UDP server NRF9151 using Hologram

[Deval]

Hello,

I am using the example on the Nordic DK to get UDP messages from the Hologram API to the Nordic Modem. 

AT#XUDPSVR=1,6002
#XUDPSVR: 3,"started"

OK

I very inconsistently get messages (if ever). 

I am not changing any of the standard operation of the modem. I am running the AT Command with CMUX and PPPd overlay. I am successfully able to connect to the network and run a pppd connnection, but when I start the UDP server I never get messages.

Is there some additional configuration required? 

I am following this guide: https://docs.nordicsemi.com/bundle/ncs-2.6.0/page/nrf/applications/serial_lte_modem/doc/slm_testing.html#generic_at_commands

Specifically this part "Test the UDP server with UDP proxy service:"

I know this service works on Hologram because we use it with a different modem. 

I know I have a connection to the network because this is my output from CEREG

+CEREG: 3,5,"8309","04C8B910",7

I know my APN is set correctly

AT+CGDCONT?
+CGDCONT: 0,"IP","hologram","10.90.66.67",0,0

So what is going wrong? Do I need to anything additional? I am not changing any power states. I have seen inconsistent results with SMS as well (and TCP has never worked). 

[dejans]

Hi,

Have you tried to test UDP connection using python script as shown in UDP server (points 1 and 2)?

Best regards,
Dejan

[Deval]

So I don't have a public IP address so I cannot use the python script. But I know the service that Hologram provides will let you send a UDP message to their SIMs since it uses their internal API and I see confirmation that the message was sent. 

And I have seen it work with this cell modem with the Hologram SIM it is just very inconsistent. 

For example when it worked:

#XUDPDATA: 24,"10.254.0.75",15694
how long does this take?
#XUDPDATA: 9,"10.254.0.75",20100
try again

I can see that I have a private IP

AT+CGDCONT?
+CGDCONT: 0,"IP","hologram","10.90.66.67",0,0

OK

So I know the service does work. 

Additionally, I am seeing low (or undefined signal quality), but a successful PPP connection. Is it possible causing the issue? Because I am seeing inconsistent results from SMS as well.

AT+CSQ
+CSQ: 99,99

OK
AT+CESQ
+CESQ: 99,99,255,255,255,255

OK

[dejans]

Hi,

Deval said:

I am using CMUX + PPP overlay for the Serial LTE Modem example project. Is the UDPSVR functionality not something that should work with this configuration?

Are you using Serial LTE modem sample or Serial Modem Add-on? Which NCS version do you use?

Deval said:

So if I am understanding this right -- you are saying I cannot have a PPP connection and receive UDP messages if I have one PDP context?

PPP connection is in essence a raw socket. One PDN context can have only a single raw socket and nothing else. If other sockets are created into the PDN, raw socket continues to work but other sockets do not work. This happens due to routing of all packets to the raw socket.

Deval said:

If I close the XPPP connection I should get the UDP messages?

You can try this and let me know the result.

Best regards,
Dejan

[Deval]

Turning off the XPPP does not work. 

I can add a second PDN context but still don't get the UDP messages. Is there a way to get the PDN context to be set for the UDP server and then other PDN context for the PPP?

AT+CGDCONT?
+CGDCONT: 0,"IP","hologram","10.90.66.67",0,0
+CGDCONT: 1,"IP","hologram","",0,0

I am using the Serial LTE Modem example. 

NCS version is 3.1.0

Is there another sample project I could use that would give me better success?

[Jimy]

 Jennifer Gibbs Here is where we are having issues.

[dejans]

Hi,

Can you verify that you have built serial LTE modem sample without PPP overlay?

Best regards,
Dejan

[Deval]

I have tried with the SLM sample without PPP and CMUX and still don't see it work. 

Can you provide an exact sample project configuration I can follow to get the UDP server working with Hologram messaging working? 

[Deval]

Okay I think I am able to make it work BUT only when I turn the PPP connection off with AT#XPPP=0

Why is this the case?

Is there a patch you can give me that will make it work when the PPP connection is running as well?

My application requires BOTH ppp and the UDP messages

[Deval]

Another idea is can I create two PDN contexts? I want them to both be the same but how would I go about creating two contexts and setting PPP to one of them and the UDP server to the other?

I created two PDN contexts but it didn't do anything...