Sisteme mobile in Internet  (Arhitectura si aplicatiile retelelor mobile)              Nicolae Tomai                 FSEGA...
Cuprins   Introducere   Wireless LANs: IEEE 802.11   Rutarea IP mobila   TCP in retele fara fir   Retele GSM   Arhit...
References J. Schiller, “Mobile Communications”, Addison Wesley, 2000 802.11 Wireless LAN, IEEE standards, www.ieee.org...
Retele fara fir Ofera servicii de acces la calcul/comunicare in miscare Retele celulare   – Sisteme cu infastrucura baza...
Dispozitive mobile                      TabletsPalm-sized                                   Clamshell handhelds   Laptop c...
Sisteme de operare pentru disozitive mobile  Symbian-promovat ca OS(open source) de un   consortiu: Nokia, Motorola, etc....
Evolutia telefoanelor mobile                               7
Spectrul alocat pentru telefoanele mobileSursa: (S60 Programming A Tutorial Guide Paul Coulton,                           ...
Elemente componente ale unui sistem de telefonie                   mobila                                              9
FDMA(Frecvency Division Multiple Access)(1G)                                           10
TDMA(Time Division Multiple      Access)(2G)                              11
CDMA(Code Division Multiple Access) Permite utilizatorilor sa imparta atit timpul cit si frecventa  in acelasi timp, prin...
CDMA(Code Division Multiple Access)                                      13
Sistemul GPRS•SGSN(Serving GPRS Support Node) controlează transmiterea pachetelorde date prin întreaga reţea şi•GGSN(Gatew...
Alocarea frecventelor in 3G                              15
Alocarea frecventelor in 3G   Europa şi Japonia au optat pentru banda largă CDMA (W- CDMA) folosind    diviziunea frecven...
W-CDMA in sistemul GSM/GPRS                              17
Evolutia spre 4G                   18
Evolutia sistemelor celulare                               19
Limitari ale sistemelor mobile Limitări datorate retelelor fara fir    Limitari ale largimii benzii de comunicatie    D...
Comparatie intre retelele fara fir si cele cu fir Reglemetari ala frecventelor   – Limitarea disponibilitatii si necesita...
Siteme celulare: ideea de baza Conectivitate fara fir cu un singur salt(hop)   – Spatiul este divizat in celule   – O sta...
Conceptul celular Numarul limitat de frecvente => limiteaza numarul canalelor Puterea de emisie a antenei => limiteaza n...
Arhitectura sistemelor celulare Fiecare celula este deservita de o statie de baza(BS-Base Station) Fiecare sitem (BSS-Ba...
Apel de configurare pentru iesirea in retea-la apel(Outgoing call setup) Apel de configurare la iesire:   – Se introduce ...
Apel de configurare la intrarea in retea-la primire(Incoming call setup) Apel de configurare la iesire:   – MSC-ul tinta ...
Termenul de hand-off(predare –preluare) se referă la procesul de transfer al unuiapel sau sesiuni de date de la un canal c...
Efectul mobilitatii asupra stivei de             protocoale Aplicatie  – Aplicatii noi si adaptari Transport  – Controlu...
Aplicatii mobile(1) Vehicule  – Transmisia de noutati, conditii de drum, etc.  – Retele ad-hoc cu vehicule apropiate pent...
Aplicatii mobile(2) Agenti de vinzari mobili   – Acces direct la baza de date centrala cu clientii   – Baze de date consi...
Aplicatii mobile(3) Servicii de informare  – Cotatii bursiere, etc.  – Vremea Operatii deconectate  – Agenti mobili, cum...
Aplicatii mobile in industrie   Wireless access: (phone.com) openwave   Alerting services: myalert.com   Location servi...
Latimea de banda si aplicatiile            UMTS             EDGE   GPRS, CDMA 2000         CDMA 2.5G                2G    ...
Evolutia retelelor celulare First-generation: Analog cellular systems (450-900 MHz)   – Frequency shift keying; FDMA for ...
