Communication methods. Communication methods. Communication methods. Dimensions to consider. Waveform

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1 Commuicatio methods Commuicatio methods Media ad sigalig covetios used to trasmit data betwee digital devices Differet physical layers methods icludig: wires, radio freuecy (RF), optical (IR, fiber) Differet ecodig schemes icludig: amplitude, freuecy, ad pulse-width modulatio Modulatio Techiue Waveform No ecodig (Basebad) O-Off Keyig (OOK) Freuecy Shift Keyig (FSK) Biary Phase Shift Keyig (BPSK) CSE/EE 474 Commuicatio 1 Commuicatio methods Dimesios to cosider badwidth umber of wires serial/parallel speed bits/bytes/words per secod timig methodology sychroous or asychroous umber of destiatios/sources arbitratio scheme daisy-chai, cetralized, distributed protocols provide some guaratees as to correct commuicatio CSE/EE 474 Commuicatio 2

2 Badwidth Serial Sigle wire or chael to trasmit iformatio oe bit at a time Reuires sychroizatio betwee seder ad receiver Sometimes icludes extra wires for clock ad/or hadshakig Good for iexpesive coectios (e.g., termials) Good for log-distace coectios (e.g., LANs) Examples: RS-232, Etheret, I2C, IrDA, USB, Firewire, Bluetooth Parallel Multiple wires to trasmit iformatio oe byte or word at a time Good for high-badwidth reuiremets (CPU to disk) More expesive wirig/coectors/curret reuiremets Examples: SCSI-2, PCI bus (PC), PCMCIA (Compact Flash) Issues Ecodig, data trasfer rates, cost of coectors ad wires, modularity, error detectio ad/or correctio CSE/EE 474 Commuicatio 3 Speed Serial low-speed, cheap coectios RS-232 1K 20K bits/sec, copper wire medium-speed efficiet coectios I2C 10K-400K bits/sec, board traces IrDA 9.6K-4M bits/sec, lie-of-sight, m high-speed, expesive coectios USB 1.5M bytes/sec, USB2 60M bytes/sec, USB3 625M bytes/s Etheret 1.5M-1G bits/sec, twisted-pair or co-axial Firewire M bytes/sec Parallel low-speed, ot too wide SCSI-2 10M bytes/sec, 8 bits wide PCI bus, 250M bytes/sec, 32 bits wide PCMCIA (CF+), 9-10M bytes/sec, 16 bits wide high-speed, very wide memory systems i large multi-processors 200M-2G bytes/sec, bits wide CSE/EE 474 Commuicatio 4

3 Speed Issues legth of the wires (atteuatio, oise, capacitace) coectors (coductors ad/or trasducers) eviromet (RF/IR iterferece, oise) curret switchig (spikes o supply voltages) umber ad types of wires (cost of coectors, cross-talk) flow-cotrol (if commuicatig device ca t keep up) CSE/EE 474 Commuicatio 5 Timig methodology Asychroous Fewer wires (o clock) o skew cocers sychroizatio overhead appropriate for loosely-coupled systems (CPU ad peripherals) commo i serial schemes Sychroous clock wires ad skew cocers o sychroizatio overhead ca be high-speed if delays are small ad ca be cotrolled appropriate for tightly-coupled systems (CPU ad memory/disk) commo i parallel schemes CSE/EE 474 Commuicatio 6

4 Timig methodology Issues clock period ad wire delay sychroizatio ad skew ecodig of timig ad data iformatio hadshakig flow-cotrol power cosumptio CSE/EE 474 Commuicatio 7 Number of devices commuicatig Sigle source sigle destiatio poit-to-poit cheap coectios, o tri-statig ecessary Sigle source multiple destiatio faout limitatios addressig scheme to direct data to oe destiatio Multiple source multiple destiatio arbitratio betwee seders tri-statig capability is ecessary collisio detectio addressig scheme priority scheme fairess cosideratios CSE/EE 474 Commuicatio 8

5 Arbitratio schemes Daisy-chai or toke passig devices either act or pass to ext fixed priority order as may wires as devices fairess issues Cetralized reuest to cetral arbiter cetral arbiter implemets priority scheme wires from/to each device ca be costly ca be dyamically chagig priority/fairess Distributed o cetral arbiter commo set of wires (or ether) observed by all devices fixed priority/fairess scheme CSE/EE 474 Commuicatio 9 Serial case studies RS-232 (IEEE stadard) serial protocol for poit-to-poit, low-cost, low-speed applicatios for PCs SPI (Motorola) 10Mbits/sec, commoly used for microcotroller to peripheral coectios I2C (Philips) TWI (Atmel) up to 400Kbits/sec, serial bus for coectig multiple compoets USB (Itel followed by USB-2, ad ow USB-3) Mbits/sec, isochroous trasfer, desktop devices Bluetooth (Ericsso cable replacemet) 700Kbits/sec, multiple portable devices, special support for audio Etheret (popularized by Xerox) most popular local area etwork protocol with distributed arbitratio IrDA (Ifrared Data Associatio) up to 115kbps wireless serial (Fast IrDA up to 4Mbs) IEEE1394 (Apple s Firewire) Mbytes/sec, cosumer electroics (video cameras, TVs, audio, etc.) CSE/EE 474 Commuicatio 10

