Devices involved in Layer 4 switching perform the following functions:
Packets are forwarded using hardware switching, based on both Layer 3 addressing and Layer 4 application information. (Layer 2 addressing is also inherently used.)
Layer 4 protocol types (UDP or TCP, for example) in packet headers are examined.
Layer 4 segment headers are examined to determine application port numbers.
Switching at Layer 4 allows finer control over the movement of information. For example, traffic can be prioritized according to the source and destination port numbers, and QoS can be defined for end users. Therefore, video or voice data can be switched at a higher level of service, with more bandwidth availability than file transfer or HTTP traffic. Layer 4 port numbers for source and destination also can perform traffic accounting. "