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(b) Central Office (CO): A facility that houses the the recipient for the
switching equipment and connects calls between duration of the call.
local loops. (d) Call termination: Once

(c) Switching centers: Equipment that routes the call is complete, the Chapter Three: Advanced Computer Networks
calls based on the phone number dialed. They circuit is disconnected,
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include local exchanges, tandem switches, and freeing up the resources.
international gateways.

(d) Transmission media: Includes copper wires, Features of PSTN
fiber optic cables, and microwave or satellite (a) Reliable and ubiquitous:
links that transmit voice and data signals. PSTN offers reliable

voice communication
Figure 3.60 shows a telephone and a telephone services and extensive
switch. The telephone is located in the Customer’s global reach.
Premises (CP, CPE), while the telephone switch is (b) Quality of Service (QoS):
located in the Central Office (CO). Provides a high-quality

Central Office (CO) Customer Premise (CP) voice communication
LOOP experience due to
its dedicated circuit-
switching approach.
(c) Emergency services:
PSTN supports
TRUNK emergency call services
like 911, providing
Customer Premise (CP)
location information to
emergency responders.

LOOP
Limitations of PSTN
(a) Limited data
Central Office (CO) Transmission: PSTN is

Figure 3.60: Customer and Cental Office communication not optimised for high-
speed data transmission
Implementation of PSTN compared to modern
(a) Call initiation: When a call is made, the analog digital communication
voice signal is converted into a digital signal. systems.

(b) Routing: The call is routed through a series of (b) Scalability issues:
switches in the central offices. S caling P STN

(c) Connection establishment: A dedicated circuit infrastructure can be
costly and complex.
or path is established between the caller and

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Student’s Book Form Five

Computer Science Form 5.indd 205 23/07/2024 12:33