08-05-2012, 03:14 PM
Circuit Switching
22Circuits.ppt (Size: 333.5 KB / Downloads: 142)
Goals of Today’s Lecture
Circuit switching
Establish, transfer, and teardown
Comparison with packet switching
Virtual circuits as a hybrid scheme
Quality of service in virtual-circuit networks
Traffic specification and enforcement
Admission control and resource reservation
Link scheduling (FIFO, priority, and weighted fairness)
Path selection (quality-of-service routing)
Quality of service for IP traffic
IP over virtual circuits
Differentiated services
Disadvantages of Circuit Switching
Wasted bandwidth
Bursty traffic leads to idle connection during silent period
Unable to achieve gains from statistical multiplexing
Blocked connections
Connection refused when resources are not sufficient
Unable to offer “okay” service to everybody
Connection set-up delay
No communication until the connection is set up
Unable to avoid extra latency for small data transfers
Network state
Network nodes must store per-connection information
Unable to avoid per-connection storage and state
Virtual Circuit Identifier (VC ID)
Virtual Circuit Identifier (VC ID)
Source set-up: establish path for the VC
Switch: mapping VC ID to an outgoing link
Packet: fixed length label in the header