GSM to GPRS Resursele radio sunt alocate numai pentru unul sau mai  multe(câteva) pachete la un moment dat, aşa ca GPRS  ...
UMTS: Universal Mobile Telecomm. (standard) Global seamless operation in multi-cell environment  (SAT, macro, micro, pico...
Evolution to 3G Technologies 2G                          3GIS-95B                         cdma2000CDMA                    ...
Tehnologii fara fir            802.11n >150 Mbps 802.11n70 Mbps                                                           ...
Comparatie intre tehnologii                     Covearge                      10                                          ...
Arhitectura retelei 3G                                         Core Network          Wireless                             ...
Retele fara fir locale WLAN Advantage  – Foarte flexibile in aria(zona) de receptie  – Posibilitatea de realizare topolog...
Topologiile retelelor fara fir(infrastructura si                      Adhoc)infrastructure network                        ...
Difference Between Wired and                   Wireless  Ethernet LAN          Wireless LAN                               ...
Hidden Terminal Problem             A        B       C– A and C cannot hear each other.– A sends to B, C cannot receive A....
IEEE 802.11 Acknowledgements for reliability Signaling packets for collision avoidance  – RTS (request to send)  – CTS (...
Spectrum War: Status todayEnterprise 802.11   Wireless Carrier     Public 802.11Network                                   ...
Spectrum War: EvolutionEnterprise 802.11   Wireless Carrier           Public 802.11Network                                ...
Spectrum War: Steady StateEnterprise 802.11   Wireless Carrier          Public 802.11Network                     Virtual C...
Routarea si mobilitatea Gasirea unei cai de la o sursa la o destinatie Probleme  – Schimbarea frecventa a rutelor  – Sch...
IP-ul mobil: Ideea de baza           MN        RouterS                       3            Home            agentRouter     ...
IP mobil: ideea de baza            miscare                            RouterS                                         MN  ...
Protocoalele TCP si UDP in cazul retelelor fara                     fir  TCP asigură:   – Livrarea sigura si ordonata a p...
TCP in retele fără fir Factorii ce afecteaza protocolul TCP in retele fara fir:   – Erorile de transmisie in mediul fara ...
Indirect TCP (I-TCP) I-TCP splits the TCP connection    – no changes to the TCP protocol for wired hosts    – TCP connect...
TCP mobil (M-TCP) Gestioneaza deconectari frecvente si interminabile M-TCP spliteaza ca si I-TCP dar,  – Nu modifica TCP...
Adaptarea aplicatiilor pentru mobilitate Probleme de proiectare   Sistem transparent sau sistem netransparent/adecvat/  ...
World Wide Web-ul si mobilitatea Caracteristicile protocolului HTTP  – A fost proiectat pentru banda larga si intirziere ...
Sisteme suport pentru WWW mobil  Browsere cu facilitati adaugate/sporite    – Suport client adecvat pentru mobilitate  P...
Modelul client/proxy/server Functiuni proxi atit pentru un client cit si pentru  serverul retelei fixe Functiuni proxi p...
Proxi Web in WebExpress    The WebExpress Intercept Model                                        60                       ...
WAP(Wireless Application Protocol) Navigator-browser   – “Micro browser”, similar navigatoarelor existente Limbajul de s...
WAP: elementele componente             fixed network                              wireless network             HTML       ...
WAP: modelul de referinta  Internet           A-SAP     WAP HTML, Java       Application Layer (WAE)               Servici...
Stiva de protocoale WAP WDP  – Functionalitati similare cu UDP in retele IP WTLS  – functionalitati similare cu SSL/TLS ...
Modelul cu agenti mobili Agentul mobil primeste cererea clientului si Agentul mobil se muta in reteaua fixa Agentul mob...
Mobile Agents: Exemplu                         66
Cuprins   Introducere   Wireless LANs: IEEE 802.11   Rutarea IP mobila   TCP in retele fara fir   Retele GSM   Arhit...
