System Architecture Evolution- overview

System Architecture
Evolution
Yousef Zanjireh
Fall 2015

High-Level Architecture of LTE
9/30/2015 Yousef Zanjireh (y_zanjireh@aut.ac.ir) 2

User Equipment: Architecture of the UE

UE Capabilities

Evolved UMTS Terrestrial Radio Access Network:
Architecture of the E-UTRAN

eNodeB (RBS in Ericsson)
• The RBS is the node in LTE that
implements the 3GPP eNodeB
concept.
• The RBS controls the radio
connections with connected UE
and manages the cell resources
including connection mobility
control.

Transport Network

Small Cells and the Home eNB:
Conceptual view of HeNB

Evolved Packet Core
Architecture of the EPC

Usual architecture of LTE for a roaming mobile
that is communicating with the Internet and the IP
multimedia subsystem

LTE Roaming Charging
• The complexities of the new charging mechanisms required to support 4G roaming are much more
abundant than in a 3G environment. Few words about both pre-paid and post-paid charging for LTE roaming
is given below:
• Prepaid Charging - The CAMEL standard, which enables prepaid services in 3G, is not supported in LTE;
therefore, prepaid customer information must be routed back to the home network as opposed to being
handled by the local visited network. As a result, operators must rely on new accounting flows to access
prepaid customer data, such as through their P-Gateways in both IMS and non-IMS environments or via their
CSCF in an IMS environment.
• Postpaid Charging - Postpaid data-usage charging works the same in LTE as it does in 3G, using versions TAP
3.11 or 3.12. With local breakout of IMS services, TAP 3.12 is required.
• Operators do not have the same amount of visibility into subscriber activities as they do in home-routing
scenarios in case of local breakout scenarios because subscriber-data sessions are kept within the visited
network; therefore, in order for the home operator to capture real-time information on both pre- and
postpaid customers, it must establish a Diameter interface between charging systems and the visited
network's P-Gateway.
• In case of local breakout of IMS services scenario, the visited network creates call detail records (CDRs) from
the S-Gateway(s), however, these CDRs do not contain all of the information required to create a TAP 3.12
mobile session or messaging event record for the service usage. As a result, operators must correlate the
core data network CDRs with the IMS CDRs to create TAP records.

Network Areas

Numbering, Addressing and Identification
• Each network is associated with a public land mobile network identity
(PLMN-ID).
• This comprises a three digit mobile country code (MCC).
• a two or three digit mobile network code (MNC). For example, the mobile country
code for the UK is 234, while Vodafone’s UK network uses a mobile network code of
15.
• Each MME pool area is identified using a 16 bit MME group identity
(MMEGI),
• 8 bit MME code (MMEC) uniquely identifies the MME within a pool area.
• Combining them gives the 24 bit MME identifier (MMEI), which uniquely
identifies the MME within a particular network.
• By bringing in the network identity, we arrive at the globally unique MME
identifier (GUMMEI), which identifies an MME anywhere in the world.

• Each tracking area has two main identities.
• The 16 bit tracking area code (TAC) identifies a tracking area within a particular
network.
• Combining this with the network identity gives the globally unique tracking area
identity (TAI).
• Cells have three types of identity.
• The 28 bit E-UTRAN cell identity (ECI) identifies a cell within a particular network,
• The E-UTRAN cell global identifier (ECGI) identifies a cell anywhere in the world.
• The physical cell identity, which is a number from 0 to 503 that distinguishes a cell
from its immediate neighbors.
• A mobile is also associated with several different identities.
• The most important are the international mobile equipment identity (IMEI), which is
a unique identity for the mobile equipment.
• The international mobile subscriber identity (IMSI), which is a unique identity for the
UICC and the USIM.

• The IMSI is one of the quantities that an intruder needs to clone a mobile,
so we avoid transmitting it across the air interface wherever possible.
Instead, a serving MME identifies each mobile using temporary identities,
which it updates at regular intervals.
• The 32 bit M temporary mobile subscriber identity (M-TMSI) identifies a
mobile to its serving MME.
• Adding the MME code results in the 40 bit S temporary mobile subscriber
identity (S-TMSI), which identifies the mobile within an MME pool area.
Finally, adding the MME group identity and the PLMN identity results in the
most important quantity, the globally unique temporary identity (GUTI).

