The authors are not discussing information security as this is understood in the world of INFOSEC. This discussion is not about securing e-mail content or encryption of computer files; these are operations that can be handled easily and inexpensively by software and, in most cases, offline. If one wonders what the system s user will say, the answer is that in most respects, no one cares whether his or her email message will be encrypted within 125 ms or in 500 ms. On the other hand, the user will certainly react and rightfully so if he or she must wait five minutes for a three-line e-mail message to be encrypted or decrypted. One also realizes from this small example that in real-time communications (especially when the transmitted content is large and unpredictable) the solution architect does not have the luxury of the offline-solution provider of passing twice over the data. This is the case for instance in a classical Lempel-Ziv type of compression algorithm, where the first pass allows the system to build the dictionary and the second pass over the data to be compressed actually encodes the content accordingly. In real-time communications things have to happen fast and correctly.

Incidentally, relative to potential user answers to exhaustive-detail questionnaires, the granularity between the extremes is the subject of traditional market analysis, where people will be asked what they need as response time, and some may say half a second, while others may say three seconds. The...