How Wireless LANs are different Destination address does not equal destination  location The media impact the design  – ...
Wireless Media Physical layers in wireless networks   – Use a medium that has neither absolute nor readily     observable...
802.11: Motivation Can we apply media access methods from fixed networks Example CSMA/CD   – Carrier Sense Multiple Acce...
Solution for Hidden/Exposed Terminals A first sends a Request-to-Send (RTS) to B On receiving RTS, B responds Clear-to-S...
IEEE 802.11 Wireless LAN standard defined in the unlicensed  spectrum (2.4 GHz and 5 GHz U-NII bands) Standards covers t...
Components of IEEE 802.11              architecture  The basic service set (BSS) is the basic building   block of an IEEE...
802.11 - ad-hoc network (DCF)        802.11 LANSTA1                                       Direct communication       BSS1...
802.11 - infrastructure network (PCF)                                                  Station (STA)         802.11 LAN  ...
Distribution System (DS) concepts The Distribution system interconnects multiple BSSs 802.11 standard logically separate...
802.11- in the TCP/IP stack                                                            fixed terminalmobile terminal      ...
802.11 - Layers and functions   MAC                                                 PLCP Physical Layer Convergence     ...
802.11 - Physical layer 3 versions: 2 radio (typically 2.4 GHz), 1 IR    – data rates 1, 2, or 11 Mbit/s FHSS (Frequency...
Spread-spectrum communications                                  80                           Source: Intersil
DSSS Barker Code modulation                               81                          Source: Intersil
DSSS properties                       82                  Source: Intersil
802.11 - MAC layer Traffic services   – Asynchronous Data Service (mandatory) – DCF   – Time-Bounded Service (optional) -...
802.11 - Carrier Sensing In IEEE 802.11, carrier sensing is performed   – at the air interface (physical carrier sensing)...
802.11 - Reliability Use of acknowledgements  – When B receives DATA from A, B sends an ACK  – If A fails to receive an A...
802.11 - Priorities defined through different inter frame spaces – mandatory idle time  intervals between the transmissio...
802.11 - CSMA/CA                                                    contention window   DIFS                         DIFS ...
802.11 –CSMA/CA example             DIFS           DIFS                DIFS                  DIFS                         ...
802.11 - Collision Avoidance Collision avoidance: Once channel becomes idle, the  node waits for a randomly chosen durati...
DCF Example  B1 = 25              B1 = 5              wait               data             data                   wait  B2 ...
802.11 - Congestion Control Contention window (cw) in DCF: Congestion  control achieved by dynamically choosing cw large...
802.11 - CSMA/CA II  station has to wait for DIFS before sending data  receivers acknowledge at once (after waiting for ...
802.11 –RTS/CTS   station can send RTS with reservation parameter after waiting for DIFS    (reservation determines amoun...
Fragmentation           DIFS                  RTS                     frag1                      frag2sender              ...
802.11 - Point Coordination Function                                   95
802.11 - PCF I              t0 t1                                       SuperFrame  medium busy PIFS                     S...
802.11 - PCF II                                                        t2   t3           t4                   PIFS        ...
CFP structure and Timing                           98
PCF- Data transmission                         99
Polling Mechanisms With DCF, there is no mechanism to guarantee  minimum delay for time-bound services PCF wastes bandwi...
Coexistence of PCF and DCF PC controls frame transfers during a Contention Free  Period (CFP).   – CF-Poll control frame ...
802.11 - Frame format         Types           – control frames, management frames, data frames         Sequence numbers ...
Frame Control Field                      103
Types of Frames Control Frames  – RTS/CTS/ACK  – CF-Poll/CF-End Management Frames  –   Beacons  –   Probe Request/Respon...
MAC address formatscenario              to DS from     address 1 address 2 address 3 address 4                            ...
802.11 - MAC management Synchronization   – try to find a LAN, try to stay within a LAN   – timer etc. Power management ...
802.11 - Synchronization All STAs within a BSS are synchronized to a common  clock   – PCF mode: AP is the timing master ...
