Fundamentals of Communications and Networking, 3rd Edition

Network Layer Basics

The Network Layer (Layer 3) of the OSI Reference Model defines the functions and activities that are to occur between the Transport Layer (Layer 4) and the Data Link Layer (Layer 2) to facilitate and ensure the transfer of data from its source to its destination. Included in the functions and actions defined on the Network Layer are:

• Datagram/packet encapsulation—Layer 3 functions include encapsulating messages passed from higher layers into datagrams (also called packets) along with Network Layer header information. The Layer 3 datagram is encapsulated within the Ethernet II frame format at the Data Link layer.
• Error handling and diagnostics—Layer 3 defines special-purpose protocols that allow logically connected devices ...