Principles Circuit switching designed for voice Resources dedicated to a particular call Much of the time a data connection is idle Data rate is fixed Both ends must operate at the same rate | PACKET SWITCHING Principles Circuit switching designed for voice Resources dedicated to a particular call Much of the time a data connection is idle Data rate is fixed Both ends must operate at the same rate Basic Operation Data transmitted in small packets Typically 1000 octets Longer messages split into series of packets Each packet contains a portion of user data plus some control info Control info Routing (addressing) info Packets are received, stored briefly (buffered) and past on to the next node Store and forward Use of Packets Advantages Line efficiency Single node to node link can be shared by many packets over time Packets queued and transmitted as fast as possible Data rate conversion Each station connects to the local node at its own speed Nodes buffer data if required to equalize rates Packets are accepted even when network is busy Delivery may slow down Priorities can be used Switching Technique Station breaks long message into packets Packets sent one at | PACKET SWITCHING Principles Circuit switching designed for voice Resources dedicated to a particular call Much of the time a data connection is idle Data rate is fixed Both ends must operate at the same rate Basic Operation Data transmitted in small packets Typically 1000 octets Longer messages split into series of packets Each packet contains a portion of user data plus some control info Control info Routing (addressing) info Packets are received, stored briefly (buffered) and past on to the next node Store and forward Use of Packets Advantages Line efficiency Single node to node link can be shared by many packets over time Packets queued and transmitted as fast as possible Data rate conversion Each station connects to the local node at its own speed Nodes buffer data if required to equalize rates Packets are accepted even when network is busy Delivery may slow down Priorities can be used Switching Technique Station breaks long message into packets Packets sent one at a time to the network Packets handled in two ways Datagram Virtual circuit Datagram Each packet treated independently Packets can take any practical route Packets may arrive out of order Packets may go missing Up to receiver to re-order packets and recover from missing packets Virtual Circuit Preplanned route established before any packets sent Call request and call accept packets establish connection (handshake) Each packet contains a virtual circuit identifier instead of destination address No routing decisions required for each packet Clear request to drop circuit Not a dedicated path Virtual Circuits v Datagram Virtual circuits Network can provide sequencing and error control Packets are forwarded more quickly No routing decisions to make Less reliable Loss of a node looses all circuits through that node Datagram No call setup phase Better if few packets More flexible Routing can be used to avoid congested parts of the network Packet Size Circuit v Packet .
