47673761 mobileinternet tomai romana 2010[1]

Sisteme mobile in Internet

(Arhitectura si aplicatiile retelelor mobile)

Nicolae Tomai

FSEGA

[email protected]

http://www.econ.ubbcluj.ro/~nicolae.tomai

449

http://www.econ.ubbcluj.ro/~nicolae.tomai

2

Cuprins

Introducere

Wireless LANs: IEEE 802.11

Rutarea IP mobila

TCP in retele fara fir

Retele GSM

Arhitectura retelelor GPRS

WAP(Wireless application protocol)

Agenti mobili(Mobile agents)

Retele mobile si peer-to-peer(MANET-Mobile

ad hoc networks)

3

References

J. Schiller, “Mobile Communications”, Addison Wesley, 2000

802.11 Wireless LAN, IEEE standards, www.ieee.org

Mobile IP, RFC 2002, RFC 334, www.ietf.org

TCP over wireless, RFC 3150, RFC 3155, RFC 3449

A. Mehrotra, “GSM System Engineering”, Artech House, 1997

Bettstetter, Vogel and Eberspacher, “GPRS: Architecture, Protocols

and Air Interface”, IEEE Communications Survey 1999, 3(3).

M.v.d. Heijden, M. Taylor. “Understanding WAP”, Artech House, 2000

Mobile Ad hoc networks, RFC 2501

Site-uri web:

– www.palowireless.com

– www.gsmworld.com; www.wapforum.org

– www.etsi.org; www.3gtoday.com

4

Retele fara fir

Ofera servicii de acces la calcul/comunicare in miscare

Retele celulare– Sisteme cu infastrucura bazata pe statii de baza

Wireless LANs– Retele locale in topologie infrastructura(cu AP)

– Foarte flexibile in zona de receptie

– Banda de transmisie destul de buna(>1 Mbit/s….)

Ad hoc Networks– Nu folosesc topologia infrastructura

– Sunt folosite pentru aplicatii militare, de salvare, acasa, etc.

Dispozitive mobile

Clamshell handhelds

Tablets

Net–enabled mobile phones

Palm-sized

Laptop computers

Sisteme de operare pentru disozitive mobile

Symbian-promovat ca OS(open source) de un

consortiu: Nokia, Motorola, etc.

Windows Mobile-Microsoft

Windows CE

Windows mobile 7.0

iPhone

RIM BlackBerry

Linux-cu varianta Android de la Google

Palm OS

6

Evolutia telefoanelor mobile

7

Spectrul alocat pentru telefoanele mobile

8Sursa: (S60 Programming A Tutorial Guide Paul Coulton,

Reuben Edwards With Helen Clemson)

Elemente componente ale unui sistem de telefonie

mobila

9

FDMA(Frecvency Division Multiple Access)(1G)

10

TDMA(Time Division Multiple

Access)(2G)

11

CDMA(Code Division Multiple Access)

Permite utilizatorilor sa imparta atit timpul cit si frecventa

in acelasi timp, prin alocarea unui numar unic de

identificare

Acest numar de identificare permite sistemului sa

separe un apel de altul, daca acestea erau facute in

acelasi timp

E o tehnica de baza pentru telefoanele de generatia a

treia (3G) si permite viteze mari de transfer pentru

fiecare utilizator

12

CDMA(Code Division Multiple Access)

13

Sistemul GPRS

14

•SGSN(Serving GPRS Support Node) controlează transmiterea pachetelor

de date prin întreaga reţea şi

•GGSN(Gateway GPRS Support Node) care are rolul de a conecta reţeaua

de telefonie mobilă la infrastructura Internetului.

Alocarea frecventelor in 3G

15

Alocarea frecventelor in 3G

Europa şi Japonia au optat pentru banda largă CDMA (W- CDMA) folosind

diviziunea frecvenţei(FDD) în două perechi de benzi ale spectrului de

frecvenţă.

USA a optat pentru CdmaOne care foloseşte benzi multiple ale sistemului

pentru a realiza aşa numita undă purtătoare CDMA prin care se permitea

accesul mai multor utilizatori în acelaşi timp.

Un alt sistem 3G, care e mai degrabă o extensie a GRPS -ului a sporit

transferul de date spre evoluţia GSM(EDGE), care modifică legăturile fără

fir între telefoanele mobile şi staţia de bază a sistemului GSM/GPRS pentru

îmbunătăţirea ratei de transfer a datelor, standard care a fost dezvoltat de

3GPP.(3G Partnership Project)care a fost creat în urma asocierii a două

categorii de organizaţii: organisme de standardizare şi reprezentaţi

comerciali. Organismele de standardizare participante sunt ETSI (Europa),

ARIB/TTC (Japonia), ANSI T1 (SUA) şi TTA (Coreea). Reprezentaţii pieţei

de telecomunicaţii sunt UMTS Forum, GSA şi GSM Association. Cele trei

reprezintă grupări majore de producători, operatori, companii de

consultanţă, etc., care susţin interese comerciale proprii legate de evoluţia

sistemului GSM

16

W-CDMA in sistemul GSM/GPRS

17

Evolutia spre 4G

18

Evolutia sistemelor celulare

19

20

Limitari ale sistemelor mobile

Limitări datorate retelelor fara fir Limitari ale largimii benzii de comunicatie

Deconectari frecvente

Eterogeneitatea si fragmentarea retelelor

Limitări datorate mobilitatii rute defecte(intrerupte)

Lipsa facilitatilor privind mobilitatea a sistemelor/aplicatiilor

Limitări datorate dispozitivelor mobile Timp scurt de viata al bateriei

Capacitati limitate(privind memoria, procesarea, etc.)

21

Comparatie intre retelele fara fir si cele cu fir Reglemetari ala frecventelor

– Limitarea disponibilitatii si necesitatea coordonarii

– Frecventele utilizate sunt deseori ocupate de alte aplicatii

Latimea benzii si intirzierile– Rate de transmisie relativ mici

• De la cativa Kbits/s la Mbit/s.

– Intirzieri mari

• Sute de milisecunde

– Rata mare a pierderilor

• susceptibile la interferenta, de ex, cu masini elecrice, siste de iluminat, etc.

Partajeaza intotdeauna un mediu comun– Securitate scazuta, simplu de atacat

– Interferente radio

– Staţii de bază false poate atrage apelurile de pe telefoanele mobile

– Necesita mecanisme de acces securizat

22

Siteme celulare: ideea de baza

Conectivitate fara fir cu un singur salt(hop)– Spatiul este divizat in celule

– O statie de baza este responsabila cu comunicarea cu hosturile in celula ei

– Hosturile mobile pot schimba celulele in timpul comunicarii

– Operatia de hand-off apare atunci când o gazdă mobila începe comunicarea prin intermediul unei noi staţii de bază

Factorii ce determina dimensiunea celulei– Numarul de utilizatori ce vor fi suportati

– Multiplexarea si tehnologiile de transmisie

23

Conceptul celular Numarul limitat de frecvente => limiteaza numarul canalelor

Puterea de emisie a antenei => limiteaza numarul utilizatorilor

Celule mai mici => posibilitatea reutilizarii frecventelor => mai multi utilizatori

Statie de baza (BS): implementeaza multiplexarea diviziunii spatiului– Cluster: group de BS apropiate care impreuna utilizeaza toate

canalele apropiate

Statiile mobile comunica numai printr-o statie de baza– FDMA, TDMA, CDMA pot fi utilizate intr-o celula

O cerere de crestere se face (mai multe canale sunt necesare)– Numarul statiilor de baza este crecut

– Puterea de transmisie este redusa(descrescuta) corespunzator pentru a reduce interferentele

24

Arhitectura sistemelor celulare Fiecare celula este deservita de o statie de baza(BS-Base Station)

Fiecare sitem (BSS-Base Station Sistem) compus din statia de baza si dispozitivele “legate” la ea este conectat la un centru de comutare mobila (mobile switching center -MSC) prin legaturi fixe

Fiecare MSC este conectat la alte MSC-uri si PSTN(Public Switched Telephone Network)

MSC MSC

HLR

VLR

HLR

VLR

La alte

MSC-uri

PSTNPSTN

25

Apel de configurare pentru iesirea in

retea-la apel(Outgoing call setup)

Apel de configurare la iesire:– Se introduce numarul şi se trimite

– Trnsmisiile mobile necesita o cerere de acces pe un canal ascendent(uplink)de semnalizare

– Dacă reţeaua poate procesa apelul, BS trimite un mesaj de alocare a canalului

– Reteaua procedeaza la setarea conexiunii(si realizeaza incasarea)

Activitatea retelei:– MSC determina locatia curenta a tintei mobile

utilizind HLR, VLR si prin comunicarea cu alte MSC-uri

– MSC-ul sursa initiaza un mesaj apel de configurare la MSC-ul care acoperă zona ţintă

26

Apel de configurare la intrarea in

retea-la primire(Incoming call setup) Apel de configurare la iesire:

– MSC-ul tinta (ce acopera locatia curenta a mobilului)

initiaza un mesaj de paginare

– BS trimite mai departe(forward) mesajul de paginare

pe canalul de aducere(downlink) in aria de acoperire

– Daca mobilul este activat(monitorizand canalul de

semnalizare), el raspunde la BS

– BS trimite un mesaj de alocare a canalului si

informeaza MSC-ul

Activitatea retelei:

– Reţeaua completează cele două jumătăţi ale

conexiunii

27

Termenul de hand-off(predare –preluare) se referă la procesul de transfer al unui

apel sau sesiuni de date de la un canal conectat la reţeaua de bază pentru un altul

Initierea BS-ului:

– Parasirea unei celule si trecerea la una noua (hand-off) apare în

cazul în care nivelul semnalului de telefonie mobilă scade sub un

prag minim

– Creste incarcarea pe BS

• Semnalul de monitorizare a fiecarui mobil

• Determinarea tintei BS pentru predare-preluare(hand-off)

Asistarea mobilului:

– Fiecare BS transmite periodic un semnal de prezenta/far(beacon)

– Mobiul la receptionarea unui semnal de prezenta/far puternic de

la un BS nou, iniţiază un proces de trecere(predare-primire)

Intersistem:

– Se mută mobilele peste zone controlate de către diferite MSC-uri

– Gestionarea similara cu cazul mobilelor asistate prin

suplimentarea unui efort aditional al HLR/VLR

28

Efectul mobilitatii asupra stivei de

protocoale

Aplicatie– Aplicatii noi si adaptari

Transport– Controlul congestiei si al fluxului

Retea– Adresarea si rutarea

Link– Accesul la mediu si trecerea de la o celula la alta

(hand-off)

Fizic– Transmisia, erorile si interferenta

29

Aplicatii mobile(1)

Vehicule

– Transmisia de noutati, conditii de drum, etc.

– Retele ad-hoc cu vehicule apropiate pentru

prevenirea accidentelor

Urgente

– Transmiterea rapidă la spital a datelor pacienţilor

– Retele ad-hoc in caz de cutremure sau dezastre

naturale

– militare ...

30

Aplicatii mobile(2)

Agenti de vinzari mobili– Acces direct la baza de date centrala cu clientii

– Baze de date consistente pentru toţi agenţii

Acces la Web– Acces la Web dinafara companiei(de pe teren)

– Ghid turistic inteligent cu informaţii actualizate sidependente de locatie

Localizarea serviciilor– Gasirea serviciilor in mediul local

31

Aplicatii mobile(3)

Servicii de informare– Cotatii bursiere, etc.

– Vremea

Operatii deconectate– Agenti mobili, cumparaturi, etc.

Divertisment– Retele ad-hoc pentru jocuri multi-utilizator

Mesagerie

32

Aplicatii mobile in industrie

Wireless access: (phone.com) openwave

Alerting services: myalert.com

Location services: (airflash) webraska.com

Intranet applications: (imedeon) viryanet.com

Banking services: macalla.com

Mobile agents: tryllian.com

….