6 RS-232 stadard serial lie CSE/EE 474 Commuicatio 11 RS-232 (stadard serial lie) Poit-to-poit, full-duplex Sychroous or asychroous Flow cotrol Variable baud (bit) rates Cheap coectios (low-uality ad few wires) Variatios: parity bit; 1, 1.5, or 2 stop bits start bit 8 data bits parity bit stop bit CSE/EE 474 Commuicatio 12

7 RS-232 wires TxD trasmit data TxC trasmit clock RTS reuest to sed CTS clear to sed all wires active low "0" = -12v, "1" = 12v RxD receive data RxC receive clock DSR data set ready DTR data termial ready special driver chips that geerate ±12v from 5v Groud CSE/EE 474 Commuicatio 13 Trasfer modes Sychroous clock sigal wire is used by both receiver ad seder to sample data Asychroous o clock sigal i commo data must be oversampled (16x is typical) to fid bit boudaries Flow cotrol hadshakig sigals to cotrol rate of trasfer CSE/EE 474 Commuicatio 14

8 Serial Peripheral Iterface (SPI) CSE/EE 474 Commuicatio 15 Serial Peripheral Iterface Commo serial iterface o may microcotrollers Simple 8-bit exchage betwee two devices Master iitiates trasfer ad geerates clock sigal Slave device selected by master Oe-byte at a time trasfer Data protocols are defied by applicatio Must be i agreemet across devices CSE/EE 474 Commuicatio 16

9 SPI Block Diagram 8-bits trasferred i each directio every time Master geerates clock Shift eable used to select oe of may slaves CSE/EE 474 Commuicatio 17 Freescale SPI module CSE/EE 474 Commuicatio 18

10 Data Payload o SPI Data is exchaged betwee master ad slave Master always iitiates May eed to poll slave (or iterrupt-drive) Decide o how may bytes of data have to move i each directio Trasfer the maximum for both directios Oe side may get more tha it eeds Decide o format of bytes i packet Startig byte ad/or edig byte? Ca they be distiguished from data i payload? Legth iformatio or fixed size? SPI buffer Write ito buffer, specify legth, master seds it out, gets data New data arrives at slave, slave iterrupted, provides data to go to master, reads data from master i buffer CSE/EE 474 Commuicatio 19 Multiple Slaves o SPI MOSI MISO LCD Module SD Card Reader Bluetooth BLE module CSE/EE 474 Commuicatio 20

11 Iter-Itegrated Circuit Bus (I2C) CSE/EE 474 Commuicatio 21 Iter-Itegrated Circuit Bus (I2C) Modular coectios o a prited circuit board Multi-poit coectios (eeds addressig) Sychroous trasfer (but adapts to slowest device) Similar to Cotroller Area Network (CAN) protocol used i automotive applicatios Similar to TWI (Two-Wire Iterface) o ATmegas +Vcc SCL SDA device 1 device 2 device CSE/EE 474 Commuicatio 22

12 Serial data format SDA goig low while SCL high sigals start of data SDA goig high while SCL high sigals ed of data SDA ca chage whe SCL low SCL high (after start ad before ed) sigals that a data bit ca be read SDA SCL START STOP CSE/EE 474 Commuicatio 23 Byte trasfer Byte followed by a 1 bit ackowledge from receiver Ope-collector wires seder allows SDA to rise receiver pulls low to ackowledge after 8 bits SDA ack SCL Multi-byte trasfers first byte cotais address of receiver all devices check address to determie if followig data is for them secod byte usually cotais address of seder CSE/EE 474 Commuicatio 24

13 Clock sychroizatio Sychroous data trasfer with variable speed devices go as fast as the slowest device ivolved i trasfer Each device looks at the SCL lie as a iput as well as drivig it if clock stays low eve whe beig drive high the aother device eeds more time, so wait for it to fiish before cotiuig risig clock edges are sychroized clk 1 clk 2 SCL CSE/EE 474 Commuicatio 25 Arbitratio Devices ca start trasmittig at ay time wait util lies are both high for some miimum time multiple devices may start together - clocks will be sychroized All seders will thik they are sedig data possibly slowed dow by receiver (or aother seder) each seder keeps watchig SDA - if ever differet (drivig high, but its really low) the there is aother driver seder that detects differece gets off the bus ad aborts message Device priority give to devices with early 0s i their address has higher priority tha CSE/EE 474 Commuicatio 26

