[PDF] - Application Layer Protocols Applications: communicating distributed PDF Document

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Page 1 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Wireless Networks III: advanced concepts

Hans-Peter Schwefel and Tatiana K. Madsen

hps@kom.auc.dk tatiana@kom.auc.dk http://www.kom.auc.dk/~hps http://www.kom.auc.dk/~tatiana

Mm1

IP Mobility Support (HPS)

Mm2

Wireless TCP (HPS)

Mm3

Wireless applications, SIP & IMS (HPS)

Mm4

Ad-hoc Networks I (TKM)

Mm5

Ad-hoc Networks II (TKM)

Note: Slide-set contains more material than covered in the lecture!

Page 2 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Application Layer Protocols

Applications: 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 based

DNS Video Streaming Multimedia Conferencing HTTP, FTP, telnet, SMTP, NNTP

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Page 3 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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)

ut-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

Page 4 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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

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Page 5 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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

Page 6 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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

Prediction: services in mobile NWs

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Page 7 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Content

1. Introduction
Application Layer Protocols, basic principles
Service categories
2. Hyper-Text Transfer Protocol (HTTP)
Properties and messages
Problems & Improvements in wireless settings
3. Video Streaming
Encoding and tranmission principles, buffering issues
Enhancements for wireless settings: layered coding,

multiple description coding

4. Service Support Infrastructure
Session Initiation Protocol (SIP)
IP based multimedia subsystems (IMS)

5. Summary

Page 8 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless 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

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Page 9 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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)

Page 10 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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

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Page 11 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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

Page 12 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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

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Page 13 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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

Proxy Proxy HTTP Server

Internet

Page 14 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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

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Page 15 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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, ...

Page 16 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

HTTP Performance Improvements

Persistent Connections

Problem: Frequently retrieval of several, small embedded objects
verhead 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

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Page 17 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

HTTP Requests and Persistent Connections

Data Transfer GET... Data ACK TCP Conn. Release FIN FIN+ACK A C K TCP Conn. Setup S Y N + A C K ACK S Y N Client Server

Minimum connection

Client Server S Y N S Y N + A C K A C K K e e p

a

l i v e + G E T D a t a F I N G E T D a t a A C K G E T + A C K D a t a A C K

Timeout (e.g. 15sec) Timeout (e.g. 15sec)

Persistent connection

Page 18 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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

rder
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...

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Page 19 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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

–

ften 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

Page 20 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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 GPRS Backbone SGSN GGSN

BSC

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

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Page 21 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Content

1. Introduction
Application Layer Protocols, basic principles
Service categories
2. Hyper-Text Transfer Protocol (HTTP)
Properties and messages
Problems & Improvements in wireless settings
3. Video Streaming
Encoding and tranmission principles, buffering issues
Enhancements for wireless settings: layered coding,

multiple description coding

4. Service Support Infrastructure
Session Initiation Protocol (SIP)
IP based multimedia subsystems (IMS)

5. Summary

Page 22 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Video Encoding: Basics

e.g. QCIF compression format:

1 picture = 176*144 pixels

e.g. YUV (luminance, chrominance,

saturation) representation, 1 pixel uses 3 Bytes

Alternative: RGB
Typically 25 or 30 Frames per second

– Types of Frames (MPEG)

Intra (I)
Predicted (P): depends on previous

I Frame

Bi-directionally coded (B): depends
n previous and next I/P frames

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Page 23 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Video Coding (cntd.)

Differential Encoding plus Motion Estimation for Pixel Blocks ( Motion Vector)
Intra-frame coding:

– Discrete Cosine Transformation within block – Quantization using threshold T and quantizer step Q: – Zig-Zag Scanning – Variable Length Coding

Page 24 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Video Traffic Models

PDF of frame sizes (Example:Friends 2x16)

GOP structure regular

pattern of frame-sizes

BUT: different sizes

depending on dynamics within movie

Typically: within scenes

smaller frames possibly causing long-range correlation

f frame-sizes

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Page 25 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Milestones in Video Compression

100 200 300 400 500 26 28 30 32 34 36 38 PSNR [dB] DCT (Motion JPEG) (1985) Foreman 10 Hz, QCIF 133 frames encoded Bit-Rate [kbps] H.263 1995

MPEG-4 1999

H.120 1988 H.261 1991

H.26L (2001)

?

