Guest editorial internet proxy services

P ROXIES have become a crucial part of the Internet infrastructure during the past few years. In the traditional client/server model, two applications communicate directly with a clear separation of roles between the client and the server. A proxy extends this model by acting as an intermediary between a client and server. Although the notion of proxies predates the Web, the rapid growth of the Web in the mid 1990s spurred a strong interest in using proxies to reduce user-perceived latency, as well as server and network load. Many organizations deployed proxy caches to move popular Web content closer to their users. In addition, proxies acted as gateways to translate messages from one protocol to another. Over time, proxies began to perform a wider range of functions. By sending requests to servers on behalf of a collection of clients, a proxy typically obscures the identity of individual users. Some proxies go one step further and remove information (such as e-mail addresses or cookies) that might compromise the users' privacy. On the other hand, some organizations use proxies to collect logs of the users' requests or to block access to certain Web pages based on the URL or the contents. A proxy may transform or adapt the server response message to compress the data, insert advertisements, or execute a Java ap-plet. Proxies form the core part of content distribution networks that transfer Web resources from a variety of locations in the Internet. The growing popularity of multimedia applications has led to proxy services for audio and video streams. In contrast to the transfer of traditional Web content, multimedia streaming imposes strict timing requirements on the delivery of data to the receiver. Caching all or part of an audio or video stream at a proxy can reduce the playback delay experienced by users. In some cases, the proxy may be able to handle client VCR functions, such as rewind and fast forward, without contacting the server. Proxies can improve the audio and video quality by retransmitting packets that have been lost in the network. Alternatively, a proxy can react to network congestion by selectively discarding less important parts of the stream, or by transcoding the audio and video data to a lower bandwidth version. A group of proxies can be used to form an application-level multicast tree for streaming data to multiple clients distributed throughout the Internet. Extending the client/server model to …