Mobileinternet tomai-romana-2010

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  • 1. Sisteme mobile in Internet (Arhitectura si aplicatiile retelelor mobile) Nicolae Tomai FSEGA nicolae.tomai@econ.ubbcluj.rohttp://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) 2
  • 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 3
  • 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. 4
  • 5. Dispozitive mobile TabletsPalm-sized Clamshell handhelds Laptop computers Net–enabled mobile phones
  • 6. 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
  • 7. Evolutia telefoanelor mobile 7
  • 8. Spectrul alocat pentru telefoanele mobileSursa: (S60 Programming A Tutorial Guide Paul Coulton, 8Reuben Edwards With Helen Clemson)
  • 9. Elemente componente ale unui sistem de telefonie mobila 9
  • 10. FDMA(Frecvency Division Multiple Access)(1G) 10
  • 11. TDMA(Time Division Multiple Access)(2G) 11
  • 12. 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
  • 13. CDMA(Code Division Multiple Access) 13
  • 14. Sistemul GPRS•SGSN(Serving GPRS Support Node) controlează transmiterea pachetelorde date prin întreaga reţea şi•GGSN(Gateway GPRS Support Node) care are rolul de a conecta reţeauade telefonie mobilă la infrastructura Internetului. 14
  • 15. Alocarea frecventelor in 3G 15
  • 16. 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
  • 17. W-CDMA in sistemul GSM/GPRS 17
  • 18. Evolutia spre 4G 18
  • 19. 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.) 20
  • 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 21
  • 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 22
  • 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 23
  • 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 HLR La alte VLR MSC-uri VLR PSTN PSTN 24
  • 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 25
  • 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 26
  • 27. Termenul de hand-off(predare –preluare) se referă la procesul de transfer al unuiapel 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 27
  • 28. Efectul mobilitatii asupra stivei de protocoale Aplicatie – Aplicatii noi si adaptari Transport – Controlul congestiei si al fluxului Retea – Adresarea si rutarea Link – Accesul la mediu si trecerea de la o celula la alta (hand-off) Fizic – Transmisia, erorile si interferenta 28
  • 29. Aplicatii mobile(1) Vehicule – Transmisia de noutati, conditii de drum, etc. – Retele ad-hoc cu vehicule apropiate pentru prevenirea accidentelor Urgente – Transmiterea rapidă la spital a datelor pacienţilor – Retele ad-hoc in caz de cutremure sau dezastre naturale – militare ... 29
  • 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 si dependente de locatie Localizarea serviciilor – Gasirea serviciilor in mediul local 30
  • 31. Aplicatii mobile(3) Servicii de informare – Cotatii bursiere, etc. – Vremea Operatii deconectate – Agenti mobili, cumparaturi, etc. Divertisment – Retele ad-hoc pentru jocuri multi-utilizator Mesagerie 31
  • 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 …. 32
  • 33. Latimea de banda si aplicatiile UMTS EDGE GPRS, CDMA 2000 CDMA 2.5G 2G Speed, kbps 9.6 14.4 28 64 144 384 2000Transaction Processing Messaging/Text Apps Voice/SMS Location Services Still Image Transfers Internet/VPN Access Database Access Document Transfer Low Quality Video High Quality Video 33
  • 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 34
  • 35. GSM to GPRS Resursele radio sunt alocate numai pentru unul sau mai multe(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 spre pachete – 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 pe cele de semnalizare ca GSM 35
  • 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 36
  • 37. Evolution to 3G Technologies 2G 3GIS-95B cdma2000CDMA FDDGSM W-CDMA TDD GPRS EDGE & 136 HS outdoorIS-136 136 HS UWC-136TDMA indoor 37
  • 38. Tehnologii fara fir 802.11n >150 Mbps 802.11n70 Mbps 802.16(WiMax)54 Mbps 802.11{a,b}5-11 Mbps 802.11b .11 p-to-p link1-2 Mbps Bluetooth 802.11 µwave p-to-p links 4G 3G384 Kbps WCDMA, CDMA2000 2G56 Kbps IS-95, GSM, CDMA Interior Exterior Exterior Exterior pe Distanta pe dist medie dist. mare lunga 10 – 30m 50 – 200m 200m – 4Km 5Km – 20Km 20m – 50Km 38
  • 39. Comparatie intre tehnologii Covearge 10 3G -HSPA WiFi 8 LTE 6 WiMAX 4 QoS Data rate 2 0 Mobility Cost effectiveness per bitLTE (Long Term Evolution)-4G 39
  • 40. Arhitectura retelei 3G Core Network Wireless Telephone Access Network Programmable Network Gateway Mobile Access Softswitch Router Application IP Intranet Server Access (HLR) IP Intranet IP Point User Profiles & Base Stations Authentication 802.11 802.11 3G Air Wired Access InternetInterface Access Point 40
  • 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) 41
  • 42. Topologiile retelelor fara fir(infrastructura si Adhoc)infrastructure network AP: Access Point AP AP wired network APad-hoc network 42 Source: Schiller
  • 43. Difference Between Wired and Wireless Ethernet LAN Wireless LAN B A B C A C 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. 43
  • 44. Hidden Terminal Problem A B C– 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. 44
  • 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 45
