Tuesday, 12 July 2016

Location Update

Location Update
Once the procedures for authentication and NAS security setup are completed, now the MME has to register the subscriber in the network, and find out what services the subscriber can use. To this end, the MME notifies the HSS the subscriber is registered in the network and located in its TAs, and then downloads information about the subscriber from the HSS. All these are done through the location update procedure, and by using Diameter protocol over the S6a interface between the MME and the HSS. The call flows during this procedure are as in below figure


1) [MME  HSS] Notifying UE Location
The MME sends an Update Location Request (IMSI, MME ID) message to the HSS in order to notify of the UE’s registration and obtain the subscription information of the UE.

2) [HSS] UE Location Update
The HSS registers the MME ID to indicate in which MME the UE is located in.

3) [MME  HSS] Delivering User Subscription Information
The HSS sends the MME subscription information of the subscriber as included in an Update Location Answer message, so that the MME can create an EPS session and a default EPS bearer for the subscriber. The subscription information included in the Update Location Answer message is as follows:
Update Location Answer (IMSI, Subscribed APN, Subscribed P-GW ID, Subscribed QoS Profile)
  Subscribed APN: APN that a user is subscribing to (e.g. Internet service)
  Subscribed P-GW ID: an ID for P-GW through which a user can access the Subscribed APN
 Subscribed QoS Profile5 (UE-AMBR(UL/DL), QCI, ARP, APN-AMBR(UL/DL))
            - UE-AMBR (UL/DL): the aggregate bandwidth of all non-GBR bearers that a UE can have                  Determined by MME and controlled by eNB.
            - QCI, ARP, APN-AMBR (UL/DL): QoS applied to the Subscribed APN

4) [MME] Storing Subscription Information

The MME receives the Update Location Answer message from the HSS, and stores the subscription information from the message.
From the downloaded subscription information, the MME can check what services

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