Could you please tell me the maximum packet size NRF9160 modem can send over UDP and TCP/IP in case we use either NB-IoT or LTE-M?

[LuckyMan]

Hi Nordic,

I am using an nRF9160 DK to survey its power consumption when a maximum packet size is sent to a server over TCP/IP and UDP. But, I do not know what the maximum packet size the modem can support.

Could you please tell me the maximum packet size NRF9160 modem can send:

   - Over UDP in case we use either NB-IoT or LTE-M?

   - Over TCP/IP in case we use either NB-IoT or LTE-M?

Thanks for your support!

Best,

Vu

[Charlie]

Hi Bui,

The UDP/TCP maximum packet size is mostly decided by the IP MTU. You can refer to the following page about packet data structure in different layers. 

IP Protocol Header Fundamentals Explained with Diagrams (thegeekstuff.com)

For nRF9160 modem, IP MTU is decided by two steps.

1) The first option for UE is to use the MTU received during LTE Attach for IPv4 and IPv6. If fresh IPv6 MTU is received in router advertisement (RA) it is updated and used for IPv6.

You can read the MTU set by the network via this AT command: https://infocenter.nordicsemi.com/topic/ref_at_commands/REF/at_commands/packet_domain/cgcontrdp_set.html?cp=2_1_6_8_0

2) nRF91 Modem default MTU values.

If MTU is not received during LTE attach, UE uses default values for MTU.
ATT and CRICKET 1430
FIRSTNET 1342
Rest of the world 1280

Application can not configure MTU. MTU is either received from network or selected by modem.

Best regards,

Charlie

[LuckyMan]

Dear Charlie,

Thank you so much for your quick reply and useful document.

Best,

Vu