Abstract: Surveillance system endpoints communicate with each other to send and receive presence information. The surveillance endpoints may react to the received presence information. For example, if one surveillance camera stops functioning, one or more other cameras can react to the presence information, or lack thereof, sent from the malfunctioning camera. Thus, one or more of the other cameras can cover the area normally covered by the malfunctioning camera. Thus, the surveillance endpoints can automatically react to presence events in a network of surveillance endpoints.

Abstract: Surveillance system endpoints communicate with each other to send and receive presence information. The surveillance endpoints may react to the received presence information. For example, if one surveillance camera stops functioning, one or more other cameras can react to the presence information, or lack thereof, sent from the malfunctioning camera. Thus, one or more of the other cameras can cover the area normally covered by the malfunctioning camera. Thus, the surveillance endpoints can automatically react to presence events in a network of surveillance endpoints.

Abstract: A tuneable multi-section semiconductor laser 100 is characterized by applying currents in step-wise increments to sections 101, 102, 103 of the laser respectively and measuring power output by the laser to determine values of the applied currents corresponding to stable operating conditions for which the laser emits radiation at wavelengths remote from mode boundaries 51, 52; 141, 142 of the laser. The wavelength of the emitted radiation is measured and variations in the applied currents required to cross a mode boundary such that the laser undergoes a mode jump to emit radiation at a significantly different wavelength are also measured. These values are stored in a look-up table for use of the laser under the characterizing conditions and state of ageing of the laser. The applied currents are changed, to cause a predetermined incremental change in wavelength of the emitted radiation, within the said mode boundaries, and the further values are also stored.