Digital local exchange
• Local or subscriber loops connect subscribers to local exchanges, which are
the lowest-level exchanges in the switching hierarchy.
These are the main tasks of the digital local exchange:-
• Detect off-hook condition, analyze the dialed number, and determine if a
route is available.
• Connect the subscriber to a trunk exchange for longer distance calls.
• Connect the subscriber to another in the same local area.
• Determine if the called subscriber is free and connect ringing signal to her.
• Provide metering and collect charging data for its own subscribers.
• Convert 2W local access to 4W circuit of the network.
• Convert analog speech into a digital signal (PCM).
Note: The size of local exchanges varies from hundreds of subscribers up to tens
of thousand subscribers or even more. A small local exchange is sometimes
known as a remote switching unit (RSU) and it performs the switching and
concentration functions just as all local exchanges do. A local exchange reduces
the required transmission capacity (number of speech channels) typically by a
factor of 10 or more;
Trunk Network
• The below Figure shows a simplified structure for a network where higher
levels than local exchanges are shown as a single level of trunk exchanges.
• The local exchanges are connected to these trunk exchanges, which are
linked to provide a network of connections from any customer to any other
subscriber in the country.
• Local or subscriber loops connect subscribers to local exchanges, which are
the lowest-level exchanges in the switching hierarchy.
These are the main tasks of the digital local exchange:-
• Detect off-hook condition, analyze the dialed number, and determine if a
route is available.
• Connect the subscriber to a trunk exchange for longer distance calls.
• Connect the subscriber to another in the same local area.
• Determine if the called subscriber is free and connect ringing signal to her.
• Provide metering and collect charging data for its own subscribers.
• Convert 2W local access to 4W circuit of the network.
• Convert analog speech into a digital signal (PCM).
Note: The size of local exchanges varies from hundreds of subscribers up to tens
of thousand subscribers or even more. A small local exchange is sometimes
known as a remote switching unit (RSU) and it performs the switching and
concentration functions just as all local exchanges do. A local exchange reduces
the required transmission capacity (number of speech channels) typically by a
factor of 10 or more;
Trunk Network
• The below Figure shows a simplified structure for a network where higher
levels than local exchanges are shown as a single level of trunk exchanges.
• The local exchanges are connected to these trunk exchanges, which are
linked to provide a network of connections from any customer to any other
subscriber in the country.
