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8 - 1 ©T.C. Chang 12/19/2014 Chapter 8. DATA COMMUNICATION Need: Design file exchange. Part program downloading. Person to person communication - e-mail,

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Presentation on theme: "8 - 1 ©T.C. Chang 12/19/2014 Chapter 8. DATA COMMUNICATION Need: Design file exchange. Part program downloading. Person to person communication - e-mail,"— Presentation transcript:

1 8 - 1 ©T.C. Chang 12/19/2014 Chapter 8. DATA COMMUNICATION Need: Design file exchange. Part program downloading. Person to person communication - , talk, video conferencing. System control: commands, status data, sensor data Remote login. 50% of plant floor computer system cost are allocated to networking costs. How to make control devices talk to each other. Solutions: Point-to-point communication Networking

2 8 - 2 ©T.C. Chang 12/19/2014 METHODS OF COMMUNICATION Point-to-Point: direct connection of two devices –Discrete I/O points – one bit at a time. –Serial port –data byte transmitted in serial pulses. –Parallel port – data byte transmitted in parallel. Network: multiple devices connected to the same media (cable, radio wave, etc.) –Ethernet –FieldBus –MAP, etc.

3 8 - 3 ©T.C. Chang 12/19/2014 A COMPUTER

4 8 - 4 ©T.C. Chang 12/19/2014 AN I/O BUFFER clock Individual bits can be used for discrete I/O.

5 8 - 5 ©T.C. Chang 12/19/2014 ASCII CODE High Bits low SOHDC1!1AQaq 0010STXDC2"2BRbr 0011ETXDC3#3CScs 0100EOTDC4$4DTdt 0101ENQNAK%5EUeu 0110ACKSYN&6FVfv 0111BELETB'7GWgw 1000BSCHN(8HXhx 1001HTEM)9IYiy 1010LFSUB*:JZjz 1011VTESC+;K[k{ 1100FFFS,N^n~ 1111SIUS/?O_oDE

6 8 - 6 ©T.C. Chang 12/19/2014 COMMUNICATION MODES Simplex can be viewed as a communications "one-way street". Data only flows in one direction. That is to say, a device can be a receiver or a transmitter exclusively. A simplex device is not a transceiver. A good example of simplex communications is an FM radio station and your car radio. Information flows only in one direction where the radio station is the transmitter and the receiver is your car radio. Simplex is not often used in computer communications because there is no way to verify when or if data is received. Duplex communications overcome the limits of Simplex communications by allowing the devices to act as transceivers. Duplex communication data flows in both directions thereby allowing verification and control of data reception/transmission. Exactly when data flows bi-directionally further defines Duplex communications.

7 8 - 7 ©T.C. Chang 12/19/2014 SIMPLEX AND DUPLEX (CONTINUE) Full Duplex devices can transmit and receive data at the same time. Half Duplex devices allow both transmission and receiving, but not at the same time. Essentially only one device can transmit at a time while all other half duplex devices receive.

8 8 - 8 ©T.C. Chang 12/19/2014 SERIAL COMMUNICATION Parallel From the Data bus DTEDCE Null Modem connector does the swapping

9 8 - 9 ©T.C. Chang 12/19/2014 INTERFACE DTE: Data Terminal Equipment (terminal), PC, male connector DCE: Data Circuit-terminating Equipment (modem, computer), female connector DCE DTE RS 232C, RS 422, X.21 RS232C 25 pin connector DB25 connector 1 < -3V 0 > 3V < 20 kbps < 15 m unbalanced signal RS pin or 9 pin twisted pair balanced 100 kbps at 1200m 10 mbps at 12 m or unbalanced (RS 423A) 3 kbps at 1000 m 300 kbps at 10 m X.21 packet transmission mode

