DATA COMMUNICATIONS AND NETWORKING

DATA COMMUNICATIONS AND NETWORKING I.

Terminals and Workstations: Equipment that finally receives/transmits and displays information. Represented as nodes,
Transmission Links: Physical connection between nodes on a network. The media used for the connection may be telephone wire, microwave beam or fiber-optic medium.
Transmissions Methods
Nodes and Switches
Architecture and Standards

Dumb Terminals: A monitor and a keyboard with network connection (usually no data storage).
Workstations: PCs or Workstations with a network card (NIC).

Telephone wire: Straight/twisted pair, shielded/unshielded. (Includes twisted-pair Ethernet.)
Coaxial Cable: The kind of cables used in cable TV. The coaxial cables used in the original Ethernet (called Thick-wire) were rather inflexible and required use of expensive equipment (Called transceivers) They were replaced, at least in office environments by thin-wire co-axial cables that were flexible. In thin-wire ethernet, the wire links the computers on the network in a chain, where each link is a "T" connection. (In the School of Business Lab (BA 220) you can see these cables with the T connectors. About a year ago, they were replaced by twisted-pair Ethernet, also popularly called 10Base-T, meaning 10 Megabits per second using Baseband signaling over Twisted-pair cabling.)
Fiber-optic cables:
Telecommunications Media:
- Infra-red Transmission
- Microwave transmission
- Satellite transmission

Circuit-switching: Used in telephone systems. A dedicated line is established between two points. The communication is assured during the time of the connection, and is not affected by network traffic. The disadvantage is that the circuit cost is fixed, independent of network traffic; you pay for the connection time, whether you talk or not.
Packet-switching: Sometimes also called connectionless transmission method. "In a packet-switched network, the data to be transmitted is divided into small pieces called packets that are multiplexed onto high capacity intermachine connections.... The network hardware delivers the packets to the specified destination, where the software reassembles them into a single file again." (Comer, 1995) The advantage of packet-switching is that the network resources are shared; the disadvantage is that during periods of high traffic density, individual machines may have to wait.

multiplexer (MUX ): Maximizes the utilisation of transmission channel capacity by bundling streams of slow-speed traffic on a high-speed line.
Front-end processor: a device that connects the multiplexer to the mainframe computer or server that is at the receiving end of the messages; it performs error checking and control functions that would otherwise have to be performed by the computer or server.
Bridge: A device used for interconnecting networks that use identical protocols or communication conventions.
Router: Connects networks that use dissimilar but compatible conventions. As the name suggests, a router selects the most efficient path to the destination by looking up routing tables of all possible paths between the origin and destination networks.
Gateway: connects networks using conventions that are not directly compatible. The gateway handles the task of making all necessary translations between the conventions used by the sending and receiving networks.

Protocol: "A protocol provides the rules for communication. It contains the details of message formats, describes how a computer responds when a message arrives, and specifies how a computer handles errors or other abnormal conditions.." (Comer, 1995)

Application Layer: What the user sees. The data here is represented in a format that the iser understands.
Presentation Layer: All the data in the session layer and below are represented in binary format. It is the function of the presentation layer to transform the data in the lower layers to the user understandable format.
Session Layer: Coordinates communication between the sender and receiver; maintains the session for as long as it is needed, performing security, logging, and any administrative functions that are needed.
Transport Layer: Defines protocols for message structure and supervises the validity of the transmission by performing error checking (Checksum).
Network Layer: Defines protocols for data routing to ensure that the data arrives at the correct destination node.
Data-Link Layer: Validates the integrity of the flow of data between nodes.
Physical Layer: is the actual transmission hardware or link along which the messages physically pass.

Each device is connected to a common "backbone.Use either the Ethernet protocol (10Mb/sec) or fast Ethernet protocol (100Mb/sec.)

Each device is connected to a common circular loop (cable).

One computer acts as the "host" computer to which all other computers and devices are connected.

Updated on September 21, 1997 by Jagdish S. Gangolly.