Windows NT TCP/IP Network Administration

Internet Layer

The layer above the Network Access Layer in the protocol hierarchy is the Internet Layer. The Internet Protocol, RFC 791, is the heart of TCP/IP and the most important protocol in the Internet Layer. IP provides the basic packet delivery service on which TCP/IP networks are built. All protocols, in the layers above and below IP, use the Internet Protocol to deliver data. All TCP/IP data flows through IP, incoming and outgoing, regardless of its final destination.

Internet Protocol

The Internet Protocol is the building block of the Internet. Its functions include:

• Defining the datagram, which is the basic unit of transmission in the Internet

• Defining the Internet addressing scheme

• Moving data between the Network Access Layer and the Host-to-Host Transport Layer

• Routing datagrams to remote hosts

• Performing fragmentation and re-assembly of datagrams

Before describing these functions in more detail, let’s look at some of IP’s characteristics. First, IP is a connectionless protocol. This means that IP does not exchange control information (called a handshake) to establish an end-to-end connection before transmitting data. In contrast, a connection-oriented protocol exchanges control information with the remote system to verify that it is ready to receive data before any data is sent. When the handshaking is successful, the systems are said to have established a connection. Internet Protocol relies on protocols in other layers to establish the connection if they require connection-oriented ...