10 ©T.C. Chang 12/19/2014 TRANSMITTING THE LETTER 'S' 2 stop bits start letter 'S' parity bit 1 start bit 7 data bit 1 parity bit 2 stop bits time 0 Volt sec/bit Baud rate = 1/ clock Even parity Some modem standards transfer more than one bit per clock cycle. e.g. V.32bis transmit 6 bits per baud. 0: Space 1: Mark

11 ©T.C. Chang 12/19/2014 RS 232 PINNAME FUNCTIONEIACCITT 1FGFrame GroundAA101 2TD>Transmitted DataBA103 3RDRequest to SendCA105 5CTSSec. Transmitted DataSBA118 15TCSec. Request to sendSCA120 20DTR>Data Terminal ReadyCD SOData Rate SelectorCH111 Data Rate SelectorCI112 24(E)TC>Ext. Transmitter ClockDA Unassigned--

12 ©T.C. Chang 12/19/2014 RS 422 RS422 is a "drop-in" replacement for most RS232 applications. It is full-duplex and capable of long distance communications. Use balanced signal over twisted pair of wire, allows much faster speed and longer distance.

13 ©T.C. Chang 12/19/2014 COMPARISIONS RS 232RS 422RS 485 Cablingsingle endedsingle ended multi-drop multi-drop Number of Devices1 transmit 1 receive 5 transmitters 10 receivers 32 transmitters 32 receivers Communication mode full duplexfull duplex half duplex half duplex Max. Distance50 feet at 19.2 kbps4000 feet at 100 kbps4000 feet at 100 Kbps Max. Data Rate19.2 kbps for 50 feet10 Mbps for 50 feet SignalingUnbalancedBalanced Mark (data 1)-5 V min. -15 V max. 2 V min. (B>A) 6 V max. (B>A) 1.5 V min. (B>A) 5 V max. (B>A) Space (data 0)5 V min. 15 V max. 2 V min. (A>B) 6 V max. (A>B) 1.5 V min. (A>B) 5 V max. (A>B) Input Level Min.+/- 3 V0.2 V difference Output Current500 mA150 mA250 mA

14 ©T.C. Chang 12/19/2014 Modem Flow control –Software through XON and XOFF –Hardware through pin outs, I.e. request to send (RTS), clear to send (CTS), data terminal ready (DTR), and data set ready (DSR) Modulating the Signal –1 baud = one audio signal transitions per second –Frequency-shift keying (FSK): 1750 Hz for 1, 1080 Hz for 0. 1 baud = 1 bps –Phase-shift keying (PSK): 0 and 1 are represented by the alteration of the carrier’s phase. Bit is coded at fixed phase shift, e.g. 0, 90, 180, and 270 degrees. More bits per baud. –Quadrature-amplitude modulation (QAM): combine both phase and frequency. At 1700 Hz or 1800 Hz of 2400 baud, each phase-shift keyed. Six bps data per baud. Only 4 data bits usable. –Trellis-coded quadrature-amplitude modulation (TCQAM or TCM): Use all 6 data bits. 14,400 bps modems use this.

15 ©T.C. Chang 12/19/2014 MODEM STANDARDS (reference only) CCITT V.XX standards (Consultative Committee for International Telephone and Telegraph) V.22, V.22 bis. : synchronous/asynchronous data transmission, full-duplex operation over 2 wire at 1,200 bps (2,400 and 1,200 bps for V.22 bis) data rate. V.32 : synchronous/asynchronous data transmission, full-duplex operation over 2 wire at 9,600 bps data rate. V.32 bis: synchronous/asynchronous data transmission, full-duplex operation over 2 wire at 14,400, 12,000, 9,600, 7,200, 4,800 bps data rate. V.34 bis: synchronous/asynchronous data transmission, full-duplex operation over 2 wire at 28.8k,... Modem-connection negotiations (training and retraining), may reduce the data rate due to line noise. Fastrain: may go up the speed as well. V.35 Duplex: full (two lines, two way), half (one line, one way) Bell standard: Bell 103, 300 bps; Bell 201B: 2,400 bps, full duplex on 4 wire, or 1,200 bps, half duplex on 2 wire. Bell 201C: 2,400 bps, half duplex on 2 wire; Bell 208 A & B: 4,800 bps Data compression: compress the data before transmission.

