Web Camera
Web Camera (or Web Camera Server) is a CCTV Camera with built-in computer server so that you can connect it to a network line such as DSL or T-1 for the Internet or LAN. When you assign an IP address to the camera, you can see the camera's video at any place where an Internet browser (Microsoft Internet Explorer or Netscape) is available because the IP address works as a website address.
The most important thing you have to know about the web camera is the speed. That is, a web camera should have a good image compression technology which can compress the video images to a size small enough to go through the network line with fast speed. For now, the Wavelet is the best compression algorithm with compression rate 30% to 300% higher than other technology such as JPEG or MPEG.
Another excellent feature of web camera is that you can program it to send you an email with up to 5 pictures when a movement is detected by the camera. And it usually has enough flash memory for you to customize your own Internet homepage.
IP Address
Internet Protocol (IP) Address works as a website address on the Internet. When it is assigned to a Web Camera, you can open its video page with any web browser such as Microsoft Internet Explorer or Netscape by typing in the IP numbers. (Sample of an IP address: 65.104.93.35 - If you type these numbers in the "Address" box of any web browser, you will see a live video from web camera.)
Public IP Address and Private IP Address
Public IP Address is for the Internet like the above mentioned sample numbers. It's like a public phone number that you can call from any phones connected to the telephone service. Private IP Address, like an intercom numbers inside an organization, works only within a limited area such as LAN or WAN system. If you assign a private IP address to a Web Camera, you can see it in the LAN or WAN system, but not on the Internet. It is a Public IP Address that works on the Internet. There are two types in Public IP Address; Static and Dynamic.
Static IP Address and Dynamic IP Address
Static IP Address, like above mentioned sample numbers, is an independent address that you can own yourself. Dynamic IP Address, or Floating IP Address is not an independent address and you have to share it with other subscribers. This also works on the Internet, but unlike Static IP Address, the address changes every time you log in. When you want to open the camera assigned with a Dynamic IP Address, you should go to the web site of the web camera's manufacturer where they have a list of all the web camera users who have Dynamic IP Address. Though it works, Dynamic address is not as convenient as Static IP Address. So, you'd better get a Static IP Address when you install a DSL for a web camera.
Image Compression and Transmission Speed
Video Image Compression Technology is the core of web cameras because the compressed video file size should be small enough to run fast through a network line of the Internet or LAN. Another main factor to decide the speed of a web camera is the speed (bandwidth) of the network line itself.
How to Compute Transmission Speed
A) " The speed of a network line” divided by 8 is numerator. Please note that 8 bits is 1 Byte. For example, if you use 192 Kbps DSL line, the numerator is 24 KBps (192 divided by 8) if you use 384 Kbps DSL line, the numerator is 48 KBps (384 divided by 8) if you use 1.1 Mbps DSL line, the numerator is 137 KBps (1,100 divided by 8)
B) " The size of the compressed file of a video picture” is denominator. It depends on the format a web camera uses to compress the video picture. For now, Wavelet is the best format for this
function. Following table compares the Wavelet and other formats.
Format
Wavelet
|
Picture Resolution
720 by 486 pixels
|
Compressed File Size
50KB/frame
|
Now, if you send video pictures of 360 by 243 resolution over 384Kbps DSL line, the speed is:
(Wavelet Format) 48 KBps divided by 3 KBpf = 16 fps (frame per second)
(Other Formats) 48 KBps divided by 15 KBpf = 3.2 fps,
iI you send a picture of 720 by 486 resolution over 1.1Mbps DSL line, the speed is:
(Wavelet Format) 137 KBps divided by 50 KBpf = 2.7 fps
(Other Formats) 137 KBps divided by 250 KBpf = 0.5 fps
*Above speeds are the maximum. Actual speed may be lower depending on the traffic and other conditions
(Wavelet Format) 48 KBps divided by 3 KBpf = 16 fps (frame per second)
(Other Formats) 48 KBps divided by 15 KBpf = 3.2 fps,
iI you send a picture of 720 by 486 resolution over 1.1Mbps DSL line, the speed is:
(Wavelet Format) 137 KBps divided by 50 KBpf = 2.7 fps
(Other Formats) 137 KBps divided by 250 KBpf = 0.5 fps
*Above speeds are the maximum. Actual speed may be lower depending on the traffic and other conditions
DSL & LAN
Remote Transmission of Video and Data
The technology in this field enables us to use the Internet or intranet line as a video transmission method. DSL and T-1 are for the Internet connection and LAN (or WAN) is for intranet.
Digital Subscriber Line
DSL, Digital Subscriber Line, is commercialized with the speeds from 144 Kbps to 1.1 Mbps. (More than 1.5 Mbps speed is called T-1). To connect a web camera to a DSL, you need a router with RJ45 jack. The router is usually provided by DSL supplier. If you need to connect multiple web cameras, you should have a hub which has multiple RJ45 jacks and which is to be connected to the router. You will have static or public IP address (provided by the DSL supplier) to assign to the web camera(s). This IP address will work as a web site address on the Internet.
At the site of web camera, business grade SDSL (Symmetric DSL) is recommended. SDSL has same upstream and downstream bandwidth, while other DSL (IDSL or ADSL) has larger downstream bandwidth than upstream. As web camera's video data should be uploaded to the Internet, a SDSL is much better for the web camera. But to see the pictures from the camera, that is to download it, a residential DSL or even Cable TV line will work fine. (See more details about the bandwidth and the speed of a web camera)
Local Area network
LAN, Local Area Network or WAN, Wide Area Network has intranet network in a limited area or organization and has a lot of computers connected to the network. Web camera servers, as like
other computers, can be connected to LAN or WAN so that other computers can share the video
data. Web camera servers can be connected to LAN or WAN through RJ45 jacks.