Achieving Reliable High Performance in LFNs

The PC hardware architecture and commodity operating systems such as Linux or Microsoft Windows are dominant in end-host infrastructure in the current Internet. It shows that many performance problems in high-speed long-distance networks (also called longfat networks or LFNs due to high possible volume of outstanding data between the sender and receiver) are caused by improper behaviour of end hosts, rather than by the network itself. Understanding of the behaviour of networking support in commodity operating systems, networking applications, their mutual interaction and their interaction with a computer network is necessary to identify and resolve these problems. Our goal is to identify the most significant problems and suggest possible solutions. Many advanced Internet users, requiring high network performance, use the Linux operating system. Therefore, we decided to concentrate on networking support in Linux. Particularly, we will show that just setting large TCP buffers and modifying TCP congestion control AIMD parameters is not sufficient to reliably achieve high throughput. We will show that smart window size moderation is required not to allow too large TCP windows. We will also describe an important performance problem in scp, a commonly used network file copy program.