16 ©T.C. Chang 12/19/2014 PARALLEL INTERFACE ADAPTER address decoder enable

17 ©T.C. Chang 12/19/2014 PC Parallel Port

18 ©T.C. Chang 12/19/2014 IEEE 488 Standard digital interface for programmable instrumentation HP interface (originally, is available on most instruments) GPIB (General Purpose Interface Bus) 1 mbps The IEEE-488 interface system consists of 16 signal lines and 8 ground lines. The 16 signal lines are divided into 3 groups (8 data lines, 3 handshake lines, and 5 interface management lines). Devices on the bus are: Listeners, Talkers, and Controllers up to 15 devices to be interconnected on one bus. Each device is assigned a unique primary address, ranging from 0-30, by setting the address switches on the device. A secondary address may also be specified,ranging from Total cable length is limited to 20 meters with a maximum of 20 devices. TTL level signal.

19 ©T.C. Chang 12/19/2014 OTHER INTERFACES TheoreticalActual First-Byte Latency USB1.5 Mbytes/s1.25 Mbytes/s20 ms Mbytes/s9.6 Mbytes/s6 ms GPIB1 Mbytes/s 110 µs HS4888 Mbytes/s7.7 Mbytes/s110 µs Mostly for instrumentation. GPIB (IEEE 488) is still the major players.

20 ©T.C. Chang 12/19/2014 DATA EXCHANGE METHODS Polling Interrupt Direct Memory Access (hard disk to computer)

21 ©T.C. Chang 12/19/2014 POLLING

22 ©T.C. Chang 12/19/2014 INTERRUPT high priority interrupt low priority interrupt Main CPU Loop

23 ©T.C. Chang 12/19/2014 NETWORKS No longer a point-to-point connection. Many devices connected together and information can be passed by one device to any of the devices on the network. Local area network - Ethernet, FDDI (Distributed Data Interface), ATM (Asynchronous Transfer Mode) Wide area network High speed local network

24 ©T.C. Chang 12/19/2014 GLOSSARY OF SELECTED TERMS Bandwidth: frequency range used by the communication system. Baseband: use voltage difference (digital) Broadband: use coaxial cable and analog (RF) signals. Higher band width, multiple channels on the same cable. Digital signals are modulated on a carrier frequency. CTV: 5 mbps per channel Carrier from M Hz Carrier: A continuous frequency capable of being modulated or impressed with a second (information) signal. DDS (Dataphone Digital Service): AT&T service in which data is transmitted in digital rather than analog form. Need no modem. FDDI (Fiber Distributed Data Interface): ANSI standard for fiberoptic links with data rates up to 100 mbps. LED or laser light source; 2 km for unrepeated data transmission at 40 mbps. ISDN (Integrated Services Digital Network): mixed digital-transmission services, basic rate at 144 kbps, and primary rates at and mbps.

25 ©T.C. Chang 12/19/2014 GLOSSARY OF SELECTED TERMS Medium Access Control: controls which device on the network get the to send data to the medium. CSMA/CD Token Ring Token Bus Packet: small chunk of data. Protocol: a set of rules that governs the operation of functional units to achieve communication. TCP/IP: Transport protocols concurrently with existing Ethernet. NFS: network file system - file system sharing, remote disk mounting.

26 ©T.C. Chang 12/19/2014 IDEAL LAN CHARACTERISTICS high speed: greater than 10 mega bits per second low cost: easily affordable on a microcomputer and/or machine controller high reliability/integrity: low error rates, fault tolerant, reliable expandability: easily expandable to install new nodes installation flexibility: easy to be installed in an existing environment interface standard: standard interface across a range of computers and controllers.

