mobileinternet tomai-romana-2010
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Sisteme mobile in Internet
(Arhitectura si aplicatiile retelelor mobile)
Nicolae Tomai
FSEGA
nicolae.tomai@econ.ubbcluj.ro
http://www.econ.ubbcluj.ro/~nicolae.tomai
449
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
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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
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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
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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
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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
Public 802.11Wireless Carrier
Market consolidation Entry of Wireless Carriers Entry of new players Footprint growth
Source: Pravin Bhagwat
48
Spectrum War: Steady StateEnterprise 802.11Network
Public 802.11Wireless Carrier
Virtual Carrier
Emergence of virtual carriers
Roaming agreements
Source: Pravin Bhagwat
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
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)
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
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)
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
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)
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
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)
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)
158
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)
162
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
176
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
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)
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
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)
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
(SA, SP, DA, DP, A, UD, C=1, H) TR-Invoke.ind
(SA, SP, DA, DP, A, UD, C=1, H„)
initiator
TR-SAP
responder
TR-SAP
TR-Invoke.res
(H„)TR-Invoke.cnf
(H)
TR-Invoke.req
(SA, SP, DA, DP, A, UD, C=1, H) TR-Invoke.ind
(SA, SP, DA, DP, A, UD, C=1, H„)
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
(SA, SP, DA, DP, A, UD, C=2, H) TR-Invoke.ind
(SA, SP, DA, DP, A, UD, C=2, H„)
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
(SA, SP, DA, DP, A, UD, C=2, H) TR-Invoke.ind
(SA, SP, DA, DP, A, UD, C=2, H„)
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”>
<DO TYPE=“ACCEPT”>
<GO URL=“/submit?N=$(N)&S=$(S)”/>
</DO>
Enter name: <INPUT KEY=“N”/>
Choose speed:
<SELECT KEY=“S”>
<OPTION VALUE=“0”>Fast</OPTION>
<OPTION VALUE=“1”>Slow</OPTION>
<SELECT>
</CARD>
</WML>
250
Wireless Telephony Application
(WTA)
Collection of telephony specific extensions– designed primarily for network operators
Example– calling a number (WML)wtai://wp/mc;07216086415
– calling a number (WMLScript)WTAPublic.makeCall("07216086415");
Implementation– Extension of basic WAE application model
– Extensions added to standard WML/WMLScript browser
– Exposes additional API (WTAI)
251
WTA features
Extension of basic WAE application model
– network model for interaction
• client requests to server
• event signaling: server can push content to the client
– event handling
• table indicating how to react on certain events from the
network
• client may now be able to handle unknown events
– telephony functions
• some application on the client may access telephony
functions
252
WTA Interface
generic, high-level interface to mobile‟s telephony functions– setting up calls, reading and writing entries in
phonebook
WTA API includes– Call control
– Network text messaging
– Phone book interface
– Event processing
Security model: segregation– Separate WTA browser
– Separate WTA port
253
Placing an outgoing call with WTAI:
Input Element
WTAI Call
<WML>
<CARD>
<DO TYPE=“ACCEPT”>
<GO URL=“wtai:cc/mc;$(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
Wireless LANs: IEEE 802.11
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
Wireless LANs: IEEE 802.11
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
Route Discovery in DSR
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
Route Discovery in DSR
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
Route Discovery in DSR
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
Route Discovery in DSR
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
Route Discovery in DSR
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
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