CCTV Systems
By John W. Colley

Grill The CCTV Expert
February, 2003 Issue

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Why was the video multiplexer created and how does it work?

The term video multiplexer pertains to an electronic device that time multiplexes video pictures/images. A multiplexer allows several video pictures or frames to be recorded on a single VCR. The electronic process allows a full video resolution to be recorded. A normal video switcher records similarly, but the multiplexer reduces the time between recorded images from 5 more or less seconds to milliseconds times the number of cameras.

NTSC video records 60 pictures or fields per second. One odd field and one even field make up one frame of video. A multiplexer will switch between camera inputs using time base multiplexing.

It is important the multiplexer is in sync with the recording device. The multiplexer will normally provide menus or dip switch settings to sync to the recording devices.

How many different multiplexers exist and are available for sale?

Several configurations are available- Simplex, Duplex and Triplex. The Simplex multiplexer is a low cost device with the least amount of features. Usually these devices will have multiple screen options. The Duplex also has limited multiscreen capability. The advantage is to view and record at the same time. Triplex will have all the features of the full duplex and an option to output the multiscreen views.

Why during playback using multiplexers and VCR do some camera images jump around?

Common causes may be the multiplexer is not properly synchronized with the recording device. Refer to your installation manual for the multiplexer and VCR manual for instructions on the synchronizing.

Our customer is questioning if our video digital recorder uses a Static or Dynamic IP Addressing scheme. Could you provide a brief understanding of each IP scheme?

A Static IP Address is a fixed number similar to telephone numbers and they rarely change which is an issue. Similar to telephone numbers IP Addressing will run out of numbers at one point. The use of Dynamic IP Addressing assigns you a temporary address number to your device and they can change as needed. Neither the device nor you will not notice the difference between the two Addressing schemes in most cases. Larger networks are now using sequential Dynamic IP addressing. Corporate networks are allowing flexibility and security to remote users randomly updating passwords using devices similar to pocket pagers. The device will display your password at that moment you are accessing the network.

Could you give me an idea of the time it takes to download large a file compared to 640X 480 color image.

First you need to understand a Bit and Byte data-measuring units. A Bit is the smallest amount of digital data. The measurement is 0 or 1. Secondly, a Byte is the largest unit of measuring digital data. One byte unit takes eight bits to make one Byte. This usually will be a letter or a number. The time it takes to download a 640X480 color image you could download a approximately 4800 word technical manual chapter. When you download broadcast quality video, you could download the complete technical manual faster than color video image. Text is always faster than a color video images or pictures. Text format is usually the most used format off the Internet when you require information to be downloaded.

Our corporate clients are always inquiring about how much our video security devices will use of network bandwidth if we recommend the use of corporate networks for security communication solution. Could you give me a quick run through of Ethernet networks, POP's and measuring bandwidth?

The most common corporate networks are Ethernet. Imagine Ethernet as a highway system. Data is the user of the highway versus cars and trucks. Ethernet networks include 10 Base-T (10,000,000 Bits per second), 100 Base-T (100,000,000) Bits per second and Gigabit (1,000,000,000 Bits per second.

POP is a protocol that stands for Post Office Protocol. The most widely used version is POP3. Using a POP3 server will allow the storage of e-mail messages whether the client is connected to the network or not connected. Measurement of bandwidth in video and data digital applications is measured by bits per second or bytes per second.

Additional multipliers are Kilo 1,000, Mega 1,000,000, and Giga 1,000,000,000. An example is a 10 Base-T Ethernet connection has a maximum bandwidth of 10 Mbits/sec or 10,000,000 bits per second. Knowing the bandwidth and the measurements of Bits per second allows network administrators the formula to evaluate whether your digital video application can co-exist with other corporate applications.

DSL is now available in our area. What do I need to know about DSL and video applications using DSL?

DSL stands for digital subscriber line, which is marketed by telephone companies. The different packages of DSL may include VDSL, IDSL, ADSL, HDSL, R-ADSL and SDSL. A common standard in all DSL is that they are all faster than dial up telephone lines. The DSL transmission package chosen will transmit on standard telephone lines. If you are interested in DSL for video transmission, the most popular and useful for video transmission are the ADSL and HDSL.

As broadband fiber networks become available, the transmission of video signals will be very cost effective and will offer additional flexibility to the customer.

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John W. Colley is president of Integrated Security Systems, Ltd. and has been in the security industry for over 25 years, beginning his experience in the CCTV segment of security and gaining knowledge through field experience, manufacturer training and designing systems to meet customer needs. Colley started his security integration firm 18 years ago, providing design, engineering, installation and service to commercial accounts using integrated systems. Send your CCTV/Surveillance questions to jwc@securityiss.com.