27 ©T.C. Chang 12/19/2014 COMMUNICATION NETWORK Protocol – defines both physical and software rules. Most widely accepted model is a 7 layered protocol model.

28 ©T.C. Chang 12/19/2014 ISO/OSI MODEL

29 ©T.C. Chang 12/19/2014 LAYERED PROTOCOL 2. DATA LINK LAYER flow control error control Activate, maintain and deactivate the link. Error free transmission on the same network. Detecting noise. (media access, logical link) 3. NETWORK LAYER provides the transparent transfer of data between transport entities. Responsible for establishing, maintaining, and terminating connections (between networks). Use globally unique node address. 4. TRANSPORT LAYER Ensures that data units are delivered error-free, in sequence, without no losses or duplications. Connection management

30 ©T.C. Chang 12/19/2014 LAYERED PROTOCOL 5. SESSION LAYER Controlling the dialogue between applications. Dialogue type: two-way simultaneous (TWS), two-way alternate (TWA), one-way, etc. Recovery after network breakage. 6. PRESENTATION LAYER Syntax of the data exchanged between application entities. e.g. teletext, videotex, encryption, virtual terminal. 7. APPLICATION LAYER Common application services (CASE) Specific application services (SASE) Management file transfer job transfer

31 ©T.C. Chang 12/19/2014 A PACKET Preamble Physical layer message Data link layer message Network layer message Transport layer message Session layer message Presentation layer message Application layer message Data Checksum Postamble SYN code

32 ©T.C. Chang 12/19/2014 CABLES Coaxial cable Twist pair cable Thick: CATV, RG-59, 75 ohms Thin: Ethernet, RG-58, 52 ohms Unshielded: Shielded: signal loss, thick Fiber-optic Cable core cladding (62.5 micron) noise immune

33 ©T.C. Chang 12/19/2014 LAN TOPOLOGIES

34 ©T.C. Chang 12/19/2014 ETHERNET

35 ©T.C. Chang 12/19/2014 COLLISION DETECTION CSMA/CD (Carrier sensing) protocol

36 ©T.C. Chang 12/19/2014 ETHERNET CONNECTIONS Standard Ethernet (10BASE5) segment length  500 m cable  4 km transceiver cable  50 m between transceivers  2.5 m  100 transceivers per segment 50 ohm terminators ThinNet Ethernet (10BASE2) segment length  185 m cable length  4 km T-connectors, 0.5 m between each  30 connections 50 ohm terminators T-connectors plugged directly to the Ethernet card. Twisted-pair Ethernet (10BASE-T) segment length  100 m unshielded twisted-pair cable devices connected to a hub in a star configuration Hub connected to the standard Ethernet Use twisted-pair transceiver. Hub computers T-connector

37 ©T.C. Chang 12/19/2014 A TOKEN RING Only one token is passed around the network. The device who has the token may transmit.

38 ©T.C. Chang 12/19/2014 A TOKEN BUS Token passing network. Whoever has the token may transmit one or more packets. When it is done, or the time has expired, it passes the token to the next station.

39 ©T.C. Chang 12/19/2014 RS 485 BASED NETWORK S485 is sometimes termed as RS485 Multidrop LAN since it can connect several devices in a LAN network environment. These devices are all connected to a single pair wire. Transmit and receive share the same two wires. Officially the RS485 specification allows only 32 nodes (devices) on the LAN. However, I.C. manufacturers have developed RS485 drivers capable of allowing 128 to 255 nodes on an RS485 LAN.

40 ©T.C. Chang 12/19/2014 FIELD BUS Foundation Field Bus - A Fieldbus is a digital, two-way, multi-drop communication link among intelligent measurement and control devices. It serves as a Local Area Network (LAN) for advanced process control, remote input/output and high speed factory automation applications. The Fieldbus Access Sublayer (FAS) maps the Fieldbus Message Specification (FMS) onto the Data Link Layer (DLL). High Speed Ethernet (HSE) is the Fieldbus Foundation's backbone network running at 100 Mbit/second. Bus speed is kbit/s. Can communicate with other devices through HSE using Ethernet protocols such as TCP/IP, SNTP, etc.

