Network Topologies, Token Passing & Structured Cabling

Network Topologies

Star topology connects each computer to a central point, which can be as simple as a junction of physical wires. When a computer sends a frame, it appears at the central device and is forwarded to the appropriate destination(s) by that central point.

Bus topology consists of a single cable that links all network stations. All computers monitor the cable for activity. When a computer transmits a frame, all computers on the bus receive it and check whether they are the intended recipient. If so, the recipient processes the frame; if not, it discards it.

Ring topology connects each computer to two others so that they form a ring. When a computer sends a frame to another, the frame travels through all intermediate stations. Many ring implementations use unidirectional transmission.

Structured Cabling (EIA/TIA-568)

Each endpoint in structured cabling typically has two lines: one for telephone and one for data. All cables terminate in a room where connections are established: telephone wires are directed to the PBX and data cables to a concentrator (hub), a device that interconnects the network. Structured wiring has been standardized by the EIA/TIA-568 specification, which includes descriptions of cables, connectors, cabinets, and other elements so that facilities are compatible.

Types of Cabling

Horizontal cabling: On each floor (when a building has multiple floors), cables run from a telecommunications closet to the terminal points.

Vertical cabling: Cabling that runs from the floor closet to a main distribution area of the building where network devices, routers (gateways) to the outside, the telephone exchange, and similar equipment are located.

Token Passing

Token passing defines a special control frame called the token. When a station receives the token, it has permission to transmit a frame on the network. Once the frame has completed a full circuit and the recipient(s) have made copies, the sending station releases the token so the next station in the ring may transmit.

CSMA/CD (Carrier Sense Multiple Access / Collision Detection)

CSMA/CD means Carrier Sense Multiple Access with Collision Detection. Computers constantly listen to the medium to detect a carrier (activity). When a station has data to send, if no activity is detected it transmits immediately; otherwise it waits. If a collision is detected during transmission, the station stops and follows the collision-resolution procedure (backoff and retry).