2005

From Talk of Ralf Schäfer Heinrich-Hertz-Institut für Nachrichtentechnik Berlin GmbH

Page 26 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Frame Statistics for Starship Troopers (MPEG 4)

Frame statistics compression ratio YUV:MP4 37.68 File Size byte 9.1e+07 Video run time msec 3.6e+06 # of Frames

89998

mean frame size byte 1e+03 var frame size

6.5e+05

CoV of frame size

0.80

min frame size byte 30 max frame size byte 7265 Mean bit rate bit/sec 2e+05 Peak bit rate bit/sec 1.5e+06 Peak/Mean of bit rate

7.20

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Page 27 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Video Streaming

– When using compression Variable Bit-rate stream (due to varying

frame sizes)

– Transmission as VBR stream

1 frame (1RTP/UDP packet) every 25ms

– Or: Transmission with Constant Bit Rate

One UDP packet with payload=average frame-size

Buffering required

QoS Parameters: Picture Signal to Noise Ration (PSNR)

Typically can sustain some packet loss (e.g. several percent)

Page 28 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

CBR Streaming: Buffer Occupancy

additional

buffered data required to deal with jitter!

Playout Buffer Occupancy in an error free channel

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Page 29 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Video over wireless: layered coding

Base Layer: essential information

– Apply more protection mechanisms (e.g. added FEC on link layer)

Enhancement Layer (one or more)

– Some loss of data can be sustained without strong quality decrease Unequal error protection (UEP)

9% Loss Rate: without protection, with unequal erasure protection

Page 30 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Multiple Description Coding

Multiple Description Coding (MDC):

– MDC codes data stream into independent descriptions (or substreams), any subset of which is decodable – At the receiver, these data streams are decoded individually and independently.

S R

Advantages

– Very robust transmission over wireless links – Support of heterogeneous terminals

Disadvantages

– Increased overhead (encoder and network)

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Page 31 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

MDC Example: Video Encoding

Splitter and encoding chain

Page 32 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Content

1. Introduction
Application Layer Protocols, basic principles
Service categories
2. Hyper-Text Transfer Protocol (HTTP)
Properties and messages
Problems & Improvements in wireless settings
3. Video Streaming
Encoding and tranmission principles, buffering issues
Enhancements for wireless settings: layered coding,

multiple description coding

4. Service Support Infrastructure
Session Initiation Protocol (SIP)
IP based multimedia subsystems (IMS)

5. Summary

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Page 33 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless 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

Page 34 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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

ther 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

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Page 35 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless 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 Server Proxy Server User Agent

Page 36 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

SIP Addressing and header format

Addressing:

Addresses specified SIP URL, in the format: user@host.
Examples of SIP URLs:
sip:hostname@vovida.org
sip:hostname@192.168.10.1
sip:14083831088@vovida.org

INVITE sip:5120@192.168.36.180 SIP/2.0 Via: SIP/2.0/UDP 192.168.6.21:5060 From: sip:5121@192.168.6.21 To: <sip:5120@192.168.36.180> Call-ID: c2943000-e0563-2a1ce-2e323931@192.168.6.21 CSeq: 100 INVITE Expires: 180 User-Agent: Cisco IP Phone/ Rev. 1/ SIP enabled Accept: application/sdp Contact: sip:5121@192.168.6.21:5060 Content-Type: application/sdp

Example: SIP Header

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Page 37 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

SIP Call Signalling: Example

302 (Moved Temporarily) INVITE 200 (OK) 200 (OK) ACK INVITE 180 (Ringing) 180 (Ringing) 180 (Ringing) 200 (OK) ACK ACK ACK RTP MEDIA PATH BYE BYE BYE 200 (OK) 200 (OK) 200 (OK)

Call Teardown Media Path Call Setup

INVITE Location/Redirect Server Proxy Server Proxy Server User Agent User Agent INVITE Page 38 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

SIP: Separation of signalling and data

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

Potential Problems with Firewalls & NATs

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Page 39 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Universal Mobile Telecommunication System (UMTS)

Currently standardized by 3rd Generation Partnership Project (3GPP),

see http://www.3GPP.org [North America: 3GPP2]

So far, four releases: R’99, R4, R5, R6

Modifications:

New methods & protocols on radio link increased access bandwidth
Coexistence of two domains in the core network

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

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

Page 40 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

User Equipment Domain User Equipment Domain Access Network Domain Access Network Domain Core Network Domain Core Network Domain Service and Application Domain Service and Application Domain Charging/ Lawful Interception/ OAM Charging/ Lawful Interception/ OAM Other Networks (IP/ ISDN) Other Networks (IP/ ISDN)

Radio Access Network

– Node B (Base station) – Radio Network Controller (RNC)

Mobile Core Network

– Serving GPRS Support Node (SGSN) – Gateway GPRS Support Node (GGSN) – Mobile Switching Center (MSC) – Home/Visited Location Register (HLR/VLR) – Routers/Switches, DNS Server, DHCP Server, Radius Server, NTP Server, Firewalls/VPN Gateways

Application/Services
IP-Based Multimedia Subsystem (IMS)
Operation, Administration & Maintenance (OAM)
Charging Network
[Legal Interception]

UMTS Network Domains

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Page 41 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

IP based Multimedia Subsystem (IMS)