33

Latimea de banda si aplicatiile

Speed, kbps

2GCDMA 2.5G

GPRS, CDMA 2000EDGE

UMTS

Transaction Processing

Messaging/Text Apps

Voice/SMS

Location Services

Still Image Transfers

Internet/VPN Access

Database Access

Document TransferLow Quality Video

High Quality Video

9.6 14.4 28 64 144 384 2000

34

Evolutia retelelor celulare

First-generation: Analog cellular systems (450-900 MHz)– Frequency shift keying; FDMA for spectrum sharing

– NMT (Europe), AMPS (US)

Second-generation: Digital cellular systems (900, 1800 MHz)– TDMA/CDMA for spectrum sharing; Circuit switching

– GSM (Europe), IS-136 (US), PDC (Japan)

– <9.6kbps data rates

2.5G: Packet switching extensions– Digital: GSM to GPRS; Analog: AMPS to CDPD

– <115kbps data rates

3G: Full-fledged data services– High speed, data and Internet services

– IMT-2000, UMTS

– <2Mbps data rates

4G

35

GSM to GPRS

Resursele radio sunt alocate numai pentru unul sau maimulte(câteva) pachete la un moment dat, aşa ca GPRS permite:

– Ca mai multi utilizatori sa partajaeze resursele radio şi transportul eficient de pachete

– conectivitate la reţele externe de date orientate sprepachete

– Tarifarea bazata pe volumul de trafic

Rata datelor mai mare (pana la 171 kbps in cazul ideal)

GPRS transmite SMS-urile pe canalele de date si nu pecele de semnalizare ca GSM

36

UMTS: Universal Mobile Telecomm. (standard)

Global seamless operation in multi-cell environment

(SAT, macro, micro, pico)

Global roaming: multi-mode, multi-band, low-cost

terminal, portable services & QoS

High data rates at different mobile speeds: 144kbps at

vehicular speed (80km/h), 384 kbps at pedestrian

speed, and 2Mbps indoor (office/home)

Multimedia interface to the internet

Based on core GSM, conforms to IMT-2000

W-CDMA as the air-interface

37

Evolution to 3G Technologies

IS-95B

CDMA

2G 3G

cdma2000

GSMFDD

TDD

W-CDMA

GPRS

IS-136

TDMAUWC-136

EDGE & 136

HS outdoor

136 HS

indoor

38

384 Kbps

56 Kbps

54 Mbps

70 Mbps

5-11 Mbps

1-2 Mbps 802.11

Tehnologii fara fir

Bluetooth

802.11b

802.11{a,b}

Interior

10 – 30m

IS-95, GSM, CDMA

WCDMA, CDMA2000

Exterior

50 – 200m

Exterior

pe dist medie

200m – 4Km

Exterior pe

dist. mare

5Km – 20Km

Distanta

lunga

20m – 50Km

µwave p-to-p links

.11 p-to-p link

2G

3G

802.16(WiMax)

802.11n>150 Mbps 802.11n

4G

Comparatie intre tehnologii

0

2

4

6

8

10

Covearge

Data rate

Cost effectiveness per bitMobility

QoS

3G -HSPA

WiFi

LTE

WiMAX

LTE (Long Term Evolution)-4G 39

40

Arhitectura retelei 3G

Mobile AccessRouter

WirelessAccess Network

IPBase Stations

Gateway

Telephone Network

Core Network

User Profiles &Authentication

(HLR)

3G AirInterface

Wired Access

802.11

IP Intranet

IP Intranet

ProgrammableSoftswitch

ApplicationServer

802.11

Access Point

Access Point

Internet

41

Retele fara fir locale WLAN

Advantage– Foarte flexibile in aria(zona) de receptie

– Posibilitatea de realizare topologii ad-hoc

– Legare usoara la retelele cablate

Dezavataje– Banda relativ joasa comparativ cu retelele cablate

– Multe solutii proprietar

Topologie infrastructura sau ad-hoc (802.11)

42

Topologiile retelelor fara fir(infrastructura si

Adhoc) infrastructure

network

ad-hoc network

APAP

AP

wired network

AP: Access Point

Source: Schiller

43

Difference Between Wired and

Wireless

If both A and C sense the channel to be idle at the same time, they send at the same time.

Collision can be detected at sender in Ethernet.

Half-duplex radios in wireless cannot detect collision at sender.

A B C

A

B

C

Ethernet LAN Wireless LAN

44

– A and C cannot hear each other.

– A sends to B, C cannot receive A.

– C wants to send to B, C senses a “free” medium

(CS fails)

– Collision occurs at B.

– A cannot receive the collision (CD fails).

– A is “hidden” for C.

Hidden Terminal Problem

BA C

45

IEEE 802.11

Acknowledgements for reliability

Signaling packets for collision avoidance

– RTS (request to send)

– CTS (clear to send)

Signaling (RTS/CTS) packets contain

– sender address

– receiver address

– duration (packet size + ACK)

Power-save mode

46

Spectrum War: Status todayEnterprise 802.11Network

Public 802.11Wireless Carrier

Source: Pravin Bhagwat

47

Spectrum War: EvolutionEnterprise 802.11Network


Market consolidation Entry of Wireless Carriers Entry of new players Footprint growth


48

Spectrum War: Steady StateEnterprise 802.11Network


Virtual Carrier

Emergence of virtual carriers

Roaming agreements


49

Routarea si mobilitatea

Gasirea unei cai de la o sursa la o destinatie

Probleme– Schimbarea frecventa a rutelor

– Schimbarea rutei poate fi in legatura cu miscareahostului

– Latimea de banda relativ mica a legaturilor

Scopul protocoalelor de rutare– Micsorarea rutarii in ce priveste cimpurile

aditionale(overhead)

– Gasirea celor mai scurte rute

– Gasirea rutelor “stabile”(despite mobility)

50

IP-ul mobil: Ideea de baza

Router

1

Router

3

Router

2

S MN

Home

agent

Source: Vaidya

51

IP mobil: ideea de baza

Router

1

Router

3

Router

2

S MN

Home agent

Foreign agent

miscare

Pachetele sunt tunelate

utilizind IP in IP

Source: Vaidya

52

Protocoalele TCP si UDP in cazul retelelor fara

fir

TCP asigură:

– Livrarea sigura si ordonata a pachetepor(utilizeaza

retransmisiile, daca este necesar)

– ACK-uri cumulative(un raspuns ACK-acknowledges

pentru date primite contiguu-contiguously received data)

– ACK-uri duplicat (ori de cite ori este receptionat un

segment “neasteptat”-cu numar de secventa incorect-

out-of-order)

– Semantici cap la cap-end-to-end(receptorul trimite ACK

dupa ce data a ajuns)

– Implementeaza evitarea congestiei si utilizeaza

controlul de tip fereasta de congestie- congestion

window

53

TCP in retele fără fir

Factorii ce afecteaza protocolul TCP in retele fara fir:

– Erorile de transmisie in mediul fara fir

• Pot cauza retransmiterea rapida- fast retransmit, ceea ce duce la

diminuarea dimensiunii ferestrei de congestie

• Reducerea ferestrei de congestie ca raspuns la erori nu este

necesara

– Rute cu multe salturi(multi-hop routes) in mediul fara fir

partajat

• Conexiunile “lungi”(rute cu multe hopuri) sunt mai dezavantajoase

decit cele “scurte” pentru ca trebuie sa contina accesul la mediul

fara fir in fiecare hop

– Defectarea rutelor datorita mobilitatii

54

Indirect TCP (I-TCP)

I-TCP splits the TCP connection

– no changes to the TCP protocol for wired hosts

– TCP connection is split at the foreign agent

– hosts in wired network do not notice

characteristics of wireless part

– no real end-to-end connection any longer

mobile hostaccess point

(foreign agent) „wired“ Internet

„wireless“ TCP standard TCP

Source: Schiller

55

TCP mobil (M-TCP)

Gestioneaza deconectari frecvente si interminabile

M-TCP spliteaza ca si I-TCP dar,

– Nu modifica TCP-ul pentru reteaua fixa la agentul

strain(FA-foreign agent)

– optimizeaza TCP pentru FA to MH

Agentul strain(FA-Foreign Agent)

– Monitorizeaza toate pachetele si daca detecteaza o

deconectare atunci:

• Seteaza fereastra emitatorului la 0

• Emitatorul(sender) trece automat in modul repetat

– Fara caching, fara retransmisii

56

Adaptarea aplicatiilor pentru mobilitate

Probleme de proiectare

Sistem transparent sau sistem netransparent/adecvat/

care cunoaste faptul ca va lucra intr-o retea fara fir

Aplicatie transparenta sau aplicatie netransparenta

/adecvata/care cunoaste faptul ca va lucra intr-o retea

fara fir

Modele

Model conventional de tip client/server

Model client/proxy/server

Mode caching/cu pre-incarcare

Model cu agenti mobili

57

World Wide Web-ul si mobilitatea Caracteristicile protocolului HTTP

– A fost proiectat pentru banda larga si intirziere mica

– E de tip client/server, iar comunicarea este de tip

cerere/raspuns

– E orientat conexiune, o conexiune pe cerere

– Utilizeaza protocolul TCP intr-un dialog in trei pasi,

foloseste de asemenea protocolul DNS

Caracteristicile HTML

– Proiectat pentru calculatoare cu performante

ridicate, afisaje color de mare definitie, mose, hard

disk, etc.

– De obicei paginile Web sunt optimizate pentru

proiectare nu pentru comunicare, ignorind

caracteristicile sistemelor clientului(end-system).

58

Sisteme suport pentru WWW mobil Browsere cu facilitati adaugate/sporite

– Suport client adecvat pentru mobilitate

Proxi– Client proxi: cu pre incarcare, memorare

temporara, utilizare off-line

– Retea proxi: transformarea adaptiva a continutului pentru conexiuni

– Proxi pentru client si retea

Servere cu facilitati sporite– Servere cu suport adecavat pentru mobilitate

– Furnizarea continutului in multiple moduri in functie de capabilitatile clientului

Protocoale/limbaje noi– WAP/WML

59

Modelul client/proxy/server

Functiuni proxi atit pentru un client cit si pentru

serverul retelei fixe

Functiuni proxi pentru server adecvate mobilitatii

la clientul mobil

Proxi-ul poate fi plasat in hostul mobil(Coda), sau

in reteaua fixa sau la ambele (WebExpress)

Permite proiectarea de de clienti

“slabi”(smart/thin client) in cazul unor dispozitive

cu resurse reduse(aplicatia se lanseaza din

browser si poate rula numai conectata si nu

autonom fat client)

60

Proxi Web in WebExpress

The WebExpress Intercept Model

Source: Helal

61

WAP(Wireless Application Protocol)

Navigator-browser

– “Micro browser”, similar navigatoarelor existente

Limbajul de script

– Similar limbajului Javascript, adaptat la dispozitivele mobile

Poarta-Gateway

– Transitie de la sistemele fara fir la cele cu fir

Serverul

– “Serverul WAP/ origine-Wap/Origin server”, similar

serverelor Web existente

Nivelele protocolului

– Nivelul transport, securitate, sesiune, etc.

Interfata cu aplicatia de telefonie

– Functii de accces la telefonie

62

WAP: elementele componente

wireless networkfixed network

WAP

proxy

WTA

server

filter/

WAP

proxyweb

server

filter

PSTN

Internet

Binary WML: binary file format for clients

Binary WML

Binary WML

Binary WML

HTML

HTML

HTML WML

WMLHTML

Source: Schiller

63

WAP: modelul de referinta

Purtatoarele (GSM, CDPD, GPRS ...)

Security Layer (WTLS)

Session Layer (WSP)

Application Layer (WAE)

Transport Layer (WDP)TCP/IP,

UDP/IP,

media

SSL/TLS

HTML, Java

HTTP

Internet WAP

WAE comprises WML (Wireless Markup Language), WML Script, WTAI etc.

Source: Schiller

Transaction Layer (WTP)

Servicii aditionale

si aplicatii

WCMP

A-SAP

S-SAP

TR-SAP

SEC-SAP

T-SAP

64

Stiva de protocoale WAP

WDP

– Functionalitati similare cu UDP in retele IP

WTLS

– functionalitati similare cu SSL/TLS (optimizat pentru retele fara fir)

WTP

– Clasa 0: analog cu UDP

– Clasa 1: analog cu TCP (fara setarea privind overhead-ul conexiunii)

– Clasa 2: analog cu RPC (optimizat pentru retele fara fir)

– features of “user acknowledgement”, “hold on”

WSP

– WSP/B: analog cu http 1.1 (cu facilitati de suspendare/reluare)

– metoda: analoaga cu RPC/RMI

– Caracteristici de invocare asincrona (confirmate/neconfirmate)

65

Modelul cu agenti mobili

Agentul mobil primeste cererea clientului si

Agentul mobil se muta in reteaua fixa

Agentul mobil actioneza la server ca si un client

Agentul mobil realizeaza transformarile si filtrarea

Agentul mobil se intoarce inapoi la platforma mobila

atunci cind clientul este conectat

66

Mobile Agents: Exemplu

67

Cuprins

Introducere


Rutarea IP mobila


Retele GSM





ad hoc networks)

68

How Wireless LANs are different

Destination address does not equal destination location

The media impact the design– wireless LANs intended to cover reasonable

geographic distances must be built from basic coverage blocks

Impact of handling mobile (and portable) stations– Propagation effects

– Mobility management

– power management

69

Wireless Media

Physical layers in wireless networks

– Use a medium that has neither absolute nor readily

observable boundaries outside which stations are unable to

receive frames

– Are unprotected from outside signals

– Communicate over a medium significantly less reliable than

wired PHYs

– Have dynamic topologies

– Lack full connectivity and therefore the assumption normally

made that every station (STA) can hear every other STA in

invalid (I.e., STAs may be “hidden” from each other)

– Have time varying and asymmetric propagation properties

70

802.11: Motivation

Can we apply media access methods from fixed networks

Example CSMA/CD

– Carrier Sense Multiple Access with Collision Detection

– send as soon as the medium is free, listen into the medium if a

collision occurs (original method in IEEE 802.3)

Medium access problems in wireless networks

– signal strength decreases proportional to the square of the

distance

– sender would apply CS and CD, but the collisions happen at the

receiver

– sender may not “hear” the collision, i.e., CD does not work

– CS might not work, e.g. if a terminal is “hidden”

Hidden and exposed terminals

71

Solution for Hidden/Exposed Terminals

A first sends a Request-to-Send (RTS) to B

On receiving RTS, B responds Clear-to-Send (CTS)

Hidden node C overhears CTS and keeps quiet

– Transfer duration is included in both RTS and CTS

Exposed node overhears a RTS but not the CTS

– D‟s transmission cannot interfere at B

A B C

RTS

CTS CTS

DATA

D

RTS

72

IEEE 802.11

Wireless LAN standard defined in the unlicensed

spectrum (2.4 GHz and 5 GHz U-NII bands)

Standards covers the MAC sublayer and PHY layers

Three different physical layers in the 2.4 GHz band

– FHSS, DSSS and IR

OFDM based PHY layer in the 5 GHz band

73

Components of IEEE 802.11

architecture

The basic service set (BSS) is the basic building

block of an IEEE 802.11 LAN

The ovals can be thought of as the coverage area

within which member stations can directly

communicate

The Independent BSS (IBSS) is the simplest LAN. It

may consist of as few as two stations

ad-hoc network BSS2BSS1

74

802.11 - ad-hoc network (DCF)

Direct communication

within a limited range

– Station (STA):

terminal with access

mechanisms to the

wireless medium

– Basic Service Set (BSS):

group of stations using the

same radio frequency

802.11 LAN

BSS2

802.11 LAN

BSS1

STA1

STA4

STA5

STA2

STA3

Source: Schiller

75

Distribution System

Portal

802.x LAN

Access

Point

802.11 LAN

BSS2

802.11 LAN

BSS1

Access

Point

802.11 - infrastructure network (PCF)Station (STA)

– terminal with access mechanisms to the wireless medium and radio contact to the access point

Basic Service Set (BSS)

– group of stations using the same radio frequency

Access Point

– station integrated into the wireless LAN and the distribution system

Portal

– bridge to other (wired) networks

Distribution System

– interconnection network to form one logical network (EES: Extended Service Set) based on several BSS

STA1

STA2 STA3

ESS

Source: Schiller

76

Distribution System (DS) concepts

The Distribution system interconnects multiple BSSs

802.11 standard logically separates the wireless medium from the distribution system – it does not preclude, nor demand, that the multiple media be same or different

An Access Point (AP) is a STA that provides access to the DS by providing DS services in addition to acting as a STA.