  • 46. Spectrum War: Status todayEnterprise 802.11 Wireless Carrier Public 802.11Network 46 Source: Pravin Bhagwat
  • 47. Spectrum War: EvolutionEnterprise 802.11 Wireless Carrier Public 802.11Network  Market consolidation  Entry of Wireless Carriers  Entry of new players  Footprint growth 47 Source: Pravin Bhagwat
  • 48. Spectrum War: Steady StateEnterprise 802.11 Wireless Carrier Public 802.11Network Virtual Carrier  Emergence of virtual carriers  Roaming agreements 48 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 miscarea hostului – 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) 49
  • 50. IP-ul mobil: Ideea de baza MN RouterS 3 Home agentRouter Router 1 2 50 Source: Vaidya
  • 51. IP mobil: ideea de baza miscare RouterS MN 3 Foreign agent Home agentRouter Router Pachetele sunt tunelate utilizind IP in IP 1 2 51 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 52
  • 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 53
  • 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 longermobile host access point (foreign agent) „wired“ Internet „wireless“ TCP standard TCP 54 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 55
  • 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 56
  • 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). 57
  • 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 58
  • 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) 59
  • 60. Proxi Web in WebExpress The WebExpress Intercept Model 60 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 61
  • 62. WAP: elementele componente fixed network wireless network HTML WML WAP Binary WMLInternet filter proxy HTML WML HTML filter/ Binary WML WAP web HTML proxy server WTA Binary WML server PSTN Binary WML: binary file format for clients 62 Source: Schiller
  • 63. WAP: modelul de referinta Internet A-SAP WAP HTML, Java Application Layer (WAE) Servicii aditionale si aplicatii S-SAP Session Layer (WSP) HTTP TR-SAP Transaction Layer (WTP) SEC-SAP SSL/TLS Security Layer (WTLS) T-SAP TCP/IP, Transport Layer (WDP) WCMP UDP/IP, media Purtatoarele (GSM, CDPD, GPRS ...)WAE comprises WML (Wireless Markup Language), WML Script, WTAI etc. 63 Source: Schiller
  • 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) 64
  • 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 65
  • 66. Mobile Agents: Exemplu 66
  • 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) 67
  • 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 68
  • 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 69
  • 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 70
  • 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 RTS RTS D A B C CTS CTS DATA 71
  • 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 72
  • 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 stationsad-hoc network BSS1 BSS2 73
  • 74. 802.11 - ad-hoc network (DCF) 802.11 LANSTA1  Direct communication BSS1 STA3 within a limited range – Station (STA): terminal with access STA2 mechanisms to the wireless medium – Basic Service Set (BSS): BSS2 group of stations using the same radio frequency STA5 STA4 802.11 LAN 74 Source: Schiller
  • 75. 802.11 - infrastructure network (PCF) Station (STA) 802.11 LAN – terminal with access 802.x LAN mechanisms to the wireless medium and radio contact toSTA1 the access point BSS1 Basic Service Set (BSS) Portal Access – group of stations using the Point same radio frequency Distribution System Access Point Access – station integrated into theESS Point wireless LAN and the distribution system BSS2 Portal – bridge to other (wired) networks Distribution System STA2 STA3 802.11 LAN – interconnection network to form one logical network (EES: Extended Service Set) based on several BSS 75 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) 76
  • 77. 802.11- in the TCP/IP stack fixed terminalmobile terminal server infrastructure network access pointapplication application TCP TCP IP IP LLC LLC LLC802.11 MAC 802.11 MAC 802.3 MAC 802.3 MAC802.11 PHY 802.11 PHY 802.3 PHY 802.3 PHY 77
  • 78. 802.11 - Layers and functions  MAC  PLCP Physical Layer Convergence Protocol – access mechanisms, fragmentation, encryption – clear channel assessment signal (carrier sense)  MAC Management – synchronization, roaming,  PMD Physical Medium Dependent MIB, power management – modulation, coding  PHY Management Station Management – channel selection, MIB LLC  Station ManagementDLC MAC MAC Management – coordination of all management functions PLCPPHY PHY Management PMD 7.8.1 78
  • 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 79
  • 80. Spread-spectrum communications 80 Source: Intersil
  • 81. DSSS Barker Code modulation 81 Source: Intersil
  • 82. DSSS properties 82 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 83
  • 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) 84
  • 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 RTS RTS D A B C CTS CTS DATA ACK 85
  • 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 86
  • 87. 802.11 - CSMA/CA contention window DIFS DIFS (randomized back-off mechanism) medium busy next frame direct access if t medium is free  DIFS slot time– 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) 87
