E-UTRAN

S-GW

The Serving Gateway (S-GW) provides user plane connectivity, the UE being on one side, and
the Packet Data Network Gateway (P-GW) on the other side of the physical S-GW element.
Depending on the network provider’s approach, these elements can be separate, or they can be
combined physically as a single element.
It should be noted that no control messaging goes between the UE and the S-GW, as the
control plane is taken care of by the MME element.

The S-GW element takes care of the following functionalities:
. S-GW is the local anchor point for the inter-eNB handover procedure;
. S-GW is also an anchor point for the inter-3GPP network mobility;
. Lawful Interception (LI);
. packet routing and forwarding;
. S-GW handles packet buffering in the E-UTRAN idle mode;
. S-GW handles the network initiated/triggered service request procedure;
. packet marking at the transport level for both DL and UL;
. Charging Data Record (CDR) collection, which can identify the UE, PDN and QCI;
. accounting on user and QCI granularity for the interoperator charging processes.

P-GW

The PDN Gateway (P-GW) provides, in the same manner as the S-GW, the user plane
connectivity between UE, S-GWand P-GW. The P-GWelement interfaces with the S-GW, and
on the other side, with the external packet data network (PDN). In addition, P-GW includes
GGSN (GPRS Gateway Support Node) functionality.

More specifically, P-GW includes the following functionalities:

. UE IP address allocation;
. Packet filtering that can be done at a user-based level. The other term for this functionality is
a deep packet inspection;
. Lawful Interception (LI);
. Packet marking in the transport level, in the DL;
. Service level charging in DL and UP, as well as gating and rate enforcement;
. Rate enforcement in DL based on APN-AMBR;
. Online charging credit control.

MME

The Mobility Management Element (MME) is meant for the control plane signaling between
the UE and other network elements like HSS. Equally, as the user plane LTE/SAE messaging
does not go through MME, the control plane signaling does not go through S-GWor the P-GW
of LTE/SAE.

MME handles the following functionalities:

. Signaling in the Non Access Stratum (NAS);
. Security of the NAS signaling;
. AS security control;
. The selection of the P-GWand S-GW elements;
. The selection of other MMEs in the handover;
. The selection of SGSN in handovers between LTE and 3GPP 2G/3G access networks;
. Inter-CN node mobility signaling between different 3GPP 2G/3G access networks;
. The management of the Tracking Area (TA) lists;
. International and national roaming;
. User authentication;
. The establishment and management of bearers;
. The support of PWS message transmission, including ETWS and CMAS;
. The management of the paging retransmission of UE and other functions related to the finding
the UE in the idle state.

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