nRF9151-DK - maximum number of simultaneous TCP connections (LTE-M)

[iotdeveloper]

Hello,

I would like to ask what is the maximum number of simultaneous TCP connections that can be operated on nRF9151-DK while using LTE-M?

Alternatively, is it possible to make some adjustments so that as many sockets as possible can be opened at once?

Thank you

[Samruddhi Jadhav]

Hi,

1) Our documentation doesn't state one specific number (as maximum) for TCP connections on nRF9151 over LTE-M. However, for nRF91 devices, the modem contains around 5 sockets on its side which are available. For TLS, there are some limits such as 2-3 active secure connections at the same time. This depends on the certificate sizes. So, for TCP (non-TLS) the limit is around those 5 sockets.

2) Within the modem limits, Zephyr can be tuned in order to make sure that the OS doesn't go out of resources before the modem. To do this, the max number of FDs can be increased. CONFIG_ZVFS_OPEN_MAX can be increased to 8 or CONFIG_POSIX_MAX_FDS can be set to 8. Also make sure to set the socket options to CONFIG_NET_SOCKETS=y and CONFIG_NET_SOCKETS_OFFLOAD=y. This should let you use all modem sockets (around 5).

Best Regards,

Samruddhi