Synchronization using a Beacon          (infrastructure)         beacon interval         B                     B          ...
Synchronization using a Beacon (ad-                  hoc)           beacon interval           B1                          ...
802.11 - Power management Idea: switch the transceiver off if not needed   – States of a station: sleep and awake Timing...
802.11 - Energy conservation Power Saving in IEEE 802.11 (Infrastructure  Mode)  – An Access Point periodically transmits...
Power saving with wake-up patterns         (infrastructure)          TIM interval          DTIM interval          D B     ...
Power saving with wake-up patterns             (ad-hoc)               ATIM               window          beacon interval  ...
802.11 - Roaming No or bad connection in PCF mode? Then perform: Scanning   – scan the environment, i.e., listen into th...
Hardware Original WaveLAN card (NCR)   –   914 MHz Radio Frequency   –   Transmit power 281.8 mW   –   Transmission Range...
802.11 current status   802.11i                                 LLC   security                                           W...
IEEE 802.11 Summary Infrastructure (PCF) and adhoc (DCF) modes Signaling packets for collision avoidance   – Medium is r...
Cuprins   Introducere   Wireless LANs: IEEE 802.11   Rutarea IP mobila   TCP in retele fara fir   Retele GSM   Arhit...
Rutarea traditională Un protocol de rutare populeaza tabela de  rutare a unui router Un protocol de rutare se bazeaza pe...
Routarea si mobilitatea Gasirea unei cai de la o sursa la o destinatie Probleme  – Schimbarea frecventa a rutelor  – Sch...
IP mobil (RFC 3220): motivarea Rutarea traditionala   – Bazata pe adrese IP; prefixul retelei determina subreteaua   – Sc...
IP-ul mobil: Ideea de baza            MN(mobile   RouterS(sender)    Node)        3                Home                age...
IP mobil: ideea de baza            miscare                            RouterS                                         MN  ...
IP mobil : terminologia Nod Mobil(Mobile Node-MN)    – Nod care se muta prin retea fara a-si schimba adresa IP Agent de ...
Transferul datelor la sistemul mobil             HA                      2                                                ...
Transferul datelor de la sistemul mobil             Agent propriu             HA-home agent                               ...
IP-ul mobil: Operatia de bază Agentul de averizare   – Periodic HA/FA trimit messaje de avertizare in subreteaua lor     ...
Agentul de averizare0           7 8              15 16       23 24      31   type            code                checksum#...
Inregistrarea(registration)    MN      FA    HA         MN   HA                         tt                                ...
Cererea de inregistrare(Registration request)       0          7 8        15 16          23 24     31           type    S ...
Incapsularea IP-in-IP Incapsularea IP-in-IP- (obligatorie in RFC 2003)   – tunel intre HA si COA          ver.   IHL     ...
IP-ul mobil: Alte probleme Tunelarea inversa  – Firewall-urile permit numai adresari topologice    “topological correct“ ...
IP-ul mobil -recapitulare Nodul mobil se muta la noua locatie Agent de avertisment de agentul strain Inregistrarea nodu...
Cuprins   Introducere   Wireless LANs: IEEE 802.11   Rutarea IP mobila   TCP in retele fara fir   Retele GSM   Arhit...
Transmission Control Protocol (TCP) Livrarea sigura si ordonata  – Prin pachete de raspuns si retransmisii Dialog de luc...
Controlul fluxului bazat pe ferestre Protocolul de transmisie cu fereastră glisantă Dimensiunea ferestrei este minimul d...
Comportamentul de baza TCP                         14                       Evitarea congestieiCongestion Window size     ...
TCP: detectarea pachetelor pierdute Timeout-ul de retransmisie  – Initiaza startul incet Raspunsuri duplicate  – Initiaz...
TCP dupa timeout                                                                   Dupa timeout                           ...
TCP dupa retransmisia rapida                                                  Dupa recuperarea rapida                     ...
