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Introduction to Data Communications
by Eugene Blanchard. A complete guide on networking and data communications. Data Communications is the transfer of data or information between a source and a receiver. Data Communication is interested in the transfer of data, the method of transfer and the preservation of the data during the transfer process. The purpose of Data Communications is to provide the rules and regulations that allow computers with different disk operating systems, languages, cabling and locations to share resources. The rules and regulations are called protocols and standards in Data Communications. Telephones and networking work hand in hand. The Internet is a good example of the collabaration between computers and the telephony industry. The Internet is a collection of computer networks connected by telecommunication systems. Most people don't realize it but the telecommunications industry is the backbone for the Internet. Pretty much all data communications that leaves a LAN utilizes a telecommunication service. There are two main methods of sending data over telephone services: voice channels and data channels. In data communications, we use voice channels for modem communication. Data channels are dedicated lines for communicating digitized voice and data. There are many different protocols (rules and standards) for data channels. Some common data channel services are T-1 lines, Frame Relay, X.25 and ADSL. A network can consist of two computers connected together on a desk or it can consist of many Local Area Networks ( LANs ) connected together to form a Wide Area Network ( WAN ) across a continent. Local Area Networks ( LANs ) are networks that connect computers and resources together in a building or buildings close together. The components used by LANs can be divided into cabling standards ( like: Cat 3, 4 and 5 cables, Unshielded Twisted Pair or UTP, Shielded Twisted Pair or STP, Ethernet cabling standards: IEEE 802.3 for 10Base5, IEEE 802.3a for 10Base2, IEEE 802.3i for 10BaseT ), hardware ( like: Network Interface Cards NICs, Ethernet Hubs, Bridges, Routers, Switches ) and protocols, like: Ethernet_II, Ethernet_SNAP, Ethernet_802.2, Ethernet_802.3, Media Access Control layer ( MAC layer ), Token Ring: IBM and IEEE 802.5, Logical Link Control Layer ( LLC ) IEEE 802.2, TCP/IP, SMB, NetBIOS and NetBeui, IPX/SPX. Metropolitan Area Networks ( MANs ) are networks that connect LANs together within a city. The main criteria for a MAN is that the connection between the LANs is through a local exchange carrier ( the local phone company ). Wide Area Networks ( WAN ) are a communication system linking LANs between cities, countries and continents. The same protocols and equipment are used as a MAN. When we look at the Data Communications model, we see that all communications must travel through some sort of medium ( Cabling, Microwave, Fibre optics, Radio Frequencies or RF, Infrared Wireless ). The Physical layer of the OSI model is concerned with the physical attributes of the medium such as cable type, frequency, voltages, etc ... Data communications over a medium can be divided into two basic types: serial data communication ( only 1 bit of information can be transmitted over the data transmission medium at a time ) and parallel data communication ( more than 1 bit of information is transmitted over the data transmission medium at a time ). Serial data transfer is used for high transfer rates over long distances. At shorter distances, typically under 15 feet, parallel data transfers are used. If 64 bit high speed data transfers were attempted for long distances, cable characteristics would cause the signals to lead or lag each other and all the bits would not arrive at the exact same time. The bits would arrive staggered and the data would be corrupted.
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