Page 91 - DCAP104_EXPOSURE_TO_COMPUTER_DISCPLINES

Exposure to Computer Disciplines

Notes 5.2.2 Classification of Network Topologies
There are also two basic categories of network topologies:

(a) Physical topologies
(b) Logical topologies
The shape of the cabling layout used to link devices is called the physical topology of the
network. This refers to how the cables are laid out to connect many computers to one network.
The physical topology you choose for your network influences and is influenced by several
factors:
(a) Office Layout
(b) Troubleshooting Techniques

(c) Cost of Installation
(d) Type of cable used
Logical topology describes the way in which a network transmits information from network/
computer to another and not the way the network looks or how it is laid out. The logical layout
also describes the different speeds of the cables being used from one network to another.

5.2.2.1 Physical Topologies
The mapping of the nodes of a network and the physical connections between them the layout
of wiring, cables, the locations of nodes, and the interconnections between the nodes and the
cabling or wiring system.

5.2.2.2 Classification of Physical Topologies

Point-to-point
The simplest topology is a permanent link between two endpoints (the line in the illustration
above). Switched point-to-point topologies are the basic model of conventional telephony.
The value of a permanent point-to-point network is the value of guaranteed, or nearly so,
communications between the two endpoints. The value of an on-demand point-to-point
connection is proportional to the number of potential pairs of subscribers, and has been
expressed as Metcalfe’s Law.

Permanent (Dedicated)
Easiest to understand, of the variations of point-to-point topology, is a point-to-point
communications channel that appears, to the user, to be permanently associated with the two
endpoints. A children’s “tin-can telephone” is one example, with a microphone to a single
public address speaker is another. These are examples of physical dedicated channels.
Within many switched telecommunications systems, it is possible to establish a permanent
circuit. One example might be a telephone in the lobby of a public building, which is
programmed to ring only the number of a telephone dispatcher. “Nailing down” a switched
connection saves the cost of running a physical circuit between the two points. The resources
in such a connection can be released when no longer needed, for example, a television circuit
from a parade route back to the studio.
Switched
Using circuit-switching or packet-switching technologies, a point-to-point circuit can be set
up dynamically, and dropped when no longer needed. This is the basic mode of conventional
telephony.

84 LOVELY PROFESSIONAL UNIVERSITY