Hopen OS

4. Network System

TCP/IP is a protocol hierarchical model composed of four layers, they are the application layer, transport layer (TCP), network layer (IP) and data link layer from the top down. TCP/IP protocol includes a group of protocols on transportation layer, network layer and data link layer, called TCP/IP Protocol Cluster. The application program interface (Socket interface), TCP and UDP protocols on transportation layer, IP protocol on network layer, IFACE interface and PPP protocol on data link layer are all implemented in Hopen system.

The TCP/IP subsystem provides the following functions:

Provide SOCKET interface compatible with Win Socket for user layer, which includes all the structure setting functions and action functions, and implementing a set of common SOCKET libraries.

Implement UDP protocol to provide the connectionless and high-efficient information transmission for application programs. UDP is used to transmit a small quantity of data message. The efficiency is high but the reliability can not be guaranteed. It is up to the application programs to ensure the reliability.

Implement IP protocol and provide the service of network layer. Two functions are realized here. First, it carries the IP data from source to destination host according to the address in IP header. Secondly, it regroups the received long segmented data according to the maximum data transmission length.

The unified interface of MAC layer can be attached to the PPP protocol based on Modem, PPP protocol based on Ethernet protocol and Cable Modem protocol.