Data moves between BSS and the DS via an AP

The DS and BSSs allow 802.11 to create a wireless network of arbitrary size and complexity called the Extended Service Set network (ESS)

77

802.11- in the TCP/IP stack

mobile terminal

access point

server

fixed terminal

application

TCP

802.11 PHY

802.11 MAC

IP

802.3 MAC

802.3 PHY

application

TCP

802.3 PHY

802.3 MAC

IP

802.11 MAC

802.11 PHY

LLC

infrastructure network

LLC LLC

78

802.11 - Layers and functions

PLCP Physical Layer Convergence Protocol

– clear channel assessment signal (carrier sense)

PMD Physical Medium Dependent

– modulation, coding

PHY Management

– channel selection, MIB

Station Management

– coordination of all management functions

PMD

PLCP

MAC

LLC

MAC Management

PHY Management

MAC

– access mechanisms, fragmentation, encryption

MAC Management

– synchronization, roaming, MIB, power management

PH

YD

LC

Sta

tion M

anag

em

ent

7.8.1

79

802.11 - Physical layer

3 versions: 2 radio (typically 2.4 GHz), 1 IR

– data rates 1, 2, or 11 Mbit/s

FHSS (Frequency Hopping Spread Spectrum)

– spreading, despreading, signal strength, typically 1 Mbit/s

– min. 2.5 frequency hops/s (USA), two-level GFSK modulation

DSSS (Direct Sequence Spread Spectrum)

– DBPSK modulation for 1 Mbit/s (Differential Binary Phase Shift Keying),

DQPSK for 2 Mbit/s (Differential Quadrature PSK)

– preamble and header of a frame is always transmitted with 1 Mbit/s

– chipping sequence: +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1 (Barker code)

– max. radiated power 1 W (USA), 100 mW (EU), min. 1mW

Infrared

– 850-950 nm, diffuse light, typ. 10 m range

– carrier detection, energy detection, synchonization

80

Spread-spectrum communications

Source: Intersil

81

DSSS Barker Code modulation

Source: Intersil

82

DSSS properties

Source: Intersil

83

802.11 - MAC layer

Traffic services

– Asynchronous Data Service (mandatory) – DCF

– Time-Bounded Service (optional) - PCF

Access methods

– DCF CSMA/CA (mandatory)

• collision avoidance via randomized back-off mechanism

• ACK packet for acknowledgements (not for broadcasts)

– DCF w/ RTS/CTS (optional)

• avoids hidden terminal problem

– PCF (optional)

• access point polls terminals according to a list

84

802.11 - Carrier Sensing

In IEEE 802.11, carrier sensing is performed

– at the air interface (physical carrier sensing), and

– at the MAC layer (virtual carrier sensing)

Physical carrier sensing

– detects presence of other users by analyzing all detected packets

– Detects activity in the channel via relative signal strength from other sources

Virtual carrier sensing is done by sending MPDU duration information in the header of RTS/CTS and data frames

Channel is busy if either mechanisms indicate it to be

– Duration field indicates the amount of time (in microseconds) required to complete frame transmission

– Stations in the BSS use the information in the duration field to adjust their network allocation vector (NAV)

85

802.11 - Reliability

Use of acknowledgements

– When B receives DATA from A, B sends an ACK

– If A fails to receive an ACK, A retransmits the DATA

– Both C and D remain quiet until ACK (to prevent collision of

ACK)

– Expected duration of transmission+ACK is included in

RTS/CTS packets

A B C

RTS

CTS CTS

DATA

D

RTS

ACK

86

802.11 - Priorities

defined through different inter frame spaces – mandatory idle time

intervals between the transmission of frames

SIFS (Short Inter Frame Spacing)

– highest priority, for ACK, CTS, polling response

– SIFSTime and SlotTime are fixed per PHY layer

– (10 s and 20 s respectively in DSSS)

PIFS (PCF IFS)

– medium priority, for time-bounded service using PCF

– PIFSTime = SIFSTime + SlotTime

DIFS (DCF IFS)

– lowest priority, for asynchronous data service

– DCF-IFS (DIFS): DIFSTime = SIFSTime + 2xSlotTime

87

t

medium busy

DIFSDIFS

next frame

contention window

(randomized back-off

mechanism)

802.11 - CSMA/CA

– station ready to send starts sensing the medium (Carrier Sense based on CCA, Clear Channel Assessment)

– if the medium is free for the duration of an Inter-Frame Space (IFS), the station can start sending (IFS depends on service type)

– if the medium is busy, the station has to wait for a free IFS, then the station must additionally wait a random back-off time (collision avoidance, multiple of slot-time)

– if another station occupies the medium during the back-off time of the station, the back-off timer stops (fairness)

slot time

direct access if

medium is free DIFS

88

802.11 –CSMA/CA example

t

busy

boe

station1

station2

station3

station4

station5

packet arrival at MAC

DIFS

boe

boe

boe

busy

elapsed backoff time

borresidual backoff time

busy medium not idle (frame, ack etc.)

bor

bor

DIFS

boe

boe

boe bor

DIFS

busy

busy

DIFS

boe busy

boe

boe

bor

bor

89

802.11 - Collision Avoidance

Collision avoidance: Once channel becomes idle, the

node waits for a randomly chosen duration before

attempting to transmit

DCF

– When transmitting a packet, choose a backoff interval in the

range [0,cw]; cw is contention window

– Count down the backoff interval when medium is idle

– Count-down is suspended if medium becomes busy

– When backoff interval reaches 0, transmit RTS

Time spent counting down backoff intervals is part of

MAC overhead

90

DCF Example

data

wait

B1 = 5

B2 = 15

B1 = 25

B2 = 20

data

wait

B1 and B2 are backoff intervals

at nodes 1 and 2cw = 31

B2 = 10

91

802.11 - Congestion Control

Contention window (cw) in DCF: Congestion

control achieved by dynamically choosing cw

large cw leads to larger backoff intervals

small cw leads to larger number of collisions

Binary Exponential Backoff in DCF:

– When a node fails to receive CTS in response to

its RTS, it increases the contention window

• cw is doubled (up to a bound CWmax)

– Upon successful completion data transfer, restore

cw to CWmin

92

802.11 - CSMA/CA II

station has to wait for DIFS before sending data

receivers acknowledge at once (after waiting for SIFS) if the packet was received correctly (CRC)

automatic retransmission of data packets in case of transmission errors

t

SIFS

DIFS

data

ACK

waiting time

other

stations

receiver

senderdata

DIFS

contention

93

802.11 –RTS/CTS

station can send RTS with reservation parameter after waiting for DIFS

(reservation determines amount of time the data packet needs the medium)

acknowledgement via CTS after SIFS by receiver (if ready to receive)

sender can now send data at once, acknowledgement via ACK

other stations store medium reservations distributed via RTS and CTS

t

SIFS

DIFS

data

ACK

defer access

other

stations

receiver

senderdata

DIFS

contention

RTS

CTSSIFS SIFS

NAV (RTS)NAV (CTS)

94

Fragmentation

t

SIFS

DIFS

data

ACK1

other

stations

receiver

senderfrag1

DIFS

contention

RTS

CTSSIFS SIFS

NAV (RTS)NAV (CTS)

NAV (frag1)NAV (ACK1)

SIFSACK2

frag2

SIFS

95

802.11 - Point Coordination Function

96

802.11 - PCF I

PIFS

stations„

NAV

wireless

stations

point

coordinator

D1

U1

SIFS

NAV

SIFSD2

U2

SIFS

SIFS

SuperFramet0

medium busy

t1

97

802.11 - PCF II

tstations„

NAV

wireless

stations

point

coordinator

D3

NAV

PIFSD4

U4

SIFS

SIFSCFend

contention

period

contention free period

t2 t3 t4

98

CFP structure and Timing

99

PCF- Data transmission

100

Polling Mechanisms

With DCF, there is no mechanism to guarantee

minimum delay for time-bound services

PCF wastes bandwidth (control overhead) when

network load is light, but delays are bounded

With Round Robin (RR) polling, 11% of time was

used for polling

This values drops to 4 % when optimized polling is

used

Implicit signaling mechanism for STAs to indicate

when they have data to send improves performance

101

Coexistence of PCF and DCF

PC controls frame transfers during a Contention Free

Period (CFP).

– CF-Poll control frame is used by the PC to invite a station to

send data

– CF-End is used to signal the end of the CFP

The CFP alternates with a CP, when DCF controls

frame transfers

– The CP must be large enough to send at least one

maximum-sized MPDU including RTS/CTS/ACK

CFPs are generated at the CFP repetition rate and

each CFP begins with a beacon frame

102

802.11 - Frame format

Types– control frames, management frames, data frames

Sequence numbers– important against duplicated frames due to lost ACKs

Addresses– receiver, transmitter (physical), BSS identifier, sender (logical)

Miscellaneous– sending time, checksum, frame control, data

Frame

Control

Duration

ID

Address

1

Address

2

Address

3

Sequence

Control

Address

4Data CRC

2 2 6 6 6 62 40-2312bytes

version, type, fragmentation, security, ...

103

Frame Control Field

104

Types of Frames

Control Frames

– RTS/CTS/ACK

– CF-Poll/CF-End

Management Frames

– Beacons

– Probe Request/Response

– Association Request/Response

– Dissociation/Reassociation

– Authentication/Deauthentication

– ATIM

Data Frames

105

MAC address format

scenario to DS fromDS

address 1 address 2 address 3 address 4

ad-hoc network 0 0 DA SA BSSID -

infrastructurenetwork, from AP

0 1 DA BSSID SA -

infrastructurenetwork, to AP

1 0 BSSID SA DA -

infrastructurenetwork, within DS

1 1 RA TA DA SA

DS: Distribution System

AP: Access Point

DA: Destination Address

SA: Source Address

BSSID: Basic Service Set Identifier

RA: Receiver Address

TA: Transmitter Address

106

802.11 - MAC management

Synchronization

– try to find a LAN, try to stay within a LAN

– timer etc.

Power management

– sleep-mode without missing a message

– periodic sleep, frame buffering, traffic measurements

Association/Reassociation

– integration into a LAN

– roaming, i.e. change networks by changing access points

– scanning, i.e. active search for a network

MIB - Management Information Base

– managing, read, write

107

802.11 - Synchronization

All STAs within a BSS are synchronized to a common

clock

– PCF mode: AP is the timing master

• periodically transmits Beacon frames containing Timing

Synchronization function (TSF)

• Receiving stations accepts the timestamp value in TSF

– DCF mode: TSF implements a distributed algorithm

• Each station adopts the timing received from any beacon that has

TSF value later than its own TSF timer

This mechanism keeps the synchronization of the TSF

timers in a BSS to within 4 s plus the maximum

propagation delay of the PHY layer

108

Synchronization using a Beacon

(infrastructure)

beacon interval

tmedium

access

pointbusy

B

busy busy busy

B B B

value of the timestamp B beacon frame

109

Synchronization using a Beacon (ad-

hoc)

tmedium

station1

busy

B1

beacon interval

busy busy busy

B1

value of the timestamp B beacon frame

station2

B2 B2

random delay

110

802.11 - Power management

Idea: switch the transceiver off if not needed– States of a station: sleep and awake

Timing Synchronization Function (TSF)– stations wake up at the same time

Infrastructure– Traffic Indication Map (TIM)

• list of unicast receivers transmitted by AP

– Delivery Traffic Indication Map (DTIM)

• list of broadcast/multicast receivers transmitted by AP

Ad-hoc– Ad-hoc Traffic Indication Map (ATIM)

• announcement of receivers by stations buffering frames

• more complicated - no central AP

• collision of ATIMs possible (scalability?)

