Computer Networking: Internet Protocols in Action

Chapter 1.2. Protocol Layering

INTRODUCTION

Computer communication, much like human communication, relies on mutually agreed upon patterns of interaction called protocols. A protocol defines the format, content, and order of messages used by communicating entities to accomplish a specified task. For example, the Hypertext Transfer Protocol or HTTP defines the set of messages exchanged between a web browser and a web server when transmitting a web page.

Computer communication is accomplished with a set of protocol layers, each layer accomplishing a portion of the required tasks. For example, in the case of a web browser and web server, HTTP is not the only protocol required. HTTP relies on the Transmission Control Protocol or TCP to ensure reliable delivery of the web page despite data loss that might occur in the network. In turn, TCP relies on the Internet Protocol or IP to route the packet through the network from the machine running the web browser to the machine running the web server.

Together, these protocol layers form the network protocol stack. The International Organization for Standardization (ISO) defined a standard seven-layer protocol stack called the Open Systems Interconnection (OSI) model. In this model, each layer provides a service to the layer above it and relies only on the layer below it. Logically, each layer interacts with its peer layer on the remote computer through an agreed upon protocol. The protocol stack in the Internet operates in a similar way, but ...