Determining Band Width of a Recording device

[anchorjoe 0]

Just a quick question. I am working on a project in which I am going to contract out part of it to a partner of mine and a question came up on output bandwidth of the recording device. Reason the question came up is there will be a wireless network with the camera images sent to a main display PC. Can someone point me in the direct of determining the device band width? Does it relate to the FPS rating of the device? What about mpeg rates. Just want to make sure I provide the correct answer.. Thanks...

[lbtech 0]

It really depends on what the camera is transmitting at.

Some cameras have options to control how many fps, what size images/frames to use, and how often to send.

If you google "bandwidth monitor" you can just install the software on a pc....connect to the camera from the pc and watch the bandwidth it is actually using.

[woodyads 0]

Bandwidth is a bit more compex than reading the manual. Just cause it says something doesn't mean it work or is true. Best to fully test your devices to see what they deliver. You can save a lot of bandwith by using your head. Work out what image you need. Are you looking long distance, focusing on numbers, need every frame, how many frames per second do you need. What you need to record and what do you need to view. Also are you network bound or storage bound. Most people are network bound.

 

Firstly if you can record what you view then you half you network bandwidth by sending the one stream instead of two. Then your recorder may have the ability to reduce the number of frames or bandwith again. So if you are network bound try to use one stream not two. Secondly if your cameras are mounted outside it is important to reduce movement as much as possible. Avoid using any poles of towers that have twisting movement. Many towers have legs that twist as the tower moves. So mount your cameras on the cross beams not the legs. Twisting creates greater image deflection than swaying especially when focusing over long distances. As mpg compression compares each frame with the previous frame then any change increases the bandwidth.

 

After this look at all your standard stuff. Frame rate, resolution, flitering, compression, seconds to new frame, bit throttle and frame throttle. Most of these can be replicated again on the recording device. You should look for a system that has its own bandwidth report on it. Whatever format it come in. Mine has a test window that tells you howmany b/s are being transmitted. Or there are many different network monitoring devices. NetBoy is pretty user friendly. So in answer to your question you can limit the bandwidth to what ever you want. You just have to know how many frames per second you will get and quality you will sacrafice to get it. The more the picture moves the more bandwidth the mpg algorithm will create. Beyond this you will need to know if you are using a multicast address. in which case you need to know the bandwith capabilities of the weekest device on the network.

 

The only other question is you asked for the bandwidth of the recording device. Are they talking about the encoder bandwidth. The server network card capabilities, in or out? Or are they talking about the servers disk bandwidth capabilities. Chances are they don't know either. Best you ask them all these questions. Knowing the answers yourself first. Next get a dev budget to do your testing during which time you thrash the network and find the weekest device and at what broadcast limit your weekest devices break. Most likely 10Mb-s. These are likely to be old printers or print servers, and wireless IP devices that do not have port filtering enabled. Best to know this before you break them rather than after.

 

Hope that helps