GSM GPRS UMTS

reference architectures Massimiliano Sbaraglia

GSM referenceGlobal System for

Mobile communications

UmUEGSM

BTS

Abis

MSMobile Station

BSSBase Station Subsystems

A

BSC

GMSC (Mobile Switching Center)

NSSNetwork and Switching Subsystems

radio

GSM channelorPCM 64 Kbit/s ISDN channel

GSM

HLR VLR AUC EIR

mobile call switched managemet

home location register visitor location register authentication center equipment identity register

Um A

Mobility managemet

location, services, autorization

PSTN

LALocation Area

OMCoperation and maintenance center

charging&billing

CS Core (Circuit Switching)RAN access

RADIO TECNOLOGY:TDD or FDDFrequency FDD uplink

Frequency FDD downlink

Uplink and Downlink in different frequencyTrasmission in parallel

Frequency FDD uplink

Frequency FDD downlink

Uplink and Downlink in the same frequencyTrasmission in different time

TCH

CCH

Handover

MSC = Mobile switching Center is element which controls the network switching subsystem elements and interfaces versus radio network.Manages communication between GSM and other networks. It has a call setup function and basic switching, call routing, billing information andcollection. Also has a Mobility management function, registration, location Updating and inter BSS and inter MSC call handoff.

MSS = Mobile switching Center Server is element which controls the network switching subsystem elements and interfaces vs radio network.This is the evolution of MSC.

A is the interface between MSS and BSC in GSM domain

IuCS is the interface between MSS and RNC in UMTS domain

GPRS referenceGeneral Packet Radio

Service

UEGPRS

radio

UmIub

BTS BSC

HLR VLR AUC EIR

MSMobile Station

BSS (class A, B, C)Base Station Subsystems

NSSNetwork and Switching Subsystems

A

SGSNGb

Gs

Gr Gf

home location register

visitor locationregister

authenticationcenter

equipmentIdentity register

IP BackboneNetwork

Gn

GGSN

IP BackboneExternal Network

Gi

OMCoperation and maintenance center

charging&billing

X.25External Network

Serving GPRS Support Node

Gateway GPRS Support Node

GPRS

Gn

RAN access PS Core (Packet Switching)

CS Core (Circuit Switching)

RARouting Area

LALocation Area

PDTCH

CCH

Handover

PSTN

Packet data network (PDN) → MS

UEGPRS

MS

LALocation Area

UEGPRS

LALocation Area

BSC

BSC

BTSNodeB

BTSNodeB

MS

Gb

Gb

intra-PLMNGPRS backbone

intra-PLMNGPRS backbone

Gn

Gn

inter-PLMNGPRS backbone

Gp

Gp

Gn

Gn

Packet Data Network PDNe.g. Internet, Intranet, IP

Gi

Gi

IP to MS

IP to MS

External networks always send packets to the GGSN corresponding to the MS addressed.The GGSN encapsulates packets received in other packageswith the address of the SGSN that currently controls theRA where the MS destination.If the MS moves to another RA, the GGSN updatesthe address of the target SGSN.

MS→ PDN

The SGSN which controls the RA is located in the MS examines the destination of the packets and determinesthrough its routing tables to which the GGSN send them. SGSN encapsulates packets in other packages with the address of the GGSN.The GGSN after receiving the packets and convert them routes to the original address to which they were sent.

Mobility management: tunneling packet networks (IP) do not support mobility.The routing is static: the packages destined to a certain address are always sentto the same destination.For support the mobility of the terminals is requires a routing of the dynamic type.

The Serving GPRS Support Node (SGSN) is a main component of the GPRS network, which handles all packet switched data within thenetwork, (e.g. the mobility management and authentication of the users)

The SGSN performs the same functions as the MSC for voice traffic.

The SGSN and the MSC are often co-located.

A serving GPRS support node (SGSN) is responsible for the delivery of data packets from and to the mobile stations within its geographicalservice area. Its tasks include packet routing and transfer, mobility management (attach/detach and location management), logical linkmanagement, and authentication and charging functions.

The location register of the SGSN stores location information (e.g., current cell, currentVLR) and user profiles (e.g., IMSI, address(es) used inthe packet data network) of all GPRS users registered with it.

