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In the second test, we looked at performance by measuring with a stopwatch the time each product took to complete the distribution.

In a variation on the second test, we gathered Sniffer statistics that let us rank each product's use of the network. In a third test, we gauged the user interface(s) of the push products by awarding quality points to their ease-of-use features. In a fourth and final test, we ju dged the security of the products by noting how difficult it would be to eavesdrop on or intercept the data distribution process.

StarBurst Multicast emerged the best product, earning itself the Editor's Choice award by scoring highest in our tests. Multicast used our network frugally as it quickly and reliably did our server-based bidding to put data where it belonged.

Plumber's Friend Vendors of push middleware tools claim four benefits from their products. They assert that you'll realize reduced or least scheduled bandwidth usage; consistent and up-to-date Web pages, client configurations, application versions and data files; central administration of data distribution; and secure, unhackable distribution of data.

Tool designers have taken different avenues to reducing bandwidth in push products. One approach spends server and client CPU time, compressing the data to reduce the number of bytes traversing the network. Another assumes the outg oing information is but a later version of already-distributed data and sends only the incremental changes to bring the client up to date. Yet another approach hopes to find friendly firewalls and respectful routers as it sends a single stream of data to multiple clients (see "The Current State of IP Multicast," page 58).

Consistent data for all clients is the key selling point for push middleware. All push tools employ some sort of feedback mechanism that each client target uses to let the server know it has successfully received a file, program, stream of data or collection of data items.

Central administration is a common feature of all push tools. Rather than configure clients to copy certain files at certain times or periodically run update utilities, you configure the server software to distribute data based on user groups and types of data. Push tools implement the common goal of central administration with rather uncommon interfaces. Some offer GUI tools for designating user groups and data type s, some let you drive the process with scripts you write, and one tool, TIBCO's TIB/Rendezvous, hands you a programming interface and expects your programmers to layer distribution rules and instructions into the applications your company uses.

Applications behave differently (sometimes badly) when a directory contains the wrong version of a program or data file. These push products give administrators control over the server's transmission of files, but none compensates for clients that copy out-of-date files (perhaps from a backup tape) onto client machines.

Whether over the Internet or even your private intranet, push can be risky business. Push middleware tools use SSL (Secure Sockets Layer), RSA or other keyed encryption, plus digital certificates to make darned sure bogus data and programs don't destroy your well-planned and carefully crafted network assets.