Wireless Data Communication

Page 1Tatiana K. Madsen

Hans Peter SchwefelWireless Data Communication: MM5, Wireless Applications, Fall03

Wireless Data Communication

www.kom.auc.dk/~tatiana/WDC

by Tatiana Madsen & Hans-Peter Schwefel

• Mm1 Short range Wireless Communication (TKM)

• Mm2 IP Mobility Support (HPS)

• Mm3 Ad hoc Networks (TKM)

• Mm4 Wireless TCP (HPS)

• Mm5 Wireless applications (HPS)

www.kom.auc.dk/~hps/teaching



Content1. Introduction

• Application Layer Protocols, basic principles

2. Hyper-Text Transfer Protocol (HTTP)• Properties and messages

• Problems & Improvements in wireless settings

3. Session Initiation Protocol (SIP)• Architectures & Entities

• Methods

• Mobility Support

4. IP Technology in 3G Networks• GSM/GPRS/UMTS architecture

• IP packet transport in UMTS

• IP based multimedia subsystems (IMS)

• Services



Application Layer ProtocolsApplications: communicating distributed processes

• ’end-user’ applications

• network services

Application Layer Protocols

• highest layer of communication reference model

• Define messages exchanged by applications

• Provide an Application Programming Interface (API)

• Use Transport Layer to exchange data

Examples: UDP based TCP basedDNSVideo StreamingMultimedia Conferencing

HTTP, FTP, telnet,

SMTP, NNTP



Design principles & approaches

• End-to-end principle– communication does not rely on functions in the network

• ASCII binary encoded protocols– ASCII frequently easier to debug and implement

– Examples for ASCII encoded: HTTP, SIP, SMTP

• Separation of Control Messages and User Data– Separate connections (e.g. SIP) out-of-band signalling

– Special character sequences (e.g. SMTP)

– Content length encoding: control messages specify length of subsequent data messages

• Client-Server peer-to-peer

in-band signalling



Client-Server Paradigm• Server (software process, not piece of

hardware!)– Offers a service to clients– accepts connections / requests on a (well-

known) port– runs continuously– Frequently starts up multiple processes to

serve multiple clients

• Client– Initiates contact to server (over an IP

network)– process runs only as long as needed– can use any port








• Methods





• Services



Hypertext Transfer Protocol (HTTP)• defined in RFCs 1768, 1945, 2616, 2617

• Client-Server Model

– All communication (Requests, Response) uses TCP transport

– Client: browser that requests, receives, and displays WWW objects

– Server• Send objects in response to requests• Well-known port 80 (but others can be specified in URL)

• Stateless protocol

– self-contained requests

– no state kept in server

– augmented by the “cookies” concept (store state in clients)

• Caching support

– HTTP allows to retrieve file properties only (“HEAD” method)

• Support for proxies



HTTP Requests• ASCII encoded methods to retrieve (and send) files

– GET, HEAD, POST, PUT, OPTIONS, DELETE, TRACE, CONNECT• headers to transport additional information

e.g. Capability selection (client lists e.g. supported character sets, server selects one)



HTTP Request Message: General Format

• Uniform resource locator (URL) for addressing– “http://” hostname [ “:”port ] [ abs_path [ “?”query ] ]– relative URL: without the “http:// hostname” [“:”port] part

• Byte-range requests– allow completion of interrupted transfers



HTTP Response

• Content description– Markup language HTML (Hypertext markup language, RFCs 1866, 1867, 1942) describes

structured contents– MIME notation to inform receiver about file types

• in addition, receivers judge file types from file name endings



HTTP State Information

• HTTP is a “stateless” protocol– server does not maintain any request related information

beyond request completion• “Cookies” can be used to store request related information

in browser (RFC 2109)– “Set-cookie:” header set cookie in browser– “Cookie:” header browser sends cookie along with request– Cookie contains

• name, value• optional: comment, domain, max. age, path, security info, version

number



e.g. corporate network

HTTP Caching and Proxies• Caching

– store file locally (e.g. in client)

– use local copy when same file is requested again reduce network traffic– ageing mechanism

• retrieve again only if local copy is “old”

– conditional requests• retrieve again only if file has changed• e.g. “If-Modified-Since: Sun, 03 Jun 2001 16:12:25 GMT” • server can respond with “304 Not Modified”

