The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)                 9  Internet Protocol Concepts and Overview

Internet Protocol Concepts and Overview 1 2 IP Functions

IP's Success Despite Its Limitations

The last three characteristics in the preceding list might be enough to make you cringe, thinking that giving your data to IP would be somewhat like trusting a new car to your sixteen-year-old son. If we are going to build our entire network around this protocol, why design it so that it works without connections, doesn't guarantee that the data will get there, and has no means of acknowledging receipt of data?

The reason is simple: establishing connections, guaranteeing delivery, error-checking and similar “insurance” functions have a cost: performance. It takes time, computer resources and network bandwidth to perform these tasks, and they aren't always necessary for every application. Now, consider that IP carries pretty much all user traffic on a TCP/IP network. To build this complexity into IP would burden all traffic with this overhead whether it was needed or not.

The solution taken by the designers of TCP/IP was to exploit the power of layering. If service quality features such as connections, error-checking or guaranteed delivery are required by an application, they are provided at the transport layer (or possibly, the application layer). On the other hand, applications that don't need these features can avoid using them. This is in fact the major distinction between the two TCP/IP transport layer protocols: TCP and UDP. TCP is full-featured but a bit slower than UDP; UDP is spartan in its capabilities, but faster than TCP. This system is really the “best of both worlds”. And unlike your teenager with the shiny new license, it has been proven to work well in the real world. J

So how is datagram delivery accomplished by IP? In the following topic I discuss in more detail the main functions that IP performs to “get the job done”, so to speak.

Internet Protocol Concepts and Overview 1 2 IP Functions