Disadvantages of packet switching relative to circuit switching are as follows:

• Each time a packet passes through a packet-switching node it incurs a delay not present in circuit switching. At a minimum, it incurs a transmission delay equal to the length of the packet in bits divided by the incoming channel rate in bits per second; this is the time it takes to absorb the packet into an internal buffer. In addi- tion, there may be a variable delay due to processing and queuing in the node.
• Because the packets between a given source and destination may vary in length, may take different routes, and may be subject to varying delay in the switches they encounter, the overall packet delay can vary substantially. This phenome- non, called jitter, may not be desirable for some applications (for example, in real-time applications, including telephone voice and real-time video).
• To route packets through the network, overhead information, including the address of the destination, and often sequencing information must be added to each packet, which reduces the communication capacity available for carrying user data. This is not needed in circuit switching once the circuit is set up.
• More processing is involved in the transfer of information using packet switch- ing than in circuit switching at each node. In the case of circuit switching, there is virtually no processing at each switch once the circuit is set up.