111

802.11 - Energy conservation

Power Saving in IEEE 802.11 (Infrastructure Mode)– An Access Point periodically transmits a beacon

indicating which nodes have packets waiting for them

– Each power saving (PS) node wakes up periodically to receive the beacon

– If a node has a packet waiting, then it sends a PS-Poll

• After waiting for a backoff interval in [0,CWmin]

– Access Point sends the data in response to PS-poll

112

Power saving with wake-up patterns

(infrastructure)

TIM interval

t

medium

access

pointbusy

D

busy busy busy

T T D

T TIM D DTIM

DTIM interval

BB

B broadcast/multicast

station

awake

p PS poll

p

d

d

ddata transmission

to/from the station

113

Power saving with wake-up patterns

(ad-hoc)

awake

A transmit ATIM D transmit data

t

station1

B1 B1

B beacon frame

station2

B2 B2

random delay

A

a

D

d

ATIM

window beacon interval

a acknowledge ATIM d acknowledge data

114

802.11 - Roaming

No or bad connection in PCF mode? Then perform:

Scanning– scan the environment, i.e., listen into the medium for beacon

signals or send probes into the medium and wait for an answer

Reassociation Request– station sends a request to one or several AP(s)

Reassociation Response– success: AP has answered, station can now participate

– failure: continue scanning

AP accepts Reassociation Request– signal the new station to the distribution system

– the distribution system updates its data base (i.e., location information)

– typically, the distribution system now informs the old AP so it can release resources

115

Hardware

Original WaveLAN card (NCR)

– 914 MHz Radio Frequency

– Transmit power 281.8 mW

– Transmission Range ~250 m (outdoors) at 2Mbps

– SNRT 10 dB (capture)

WaveLAN II (Lucent)

– 2.4 GHz radio frequency range

– Transmit Power 30mW

– Transmission range 376 m (outdoors) at 2 Mbps (60m

indoors)

– Receive Threshold = –81dBm

– Carrier Sense Threshold = -111dBm

116

802.11 current status

MAC

MIB

DSSS FH IR

PHY

WEP

LLC

MAC

Mgmt

802.11b5,11 Mbps

802.11g20+ Mbps

802.11a6,9,12,18,24

36,48,54 Mbps

OFDM

802.11isecurity

802.11fInter Access Point Protocol

802.11eQoS enhancements

117

IEEE 802.11 Summary

Infrastructure (PCF) and adhoc (DCF) modes

Signaling packets for collision avoidance

– Medium is reserved for the duration of the transmission

– Beacons in PCF

– RTS-CTS in DCF

Acknowledgements for reliability

Binary exponential backoff for congestion control

Power save mode for energy conservation

118

Cuprins

Introducere


Rutarea IP mobila


Retele GSM





ad hoc networks)

119

Rutarea traditională

Un protocol de rutare populeaza tabela de rutare a unui router

Un protocol de rutare se bazeaza pe algoritmii Distance-Vector sau Link-State

120

Routarea si mobilitatea

Gasirea unei cai de la o sursa la o destinatie

Probleme– Schimbarea frecventa a rutelor

– Schimbarea rutei poate fi in legatura cu miscareahostului

– Latimea de banda relativ mica a legaturilor

Scopul protocoalelor de rutare– Micsorarea rutarii in ce priveste cimpurile

aditionale(overhead)

– Gasirea celor mai scurte rute

– Gasirea rutelor “stabile”(despite mobility)

121

IP mobil (RFC 3220): motivarea

Rutarea traditionala– Bazata pe adrese IP; prefixul retelei determina subreteaua

– Schimbarea fizica a subretelei implica

• Schimbarea adresei IP (dupa noua subretea), sau

• O tabela de rutare cu intrari speciale pentru transmitrea pacheteor la noua subretea

Schimbarea adeselor IP– Actualizarea DNS necesita un timp mare

– Conexiunile TCP se opresc

Schimbarea intrarilor in tabelele de rutare– Nu exista o evidenta cu numarul hosturilor mobile si

schimbarile frecvente a locatiilor lor

– Probleme de securitate

Cerintele solutiei– Folosirea aceleiasi adrese IP, utilizarea acelorasi protocoale

– Autentificarea mesajelor, …

122

IP-ul mobil: Ideea de baza

Router

1

Router

3

Router

2

S(sender)MN(mobile

Node)

Home

agent

Source: Vaidya

123

IP mobil: ideea de baza

Router

1

Router

3

Router

2

S MN

Home agent

Foreign agent

miscare

Pachetele sunt tunelate

utilizind IP in IP

Source: Vaidya

124

IP mobil : terminologia

Nod Mobil(Mobile Node-MN)

– Nod care se muta prin retea fara a-si schimba adresa IP

Agent de acasa/local(Home Agent-HA)

– Host din reteaua de-acasa/proprie a nodului mobil( MN), de obicei

un router

– Inregistreaza locatia nodului MN, tuneleaza pachetele IP la COA

Agent strain( Foreign Agent -FA)

– Host din reteaua curenta/straina, unde se gaseste momentan MN,

de obicei un router

– Forwardeaza pachetele tunelate la MN, de obicei ruterul implicit al

lui MN din reteaua de acasa/proprie

“Ingrijitorul/gestionarul” de adrese(Care-of Address -COA)

– Adreseaza punctele de capat ale tunelului curent( tunnel end-

point) de la MN( la FA sau MN)

– Acualizeaza locatia MN-ului din punctul de vedere al IP

Nodul corespondent(Correspondent Node (CN)

– Hostul cu care MN doreste sa “corespondeze” ( conexiunea TCP )

125

Transferul datelor la sistemul mobil

Internet

Emitator(sender)

FA

HA

MN

Reteaua proprie

(home network)

foreign

network

Receptor

(receiver)

1

2

3

1. Emitatorul trimite la adresa IP a nodului

mobil MN, iar HA intercepteaza

pachetele (proxy ARP)

2. HA tuneleaza pachetele la COA, aici FA,

prin incapsulare

3. FA trimite pachetele mai departe la MN

Soursa: Schiller

CN

126

Transferul datelor de la sistemul mobil

Internet

Receptor(receiver)

FA

Agent propriu

HA-home agentMN

Retea proprie

(home network)

Retea straina

(foreign

network)

Emitator

(sender)

1

1. Emitatorul trimite la adresa IP a

a receptorului;de obicei FA

lucreaza ca si un router implicit

Source: Schiller

CN

127

IP-ul mobil: Operatia de bază

Agentul de averizare– Periodic HA/FA trimit messaje de avertizare in subreteaua lor

fizica

– MN asculta mesajele si detecteaza daca acestea sunt din reteaua proprie sau straină

– MN citeste o/un COA din mesajele de averizare a FA

Inregistrarea MN– MN semnaleaza COA la HA prin FA

– HA raspundela MN prin FA

– Timpul de viata este limitat, necesar sa fie securizat dupa autentificare

Proxi-ul HA– HA avertizeaza asupra adresei IP a lui MN (ca si pentru

sistemele fixe)

– Pachetele pentru MN sunt trimise la HA

– Schimbari in COA/FA

Tunelarea pachetelor– HA la MN prin FA

128

Agentul de averizare

preference level 1router address 1

#addressestype

addr. size lifetimechecksum

COA 1COA 2

type sequence numberlength

0 7 8 15 16 312423

code

preference level 2router address 2

. . .

registration lifetime

. . .

R B H F M G V reserved

129

Inregistrarea(registration)

t

MN HA

t

MN FA HA

130

Cererea de inregistrare(Registration request)

home agenthome address

type lifetime

0 7 8 15 16 312423

rsv

identification

COA

extensions . . .

S B DMGV

131

Incapsularea IP-in-IP

Incapsularea IP-in-IP- (obligatorie in RFC 2003)

– tunel intre HA si COA

Care-of address COAIP address of HA

TTLIP identification

IP-in-IP IP checksumflags fragment offset

lengthTOSver. IHL

IP address of MNIP address of CN

TTLIP identification

lay. 4 prot. IP checksumflags fragment offset

lengthTOSver. IHL

TCP/UDP/ ... payload

132

IP-ul mobil: Alte probleme

Tunelarea inversa

– Firewall-urile permit numai adresari topologice

“topological correct“

– Un pachet de la MN incapsulat de FA este corect din

punct de vedere topologic(topological correct)

Optimizari

– Rutarea triunghiulara

• HA informeaza emitatorul privitor la locatia curenta a lui MN

– Schimbarea lui FA

• noul FA informeaza vechiul FA sa evite pachetul pierdut, iar

vechiul FA forvardeaza pachetele ramase la noul FA.

133

IP-ul mobil -recapitulare

Nodul mobil se muta la noua locatie

Agent de avertisment de agentul strain

Inregistrarea nodului mobil cu agentul de acasa

Realizarea proxi-ului de agentul de-acasa

pentru nodul mobil

Incapsularea pachetelor

Tunnelarea agentului de-acasa la nodul mobil

prin nodul strain

Tunelarea inversa

Optimizarea pentru rutarea triunghiulara(in

bucla)

134

Cuprins

Introducere


Rutarea IP mobila


Retele GSM





ad hoc networks)

135

Transmission Control Protocol (TCP)

Livrarea sigura si ordonata – Prin pachete de raspuns si retransmisii

Dialog de lucru cap la cap(end-to-end semantics)– Raspunsurile trimise la emitator confirma livrarea

datelor primite de receptor

– Ack este trimis numai dupa ce data a ajuns la receptor

– Ack cumulativ(pentru mai multe segmente)

Implementeaza evitarea congestiei si controlul de flux

136

Controlul fluxului bazat pe ferestre

Protocolul de transmisie cu fereastră glisantă

Dimensiunea ferestrei este minimul din

– Fereastra de averizare a receptorului- determinata

de spatiul disponibil in bufferul(memoria tampon) a

receptorului

– Fereastra de congestie – determinata de emitator

pe baza reactiei retelei

2 3 4 5 6 7 8 9 10 11 131 12

Fereastra emitatorului

Ack-urile primite Ne transmise

137

0

2

4

6

8

10

12

14

0 1 2 3 4 5 6 7 8

Time (round trips)

Co

ng

esti

on

Win

do

w s

ize

(seg

men

ts)

Startul incet

Evitarea congestiei

Nivelul startului

incet

Exemplul presupune ca ACK-urile nu sunt intirziate

Comportamentul de baza TCP

138

TCP: detectarea pachetelor pierdute

Timeout-ul de retransmisie

– Initiaza startul incet

Raspunsuri duplicate

– Initiaza retransmiterea rapida

Presupunerea ca toate pachetele sunt pierdute

datorita congestiei

139

TCP dupa timeout

0

5

10

15

20

25

0 3 6 9 12 15 20 22 25

Time (round trips)

Co

ng

esti

on

win

do

w (

seg

men

ts)

Nivelul startului incet

ssthresh = 8

Nivelul startului

Incet ssthresh = 10

Fereastra de

congestie(cwnd) =20

Dupa timeout

140

0

2

4

6

8

10

0 2 4 6 8 10 12 14

Time (round trips)

Win

do

w s

ize (

seg

men

ts)

Dupa retransmisia rapida si recuperarea rapida

dimensiunea ferestrei este redusa la jumatate.

Fereastra initiata de receptor

Dupa recuperarea rapida

TCP dupa retransmisia rapida

141

Impactul erorilor de transmisie

Canalele fara fir pot avea erori aleatoare in avalansa

Erorile in avalansa pot cauza timeout

Erorile aleatoare pot cauza retransmisii rapide

TCP nu poate face distinctia intre pachetele pierdute datorita congestiei si cele pierdute datorita erorilor de transmisie

Nu totdeauna este necesara reducerea ferestrei de congestie la erori (multe fiind datorate inrautatirii

transmisiei prin mediu)

142

Splitarea conexiunii

Conexiunea TCP capat la capat(end-to-end) este

Impartita/”sparta” intr-o conexiune pe partea

cablata a rutei si una pe partea fara fir a rutei

Conexiunea intre hostul fara fir MH si hostul fix FH

trece prin statia de baza BS

FH-MH = FH-BS + BS-MH

FH MHBS

Statia de baza Hostul mobilHost fix

143

I-TCP: Consideratii privind splitarea

conexiunii

Fara fir(wireless)

physical

link

network

transport

application

physical

link

network

transport

application

physical

link

network

transport

applicationrxmt

Starea conexiunii prin-TCP

Conexiunea TCP Conexiunea TCP

144

Protocolul snoop

Pachetele de date sunt memorate(bufferate) in statia se

baza BS

– Se permite astfel nivelului legatura de date retransmisia

lor

Cind raspunsurile duplicat sunt primite de BS de la MH

– Se retransmit pe legatura fara fir, daca pachetul este

prezent in buffer

– Se arunca raspunsul duplicat(drop dupack)

Se previne retransmisia rapida TCP de emitatorul FH(fix

host)

FH MHBS

145

Protocol snoop

FH MHBSwireless

physical

link

network

transport

application

physical

link

network

transport

application

physical

link

network

transport

application

rxmt

Starea conexiunii prin TCP

TCP connection

146

Impactul trecerii de la un nod la altul( la alt BS)(Hand-offs)

Splitarea conexiunii– Starea “hard” a conex. din statia de baza trebuie sa fie mutata la

noua statie de baza

Protocolul Snoop– Starea “soft” a conex. nu e nevoie sa fie mutata

– In timp ce noua statie de baza construieste noua stare, pachetele pierdute nu pot fi recuperate local

Trecerile frcvente de la un nod la altul constituie o problema pentru schemele care realizeaza o cantitate semnificativa a starilor de conexiune la statiile de baza– Starea” hard” a conex. nu se pierde

– Starea “soft” a conex. tebuie sa fie recreata pentru a obtine o performanta buna

147

M-TCP(mobile TCP)

Similar cu splitarea conexiunii, M-TCP spliteaza o

conexiune TCP in doua parti logice

– Cele doua parti au control de flux independent ca si

in I-TCP

BS nu trimite un ACK la MH, pina cind BS a primit un

ACK de la MH

– Pastreaza semanticile(modul de lucru) capat la capat

BS cu mentinerea ack pentru ACK-ul ultimului octet al

lui MH(?)

FH MHBS

Ack 1000Ack 999

148

M-TCP

Cind este receptionat un nou ACK impreuna cu un avertisment al receptorului de tipul Window=0, emitatorul intra in modul “continuare”

Emitatorul nu trimite nici o data in modul– Cu exceptia cazului in care modul “continuare” este

anulat

Cind este primit un avertisment de tip fereastra pozitiva, emitatorul iese din modul “continuare”

La iesirea din modul “continuare” , valorile pentru RTO si cwnd sunt aceleasi ca si inaintea modului “continuare”

149

BlocareaTCP

M-TCP are nevoie de ajutor de la statia de

baza(base station)

– Statia de baza mentine ack pentru un octet(?)

