Introduction to Mobile Cellular Networks

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Introduction to Mobile Cellular Networks

Part I: 3G Mobile Core Network in a Nutshell

VU 389.134

Video and Multimedia Transmissions over Cellular Networks


3.10.2011

2

Video and Multimedia Transmissions over Cellular Networks 389.134

What this lecture is about …


Video and Multimedia Transmissions over Cellular
Networks


Cellular networks (GSM, UMTS, LTE, LTE
-
A)


Packet switched data transmission


Video and other services


Cross layer approaches



How to measure/analyze/optimize such services



What you should already know


Cellular network (basics)


UDP, TCP, IP, …


eMail

/ HTTP / streaming (basics)

HTTP

HyperText

Transport Protocol

IP

Internet Protocol

TCP

Transport Control Protocol

UDP

User Datagram Protocol

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Video and Multimedia Transmissions over Cellular Networks 389.134

The Problem


Today data services generate more traffic than voice


Radio link is expensive and limit resource



Data services


consume more bandwidth at less revenue


QoS

definition is problematic



Looking for ways to offer constant
QoS

at reduced data
-
rate/bandwidth needs


Measurement and analysis of existing traffic


Link layer modeling from IP point of view


Cross layer optimization (video streaming, …)


Traffic modeling with respect to cellular networks


QoS

Quality of Service

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Video and Multimedia Transmissions over Cellular Networks 389.134

Possible Solutions


Communication system are split into independent atomic
layers


Open Systems Interconnection (OSI) reference model








Data transmission


Two consecutive layers: payload


Two corresponding layers: payload, signaling


Processing information stays within the layer

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Video and Multimedia Transmissions over Cellular Networks 389.134

Some (more) Motivation


Today every layer is optimized to a large extend


e.g.: receivers fight for < 1dB improvement


Idea: use processing information from multiple layers


Soften the boundaries between two layers


e.g.: variable priority for video streaming and web browsing


Optimization problems get much harder


Optimum often hard to prove


X

X

X

TB

Transport Block

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Video and Multimedia Transmissions over Cellular Networks 389.134

Outline of this Lecture


Cellular Mobile Networks: (5.10.2009
-

16.11.2009 / Svoboda)


PS
-
Core Network


Link Error Analysis


Link Error Prediction


Measurement and Analysis



Video in Error Prone Environments (23.11.2009
-

14.12.2009 / Rupp)


Principles of Video Encoding


Error Detection and Concealment


Cross Layer Error Resilience in Video Streaming


End to End Video Quality Estimation



Traffic in Mobile Networks (11.01.2010
-

25.01.2010 / Svoboda)


Detection of Anomalies in a Network


Traffic Flows


Traffic Modeling in High
-
Delay Environments


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Video and Multimedia Transmissions over Cellular Networks 389.134

Outline of today's talk


Evolution of mobile cellular networks



3G Network Hierarchy



3G core network Elements



3G protocol Hierarchy



Simple procedures in mobile cellular networks



Journey of a packet through the network

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Video and Multimedia Transmissions over Cellular Networks 389.134

Network Architecture


Hierarchical ordering of functional groups


Functional structures/groups


Defined by “functions” / procedures


Consist of one or several physical elements


Interfaces (reference points)


Points allowing for interconnection between functional structures


IP

Internet Protocol

MS

Mobile Station

UE

User Equipment

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Video and Multimedia Transmissions over Cellular Networks 389.134

Network Architecture: Example GSM/GPRS


GSM (2G): digital circuit switched network for voice


All services reserve the same fixed bandwidth


Charging on time unit basis


Data rate: 9.6
kbit
/s


GPRS (2.5G): extension for packet switched traffic


Packet switched (PS) domain is introduced


PS oriented shared data channels at the radio link


Data rate: ~114
kbit
/s

GSM

Global System for Mobile


Communication

GPRS

General Packet Radio Service

SIM

Subscriber Identity Module

BTS

Base Transceiver Station

BSC

Base Station Controller

PCU

Packet Control Unit

MSC

Mobile Switching Center

SGSN

Serving GPRS Support Node

GGSN

Gateway SGSN

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Video and Multimedia Transmissions over Cellular Networks 389.134

Network Architecture: Example UMTS/HSPA


UMTS (3G):


The UTRAN (UMTS RAN) is added to existing 2.5G networks


WCDMA, soft handover,
QoS
, …


Link speed is variable but fixed to certain values.


