IP Routing Protocols

END-TO-END COMMUNICATIONS

The layers of the OSI Model and the layers of vendor's models (such as IBM's SNA, or the Internet layered model) contain the communications functions at the lower three or four layers. From the OSI perspective, it is intended that the upper four layers reside in the host computers, as depicted in Figure A-2.

Figure A-2. End-to-End Operations

This does not mean that the lower three layers reside only in the network. In order to effect complete communications, the hardware and software implemented in the lower three layers also exist at the host machine. End-to-end communications, however, occurs between the hosts by invoking ...