– Statia de baza utilizeaza acest ack sa trimita o

fereastra de avertisment egala cu zero cind un host

mobil se muta la alta celula

Blocarea TCP cere receptorului sa trimita o

fereastra de avertizare egala cu zero (ZWA)

FH MHBS

Mobile

TCP receiver

150

TCP in medii fara fir-recapitulare

Presupunerea ca pachetele pierdute implica o

congestie nu este adevarata in mediile fara fir

Nu este adecvata invocarea controlului

congestiei ca raspuns la pachetele pierdute

Citeava propuneri de adaptare a TCP in mediile

fara fir

Modificări la:

– Nodul fix(FH)

– Statia de baza(BS)

– Nodul mobil(MH)

151

Cuprins

Introducere


Rutarea IP mobila


Retele GSM





ad hoc networks)

152

GSM: Arhitectura

PSTN-Public Switched Telephone Network,

ISDN-Integrated Services Digital Network,

PDN-Packet Data Network

153

Base Transceiver Station (BTS) Una pe celula

E compusa dintr-un transmitator si un receptor de mare

viteza

Functiile statiei BTS

– Are doua canale

Un canal de semnalizare si unul pentru date(Signalling

and Data Channel)

Programarea mesajelor

Detectarea accesului aleatoriu

– Realizeaza codificarea pentru protectia la erori a

canalului radio

• Adaptarea vitezei in functie de erori, conditii de propagare,

etc.

Identificarea BTS prin codul de identitate (BtS Identity

Code-BSIC)

154

Base Station Controller (BSC)

Controleaza mai multe BTS-uri

Consta dintr-o entitatea de control si din una pentru un protocol inteligent

Functiile BSC– Asigura managementul resursei radio

– Asigneaza si elibereaza frecvente si sloturi de timp pentru toate MS-urile din aria sa de acivitate/actiune

– Realocarea de frecvente pentru toate celulele

– Realizeaza protocolul de predare primire a unei MS

– Semnale de sincronizare a timpului si frecventei la BTS-uri

– Masurarea timpului de intirziere si notificarea unui MS la BTS

– Mangementul puterii la BTS si MS

155

Mobile Switching Center (MSC)

Comuta nodul la un PLMN(Public/Private

Land Mobile Network)

Aloca resursa radio (RR)

– Realizeaza primirea predarea unei MS ublic

Mobilitatea subscrierii

– Inregistrarea locatiei de subscriere

Pot fi citeva MSC pentru un PLMN

156

Gateway MSC (GMSC)

Conecteaza reteaua mobila la reteaua fixa

– Punct de intrare la un PLMN

Usual unul pentru PLMN

Cere informatia de rutare de la HLR si ruteaza

conexiunea la MSC-ul local

157

Canalul fizic

Legatura ascendenta/descendenta (Uplink/Downlink) la 25MHz

– 890 -915 MHz pentru legatura ascendenta

– 935 - 960 MHz pentru legatura descendenta

Combinatie de FDMA si TDMA– FDMA

– 124 canale a 200 kHz

– 200 kHz banda de garda

– TDMA– Sit de biti/Avalansa(Burst)

Modulatia utilizataGaussian Minimum Shift Keying (GMSK)

159

Bursts

Building unit of physical channel

Types of bursts

– Normal

– Synchronization

– Frequency Correction

– Dummy

– Access

160

Normal Burst

Normal Burst

– 2*(3 head bit + 57 data bits + 1 signaling bit) + 26

training sequence bit + 8.25 guard bit

– Used for all except RACH, FSCH & SCH

161

Air Interface: Logical Channel

Traffic Channel (TCH)

Signaling Channel

– Broadcast Channel (BCH)

– Common Control Channel (CCH)

– Dedicated/Associated Control Channel

(DCCH/ACCH)

163

Traffic Channel

Transfer either encoded speech or user data

Bidirectional

Full Rate TCH– Rate 22.4kbps

– Bm interface

Half Rate TCH– Rate 11.2 kbps

– Lm interface

164

Full Rate Speech Coding

Speech Coding for 20ms segments– 260 bits at the output

– Effective data rate 13kbps

Unequal error protection– 182 bits are protected

• 50 + 132 bits = 182 bits

– 78 bits unprotected

Channel Encoding – Codes 260 bits into (8 x 57 bit blocks) 456 bits

Interleaving– 2 blocks of different set interleaved on a normal

burst (save damages by error bursts)

165

3 4 87651 2

1 26 8.253 57

Speech 20 ms 20 ms

1 57 3

260 260

456 bit 456 bit

Speech Coder Speech Coder

Channel Encoding Channel Encoding

Interleaving

NORMAL BURST

Out of first 20 msOut of second 20ms

166

T

Traffic Channel Structure for Full Rate Coding

23 4 18765432187651 2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 26

T T T T T T T T TT T T S T T T T I

Slots

Bursts for Users allocated in Slot

T = TrafficS = Signal( contains information about the signal strength in neighboring cells)

167

T

Traffic Channel Structure for Half Rate Coding

T

23 4 18765432187651 2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 26

T T T T T T S T T

Slots

Burst for one users

T

=

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 26

T T T T T T T T S

Bursts for another users allocated in alternate Slots

168

BCCH

Broadcast Control Channel (BCCH)

– BTS to MS

– Radio channel configuration

– Current cell + Neighbouring cells

– Synchronizing information

– Frequencies + frame numbering

– Registration Identifiers

– LA + Cell Identification (CI) + Base Station Identity Code

(BSIC)

169

FCCH & SCH

Frequency Correction Channel– Repeated broadcast of FB

Synchronization Channel – Repeated broadcast of SB

– Message format of SCH

PLMN color 3 bits

BS color 3 bits

T1 Superframeindex 11 bits

T2 multiframe index 11 bits

T3 block frameindex 3bits

BSIC 6 bits"

FN 19bits

170

RACH & SDCCH

Random Access Channel (RACH)– MS to BTS

– Slotted Aloha

– Request for dedicated SDCCH

Standalone Dedicated Control Channel (SDCCH)

– MS BTS

– Standalone; Independent of TCH

171

AGCH & PCH

Access Grant Channel (AGCH)

– BTS to MS

– Assign an SDCCH/TCH to MS

Paging Channel (PCH)

– BTS to MS

– Page MS

172

SACCH & FACCH

Slow Associated Control Channel (SACCH)– MS BTS

– Always associated with either TCH or SDCCH

– Information– Optimal radio operation; Commands for synchronization

– Transmitter power control; Channel measurement

– Should always be active; as proof of existence of physical radio connection

Fast Associated Control Channel (FACCH) – MS BTS

– Handover

– Pre-emptive multiplexing on a TCH, Stealing Flag (SF)

173

Example: Incoming Call SetupMS BSS/MSC ------ Paging request (PCH)

MS BSS/MSC ------ Channel request (RACH)

MS BSS/MSC ------ Immediate Assignment (AGCH)

MS BSS/MSC ------ Paging Response (SDCCH)

MS BSS/MSC ------ Authentication Request (SDCCH)

MS BSS/MSC ------ Authentication Response (SDCCH)

MS BSS/MSC ------ Cipher Mode Command (SDCCH)

MS BSS/MSC ------ Cipher Mode Compl. (SDCCH)

MS BSS/MSC ------ Setup (SDCCH)

MS BSS/MSC ------ Call Confirmation (SDCCH)

MS BSS/MSC ------ Assignment Command (SDCCH)

MS BSS/MSC ------ Assignment Compl. (FACCH)

MS BSS/MSC ------ Alert (FACCH)

MS BSS/MSC ------ Connect (FACCH)

MS BSS/MSC ------ Connect Acknowledge (FACCH)

MS BSS/MSC ------ Data (TCH)

174

YES

NO

NO

NO

YES

YES

Power On Scan Channels,monitor RF levels

Select the channel with highest RF level among the control channels

Scan the channel for theFCCH

IsFCCH detected?

Scan channel for SCH

IsSCH detected?

Read data from BCCHand determine is it BCCH?

Isthe current BCCHchannel included?

Camp on BCCH and start decoding

Select the channel withnext highest Rf level fromthe control list.

From the channel dataupdate the control channel list

175

Adaptive Frame Synchronization

Timing Advance

Advance in Tx time corresponding to

propagation delay

6 bit number used; hence 63 steps

63 bit period = 233 micro seconds (round trip

time)

– 35 Kms

177

GSM: Channel Mapping Summary

Logical channels

– Traffic Channels; Control Channels

Physical Channel

– Time Slot Number; TDMA frame; RF Channel Sequence

Mapping in frequency

– 124 channels, 200KHz spacing

Mapping in time

– TDMA Frame, Multi Frame, Super Frame, Channel

– Two kinds of multiframe:

– 26-frame multiframe; usage -Speech and Data

– 51-frame multiframe; usage -Signalling

178

GSM call routing

1. MSISDN

2. MSISDN

VLR

HLR

AUC

EIR

GMSC/I

WF

MSC

BSC

BSC

BTS

BTS

BTS

ISDN

3. MSRN

4. MSRN

5. MSRN

6. TMSI

7. TMSI

7. TMSI

7. TMSI

8. TMSI

LA2

LA1

MS

MS

179

Options for data transfer

Two enhancements to GSM for data

– HSCSD - High Speed Circuit Switched Data

– GPRS - General Packet Radio Service

Both have capacity to use new coding schemes

and to make multislot allocation

GPRS, being a packet switched service, is

known to be more efficient and flexible for data

transfer purposes

It delivers circuit and packet-switched services

in one mobile radio network

180

1 Hyper frame = 2048 Super frames =2715648 TDMA frames (3h 28 min 53 sec 760 ms)

1 Super frame = 1326 TDMA frames (6.12s)

= 51(26 frames) Multi frame

1(26 frames) Multi frame = 26 TDMA frames (120 ms) 1 ( 5 1 f r a m e s ) M u l t i f r a m e = 5 1 T D M A f r a m e s ( 3 0 6 0 / 1 3 m s )

1 t i m e s l o t = 1 5 6 . 2 5 b i t d u r a t i o n ( 1 5 / 2 6 o r 0 . 5 7 7 m s )

( 1 b i t d u r a t i o n = 4 8 / 1 3 o r 3 . 6 9 s )

1 T D M A f r a m e

= 8 t i m e s l o t s ( 1 2 0 / 2 6 o r 4 . 6 1 5 m s )

0 1 2 3 2045 2046 2047

0 1 2 3 4 5 76

0 1 2

30 1 2

3 50

23

24 25

49 50T0 T1 I 1 2T2 3T12

(SACCH)

T23 0

1 S u p e r f r a m e = 1 3 2 6 T D M A f r a m e s ( 6 . 1 2 s )

= 2 6 ( 5 1 f r a m e s ) M u l t i f r a m e

181

Cuprins

Introducere


Rutarea IP mobila


Retele GSM





ad hoc networks)

182

GPRS

Resursele radio sunt alocate pentru unul sau

mai multe(putine) pachete la un moment dat

– multi utilizatori partajeaza resursele radio si permit un

transport eficient al pachetelor

– Timpi redusi de acces(setup/access)

– Conectivitate la datele pachetelor externe( n/w)

– Incarcarea bazata pe volum

GPRS de asemenea transporta SMS prin

canalele de date spre deosebire de canalele de

semnalizare din GSM

183

Architectura GPRS

184

Architectura GPRS

Are in plus fata de GSM o noua clasa de noduri numita

xGSN

• SGSN: Serving Gprs Support Node, controlează transmiterea

pachetelor de date prin întreaga reţea

• GGSN(Gateway GPRS Support Node) care are rolul de a

conecta reţeaua de telefonie mobilă la infrastructura Internetului

BSC are un PCU (Packet Control Unit) si diverse alte

elemente fata de GSM, elemente care necesita soft

corespunzator

Toate nodurile xGSN sunt conectate prin protocolul IP la

o magistrala( backbone). Datele(Protocol data units-

PDUx) sunt incapsulate si tunelate prin GSN-uri

185

GGSN

Serveste ca si interfata la retelele IP externe care vad GGSN-ul ca un router IP ce serveste toate adresele IP a MS-urilor

GGSN memoreaza adresa curenta a SGSN si schiteaza/contureaza utilizatorul in registrul sau de locatie.

El tuneleaza pachetele de date la si de la SGSN current servind MS-ul

El asigura de asemenea autentificarea

GGSN poate include de asemenea firewall si mecanisme de filtrare a pachetelor

186

SGSN

Functioneaza analog MSC-ului de la GSM

Routeaza pachetele primite sau trimise,

adresate la si de la orice abonat GPRS

localizat, din aria geografica servita de SGSN

Registrul de locatie/localizare(Location

Register) a SGSN-ului memoreaza informatia

(precum celula curenta si VLR) si profilele

utilizator(ex. adresele IMSI) ale tuturor

utilizatorilor inregistrati cu acest SGSN

187

BSC si altele

BSC foloseste un PCU(Packet Control Unit)

pentru

– setare, supervizare si deconectare- la apelurile de

comutare

– De asemenea asigura suportul la schimbarea celulei,

configurarea resurselor radio si stabilirea canalului

MSC/VLR, HLR si centrul SMS faciliteaza

interconectarea cu GPRS

MS trebuie sa fie echipat cu stiva de protocoale

GPRS

188

HLR - Home Location Register

Partajeaza baza de date cu GSM

Faciliteaza abonatului GPRS rutarea datelor si informatiilor

Pentru toti utilizatorii inregistrati in retea, HLR pastreaza profilul utilizatorului, SGSN-ul curent si adresa/adresele informatiei de tipul Packet Data Protocol (PDP)

SGSN schimba informatii cu HLR, de ex informeaza HLR-ul privitor la locatia curenta a MS

Cind MS se inregistreaza cu un nou SGSN, HLR-ul trimite profilul utilizatorului la noul SGSN

189

MSC/VLR-Visitor Location Register

VLR este responsabil pentru un grup din zona

de localizare/determinare a pozitiei . El

memoreaza datele acestor utilizatori din zona

sa de responsabilitate

MSC/VLR poate avea in plus functii de

inregistrare a intrarilor care permit o coordonare

eficienta intre serviciile GPRS si GSM

– Actualizarea combinate a pozitiei/locatiei

– Proceduri combinate de atasare

190

Planurile transmisiei in GPRS

191

Interfata cu mediul de transmisie Um Este unul din aspectele centrale a sistemului

GPRS– Gestioneaza/se ocupa de comunicarea intre MS si

BSS la nivelele fizic, MAC si RLC

– Canalul fizic dedicat traficului de pachete de date este numit canal pentru date(packet data channel --PDCH)

Capacitatea si cererea: – Alocation/dealocation a traficului PDCH la GPRS

este dinamica

– BSC controleaza resoursele in ambele directii

– Fara conflicte in cadrul legaturii descendente(downlink)

– Conflictele in cadrul legaturii ascendente(uplink) sunt rezolvate prin utilizarea de slot-uri ALOHA

192

Transferul datelor intre MS si SGSN

SNDCP transforma pachetele IP/X.25 packets in cadre LLC, dupa compresia optionala a header-ului/datei , segmentare si criptare

Dimensiunea maxima a cadrului LLC este de 1600 octeti

Un cadru LLC este segmentat in blocuri de date RLC care sunt codificate in blocuri radio

Fiecare bloc radio cuprinde 4 siruri de biti(114 biti) in cadre TDMA consecutive.