Impactul erorilor de transmisie Canalele fara fir pot avea erori aleatoare in  avalansa Erorile in avalansa pot cauza ti...
Splitarea conexiunii Conexiunea TCP capat la capat(end-to-end) este  Impartita/”sparta” intr-o conexiune pe partea  cabla...
I-TCP: Consideratii privind splitarea            conexiunii                                          Starea conexiunii pri...
Protocolul snoop Pachetele de date sunt memorate(bufferate) in statia se  baza BS   – Se permite astfel nivelului legatur...
Protocol snoop                                  Starea conexiunii prin TCP                 TCP connectionapplication      ...
Impactul trecerii de la un nod la altul( la alt BS)(Hand-offs) Splitarea conexiunii    – Starea “hard” a conex. din stati...
M-TCP(mobile TCP) Similar cu splitarea conexiunii, M-TCP spliteaza o  conexiune TCP in doua parti logice   – Cele doua pa...
M-TCP Cind este receptionat un nou ACK impreuna cu  un avertisment al receptorului de tipul  Window=0, emitatorul intra i...
BlocareaTCP M-TCP are nevoie de ajutor de la statia de  baza(base station)  – Statia de baza mentine ack pentru un octet(...
TCP in medii fara fir-recapitulare Presupunerea ca pachetele pierdute implica o  congestie nu este adevarata in mediile f...
Cuprins   Introducere   Wireless LANs: IEEE 802.11   Rutarea IP mobila   TCP in retele fara fir   Retele GSM   Arhit...
GSM: ArhitecturaPSTN-Public Switched Telephone Network,ISDN-Integrated Services Digital Network, PDN-Packet Data Network  ...
Base Transceiver Station (BTS) Una pe celula E compusa dintr-un transmitator si un receptor de mare   viteza Functiile ...
Base Station Controller (BSC) Controleaza mai multe BTS-uri Consta dintr-o entitatea de control si din una  pentru un pr...
Mobile Switching Center (MSC) Comuta nodul la un PLMN(Public/Private  Land Mobile Network) Aloca resursa radio (RR) – Re...
Gateway MSC (GMSC) Conecteaza reteaua mobila la reteaua fixa – Punct de intrare la un PLMN Usual unul pentru PLMN Cere ...
Canalul fizic Legatura ascendenta/descendenta  (Uplink/Downlink) la 25MHz – 890 -915 MHz pentru legatura ascendenta – 935...
158
Bursts Building unit of physical channel Types of bursts –   Normal –   Synchronization –   Frequency Correction –   Dum...
Normal Burst Normal Burst – 2*(3 head bit + 57 data bits + 1 signaling bit) + 26   training sequence bit + 8.25 guard bit...
Air Interface: Logical Channel Traffic Channel (TCH) Signaling Channel – Broadcast Channel (BCH) – Common Control Channe...
162
Traffic Channel Transfer either encoded speech or user data Bidirectional Full Rate TCH – Rate 22.4kbps – Bm interface...
Full Rate Speech Coding Speech Coding for 20ms segments – 260 bits at the output – Effective data rate 13kbps Unequal er...
Speech               20 ms                                20 ms                      Speech Coder                         ...
Traffic Channel Structure for Full Rate  CodingSlots 1   2   3   4   5   6   7   8   1   2   3   4   5   6   7   8   1    ...
Slots 1    2   3   4   5   6       7   8   1   2   3   4   5   6   7   8   1   2                           Burst for one u...
BCCH Broadcast Control Channel (BCCH) – BTS to MS – Radio channel configuration     –   Current cell + Neighbouring cell...
FCCH & SCH  Frequency Correction Channel    – Repeated broadcast of FB  Synchronization Channel    – Repeated broadcast ...
RACH & SDCCH Random Access Channel (RACH) – MS to BTS – Slotted Aloha – Request for dedicated SDCCH Standalone Dedicated...
AGCH & PCH  Access Grant Channel (AGCH) – BTS to MS – Assign an SDCCH/TCH to MS Paging Channel (PCH) – BTS to MS – Page M...
