Communication methods in networks

This is a section of the chapter "Internet" of the book “Principles of Digital Multimedia”.
The text introduces the different modes of communication in networks

Circuit switching

Circuit switching (or connection-oriented) is the system for temporarily connecting two users, as happens for example with the telephone in which during the phone call a temporary circuit is created that connects the two interlocutors through a
series of connections between one telephone exchange and the next.
The transmission resources (telephone, lines, portions of exchanges) remain allocated to the two interlocutors until the call ends.

Connection-oriented services have an inefficient use of transmission resources, since if the two interlocutors do not transmit any signal (for example, they are silent) the resources are not exploited.

Example
Let's imagine we have two telephones, one in city A and the other in city B, and we want to establish a direct telephone call between them using circuit switching:

Initialization: When the user in city A dials the telephone number in city B, the circuit switching system in the local telephone exchange in A detects the call request and reserves a dedicated connection for communication between A and B.

Connection: Telephone exchange A establishes a physical or virtual connection (circuit) through the telecommunications network to the telephone exchange in city B. During this phase, resources and communication channels are reserved for the entire duration of the call.

Communication: Once the connection is established, users in cities A and B can begin talking and listening to each other. Because a dedicated connection has been established, voice data is transmitted continuously and without interruption, providing real-time communication between the two users.

Termination: When one of the users hangs up the phone or ends the call, the circuit-switching system releases the dedicated connection, freeing up network resources previously reserved for that call.

Packet switching

Packet switching (or connectionless) is a communication system that does not establish any pre-established path between two users.
The information to be sent is packaged in data packets and entrusted to the network with the recipient's address indicated, as happens for example in the postal system.
In fact, it will be the network's job to transport, and then route, the packet to its destination.
Unlike circuit switching, packet switching:

It uses transmission resources more efficiently, since they are allocated to a user for the time strictly necessary for the transmission of packets and are then allocated to another user.

It does not guarantee the minimum time for the information to travel, nor an exact order of arrival of the packets: the network will try to "do its best" (best effort).

Packet switching is suitable when a delay of a few seconds in reception can be tolerated.
For example, when receiving a file or an email, the user is not aware of a delay, but in the case of a real-time event (for example, a phone call), even a second's delay is perceived by both parties.
The Internet is an example of a connectionless network.

Example
Suppose you want to send an email containing a text message and some images to a friend. Using packet switching, the process might look like this:

Packeting: The text message and images are split into small data packets. For example, the text message could be split into multiple packets, as could each image.

Routing: Packets are now routed through the network. During this process, each packet can take a different path to its destination. This is because packets can be routed to their destination via the most efficient path available at that time.

Transmission: Packets travel across the network, passing through various routers along the way. Each network device forwards them to the next node, following routing instructions to reach their destination.

Arriving at the destination: Once the packets reach their destination, they are processed. Each packet has information about the correct order in which they should be rejoined. All the packets are then reunited to reconstruct the original email, including the text message and images.

Message View: Your friend receives the email, opens the attachment, and sees the text message and images as sent.

Types of transmission channels

There are two types of transmission channels that are widely used:

Broadcast

Unicast

Point-to-point links (or unicast) connect pairs of computers.
Packets must visit one or more intermediate machines to move to their source or destination in a network composed of point-to-point links.
Individual point-to-point connections are called links.
In its most basic sense, a link represents the direct communication line between two nodes.

A set of links that connect a client to a server

In contrast, broadcast networks have a single communication channel shared by all machines on the network: packets sent by any machine are received by any machine on the network.
Upon receiving the message, each machine checks the address field. If the address in the field is equivalent to the current machine, it is processed; otherwise, it is ignored.

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febogamedeveloper@gmail.com – 9 June 2026 – 8:14 am

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