RLC este responsabil pentru transmisia datelor prin interfata pentru mediul fara fir si pentru corectia erorilor

Nivelul MAC realizeaza alocarea mediului la cerere prin alocarea mai multor sloturi

Nivelul fizic PHY este identic cu cel de la GSM

193

Transferul datelor intre GSN-uri

Desi reteaua GPRS consta din mai multe noduri

diferite, ea reprezinta numai un hop IP

GTP realizeaza tunelarea PDU-urilor intre GSN-

uri, in functie de informatia de rutare

GTP, TCP / IP şi IP sunt folosite ca protocoale

pentru magistrala/backbone/coloana vertebrală

GPRS

194

Modelul starilor MS În starea de

repaus(IDLE) MS nu este accesibilă

Cu GPRS atach MStrece în starea READY-gata

Cu detach, acesta revine la starea Idle: toate contextele PDP suntsterse

Stare de aşteptare(Standby) este atinsaatunci când MS nu trimite date pentru o perioadă lungă de timp şi timer pentru pregatit expira

195

GPRS –contextul PDP

MS aduce un pachet de identitate temporara al abonatului

de telefonie mobilă (p-TMSI), în timpul Attach

MS face cereri pentru una sau mai multe adrese folosite în

reţeaua de pachete de date, de exemplu o adresă IP

GGSN creează un context PDP pentru fiecare sesiune

– tipul PDP (IPv4), adresa PDP (IP) pentru MS,

– Cereriea privind calitatea serviciilor (QoS) şi adresa de GGSN

Contextul (elementele)PDP este stocat in MS, SGSN si

GGSN

Realizeaza maparea intre cele două adrese, activeaza

GGSN pentru a permite transferul de pachete între MS şi

PDN

196

GPRS - Rutarea

197

GPRS - Rutarea

MS trece de la PLMN-2 la PLMN-1.

Prefixul adresei IP a MS estea aceelasi cu cel

al GGSN-2

Pachetele sosite la MS sunt rutate la GGSN-2

GGSN-2 interogheazas HLR si afla ca MS este

acum in PLMN-1

Se încapsulează pachete IP şi sunt tunelate prin

coloana vertebrală a GPRS, la SGSN-ul

corespunzător al PLMN-1

SGSN decapsuleaza pachetele si le livreaza la

MS

198

GPRS recapitulare

Permite mai multor utilizatoril sa partajeze

dinamic resursele radio de, la cerere, prin multi-

alocarea sloturilor

Oferă conectivitate spre reţelele externe de

pachete de date

E modificata interfata cu mediul de transmisie

fara de GSM

Adauga noi noduri GPRS

Asigneaza un PDP de context la MS

Permite tarifarea pe baza de volum precum şi

tarifare bazata pe durata incarcare

199

Integrarea retelelor

IP Based Core Networks

Media Access Systems

Services and Applications

Short Range

Connectivity

cellular

Wireline

DSL/modem

WLAN

Interworking

Mobility

Management

Roaming

Network of Networks

200

Everyday Usage Scenarios

Internet

EthernetWi-Fi

Cellular

Wi-Fi

Wi-Max

In the office

In the car

Out of Town

Wi-Fi

Wi-Fi

Wi-Fi

AP1AP2

AP3

201

Emergency Response Scenario

Satellite

Satellite3G

WiFi

3G

202

Military Usage Scenario

Satcom

Satcom

GPRS

3G

WiMax

Satcom

WiMax

WiMax

“Always Best Connected”

203

Mobility Granularity

Horizontal Handover

Vertical Handover

Multiple Interface Management

Multiple Flow Management

A handover is initiated when mobile device exits the

boundaries of an administrative domain. Single interface

is used.

A mobile device does need to move in order to initiate a

handover. Multiple interfaces are required, but use one

interface at a time.

Simultaneous use of multiple interfaces and access

networks. Association of an application with an interface

Ability to split individual flows between links with

respect to the requirements of the flows and the user

preferences

204

Key Challenges

Scalability – roaming from any access network to any other

access network (2G, 3G, 4G, Wi-Fi, Wi-Max, Bluetooth,

Satellite, Ethernet)

Standard handover interfaces – interoperability between

different vendor equipment.

Cross-layer solutions - extensions to layer 1 & layer 2

functionalities in order to optimize higher layer mobility

architectures (MIPv4, MIPv6, SIP).

QOS guarantees during handover – no disruption to user

traffic: extreme low latency, signaling messages overhead

and processing time, resources and routes setup delay,

near-zero handover failures and packet loss rate

Security – user maintains the same level of security when

roaming across different access networks.

205

Access Media Properties

Different media and coverage areas from few

square meters to hundred of kilometers

Different architectures and protocols for routing,

transport, mobility management

Different authentication, key management and

encryption schemes

Different services offered and user demands

ranging from low-data-rate non-real-time

applications, to high-speed real-time multimedia

applications.

206

Access Scalability

Wide variety of access network technologies including cellular

(2G, 2.5G, 3G), wireless (Wi-Fi, Wi-Max, Bluetooth, UWB) and

wired (DSL, cable modems, Ethernet)

207

Industry and Standards Activities

UMA TechnologySession Initiation ProtocolIP

Multimedia

Subsystem

Internet Engineering Task Force

– Detecting Network AttachmentProcessing Layer 2 Triggers

– Mip4Mobile IP version 6

– Mip6Mobile IP version 4

– MipshopMIPv6 signaling and Handoff Optimization

– MoboptsIP Mobility optimizations research group

– NemoNetwork Mobility

Higher

Layers

No single standard interface!

IEEE 802

IEEE 802.21

Media Independent Handovers

IEEE 802.11r

IEEE 802.11 Fast handovers

IEEE 802.11u

Interworking with external networks

IEEE 802.20

Mobile broadband wireless access

Layer 2

Layer 3

FMCA NOKIA

KT

208

Cross-Layer Protocol Interactions

Profile Manager

AccessMedia

Applications

Policy

Mobility

Decision

Cellular

PHY

MAC

Link measurements:

RSSI, Noise, Interference

Performance Measure.:QOS, ACK

Handover Layer

Network LayerMobile IP

Transport Layer

SCTP

Application Layer

SIP

What are the mobility architectures considered?

What are the protocols and messages needed?

What measurements will be used in the handover decision?

What are the mobility scenarios envisaged?

How can mobility performance be evaluated?

209

Cuprins

Introducere


Rutarea IP mobila


Retele GSM





ad hoc networks)

210

Mobilitatea

Connectivitatea

nodurilor• connectate

• semi-connecte

(asimmetric)

• disconnectate

Capacitatea

dispozitivelor mobile• tipul si caracteristicile

• Interfata grafica utilizator

(Graphics User Interface-GUI

• multimedia

• multimedia in timp real

Mobilitatea• stationar

• nomadic (mers la pas pe jos)

• mobil (vioteza unui vehicul)

• roaming (mobilatea intre retele)

211

Wireless Application Protocol (WAP)

HTTP / HTML nu au fost proiectate pentru

dispozitive mobile şi aplicaţii

WAP permite utilizatorilor mobili ce folosesc

dispozitive mobile(in medii fără fir) sa

acceseze si sa interactioneze cu uşurinţă

informaţii şi servicii.

Un "standard", creat de companii ce se ocupa

de retele fara fir si de Internet, pentru a

permite accesul la Internet de la un telefon

celular

212

HTTP/HTML

Capacitatea mare de transport si capacitatea mica

Wireless network<HTML>

<HEAD>

<TITLE>NNN Interactive</TITLE>

<META HTTP-EQUIV="Refresh" CONTENT="1800,

URL=/index.html">

</HEAD>

<BODY BGCOLOR="#FFFFFF"

BACKGROUND="/images/9607/bgbar5.gif" LINK="#0A3990"

ALINK="#FF0000" VLINK="#FF0000" TEXT="000000"

ONLOAD="if(parent.frames.length!=0)top.location='ht

tp://nnn.com';">

<A NAME="#top"></A>

<TABLE WIDTH=599 BORDER="0">

<TR ALIGN=LEFT>

<TD WIDTH=117 VALIGN=TOP ALIGN=LEFT>

<HTML>

<HEAD>

<TITLE

>NNN

Intera

ctive<

/TITLE

>

<META

HTTP-

EQUIV=

"Refre

sh"

CONTEN

T="180

0,

URL=/i

ndex.h

tml">

Internet<WML>

<CARD>

<DO TYPE="ACCEPT">

<GO URL="/submit?Name=$N"/>

</DO>

Enter name:

<INPUT TYPE="TEXT" KEY="N"/>

</CARD>

</WML>

010011

010011

110110

010011

011011

011101

010010

011010

Content encoding

HTTP/HTML WAP

Source: WAP Forum

213

WAP Reţelele fără fir şi telefoanele celulare

– au nevoi şi cerinţe specifice – Adresarea nu este similara tehnologiilor existente pe Internet

WAP – Permite transportul oricarei date

• TCP / IP, UDP / IP, curaj (IS-135 / 6), SMS sau USSD. – Optimizează conţinutul şi protocoalele de legatura prin mediul fara fira– Utilizeaza servere de Web HTTP 1.1

• Utilizeaza tehnologia standard de marcare (eXtensible Markup Language-XML)

• Conţinutul de tip WML este accesat prin intermediul cererilor de tip HTTP 1.1

– Componente de interfaţă utilizator WML UI(WML user Interface) se mapeaza/arată bine ca si interfata utilizator pe telefoanele mobile existente

• Nu e nevoie de invatarea unui limbaj nou de catre utilizatorii finali • Atuu pentru pătrunderea pe piaţă a dispozitivelor mobile

214

WAP: main features

Browser – "Micro browser-ul", similar cu browserele Web existente

Limbaj de marcare – Similar cu HTML, doar adaptat la dispozitive mobile

Limba Script– Similar cu Javascript, adaptate la dispozitive mobile

Gateway– Tranziţia de la retelele fara fir(wireless) la retele cu fir

Server– "WAP / server de origine", similar cu serverele de web existente

Straturi de protocol– Transport Layer, strat de securitate, sesiune strat etc

Telefonie interfaţa de aplicare– Accesul la funcţiile de telefonie

215

Internet model

HTML

HTTP

TLS/SSL

TCP/IP

216

Web Server

Continut

Scripturi

CGI, etc.

Pu

nti

WM

L

cu s

crip

turi

W

ML

WAP Gateway

Codificator WML

Compilator pentru

scripturi WML

Adaptor/e de protocol

Client

WML

WML-

Script

WTAI

Etc.

HTTPWSP/WTP

Architectura WAP

Source: WAP Forum

217

Serverul WAP de aplicatie

Continut

Logica

aplicatiei

Pu

nti

le W

ML

cu s

crip

t W

MLCodificator WML

WMLScript

Compiler

Adaptoare de protocol

Client

WML

Script

WML-

WTAI

Etc.

WSP/WTP

Serverul de aplicatie WAP

Source: WAP Forum

218

Specificatii(definirea) WAP

Mediul aplicatiei fara fir(WAE-Wireless

Application Environment)– WML Microbrowser– WMLScript Virtual Machine– WMLScript Standard Library– Wireless Telephony Application Interface (WTAI)– Tipuri de continut WAP

Wireless Protocol Stack– Wireless Session Protocol (WSP)– Wireless Transport Layer Security (WTLS)– Wireless Transaction Protocol (WTP)– Wireless Datagram Protocol (WDP)– Definirea interfetelor cu retelele fara fir

219

Stiva(protocoale) WAP

WAE (Wireless Application Environment):

– Architectura: modelul aplicatiei, browser-ul,

gateway-ul, server-ul

– WML: Sintaxa XML-Syntax, bazata pe taguri,

variable,etc. ...

– WTA: servicii de telefonie, precum controlul

apelului, carte de telefon( phone book), etc.

WSP (Wireless Session Protocol):

– Asigura functionalitatea protocolului HTTP 1.1

– Suport de gestionare a sesiunii, de securitate, etc.

