EPC is the 4th Generation Core Networks for Mobile Communications. These slides are part of the training i conducted on 4G/LTE/EPC

1. SAE-EPC
Introduction
Inam Ullah
Head of Product Development

2. Contents
What is SAE/EPC
SAE Advantages
SAE Architecture
Description of SAE Components
Services in EPS Networks

3. What is SAE/EPC
System Architecture Evolution (aka SAE) is the core network architecture
of 3GPP's LTE wireless communication standard
SAE is the evolution of the GPRS Core Network, with some differences:
Simplified architecture
All-IP Network (AIPN)
Support for higher throughput and lower latency radio access
networks (RANs)
Support for, and mobility between, multiple heterogeneous access
networks, including E-UTRA (LTE and LTE Advanced air interface), 3GPP
legacy systems (for example GERAN or UTRAN, air interfaces
of GPRS and UMTS respectively), but also non-3GPP systems (for
example WiMAX or cdma2000)

4. SAE - Advantages
Improved data capacity: With 3G LTE offering data download rates of 100 Mbps, and the
focus of the system being on mobile broadband, it will be necessary for the network to be
able to handle much greater levels of data. To achieve this it is necessary to adopt a
system architecture that lends itself to much grater levels of data transfer.
All IP architecture: When 3G was first developed, voice was still carried as circuit switched
data. Since then there has been a relentless move to IP data. Accordingly the new SAE,
System Architecture Evolution schemes have adopted an all IP network configuration.
Reduced latency: With increased levels of interaction being required and much faster
responses, the new SAE concepts have been evolved to ensure that the levels of latency
have been reduced to around 10 ms. This will ensure that applications using 3G LTE will be
sufficiently responsive.
Reduced OPEX and CAPEX: A key element for any operator is to reduce costs. It is
therefore essential that any new design reduces both the capital expenditure (CAPEX)and
the operational expenditure (OPEX). The new flat architecture used for SAE System
Architecture Evolution means that only two node types are used. In addition to this a high
level of automatic configuration is introduced and this reduces the set-up and
commissioning time.

6. Description of SAE Components
LTE SAE Evolved Packet Core, EPC consists of four main
elements as listed below:
Mobility Management Entity –MME
Serving Gateway –SGW
Packet Gateway –PGW
Policy Charging and Rule Function -PCRF

7. Mobility Management Entity, MME
The MME is the main control node for the LTE SAE access network, handling a number of features:
Idle mode UE tracking
Bearer activation / de-activation
Choice of SGW for a UE
Intra-LTE handover involving core network node location
Interacting with HSS to authenticate user on attachment and implements roaming restrictions
It acts as a termination for the Non-Access Stratum (NAS)
Provides temporary identities for UEs
The SAE MME acts the termination point for ciphering protection for NAS signaling. As part of this it
also handles the security key management. Accordingly the MME is the point at which lawful
interception of signaling may be made.
Paging procedure
The S3 interface terminates in the MME thereby providing the control plane function for mobility
between LTE and 2G/3G access networks.
The SAE MME also terminates the S6a interface for the home HSS for roaming UEs.
It can therefore be seen that the SAE MME provides a considerable level of overall control
functionality.

8. Serving Gateway, SGW:
The Serving Gateway, SGW, is a data plane element within the LTE SAE.
Its main purpose is to manage the user plane mobility and it also acts as the
main border between the Radio Access Network, RAN and the core
network.
The SGW also maintains the data paths between the eNodeBs and the PDN
Gateways. In this way the SGW forms a interface for the data packet
network at the E-UTRAN.
Routing and forwarding user data packets
acts as mobility anchor for the user plane during inter-eNB handovers and
for mobility between LTE and other 3GPP
for idle state UEs, terminates the DL data path and triggers paging when DL
data arrives for the UE
performs replication of the user traffic in case of lawful interception.

9. PDN Gateway, PGW:
Like the SGW, the Packet Data Network Gateway (PDN GW) is the termination
point of the packet data interface towards the Packet Data Network(s).
As an anchor point for sessions towards the external Packet Data Networks, the
PDN GW supports:
Policy enforcement features (applies operator-defined rules for resource allocation
and usage)
Packet filtering (for example, deep packet inspection for application type detection)
Charging support (for example, per-URL charging)
One bearer, a datapath between a UE and a PDN, has three segments:
Radio bearer between UE and eNodeB
Data bearer between eNodeB and SGW
Data bearer between SGW and PGW

10. Policy and Charging Rules Function,
PCRF:
the Policy and Charging Enforcement
Function(PCEF) is the generic name
for the functional entity that supports
service data flow detection , policy
enforcement and flow-based
charging.
The Application Function (AF)
represents the network element that
supports applications that require
dynamic policy and/or charging
control.
In the IMS model, the AF is
implemented by the Proxy Call
Session Control Function (P-CSCF).

11. Services in IMS Network

12. End