14 Iter-Itegrated Circuit Bus (I2C) Supports data trasfers from 0 to 400KHz Philips (ad others) provide may devices microcotrollers with built-i iterface A/D ad D/A coverters parallel I/O ports memory modules LCD drivers real-time clock/caledars DTMF decoders freuecy sythesizers video/audio processors CSE/EE 474 Commuicatio 27 Freescale Block Diagram CSE/EE 474 Commuicatio 28

15 Freescale I2C module CSE/EE 474 Commuicatio 29 USB CSE/EE 474 Commuicatio 30

16 Uiversal Serial Bus Coectig peripherals to PCs Ease-of-use Low-cost Up to 127 devices (optioally powered through bus) Trasfer rates up to 480 Mb/s (USB 2.0) Variable speeds ad packet sizes Full support for real-time data for voice, audio, ad video Protocol flexibility for mixed-mode isochroous data trasfers ad asychroous messagig PC maages bus ad allocates slots (host cotroller) Ca have multiple host cotrollers o oe PC Support more devices tha 127 CSE/EE 474 Commuicatio 31 USB versios CSE/EE 474 Commuicatio 32

17 USB Peripherals CSE/EE 474 Commuicatio 33 USB Tree of devices oe root cotroller CSE/EE 474 Commuicatio 34

18 USB Data Trasfer Data trasfer speeds Low is <0.8v, high is >2.0v differetial 480Mb/sec, 12Mb/sec, 1.5Mb/sec Data is NRZI ecoded (data ad clock o oe wire) SYNC at begiig of every packet CSE/EE 474 Commuicatio 35 NRZI Ecodig NRZI No-retur to zero iverted Toggles a sigal to trasmit a 0 ad leaves the sigal uchaged for a 1 Also called trasitio ecodig Log strig of 0s geerates a regular waveform with a freuecy half the bit rate Log strig of 1s geerates a flat waveform bit stuff a 0 every 6 cosecutive 1s to guaratee activity o waveform CSE/EE 474 Commuicatio 36

19 NRZI Ecodig (cot d) CSE/EE 474 Commuicatio 37 USB Data Trasfer Types Cotrol Trasfers: Used to cofigure a device at attach time ad ca be used for other device-specific purposes, icludig cotrol of other pipes o the device. Bulk Data Trasfers: Geerated or cosumed i relatively large ad bursty uatities ad have wide dyamic latitude i trasmissio costraits. Iterrupt Data Trasfers: Used for timely but reliable delivery of data, for example, characters or coordiates with huma-perceptible echo or feedback respose characteristics. Isochroous Data Trasfers: Occupy a preegotiated amout of USB badwidth with a preegotiated delivery latecy. (Also called streamig real time trasfers) CSE/EE 474 Commuicatio 38

20 USB Packet Format Syc + PID + data + CRC Basic data packet Syc: 8 bits ( ) PID: 8 bits (packet id type) Data: bits (1K bytes) CRC: 16 bits (cyclic redudacy check sum) Other data packets vary i size May be as short as oly 8 bits of PID CSE/EE 474 Commuicatio 39 USB Protocol Stack FTDI USB chip implemets right side Commuicates to physical device through SPI CSE/EE 474 Commuicatio 40

21 USB-C techically kow as USB Type-C a 24-pi USB coector system, which is distiguished by its rotatioally-symmetrical coector. The USB Type-C Specificatio 1.0 was published by the USB Implemeters Forum (USB-IF) ad was fialized i August It was developed at roughly the same time as the USB 3.1 specificatio. A device that implemets USB-C does ot ecessarily implemet USB 3.1, USB Power Delivery, or Alterate Mode. CSE/EE 474 Commuicatio 41 USB-C CSE/EE 474 Commuicatio 42

22 USB-C CSE/EE 474 Commuicatio 43 USB-C CSE/EE 474 Commuicatio 44

23 USB-C CSE/EE 474 Commuicatio 45 USB-C Alterate Modes CSE/EE 474 Commuicatio 46

24 Etheret CSE/EE 474 Commuicatio 47 Etheret (Xerox local area etwork) Local area etwork up to 1024 statios up to 2.8 km distace 10Mbits/sec serially o shielded co-axial cable 1.5Mbits/sec o twisted pair of copper pair Developed by Xerox i late 70s still most commo LAN right ow beig displaced by fiber-optics (ca't hadle video/audio rates or make reuired service guaratees) High-level protocols to esure reliable data trasmissio CSMA-CD: carrier sese multiple access with collisio detectio CSE/EE 474 Commuicatio 48