  • 88. 802.11 –CSMA/CA example DIFS DIFS DIFS DIFS boe bor boe bor boe busystation1 boe busystation2 busystation3 boe busy boe borstation4 boe bor boe busy boe borstation5 t busy medium not idle (frame, ack etc.) boe elapsed backoff time packet arrival at MAC bor residual backoff time 88
  • 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 89
  • 90. DCF Example B1 = 25 B1 = 5 wait data data wait B2 = 20 B2 = 15 B2 = 10 B1 and B2 are backoff intervalscw = 31 at nodes 1 and 2 90
  • 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 91
  • 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 DIFS datasender SIFS ACKreceiver DIFSother datastations t waiting time contention 92
  • 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 DIFS RTS datasender SIFS SIFS CTS SIFS ACKreceiver NAV (RTS) DIFSother NAV (CTS) datastations t defer access contention 93
  • 94. Fragmentation DIFS RTS frag1 frag2sender SIFS SIFS SIFS CTS SIFS ACK1 SIFS ACK2receiver NAV (RTS) NAV (CTS) NAV (frag1) DIFSother NAV (ACK1) datastations t contention 94
  • 95. 802.11 - Point Coordination Function 95
  • 96. 802.11 - PCF I t0 t1 SuperFrame medium busy PIFS SIFS SIFS D1 D2pointcoordinator SIFS SIFS U1 U2wirelessstationsstations„ NAVNAV 96
  • 97. 802.11 - PCF II t2 t3 t4 PIFS SIFS D3 D4 CFendpointcoordinator SIFS U4wirelessstationsstations„ NAVNAV contention free period contention t period 97
  • 98. CFP structure and Timing 98
  • 99. PCF- Data transmission 99
  • 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 100
  • 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 101
  • 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, databytes 2 2 6 6 6 2 6 0-2312 4 Frame Duration Address Address Address Sequence Address Data CRC Control ID 1 2 3 Control 4 version, type, fragmentation, security, ... 102
  • 103. Frame Control Field 103
  • 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 104
  • 105. MAC address formatscenario to DS from address 1 address 2 address 3 address 4 DSad-hoc network 0 0 DA SA BSSID -infrastructure 0 1 DA BSSID SA -network, from APinfrastructure 1 0 BSSID SA DA -network, to APinfrastructure 1 1 RA TA DA SAnetwork, within DS DS: Distribution System AP: Access Point DA: Destination Address SA: Source Address BSSID: Basic Service Set Identifier RA: Receiver Address TA: Transmitter Address 105
  • 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 106
  • 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 107
  • 108. Synchronization using a Beacon (infrastructure) beacon interval B B B Baccesspoint busy busy busy busymedium t value of the timestamp B beacon frame 108
  • 109. Synchronization using a Beacon (ad- hoc) beacon interval B1 B1station1 B2 B2station2 busy busy busy busymedium t value of the timestamp B beacon frame random delay 109
  • 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?) 110
  • 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 111
  • 112. Power saving with wake-up patterns (infrastructure) TIM interval DTIM interval D B T T d D Baccesspoint busy busy busy busymedium p dstation t T TIM D DTIM awake B broadcast/multicast p PS poll d data transmission to/from the station 112
  • 113. Power saving with wake-up patterns (ad-hoc) ATIM window beacon interval B1 A D B1station1 B2 B2 a dstation2 t B beacon frame random delay A transmit ATIM D transmit data awake a acknowledge ATIM d acknowledge data 113
  • 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 114
  • 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 115
  • 116. 802.11 current status 802.11i LLC security WEP MAC 802.11f MAC MgmtInter Access Point Protocol 802.11e MIB QoS enhancements PHY DSSS FH IR OFDM 802.11b 5,11 Mbps 802.11a 6,9,12,18,24 802.11g 36,48,54 Mbps 20+ Mbps 116
  • 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 117
  • 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) 118
  • 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 119
  • 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 miscarea hostului – 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) 120
  • 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, … 121
  • 122. IP-ul mobil: Ideea de baza MN(mobile RouterS(sender) Node) 3 Home agent Router Router 1 2 122 Source: Vaidya
  • 123. IP mobil: ideea de baza miscare RouterS MN 3 Foreign agent Home agentRouter Router Pachetele sunt tunelate utilizind IP in IP 1 2 123 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 ) 124
  • 125. Transferul datelor la sistemul mobil HA 2 MNReteaua proprie 3 Receptor(home network) Internet (receiver) FA foreign network 1 1. Emitatorul trimite la adresa IP a nodului CN mobil MN, iar HA intercepteaza pachetele (proxy ARP) 2. HA tuneleaza pachetele la COA, aici FA, Emitator(sender) prin incapsulare 3. FA trimite pachetele mai departe la MN 125 Soursa: Schiller
  • 126. Transferul datelor de la sistemul mobil Agent propriu HA-home agent 1 MNRetea proprie Emitator(home network) Internet (sender) FA Retea straina (foreign network) 1. Emitatorul trimite la adresa IP a CN a receptorului;de obicei FA lucreaza ca si un router implicit Receptor(receiver) 126 Source: Schiller
