Introduction to PPP

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Introduction to PPP

  1. 1. IntroductionIntroduction toto Point-to-Point ProtocolPoint-to-Point Protocol (PPP)(PPP) Frank Fang Kuo YuFrank Fang Kuo Yu 10/12/200610/12/2006
  2. 2. AgendaAgenda  PPP in Wired PC-to-PC Dial-up ProcessPPP in Wired PC-to-PC Dial-up Process  Modem, AT Command, PPP OverviewModem, AT Command, PPP Overview  PPP in Wireless Internet AccessPPP in Wireless Internet Access  WAP over CSD, WAP over GPRS, Phone as ModemWAP over CSD, WAP over GPRS, Phone as Modem  PPP IllustratedPPP Illustrated  Packet Format, LCP, PAP, CHAP, IPCPPacket Format, LCP, PAP, CHAP, IPCP  Protocol Analysis in EtherealProtocol Analysis in Ethereal  SI2 MMS ~ HTTP-TCP-IP-PPP-CSDSI2 MMS ~ HTTP-TCP-IP-PPP-CSD
  3. 3. Wired PC-to-PC Dial-Up ProcessWired PC-to-PC Dial-Up Process  Modem = modulation + demodulationModem = modulation + demodulation  AT CommandAT Commands for Modem Controls for Modem Control  Control Mode and Data ModeControl Mode and Data Mode  Protocol Stack in Data ModeProtocol Stack in Data Mode
  4. 4. Modem and Modem ControlModem and Modem Control  Modem = modulation + demodulationModem = modulation + demodulation  Perform the conversion ofPerform the conversion of digitaldigital signals into ansignals into an analoganalog formform suitable for transmission over ordinary telephone linessuitable for transmission over ordinary telephone lines  AutomaticAutomatic DDetection andetection and NNegotiation ofegotiation of DDifferentifferent CCarrierarrier RRates andates and MModulationodulation MMethodsethods – e.g., V.90, K56Flex, USR X2, V.34, V.FC, V.32bis, V.32, …e.g., V.90, K56Flex, USR X2, V.34, V.FC, V.32bis, V.32, …  ErrorError DDetection andetection and CCorrectionorrection – e.g., V.42, LAPM, MNP4e.g., V.42, LAPM, MNP4  DataData CCompressionompression – e.g., V.42bis, MNP5e.g., V.42bis, MNP5  AT CommandAT Commandss  CControl modem’s operation and configurationontrol modem’s operation and configuration
  5. 5. Command Mode and Data ModeCommand Mode and Data Mode  Command ModeCommand Mode  PC sidePC side – Issues AT commandsIssues AT commands – Handles responses of AT commandsHandles responses of AT commands – Monitors unsolicited result codesMonitors unsolicited result codes  modem sidemodem side – AT Command InterpreterAT Command Interpreter  Data ModeData Mode  PPP uses a collection of protocols to establish and configure aPPP uses a collection of protocols to establish and configure a point-to-point link, and to transport packets over the link.point-to-point link, and to transport packets over the link.  Switching between Command Mode and Data ModeSwitching between Command Mode and Data Mode
  6. 6. Protocol Stack in Data ModeProtocol Stack in Data Mode
  7. 7. WWAPAP over GSM CSDover GSM CSD
  8. 8. WWAAP over GPRSP over GPRS
  9. 9. PPP in Terminal EquipmentPPP in Terminal Equipment
  10. 10. TE/MT Separation Case 1TE/MT Separation Case 1 Data Transfer inData Transfer in ““IPIP”” Based ServiceBased Service
  11. 11. TE/MT Separation Case 2TE/MT Separation Case 2 Data Transfer inData Transfer in ““PPPPPP”” Based ServiceBased Service
  12. 12. The Roles of PPP in Mobile PhoneThe Roles of PPP in Mobile Phone  Case 1 ~ For “browser on phone”Case 1 ~ For “browser on phone”  WAP over CSD ~ PPP is used for Dial-OutWAP over CSD ~ PPP is used for Dial-Out  Case 2 ~ For “phone as modem”Case 2 ~ For “phone as modem”  IP Based Service ~ PPP is used for Dial-InIP Based Service ~ PPP is used for Dial-In
  13. 13. The Architecture of PPP in MobileThe Architecture of PPP in Mobile PhonePhone 1.1. WAP over CSDWAP over CSD ~ IP~ IP  PPP Dial-OutPPP Dial-Out  CSDCSD 2.2. WAP over GPRSWAP over GPRS ~ IP~ IP  SNDCPSNDCP 3.3. Modem RouteModem Route ~ PPP Dial-In~ PPP Dial-In  SNDCPSNDCP 11 22 33 Question: Can 2 and 3 coexist?Question: Can 2 and 3 coexist? Question: Can 1 and 3 coexist?Question: Can 1 and 3 coexist? Hint: Does the handset supportHint: Does the handset support multiple PDP contexts?multiple PDP contexts? Hint:Hint: Class B Mode of Operation:Class B Mode of Operation: the MS is attached tothe MS is attached to bothboth GPRSGPRS and other GSM services, but theand other GSM services, but the MS canMS can onlyonly operateoperate oneone set ofset of services at a time.services at a time.
