+KSRAT Reference note indicates selecting 3G, but always goes to the last FORCED technology

IoT Modules Legacy HL Series
1

Here is a strange issue I’m observing with a SIM that has support for 2G and 3G and both towers present to connect with (AT&T and T-Mobile).

1.We use +KSRAT=3 normally to connect to 2G First (T-Mobile). With this particular SIM, it always connects to 2G.

  1. Change to +KSRAT=4 and it still connects to 2G (T-Mobile) even though it should go to 3G (AT&T) [takes approximately 25 seconds from power-on to attach]
  2. Change to +KSRAT=2, the devices takes an additional 35 seconds to attach, but will finally attach to 3G (AT&T) [takes approximately 90 seconds from power-on to attach. Restarting again will take ~25 seconds]
  3. Change to +KSRAT=3. the SIM now attaches to 3G (AT&T) in 19 seconds. I was expecting to connect to 2G T-Mobile.

Reading the Write Command Parameters of +KSRAT, mode 3 reads as just a “search” and maybe not true in terms of which network it catches. Then the Reference Notes indicate the module will select 3G by default when both networks are present. However, the example above is proving a slightly different story.

Also, there appears to be a sticking point by using KSRAT=1 or KSRAT=2 to “fix” the technology that the SIM defaults to for +KSRAT=3 or +KSRAT=4.

I also observed +KCELL=1 only returns the towers for the connected technology. It is not showing both UMTS (3G) and GSM (2G)

The technology type is following the SIM and not the radio. Lends me to believe something is getting coded into the SIM when +KSRAT=1 or +KSRAT=2 is used.

Here are my questions:

  1. If Searching for 3G first, why did it use 2G in the first sequence? Why does it now work properly after performing a FORCE 3G before? Note using +KSRAT=1 (2G Only) will put us back to what happens in step 1 above.
  2. How does the reference note from the AT guide align with mode 3 ad mode 4? Mode 4 seems to match the note, but mode 3 does not.

Radio Information (used two different versions:
RHL85xx.5.5.23.0.201610311418.x6250_7
RHL85xx.5.5.25.0.201804161340.x6250_2

[edit->]
I tried another carriers SIM that connects to two different technology types (2G and 3G) and the issue is seen on this as well.

2

Hi robvice,

For roaming network, I suggest you select the network manually, e.g.
AT+COPS=1,2,“46000”,0 //GSM
AT+COPS=1,2,“46001”,2//UMTS

Check first the avaiable network by AT+COPS=?

3

While I can do that, this is more around the documentation of +KSRAT and how using only 2G or 3G seems to “burn in” the SIM to the 2G or 3G Only modes.

Additionally, when running AT+COPS=? I only get the tower for the last 2G ONLY or 3G ONLY operation and not both.