Figure 5-28 shows examples of circuitswitched
WAN connections.
Figure 5-28 Circuit-Switched Communications
In circuit switching, a dedicated path is established, maintained, and terminated through a
carrier network for each communication session. Only the access path is a dedicated
physical circuit; the network uses some form of multiplexing technology within the cloud.
Circuit switching operates much like a normal dialup telephone call and is used extensively
in telephone company networks. Circuit switching establishes a dedicated physical
connection for voice or data between a sender and receiver. Before communication can
start, it is necessary to establish the connection by setting the switches through a dialup
activity. Whereas point-to-point communication links can accommodate only two sites on
a single connection, circuit switching allows multiple sites to connect to the switched
network of a carrier and communicate with each other.
An example of a circuit-switched connection is a public switched telephone network
(PSTN).
Telephone
Company
PPP, HDLC, Layer 2
Telephone
Company
Asynchronous Serial
382 Chapter 5: WAN Connections
Public Switched Telephone Network
The most common type of circuit-switched WAN communications is the PSTN (also
referred to as the plain old telephone service [POTS]).
Pages:
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527