If you can convert information to digital data, you can transmit that data through a network and either convert it back to its original form or use it as input data for a computer. With the right kind of input and output devices, you can use the same network that shares computer resources to monitor and control industrial processes, listen to sound from a microphone or watch images from a camera, distribute audio and video through your home or business, and operate equipment by remote control. And if the network is connected to the Internet, you can do all those things to or from anywhere with an Internet connection.
Many of these network applications are extremely specialized (such as monitoring the temperature of the water in a stream), but others are often practical for a home or small business network. For example, you can use your network to watch or listen to activity in another room or to distribute audio and video files from an entertainment server to speakers and video displays in several locations around your home. This chapter explains how to connect and use additional devices with your network.
A microphone connected to a computer or audio server can capture sounds and convert them into digital audio files. A camera (known as a webcam) can capture images that a computer or server can convert to still or moving image files. An audio or video server can be either a computer with an internal or external microphone or a camera (or both) or a stand-alone device that connects directly to the network. When another computer receives the same audio and/or video files through a network, it can display the images on a display monitor and play the sounds through one or more speakers or through a pair of headphones.
One widely used remote webcam service is the familiar online traffic monitor, like the one shown in Figure 15-1.
Figure 15-1. A traffic webcam uses a networked camera. This one shows cars and pedestrians on the Brooklyn Bridge.
A video camera can connect to a network through a controller mounted inside a computer on a plug-in PCI expansion card or as an external USB device. The controller scans the light-sensitive portion of the camera from side to side and from top to bottom at a constant rate; when it reaches the end of one row, the controller automatically moves on to the next row; when it reaches the end of the bottom row, the controller returns to the top.
At some point in the signal chain, the analog image from the camera's lens converts to a continuous digital data stream; in most cases, this occurs inside the camera itself, but some equipment might perform the analog-to-digital conversion in the controller card. As an alternative, a camera captures still images one at a time and stores them or transmits them through the network as a series of image files.
Note
Many camera controller cards include two or more camera inputs. In general, a multiple-input card costs more than a single-input card with similar image quality and performance.
The computer can use a sound card or a USB or FireWire port to handle audio in a similar manner. The sound card accepts analog audio directly from a microphone or through an external amplifier, mixing desk, or other source; the USB port receives digital audio from an external analog-to-digital converter.
After the computer receives one or more video streams, audio streams, or still pictures, it can do the following:
Store them on a hard drive or other mass storage device
Display the pictures on the computer's video monitor as "live" images
Play the sound stream through the computer's speakers or through headphones plugged into the computer
Incorporate them into another program or document, such as a web page or a word-processing document
Transmit them through the computer's network connection
The alternative to a camera connected to a networked computer is a network webcam—a camera and control unit that connects directly to the network as a separate node. A typical network webcam includes a remote control program on a web page that a user can operate through the network, or, with the correct set of passwords and authorization, through the Internet. Depending on each camera unit's specific features, the remote control might allow an operator to zoom the image in and out, rotate or tilt the camera, or choose a different image through the same control unit. Some network webcams also include a wireless network interface that can connect to the network through a Wi-Fi base station.
Attaching a camera to your network—with or without a microphone at the same location—can add many useful features and functions. Anyplace where you want or need a distant set of eyes and ears, you can install a camera, a microphone, or both. Here are some examples:
- Surveillance monitors
One or more cameras aimed at unattended entryways, corridors, and other locations can transmit pictures to a distant computer's video display monitor.
- Baby monitors
A networked computer with a camera and microphone in a nursery or child's room can replace a conventional baby monitor transmitter unit. You can keep an eye on the baby while you work—through a small window on your desktop that contains the image from the camera in the other room.
- Live conversations
When both parties have a webcam and microphone connected to their computer, it's easy to conduct a "face to face" conversation through the network.
- Remote conferencing
One or more participants in a meeting or conference can participate from a remote location.