Читать книгу Mobile Communications Systems Development - Rajib Taid - Страница 131

In the LTE/EPC system, the eNodeB and the MME exchanges control plane protocol messages over the S1 logical interface. Similarly, the eNodeBs exchange control plane protocol messages over the X2 logical interface. For unique identification of a UE over the S1 interface, the eNodeB and MME assign the eNB UE S1AP ID and MME UE S1AP ID, respectively, during the initial registration request made by the UE to the CN. The eNodeB and the MME include these identities in all the application protocol (S1AP) signaling messages that are exchanged between them for the particular UE following its initial registration request message.

For example, consider the LTE/EPS attach request message sent by the UE to MME. The eNodeB shall assign the eNB UE S1AP ID to identify the particular UE within the eNB and send it in the S1AP initialUEMessage to the MME. For more information on the definition of the initialUEMessage, refer to TS 36.413 [97].

The MME will also allocate the MME UE S1AP ID to identify the particular UE within the MME. From this instance onward, both the eNodeB and the MME shall include the respective S1AP identities in all the application protocol S1AP messages, e.g. Uplink/Downlink NAS Transport, exchanged between them on behalf of the particular UE. Similarly, the eNodeB assigns the eNB UE X2AP ID to identify a UE over the X2 interface. This identity is included in the X2AP messages exchanged between two eNodeBs.