The OSI model (Open Systems Interconnection model) is a standard description or “reference model” for how messages should be transmitted between any two points in a network. In this model, Layer 4 is referred to as the Transport Layer, Layer 3 the Network Layer and Layer 2 the Data Link Layer. While Layer 2 switches forward packets based on MAC addresses and Layer 3 switches forward/route packets based on IP addresses, Layer 4 defines the quality and nature of data delivery and provides for end-to-end integrity controls such as flow control, retransmission, and so on.

For more information on Layer 4 switching, visit Telco Systems’ Web site.