SACCH & FACCH Slow Associated Control Channel (SACCH) – MS  BTS – Always associated with either TCH or SDCCH – Informati...
Example: Incoming Call SetupMS  BSS/MSC   ------   Paging request            (PCH)MS  BSS/MSC   ------   Channel request...
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Mobileinternet tomai-romana-2010
Upcoming SlideShare
Loading in...5
×

Mobileinternet tomai-romana-2010

1,183

Published on

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
1,183
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
17
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Mobileinternet tomai-romana-2010

  1. 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. 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. 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. 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. 5. Dispozitive mobile TabletsPalm-sized Clamshell handhelds Laptop computers Net–enabled mobile phones
  6. 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. 7. Evolutia telefoanelor mobile 7
  8. 8. Spectrul alocat pentru telefoanele mobileSursa: (S60 Programming A Tutorial Guide Paul Coulton, 8Reuben Edwards With Helen Clemson)
  9. 9. Elemente componente ale unui sistem de telefonie mobila 9
  10. 10. FDMA(Frecvency Division Multiple Access)(1G) 10
  11. 11. TDMA(Time Division Multiple Access)(2G) 11
  12. 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. 13. CDMA(Code Division Multiple Access) 13
  14. 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. 15. Alocarea frecventelor in 3G 15
  16. 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. 17. W-CDMA in sistemul GSM/GPRS 17
  18. 18. Evolutia spre 4G 18
  19. 19. Evolutia sistemelor celulare 19
  20. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 42. Topologiile retelelor fara fir(infrastructura si Adhoc)infrastructure network AP: Access Point AP AP wired network APad-hoc network 42 Source: Schiller
  43. 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. 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. 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. 46. Spectrum War: Status todayEnterprise 802.11 Wireless Carrier Public 802.11Network 46 Source: Pravin Bhagwat
  47. 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. 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. 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. 50. IP-ul mobil: Ideea de baza MN RouterS 3 Home agentRouter Router 1 2 50 Source: Vaidya
  51. 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. 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. 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. 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. 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. 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. 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. 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. 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. 60. Proxi Web in WebExpress The WebExpress Intercept Model 60 Source: Helal
  61. 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. 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. 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. 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. 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. 66. Mobile Agents: Exemplu 66
  67. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 80. Spread-spectrum communications 80 Source: Intersil
  81. 81. DSSS Barker Code modulation 81 Source: Intersil
  82. 82. DSSS properties 82 Source: Intersil
  83. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 95. 802.11 - Point Coordination Function 95
  96. 96. 802.11 - PCF I t0 t1 SuperFrame medium busy PIFS SIFS SIFS D1 D2pointcoordinator SIFS SIFS U1 U2wirelessstationsstations„ NAVNAV 96
  97. 97. 802.11 - PCF II t2 t3 t4 PIFS SIFS D3 D4 CFendpointcoordinator SIFS U4wirelessstationsstations„ NAVNAV contention free period contention t period 97
  98. 98. CFP structure and Timing 98
  99. 99. PCF- Data transmission 99
  100. 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. 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. 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. 103. Frame Control Field 103
  104. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 122. IP-ul mobil: Ideea de baza MN(mobile RouterS(sender) Node) 3 Home agent Router Router 1 2 122 Source: Vaidya
  123. 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. 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. 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. 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. 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. 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. 129. Inregistrarea(registration) MN FA HA MN HA tt 129
  130. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 152. GSM: ArhitecturaPSTN-Public Switched Telephone Network,ISDN-Integrated Services Digital Network, PDN-Packet Data Network 152
  153. 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. 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. 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. 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. 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. 158
  159. 159. Bursts Building unit of physical channel Types of bursts – Normal – Synchronization – Frequency Correction – Dummy – Access 159
  160. 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. 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. 162
  163. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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
  1. A particular slide catching your eye?

    Clipping is a handy way to collect important slides you want to go back to later.

×