Hi Romeu, I'm really appreciate testing CSFB even though I have never been testing this feature in the lab. BTW, I have one question. If we want to remove Security-Related IE in UE Context Modification Request, I think NextEPC should not derive kENB in Extended Service Request handler. Nevertheless, I've merged your pull request since it is properly worked at first. ^^; If your lab is available, could you test one more by removing the following code? In src/mme/emm-handler.c 586 if (SECURITY_CONTEXT_IS_VALID(mme_ue)) { 587 mme_kdf_enb(mme_ue->kasme, mme_ue->ul_count.i32, mme_ue->kenb); 588 mme_kdf_nh(mme_ue->kasme, mme_ue->kenb, mme_ue->nh); 589 mme_ue->nhcc = 1; 590 } Just test it. If my expectation is true, I will fix all other things. Thank you for your GREAT job! Best regards, Sukchan On Sun, Jul 14, 2019 at 8:04 AM Romeu Medeiros &lt;medeiros(a)medeiros.eng.br&gt; wrote: > Hello Sukchan, > > Now after remove this everything run correctly. > > [image: image.png] > > I will made the change more beatiful and pull the modification to the git > to you aprove. > > Thanks > > Romeu Medeiros > > On Sat, Jul 13, 2019 at 6:50 PM Romeu Medeiros &lt;medeiros(a)medeiros.eng.br&gt; > wrote: > >> I found this in the 3GPP documentations [1]: >> >> [image: image.png] >> >> I will change the code to send only the CSFallback indicator in this >> case to see if can solve the problem. >> >> Thanks >> >> Romeu Medeiros >> >> 1. >> https://www.etsi.org/deliver/etsi_ts/136400_136499/136413/09.10.00_60/ts_13… >> >> On Sat, Jul 13, 2019 at 6:35 PM Romeu Medeiros &lt;medeiros(a)medeiros.eng.br&gt; >> wrote: >> >>> Hello Sukchan and friends. >>> >>> I'm trying to use the CSFB in test lab, and every time that nextepc >>> send the UEContextModificationRequest, the UE respond with an >>> UEContextModificationFaliure [ Protocol-cause=semantic-error ]. >>> >>> [image: image.png] >>> >>> I'm looking why I'm getting this. Someone have any idea? >>> >>> Thanks >>> >>> Romeu Medeiros >>> >>> On Thu, Jul 11, 2019 at 12:15 PM Sukchan Lee &lt;acetcom(a)gmail.com&gt; wrote: >>> >>>> Dear Osmocom & NextEPC Community, >>>> >>>> Today I've added CS Fallback and released NextEPC v0.5.0 >>>> >>>> So, I'd just like to test this part with Osmocom project, but it seems >>>> to be a difficult task. The reason is why I have little knowledge about >>>> 2G/3G. Nevertheless, I will try to do it >>>> >>>> BTW, I don't know if there is anyone who wants to integrate this big >>>> thing. >>>> Even though I'm not sure if this will help, but let me introduce the >>>> configuration of the NextEPC. >>>> >>>> To use SGsAP, change the mme.conf as follows: >>>> >>>> # >>>> # <sgsap> >>>> # >>>> # o Single MSC/VLR >>>> # sgsap: >>>> # addr: 127.0.0.2 >>>> # plmn_id: >>>> # mcc: 001 >>>> # mnc: 01 >>>> # tac: 4130 >>>> # lac: 43690 >>>> # >>>> # o Multiple MSC/VLR >>>> # sgsap: >>>> # - addr: 127.0.0.2 >>>> # plmn_id: >>>> # mcc: 001 >>>> # mnc: 01 >>>> # tac: 4131 >>>> # lac: 43692 >>>> # - addr >>>> # - 127.0.0.3 >>>> # - fe80::2%lo0 >>>> # plmn_id: >>>> # mcc: 001 >>>> # mnc: 01 >>>> # tac: 4132 >>>> # lac: 43692 >>>> # - name: msc.open5gs.org >>>> # plmn_id: >>>> # mcc: 001 >>>> # mnc: 01 >>>> # tac: 4133 >>>> # lac: 43693 >>>> # >>>> >>>> FYI, I also attach the pcap that I run with nextepc simulator as below. >>>> >>>> $ ./tests/testcsfb >>>> mo-idle-test : SUCCESS >>>> mt-idle-test : SUCCESS >>>> mo-active-test : SUCCESS >>>> mt-active-test : SUCCESS >>>> All tests passed. >>>> >>>> Feel free to raise any questions about this things. >>>> >>>> Best Regards, >>>> Sukchan >>>> >>>>