Internet Core Protocols: The Definitive Guide

Application I/O Management

The primary benefit of the virtual circuit metaphor is the reliability that it allows. However, another set of key benefits is the I/O management services that this design provides.

One of the main features that comes from this design is that applications can send and receive information as streams of data, rather than having to deal with packet-sizing and management issues directly. This allows a web server to send a very large graphic image as a single stream of data, rather than as a bunch of individual packets, leaving the task of packaging and tracking the data to TCP.

This design helps to keep application code simple and straightforward, resulting in lower complexity, higher reliability, and better interoperability. Application developers don’t have to build flow control, circuit-management, and packaging services into their applications, but can instead use the services provided by TCP, without having to do anything special. All an application has to do is read and write data; TCP does everything else.

TCP provides four distinct application I/O management services to applications:

• Internal Addressing. TCP assigns unique port numbers to every instance of every application that is using a TCP virtual circuit. Essentially, these port numbers act as extension numbers, allowing TCP to route incoming data directly to the appropriate destination application.

• Opening Circuits. Applications inform TCP when they need to open a connection to a remote application, ...