Packet switching

Packet switching is a method of sending data in a computer network . A packet is an information group consisting of two parts: the data itself and the control information, which indicates the route to be followed along the network to the destination of the packet. There is an upper limit for packet size; If it is exceeded, it is necessary to divide the package into smaller ones, Ethernet uses frames (frames) of 1500 bytes, while FDDI uses 4500 byte frames.

• The packets form a queue and are transmitted as fast as possible.
• They allow the conversion in the speed of the data.
• The network can continue to accept data even though transmission is slow.
• There is the possibility of managing priorities (if one group of information is more important than the others, it will be transmitted before others).

Techniques 

Two types of techniques have been defined for the use of packet switching: datagrams and virtual circuits.

Data grams

• The Internet is a network of large datagrams.
• In Internet there are 2 trends: connection oriented and not connection oriented.
• In the connection-oriented case, the protocol used for transport is TCP .
• In the non-connection-oriented case, the protocol used for transport is UDP .
• TCP ensures that all data arrives correctly and in order.
• UDP has no warranty.
• Not all packages follow the same route.
• A packet can be destroyed on the way, whose recovery is the responsibility of the originating station (this implies that all other packets are intact).

Virtual circuit-based packet switching 

See also: Multiplexing and Virtual Circuit .

• Its operation is based on both message switching and circuit switching . However, in virtual circuits, the route is not dedicated to the sender and receiver as in classical circuit switching, but rather that the medium (including each single link between two adjacent nodes) is shared for the transmission and reception of packets from different transmitters and receivers, in a manner analogous to what happens in message switching.
• Before establishing communication between sender and receiver, a fixed (not permanent) route must be established for all packets of this one, unlike packet switching based on datagrams, where each fragment is sent through the available route Faster for each hop between each node and the next, which is determined based on parameters such as the state and load of the network at that time, or more specific specific factors (for example, a priority index contained in the header A datagram, or the priority of one or the other route in link state dynamic routing protocols ).
• Each packet contains a virtual circuit identifier, in addition to the source and destination address, throughout the communication. Omitting thus the encapsulation of the direction of next hop in each node of the route through which passes.