– browser can force revalidation of page

• Proxy Support– Split end-2-end client-server connection– used for performance & security reasons– often combined with caching (performance)– explicitly supported in HTTP/1.1

ProxyProxy

HTTP Server

Internet



Traffic models: General hierarchical models

• Mathematical /stochastic description of traffic• Frequently used: Several levels with increasing granularity

– E.g. 3 levels: sessions, connections, packets– Or: 5-level model:



Traffic models: HTTP specifics • ‘Main’ objects contain zero or more embedded objects that the browser retrieves

Correlated requests for embedded objects within retrieval of main object

HTTP Session (User A)

HTTP Session (User B)

HTTP Session (User C)...

Session Level

Download Phase 1 Download Phase 2 Dld. Phase 3 ...Idle timeRead time

’exit browser’’click’ ’click’

Dld. Phase K

’click’’start browser’

Get Main Object Get embedded Obj. 1 Get emb. Obj. 2 Get emb. Obj. N...

Connection/ Flow Level

Packet Level, TCP dynamics (not shown here)

• Statistics:– Session arrivals: Renewal process (Poisson)– Idle time: heavy-tail

– # embedded objects: geometric (measurements e.g. mean 5)

– Object size: heavy-tailed



HTTP in wireless settings• Wireless links tend to show special properties, in particular

– Large delays– Low throughput

• Mobility can make network-internal caches and pre-fetching difficult • Wireless devices pose restrictions

– User interfaces: Small screens, limited keyboards

Potential problems of HTTP transmissions-- performance / efficient use of resources

-- presentation of content on mobile devices

Typical transfer sizes of HTTP:– HTTP request: 100-350 byte– responses avg. <10 kbyte, header 160 byte, GIF 4.1kByte, JPEG 12.8 kbyte, HTML 5.6 kbyte– but also many large files that cannot be ignored



HTTP in wireless settings: Problems (cntd.)• big and redundant protocol headers (readable for humans (ASCII), all state

needs to be transferred in headers)• uncompressed content transfer• uses one TCP connection for each request-response pair (HTTP1.0)

– huge overhead per request (3-way-handshake) compared with the content, e.g., of a GET request

– slow-start problematic

• DNS lookup by client causes additional traffic & delay

• Caching– quite often disabled by information providers to be able to create user

profiles, usage statistics etc.– mobility can decrease network cache hit-ratios (if hand-overs to different

caching devices occur)– security problems (how to use SSL/TLS together with proxy-caches?)– frequent use customized pages, dynamically generated on request via

CGI, ASP, ...



HTTP Performance ImprovementsPersistent Connections• Problem: Frequently retrieval of several, small embedded objects

overhead for establishment and termination of many TCP connections• Solution: More than one item transferred in one connection

– HTTP/1.0: requested by “Connection: Keep-alive” header– default in HTTP/1.1

• requires specification of content length (“Content-Length” header)

• for ‘dynamic’ pages: length is not known before transmission– server notifies the client

• sends “Connection: close” header instead of “Content-Length”– closes the connection after transmission (see p. 4-8)

Pipelining (HTTP/1.1)– send multiple GET requests (without waiting for response in between)

– increase TCP efficiency for transfers of small elements– Potentially problems with servers closing connections



HTTP Requests and Persistent Connections

DataTransfer

GET...

Data

ACK

TCPConn.Release

FIN

FIN+ACK

ACK

TCPConn.Setup SYN+ACK

ACK

SYN

Client Server

Minimum connection

Clie

nt

Ser

ver

SYN

SYN+ACK

ACKKeep-alive + GET

Data

FIN

GET

Data

ACK

GET+ACK

Data

ACK

Tim

eout

(e.

g. 1

5sec

)T

imeo

ut (

e.g.

15s

ec)

Persistent connection



Improvements in HTTP1.1

• Default use of persistent connections (for several request/response transactions)

• Support of pipelining – multiple ‘get’ requests at beginning of session, several responses in same

order

• enhanced caching of responses (useful if equivalent responses!)– several more tags and options for controlling caching (public/private, max-age, no-

cache etc.)

