General purpose proxies: solved and unsolved problems

Proxies are becoming increasingly common. One use of a proxy is to address network heterogeneity, which can arise especially in mobile computing. In this setting, a proxy can process the traffic flowing to and from a network limited mobile host, damping the variations in application performance as well as providing other benefits such as reduced cost and increased security. We describe the issues we faced in designing such a proxy system, how we solved some problems, and why others could not be solved.