  • 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 127
  • 128. Agentul de averizare0 7 8 15 16 23 24 31 type code checksum#addresses addr. size lifetime router address 1 preference level 1 router address 2 preference level 2 ... type length sequence number registration lifetime R B H F M G V reserved COA 1 COA 2 ... 128
  • 129. Inregistrarea(registration) MN FA HA MN HA tt 129
  • 130. Cererea de inregistrare(Registration request) 0 7 8 15 16 23 24 31 type S B DMG V rsv lifetime home address home agent COA identification extensions . . . 130
  • 131. Incapsularea IP-in-IP Incapsularea IP-in-IP- (obligatorie in RFC 2003) – tunel intre HA si COA ver. IHL TOS length IP identification flags fragment offset TTL IP-in-IP IP checksum IP address of HA Care-of address COA ver. IHL TOS length IP identification flags fragment offset TTL lay. 4 prot. IP checksum IP address of CN IP address of MN TCP/UDP/ ... payload 131
  • 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. 132
  • 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) 133
  • 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) 134
  • 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 135
  • 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 Fereastra emitatorului 1 2 3 4 5 6 7 8 9 10 11 12 13 Ack-urile primite Ne transmise 136
  • 137. Comportamentul de baza TCP 14 Evitarea congestieiCongestion Window size 12 10 (segments) 8 Nivelul startului 6Startul incet incet 4 2 0 0 1 2 3 4 5 6 7 8 Time (round trips) Exemplul presupune ca ACK-urile nu sunt intirziate 137
  • 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 138
  • 139. TCP dupa timeout Dupa timeout Fereastra deCongestion window (segments) 25 congestie(cwnd) =20 20 15 10 Nivelul startului Nivelul startului incet 5 Incet ssthresh = 10 ssthresh = 8 0 12 15 20 22 25 0 3 6 9 Time (round trips) 139
  • 140. TCP dupa retransmisia rapida Dupa recuperarea rapida 10Window size (segments) Fereastra initiata de receptor 8 6 4 2 0 0 2 4 6 8 10 12 14 Time (round trips) Dupa retransmisia rapida si recuperarea rapida dimensiunea ferestrei este redusa la jumatate. 140
  • 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) 141
  • 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 BS MH Host fix Statia de baza Hostul mobil 142
  • 143. I-TCP: Consideratii privind splitarea conexiunii Starea conexiunii prin-TCP Conexiunea TCP Conexiunea TCP application application application rxmt transport transport transport network network network link link link physical physical physical Fara fir(wireless) 143
  • 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 BS MH 144
  • 145. Protocol snoop Starea conexiunii prin TCP TCP connectionapplication application applicationtransport transport transportnetwork network network rxmtlink link linkphysical physical physical FH BS MH wireless 145
  • 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 146
  • 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(?) Ack 999 Ack 1000 FH BS MH 147
  • 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” 148
  • 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) Mobile TCP receiver FH BS MH 149
  • 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) 150
  • 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) 151
  • 152. GSM: ArhitecturaPSTN-Public Switched Telephone Network,ISDN-Integrated Services Digital Network, PDN-Packet Data Network 152
  • 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 153 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 154
  • 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 155
  • 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 156
  • 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 utilizata Gaussian Minimum Shift Keying (GMSK) 157
  • 158. 158
  • 159. Bursts Building unit of physical channel Types of bursts – Normal – Synchronization – Frequency Correction – Dummy – Access 159
  • 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 160
  • 161. Air Interface: Logical Channel Traffic Channel (TCH) Signaling Channel – Broadcast Channel (BCH) – Common Control Channel (CCH) – Dedicated/Associated Control Channel (DCCH/ACCH) 161
  • 162. 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 163
  • 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) 164
  • 165. Speech 20 ms 20 ms Speech Coder Speech Coder 260 260 Channel Encoding Channel Encoding 456 bit 456 bit Interleaving 1 2 3 4 5 6 7 8 NORMAL BURST 3 57 1 26 1 57 3 8.25Out of first 20 ms 165 Out of second 20ms
  • 166. Traffic Channel Structure for Full Rate CodingSlots 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 Bursts for Users allocated in Slot 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 T T T T T S T T T T I T = Traffic S = Signal( contains information about the signal strength in neighboring cells) 166
  • 167. Slots 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 Burst for one users 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 Bursts for another users allocated in alternate T 1 2 Slots4 5 6 T 3 7 8 9 10 11 12 13 14 15 16 17 26 T T T T T T T T S = T Traffic Channel Structure for Half Rate Coding 167
  • 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) 168