• Enhanced proxy support• encoding/compression mechanism, integrity check, security of

proxies, authentication, authorization...



HTML and mobile devices• HTML

– designed for computers with “high” performance, color high-resolution display, mouse, hard disk

– typically, web pages optimized for design, not for communication

• Mobile devices– often only small, low-resolution displays, very limited input interfaces (small touch-

pads, soft-keyboards)

• Additional “features”– animated GIF, Java AWT, Frames, ActiveX Controls, Shockwave, movie clips,

audio, ...– many web pages assume true color, multimedia support, high-resolution and many

plug-ins

• Web pages ignore the heterogeneity of end-systems!– e.g., without additional mechanisms, large high-resolution pictures would be

transferred to a mobile phone with a low-resolution display causing high costs



Improvements for wireless settings• Improved, ‘wireless-aware’ browers (clients)

– Local caches & Prefetching– Strategies for content selection (e.g. do not retrieve all

embedded objects immediately)– Content adaptation to device capabilities

• Improved HTTP servers & content design

• HTTP proxies (application gateways)– Caching & pre-fetching– Content compression, filtering, translation– automatic adaptation to network characteristics– TCP optimizations (initial window size,…)– In addition security and charging functions

GPRSBackbone

SGSN GGSNBSC

HTTP Server

RADIUS

DHCP

HTTP Proxy

But: additional complexity on devices / special SW needed!

But: servers not aware of wireless access

– With modifications of browser SW• http commands and header

compression• Pre-computation proxy for content

presentation

RAN

Example: GPRS








• Methods





• Services



Session Initiation Protocol -- SIP

SIP: Application layer signalling protocol (RFC 3261) Provides call control for multi-media services

initiation, modification, and termination of sessions terminal-type negotiation and selections call holding, forwarding, forking, transfer media type negotiation (also mid-call changes) using Session Description Protocol (SDP)

Provides personal mobility support Independent of transport protocols (TCP, UDP, SCTP,…) ASCII format SIP headers Separation of call signalling and data stream

Application types/examples: Interactive Voice over IP (VoIP) Multimedia conferences (multi-party, e.g. voice & video) Instant messaging Presence service Support of location-based services



SIP: Architecture & Entities

User agent: An application program which initiates SIP requests (User agent client) and also acts upon (accepts, rejects or re-directs) incoming SIP requests (User agent server)

Location server provides SIP redirect or proxy servers information about a callee's possible location(s).

Proxy server takes requests on behalf other user agents or servers and forwards them to the next hop.

Redirect server accepts a SIP request, maps the address into zero or more new addresses and returns these addresses to the client. Unlike a proxy server, it does not initiate its own SIP request.

Registrar is a server that accepts REGISTER requests. A registrar is typically co-located with a proxy or redirect server and may offer location services.

Redirect Server

Location Server

Registrar Server

User Agent Proxy ServerProxy Server User Agent



SIP – Basic messages

• Selected Requests (Methods)– INVITE: initiate call– ACK: confirm final response (after ‘invite’)– BYE: terminate call– CANCEL: cancel pending requests– OPTIONS: queries features supported by

other side– REGISTER: register with location service

• Responses– 1xx Intermediate results

e.g. 180 Ringing– 2xx Successful Responses

e.g. 200 OK– 3xx Redirections

e.g. 302 Moved Temporarily– 4xx Request Failures– 5xx Server Failures– 6xx Global Errors



SIP Addressing and header formatAddressing:• Addresses specified SIP URL, in the format: user@host. • Examples of SIP URLs:

• sip:[email protected]• sip:[email protected]• sip:[email protected]

INVITE sip:[email protected] SIP/2.0Via: SIP/2.0/UDP 192.168.6.21:5060From: sip:[email protected]: <sip:[email protected]>Call-ID: [email protected]: 100 INVITEExpires: 180User-Agent: Cisco IP Phone/ Rev. 1/ SIP enabledAccept: application/sdpContact: sip:[email protected]:5060Content-Type: application/sdp

• Example: SIP Header



SIP Call Signalling: Example

302 (Moved Temporarily)

INVITE

200 (OK)200 (OK)

ACK

INVITE

180 (Ringing)180 (Ringing)180 (Ringing)