Data rate: 384
kbit
/s


HSPA (3.5G):


Real packet switched radio bearers (similar to GPRS)


No more soft handover


Data rate: 7.2
Mbit
/s


PS

Packet Switched

UMTS

Universal Mobile


Telecommunications System

HSPA

High Speed Packet Access

USIM

Universal SIM

NodeB

NodeB

RNC

Radio Network Controller

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Video and Multimedia Transmissions over Cellular Networks 389.134

Evolution of (digital) Cellular Networks


GSM (2G)


GPRS (2.5G)


No changes on the radio interface


Large changes in RAN


Birth of the PS
-
Core (!)



GPRS

(2.5G)



UMTS (3G)


Large changes in the RAN


The first network designed for PS traffic


Small changes in the Core



UMTS R99 (3G)


HSPA (3.5G)


Changes in the radio interface


No changes in the Core


RAN

Radio Access Network

PS

Packet Switched

GSM

Global System
for

Mobile


Communication

GPRS

General Packet Radio Service

UMTS

Universal Mobile


Telecommunications System

HSPA

High Speed Packet Access

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Video and Multimedia Transmissions over Cellular Networks 389.134

The
Complete Picture of a 3G Core Network

2G

3G

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Video and Multimedia Transmissions over Cellular Networks 389.134

Summary of (digital) Cellular Networks


Main Components of a Cellular Network


User equipment


Radio access network


Core network



GSM: digital and circuit switched



GPRS: adds the CN PS
-
domain to GSM



UMTS: pseudo PS radio links, RAN


UTRAN



HSPA: PS radio links for UMTS, no soft handover



RAN

Radio Access Network

PS

Packet Switched

GSM

Global System
for

Mobile


Communication

GPRS

General Packet Radio Service

UMTS

Universal Mobile


Telecommunications System

HSPA

High Speed Packet Access

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The Core Network Elements

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Video and Multimedia Transmissions over Cellular Networks 389.134

The

Mobile Switching Center (MSC)


Routing
grid
for Circuit Switched
(CS) services


Main
functions
:


Interconnect of CS
services


Mobility Management


Localization


Signaling


Protocols:


PCM30 / PCM30 (not AMR!)


Interfaces:


IuCS

/ SS7(E)


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Video and Multimedia Transmissions over Cellular Networks 389.134

The Serving GPRS Support Node


Counter part
to the MSC in the Packet Switched (PS)
domain


Main
functions
:


Security /
authentication


Mobility
Management (MM): cell update,
etc
.


Handling of data sessions (routing)


Caching user subscriber data


Protocols:


GTP / GTP (not terminated in SGSN!)


Interfaces:


IuPS

/
Gn


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Video and Multimedia Transmissions over Cellular Networks 389.134

The Gateway GPRS Supporting Node (GGSN)


„The Gatekeeper to the outer Territories“


GGSN ‘hides’ the GPRS infrastructure


Main functions
:


Handling of the
PDP Context


Building a
bridge
to the external
networks


eg
. Internet


Converting the IP
packets
to GTP
protocol


Billing,
QoS
, …


Protocols:


GTP / IP


Interfaces:


Gn

(GTP)
/
Gi

(IP)


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Video and Multimedia Transmissions over Cellular Networks 389.134

The Home Location Register (HLR)


Database holding
static
user information


Telephone
number (MSISDN =
CC + NDC + SN)


Subscriber number (IMSI =
MCC + MNC + MSIN
)


Security issues


AUC (key
)


QoS

parameters


Available
services
(voice, packet....)


