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,

Is UDP server functionality working locally on your private network?

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

What is the role of Nordic modem in your setup? Is it intended to be used as UDP server?

Best regards,
Dejan

[Deval]

Yes the Nordic modem is a UDP server and the Hologram API allows us to send UDP messages to it. 

It uses this service: docs.hologram.io/.../send-messages-to-sims

[dejans]

Hi,

dejans said:

Is UDP server functionality working locally on your private network?

For testing, you could try to run python client script on your local private network.

Which network does your device connect to?

Looking at AT+CGDCONT, your device has IPv4 address from private addressing range. Documentation suggests that in this case you should use IPv6 address instead. Please have a look at udp server.

To act as a UDP server, the nRF91 Series DK must have a public IP address and the radio network must be configured to route incoming IP packets to the nRF91 Series DK. These depend on the network and SIM card used.

Best regards,
Dejan

[Jimy]

dejans we don't have IPv6 so your recommendation is not possible. Can we escalate this issue to someone who is an expert in UDP messaging?

[dejans]

Hi,

Which application has been flashed to nrf9151-dk?

Best regards,
Dejan

[dejans]

Hi,

The issue might be related to the use of cellular network that your device connects to. Using NAT might only be possible for several minutes. It is problematic to wait for connection on cellular device. It is recommended that (if you need to use UDP) you use device in such a way that it regularly checks for messages.

We have removed support for #UDPSVR functionality in Serial Modem Add-On. It is still possible to use UDP server with socket interface but it is not recommended.
Another issue is that since PPP in Serial Modem uses RAW socket and receiving UDP data for the same PDN context is not possible. You need to choose another PDN context if you want to use PPP and receive anything on UDP socket.

Best regards,
Dejan