200 (OK)ACKACK ACK

RTP MEDIA PATH

BYEBYE BYE

200 (OK)200 (OK) 200 (OK)Call Teardown

MediaPath

Call Setup

INVITE

Location/Redirect ServerProxy Server Proxy Server User AgentUser AgentINVITE



SIP: Separation of signalling and data

• Route of SIP messages (proxy chain) different than media stream route:

Potential Problems with Firewalls & NATs



SIP: Mobility support

User Mobility (change of terminal)• Registration via SIP ‘REGISTER’• mid-session mobility (application mobility):

call transfer, SIP method ‘REFER’ (RFC3515)

Host Mobility (change of IP address)• Pre-call: re-register, routing of ‘INVITE’ based

on SIP-URL• mid-call: re-invite



SIP: additional topics

Not touched in this lecture, see IETF SIP WG:• Multitude of SIP extensions: new methods (e.g. instant messages)• SIP over NAT/FW• Authentication and security aspects• Support of location based services• Discovery of SIP entities (e.g. DNS SRV records)• Service Discovery (e.g. SLP)• Reliability aspects of SIP-based call control








• Methods





• Services



GSM: Global System for Mobile Communication

• 2nd Generation of Mobile Telephony Networks• 1982: Groupe Spèciale Mobile (GSM) founded• 1987: First Standards defined• 1991: Global System for Mobile

Communication, Standardisation by ETSI (European Telecommunications Standardisation Institute) - First European Standard

• 1995: Fully in Operation

History:



GSM – Architecture

Components:• BTS: Base Transceiver Station• BSC: Base Station Controller• MSC: Mobile Switching Center• HLR/VLR: Home/Visitor Location

Register• AuC: Authentication Center• EIR: Equipment Identity Register• OMC: Operation and

Maintenance Center

Transmission: • Circuit switched transfer• Radio link capacity: 9.6 kb/s

(FDMA/TDMA)• Duration based charging

BSC

BSC

MS

BTS

BTS

BTS

MS

MS

MSC

HLR

VLR

OMC

EIR

AuC

O

Abis AUm

Radio Link

Base StationSubsystem

Network andSwitchung Subsystem

OperationSubsystem

Connection toISDN, PDNPSTN

Radio Subsystem (RSS)



GPRS: General Packet Radio Service

• Packet Switched Extension of GSM• 1996: new standard developed by ETSI• Components integrated in GSM architecture• Improvements:

– Packet-switched transmission– Higher transmission rates on radio link (multiple

time-slots)– Volume based charging ‚Always ON‘ mode

possible• Operation started in 2001 (Germany)



GPRS - Architecture

PDN

Other

PLMN

GSM GPRS

BTS

CCU

MSC

BSC

PCU

HLR GR

GGSN

Components

A Abis Gb Gp

Gs

Gn

G Gr

Gi

UmBSS

SGSN

MS

Components:• CCU: Channel Coding Unit

• PCU: Packet Control Unit

• SGSN: Serving GPRS Support Node

• GGSN: Gateway GPRS Support Node

• GR: GPRS Register

Transmission: • Packet Based Transmission• Radio link:

– Radio transmission identical to GSM– Different coding schemes (CS1-4)– Use of Multiple Time Slots

• Volume Based Charging



Universal Mobile Telecommunication System (UMTS)

• Currently standardized by 3rd Generation Partnership Project (3GPP), see http://www.3GPP.org[North America: 3GPP2]

• So far, three releases: R’99, R4, R5

Modifications:• New methods & protocols on radio link increased access bandwidth• Coexistence of two domains

– Packets Switched (PS)– Circuit Switched (CS)

• New Services• IP Service Infrastructure: IP Based Multimedia Subsystems (IMS) (R5)



UMTS Domains (Rel 5)

IMS

SGSN

GGSN

MSCServer

MSCGMSC

MGW

P-CSCF

S-CSCF I-CSCF

MRFAppServ

AppServ

SCP

HSS

IP based MultimediaSubsystem

PS DomainCS Domain

Application and Services

RAN

Gi

Iu PSIu CS



UMTS Radio Access Network (UTRAN): architecture

• W-CDMA (Wideband Code Division Multiple Access) on Radio Link

• transmission rate theoretically up to 2Mbit/s (realistic up to 300kb/s)