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

Standardized interfaces to applications Authentication and authorisation of service access Service based charging QoS control Global 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)

Page 42 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

SIP

Network Entities and Protocols

IM Subsystem Applications and Services Multimedia IP Networks CS Domain

or-

PSTN

or-

Legacy

or-

External PS Domain

HSS R-SGW CSCF CSCF GGSN MRF-C SCP MGCF MGW SGSN

Cx Sh Sc Gr Mm Mw Mc Gc Mg Gn

BGCF T-SGW BGCF

Mi Go Gm

SLF

Dx

AS

Alternative Access Networks

„Gi-Cloud“

PCF OSA-SCS IM-SSF MRF-P

Mp Sr ISC SIP SIP ? ? Diameter H248 SIP H248 COPS TCP/IP/UDP/RTP/… SIP ? MAP CAP SIP SIP Mj SIP TCP UDP HTTP Others ? ? SIP ?

R-SGW

CAP OSA

UE

UTRAN MT TE

Uu Iu R

GERAN

Mr SIP Mk

SLIDE 22

Page 43 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Additionally:

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

Page 44 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

IMS: Important Network Elements

HSS : Home Subscriber Service

Database 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

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Page 45 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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

Page 46 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Levels of Registration

UE xGSN

Visited Network Home Network

UMS CSCF DHCP AS HLR Bearer Level IM Subsystem Application? DHCP CSCF HSS

SLIDE 24

Page 47 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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

REGISTER

I-CSCF-A HSS-A

User Profile

1 2 4 5

REGISTER

I-CSCF-A

4

HSS-A

User Profile

5

Page 48 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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

REGISTER User Profile

1 2 3 4 5 6 7

INVITE Call Control REGISTER

I-CSCF-A HSS-A

User Profile

SLIDE 25

Page 49 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Call Establishment with QoS

Page 50 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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

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Page 51 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

IMS: Services are Home Controlled

3rd Party Service Provider Visited Network Home Network UE Serving CSCF Application Server Proxy CSCF Application Server SIP ISC SIP SIP Application Server

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.

? ?

Page 52 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

IMS security architecture overview

SLIDE 27

Page 53 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Security features for the IMS

Mutual authentication and key agreement between UE

and home network

Integrity protection between UE and first-hop SIP proxy

(P-CSCF) (in later UMTS releases confidentiality protection is likely to be provided in addition)

IPsec tunnels between IMS network nodes (core

network signalling security)

Page 54 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Security mechanisms for the IMS

The security mechanisms specified for the IMS can be implemented

independently of the mechanisms for the underlying packet service

IETF-defined SIP security mechanisms were first choice, but turned out

to be unfit for the purpose

Authentication and key agreement: re-use of AKA protocol, integrated

with SIP registration

SIP integrity and confidentiality protection: IPsec ESP between user and

first hop SIP proxy (P-CSCF)

Negotiation of security associations for IPsec ESP: Security Mechanism

Agreement protocol for SIP (see references)

IKE not used because thought too heavyweight for mobile environment

SLIDE 28

Page 55 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

IMS authentication message flow (simplified)

SIP Register Visited Network Home Network P-CSCF Register UE I-CSCF HSS S-CSCF Register 401 Unauthorised RAND||AUTN Cx-AuthDataReq Register RES Cx-AuthDataResp RAND||AUTN||XRES||IK||CK 401 Unauthorised RAND||AUTN||IK(||CK) Register RES 401 Unauthorised RAND||AUTN||IK||CK Authentication Register RES OK OK OK Authentication

Page 56 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Summary

1. Introduction
Application Layer Protocols, basic principles
Service categories
2. Hyper-Text Transfer Protocol (HTTP)
Properties and messages
Problems & Improvements in wireless settings
3. Video Streaming
Encoding and tranmission principles, buffering issues
Enhancements for wireless settings: layered coding,

multiple description coding

4. Service Support Infrastructure
Session Initiation Protocol (SIP)
IP based multimedia subsystems (IMS)

5. Summary

SLIDE 29

Page 57 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless 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 slides ‘Video Compression’, Frank Fitzek, Uni Ferrara.
Lecture notes: Mobile Communciations, Jochen Schiller, www.jochenschiller.de
F. Fitzek et al. ’Application of multiple description coding in 4G wireless communication systems’.

WWRF meeting, see http://kom.aau.dk/~ff

M. A. Ben Abid, ’Video Streaming for 802.11b WLAN’, Master Project, Aalborg University, Spring

2004.

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.

