Is there any pattern to setting up a working PDP context for whatever sim someone puts in these modems?
It seems like sometimes PDP contexts are available to use, sometimes they’re not.
A while back I switched our firmware to use KCNXCFG=3… because using KCNXCFG=1 would fail with a telus card because context 1 was in use by ‘attach.telus.com’.
Now we have customers trying to use Hologram sim cards and in this case the only context that works is 1.
The 7500 documentation says that PDP Contexts 1-5 are reserved for IMS / Verizon / AVMS and that customer applications should use 6-10, but of course none of the AT+K commands support those contexts (just 1-5).
Do we really need firmware that does different things depending on which sim card is in use? All I want to do is set the apn and open a TCP socket…
Hi Bob1974,
If you want to use PDP context 6-10, you need to define them by command “AT+CGDCONT” before using.
In this case, you just want to open TCP socket and AVMS feature is not used, so you can use pdp context 5 for TCP.
Example, I have Verizon sim card and I use these command to configure:
AT+KTCPCFG and other AT+K command can’t use 6-10, so setting them up with AT+CGDCONT is of no use.
As for using context 5 - that doesn’t ‘just work’ either. If the SIM being used automatically sets up an APN (sometimes in context 1, sometimes in context 3), then you can’t define 5 to be the same apn (e.g. “vzwinternet”) because it already exists. Well you can, it just won’t actually work.
That means that the host using the modem has to scan the context list to see if the desired apn exists and use that context number in subsequent commands or if not found then define the apn in an unused slot.
This complicates the host firmware.
We’ve also discovered that modem registration is SIM dependent as well (needed to know if the context list has been auto-populated yet). The host has to check all three CREG,CGREG and GEREG because it might only register on one of them. Or it might not register on any unless you do a COPS=0, COPS=2 to force a re-registration.
What makes this really fun is that you don’t learn about these quirks until the customer tries to use it in a new location.