EPC – UMTS Question

Posted: October 13, 2011 in technical
Tags: , , ,

Hey, Everybody

Long time no see

I’ve got a question for you:

What happens with an UE connected to a 3G network but without active pdp contexts that needs to move into a 4G network?

I know is a bit handful, so I promise to come back with a picture and more detailed/step-by-step questions on what I want from you. The idea is that I don’t know how this shiny procedure looks like.

Many thanks

— Later edit:

 Q1. What messages are exchanged between the entities in the picture when an UE that has no active PDP context wants to move from 3G to 4G?

Q2. Where can I find information about this situation? (TS no., section no., etc. )

  1. krishnaKishore says:

    First cut :
    But as you mentioned UE is not having a PDP context Bearer context, so I hope we need to consider this as idle mode UE entering into LTE n/w.
    So, this will include just cell change procedure at RRC level in eNB and as there is a change in Tracking area TAU should happen.

    Let me back with few more updates on this…

  2. Alexandra says:


    My problem here comes from the fact that there is no PDP context in the GGSN, therefore the UE has no IP address. As far as I could see all the Inter-RAT handover procedures assume an active PDP context in the GGSN(which is PGW too). I wonder in this case how will the UE be moved to a technology based on the idea of the UE having an IP address at all times.

  3. Dumitru says:


    I’ve tested this scenario and bellow is the explanation:
    1. UE performs TAU with the “EPS Bearer Context Status” indicating that there’s no EPS bearer activated.
    2. MME sends TAU reject with cause “no-EPS-bearer-context-activated (40)” to UE.
    3. UE performs regular EPS attach procedure…

    If you want I could share traces with you.

  4. Dumitru says:

    IMHO it should not behave this way, it’s not logical. UE should not initiate TAU during iRAT if there’s no PDP activated, in this case it should always initiate normal Attach…

  5. @Dumitru: thanks a bunch! 🙂

  6. Salman says:

    Is there any reference to this procedure, My specific question here is the following.

    1. After MME send TAU Reject with EMM cause 40, does the network need to release RRC or the UE should send the attach instantly.

    Problem with me is that UE does not send the Attach instantly and is waiting till the RRC conection is released.

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