Data bandwidth estimation


#1

Hi,

On my system 2 racks of modules (~120 points) are in a remote place the ethernet connection will have to support IP cameras, I am a bit concern by the bandwidth consumption. Do you have recommendation about the bandwidth that is necessary for PAC communication?
regards,
Pierre


#2

Hi Pierre,

Hard to say from your description, but here is some things to consider…

Are you using PAC Display to poll the 120 points? If so, are you polling them all at the same time (same freshness), what is the poll rate, are all 120 points on the same page, are any of them in super trends, if they are on separate freshness rates are those rates mathematically related (ie 1sec and 2 sec), or are the freshness rates prime numbers?

If you are not using PAC Display are you in control of the other program that you are using? Is it using sensible refresh rates?

Whats the connection to the remote place? Is it over cell modem, dial up, fiber link, standard wifi or some sort of super wifi?

Is there an Opto controller at the other end? Is it doing any data compacting?
Are you polling 120 individual points or are you getting a few tables with all 120 points in it?

Obviously you don’t need to answer all the questions, I’m just pointing out that the efficiency of getting those points depends on a few different things.

Bottom line is this. In my experience, 120 points (in a table) will just about fit in a single TCP/IP packet. Thus it will be transferred pretty quickly, in the mSec range… your video on the other hand…
Are they streaming (ie an IP camera with something like url/videostream.cgi), or are they single shot jpg frames with an adjustable update rate? How many of them are there? Whats the jpg compression value? Are they high-def or are they 320x240, or something like 640x480?
In other words, the 120 points are going to be a drop in the bucket next to those video frames.
That said, if you are trying to poll the 120 points separately at a high rate, they will have to be considered, but even then, in my rough and ready slap dash opinion, that video is the real payload, not the Opto data…

Lets know how you get on. I’m always interested in streaming video applications, been messing around with it over the web for about 10 years now…

Cheers,

Ben.