  • 169. FCCH & SCH  Frequency Correction Channel – Repeated broadcast of FB  Synchronization Channel – Repeated broadcast of SB – Message format of SCHPLMN color BS color T1 Superframe T2 multiframe T3 block frame3 bits 3 bits index 11 bits index 11 bits index 3bits BSIC 6 bits" FN 19bits 169
  • 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 170
  • 171. AGCH & PCH Access Grant Channel (AGCH) – BTS to MS – Assign an SDCCH/TCH to MS Paging Channel (PCH) – BTS to MS – Page MS 171
  • 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) 172
  • 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) 173
  • 174. Select the channel withPower On Scan Channels, highest RF level among monitor RF levels the control channels Scan the channel for the FCCH Select the channel with NO next highest Rf level Is from FCCH detected? the control list. YES Scan channel for SCH NO Is SCH detected? YES Read data from BCCH and determine is it BCCH? From the channel data NO Is update the control the current BCCH channel list channel included? YES Camp on BCCH and start decoding 174
  • 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 175
  • 176. 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 177
  • 178. GSM call routing 1. MSISDN LA2 ISDN 4. MSRN BSCMS GMSC/I WF BTS 2. MSISDN MSC 3. MSRN 7. TMSI 7. TMSI EIR BSC AUC HLR VLR BTS LA1 7. TMSI 5. MSRN BTS 6. TMSI MS 8. TMSI 178
  • 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 179
  • 180. 1 Hyper frame = 2048 Super frames =2715648 TDMA frames ( 28 min 53 sec 760 ms) 3h 0 1 2 3 2045 2046 2047 1 Super frame = 1326 TDMA frames (6.12s) = 51(26 frames) Multi frame 0 12 3 5 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 ) 0 1 2 3 = 2 6 (5 1 fra m e s ) M u lti fra m e 2 24 2 3 5 1(26 frames) Multi frame = 26 TDMA frames (120 ms) 1 (5 1 fra m e s ) M u lti fra m e = 5 1 T D M A fra m e s (3 0 6 0 /1 3 m s ) T12 T23 I 0 1 2 3 49 50T0 T1 T2 (SACCH ) 1 T D M A f r a m e o r 4 .6 1 5 m s ) 2 0 /2 6 = 8 tim e s lo ts (1 0 1 2 3 4 5 6 7 n ( 1 5 /2 6 o r 0 .5 7 7 m s ) 1 tim e s lo t = 1 5 6 .2 5 b it d u r a tio ( 1 b i t d u r a t i o n = 4 8 / 1 3 o r 3 . 6 9 s ) 180
  • 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) 181
  • 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 182
  • 183. Architectura GPRS 183
  • 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 184
  • 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 185
  • 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 186
  • 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 187
  • 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 188
  • 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 189
  • 190. Planurile transmisiei in GPRS 190
  • 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 191
  • 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 192
  • 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 193
  • 194. Modelul starilor MS  În starea de repaus(IDLE) MS nu este accesibilă  Cu GPRS atach MS trece în starea READY- gata  Cu detach, acesta revine la starea Idle: toate contextele PDP sunt sterse  Stare de aşteptare (Standby) este atinsa atunci când MS nu trimite date pentru o perioadă lungă de timp şi timer pentru pregatit 194 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 195
  • 196. GPRS - Rutarea 196
  • 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 197
  • 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 198
  • 199. Integrarea retelelorNetwork of Networks Services and Applications Wireline Interworking DSL/modem Mobility Media Access Systems Management Roaming IP Based Core Networks cellular WLAN Short Range Connectivity199
  • 200. Everyday Usage Scenarios Internet Out of Town Wi-Max In the officeWi-Fi Ethernet Wi-Fi In the car Cellular Wi-Fi AP3 Wi-Fi Wi-Fi AP2 AP1 200
  • 201. Emergency Response Scenario Satellite 3G 3G Satellite WiFi201
  • 202. Military Usage Scenario Satcom Satcom WiMax Satcom GPRS WiMax WiMax 3G “Always Best Connected”202
  • 203. Mobility Granularity Horizontal Handover A handover is initiated when mobile device exits the boundaries of an administrative domain. Single interface is used. Vertical Handover A mobile device does need to move in order to initiate a handover. Multiple interfaces are required, but use one interface at a time. Multiple Interface Management Simultaneous use of multiple interfaces and access networks. Association of an application with an interface Multiple Flow Management Ability to split individual flows between links with respect to the requirements of the flows and the user preferences203
  • 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. 204
  • 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.205
  • 206. Access ScalabilityWide variety of access network technologies including cellular(2G, 2.5G, 3G), wireless (Wi-Fi, Wi-Max, Bluetooth, UWB) andwired (DSL, cable modems, Ethernet)206