Page 58 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Backup: GSM-GPRS-UMTS

SLIDE 30

Page 59 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless 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:

Page 60 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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 A Um

Radio Link Base Station Subsystem

Network and Switchung Subsystem Operation Subsystem

Connection to ISDN, PDN PSTN

Radio Subsystem (RSS)

SLIDE 31

Page 61 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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)

Page 62 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

GPRS - Architecture

PDN

Other

PLMN GSM GPRS B T S C C U MSC B S C P C U HLR GR GGSN

Components A Abis Gb Gp Gs Gn G Gr Gi Um BSS

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

SLIDE 32

Page 63 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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)

Page 64 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

UMTS Domains (Rel 5)

IMS

SGSN GGSN MSC Server MSC GMSC MGW P-CSCF S-CSCF I-CSCF MRF AppServ AppServ SCP

HSS

IP based Multimedia Subsystem PS Domain CS Domain Application and Services RAN

Gi Iu PS Iu CS

SLIDE 33

Page 65 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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)

Page 66 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

TSG CN

Core Networks

TSG GERAN

GSM EDGE Radio Access Network

TSG RAN

Radio Access Network

TSG SA

Services & System Aspects

TSG T

Terminals

CN WG 1

MC/CC/CS (lu)

CN WG 3

Interworking with External Networks

CN WG 2

CAMEL

CN WG 5

OSA (Open Service Architecture)

CN WG 4 MAP/GTP/BCH/SS GERAN WG 1

Radio Aspects

GERAN WG 2

Protocol Aspects

GERAN WG 3

Base Station Testing and O & M

GERAN WG 4

Mobile Station Testing

RAN WG1

Radio Layer 1 specification

RAN WG2

Radio Layer 2

spec. & Radio

Layer 3 RR spec.

RAN WG3

lub spec, lur spec lu spec & UTRAN O&M requirements

RAN WG4

Radio performance & Protocol aspects

SA WG 1

Services

SA WG 2

Architecture

SA WG 3

Security

SA WG 4

Codec

SA WG 5

Telecom Management

T WG 1

Mobile Terminal Conformance testing

T WG 2

Mobile Terminal Services & capabilities

T WG 3

Universal Subscriber Identity Module (USIM)

3GPP TSG ORGANIZATION

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

SLIDE 34

Page 67 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

UMTS: Transport of user IP packets

Application Server GGSN Terminal SGSN UTRAN

GTP-U GTP-U User IP (v4 or v6) Radio Bearer

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

L1 RLC PDCP MAC IP v4 or v6 Application L1 RLC PDCP MAC ATM UDP/IP v4 or v6 GTP-U AAL5 Relay L1 UDP/IP v4 or v6 L2 GTP-U IP v4 or v6 Iu-PS Uu Gn Gi ATM UDP/IP v4 or v6 GTP-U AAL5 L1 UDP/IP v4 or v6 GTP-U L2 Relay L1 L2 IP v4 or v6 [Source: 3GPP]

Page 68 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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
ne 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.

SLIDE 35

Page 69 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services GGSN

IP Transport: PDP Context & APNs

Terminal SGSN GGSN PDP Context X2 (APN X, IP address X, QoS2) PDP Context X1 (APN X, IP address X, QoS1)

ISP X ISP Z ISP Y

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

APN Y APN Z APN X

Same PDP (IP) address and APN PDP Context selection based on TFT (downstream)

[Source: 3GPP]

Page 70 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

UMTS Data Transport: Bearer Hierarchy

TE MT UTRAN/ GERAN CN Iu EDGE NODE CN Gateway TE/AS End-to-End Service (IP Bearer Service) TE/MT Local Bearer Service UMTS Bearer Service External Bearer Service UMTS Bearer Service Radio Access Bearer Service CN Bearer Service Backbone Bearer Service Iu Bearer Service Radio Bearer Service Physical Radio Service Physical Bearer Service Air Interface 3G GGSN 3G SGSN RAN User Equipment

SLIDE 36

Page 71 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

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)

Page 72 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

Example: PDP Context Setup

… …

SLIDE 37

Page 73 Hans Peter Schwefel Wireless Networks III, Fall 2005: MM3, Wireless Services

The ’full picture’ of the UMTS packet switched domain

G G SN SG SN D HC P R ADIU S IM S D om ain H SS H LR/AuC

RNC Node B Node B

N etw ork Services SS7, Gr SS7, Gc G RX Netw ork D N S

G n-SEC

DN S

G n-PRI

Gn Network D N S

Ext

BG Gi Network

D M Z

D NS

Ext

E -m ail HT T P proxy D N S

NS

D N S

IM S

P-CS CF I/S -CS CF MNO 1`s B ackbone AS N etw ork Messages FT P V ideo DN S

AS

Corp. Network VPN -GW Y AS BG IDS ID S

M NO 1`s Netw ork

BG

1 2 3 4 5 6 7 8 9 * 0 # U E1

BG

Internet

AS

M NO 3

UE3

M NO 2

UE2 IMS

Roaming Support:

UE attaches with SGSN in visited network
PDP context is set-up to GGSN in home network (via Gp interface, GRX network)