Designing an Ethernet switch that can assure normal interaction of protocol packets between switches in a network environment of massive traffic is an important matter. Taking the L3 Ethernet switch based on Applicati...Designing an Ethernet switch that can assure normal interaction of protocol packets between switches in a network environment of massive traffic is an important matter. Taking the L3 Ethernet switch based on Application Specific Integrated Circuit (ASIC) as an example,this article analyzes several typical issues about packet receiving and sending by the CPU in a multi-progress environment,including CPU load,software and hardware queue settings,and communication mechanism between CPU and the switch chip. This article gives solutions to these issues mentioned above. The solutions are applicable to Network Processor (NP) issues as well.展开更多
In this paper, a modified access mechanism named Constrained-send DCF (CDCF) is proposed to improve the performance of IEEE 802.11 DCF protocol. It is found that, in DCF, the transmission probability is higher than th...In this paper, a modified access mechanism named Constrained-send DCF (CDCF) is proposed to improve the performance of IEEE 802.11 DCF protocol. It is found that, in DCF, the transmission probability is higher than the reasonable value when the node number is greater than 4 under basic access scheme or than 17 under RTS/CTS scheme, and it results in serious collision. To avoid collision of high access loading, a constrained-send probability is introduced at the end of each back off procedure for the station transmitting. The performance of this mechanism is analyzed based on a 2-Dimension Markov analytical model, after that the optimum constrained-send probability is derived. Numerical results show that the CDCF mechanism has much better performance than DCF with respect to both system throughput and average packet delay. And under RTS/CTS scheme, although CDCF slightly improve the throughput performance (due to the natural good throughput performance of RTS/CTS-scheme DCF), it leads to a much better average packet delay performance compared to DCF. The CDCF keeps all the features of the IEEE 802.11 DCF protocol and is quite easy to implement.展开更多
文摘Designing an Ethernet switch that can assure normal interaction of protocol packets between switches in a network environment of massive traffic is an important matter. Taking the L3 Ethernet switch based on Application Specific Integrated Circuit (ASIC) as an example,this article analyzes several typical issues about packet receiving and sending by the CPU in a multi-progress environment,including CPU load,software and hardware queue settings,and communication mechanism between CPU and the switch chip. This article gives solutions to these issues mentioned above. The solutions are applicable to Network Processor (NP) issues as well.
基金Sponsored by the National Natural Science Foundation of China(Grant No.60832008)the National S&T Major Project (Grant No.2010ZX03003-002-02)the National Key Basic Research and Development Project (Grant No.2012CB316006)
文摘In this paper, a modified access mechanism named Constrained-send DCF (CDCF) is proposed to improve the performance of IEEE 802.11 DCF protocol. It is found that, in DCF, the transmission probability is higher than the reasonable value when the node number is greater than 4 under basic access scheme or than 17 under RTS/CTS scheme, and it results in serious collision. To avoid collision of high access loading, a constrained-send probability is introduced at the end of each back off procedure for the station transmitting. The performance of this mechanism is analyzed based on a 2-Dimension Markov analytical model, after that the optimum constrained-send probability is derived. Numerical results show that the CDCF mechanism has much better performance than DCF with respect to both system throughput and average packet delay. And under RTS/CTS scheme, although CDCF slightly improve the throughput performance (due to the natural good throughput performance of RTS/CTS-scheme DCF), it leads to a much better average packet delay performance compared to DCF. The CDCF keeps all the features of the IEEE 802.11 DCF protocol and is quite easy to implement.