  • 207. Industry and Standards Activities HigherInternet Engineering Task Force Session Initiation Protoc Layer 3 UMA Technology Layers– Detecting Network Attachment IP IEEE 802 Processing Layer 2 Triggers Layer 2– Mip4 Multimedia  IEEE 802.21 Mobile IP version 6 Subsystem Media Independent– Mip6 Mobile IP version 4 Handovers– Mipshop  IEEE 802.11r MIPv6 signaling and Handoff Optimization IEEE 802.11 Fast– Mobopts handovers IP Mobility optimizations research group No IEEE 802.11u interface! single standard– Nemo Interworking with external Network Mobility networks  IEEE 802.20 Mobile broadband wireless access FMCA NOKIA207 KT
  • 208. Cross-Layer Protocol Interactions Access Application Layer Media Applications SIP Policy Transport Layer SCTP Profile Manager Network Layer Mobile IPHandover Layer Mobility Decision MACCellular Performance Measure.: QOS, ACK What are the mobility architectures considered? PHY Link measurements: RSSI, Noise, Interference 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? 208
  • 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) 209
  • 210. Mobilitatea Mobilitatea • stationar • nomadic (mers la pas pe jos) • mobil (vioteza unui vehicul) • roaming (mobilatea intre retele) ConnectivitateaCapacitatea nodurilor • connectatedispozitivelor mobile • semi-connecte• tipulsi caracteristicile (asimmetric)• Interfata grafica utilizator • disconnectate(Graphics User Interface-GUI• multimedia• multimedia in timp real 210
  • 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 211
  • 212. HTTP/HTMLCapacitatea mare de transport si capacitatea mica Internet Wireless network <HTML> HTTP/HTML <WML> <CARD> WAP <HEAD> <TITLE>NNN Interactive</TITLE> <DO TYPE="ACCEPT"> <META HTTP-EQUIV="Refresh" CONTENT="1800, <GO URL="/submit?Name=$N"/> URL=/index.html"> </DO> </HEAD> Enter name: <BODY BGCOLOR="#FFFFFF" <INPUT TYPE="TEXT" KEY="N"/> BACKGROUND="/images/9607/bgbar5.gif" LINK="#0A3990" </CARD> ALINK="#FF0000" VLINK="#FF0000" TEXT="000000" </WML> 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> Content encoding <HTML> 010011 <HEAD> 010011 <TITLE 110110 >NNN 010011 Intera 011011 ctive< 011101 /TITLE 010010 > 011010 <META HTTP- EQUIV= "Refre sh" CONTEN T="180 0, URL=/i ndex.h tml"> 212 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 213
  • 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 214
  • 215. Internet model HTML HTTP TLS/SSL TCP/IP 215
  • 216. Architectura WAPClient Web Server WAP Gateway WML cu scripturi WML Codificator WML Scripturi Punti WML WML- WSP/WTP HTTP CGI, etc. Script Compilator pentru scripturi WML WTAI Adaptor/e de protocol Continut Etc. 216 Source: WAP Forum
  • 217. Serverul de aplicatie WAPClient Serverul WAP de aplicatie WML Codificator WML cu script WML Puntile WML Logica Script WSP/WTP WMLScript aplicatiei WML- Compiler WTAI Adaptoare de protocol Continut Etc. 217 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 218
  • 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. 219
  • 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 UDPCodarea continutului, optimizarea lăţimii de bandă a canalelor de banda ingusta, simplificarea dispozitivelor 220
  • 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 221
  • 222. WDP: primitive de serviciu T-SAP T-SAPT-DUnitdata.req(DA, DP, SA, SP, UD) T-DUnitdata.ind (SA, SP, UD)T-DUnitdata.req(DA, DP, SA, SP, UD)T-DError.ind SAP: Service Access Point(EC) DA: Destination Address DP: Destination Port SA: Source Address SP: Source Port UD: User Data EC: Error Code 222 Source: Schiller
  • 223. Servicii, protocoale, purtatoare: exemple WAP pentru GSM cu circuite comutate WAP Mobile Proxy/Server WAE WAE Apps on Other Servers WSP WSP IWF ISP/RAS WTP WTP UDP UDP IP IP IP PPP PPP CSD-RF CSD- PSTN PSTN Subretea Subretea RF Circuit CircuitRAS - Remote Access ServerIWF - InterWorking Function 223 Source: WAP Forum
  • 224. Servicii, protocoale, purtatoare: exemple WAP per GSM pentru SMS(Short Message Service) WAP Mobile Proxy/Server WAE WAE Apps on other servers WSP WSP WTP SMSC WTP WDP WDP SMS SMS WDP Tunnel WDP Tunnel Protocol Protocol Subretea Subretea 224 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) 225
  • 226. WTLS: securizarea sesiunii, dialogul complet originator peer SEC-SAP SEC-SAPSEC-Create.req(SA, SP, DA, DP, KES, CS, CM) SEC-Create.ind (SA, SP, DA, DP, KES, CS, CM) SEC-Create.res (SNM, KR, SID, KES„, CS„, CM„)SEC-Create.cnf SEC-Exchange.req(SNM, KR, SID, KES„, CS„, CM„) KES: Key Exchange SuiteSEC-Exchange.ind CS: Cipher SuiteSEC-Exchange.res CM: Compression Mode(CC) SNM: Sequence Number ModeSEC-Commit.req SEC-Exchange.cnf (CC) SEC-Commit.indSEC-Commit.cnf KR: Key Refresh Cycle SID: Session Identifier CC: Client Certificate 226 Source: Schiller
  • 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 227
  • 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 228
  • 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 229
  • 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 230
  • 231. WTP Class 0 Transaction initiator responder TR-SAP TR-SAPTR-Invoke.req(SA, SP, DA, DP, A, UD, C=0, H) TR-Invoke.ind (SA, SP, DA, DP, A, UD, C=0, H„) A: Acknowledgement Type (WTP/User) C: Class (0,1,2) H: Handle (socket alias) 231 Source: Schiller
  • 232. WTP Class 1 Transaction, no user ack & user ack initiator responder TR-SAP TR-SAPTR-Invoke.req(SA, SP, DA, DP, A, UD, C=1, H) TR-Invoke.ind (SA, SP, DA, DP, A, UD, C=1, H„)TR-Invoke.cnf(H) initiator responder TR-SAP TR-SAPTR-Invoke.req(SA, SP, DA, DP, A, UD, C=1, H) TR-Invoke.ind (SA, SP, DA, DP, A, UD, C=1, H„) TR-Invoke.res (H„)TR-Invoke.cnf(H) 232 Source: Schiller
