How a UE is identified on S11 during Downlink Data Notification?

Question

At both places MME and SGW

Comments

I believe it should be GTP-C TEID for the identification.
I hope I got your question correctly.

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S1 Bearers (signaling + Data) deleted If UE is in idle mode, then the session between the MME and SGw also deleted. So in this case if UE gets any incoming data SGw will initiate Downlink Data Notification by using what information element? is that IMSI?
Becuase when session deleted during idle mode all these GTP-C TEID's  also deleted, then how SGw will use TEID of MME...?

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no,then the session between the MME and SGw are not deleted

Answer 1

When UE in ECM /RRC-IDLE state, if it is getting new traffic in that case P-GW pump the UE traffic based on the IP address, And the UE is already EMM Registered so it is always connectivity provision of connection between the S-GW and P-GW.
So once Incoming downlink data arrives at S-GW trough S5 bearer, then S-GW triggers Downlink Data Notification to wards MME.now MME need to Page the UE in order to get the UE from ECM/RRC-IDLE to ECM/RRC-Connected. Once eNodeB got this message it just forward the paging on UE based on available UE identity. after that UE will get the resources and start sending and receiving the data.

Below IE are the main IE’s which used as a part of Downlink Data Notification.
Information Elements in a Downlink Data Notification

EPS Bearer ID:
If the Downlink Data Notification is triggered by the arrival of downlink data packets at the SGW, the SGW shall include the EPS Bearer ID stored in the EPS bearer context of the bearer on which the downlink data packet was received

Allocation/Retention Priority:
If the Downlink Data Notification is triggered by the arrival of downlink data packets at the SGW, the SGW shall include the ARP stored in the EPS bearer context of the bearer on which the downlink data packet was received;

IMSI :
This IE shall be included on the S11/S4 interface as part of the network triggered service restoration procedure if both the SGW and the MME/S4-SGSN support this optional feature

Reference: 29.274 rel10 clause 7.2.11.1

Once MME receives the Downlink Data Notification message it triggers paging to towards enodeb.
MME contain UE information given below.

Message type: paging

UE Identity Index value: IMSI NO(i.e:xxxxxxxxxx) 10bit string

UE Paging Identity: IMSI or S-TMSI(OCTET String size)

Paging DRX: Timing(i.e:32,64,128 etc)

CN Domain: CS,PS

TAI: PLMN ID+TAC

CSG ID: BIT STRING (SIZE (27))

Reference 36.413 rel 9
hope this info is helpful to you @ Srinivas Sambari

Comments

Thanks for your Answer..

Today I observed the same senario and analysed the entire pcap file... when downlinkdata notification issued by S-Gw, then S-Gw is using MMC side GTP-C tunnel identifier of the IMSI. and this GTP-C TEID was created at the time of initial session creation by MME.
so what I understood is when Release Access bearer issued by MME only S1 Bearers and S1 signaling connection removed, so how long the session is still open (if UE is not at all doing any activity after successfull attach? Is the session remain active until Detach when UE is in Idle mode? )