TSG CNCore Networks

TSG GERANGSM EDGE

Radio Access Network

TSG RANRadio Access

Network

TSG SAServices & System

Aspects

TSG TTerminals

CN WG 1MC/CC/CS (lu)

CN WG 3Interworking withExternal Networks

CN WG 2CAMEL

CN WG 5OSA

(Open Service Architecture)

CN WG 4 MAP/GTP/BCH/SS

GERAN WG 1Radio Aspects

GERAN WG 2Protocol Aspects

GERAN WG 3Base Station Testing

and O & M

GERAN WG 4Mobile Station

Testing

RAN WG1Radio Layer 1specification

RAN WG2Radio Layer 2 spec. & Radio

Layer 3 RR spec.

RAN WG3lub spec, lur speclu spec & UTRAN

O&M requirements

RAN WG4Radio performance & Protocol aspects

SA WG 1Services

SA WG 2Architecture

SA WG 3Security

SA WG 4Codec

SA WG 5Telecom

Management

T WG 1Mobile Terminal

Conformance testing

T WG 2Mobile Terminal

Services & capabilities

T WG 3Universal Subscriber

Identity Module (USIM)

3GPP TSGORGANIZATION

UMTS Standardisation: 3GPP• Collaboration Agreement,

Partners: ARIB, CCSA, ETSI, T1, TTA, and TTC

• Technical Work Done in WGs

• Deliverables– Technical Reports/Technical

Specifications

– Approval by Consensus or Vote

– Change Control When Sufficiently Stable

• Inter-WG Coordination – In TSGs

– Information Exchange through Liaison Statements



UMTS: Transport of user IP packets

ApplicationServer

GGSNTerminal SGSNUTRAN

GTP-UGTP-U

User IP (v4 or v6)

Radio Bearer

IP tackets are tunnelled through the UMTS network (GTP – GPRS tunneling protocol)

L1

RLC

PDCP

MAC

IPv4 or v6

Application

L1

RLC

PDCP

MAC

ATM

UDP/IPv4 or v6

GTP‑U

AAL5

Relay

L1

UDP/IPv4 or v6

L2

GTP‑U

IPv4 or v6

Iu-PSUu Gn Gi

ATM

UDP/IPv4 or v6

GTP‑U

AAL5

L1

UDP/IPv4 or v6

GTP‑U

L2

Relay

L1

L2

IPv4 or v6

[Source: 3GPP]



IP Transport: Concepts• PDP contexts (Packet Data Protocol) activation

• done by UE before data transmission• specification of APN and traffic parameters• GGSN delivers IP address to UE• set-up of bearers and mobility contexts in SGSN and GGSN• activation of multiple PDP contexts possible

•Access Point Names (APN)• APNs identify external networks (logical Gi interfaces of GGSN)• At PDP context activation, the SGSN performs a DNS query to find out the GGSN(s) serving the APN requested by the terminal.• The DNS response contains a list of GGSN addresses from which the SGSN selects one address in a round-robin fashion (for this APN).

•Traffic Flow Templates (TFTs)• set of packet filters (source address, subnet mask, destination port range, source port range, SPI, TOS (IPv4), Traffic Class (v6), Flow Label (v6)• used by GGSN to assign IP packets from external networks to proper PDP context

• GPRS tunneling protocol (GTP) •For every UE, one GTP-C tunnel is established for signalling and a number of GTP-U tunnels, one per PDP context (i.e. session), are established for user traffic.



GGSN

IP Transport: PDP Context & APNs

Terminal SGSNGGSN

PDP Context X 2 (APN X, IP address X, QoS 2)

PDP Context X 1 (APN X, IP address X, QoS 1)

ISP X

ISP Z

ISP Y

PDP Context Z (APN Z, IP address Z, QoS)

PDP Context Y (APN Y, IP address Y, QoS)

AP

N Y

AP

N Z

AP

N X

Same PDP (IP) address and APN

PDP Context selectionbased on TFT (downstream)

[Source: 3GPP]



UMTS Data Transport: Bearer Hierarchy

TE MT UTRAN/GERAN

CN IuEDGENODE

CNGateway

TE/AS

End-to-End Service(IP Bearer Service)