  • 233. WTP Class 2 Transaction, no user ack, no hold on initiator responder TR-SAP TR-SAPTR-Invoke.req(SA, SP, DA, DP, A, UD, C=2, H) TR-Invoke.ind (SA, SP, DA, DP, A, UD, C=2, H„) TR-Result.req (UD*, H„)TR-Invoke.cnf(H)TR-Result.ind(UD*, H)TR-Result.res(H) TR-Result.cnf (H„) 233 Source: Schiller
  • 234. WTP Class 2 Transaction, user ack initiator responder TR-SAP TR-SAPTR-Invoke.req(SA, SP, DA, DP, A, UD, C=2, H) TR-Invoke.ind (SA, SP, DA, DP, A, UD, C=2, H„) TR-Invoke.res (H„)TR-Invoke.cnf(H) TR-Result.req (UD*, H„)TR-Result.ind(UD*, H)TR-Result.res(H) TR-Result.cnf (H„) 234 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 235
  • 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 236
  • 237. WSP/B session establishment client server S-SAP S-SAPS-Connect.req(SA, CA, CH, RC) S-Connect.ind (SA, CA, CH, RC) S-Connect.res (SH, NC)S-Connect.cnf(SH, NC) CH: Client Header WTP Class 2 RC: Requested Capabilities transaction SH: Server Header NC: Negotiated Capabilities 237 Source: Schiller
  • 238. WSP/B session suspend/resume client server S-SAP S-SAPS-Suspend.req S-Suspend.indS-Suspend.ind (R)(R) WTP Class 0 transaction R: Reason for disconnectionS-Resume.req(SA, CA) ~ ~ S-Resume.ind (SA, CA) S-Resume.resS-Resume.cnf WTP Class 2 transaction 238 Source: Schiller
  • 239. WSP/B session termination client server S-SAP S-SAPS-Disconnect.req(R) S-Disconnect.indS-Disconnect.ind (R)(R) WTP Class 0 transaction 239 Source: Schiller
  • 240. confirmed/non-confirmed push client server S-SAP S-SAP S-Push.req (PH, PB)S-Push.ind(PH, PB) WTP Class 0 PH: Push Header transaction PB: Push Body SPID: Server Push ID client server CPID: Client Push ID S-SAP S-SAP S-ConfirmedPush.req (SPID, PH, PB)S-ConfirmedPush.ind(CPID, PH, PB)S-ConfirmedPush.res(CPID) S-ConfirmedPush.cnf (SPID) WTP Class 1 transaction 240 Source: Schiller
  • 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) 241
  • 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 242
  • 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) 243
  • 244. WAE: logical modelOrigin Servers Gateway Client response encoded WTA web Method proxy with response user agent server content with content Push proxy WML other content user agent server push encoded content push content encoders other & WAE decoders user agents request encoded request 244
  • 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 245
  • 246. WML: Wireless Markup Language Tag-based browsing language: Content (XML) – Screen management (text, images) – Data input (text, selection lists, etc.) XSL Processor – Hyperlinks & navigation WML Stylesheet HTML StyleSheet support Takes into account WML Browsers HTTP Browser limited display, navigation capabilities of devices 246
  • 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 247
  • 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 WML File Structure <?xml version="1.0"?> <!DOCTYPE WML PUBLIC "-//WAPFORUM//DTD WML 1.0//EN" "http://www.wapforum.org/DTD/wml.xml"> <WML> ... </WML> 248
  • 249. WML cards <WML> <CARD> <DO TYPE=“ACCEPT”>Navigatio <GO URL=“#eCard”/> </DO Cardn Welcome! </CARD> <CARD NAME=“eCard”> <DO TYPE=“ACCEPT”> Variables <GO URL=“/submit?N=$(N)&S=$(S)”/> Deck </DO> Enter name: <INPUT KEY=“N”/> Choose speed: <SELECT KEY=“S”> Input <OPTION VALUE=“0”>Fast</OPTION>Elements <OPTION VALUE=“1”>Slow</OPTION> <SELECT> </CARD> </WML> 249
  • 250. Wireless Telephony Application (WTA) Collection of telephony specific extensions – designed primarily for network operators Example – calling a number (WML) wtai://wp/mc;07216086415 – calling a number (WMLScript) WTAPublic.makeCall("07216086415"); Implementation – Extension of basic WAE application model – Extensions added to standard WML/WMLScript browser – Exposes additional API (WTAI) 250
  • 251. WTA features Extension of basic WAE application model – network model for interaction • client requests to server • event signaling: server can push content to the client – event handling • table indicating how to react on certain events from the network • client may now be able to handle unknown events – telephony functions • some application on the client may access telephony functions 251
  • 252. WTA Interface generic, high-level interface to mobile‟s telephony functions – setting up calls, reading and writing entries in phonebook WTA API includes – Call control – Network text messaging – Phone book interface – Event processing Security model: segregation – Separate WTA browser – Separate WTA port 252
  • 253. WTA Example (WML) Placing an outgoing call with WTAI: <WML> <CARD> <DO TYPE=“ACCEPT”> WTAI Call <GO URL=“wtai:cc/mc;$(N)”/> </DO> Enter phone number:Input Element <INPUT TYPE=“TEXT” KEY=“N”/> </CARD> </WML> 253 Source: WAP Forum
  • 254. WTA Logical Architecture other telephone networks WTA Origin Server Client WML Scripts mobile WTA WTA & WML network user agent serverWMLdecks WAE WAP Gateway services WTA services encoders &network operator decoderstrusted domain other WTA servers third party firewallorigin servers 254 Source: Schiller
  • 255. WTA Framework Components 255 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 256
