I am attempting to allow access to a legacy serial device (19200baud) using a serial bridge as per some of the samples. The serial device is connected to the modem and the modem is making a tcp connection to a PC that connects a virtual com port to the tcp port.
I was wondering if anyone could provide guidance as to some TCP/IP settings that would provide good results in minimizing latency and giving the application on the PC the best chance of not really being aware that the device not just connected locally. I am thinking of SCFG settings, but other suggestions from anyone who has done this would be appreciated.
My thoughts are to use a small packet size and a small txTo value (eg AT#SCFG=1,1,128,90,600,1), but I still get some issues with timeouts in the PC application.
The latency of a GSM/UMTS network is anywhere but near the one of serial connection, especially for small packets and connect/disconnect scenarios, more, is variable because of the conditions. The way to go is to tweak the PC application to be more permissive with the timeouts, handle larger data chunks and maybe do some packets buffering.
The virtual port software on the PC is very good at buffering/queueing data at is comes in/goes out. It also allows for strict emulation of the baud rate in the virtual COM port. Based on what you are saying, I am thinking that on the module side I should not go with such a small packet size, but instead set up the packet size and the txTo to maximize the number of bytes that get sent in a packet.
For example if 19200 baud is around 2400 bytes/sec, then I could use:
packet size=240, txTo=1
packet size=480, txTo=2
packet size=1200, txTo=5
I will see what works best.
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