r contends that it enhances the standard, this is to what they are referring. Dissimilar codecs are oblivious to pre- and post-processing steps and, therefore, gain no advantage from supplementary processing as do homogeneous codecs. That is why in a one-manufacturer H.320 demonstration (in which codecs on both ends are identical) images are cleaner and motion handling is smoother. NETWORK CONSIDERATIONS Low-end group systems usually support transmission speeds of 56-384 Kbps. Large Video Communications: The Whole Picture systems sold in the U.S. and Japan usually support speeds of 56 Kbps-1.536 Mbps. In the rest of the world, speeds range from 64-1.920 Mbps. Of course, bandwidth is only one aspect of signal transmission. How bandwidth is packaged is another. Standard transmission services include ISDN (BRI and PRI), switched 384 Kbps (H0), switched 1.536 Mbps (H11), and DSO multiples up to and including T-1/E-1. Any system should support IP. An H.323 requires more bandwidth than an equivalent H.320 call, which uses out-of- band signaling. Consequently, one should plan for about 20% more bandwidth to allow for TCP/IP traffic overhead. For instance, for an H.320 256 Kbps equivalent call, one should allow 307 Kbps. Bandwidth control is critical for an IP video communication session that might choke an entire data network. It is usual for a headquarters system to maximize its bandwidth and thereby choke branch networks. For that reason it may be useful to leverage advanced routing configurations or, better yet, to use sophisticated dedicated bandwidth management devices. Network Interfaces It is advisable to make network decisions before making system decisions. Information provided to a supplier should indicate network speed, and whether the network connection will be public or private, and whether it will be switched or dedicated. Varying image quality-requirements may require multiple speeds. A meeting between project managers and engineers may not demand the same quality requirements as a meeting between executi