220

Stiva(protocoale) WAP

WTP (Wireless Transaction Protocol):– Oferă mecanisme fiabile de transfer al mesajelor

– Bazat pe concepele protocoalelor TCP / RPC

WTLS (Wireless Transport Layer Security):

– Realizeaza/asigura facilitati privind integritatea datelor, intimitatea lor, functii de autentificare

– Bazat pe conceptele protocoalelor TLS/SSL

WDP (Wireless Datagram Protocol):– Realizeaza/asigura functiile nivelului transort

– Bazat pe conceptele protocolului UDP

Codarea continutului, optimizarea lăţimii de bandă a canalelor de banda ingusta, simplificarea dispozitivelor

221

WDP: Wireless Datagram Protocol

Scopuri

– crearea unui sistem de transport interoperabil în întreaga lume, prin adaptarea WDP la diferitele tehnologii

– Asigurarea de servicii de transmisie, precum SMS-urile în GSM care ar putea fi inlocuite schimba cu alte servicii mai noi

WDP

– Protocol la nivel transport cu arhitectura WAP

– Utilizeaza servicii cu primitive de tipul:

• T-UnitData.req .ind

– Utilizeaza mecanisme de transport pentru diferitele tipuri de tehnologii la nivel fizic(modulatii)

– Ofera o interfata comuna pentru protocoalele de nivel inalt

– permite o comunicare transparentă, în ciuda diferitelor tehnologii

– adresarea foloseste numere de port

– WDP pe IP este UDP/IP

222

WDP: primitive de serviciu

T-SAP T-SAP

T-DUnitdata.req

(DA, DP, SA, SP, UD) T-DUnitdata.ind

(SA, SP, UD)

T-DUnitdata.req

(DA, DP, SA, SP, UD)

T-DError.ind

(EC) SAP: Service Access Point

DA: Destination Address

DP: Destination Port

SA: Source Address

SP: Source Port

UD: User Data

EC: Error Code

Source: Schiller

223

WAP pentru GSM cu circuite comutate

RAS - Remote Access Server

IWF - InterWorking Function

WSP

WAE

Subretea

IP

WSP

WAE Apps on

Other Servers

WAP

Proxy/Server

CSD-RF

PPP

IP

Mobile

IWF

PSTN

Circuit

CSD-

RF

ISP/RAS

SubreteaPSTN

Circuit

PPP

IP

WTP

UDP

WTP

UDP

Servicii, protocoale, purtatoare: exemple

Source: WAP Forum

224

WAP per GSM pentru SMS(Short Message Service)

SMS

WDP

WTP

WSP

WAE

SMS

Subretea

WDP

WDP Tunnel

Protocol

Subretea

WDP Tunnel

Protocol

WTP

WSP

WAE Apps on

other servers

SMSC

WAP

Proxy/ServerMobile

Servicii, protocoale, purtatoare: exemple

Source: WAP Forum

225

WTLS:Wireless Transport Layer Security

Functionalitati/scopuri– Furnizarea de mecanisme pentru transferul sigur de

conţinut, pentru aplicaţii care au nevoie de intimitate, de identificare, integritatea mesajului şi non-repudierea

WTLS – Este bazat pe protocolulTLS/SSL (Transport Layer Security)

– Optimizarea canalelor de comunicatie de banda ingusta

– asigura• intimitatea (prin criptare)

• integritatea datelor

• autenticitatea (lucru cu chei publice si criptare asimetrica)

– Foloseşte mecanisme special adaptate pentru utilizare in retele fără fir

• Durată mare de viata a sesiunilor securizate

• Proceduril de dialog optimizate

• Oferă fiabilitate datelor transmise prin datagrame(folosind UDP)

226

WTLS: securizarea sesiunii, dialogul

complet

SEC-Create.req

(SA, SP, DA, DP, KES, CS, CM)SEC-Create.ind

(SA, SP, DA, DP, KES, CS, CM)

originator

SEC-SAP

peer

SEC-SAP

SEC-Create.cnf

(SNM, KR, SID, KES„, CS„, CM„)

SEC-Create.res

(SNM, KR, SID, KES„, CS„, CM„)

SEC-Exchange.req

SEC-Exchange.ind

SEC-Exchange.res

(CC)

SEC-Commit.req SEC-Exchange.cnf

(CC)

SEC-Commit.ind

SEC-Commit.cnf

Source: Schiller

KES: Key Exchange Suite

CS: Cipher Suite

CM: Compression Mode

SNM: Sequence Number Mode

KR: Key Refresh Cycle

SID: Session Identifier

CC: Client Certificate

227

WTP: Wireless Transaction Protocol Functionalitati/scopuri

– Servicii de tranzacţii care permit diferitelor aplicaţii

selectarea unor niveluri adecvate de fiabilitate si

eficienta/randament

– Cerinţe reduse de memorie, adecvate dispozitive simple

cu care se lucreaza(<10kbyte)

– eficientizarea transmisiunilor radio(in mediul fără fir)

WTP

– suport pentru aplicatii de tip peer-to-peer, client / server

şi multicast

– Eficientizarea transmisiilor rado(fără fir)

– suport pentru diferite scenarii de comunicare

228

Tranzactii WTP

class 0: transfer nesigur de mesaje– Mesajul Inveke(Invocare) neconfirmat cu nici un mesaj Result(

Rezultatul)

– o datagrama poate fi trimisa în/cu contextul/cadrul unei sesiuni de lucru existente

class 1: transfer sigur de mesaje fără un mesaj rezultat – Mesajul Invoke(Invocare) confirmat dar fara un mesaj Rezultat

– folosite pentru împingerea/trimiterea datelor, în cazul în care nu este de aşteptat un răspuns de la destinaţie

class 2:transfer fiabil de mesaje, pentru fiecare mesaj cu un mesaj(sigur) rezultat – mesaj Invocare confirmat cu un mesaj de rezultat confirmat

– o singură cerere produce un răspuns unic

229

WTP: servicii si protocoale

WTP (Transaction)

– Asigura un transfer fiabil de date bazat pe paradigma cerere/raspuns

• nici presupune setarea explicita a unei conexiuni sau una una restinsa

• setup optimizat (cu datele transmise în primul pachet al protocolului de schimb)

• urmăreşte să reducă dialogul cu trei cai(3-way handshake), la cererea iniţiala

– suporturi./facilitati• de compresie antet

• de segmentare / re-asamblare

• retransmisie a pachetelor pierdute

• Retransmisie-selectiva

• Adresare prin numare de port(numere de port UDP)

• de control al fluxului/debitului

230

Servicii WTP

orientată spre mesaj (nu curge)

susţine o funcţie Abort pentru cereri de curs

sprijină concatenarea PDUs

suportă două opţiuni de confirmare

Confirmare de utilizator

ACK-uri pot fi obligat de la utilizatorul WTP

(stratul superior)

Stack confirmare: default

231

WTP Class 0 Transaction

TR-Invoke.req

(SA, SP, DA, DP, A, UD, C=0, H) TR-Invoke.ind

(SA, SP, DA, DP, A, UD, C=0, H„)

initiator

TR-SAP

responder

TR-SAP

Source: Schiller

A: Acknowledgement Type

(WTP/User)

C: Class (0,1,2)

H: Handle (socket alias)

232

WTP Class 1 Transaction,

no user ack & user ack

TR-Invoke.req



initiator

TR-SAP

responder

TR-SAP

TR-Invoke.res

(H„)TR-Invoke.cnf

(H)

TR-Invoke.req



initiator

TR-SAP

responder

TR-SAP

TR-Invoke.cnf

(H)

Source: Schiller

233

WTP Class 2 Transaction,

no user ack, no hold on

TR-Invoke.req



initiator

TR-SAP

responder

TR-SAP

TR-Result.req

(UD*, H„)

TR-Result.ind

(UD*, H)

TR-Invoke.cnf

(H)

TR-Result.res

(H)TR-Result.cnf

(H„)

Source: Schiller

234

WTP Class 2 Transaction, user ack

TR-Invoke.req



initiator

TR-SAP

responder

TR-SAP

TR-Result.ind

(UD*, H)

TR-Invoke.res

(H„)TR-Invoke.cnf

(H) TR-Result.req

(UD*, H„)

TR-Result.res

(H)TR-Result.cnf

(H„)

Source: Schiller

235

WSP - Wireless Session Protocol

Goals

– HTTP 1.1 functionality

• Request/reply, content type negotiation, ...

– support of client/server transactions, push technology

– key management, authentication, Internet security services

WSP Services

– provides shared state between client and server, optimizes

content transfer

– session management (establish, release, suspend, resume)

– efficient capability negotiation

– content encoding

– Push

236

WSP overview

Header Encoding– compact binary encoding of headers, content type identifiers

and other well-known textual or structured values

– reduces the data actually sent over the network

Capabilities (are defined for):– message size, client and server

– protocol options: Confirmed Push Facility, Push Facility, Session Suspend Facility, Acknowledgement headers

– maximum outstanding requests

– extended methods

Suspend and Resume– server knows when client can accept a push

– multi-bearer devices

– dynamic addressing

– allows the release of underlying bearer resources

237

WSP/B session establishment

S-Connect.req

(SA, CA, CH, RC) S-Connect.ind

(SA, CA, CH, RC)

client

S-SAP

server

S-SAP

S-Connect.res

(SH, NC)S-Connect.cnf

(SH, NC)

WTP Class 2

transaction

Source: Schiller

CH: Client Header

RC: Requested Capabilities

SH: Server Header

NC: Negotiated Capabilities

238

WSP/B session suspend/resume

S-Suspend.req S-Suspend.ind

(R)

client

S-SAP

server

S-SAP

S-Resume.res

WTP Class 2

transaction

S-Suspend.ind

(R)

~ ~S-Resume.req

(SA, CA) S-Resume.ind

(SA, CA)

S-Resume.cnf

WTP Class 0

transaction

Source: Schiller

R: Reason for disconnection

239

WSP/B session termination

S-Disconnect.ind

(R)

client

S-SAP

server

S-SAP

S-Disconnect.ind

(R) WTP Class 0

transaction

S-Disconnect.req

(R)

Source: Schiller

240

confirmed/non-confirmed push

S-Push.req

(PH, PB)

client

S-SAP

server

S-SAP

WTP Class 1

transaction

S-Push.ind

(PH, PB)

S-ConfirmedPush.res

(CPID)

S-ConfirmedPush.ind

(CPID, PH, PB)

WTP Class 0

transaction

S-ConfirmedPush.req

(SPID, PH, PB)

client

S-SAP

server

S-SAP

S-ConfirmedPush.cnf

(SPID)

Source: Schiller

PH: Push Header

PB: Push Body

SPID: Server Push ID

CPID: Client Push ID

241

WAP Stack Summary

WDP

– functionality similar to UDP in IP networks

WTLS

– functionality similar to SSL/TLS (optimized for wireless)

WTP

– Class 0: analogous to UDP

– Class 1: analogous to TCP (without connection setup overheads)

– Class 2: analogous to RPC (optimized for wireless)

– features of “user acknowledgement”, “hold on”

WSP

– WSP/B: analogous to http 1.1 (add features of suspend/resume)

– method: analogous to RPC/RMI

– features of asynchronous invocations, push (confirmed/unconfirmed)

242

Wireless Application Environment

(WAE)

Goals

– device and network independent application

environment

– for low-bandwidth, wireless devices

– considerations of slow links, limited memory, low

computing power, small display, simple user interface

(compared to desktops)

– integrated Internet/WWW programming model

– high interoperability

243

WAE components

Architecture

– Application model, Microbrowser, Gateway, Server

User Agents

– WML/WTA/Others

– content formats: vCard, vCalendar, Wireless Bitmap, WML..

WML

– XML-Syntax, based on card stacks, variables, ...

WMLScript

– procedural, loops, conditions, ... (similar to JavaScript)

WTA

– telephone services, such as call control, text messages,

phone book, ... (accessible from WML/WMLScript)

Proxy (Method/Push)

244

Origin Servers

WAE: logical model

web

server

other content

server

Gateway Client

other

WAE

user agents

WML

user agent

WTA

user agent

Push proxy

encoded

request

request

encoded

response

with

content

response

with

content

push

content

encoded

push

content

Method proxy

encoders

&

decoders

245

WAP microbrowser

Optimized for wireless devices

Minimal RAM, ROM, Display, CPU and keys

Provides consistent service UI across devices

Provides Internet compatibility

Enables wide array of available content and applications

246

WML: Wireless Markup Language

Tag-based browsing

language:

– Screen management (text,

images)

– Data input (text, selection

lists, etc.)

– Hyperlinks & navigation

support

Takes into account

limited display,

navigation capabilities of

devices

Content (XML)

XSL Processor

HTTP Browser

HTML StyleSheet

WML Browsers

WML Stylesheet

247

WML

XML-based language– describes only intent of interaction in an abstract

manner

– presentation depends upon device capabilities

Cards and Decks– document consists of many cards

– User interactions are split into cards

– Explicit navigation between cards

– cards are grouped to decks

– deck is similar to HTML page, unit of content transmission

Events, variables and state mgmt

248

WML

The basic unit is a card. Cards are grouped together into Decks Document ~ Deck (unit of transfer)

All decks must contain

– Document prologue

• XML & document type declaration

– <WML> element

• Must contain one or more cards

<?xml version="1.0"?>

<!DOCTYPE WML PUBLIC "-//WAPFORUM//DTD WML 1.0//EN"

"http://www.wapforum.org/DTD/wml.xml">

<WML>

...

</WML>

WML File Structure

249

WML cards

Input

Elements

Deck

CardNavigatio

n

Variables

<WML>

<CARD>

<DO TYPE=“ACCEPT”>

<GO URL=“#eCard”/>

</DO

Welcome!

