Packet and Circuit Switching

1. What are the current advantages and disadvantages of packet-switching compared to circuit switching?

Circuit switching is typically used in older analogue systems such as phone or PSTN systems. Circuit switching routes data by first establishing a path or “circuit” from the point of origin to the destination. Once the path has been established, data (such as the voice data in a phone call) can be forward. Packet switching does not establish a point to point path. Instead packet switching breaks the data to be forwarded into chunks called “packets” and places the source and destination address on each packet along with a sequence number if required by the protocol in use. Data packets are forwarded to the destination over a network of devices (routers and switches) that use a routing table to determine where to send each packet based upon the destination address in the packet. Packets may be forwarded over different paths to arrive at the same destination where they are reassembled back into the original data format. Circuit switching does not require the overhead of breakdown and reassembly of packets however path bandwidth is not used efficiently because it is dedicated to a single conversation or session. Packet switching has more overhead to breakdown, package and reassemble data however it more effectively utilizes available network bandwidth and resources. Packet switching is now more commonly used as the world moves all information transmission, including phone networks, to IP based technologies.

2. Explain the difference between the network layer in a connection-oriented packet switching network and the network layer in a connectionless packet switching network.

The network layer in the DoD network model, handles connection-oriented packet switching by first establishing a connection session using a handshake method such as the three-way handshake employed by the TCP or Transmission Control Protocol in which a “Syn,”, “Syn Ack” and “Ack” message packets must be exchanged before data is sent. With connectionless packet switching there is no session setup and instead data is sent to the destination using a “best effort” method, such as is the case with UDP or User Datagram Protocol.