when the mobile has changed its location area. The mobile, in the registered state, sends the message EMM TRACKING AREA UPDATE REQUEST to the MME entity. The MME entity responds either with the message EMM TRACKING AREA UPDATE ACCEPT if it accepts the update, or else with the message EMM TRACKING AREA UPDATE REJECT, indicating the cause of the rejection. If the message EMM TRACKING AREA UPDATE ACCEPT attributes a new GUTI to the mobile, the mobile confirms receipt of this by sending the message EMM TRACKING AREA UPDATE COMPLETE. 2.1.1.5. Service request The service request is sent, when the mobile is in idle mode, to re- establish the default bearers on the LTE-Uu and S1-U interfaces. The service request is initiated by the mobile, by sending the EMM SERVICE REQUEST when signaling or traffic data is waiting. The mobile is notified of awaiting data at the level of the network by way of the paging procedure. The MME entity may reject the request, in which case it responds with the message EMM SERVICE REJECT. This response causes the switch of the mobile to the deregistered state. 2.1.2. ESM messages The mobile sends the request to establish the default bearer when the mobile attaches to the MME entity. The establishment request for the dedicated bearer can be transmitted by the network or the mobile. Signaling Protocols The dedicated bearer corresponds to a specific request by the mobile, following for example the establishment of a voice or a conversational video. The dedicated bearer is associated with a particular quality of service, corresponding to a particular QoS class identifier (QCI) which is different to that of the default bearer. Table 2.1 summarizes the ESM messages exchanged for the establishment, modification and release of the default bearer and the dedicated bearer. Establishment of default bearer, initiated by the network Source Message Destination ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT or ACTIVATE DEFAULT EPS BEARER CONTEXT REJECT Establishment of d