BG77 - downlink only possible after uplink

I am currently working with a BG77 module. I can communicate in UDP to send and receive messages.

My current problem is that I can’t receive a message in downlink if I haven’t previously sent a message in uplink. If I wait for example 2 minutes and I send a message in downlink, I don’t receive it on my NB-IoT module.

And I have to use PSM and EDRX so disabling those is not an option.

Can you help me? Thank you in advance.

if you are on EDRX mode , the DL link will be delay but not be lost . it will be pend at network one EDRX cycle

if you under PSM mode , This depends on the strategy of the operators. Some operators will not cache DL data in the PSM down time, so you have to control the DL data time from the server side

According to GSMA most operators store at least one downlink packet. But you need to wake up from PSM. The easiest way is to set TAU timer to a reasonable value and the module will wake up according to it and wait for possible downlink message.

Hi stephan,

Thanks for the reply. According to network operator (telekom germany),DLs are stored and should be there on wake up after PSM.

But, I do not get the DL for some reason. What is ideal procedure to PSM wake up in order to make sure, BG77 is attaching and UDP connection downlink? (may be an example for working downlink directly after PSM wake up by TAU timer will help a lot)

Yes, I wait usually for 2 minutes for down link but nothing arrives despite of network having stored message. And if i send something, I get stored message immediately.

useful info about NB-IoT and LTE-M implementation on Telekom operator.