Technique of the Netcam (Part 1)
Part 2

Surveillance cameras belong to the cityscape of London. Big Brother is Watching You! In the future, cameras should speak to conspicuous passers-by via Voice over IP (VoIP). In some US cities, network cameras have public Internet addresses. Meetings are arranged by SMS with acquaintances from the "old world" for a short "Hi over IP" in front of the IP camera in the USA. Network cameras take over functions of surveillance in public life, in production technology and provide illustrative material for tourism. Even in the private sector, the cameras are increasingly used.

In addition to the video camera components, a network camera or Netcam contains a small computer that compresses the images and sends them directly via an IP network (Internet, LAN or WLAN) to the recipient. The computer essentially consists of a CPU, a flash memory (similar to the USB stick) and a DRAM memory (dynamic random access memory). The network camera software makes it possible to use the camera as a web server, FTP server, FTP client and email client.

The classic video camera or Videocam has no computer for the transmission of live images, it requires a connection to a PC or video encoder / server, only then is it possible to send pictures ins Internet. A network camera can be addressed from several, different distant locations, a video camera only from the one computer to which it is connected. Internet access to a video camera via a PC should be avoided for security reasons of the PC. The network camera is equipped with digital input and output channels. Built-in motion sensors in the optical field of the camera’s view perceive changes via definable areas (windows) that trigger signals. For example it starts a video recording, or it will send a set of picturs to an email address.

The motion sensor of the camera forwards a signal to an external PC. From this PC a login to the monitored room is possible (VoIP). Microphone and speakers can be turned on and off via the camera channels.

A reliable integration of the network camera on the Internet requires fast, professional routers and high data transmission rates (measured in megabits per second) with high reliability over time. If a network camera has to deliver images of a comparable quality to a normal video film, it should generate 25 frames per second and transfer them to the network at a 4CIF resolution (704 x 576 pixels) in DVD quality. The upstream data rate should be at least 8Mbit/s. For a CIF resolution (352 x 288 pixels) it would still need an upstream data rate of about 2 Mbit/s. For home or small business applications the network providers pretend downstream data rates of 50 Mbit/s and upstream data rates of 10 Mbit/s. However, the data rates advised by the network providers are rarely achieved, depending on the location, time and provider. In large cities, depending on expansion and load, 60 to 80% and in rural areas 20 to 60% of the purchased capacity can be achieved always for the same, fixed tariff. Via the link: http://www.speedmeter.de the current data performance can be measured.

The lower upstream data rate, however, determines the number of images that can be sent from the camera to the Internet every second. With a 4CIF resolution and a data rate of 1.3 Mbit/s about 4 images per second and with a simple CIF resolution about 16 images per second are transmitted. Jerking movements and sometimes smeared image structures are the result. A suitable connection with at least 25 Mbit/s in the downstream and 8 Mbit/s in the upstream is usually only available in urban centres. There are short distances with correspondingly thick copper cables to the next larger connection node available.

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