The GGSN is responsible for the internetworking between the GPRS network and external packet switched networks, like the Internet.

From an external network's point of view, the GGSN is a router to a "sub-network", because the GGSN ‘hides’ the GPRS infrastructure fromthe external network.

When the GGSN receives data addressed to a specific user, it checks if the user is active.

If it is, the GGSN forwards the data to the SGSN serving the mobile user, but if the mobile user is inactive, the data is discarded.

On the other hand, mobile-originated packets are routed to the right network by the GGSN.

Some functions are subscriber screening, IP pool management and address mapping, QoS and PDP enforcement.

With LTE scenario the GGSN functionality moves to SAE gateway (with SGSN functionality working in MME).

Quality of service (QoS): the radio channel is very different from the fixed network and is necessary to introduce requirements that describe the call:

Precedence: indicates the priority in relation to other services (high, normal and low);

Reliability: indicates the features (BER, retransmissions, etc.) of the transmission request from service (class 1, 2 and 3);

Delay: indicates the overall delay that the packet data experiences to cross all the GPRS network, including the time of connection to the network (class 1, 2, 3 and 4);

Throughput: shows the bit / rate average and maximum of a service.

UMTS referenceUniversal Mobile

Telecommunication Systems

UuUEUMTS

NodeB

Iub

MSMobile Station

BSSBase Station Subsystems

IuCS

RNC GMSC (Mobile Switching Center)

NSSNetwork and Switching Subsystems

UMTS

HLR VLR AUC EIR

mobile call switched managemet

home location register visitor location register authentication center equipment identity register

Um

location, services, autorizationLALocation Area

OMCoperation and maintenance center

charging&billing

CS Core (Circuit Switching)

UTRAN access

Voice Traffic

SGSN

GGSN

IP BackboneINTERNET

PS Core (Packet Switching)

Gn Gi

WCDMA.UMTSchannel

PSTN

IuPS

E

Data Traffic

Node B is a term used in UMTS equivalent to the BTS.

It is the hardware that is connected to the mobile phone network that communicates directly with mobile handsets; in contrast withGSM base stations, Node B uses WCDMA/TD-SCDMA as the air interface technology.

As in all cellular systems, such as UMTS and GSM, the Node B contains radio frequency transmitter(s) and the receiver(s) used tocommunicate directly with mobile devices, which move freely around it. In this type of cellular network, the mobile devices cannotcommunicate directly with each other but have to communicate with the Node B.

IuB is the interface between RNC and NodeB

The Radio Network Controller (or RNC) is a governing element in the UMTS radio access network (UTRAN) and is responsible forcontrolling the Node-Bs that are connected to it.

The RNC carries out radio resource management, some of the mobility management functions and is the point where encryption is donebefore user data is sent to and from the mobile.

The RNC connects to the Circuit Switched Core Network through Media Gateway (MGW) and to the SGSN (Serving GPRS Support Node) inthe Packet Switched Core Network.

Handover in a UMTS system are carried out for two reasons:

Deterioration of the channel (for example due to mobility);

Balance traffic: if a cell is overloaded, the MS are redistributed on adjacent cells.

They identify three types of handover:

Hard handover: the radio channel is switched off in a cell and switched into another.

Soft handover: changes the active September on the Connectivity concerns more node B.

Softer handover: occurs when the cells that are found September in the Active belong to a single node B.

The macrodiversity uplink is exploited to rake receiver of node B.

handover:

Intra-mode handover:

Intra-frequency: hard, soft, softer; Inter-frequency: hard

Inter-system handover: hard.

WCDMA Wideband Code Division Multiple Access uses a technique called FDD, Frequency Division Duplex.

The WCDMA standard is the air-interface of the UMTS system. This technique spreads the users signal over a wide bandwidth; inthe old GSM system, every User Equipment (UE) had only 200 kHz of bandwidth, but in this system there exists a 5 MHzbandwidth.

The signal is split using different codes for different users. This way multiple calls and/or connections can exist on the samefrequency.

This removes the need of doing frequency planning, as done in the old system, and you can have a frequency reuse factor of 1, thatis you can utilize the same frequency in adjacent cells.

The WCDMA technique also gives a higher data-rate, more handover choices, adaptive power control, and so on.