41 ©T.C. Chang 12/19/2014 FIELDBUS MODEL Fieldbus message specification Fieldbus access sublayer Data link layer Physical layer Layer 7. Application Layer 2. Data link Layer 1. Physical

42 ©T.C. Chang 12/19/2014 MEDIA ACCESS CONTROL Token passing network Token controlled by a Link Active Scheduler (master of the network). Other devices on the network are basic devices. The device which holds the token can transmit to any other devices on the network.

43 ©T.C. Chang 12/19/2014 APPLICATIONS OF FIELDBUS Sensors and actuators.

44 ©T.C. Chang 12/19/2014 NETWORK HIERARCHY Plant wide network Control system and LANs Fieldbus network Office automation and department computers Automation and display systems Factory/plant instrumentation and control devices

45 ©T.C. Chang 12/19/2014 Allen-Bradley Networks

46 ©T.C. Chang 12/19/2014 DEVICE NET From Rockwell Automation, Allen-Bradley devision. Based on the Fieldbus. Low level, 64-node multidrop network using single cable to interface devices up to 500 m to PLC. Use either two twisted pair wires (24V) in a round cable, or two pair wires flat cable. Data rates, 500 kbps (100 m), 250 kbps (250 m), 125 kbps (500 m). Many sensors are device net ready.

47 ©T.C. Chang 12/19/2014 CONTROL NET By Rockwell Automation, Allen-Bradley For time critical applications. High-speed link between controller and I/O devices. 5 mbps 30 km or more using repeaters (in star, tree, or bus configuration), 1000 m w/o repeater. Physical layer can be fiber optic or 75 o cable.

48 ©T.C. Chang 12/19/2014 ETHERNET II Preamble 8 bytes Destination 6 bytes Source6 bytes Ethernet type2 bytes (IPX/SPX, TCP/IP, etc) Data46 – 1500 bytes Pad Characterup to 46 bytes Frame check sequence4 bytes Frame length: bytes (not including preamble)

49 ©T.C. Chang 12/19/2014 NOVELL’S LAN Physical layer – 3C5X9.com LAN driver Data link Layer – LSL.com Network Layer – IPX0D1.com ODI NDIS Transport – TCP/IP.exe Socket API - winsock.dll Application layer - windows ftp, http, telnet

50 ©T.C. Chang 12/19/2014 MAP 2.1 STANDARD LayerMAP implementation Layer 7ISO FTAM {DP} 8571 ApplicationFile Transfer Protocol Manufacturing Messaging Format Standard (MMFS) MAP Directory Services MAP Network Management Layer 6 PresentationNULL/MAP transfer Layer 5ISO Session{IS} 8327 SessionBasic Combined Subset & Session Kernel, Full Duplex Layer 4 TransportISO Transport{IS} 8073 Class 4 Layer 3ISO Internet{DIS} 8473 NetworkConnectionless, SubNetwork Dependent Convergence Protocol Layer 2ISO Logical Link Control {DIS} 8802/2 (IEEE 802.2) Data LinkType 1, Class 1 ISO/IEEE Token Passing Bus Medium Access Control Layer 1ISO Token Passing Bus{DIS} 8802/4 (IEEE 802.4) Physical10 Mbps Broadband

51 ©T.C. Chang 12/19/2014 An Integrated Corporate Communication Network Bridge Corporate TOP network Gateway IBM SNA network Corporate Ethernet Division TOP network CAD/CAM CRT Finance/accounting Office MAP Backbone Gateway MAP Sub Network Router Data base Terminal server CRT Office TOP network Gateway Vendor Network Gateway Robots Machines PLCs Robots Corporate Offices Factory

