High Data Usage

I have an LS300 connected to a PLC via Serial RS232. I am bring in (4) 16Bit words in every minute from a remote server. For some reason, the data usage on the cellular network is over 1Meg/Day. If I look at wire shark, the length of data per poll is around 259. Why is it so High?


Don’t forget that there are 8 bytes of framing info around every packet of data that you send.

So … if you are receiving 8 bytes (your 4 16 bit words), the packet is going to be at a minimum 16 bytes long.

24 hours = 1440 minutes = 23040 bytes (approx 22.5 kbytes) - which sounds pretty good.


Depending on your ISP’s plans, you may be being charged not by the byte, but by the block - and I’ve seen some ISPs charge by rounding up to the nearest 1k block of data. This is especially true when the GPRS connection is being set-up/torn down on a regular basis (so you’ve also got the additional traffic for set-up/tear-down). If you are being charged by the minimum 1k block, then I suspect that you would be seeing about 1.5Mbyte per day:

1440 minutes x 1k = 1.4Mbyte

Additionally, the device may also be talking to the network for other things. I know the GX400’s used to talk to the network for things like NTP time info etc and had a fixed data usage per day.

Have a look at your data plans and see how you’re being charged.

Or, the device could be padding your data to completely fill the packet (around 1492 bytes).

Just my 2c.

ciao, Dave