For each UE associated with the EPS, at any given point of time, there is a single S-GW assigned. The S-GW is the entity which terminates the interface toward E-UTRAN access network. Sassan Ahmadi, in LTE-Advanced, 2014 2.2.4 Serving gateway In the case of roaming corresponding to the HR architecture, the SGW entity of the visited network diverts mobile traffic in the framework of lawful interceptions. However, it is no longer connected to the eNB entity, and thus the radio bearer and the S1 bearer, built between the eNB and SGW entities, are deactivated. The SGW entity informs the MME entity of incoming data when the mobile is in idle state, which allows the MME entity to trigger paging of all eNB entities of the location area.ДЄ mobile in the idle state remains attached to the MME entity.

The SGW entity is also the anchor point at the inter-system handover in PS (Packet-Switched) mode, requiring the transfer of traffic data from the mobile to the 2nd or 3rd generation mobile network. Otherwise, the PGW entity performs this function. The SGW entity is the anchor point for intra-system handover (mobility within EPS network) provided that the mobile does not change group. The SGW entity can perform marking of the DSCP field of IP header based on the assigned QCI identifier for incoming and outgoing data. When the SGW entity receives data from the eNB or PGW entities, it refers to the QCI identifier for the implementation of the data scheduling mechanism. The SGW entity forwards incoming data from the PGW entity to the eNB entity and outgoing data from the eNB entity to the PGW entity. To ensure load balancing of SGW load, each eNB entity within a group must have access to each SGW entity of the same group. The SGW entities are also organized into groups (pools). AndrГ© Perez, in Implementing IP and Ethernet on the 4G Mobile Network, 2017 1.1.3 SGW entity

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