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[Type text]MOBILE APPLICATION DEVELOPMENT
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4G
M COMMUNICATIONS
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[Type text]MOBILE APPLICATION DEVELOPMENT
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Contents1. Introduction ............................................................................................................................................. 3
1.1 Introduction to 4G .............................................................................................................................. 3
1.2 4G Network Hierarchy ........................................................................................................................ 4
1.3 Features of 4G Networks .................................................................................................................... 5
2. Introduction to LTE ................................................................................................................................... 6
2.1 Introduction ........................................................................................................................................ 6
2.2 Overall Architecture Overview ........................................................................................................... 7
2.2.1 Core Network .............................................................................................................................. 8
2.2.2 The Access Network ........................................................................................................................ 9
2.2.3 The Roaming Architecture ........................................................................................................... 10
3. Protocol Architecture .............................................................................................................................. 11
3.1 User Plane ......................................................................................................................................... 11
3.2 Control Plane ..................................................................................................................................... 12
4. The EUTRAN Network interfaces: S1 Interface ................................................................................... 13
4.1 Protocol Structure Over S1 ............................................................................................................... 13
4.1.1 Control Plane ............................................................................................................................. 13
4.1.2 User Plane ................................................................................................................................. 14
4.2 Context Management over S1 .......................................................................................................... 15
4.3 Mobility over S1 ................................................................................................................................ 16
4.3.1 Intra LTE mobility ...................................................................................................................... 16
4.3.2 InterRadio Access Technology Mobility ............................................................................... 17
5. The EUTRAN Network interfaces: X2 Interface ................................................................................... 18
5.1 Protocol Structure Over X2 ............................................................................................................... 18
5.2 Mobility Over X2 ............................................................................................................................... 19
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1. Introduction1.1 Introduction to 4G
The 4G Mobile Networks are being developed with 2 main objectives. One of the Objectives is to
overcome the shortcomings and limitations of 3G.
The 4G Mobile Networks are being envisioned to offer higher bandwidths upto value of 100Mbps.
Unlike the predecessor networks of 4G(i.e 2G and 3G) which consisted of welldefined cellular
network components, 4G are expected to consist of a collection of wireless networks.
These include the Personal Area Network using, for example Bluetooth, the local area networks
using WLAN, the satellitebased mobile networks, and enhanced 3G cellular networks.
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1.2 4G Network Hierarchy
Satellite Network Level
Horizontal Handovers
Cellular Network Level
Local Network Level
Personal Network Level
VerticalHandovers
At the Lowest Layer are the personal networks, which constitute of smart devices communicating
with each other over wireless links.
At the next level are the local networks. These could consist of local area networks using the
wireless LAN technology.
The Cellular Network level comes next, which will consist of existing 2G and 3Gcellular networks, as
well as enhanced 3G cellular networks.
At the topMost level will be satellitebased mobile networks, which have a much greater
coverage area than the cellular networks, or any of the networks at the lowest levels.
Horizontal Handovers will take place within one network.
Vertical Handovers will be performed between different network levels.
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1.3 Features of 4G Networks
Higher bandwidths4G networks provides higher bandwidths to support multimedia services.
PacketSwitched Network4G Networks are based on PacketSwitched networks.
Stringent Network SecurityNetwork Security in 4G Networks is expected to be improvised.
Global Mobility and Network ScalabilityThis is Requirements of 4G networks.
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2. Introduction to LTE
2.1 Introduction
LTE has been designed to support only packetswitched services.
It aims to provide seamless internet protocol (IP) connectivity between User Equipment and Packet
data n/w (PDN).
LTE encompasses the evolution of universal Mobile Telecommunication System (UMTS) Radio
Access through the evolved UTRAN (E-UTRAN) , it is accompanied by an evolution of the non radioaspects under the term System Architecture Evolution (SAE) which include the evolved packet
core (EPC) n/w.
Together the LTE and SAE Comprises the evolved packet system (EPS).
EPS uses the concept of EPS bearers to route IP traffic from a gateway in the PDN to UE.
A bearer is an IP Packet flow with a defined (QoS) between Gateway and UE.
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2.2 Overall Architecture Overview
UE eNode B S - GW
MME
HSS
P -GW
PCRF
Operators
IP services( for eg.IMS, PSS)LTE - Uu
S1 - MME
SI - U
S6a
S11
S5/S8
Gx Rx
SGi
Network Architecture
Network Architecture Includes the network elements and the standardized interfaces.
At a high level, the n/w is comprised of CN (EPC) and the access n/w E- UTRAN.
CN consists of many logical nodes access n/w is made up of one node the evolved node B (e-Node B)
Which connects to UEs.
