How to change default MTU of SARA-R410M-02B modem

0 votes
Currently SARA-R410M-02B modem in ) sends ) sends Protocol Configuration Options (PCO) in PDN Connectivity Request with request for IPv4 Link MTU. How to disable this PCO and set default MTU for the modem? Does anybody know? Is it even possible?
by dextras asked May 9, 2018
0 votes
Isn't it part of the 3GPP spec for registration?  I can see +UAUTHREQ command in the AT commands manual that allows some changes.  Maybe that will work for what you are trying to do (not sure what and why you are doing though).
by grumpy answered May 9, 2018
It is not part of 3GPP specification: 3GPP TS23.060  Chapter 9.3:
"The TE when it is separated from the MT can perform MTU configuration itself and this is out of scope
of 3GPP standardization. Thus, when the MT component in the terminal obtains MTU configuration from
the network, this does not imply that the behavior of the MS considered as a whole will always employ
this MTU. In many terminals having a separated TE, the TE component configured by default to use an
MTU of 1500 octets"

I need it as if the network does not have MTU configured in its P-GW (which happens) then this modem assumes lowest possible MTU (68B) it causes issues with TCP packets transmission as by default (at least MS Windows) does not allow to fragment TCP packets by IP layer (Don't fragment flag set). Also it  causes huge performance issues as such a low MTU will generate a lot of overhead from IP an TCP packet headers.
To be more specific: 3GPP defines Attach procedure with its PCO etc. It does not define on how to configure MTU on the modem and how later a TE, e.g a PC is going to use it.
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