TE/MT LocalBearer Service

UMTS BearerService

External BearerService

UMTS Bearer Service

Radio Access BearerService

CN BearerService

BackboneBearer Service

Iu BearerService

Radio BearerService

PhysicalRadio

Service

PhysicalBearer Service

Air Interface

3G GGSN3G SGSNRAN

User Equipment



UMTS Bearer: Traffic Classes (Source TS23.107, V5.2.0)

UMTS Bearer: Selected Traffic/QoS Parameters• Maximum Bitrate (kb/s)• Guaranteed Bitrate (kb/s)• Source statistics descriptor (`speech´, `unknown´)

• Transfer delay (ms)• SDU error ratio• Maximum SDU size (bytes)



Example: PDP Context Setup

…

…



IP based Multimedia Subsystem (IMS)

Additional domain in UMTS Rel. 5, based on Packet-switched domainEstablishment and Control of IP based multimedia calls based on SIP

Standardized interfaces to applicationsAuthentication and authorisation of service accessService based chargingQoS controlGlobal roaming and access to home services

Originally planned to be based on IPv6‘Network centric’ approach (as opposed to IETF SIP)In principle access independent (e.g. also WLAN access)No Network layer mobility support in IMS (mobility via SIP or in access networks)



SIP

Network Entities and Protocols

IM SubsystemApplicationsand

Services

MultimediaIP

Networks

CS Domain-or-

PSTN-or-

Legacy-or-

External

PS Domain

HSS

R-SGW

CSCF

CSCF

GGSN

MRF-CSCP

MGCF

MGW

SGSN

Cx

Sh

Sc

Gr

Mm

Mw

Mc

Gc

Mg

Gn

BGCF

T-SGW

BGCFMi

GoGm

SLF

Dx

AS

AlternativeAccess Networks

„Gi-Cloud“

PCF

OSA-SCS

IM-SSF

MRF-PMp

Sr

ISC

SIPSI

P

?

?

Dia

met

er

H248

SIP

H248

CO

PS

TCP/IP/UDP/RTP/…

SIP

?

MAP

CAP SIP

SIP

Mj

SIP TCP UDP

HTTP Others

? ?

SIP

?

R-SGW

CA

PO

SA

UE

UTRANMT TE

Uu IuR

GERAN

Mr

SIP Mk



Network Entities

• CSCF (Call State/Service Control Function)• PCF (Policy Control Function)• HSS (Home Subscriber Service)• SLF (Subscription Locator Function)• MRF (Multimedia Resource Function)• BGCF (Breakout Gateway Control Function)• MGCF (Median Gateway Control Function)• MGW (Media Gateway)• T-SGW (Transport Signaling Gateway)• R-SGW (Roaming Signaling Gateway)• AS (Application Server)• SCP (Service Content Provider)• IM-SSF (Service Switching Function)• OSA-SCS (Service Capability Server)

Additionally:- Charging Entities- Security Entities- Lawful Interception- Firewalls- DNS, DHCP, TRIP, …- QoS Entities- OAM and NM- …



IMS: Important Network ElementsHSS : Home Subscriber ServiceDatabase for subscriber related information• Identification (SIP, Mail, E.164, Label, IMSI, ...)• Location management (P-CSCF, S-CSCF, IP address)• List of authorized services, List of subscribed services• Quintuplets for Security

Proxy Call State Control Function (P-CSCF)First contact point of an operator‘s network (for the mobile terminal)• Forwarding of SIP messages between terminal and core network• Generation of charging records• Translation of IDs other than SIP URIs into SIP URIs

(e.g. E.164 numbers)• Termination of confidentiality and integrity, Lawful interception• Authorisation of bearer resources and QoS management• Detection of emergency calls and selection of a emergency S-CSCF• Translation of SIP URIs for local services• SIP header compression



IMS: Important Network Elements (cntd.)Interrogating Call State Control Function (I-CSCF)First contact point of an operator‘s network (for other operators)• Forwarding of SIP messages (proxy functionality)• Assignment of a S-CSCF

– during registration and during invite (for services for not registered subscribers)• Generation of charging records• Hiding of internal network configuration/capacity/topology

