The Research On Network Subsystem In Extensible Operating System And Its Implementation

Operating system design is one of the most important fields in computer science domain. Since 1990s with the development of hardware as well as network technologies and driving of rapid increasing application requirements, traditional operating system hasn't keep up with the various requirements of applications,people begin to study extensible ability of operating system,and after ten years work many achievemens have been gotten,this may result in another revolution of operating system design.Having studied architectures and technologies of extensible operating system at home and aboard ,we adopt an vertical architecture based on library operating system and then we try to implement a prototype with user level protocols library aiming at characters of user level network subsystem under that architecture.We carry out a three layers network subsystem structure that is protocol independent layer in kernel,protocol dependent layer in kernel and user level protocol stack.The implement of user level stack in vertical and extensible operating system architecture improves the network subsystem's extensible ability ,the necessary technique of early demultiplexing also improves performance and makes up for the limitations in traditional network subsystem. Protocol independent layer and protocol dependent layer separates universality of protocol himself and specialties of protocol implement which guarantees protocol syntax and improves performance. Protocol independent layer can deal with packages in spite of differences of protocols by extending package filiter technique,which solve the most important problem in protocol data unit(PDU) demultiplexing.Lazy Receiver Processing technique can optimize the network subsystem as well as reduce the possibility of livelock taking place which also improve the system's security.The use of mbuf in buffer management and override technique can alleviate the bottleneck of protocol processing by reduce the copy and improve the perfomance of PDU send and receive.