Functional Split between E-UTRAN and EPC
PHY
RLC
MAC
PDCP
RRC
Dynamic Resource Allocation (Scheduler)
eNB measurement configuration and
provision
Radio Admission Control
Connection Mobility Control
RB Control
Inter-cell RRM
eNode B
E - UTRAN
NAS Security
Idle State Mobility handling
EPS Bearer Control
MME
Mobile Anchoring
S - GW
UE IP Address Allocation
P - GW
EPC
S1
Internet
Packet Filtering
Functional Spit between E-UTRAN and UE
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2.2.1 Core Network
The Core N/w (Called EPC in SAE) is responsible for overall control of UE and establishment of
bearers.
The main nodes of EPC are
o PDN Gateway ( PGW)
o Serving Gateway (SGW)
o Mobility Management Entity (MME)
EPC includes logical nodes and functions such as Home Subscriber server (HSS) and the Policy
control and charging Rules function (PCRF).
The Logical CN Nodes
PCRF
o The policy control and charging rules function is responsible for policy control decision-
making as well as for controlling functionalities in policy control enforcement function
(PCEF) which resides in PGW.
HSS
o The Home Subscriber Server contains users SAE subscription data such as the EPS-
subscribed QoS profile and any access restrictions for roaming.
o It also holds information about the PDNs to which the user can connect.
o This could be in the form of an access point name (APN) or a PDN address.
o The HSS holds dynamic information such as the identity of the MME to which the user is
currently attached or registered.
PGW
o The PDN Gateway is responsible for IP address allocation for the UE.
o It is responsible for the filtering ofdownlink user IP packets into the different QoS-based
bearers. SGW
o All user IP packets are transferred through the Serving Gateway, which serves as the local
mobility anchor for the data bearers when the UE moves between eNodeBs.
MME
o The Mobility Management Entity (MME) is the control node that processes the signaling
between the UE and the CN.
o The protocols running between the UE and the CN are known as the Non Access Stratum
(NAS) protocols.
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2.2.1.1 Non Access Stratum Procedures
The Non Access Stratum procedures are connection management procedures and similar to UMTS.
The main Change from UMTS is that EPS allows concatenation of some procedure to allow faster
establishment of the connection and the bearers.
The MME creates a UE context when UE is turned on and attaches to the network.
It assigns a unique identity termed the SAE Temporary mobile subscriber identity (STMSI) to the
UE that identifies the UE context in the MME.
This UE context holds user subscription downloaded from the HSS.
The UE context also holds the dynamic information such as list of bearers that are established and
the terminal capabilities.
2.2.2 The Access Network
MME/S -GW MME/S -GW
eNode B #1 eNode B #3
eNode B #2
S1 S1
X2
S1 S1
X2X2
E -UTRAN
EUTRAN Architecture
The Access Network of LTE and E- UTRAN consists of a network of eNodeBs.
The eNodeB is interconnected with each other by means of interface known as X2 and to the EPC
by means of S1 interface to the MME by means of S1-MME interface and to the S-GW by means of
S1U interface.
The protocols that run between eNodeBs and UE are known as AS Protocols.
EUTRAN is responsible for all radio related functions.
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2.2.3 The Roaming Architecture
UE E - UTRAN S - GW
MME
HSS
P - GW
PCRF
Operators IP services(for
example, IMS, PSS)
HPMN
VPLMN
LTE - Uu S1 - U
S1 - MMES11
S8
SGi
Gx Rx
Roaming Architecture
The network run by one operator in one country is known as Public land Mobile Network .
Roaming is where users are allowed to connect to PLMNs.
A Roaming user is connected to the EUTRAN , MME and SGW of the visited LTE Network.
LTE/SAE allows the PGW of either visited or the home network to be used.
Using the home networks P GW allows user to access the home operators service even in the
visited network.
A PGW in a visited network allows a local breakout to the internet in the visited network.
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3. Protocol Architecture
3.1 User Plane
L1
MAC
RLC
PDCP
IP
Application
L1
MAC
RLC
L1
L2
UDP/IP
L1 L1`
L2 L2
UDP/IP UDP/IP
L1
L2
UDP/IP
GTP - U
IP
PDCP GTP - U GTP - U GTP - U
Relay Relay
UE eNode B S - GW P - GWLTE - Uu S1 - U S5/S8 SG
E -UTRAN User Plane Protocol Stack
IP Packet for UE is encapsulated in an EPC Specific protocol and tunneled between the P-GW and the
eNodeB for transmission to the UE.
Different Tunneling protocol are used across the different interfaces.
The EUTRAN user plane protocol stack of the Packet Data Convergence Protocol (PDCP) , Radio
Link Controller (RLC) and Medium Access Control (MAC) sublayers are terminated in the eNodeB on
the network side.
