About LSAM

What is LSAM

Current implementations of such services rely on individual components, such as Web servers, WAIS servers, and host clients. Some resource sharing is provided via distributed indexing systems, e.g., Harvest, or manually configured proxy caches. The goal of LSAM is to develop middleware to support large-scale deployment of distributed information services with effective economies of scale.

LSAM achieves these goals by using automatic multicast channel management and server-based information push.

The LSAM system is based on a few key assumptions about web systems:

• Existing caching techniques are relatively effective.
• Hot-spots generate significant traffic, important to users.
• Hot-spots defeat existing caching techniques.

The LSAM Proxy

For caching to be effective, the proxy must be central to the sites with similar interests. Because these interests are dynamic, no single proxy can provide effective resource sharing.

LSAM replaces the concept of a single, central proxy with that of a virtual proxy. Multiple local proxies act together over multicast channels to provide the benefits of a single, central proxy, even where there is no central location from which one proxy could suffice.

The LSAM self-organizing web cache system provides efficient and intelligent cache service for distributed information access. The system is implemented in a proxy, which coordinates with other instances of itself to create a self-organized system. This system adjusts to support both conventional object access and meta-data such as aggregated query responses and their prefetched components. The proxy uses multicast networking to self-configure, and to reduce its aggregate bandwidth requirements while providing enhanced performance. It also uses multicast to leverage access affinity patterns to provide enhanced performance for groups of clients, supporting growth and scalability of distributed information service, and facilitating their use in unpredictable environments.

• Multicast Channel Program Guide
• Dynamic Cache Control
• Object Scheduling
• Intelligent Request Routing
• Mobility Management
• Environment Analysis

Relationship to the DARPA Information Management Program

An example:

Specific IM projects enhanced or enabled:

CNRI's Digital Object Infrastructure includes Distributed Indexing, which can use multicast channels where each index is a channel, enabling fast access to indexed information grouped by affinity.

UTennesee's Evolving Software Repositories can use multicast to update and aggregate its software libraries based on groupings such as host architecture or application use.

Both MIT/LCS's Intelligent Query Access and UMD's Dynamic Query Management summarize responses via sets, the components of which are prefetched, requiring prioritized client request ordering and server processing, provided by the LSAM proxy's object scheduling mechanism. Further, the proxy channels can be mapped to their query refinement groups, where observation of channel activity indicates group interest in related information, signaling the individual client to additional relationships, enhancing information discovery.

The Open Group's Distributed WWW Clients , in DARPA's IC&V Program, can use channels for object working sets, using explicit group information to govern channel creation and content, a multicast proactive version of their unicast client-side system, but with lower upstream request bandwidth and even further reduced downstream bandwidth.

Earlier LSAM research

That earlier work focused on four major tasks:

• Intelligent Bandwidth (IB) Organizes the use of distributed caches based on network parameters and usage information. This work led to the multicast channel architecture of the current LSAM proxy.
• Replication Supports copy management and copy selection to increase performance and reliability. This is used to support the management of copies of data, such as are created by the multicast data distribution of the current proxy.
• Security Integrates emerging authentication and privacy mechanisms, and augment those services to accommodate LSAM's new middleware. This is used to support the distributed management of data, such as used in the current proxy.
• Performance Examines protocol extensions to improve the performance of distributed object access. These protocol modifications affect the access latency of both cached and non-cached objects. The overall goal of the current LSAM proxy is to reduce access latency and network load for accessing hot-spot objects. These protocol modifications increase the performance of the underlying object access system, which both highlights the need for the LSAM proxy's enhancements, as well as to further increase the performance of the proxy. 

 
Page maintainer: the LSAM project