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The network layer is the third layer from the bottom in the OSI (Open Systems Interconnection) seven layer model. Also called the OSI reference model, this model was originally developed in 1977 in order to standardize and simplify definitions with regard to computer networks. It divides the networking process into seven logical layers, starting at the physical level (i.e., cable and network interface cards) and ascending to the application level (i.e., the layer that interfaces with application programs on computers), specifying services and protocols for each layer. The network layer is the layer at which IP (Internet protocol) operates. Other protocols in the TCP/IP suite of protocols, which forms the basis of the Internet and most other networks, that also operate in this layer are ICMP, IPsec, ARP, RIP, OSPF and BGP. The network layer is responsible for routing, which is moving packets (the fundamental unit of data transport on modern computer networks) across the network using the most appropriate paths. It also addresses messages and translates logical addresses (i.e., IP addresses) into physical addresses (i.e., MAC addresses). This contrasts with the data link layer below it, which is responsible for the device-to-device delivery of packets using MAC addresses. Above the network layer is the transport layer, which is responsible for making certain that packets are delivered in sequence and without errors, loss or duplication. Created September 16, 2005. |