Director Product Development
What is SAE/EPC
Description of SAE Components
Services in EPS Networks
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)
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
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.
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
Mobility Management Entity,
The MME is the main control node for the LTE SAE access network, handling a number
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
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
• 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.
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
– 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
Policy and Charging Rules
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