Identities used by the MME

Temporary identities used by the mobile

Communication Protocols:
Protocol Model
High-level protocol architecture of LTE

Relationship between the access stratum and
the non-access stratum on the air interface

Air Interface Transport Protocols:
Transport protocols used on the air interface. Source: TS 36.300.

Air Interface
Transport
Protocols

LTE Layers
Data Flow

Network Transport Protocols

User Plane Protocols

Signaling Protocols

Example Signaling Flows:
Access Stratum Signaling
UE capability transfer procedure

Protocol stacks used to exchange RRC signaling
messages between the mobile and the base
station. Source: TS 36.300.

Non-Access Stratum Signaling
GUTI reallocation procedure. (a) Non-access stratum messages. (b) Message transport using the
access stratum

Protocol stacks used to exchange non-access
stratum signaling messages between the mobile
and the MME. Source: TS 23.401.

Bearer Management
The EPS Bearer
• LTE has to address two issues that the internet does not support.
• The first of these is mobility.
• The second issue is quality of service (QoS)
• To address these issues, LTE transports data from one part of the
system to another using EPS bearers.
• An EPS bearer can be thought of as a bi-directional data pipe, which
transfers data on the correct route through the network and with the
correct quality of service.
• The bearer runs between the mobile and the PDN gateway if the
S5/S8 interface is based on GTP or between the mobile and the
serving gateway if the S5/S8 interface is based on PMIP.

Default and Dedicated Bearers:
Default and dedicated EPS bearers, when using an
S5/S8 interface based on GTP

Bearer Implementation Using GTP:
Bearer architecture of LTE, when using an S5/S8
interface based on GTP. Source:
TS 36.300.

Protocol stacks used to exchange data between
the mobile and an external server, when
using an S5/S8 interface based on GTP. Source: TS
23.401.

Bearer Implementation Using GRE and PMIP
• The GRE protocol also uses tunnels, each of which is identified using a
32 bit key field in the GRE packet header. Unlike GTP-C, however,
PMIP does not include any signaling messages that can specify the
quality of service of a data stream.
• If the S5/S8 interface is implemented using GRE and PMIP, then a
mobile has only one GRE tunnel on that interface, which handles all
the data packets that the mobile is transmitting or receiving without
any quality of service guarantees. The EPS bearer only extends as far
as the serving gateway [55], but is otherwise implemented in the
same way that we have been describing.

Signaling Radio Bearers (SRB)
• To carry signaling messages between the mobile and the base station.
• The mobile and base station can agree on how the signaling messages
should be transmitted and received.
• SRB0 is only used for a few RRC signaling messages, which the mobile and
base station
• Use to establish communications in a procedure known as RRC connection
establishment. Its
• Configuration is very simple and is defined in special RRC messages known
as system information messages, which the base station broadcasts across
the whole of the cell to tell the mobiles about how the cell is configured.
• SRB1 is configured using signaling messages that are exchanged on SRB0, at
the time when a mobile establishes communications with the radio access
network.

SRBs

State Diagrams:
EPS Mobility Management
• A mobile’s behaviour is defined using three state diagrams, which
describe whether the mobile is:
• Registered with the EPC
• Whether it is active
• Idle.

EPS mobility management (EMM) state
diagram

Radio Resource Control (RRC)

Spectrum Allocation:
FDD frequency bands
(TS 36.101 and TS
36.104)

TDD frequency bands (TS 36.101 and TS
36.104)

Frequency bands used by operational and
planned LTE networks in November 2013.

Functional
split between
the E-UTRAN
and the EPC

2G/3G Versus LTE
2G/3G LTE
GERAN and UTRAN E-UTRAN
SGSN/PDSN-FA S-GW
GGSN/PDSN-HA PDN-GW
HLR/AAA HSS
VLR MME
SS7-MAP/ANSI-41/RADIUS Diameter
DiameterGTPc-v0 and v1 GTPc-v2
MIP PMIP

2G/3G – LTE Interworking
S3 – Exchange of bearer information, QoS,
S4 – U-Plane traffic

Self Organising Network Principles
• Automatic software management
• Self test
• Automatic neighbor relation configuration
• Tracking area planning
• Physical cell ID planning
• Load balancing
• Handover optimisations

System Architecture Evolution- overview

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