Change in libosmocore[master]: gprs_ns2: inform the NS user (BSSGP) about the MTU of a NSE

[laforge]

laforge has posted comments on this change. ( https://gerrit.osmocom.org/c/libosmocore/+/22343 )

Change subject: gprs_ns2: inform the NS user (BSSGP) about the MTU of a NSE
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Patch Set 9:

(2 comments)

https://gerrit.osmocom.org/c/libosmocore/+/22343/9/src/gb/gprs_ns2_fr.c 
File src/gb/gprs_ns2_fr.c:

https://gerrit.osmocom.org/c/libosmocore/+/22343/9/src/gb/gprs_ns2_fr.c@804 
PS9, Line 804: /* 48.016 § 6.1.4.2 default maximum information field size of 1600 octets
             : 	 * FR has 2 byte header */
             : 	bind->mtu = 1600 - 2;
I think the "information field" is what comes after the header, so (without checking the specs again) my assumption was that on the wire it is 1600 bytes plus FR header plus CRC plus flag octets.  And hence here mtu = 1600.  
I just checked FRF.1.2 and Q.922 and I think it supports my position here.

Nevertheless, the actual device MTU should be read from the net-device once we actually bind to it.  I guess you're doing this in a follow-up patch in this series (haven't looked throuhg it yet).


https://gerrit.osmocom.org/c/libosmocore/+/22343/9/src/gb/gprs_ns2_frgre.c 
File src/gb/gprs_ns2_frgre.c:

https://gerrit.osmocom.org/c/libosmocore/+/22343/9/src/gb/gprs_ns2_frgre.c@577 
PS9, Line 577: 	bind->mtu = 1600 - 2;
same here. Also, probably worth adding a #define in the frame_relay.h file for this?



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Gerrit-Project: libosmocore
Gerrit-Branch: master
Gerrit-Change-Id: I5016b295db6185ec131d83089cf6c806e34ef1b6
Gerrit-Change-Number: 22343
Gerrit-PatchSet: 9
Gerrit-Owner: lynxis lazus <lynxis at fe80.eu>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: daniel <dwillmann at sysmocom.de>
Gerrit-Reviewer: laforge <laforge at osmocom.org>
Gerrit-Comment-Date: Fri, 12 Feb 2021 08:54:33 +0000
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