Detach Request initiated by UE

Ask the Expert!

Ask the Expert!
Members can sign in to post a question to our Subject Matter Experts.

Detach Request initiated by UE

This question has suggested answer(s)

Hi experts,

While doing an LTE integration, we found that we have some problems with certain type of phone.

For ie, Sony's phone are able to perfectly attach on the 4G networks, but LG's cannot.

When doing some traces with the LG, we found that a Detach Request is sent from the UE with Detach Type as "EPS detach" and Switch off as "Normal detach".

After checking on the 3GPP 24.301, I can't understand why this Detach Message is sent from the phone.

Do you have any idea about this ? Please let me know if you need further information.



All Replies
  • This might be happening because device did not linke something in signalling message. At what time during signalling it sends detach request. if you compare log then u may get something.

  • But it only happens with some phones. What could possibly do this reject in the signalling then ? because the phone is not 3GPP compliant ?

    Actually, when comparing with OK and NOK cases, it seems exactly the same behaviour.

    Sorry I don't know yet much about signalling with LTE interfaces, but the Detach Request is after an InitialContextSetup.

    Would you mind exchanging emails so that I can send you the trace ?


  • I have meet the similar problem with SONY mobile. After attach complete, UE send detach request immediately. Then UE would be in the state of no-service.

  • what is the attach type sent by this UE.

    Is it 'EPS Attach' or 'Combined EPS attach'?

  • Please check whether there is EMM cause IE within the Attach Accept message indicating that something wrong with the attach procedure? If the EMM cause is "CS Domain not available", that means mobile phone should initiate an combine EPS/IMSI attach and EPS only support EPS. The mobile phone may trigger the Detach procedure after Attach procedure.

  • it is combined attach request,and eps only in attach accept. Maybe that's why the UE initiated the eps detach?

  • as leodeng stated before, I think your LG UE is set to be "voice centric" and the network is not supporting CS Fallback. In this case, the UE will do a detach and try to attach to 3G/2G network.  The Sony UE is set to be data centric and hence does not detach.

  • Thank you all for your answers. I really appreciate, and sorry for the late response :)

    @kishore.nittala it is "EPS attach" only for the EPS Attach Type

    @leodeng the Attach Accept result is "EPS only" and I don't see any error cause.

    @irfan you are right, as an LTE demo, we didn't implement CS fallback to 3G/2G. Our LTE network for now is completely separated from our 2G/3G core network.

    Also for the phones, we set the Sony UE in "LTE only mode", and for the LG, we couldn't force the phone to be on LTE only mode.

    So that means, unless we implement CS fallback, we need phones to be on LTE only mode ?


    Thierry Kennes

  • Dear Thierry,

    If you attach type is "EPS Attach" and not "combined EPS/IMSI attach", then the problem is probably not with CS Fallback.  You may still want to check with LGE about how to find out if the UE's usage setting is set to "voice centric" or "data centric". If the mobile is set to "voice centric", it should not send attach type set to "EPS attach", which is what you are seeing.



  • Does anybody have any idea how to check "voice centric" or "data centric" with the Apple iPad mini? I am getting the same problem.

    After the "attach complete" message, the UE is sending a "detach request" with "switch off flag" SET (1) and with "Detach type: EPS detach". The attach type is always "EPS attach" though. A "detach accept" is also coming from the MME, which is confusing, as I read somewhere that the MME does not send "detach accept" if the "switch off flag" is set in the "detach request".

    Also, I am not at all switching off the UE or enabling airplane mode. So I'm wondering why it is setting the "switch off flag" in the "detach request".

  • Hi reubs,

       I am facing same issue with HTC mobile, Please help me if attach-detach issue resolved

    "After the "attach complete" message, the UE is sending a "detach request" with "switch off flag" SET (1) and with "Detach type: EPS detach". The attach type is always "EPS attach" though."

  • Hi,

    The problem might be in Mismatched/Wrong PTI value. UE detaches if ESm contents are not matched during Attach accept message.

    As your UE only supports LTE, then "voice centric" and "data centric" may not be causing this problem.

  • Hi

    As for us, as a workaround, we are setting our phones in LTE only mode.

    Code for some phones :

    Sony : *#*#4636#*#*

    LG : 3845#*936#

    Samsung :  *#0011#


    Thierry Kennes

  • Thanks all. UE is in LTE only mode and PTI value same in attach request message and attach complete message.  

    I was observed different behavior from UE based on PDN Type. UE is sending PDN type IPV4V6 if EPC assign IPV4 only or IPV4V6 then UE is sending detach request (Switch off ) message after attach complete.

    If EPC assign IPV6 only then UE is sending detach request (Normal detach) after initial context setup response( instead of attach complete message, UE is triggering detach ).

    Does anyone having idea why UE is behaving differently based on PDN type .

  • Thank you for your replies, lakazico and tpkennes. However, could you tell me where to check for a mismatched/wrong PTI value? I don't see the PTI value in the attach accept message.