where bits are transferred synchronised at a fixed rate. This would have been expensive though more efficient. The baud rate is the number of signalling events per second and was 38 400 for my modem.

Terminal emulation allows my computer to download and upload data from a mainframe as well as operate as a terminal. Handshaking is important to establish a connection channel for senders and receivers. Protocol establishes speed of transmission and controls transmission. Protocol is a strict procedure and must be adhered to in carrying out computer communication.

Error detection helps prevent problems such as noise interfering with data transmissions. Parity checking can detect one error but is stumped if there are two. Cyclic redundancy checks (CRC) were with my modem as they are less likely to let errors slip through. Our school works with a local area network (LAN) which connects computers physically close together such as in the same building. With my modem I was able to access a wide area network (WAN) allowing me to communicate with the entire world, though at a slower speed than a LAN. Gateways were important to connect dissimilar networks.

WANs connect many types of networks together. Some are ring topologies which consist of stations in a closed loop. Token Ring Networks wait for a lull in a ring network before transmitting. Bus topologies are like an open-ended ring. Star topologies have a central station connecting several nodes. WANs are usually mixed topologies which contain more than one of the above topologies.

The network I connected on with my modem consisted of various servers. These included mail servers which handle electronic mail and file servers which provide quick access to files. Logging on to my file server required a password. This helped ensure network security. This entire website has been uploaded to a file server.

Electronic mail or e-mail allows people to send messages by connecting on to a communication channel. Standards for e-mail include X.400 and X.25. The e-mail package I used was Microsoft Outlook. E-mail was used to communicate with various users of my website by allowing them to provide feedback and ask questions. Another program I used to communicate with users of my website was Mirabilis ICQ.

I connected to the Internet via a bulletin board system (BBS). Bulletin boards allow files to be shared and are inexpensive to set up. They are a type of remote database. Files were transferred from the BBS with the ZModem protocol. This is more reliable and can transmit larger files than the XModem protocol. Before files could be transmitted, the parameters such as bits per second and parity needed to be set. Due to the slow nature of serial transmission data needed to be compressed to be efficient. PKZIP is an example of a software program I used for this purpose. My modem used the V.42bis data compression standard and can speed data transfer by up to 57 600 bps.