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3.2 Control Plane
L1
MAC
RLC
PDCP
RRC
NAS
L1
MAC
RLC
L1
L2
IP
L1
L2
IP
SCTP
S1 -APRelay
UE eNode B MMELTE - Uu
E -UTRAN Control Plane Protocol Stack
PDCP SCTP
RRC S1 - AP
NAS
S1 - MME
The protocol stack for the control plane between the UE and MME is shown above.
The AS protocol are L1, MAC, RLC, PDCP and RRC.
The lower layers perform the same functions as for user plane with the exception that there is noheader compression function for control plane.
The Radio Resource Control (RRC) Protocol is known as layer 3in the AS protocol stack.
It is the main controlling function in AS, responsible for establishing the radio bearers and
configuring all the lower layers using RRC Signalling between eNodeB and the UE.
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4. The E UTRAN Network interfaces: S1 Interface
4.1 Protocol Structure Over S1
The Protocol Structure Over S1 is based on a full IP transport stack as used in GSM or UMTS
networks.
4.1.1 Control Plane
Physical Layer
SCTP
IP
Data Link Layer
S1 - AP
Transport
Network Layer
Radio Network
Layer
S1 Control Plane Protocol Stack
The protocol structure is based on Stream Control Transmission Protocol/IP (SCTP/IP) Stack.
The SCTP is known for its advanced features inherited from TCP that ensures the required delivery
of signaling messages.
An area of simplification in LTE is the direct mapping of S1 Application Protocol (S1AP) on top of
SCTP.
This results in simplified protocol stack with no intermediate connection management protocol ,
since connection are handled in application layer.
Multiplexing takes place between S1AP and SCTP.
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4.1.2 User Plane
Physical Layer
UDP
IPv6(IETF RFC 2460)
And/or
IPv4(IETF RFC 791)
Data Link Layer
S1U User Plane Protocol Stack
GTP - U
The Protocol structure of S1 User plane is based on the GTP/UDP5/IP stack which is known to UTMS
networks.
One of the advantage of using GPRS tunneling protocol user plane (GTPU) is its inherent facility to
identify tunnels.
A transport bearers is identified by the GTP tunnels endpoints and the IP address.
The S-GW sends the downlink packets of a given bearer to the eNodeB IP address.
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4.2 Context Management over S1
UE is associated with one particular MME for all its communications during its stay in pool area.
This creates context in MME for the UE.
This Particular MME is selected by the NAS Node Selection Function (NNSF) in the first eNodeB from
which the UE entered the pool area.
eNodeB MME
Initial Context Setup Request
Initial Context Setup Request
Initial Context Setup procedure
The UE becomes active under the coverage of a particular eNodeB in the pool area, the MME
provides the UE context information to this eNodeB using initial context Setup request message.
This enables eNodeB turn to create a context and manage the UE for the duration of its activity in
active mode.
The creation of the eNodeB context by the initial Context setup procedure also includes the creation
of one or several bearers including the default bearer.
UE context release command message sent from the MME, the UE context in the eNodeB is erased
and only the UE context in the MME remains.
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4.3.2 Inter Radio Access Technology Mobility
eNodeB MME
Uplink S1 CDMA 2000 Tunneling
Uplink S1 CDMA 2000 Tunneling procedure
Mobility toward CDMA 2000 dedicated uplink and Downlink procedures have been introduced inLTE.
The CDMA 2000 signalling between the UE and the CDMA 2000 system over S1 interface.
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5. The E UTRAN Network interfaces: X2 Interface
The X2 interface is used to interconnect eNodeBs.
5.1 Protocol Structure Over X2
Physical Layer
Data Link Layer
IP
SCTP
X2 - APRadio
Network
Layer
Transport
Network
Layer
X2 Signalling Bearer Protocol Stack
Physical Layer
Data Link Layer
IPv6 (IETF RFC 2460)
And orIPv4(IETF RFC 791)
UDP
GTP - U
Transport Network Layer for data streams over X2
The Control and User plane Stack over the X2 interface is shown in fig are same as those for the S1
Interface, with the exception that X2AP is substituted for S1AP.
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5.2 Mobility Over X2
UESource LTE
eNodeBTarget LTE eNodeB MME/S-GW
1. Provisions of Area Restrictions2. Measurement Control
3. Handover Decision
5. Resource Setup
4. Handover Request
6. Handover Request ACK
7. Handover Command
8. Status Transfer
9. Handover Complete
10. Path Switch Request
11. Path Switch Request
ACK
12. Release Resource
Data Forwarding
Over X2 Interfaceto avoid data loss
X2 based handover procedure