</CARD>

<CARD NAME=“eCard”>


<GO URL=“/submit?N=$(N)&S=$(S)”/>

</DO>

Enter name: <INPUT KEY=“N”/>

Choose speed:

<SELECT KEY=“S”>

<OPTION VALUE=“0”>Fast</OPTION>

<OPTION VALUE=“1”>Slow</OPTION>

<SELECT>

</CARD>

</WML>

250

Wireless Telephony Application

(WTA)

Collection of telephony specific extensions– designed primarily for network operators

Example– calling a number (WML)wtai://wp/mc;07216086415

– calling a number (WMLScript)WTAPublic.makeCall("07216086415");

Implementation– Extension of basic WAE application model

– Extensions added to standard WML/WMLScript browser

– Exposes additional API (WTAI)

251

WTA features

Extension of basic WAE application model

– network model for interaction

• client requests to server

• event signaling: server can push content to the client

– event handling

• table indicating how to react on certain events from the

network

• client may now be able to handle unknown events

– telephony functions

• some application on the client may access telephony

functions

252

WTA Interface

generic, high-level interface to mobile‟s telephony functions– setting up calls, reading and writing entries in

phonebook

WTA API includes– Call control

– Network text messaging

– Phone book interface

– Event processing

Security model: segregation– Separate WTA browser

– Separate WTA port

253

Placing an outgoing call with WTAI:

Input Element

WTAI Call

<WML>

<CARD>


<GO URL=“wtai:cc/mc;$(N)”/>

</DO>

Enter phone number:

<INPUT TYPE=“TEXT” KEY=“N”/>

</CARD>

</WML>

WTA Example (WML)

Source: WAP Forum

254

WTA Logical Architecture

other WTA

servers

Client

WAE

services

WTA

user agent

WAP Gateway

encoders

&

decoders

other telephone networks

WTA Origin Server

WTA & WML

server

WML

Scripts

WML

decks

WTA

services

mobile

network

firewallthird party

origin servers

network operator

trusted domain

Source: Schiller

255

WTA Framework Components

Source: Heijden

256

WTA User Agent

WTA User Agent

– WML User agent with extended functionality

– can access mobile device‟s telephony functions

through WTAI

– can store WTA service content persistently in a

repository

– handles events originating in the mobile network

257

WTA User Agent Context

Abstraction of execution space

Holds current parameters, navigation history, state of user agent

Similar to activation record in a process address space

Uses connection-mode and connectionless services offered by WSP

Specific, secure WDP ports on the WAP gateway

258

WTA Events

Network notifies device of event (such as

incoming call)

WTA events map to device‟s native events

WTA services are aware of and able to act on

these events

example: incoming call indication, call cleared,

call connected

259

WTA Repository

local store for content related to WTA services

(minimize network traffic)

Channels: define the service

– content format defining a WTA service stored in repository

– XML document specifying eventid, title, abstract, and

resources that implement a service

Resources: execution scripts for a service

– could be WML decks, WML Scripts, WBMP images..

– downloaded from WTA server and stored in repository

before service is referenced

Server can also initiate download of a channel

260

WTA Channels and Resources

Source: Heijden

261

WTA Interface (public)

for third party WML content providers

restricted set of telephony functions available to any WAE User Agent– library functions

• make call: allows application to setup call to a valid tel number

• send DTMF tones: send DTMF tones through the setup call

user notified to grant permission for service execution– cannot be triggered by network events

– example: Yellow pages service with “make call” feature

262

WTA Interface (network)

Network Common WTAI

– WTA service provider is in operator‟s domain

– all WTAI features are accessible, including the

interface to WTA events

– library functions

• Voice-call control: setup call, accept, release, send DTMF

tones

• Network text: send text, read text, remove text (SMS)

• Phonebook: write, read, remove phonebook entry

• Call logs: last dialed numbers, missed calls, received calls

• Miscellaneous: terminate WTA user agent, protect context

– user can give blanket permission to invoke a function

– example: Voice mail service

263

WTAI (network)

Network Specific WTAI

– specific to type of bearer network

– example: GSM: call reject, call hold, call transfer, join

multiparty, send USSD

264

WTA: event handling

Event occurrence

– WTA user agent could be executing and expecting

the event

– WTA user agent could be executing and a

different event occurs

– No service is executing

Event handling

– channel for each event defines the content to be

processed upon reception of that event

265

WTA: event binding

association of an event with the corresponding handler

(channel)

Global binding:

– channel corresponding to the event is stored in the repository

– event causes execution of resources defined by the channel

– example: voice mail service

Temporary binding:

– resources to be executed are defined by the already executing

service

– example: yellow pages lookup and call establishment

266

Event Handling (no service in

execution)

Source: Heijden

267

Event Handling (service already

execution)

1: Temporary binding exists

2. No temporary binding and context is protected

3: No temporary binding and context is not protectedSource: Heijden

268

WAP Push Services

Web push

– Scheduled pull by client (browser)

• example: Active Channels

– no real-time alerting/response

• example: stock quotes

Wireless push

– accomplished by using the network itself

• example: SMS

– limited to simple text, cannot be used as starting point for service

• example: if SMS contains news, user cannot request specific news

item

WAP push

– Network supported push of WML content

• example: Alerts or service indications

– Pre-caching of data (channels/resources)

269

WAP push framework

Source: Heijden

270

Push Access Protocol

Based on request/response model

Push initiator is the client

Push proxy is the server

Initiator uses HTTP POST to send push message to proxy

Initiator sends control information as an XML document, and content for mobile (as WML)

Proxy sends XML entity in response indicating submission status

Initiator can – cancel previous push

– query status of push

– query status/capabilities of device

271

Push Proxy Gateway

WAP stack (communication with mobile device)

TCP/IP stack (communication with Internet push

initiator)

Proxy layer does

– control information parsing

– content transformation

– session management

– client capabilities

– store and forward

– prioritization

– address resolution

– management function

272

Over the Air (OTA) Protocol

Extends WSP with push-specific functionality

Application ID uniquely identifies a particular application

in the client (referenced as a URI)

Connection-oriented mode

– client informs proxy of application IDs in a session

Connectionless mode

– well known ports, one for secure and other for non-secure push

Session Initiation Application (SIA)

– unconfirmed push from proxy to client

– request to create a session for a specific user agent and bearer

273

WAE Summary

WML and WML Script

– analogous to HTML and JavaScript (optimized for wireless)

– microbrowser user agent; compiler in the network

WTA

– WTAI: different access rights for different applications/agents

– WTA User Agent (analogy with operating systems)

• Context – Activation Record

• Channel – Interrupt Handler

• Resource – Shared routines invoked by interrupt handlers

• Repository – Library of interrupt handlers

– feature of dynamically pushing the interrupt handler before

the event

Push

– no analogy in Internet

274

Outline

Introduction and Overview


Mobile IP routing

TCP over wireless

GSM air interface

GPRS network architecture

Wireless application protocol

Mobile agents

Mobile ad hoc networks

275

Call to server procedure

DataClient Serverresults

Procedure

DataClient ServerProcedure

Client Server

Code on Demand

DataClient Serverresults

Procedure

Remote Evaluation

Structuring Distributed Applications

276

DataClient Server

DataServer

DataServer

Procedure+

State

DataServer

Procedure+

State

Procedure+

State

Procedure+

State

Mobile Agents

Procedure+

State

277

Interaction Model

Client Server

Request

Response

Client/server communication

Client Server

Request

Response

Mobile agent communication

Mobile agent

278

A generic Mobile Agent Framework

•Agent state

•Agent checkpoint(fault tolerance)

•Execution environment

•Communication (agent dispatching)

•Agent life cycle (creation, destruction)

•Event notification

•Agent collaboration support

•User identification

•Protection (agent, server)

•Authentication

Persistent Manager

Agent Manager

Event Manager

Security Manager

Mobile Agent

279

Comprehensive Question Paper

Paper Assembler

To Distribution Center

Cloning

= Paper Setter Nodes

= Install Agent

= Fetch Agent

1

6

4

2

5

Partial Question

Paper

3

Example: Student Examination Scenario

280

Dynamic Upgrade

281

Distribution

ServerExam Center

Distribution

Server

Single copy of paper

c9611060

Separate Copy per user

List of Students enrolled

…

…

Each Candidate get a Copy

1

4

3

2

Answered and Returned

5

Each copy returned

Example: Distribution and Testing

282

c9611060

Examiner B

Examiner A

Examiner D

Examiner C

Distributor

Results

…

…Agents collaborate to produce the final result

Objective Questions Evaluator

Distribution Server

Example: Evaluation and Results

283

Mobile Agents Summary

Appears to be a useful mechanism for

applications on mobile and wireless devices

– Reduce the network load

– Help in overcoming latency

– Execute asynchronously and autonomously

Several issues yet to be addressed

– Heavy frameworks

– Interoperability

– Security concerns

284

Outline

Introduction and Overview


Mobile IP routing

TCP over wireless

GSM air interface

GPRS network architecture

Wireless application protocol

Mobile agents

Mobile ad hoc networks

285

Multi-Hop Wireless

May need to traverse multiple links to reach destination

Mobility causes route changes

286

Mobile Ad Hoc Networks (MANET)

Host movement frequent

Topology change frequent

No cellular infrastructure. Multi-hop wireless links.

Data must be routed via intermediate nodes.

AB A

B

287

Many Applications

Ad hoc networks:

– Do not need backbone infrastructure support

– Are easy to deploy

– Useful when infrastructure is absent, destroyed or impractical

– Infrastructure may not be present in a disaster area or war zone

Applications:

– Military environments

– Emergency operations

– Civilian environments

• taxi cab network

• meeting rooms

• sports stadiums

288

MAC in Ad hoc Networks

IEEE 802.11 DCF is most popular– Easy availability

802.11 DCF:– Uses RTS-CTS to avoid hidden terminal problem

– Uses ACK to achieve reliability

802.11 was designed for single-hop wireless– Does not do well for multi-hop ad hoc scenarios

– Reduced throughput

– Exposed terminal problem

289

Exposed Terminal Problem

– A starts sending to B.

– C senses carrier, finds medium in use and has to

wait for A->B to end.

– D is outside the range of A, therefore waiting is not

necessary.

– A and C are “exposed” terminals

A B

CD

290

Routing Protocols

Proactive protocols– Traditional distributed shortest-path protocols

– Maintain routes between every host pair at all times

– Based on periodic updates; High routing overhead

– Example: DSDV (destination sequenced distance vector)

Reactive protocols– Determine route if and when needed

– Source initiates route discovery

– Example: DSR (dynamic source routing)

Hybrid protocols– Adaptive; Combination of proactive and reactive

– Example : ZRP (zone routing protocol)

291

Dynamic Source Routing (DSR)

Route Discovery Phase:– Initiated by source node S that wants to send packet to

destination node D

– Route Request (RREQ) floods through the network

– Each node appends own identifier when forwarding RREQ

Route Reply Phase:– D on receiving the first RREQ, sends a Route Reply (RREP)

– RREP is sent on a route obtained by reversing the route appended to received RREQ

– RREP includes the route from S to D on which RREQ was received by node D

Data Forwarding Phase:– S sends data to D by source routing through intermediate nodes

292

Route Discovery in DSR

B

A

S E

F

H

J

D

C

G

I

K

Z

Y

Represents a node that has received RREQ for D from S

M

N

L

293


B

A

S E

F

H

J

D

C

G

I

K

Represents transmission of RREQ

Z

YBroadcast transmission

M

N

L

[S]

[X,Y] Represents list of identifiers appended to RREQ

294


B

A

S E

F

H

J

D

C

G

I

K

• Node H receives packet RREQ from two neighbors:

potential for collision

Z

Y

M

N

L

[S,E]

[S,C]

295


B

A

S E

F

H

J

D

C

G

I

K

• Node C receives RREQ from G and H, but does not forward

it again, because node C has already forwarded RREQ once

Z

Y

M

N

L

[S,C,G]

[S,E,F]

296


B

A

S E

F

H

J

D

C

G

I

K

Z

Y

M

• Nodes J and K both broadcast RREQ to node D

• Since nodes J and K are hidden from each other, their

transmissions may collide

N

L

[S,C,G,K]

[S,E,F,J]

297


B

A

S E

F

H

J

D

C

G

I

K

Z

Y

• Node D does not forward RREQ, because node D

is the intended target of the route discovery

M

N

L

[S,E,F,J,M]

298

Route Reply in DSR

B

A

S E

F

H

J

D

C

G

I

K

Z

Y

M

N

L

RREP [S,E,F,J,D]

Represents RREP control message

299

Data Delivery in DSR

B

A

S E

F

H

J

D

C

G

I

K

Z

Y

M

N

L

DATA [S,E,F,J,D]

Packet header size grows with route length

300

TCP in MANET

Several factors affect TCP in MANET:

Wireless transmission errors

– reducing congestion window in response to errors

is unnecessary

Multi-hop routes on shared wireless medium

– Longer connections are at a disadvantage

compared to shorter connections, because they

have to contend for wireless access at each hop

Route failures due to mobility

301

MANET Summary

Routing is the most studied problem

Interplay of layers is being researched

Large number of simulation based expts

Small number of field trials

Very few reported deployments

Fertile area for imaginative applications– Standardizing protocols does not seem to be a

very good idea

– Scope for proprietary solutions with limited interop

302

References

J. Schiller, “Mobile Communications”, Addison Wesley, 2000

802.11 Wireless LAN, IEEE standards, www.ieee.org

Mobile IP, RFC 2002, RFC 334, www.ietf.org

TCP over wireless, RFC 3150, RFC 3155, RFC 3449

A. Mehrotra, “GSM system engineering”, Artech House, 1997

Bettstetter, Vogel and Eberspacher, “GPRS: Architecture, Protocols

and Air Interface”, IEEE Communications Survey 1999, 3(3).

M.v.d. Heijden, M. Taylor. “Understanding WAP”, Artech House, 2000

Mobile Ad hoc networks, RFC 2501

Others websites:

– www.palowireless.com

– www.gsmworld.com; www.wapforum.org

– www.etsi.org; www.3gtoday.com

47673761 mobileinternet tomai romana 2010[1]

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