Serving Call State Control Function (S-CSCF)Performs session control and service triggering• Acts as a registrar according to RFC2543• May behave as a Proxy Server as defined in RFC2543, i.e. it accepts requests and services them

internally or forwards them on, possibly after translation.• May behave as a User Agent as defined in RFC2543, i.e. it may terminate and independently

generate SIP transactions.• Interaction with service platform(s), provides endpoints with service event related information • Authentication (based on quintuplets from HSS), Generation of charging records



Registration in a Roaming Scenario

Home Network of MS B

Network visited by MS B

MS B

P-CSCF-B

S-CSCF-B

2

1

Home Network of MS A

Network visited by MS A

MS A

P-CSCF-A

S-CSCF-A

REG

ISTE

R

I-CSCF-A

HSS-A User Profile

1

2

4

5

REG

ISTE

R

I-CSCF-A4

HSS-AUser Profile

5



Routing of Mobile-To-Mobile Calls

Home Network of MS A

Network visited by MS A

Home Network of MS B

Network visited by MS B

MS A MS B

P-CSCF-A

I-CSCF-B

P-CSCF-B

HSS-B

S-CSCF-A S-CSCF-B

REG

ISTE

R

User Profile

1 2

34

5

6

7

INVI

TE

Call C

ontro

l

REG

ISTE

R

I-CSCF-A

HSS-A User Profile



SIP in IMS• Mandatory existence of P-CSCF as first point of contact• Network initiated call release (e.g. due to missing coverage or administrative reasons)

– Proxies are able to send BYE

• Network Control of Media Types– P/S-CSCF checks the SDP in the SIP body– If SDP contains invalid parameters (e.g. not supported codecs), P/S-CSCF rejects the SIP request by sending a

488 (“not acceptable here”) response that contains a SDP body indicating parameters that would be acceptable by the network

• Network Hiding (Encryption of Route and Via Headers)• Additional Signaling Information

– For example Cell-ID, Mobile Network/Country Code, Charging-IDs – Information transported P-header based solution

• Compression– SIP Compression is mandatory as radio interface is a scarce resource– Compression / decompression of SIP will be performed by the UE and the P-CSCF

• Authentication & Integrity protection– S-CSCF performs the Authentication using AKA – P-CSCF checks the integrity of messages received via the air interface via IPsec ESP



IMS: Services are Home Controlled

3rd Party ServiceProvider

Visited Network Home Network

UEServingCSCF

ApplicationServer

ProxyCSCF

ApplicationServer

SIP

ISC

SIPSIP

ApplicationServer

The Serving CSCF (S-CSCF) is located in the Home Network The Visited Network only provides a proxy (P-CSCF): all calls are always first

routed to the Home Network.

??



Entertainment

•m-Gaming

•Gambling

•Audio

•Video

•Unified Messaging

•MMS

•Chat

•Conferencing

•Voice over IP

•Buddy list

•Presence configuration

•Availability configuration

Information

•Dynamic Info Svcs.

•Static Info Svcs.

Commerce

•m-Banking

•m-Shopping

•m-ticketing & reservations

•m-advertisement

End User Services: Categorization

Communication



Within the next six years data and multimedia traffic will overrule voice

In 2008 Multimedia Communication will account for ¼ of mobile traffic

Mbit/

User/

Month

Browsing & Download

Messaging

Real-Time Multimedia

Voice (Minutes of Use x 9,6 kb/s)50

100

150

200

250

300

350

2003 2004 2005 2006 2007 2008

0

Prediction: services in mobile NWs



Summary1. Introduction





• Methods





• Services



Acknowledgements• InfotechLecture notes: IP Based Networks and Applications,

Chapter 4 (J. Charzinski), www.jcho.de/jc/IPNA• Lecture Notes: Networking Introduction (J. Kurose, K. Ross)• Tutorial: IP Technology in 3rd Generation mobile networks,

Siemens AG (J. Kross, L. Smith, H. Schwefel)• Lecture notes: Mobile Communciations, Jochen Schiller,

www.jochenschiller.de• Tutorial: Voice over IP Protocols – An Overview, www.vovida.org

Other References• IETF (www.ietf.org)

– WGs: MMUSIC (old), SIP• 3GPP: www.3gpp.org• J. Schiller: ’Mobile Communications’. Addison-Wesley, 2000.

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