Packet Switching

Packet Switching

In packet switching messages are divided into smaller piece called PACKET
Each packet includes source and destination address information so that individual packets can be routed through the internetworks independently.
The packet that makes up a message can take very different routs through the internetworks.
Packet Switching looks concededly like messages switching but the different characteristic is that packets are restricted is that packets to a size that enables the switching device to manage the packet. The packet data entirely in memory.
This eliminates the need for switching device to store the data temporary on disc.
Packet switching routes packets through the networks much more rapidly and efficiently then is possible with messages switching.

Two Common methods of packets as follow :

Datagram
Virtual Circuits

1. Datagram

It service treat each packets as an independently message.
Each packet is routed through the internetworks independently and each switch mode determines which network segment should be used for the next step in packets rout.
This capability enables switches to bypass busy segment and take other step to speed packets through the internetworks.
Datagram is frequency used on LAN's (Local Area Network).
Network layer protocols are responsible for delivering the frame to the appropriate networks.
Each datagram include destination address information device on the local network can recognize and receive appropriate datagram.
Packet switching needs the need to transmit large message with the small frame size that can be accommodate by the physical layer.
The network layer is responsible for fragmenting messages from upper layer into smaller datagram that are appropriate for physical layer.
The network layer is also responsible for reconstruction messages from datagrams as they are received.

2. Virtual Circuits

It's operate by established by formal connection between two devices in communication.
When devices begin a season they negotiate communication parameters such as maximum messages size, communication window and network path.
This negotiation established virtual circuits which are a well define pat through the internetworks by which the device communicate.
This virtual circuits remains in effect until the devices stop communicating.
Virtual circuits are define by the establishment of a logical connection
Virtual means that the network behaves as through a dedicated physical circuits has been established between the communication device.

Even through no such physical circuits actually exists the network presents the appearance of a physical connections to the devices at the end of the circuits.