Position
information: Visitor Location Register (VLR)


Protocols:


IP


Interfaces:


Gr
, C



MSISDN = MS
-

ISDN

CC

Country Code

NDC

National
Dest
. Code

SN

Subscriber
Number


IMSI

Int. Mobile Subscriber
Id

MCC

Mobile Country Code

MNC

Mobile Network Code

MSIN

Mobile Station
Id

Number


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Video and Multimedia Transmissions over Cellular Networks 389.134

Summary of Core Network Elements


Core Network Elements


CS: MSC, G
-
MSC


PS: SGSN, GGSN


OM: HLR, VLR, EIR, …



MSC / SGSN interconnect RAN to the CN


G
-
MSC / GGSN interconnect CN with other networks


HLR holds all “static” user information


VLR local copy of HLR in SGSN


Further Management units:


EIR, OMC, …



CS

Circuit Switched

PS

Packet Switched

OM

Operation and Maintenance

MSC

Mobile Switching Center

G
-
MSC

Gateway MSC

SGSN

Serving GPRS Supporting Node

GGSN

Gateway GPRS Supporting Node

HLR

Home Location Register

VLR

Visiting Location Register

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Video and Multimedia Transmissions over Cellular Networks 389.134






The Protocols

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The Protocol
Hierarchy



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The Control Plane




SDH

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Video and Multimedia Transmissions over Cellular Networks 389.134

The User Plane




SDH

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Video and Multimedia Transmissions over Cellular Networks 389.134

The GPRS Mobility Management (GMM)







GPRS version of the MM
protocol
(MM still needed)


Managing the
mobility
of the
terminals


Present location


Connections management services


User identity
confidentiality


User states:


Idle: the subscriber is not attached


Standby: the subscriber is attached


Ready: the subscriber is active







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Video and Multimedia Transmissions over Cellular Networks 389.134

The
RAN Application
Part (RANAP)






Handles the
signaling
between UTRAN and
PS
-
CN
(
Iu
)


Booking ATM lines, Changing Setup, ….


Includes all
control
information for UTRAN


3 Classes of
elementary
procedures:


General control services


Notification services


Dedicated
control services



Some
functions
:


Iu

Release (1)


Overload Control (2)


RAB Assignment (3)

RAB

Radio Access Bearer

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Video and Multimedia Transmissions over Cellular Networks 389.134

The Signaling Connection Control Part (SCCP)






Task:


Abstraction between UMTS
and transport system
(ATM, IP)




Transport System is hidden.



Supports


connection
-
less and

oriented extension to MTP


Address translation


Full OSI
layer
3 compatibility


Below SS7
protocol

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Video and Multimedia Transmissions over Cellular Networks 389.134

The GPRS Tunneling Protocol (GTP v0)


For the connection
between RNC
, SGSN, GGSN


Payload is attached to GTP headers (8Bytes)


Used for
signaling
and
data


Fields:


Version: GTP v0 or v1


Protocol Type: GTP, GTP’ (GTP’ protocol is used to transfer charging data to the
Charging Gateway Function)


Flags: Extension, Sequence, N
-
PDU


Message Type: What is this GTP message about


Length: length of payload


Tunnel Endpoint Identifier: Start/End point of the GTP tunnel (user, APN)





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Video and Multimedia Transmissions over Cellular Networks 389.134

The GTP
-
U /
-
C


GTP
-
C(
ontrol
)


GPRS mobility management between GSNs


Logically attached to the GTP
-
U tunnel


physically separated


Functions:


Create/Update/Change PDP Context


Echo Request/Response


RAN Information



GTP
-
U(ser)


Hides mobility from IP layer


Supports reordering of T
-
PDUs


TEID
is always unique


Functions:


Data Transmission


Tunnel Setup/Release/Error


Echo Request/Response

TEID

Tunnel Endpoint
IDentifier

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Video and Multimedia Transmissions over Cellular Networks 389.134

Summary of Core Network Protocols


Protocol hierarchy


Non
-
access / Access Stratum


Radio / Transport Network Layer



Core network protocols:


GMM:

location, user mobility, …


RANAP:

signaling between UTRAN and CN


SCCP:

abstraction between UMTS layers and transport layer


GTP
-
U:

transport of user data payload


GTP
-
C:

managing of corresponding GTP
-
U (always in pairs)



Every user has a least one GTP tunnel (pair) active


SGSN records the states of these protocols for every user




CS

Circuit Switched

PS

Packet Switched

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Video and Multimedia Transmissions over Cellular Networks 389.134






Let's start the Journey . . .

