Abstract: A method and apparatus for measuring channel characteristics of a multi-channel system. In accordance with the method and the apparatus, a first chirp is applied as an input to one channel of a multi-channel system at a first time, and a second chirp is applied as an input to another channel of the multi-channel system at a second time, the second time being separated from the first time by a predetermined first time interval. An output signal is acquired from a selected one of the channels. At least one crosstalk component is separated from non-crosstalk components in the output signal to characterize the selected channel based on non-crosstalk components. Preferably, the chirp is an exponential chirp that enables harmonic distortion components to be distinguished and measured in one channel in the presence of crosstalk from one or more other channels.

Abstract: An Internet-based printing system allows for the distribution and printing of documents and images in a secure, controlled manner. The system includes a secure printer that receives, decrypts and prints documents supplied by a document server. Security of the system is realized by an aggregate of a secure communication protocol, smart card technology and the computational infeasibility of breaking a public key cryptographic system. The system may be used for electronic commerce, in which copies are made on a “pay-per-print” basis.