  • 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 257
  • 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 258
  • 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 259
  • 260. WTA Channels and Resources 260 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 261
  • 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 262
  • 263. WTAI (network) Network Specific WTAI – specific to type of bearer network – example: GSM: call reject, call hold, call transfer, join multiparty, send USSD 263
  • 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 264
  • 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 265
  • 266. Event Handling (no service in execution) 266 Source: Heijden
  • 267. Event Handling (service already execution)1: Temporary binding exists2. No temporary binding and context is protected3: No temporary binding and context is not protected 267 Source: 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) 268
  • 269. WAP push framework 269 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 270
  • 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 271
  • 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 272
  • 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 273
  • 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 274
  • 275. Structuring Distributed Applications Call to server procedure Client Server Data results Procedure Client Server Procedure Client Server Data results Remote Evaluation Client Server Data Procedure Code on Demand 275
  • 276. Procedure + StateClient Server Data Procedure + State Procedure + Server Data State Procedure + State Procedure + State Server DataServer Data Mobile Agents 276
  • 277. Interaction Model Request Client Server Response Client/server communication Mobile agent RequestClient Server Response Mobile agent communication 277
  • 278. A generic Mobile Agent Framework •Event notification •Agent collaboration support Event Manager•Execution •User identificationenvironment Mobile Agent •Protection•Communication (agent, server)(agent dispatching) •Authentication•Agent life cycle(creation, destruction)Agent Manager •Agent state Security Manager •Agent checkpoint (fault tolerance) 278 Persistent Manager
  • 279. Example: Student Examination Scenario = Paper Setter NodesComprehensive Question Paper = Install Agent = Fetch Agent 5 4 3 Paper Assembler 1 2 Cloning 6 Partial Question Paper To Distribution Center 279
  • 280. Dynamic Upgrade 280
  • 281. Example: Distribution and Testing List of Students enrolled Single copy of paper …Distribution 1 2 … Exam Center Server Distribution Server 5 c9611060 Each copy returned Separate Copy per user 4 Answered and Returned 3 Each Candidate get a Copy 281
  • 282. Example: Evaluation and Results Objective Questions Evaluatorc9611060 Examiner B Distributor Distribution Server Examiner A Examiner C Examiner D Results … … 282 Agents collaborate to produce the final result
  • 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 283
  • 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 284
  • 285. Multi-Hop Wireless May need to traverse multiple links to reach destination Mobility causes route changes 285
  • 286. Mobile Ad Hoc Networks (MANET) Host movement frequent Topology change frequent B A B A No cellular infrastructure. Multi-hop wireless links. Data must be routed via intermediate nodes. 286
  • 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 287
  • 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 288
  • 289. Exposed Terminal Problem A B D C– 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 289
  • 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) 290
  • 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 291
  • 292. Route Discovery in DSR Y Z S E F B C M L JA G H D K I NRepresents a node that has received RREQ for D from S 292
  • 293. Route Discovery in DSR YBroadcast transmission [S] Z S E F B C M L J A G H D K I N Represents transmission of RREQ [X,Y] Represents list of identifiers appended to RREQ 293
  • 294. Route Discovery in DSR Y Z S [S,E] E F B C M L J A [S,C] G H D K I N• Node H receives packet RREQ from two neighbors: potential for collision 294
  • 295. Route Discovery in DSR Y Z S E F [S,E,F] B C M L J A G H D [S,C,G] K I N• Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once 295
  • 296. Route Discovery in DSR Y Z S E F [S,E,F,J] B C M L J A G H D K I [S,C,G,K] N• Nodes J and K both broadcast RREQ to node D• Since nodes J and K are hidden from each other, their transmissions may collide 296
  • 297. Route Discovery in DSR Y Z S E [S,E,F,J,M] F B C M L J A G H D K I N• Node D does not forward RREQ, because node D is the intended target of the route discovery 297
  • 298. Route Reply in DSR Y Z S RREP [S,E,F,J,D] E F B C M L JA G H D K I NRepresents RREP control message 298
  • 299. Data Delivery in DSR Y DATA [S,E,F,J,D] Z S E F B C M L J A G H D K I NPacket header size grows with route length 299
  • 300. TCP in MANETSeveral 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 300
  • 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 301
  • 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 302