Packet switching in Transmission modes

Explain the size of packets in the packet switching in Transmission modes and in which case the link/ session created either for packet switching or circuit switching.? 

Packet size on network vary according to the communication technique used over there for data transfer, like minimum Ethernet packet size is 64 bytes

IP datagrams of at least 576 bytes (for IPv4) or 1280 bytes (for IPv6).

ATM works as a stream of fixed-length packets (known as 'cells'). Each of which can carry a payload of 48 bytes of user data with 5 bytes of overhead for a total cost of 53 bytes per cell.

You can visit this link for more details

http://en.wikipedia.org/wiki/Maximum_transmission_unit

Circuit switching is old and expensive. Circuit-switched networks were used for phone calls and packet-switched networks handled data as VOIP.