  14. 14. Protocol Stack in Data Mode (revisited)Protocol Stack in Data Mode (revisited)
  15. 15. Format of PPP FrameFormat of PPP Frame • FlagFlag 0x7E0x7E the escape of 0x7E in data ~ (0x7D, 0x5E)the escape of 0x7E in data ~ (0x7D, 0x5E) the escape of 0x7D in data ~ (0x7D, 0x5D)the escape of 0x7D in data ~ (0x7D, 0x5D) the escape of control characterthe escape of control character • AddressAddress 0xFF0xFF omitted if LCP/ACFC is negotiatedomitted if LCP/ACFC is negotiated • ControlControl 0x030x03 omitted if LCP/ACFC is negotiatedomitted if LCP/ACFC is negotiated • ProtocolProtocol 0x00210x0021 IP in “information field”IP in “information field” 0x80210x8021 IPCP in “information field”IPCP in “information field” 0xC0210xC021 LCP in “information field”LCP in “information field” 0xC0230xC023 PAP in “information field”PAP in “information field” 0xC2230xC223 CHAP in “information field”CHAP in “information field”
  16. 16. PPP Connection EstablishmentPPP Connection Establishment http://www.tcpipguide.com/free/t_PPPLinkSetupandPhases.htmhttp://www.tcpipguide.com/free/t_PPPLinkSetupandPhases.htm
  17. 17. LCP Message ExchangesLCP Message Exchanges LCP Configuration OptionsLCP Configuration Options • Maximum-Receive-Unit (MRU)Maximum-Receive-Unit (MRU) • Async-Control-Character-Map (ACCM)Async-Control-Character-Map (ACCM) • Authentication-ProtocolAuthentication-Protocol - C023 PAP- C023 PAP - C223 CHAP- C223 CHAP - …- … • Protocol-Field-CompressionProtocol-Field-Compression (PFC)(PFC) - used to reduce the protocol field from 2 bytes- used to reduce the protocol field from 2 bytes to 1 byteto 1 byte • Address-and-Control-Field-Compression (ACFC)Address-and-Control-Field-Compression (ACFC) - used to omit the address field (0xff) and the- used to omit the address field (0xff) and the control field (0x03)control field (0x03) • ……
  18. 18. Password Authentication ProtocolPassword Authentication Protocol (PAP)(PAP)
  19. 19. Challenge-Handshake Authentication ProtocolChallenge-Handshake Authentication Protocol (CHAP)(CHAP)
  20. 20. IPCP Message ExchangesIPCP Message Exchanges IPCP Configuration OptionsIPCP Configuration Options • IP-Compression-ProtocolIP-Compression-Protocol • IP-AddressIP-Address • Primary DNS Server AddressPrimary DNS Server Address • Secondary DNS Server AddressSecondary DNS Server Address • ……
  21. 21. Protocol Analysis in EtherealProtocol Analysis in Ethereal LCPLCP PAPPAP IPCPIPCP Model:Model: XYZXYZ Application:Application: MMS sendingMMS sending Protocol:Protocol: HTTP / TCP / IP / PPP / CSDHTTP / TCP / IP / PPP / CSD Operator:Operator: China MobileChina Mobile
  22. 22. ConclusionsConclusions  PPP consists of three key components:PPP consists of three key components:  aa method for encapsulating multi-protocol datagramsmethod for encapsulating multi-protocol datagrams  aa Link Control Protocol (LCP)Link Control Protocol (LCP) for establishing, configuring,for establishing, configuring, and testing the data link connectionand testing the data link connection  aa family offamily of Network Control Protocols (NCPs)Network Control Protocols (NCPs) forfor establishing and configuring different network-layerestablishing and configuring different network-layer protocolsprotocols  Roles of PPP in Mobile PhoneRoles of PPP in Mobile Phone  WAP over CSD ~ PPP Dial-OutWAP over CSD ~ PPP Dial-Out  Phone as Modem ~ PPP Dial-InPhone as Modem ~ PPP Dial-In  Protocol Analysis ~ SI2 MMS HTTP/TCP/IP/PPP/CSDProtocol Analysis ~ SI2 MMS HTTP/TCP/IP/PPP/CSD
  23. 23. ReferencesReferences  W. Richard Stevens,W. Richard Stevens, ““TCP/IP Illustrated, Volume 1.”TCP/IP Illustrated, Volume 1.”  James D. Carlson,James D. Carlson, “PPP Design, Implementation and“PPP Design, Implementation and Debugging.”Debugging.”  Andrews Sun,Andrews Sun, “Using & Managing PPP.”“Using & Managing PPP.”  RFC SourcebookRFC Sourcebook ((http://www.networksorcery.com/enp/default0803.htm)http://www.networksorcery.com/enp/default0803.htm)  The TCP/IP GuideThe TCP/IP Guide ((http://www.tcpipguide.com/free/t_PointtoPointProtocolPPP.htm)http://www.tcpipguide.com/free/t_PointtoPointProtocolPPP.htm)

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