Internet Core Protocols: The Definitive Guide

Services Provided by TCP

Although it is possible for applications to provide their own reliability and flow control services, it is impractical for them to do so. Rather than developing (and debugging) these kinds of services, it is much more efficient for applications to leverage them as part of a transport-layer protocol, where every application has access to them. This arrangement allows shorter development cycles, better interoperability, and less headaches for everybody.

TCP provides five key services to higher-layer applications:

Virtual circuits

Whenever two applications need to communicate with each other using TCP, a virtual circuit is established between the two TCP endpoints. The virtual circuit is at the heart of TCP’s design, providing the reliability, flow control, and I/O management features that distinguish it from UDP.

Application I/O management

Applications communicate with each other by sending data to the local TCP provider, which then transmits the data across a virtual circuit to the other side, where it is eventually delivered to the destination application. TCP provides an I/O buffer for applications to use, allowing them to send and receive data as contiguous streams, with TCP converting the data into individually monitored segments that are sent over IP.

Network I/O management

When TCP needs to send data to another system, it uses IP for the actual delivery service. Thus, TCP also has to provide network I/O management services to IP, building segments that ...