Cisco ASR 5000 series Product Overview page 851

Mobility Management Entity Overview
Figure 202. Architecture of LTE/SAE Network
Another EPC
e-NodeB
E-UTRAN
In accordance with 3GPP standard, the MME provides following functions and procedures in LTE/SAE network:
Non Access Strutum (NAS) signalling
NAS signalling security
Inter CN node signalling for mobility between 3GPP access networks (terminating S3)
UE Reachability in ECM-IDLE state (including control and execution of paging retransmission)
Tracking Area list management
PDN GW and Serving GW selection
MME selection for handover with MME change
SGSN selection for handover to 2G or 3G 3GPP access networks
Roaming (S6a towards home HSS)
Authentication
Bearer management functions including dedicated bearer establishment
Lawful Interception of signalling traffic
Warning message transfer function (including selection of appropriate eNodeB)
UE Reachability procedures
Interfaces with MSC for Voice paging
Interfaces with Gn/Gp SGSN for interconnecting to legacy network
OL-22938-02
MME
HSS
S6a
S10
S3
S11
MME
S1-U
GERAN
UTRAN
SGSN
S12
S4
S-GW
S5/S8
Evolved Packet Core (EPC)
PCRF
Gxc
Gx
P-GW
SGi
Internet
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