Please provide some details on Tracking Area List in LTE

Question

I have some doubts about tracking area list in LTE. A TAL contains 1 or more TACs and a UE need not perform TAU while moving across TAs belonging to its TAL.

On the other hand, UE will be pagged in all the TACs included in its TAL. This could have been achieved by simply defining a bigger TA (i.e. TA equivalent to all the TAs in a TAL) ? Is it due to maximum number of eNBs limitation in a TA (typically 100 or less) ? Or is it intended for having UEs in the same area with different TALs ?

Answer 1

when UE moves within TAs mentioned in TAL, UE will not trigger TAU since MME already know that UE can belong to any of the TA mentioned in the list. When UE moves to a tracking area which is not in the TAL. UE send TAU either UE in RRC-IDLE or RRC - connected.

There is tradeoff between TA size and frequency of TAU. So if TA size is too less then frequency of TAU increases. And when TA size is too large then MME will sends paging message to more number of eNodeB when UE is in RRC -IDLE mode and downlink data is coming for him from then core network.

So a wiser decision need to be taken with respect to TA size.