52 ©T.C. Chang 12/19/2014 ISDN: Integrated Service Digital Network B channel: 64 kbps - basic user channel D channel: 16 or 64 kbps - control, setup, calls on B.ch. common chan H0: 384 kbps H11: Mbps H12: 1.92 Mbps Basic access: two B-channels and one D channel - total 144 kbps Primary access: T-1 transmission at Mbps, 23 B-channels, 1 D channel terminal equip. ISDN switch packet-switched capabilities circuit-switched nonswitched common-channel signaling terminal equip. ISDN switch

53 ©T.C. Chang 12/19/2014 Frame Relay and ATM On top of the physical layer Frame Relay: –Use on ISDN line, assume less transmission error. Less overhead than X.25 packet-switching. –Block data transfer, up to 2 Mbps ATM: Asynchronous Transfer Mode –For broadband ISDN –packet switching »X.25 - control, data on the same channel, variable length »ATM - separate, fixed length (cells), 10s and 100s Mbps

54 ©T.C. Chang 12/19/2014 COMMUNICATION REQUIREMENTS 10 Kbps56 Kbps 1.54 Mbps Mbps 100 Mbps 1.2 Gbps Ordinary PhoneBasic rate ISDN Primary rate ISDN Ethernet and Token Ring Fast Ethernet, FDDI Asynchronous Transfer Mode (ATM) Speech grade audio (32-64 Kbps) Low quality compressed video (50 Kbps Mbps) High fidelity audio (64 Kbps Mbps) Medium quality compressed video (1.5 Mbps - 6 Mbps) High quality compressed video (6 Mbps - 24 Mbps)

55 ©T.C. Chang 12/19/2014 COMMUNICATION ON UNIX NETWORK INTERFACE LAYER PROTOCOL LAYER SOCKET LAYER IN buffer Out buffer Application e.g. ftp telnet Protocol Network interface out packet In packet Hardware determines the route of travel when a communication is desired, create a socket get protocol

56 ©T.C. Chang 12/19/2014 EXAMPLE s = socket(AF_INET, SOCK_STREAM,0); /* create a socket*/ connect(s,&server, sizeof(server)); /* establish connection */ write(s,buf,sizeof(buf)); /* send data */ close(s); /* close socket*/ internet domainfor TCP protocol #include sockaddr server;

57 ©T.C. Chang 12/19/2014 TCP/IP PROTOCOL UDP: User datagram protocol FTP: File transfer protocol SMTP: Simple mail transfer protocol TELNET: Virtual terminal protocol TCP: Transmission control protocol IP: Internetwork protocol Application Presentation Session Transport Network Data Link Physical Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 User Program UDP FTP SMTP TELNET TCP IP ETHERNET

58 ©T.C. Chang 12/19/2014 DATA COMMUNICATION ALTERNATIVES Phone and fax BBS (bulletin board system) run your own. Commercial information vendors: CompuServe, Prodigy, America Online, GEnie Internet connection

59 ©T.C. Chang 12/19/2014 WHAT IS INTERNET? Internet is a loosely connected wide area network. It is a group of worldwide information resources open to everyone on the network. Some characteristics of the internet: Origin: Arpanet sponsored by US DOD in the 1970s. Who may participate? Anyone who pays a nominal fee to connect to a nearby network and agrees to follow a set of rules. Who runs the network? Nobody is in charge. Who pays for it and to whom? The organization who is connected to the network must pay it own segment of the network. There is no central organization to collect the payment. What kind of hardware is needed to run the network? Any kind of computer hardware. How to connect to a network? Find a closest node and negotiate the connection. What is the limitation of using it? No direct commercial use. What is most widely used operating system on the net? Unix. How big is the network? Too big and growing to be even bigger every minute.

60 ©T.C. Chang 12/19/2014 INTERNET ROUTERS INTERNET network layer data link physical layer network layer data link physical layer network layer data link physical layer Network A Network B Network C


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