北邮高级计算机网络课件 3-Async

Asynchronous Serial Communicationin the real world 异步串行通信北京邮电⼤大学信息⺴⽹网络中⼼心Information Network CenterBeijing University of Posts and Telecommunications版权所有， 1999~2011©1Aganda• What / Why / where to use asynchronous • Compare to synchronous communication • Asynchronous communication• Major technologies– RS232C– Programming API– Modems– Its applications– Testing23 What is Asynchronous Communication • Asynchronous – The transmitter / receiver have clocks with approximately the same frequency. The receiver starts its timing when the first bit arrives, normally not using an external clock. • Synchronous – Synchronous communication system uses a self-synchronizing code which containing the information in addition to the transmitted bits, without using an external clock signal. 什么是异步通信异步同步Asynchronous transmission over a transmission line传输线上的异步通信1 1 0 1 0 0 1Synchronous transmissionover a transmission line传输线上的同步通信• Some widely used self-sync baseband modulation method0 1 0 0 1 1 0 1 0 0 1 10 1 0 0 1 1Manchester NRZI MLT-36Why should we use Asynchronous serial Communications • Economic reason– Devices– Daily / Monthly communication – Maintenance– …• Facility limitation: long distance PSTN • Easy obtain: PC everywhere 为什么使用异步串行通信Async: RS232-C• Standardized by EIA• Electrical Interfaces– ITU-T V.24 Does not specify pin numbers. Details the types of signals to be exchanged. Specifies the absolute voltage levels,impedance's, and timing characteristics for each line.– EIA RS232-C Mechanical Standard Uses V.24 recommendations and further specifies the mechanical connector typeand pin numbers to be used (DB-25 pin connector).– EIA RS232-C Electrical Standard Cables length=15 meters (50 feet), Data line Voltage:1=-3~-25V; 0=+3~+25V7Physical Layout DB-25 DB-9• Picture from Cisco Systems.8PinOut9电气标准Electric StandardDB-25 to DB-9 connection11波形Wave form (with no parity)0 0 1 0 1 1 0异步数据性质波形Async data character waveform13RS-232 communication process monitoring通信过程监控• Hardware– Multi-meter– Protocol analyzer– …• Software– DOS based– Win/xx 14PC结构中的RS232RS-232 in the PC architectureApplicationOSBIOSMotherBoardRS-232CData lines Control linesMicrosoft(R) Windows 95(C)Copyright Microsoft Corp 1981-1996.COM1: 3F8H COM2: 2F8H LPT1: 3BCHC:\WINDOWS> debug-d40:00040:0000 F8 03 F8 02 00 00 00 00-BC 03 00 00 00 00 0F 02 ................ 0040:0010 27 C4 00 80 02 00 00 00-00 00 2E 00 2E 00 67 22 '.............g" 0040:0020 0D 1C 64 20 34 05 30 0B-3A 27 30 0B 0D 1C 00 41 ..d 4.0.:'0....A 0040:0030 00 41 00 41 00 41 64 20-65 12 62 30 75 16 00 00 .A.A.Ad e.b0u... 0040:0040 8A 00 C3 00 00 00 00 00-00 03 50 00 00 10 00 00 ..........P..... 0040:0050 00 0C 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................ 0040:0060 0E 0D 00 D4 03 29 30 76-07 C5 1C 00 48 FF 0B 00 .....)0v....H... 0040:0070 00 00 00 00 00 01 00 00-14 14 14 28 01 01 01 01 ...........(.... -RS-232C RegistersI / O Address I / O Direction Function of register3F8H 3F8H 3F8H * 3F9H * 3F9H 3FAH 3FBH 3FCH 3FDH 3FEH OUTINOUTOUTOUTINOUTOUTININOutput registerInput registerLSBMSBInterrupt enableInterrupt identificationLine controlModem controlLine statusModem statusLine control register (3FBH) bit7 = 1Performance• Relatively Low speed compared with LAN technology !18Typical Connections with DeviceNull-Modem connection20Limitations限制条件• Distance• Speed• Ground2122APIs• JAVA example– SerialPort– SerialPortLocal – SerialConfig – SerLooker– SerOutputStream – SerInputStream – SerByteQueue– SnoopInputStream – SnoopListener – SnoopLoop– SnoopLoopListener• Test • Open • Initialization– Speed – Start bit – Data bits – Stop bit – Parity• Input • Output • Status check • Interrupt handle • Close建立通信的框架Skeleton For Setup communication • Initialization...Setup channeltransmit/receiveflow controlkeyboard/file controlerror detection and error recovery memory managementmodem controlclose connection23Async Comm ProgrammingCom port Test Parameter setup Open connection Ok ?Ok ?Data transmission with error control Retry Ok?Flow control buffer controlfile control Keyboard / voicecontrol Close connection25Flow Control• Definition – techniques for assuring a transmitting device doesn ’t overwhelm a receiving device with data • Stop and Wait Flow Control– 1. Source sends frame – 2. Destination receives frame– 3. Destination sends acknowledgement – 4. Source sends another frame– Source can ’t send another frame until receiver sends acknowledgement – Becomes inefficient with a large number of frames 流控制停等流控制Flow Control滑动窗口流控制• Sliding Window Flow Control– Allows multiple frames to be sent– Full duplex line– Each frame labeled with a sequence number –restarts at 0 once max number is reached– Receiver and sender agree on a fixed number of frames sent or received. Acknowledgement is anumber that indicates the next frame. Implieslower numbered frames have been received26Sliding windows2728Error Control• Error Detection– Parity checks• Append a bit at end of block of data• Even parity – character has even number of 1’s • Odd parity – character has odd number of 1’s– Example• Using 7bit ASCII and odd parity • Send a one byte ---- 1110001• Since using odd parity and there are 4 (even) number of ones a 1 is added to end• Receiver gets character and sees 4 ones and 1 for a parity bit which is odd and since using odd parity says character transmitted ok– If 2 bits inverted it does not pick up error差错控制差错检测OperationTRANSMITTING DATA (DTE to DCE) 1: Assert DTR and RTS2: Wait for DSR3: Wait for CTS4: Transmit the data RECEIVING DATA (DCE to DTE) 1: Assert DTR2: Wait for DSR3: Receive the data操作过程29Flow Control: Hardware /Software流控制硬件软件• Software: Xon / Xoff• Hardware: wiring as -特点General Modem Features • Half-Dup / Full-Dup• Async / Sync• Dial-up / Leased-line• Voice-band / Baseband• FAX / Auto-Answer• ITU-T Standards• Interface: RS-232C / Parallel• Build-in / External• Compress: V.42bis / MNP5• Loop back test.31Modem Setup with ‘at’ command• at is an abbreviation of ‘attention’• atdt • atdp • at&f • at&w • ath • +++• ata• ate0 / ate1 • atz • ...32Protocols• Microcom: MNP 1~10, outdated now.• V.42 Error correction• V.42bis Compression• V.32 9.6Kbps standard, Sync/Duplex • V.34 28.8Kbps standard• V.90 56Kbps3334Async file transfer protocolsXmodem Ymodem Zmodem KermitXon/Xoff × √ × √ 1 Byte Checksum √ × √ × 2 Byte Checksum × × × √Multi File Tranfer × √ √ √Max Block 128 1K 8K 9K Min Block 128 128 10 64 异步文件转换协议Async communication softwares异步通信软件• Commercial– Platform: DOS/Win/UNIX– LAPLINK– PROCOMM– …• Public domain– A lot of on the net for various OS– available for source code of the protocol and software – You may search on the network35Synchronous Comm Baseband信和计算机网络中的信号Sync Signal & Signaling working in the Telecommunication and Computer Network• EIA RS-232C < 200Kbps • EIA RS-422 < 2Mbps• ITU-T V.35 < 2Mbps• E1• E1 DA15 (D-type)• E1 DA15 cables have D-type 15 pin connectors. The pin assignments for the