Packet switching
• packet = string of bits (up to a few thousand, typically)
•uses store-and-forward operation
2 basic types of packet switching:datagrams. virtual circuit
• Datagram packet switching:
•each packet is treated individually within the network, so successive packets may follow different routes through it
•each packet contains the receiver’s address and a sequence number (so that receiver can put them into correct order)
Datagram packet switching
•no connection set-up needed
•flexible routing possible (e.g. if a router crashes)
•network resources are not shared at the same time
•each packet mono policies a link during its transmission, after which the link is available for other packet transmissions
•ideal for short-lived busy traffic
•less suitable for long-lived&/or interactive busy traffic
Virtual circuit packet switching:•a routers set up in the network between sender and receiver (by making appropriate entries in the routing tables)
•resources may or may not be reserved for this route. If resources need to be reserved and are not available, the connection request is blocked
•each packet contains its virtual circuit identifier
Virtual circuit packet switching
•connection set-up required, which may involve significant delay
•network resources are not shared at the same time
•each packet mono policies a link during its transmission, after which the link is available for other packet transmissions
•less work required at intermediate routers than for datagram p.s
•given a packet’s input link and virtual circuit identifier, the router can look up its routing table to find the output link
•virtual circuits not as robust to network problems as datagram p.s
Comparison
•virtual circuit p.s. represents a “compromise” between circuit switching anddatagramp.s.
•circuit switching creates a pathin the network; virtual circuit p.s. creates a routewhich exists only in software;datagramp.s. doesn’t have routes
•in circuit switching, the links in the path cannot be sharedduring the connection; in virtual circuit anddatagram p.s. they can
• packet = string of bits (up to a few thousand, typically)
•uses store-and-forward operation
2 basic types of packet switching:datagrams. virtual circuit
• Datagram packet switching:
•each packet is treated individually within the network, so successive packets may follow different routes through it
•each packet contains the receiver’s address and a sequence number (so that receiver can put them into correct order)
Datagram packet switching•no connection set-up needed
•flexible routing possible (e.g. if a router crashes)
•network resources are not shared at the same time
•each packet mono policies a link during its transmission, after which the link is available for other packet transmissions
•ideal for short-lived busy traffic
•less suitable for long-lived&/or interactive busy traffic
Virtual circuit packet switching:•a routers set up in the network between sender and receiver (by making appropriate entries in the routing tables)
•resources may or may not be reserved for this route. If resources need to be reserved and are not available, the connection request is blocked
•each packet contains its virtual circuit identifier
Virtual circuit packet switching•connection set-up required, which may involve significant delay
•network resources are not shared at the same time
•each packet mono policies a link during its transmission, after which the link is available for other packet transmissions
•less work required at intermediate routers than for datagram p.s
•given a packet’s input link and virtual circuit identifier, the router can look up its routing table to find the output link
•virtual circuits not as robust to network problems as datagram p.s
Comparison
•virtual circuit p.s. represents a “compromise” between circuit switching anddatagramp.s.
•circuit switching creates a pathin the network; virtual circuit p.s. creates a routewhich exists only in software;datagramp.s. doesn’t have routes
•in circuit switching, the links in the path cannot be sharedduring the connection; in virtual circuit anddatagram p.s. they can
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