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Hey, thanks for the mentioning the blog!



The routing area update is performed in UMTS in connected state too. As far as I am aware, in case of a voice call in GSM, as soon as the voice call is released, the RAU procedure occurs if RA was changed, it is just delayed as most UEs can't do PS signalling while in a CS call. As for the TA list, yes it is new. The intention is to assign different TAs to different UEs in the same location, so as to mitigate signalling load e.g. when a train crosses a TA border.


Hi David,

in UMTS PMM-Connected state, in most cases no Routing Area Update is
made when changing the RA unless the SGSN/MSC changes as well. In this
case an SRNS Relocation is made which includes a Routing Area Update
procedure at the end.

Heres the relevant section in 3GPP TS 23.060, section

The SRNC may provide a PMM-CONNECTED state MS with MM
information like RAI by dedicated signalling. Typically, the SRNC should
not provide a RAI to an MS in PMM-CONNECTED state. An exception is
after an SRNS relocation, in which case the new SRNC shall indicate the
RAI to the MS.

From what I can see, this is how it is also done in practice, i.e. a
RAU is only performed once Cell-DCH state is left.




Hi Martin,

Thanks for the explanations. Just to confirm one point: if I understood you well, if SRNS relocation occurs but the same SGSN/MSC is used, real networks don't send the RAI information to the UE, and the RA update is delayed until the Cell_DCH state is left. Is it what you said you saw?


Hi David,

The way I read the spec it says that a rau should (not must!) be made when the serving rnc changes while being in NAS connected state.


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