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Video and Multimedia Transmissions over Cellular Networks 389.134

Processed Steps


Now we will use the basics.


GPRS
attach


PDP
context activation


Mobile Station starts to send data (IP Packets)


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Video and Multimedia Transmissions over Cellular Networks 389.134

Svoboda

Activating a PDP Context


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Protocol Mapping



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Video and Multimedia Transmissions over Cellular Networks 389.134

Sending the Packet: UTRAN
-
SGSN



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Video and Multimedia Transmissions over Cellular Networks 389.134

Sending the Packet: SGSN
-
GGSN



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Video and Multimedia Transmissions over Cellular Networks 389.134

Sending the Packet: Outer Regions



Where
is the
bird?

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Video and Multimedia Transmissions over Cellular Networks 389.134

Summary of this lecture


Network hierarchy


Core network elements


Protocol hierarchy


How a data (IP) transmission over mobile cellular networks
works


Important things/abbreviations


Subscriber:

IMSI, TIMSI, GTP


Elements:

RNC, SGSN, GGSN,
NodeB


Interfaces:

Gi
,
Gn
,
IuCS
,
IuPS


Procedures:

PDP, GMM



Next stop: UTRAN

Thank you for your attention


Questions?

psvoboda@nt.tuwien.ac.at


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Video and Multimedia Transmissions over Cellular Networks 389.134

Where to look?



[1]

RANAP on Iu: 3gpp 25.413; 23.108 (E Interface)

[2]

Iu User Plane: 3gpp 25.415

[3]

GTP: 3gpp 29.060

[4]

Core Network Basics: 3gpp 23.002

[5]

www.umtslink.at

[6]

http://www.techfest.com/networking/

[7]

http://www.manualy.sk/protocols2/pbook/gprs.htm#GTP

[8]

http://www.manualy.sk/protocols2/pbook/umts.htm

[9]

http://www.tkn.tu
-
berlin.de/curricula/ws0405/vl
-
umts/





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Video and Multimedia Transmissions over Cellular Networks 389.134

Abbreviations (1)



AAL2

ATM Adaptation Layer type 2

ALCAP

Access Link Control Application Part

APN

Access Point Name

AS

Access Stratum

ASN.1

Abstract Syntax Notation One

ATM

Asynchronous Transfer Mode

BSC

Base Station Controller

BTS

Base Transceiver Station

CC

Call Control

CN

Core Network

CRNC

Controlling RNC

CS

Circuit Switched

DCH

Dedicated Channel

DL

Downlink

DRNC

Drift RNC

DRNS

Drift RNS

DSCH

Downlink Shared Channel

EP

Elementary Procedure

GERAN

GSM/EDGE Radio Access Network

GGSN

Gateway GPRS Supporting Node

G
-
MSC

Gateway Mobile Switching Center

GMM/SM

GPRS Mobility Management / Session
Management

GPRS

General Packet Radio System

GSM

Global System for Mobile communications

GTP

GPRS Tunneling Protocol

GWCN

GateWay Core Network

HLR

Home Location Register

IE

Information Element

IMEI

International Mobile Equipment Identity

IMSI

International Mobile Subscriber Identity

IPv4

Internet Protocol (version 4)

IPv6

Internet Protocol (version 6)

MAC

Media Access Control

MBMS

Multimedia Broadcast Multicast Service

MM

Mobility Management

MOCN

Multi Operator Core Network

MSC

Mobile services Switching Centre

MTP

Message Transfer Part

NACC

Network Assisted Cell Change

NAS

Non Access Stratum

NRT

Non
-
Real Time

N
-
PDU

Network


Protocol Data Unit

P
-
TMSI

Packet TMSI

PCM

Puls Code Modulation

PCU

Packet Control Unit

PDCP

Packet Data Convergence Protocol

PDP

Packet Data Protocol

PDU

Protocol Data Unit

PLMN

Public Land Mobile Network

PS

Packet Switched

PSTN

Public Switched Telephone Network

QoS

Quality of Service

RAB

Radio Access Bearer

RANAP

Radio Access Network Application Part

RLC

Radio Link Control

RNC

Radio Network Controller

RNS

Radio Network Subsystem

RRC

Radio Resource Control

RT

Real Time