cables are as follows:37V.35 Plug and PinoutA - Ground -B 102(SG) Sig GND -C 105(RS) Snd Request V.28D 106(CS) Send Permit V.28E 107(DR) Snd Ready V.28F 109(CD) CarrierDetect V.28 P 103(SD) Snd Data(A) V.28 R 104(RD) Rcv Data(A) V.28 S 103(SD) Snd Data(B) V.28 T 104(RD) Rcv Data(B) V.28 V 115(RT) Rcv Clk(A) V.28 X 115(RT) Rcv Clk(B) V.28 Y 114(ST2) Snd Clk(A) V.28 AA 114(ST2) Snd Clk(B) V.28C H M S W AA EE KKD J N T X BB FF LLA E K P U Y CC HH MMB F L R V Z DD JJ NN　PC并行通信高速接口 Parallel CommCentronic Port in PCHigh speed ?• Short distance data transfer• 8 bits in parallel• various device: printer, disk, PC,sensors, ...39其他系列的硬件接口Other serial hardware Interfaces • Current LoopRS-422A,RS-449RS-530RS-366IEEE1394USBHSSI• ...4041Other Serial Communication systems in the Real World • IrDA• Bluetooth• HSSI• IEEE 1349• USB• ...实际中其他通信系统42Infra-red communication• Defined by IrDA (Infra-red Data Association)• Wavelength: 0.85µm~0.9µm• A point to point link• IrDA established in 1993/6/28.• IrDA1.0 called SIR(Serial InfraRed), UART based, 115.2Kbps. • IrDA1.1 called Fast InfraRed, FIR, 4Mbps, 4PPM (Pulse Position Modulation), in 1996,• IrDA defined 3 basic protocols, and others– Physical Layer Link Specification– IrLAP - Link Access Protocol– IrLMP - Link Management Protocol– TinyTP, IrOBEX, IrCOMM, IrLAN, IrTran-P• May encounter interferences /红外线通信红外线传输协议栈IrDA protocol stack43Bluetooth• Used for creating wireless personal area networks (PANs) • capable of connecting multiple devices and overcomingproblems arising from synchronization• Communication uses a secure, globally unlicensed Industrial, Scientific, and Medical (ISM) 2.4 GHz frequency band• transmission power of up to 100 mW• a range of up to 100 meters or more depending on environmental conditions• use a 128-bit encryption mechanism• uses 79 channels and has a hopping scheme of 1600 hops per second• Current version is Bluetooth 2.145 Bluetooth protocol stack • LMP (Link Management Protocol)– control of the radio link between two devices • L2CAP (Logical Link Control & Adaptation Protocol) – multiplex multiple logical connections between two devices • SDP (Service Discovery Protocol)– allow devices to discover what services each other support, and what parameters to use• Others:– HCI (Host/Controller Interface) – RFCOMM (Cable replacement protocol) – BNEP (Bluetooth Network Encapsulation Protocol) – AVCTP (Audio/Visual Control Transport Protocol) – AVDTP (Audio/Visual Data Transport Protocol) – Telephony control protocol – others蓝牙协议栈46 USB - Universal Serial Bus• USB is peripheral bus standard developed by PC and telecom industry leaders -- Compaq, DEC, IBM, Intel, Microsoft, NEC and Northern Telecom, 1995 • Feature: plug and play of computer peripherals outside the box, eliminating the need install cards into dedicated computer slots and reconfigure the system• USB v1/v2/v3• Electrical: 3.3V-5v (500mA)• Cable Physical length: <5M• Max devices on the bus: up to 127 USB 接口USB ready devices• cameras, modems, printers, scanners, mice, joysticks, keyboards, sound cards and sound systems, telephony devices, network connections, robotic devices, ...47Wireless USB• Wireless USB Promoter Group • <=3Meters, 480Mbps • <=10m, 110Mbps • Standardization inprogress无线USB4849A RS232 serial to USB converter cable designBenefits of USB DeviceUSB设备的优点• Hot swap• Plug and Play• No extra jumper, no interruption occupied• Power supplied internally with USB cable • High speed transfer rate50。