| The Ethernet technology is based on the non-deterministic protocols such as CSMA/CD, which can performance well on office environment due to their big throughput and cheap price. But in the real time application of industrial environment, the deterministic behaviors become the most important issue which can not be satisfied by these protocols. It is difficult to build a real time control network using standard Ethernet, because its MAC protocol is based on CSMA/CD. The transport of a packet from one node to another node may experience a large delay which is unable to be predicted.Therefore, in order to achieve transplant from the office Ethernet to industrial Ethernet, we must replace the non-deterministic Ethernet protocols by deterministic protocols. We build a new kind of Ethernet which can guarantee the real time application under the office Ethernet media. A device called Central Network Control Unit is introduced in the thesis, which is the central control unit of the network and is used to arbitrate the usage of network media. All other devices in the network must work under its control. They can only send packets when it orders them to do so.The packets are divided into three priorities duo to their importance. The first priority packets are the control packets which must be sent to the destinations in a certain time. The second priority packets are the multimedia packets. The third priority packets are other less important packets which have no real time requires and whose reliabilities can be achieved by upper level protocols. When the network is overloading, the Central Network Control Unit can perceive it and dropout some low priorities fluent to keep the real time behavior of high priorities fluent.The details of the network control rules are introduced in the thesis and the computer emulations are provide to prove the feasibility of these rules.The designs of the Central Network Control and some devices under the control of it are also introduced by the author. |
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