25 The ISO OSI Referece Model Host A Applicatio Presetatio Sessio Trasport Network Data Lik Physical Host B Applicatio Presetatio Sessio Trasport Network Data Lik Physical Physical Medium CSE/EE 474 Commuicatio 49 The ISO OSI Referece Model Layer 6/7 Iterface Layer 5/6 Iterface Layer 4/5 Iterface Layer 3/4 Iterface Layer 2/3 Iterface Layer 1/2 Iterface Host A Applicatio Presetatio Sessio Trasport Network Data Lik Physical Layer 7 Protocol Layer 6 Protocol Layer 5 Protocol Layer 4 Protocol Layer 3 Protocol Layer 2 Protocol Layer 1 Protocol Host B Applicatio Presetatio Sessio Trasport Network Data Lik Physical Physical Medium CSE/EE 474 Commuicatio 50

26 The ISO OSI Referece Model Iterface: It defies which primitive operatios ad services the lower layer offers to the upper layer. Peer: The similar layer o a differet machie. Protocol: It is a set of rules ad covetios used by the layer to commuicate with similar peer layer i aother (remote) system. The peer processes commuicate with each other usig a protocol. A set of layers ad protocols is called a etwork architecture. CSE/EE 474 Commuicatio 51 The ISO OSI Referece Model I reality, o data are directly trasferred from layer i o oe machie to layer i o aother machie. Istead, each layer passes data ad cotrol iformatio to the layer immediately below it, util the lowest layer is reached. Below layer 1 is the physical medium through which actual commuicatio occurs. Host A Host B Protocol Sed-To-Other-side ( ) Get-From-Other-side ( ) Layer i (Virtual Commuicatio) Layer i CSE/EE 474 Commuicatio 52

27 Etheret layered orgaizatio Physical ad data-lik layers are our focus Cliet Layer Trasport Layer Data-lik Layer Physical Layer To Host Host-specific Iterface Data-lik Cotroller Physical Chael Data Ecapsulatio Lik Maagemet Serial Ecode ad Decode Trasmit ad Receive Electrical Iterface Etheret Cable Etheret Cotroller IC Trasceiver parallel data serial data CSE/EE 474 Commuicatio 53 Serial data format Machester ecodig sigal ad clock o oe wire (XORed together) "0" = low-goig trasitio "1" = high-goig trasitio Extra trasitios betwee 00 ad 11 eed to be filtered preamble at begiig of data packet cotais alteratig 1s ad 0s allows receivers to get used to where importat trasitios should be ad igore extra oes (this is how sychroizatio is achieved) preamble is 48 bits log: CSE/EE 474 Commuicatio 54

28 Etheret packet Packets size: 64 to 1518 bytes + 6 bytes of preamble preamble (6 bytes) destiatio address (6 bytes) source address (6 bytes) type (2 bytes) data ( bytes) checksum (4 bytes) compute from data CSE/EE 474 Commuicatio 55 Arbitratio Wait for lie to be uiet for a while the trasmit detect collisio average value o wire should be exactly betwee 1 ad 0 if ot, the two trasmitters are tryig to trasmit data If collisio, stop trasmittig wait a radom amout of time ad try agai if collide agai, pick a radom umber from a larger rage (2x) ad try agai Expoetial backoff o collisio detectio Try up to 16 times before reportig failure CSE/EE 474 Commuicatio 56

29 Arbitratio CSE/EE 474 Commuicatio 57 Extedig Etheret Segmets, repeaters, ad gateways segmet: a sigle cable repeater: trasfers all messages o oe segmet to aother ad vice-versa gateway: selectively forwards messages to other segmets ad helps isolate traffic Segmet Repeater Gateway CSE/EE 474 Commuicatio 58

30 IrDA: Ifrared Data Associatio CSE/EE 474 Commuicatio 59 Ifrared Data Associatio Cosortium of over 160 compaies Meet eeds of the mobile professioal Short iteractios with other devices (file trasfer, pritig) Possibly usig others peripherals (visitig a customer s office) Goals: Suitable replacemet for cables Iteroperability Miimal cost Poit-ad-shoot model (iteded use ad to reduce iterferece) History: First stadard developed i 1994 Revisios as recetly as late 2011 (i.e., still active) CSE/EE 474 Commuicatio 60

31 IrDA: Ifrared Data Associatio Characteristics of IR: Implemetatio costs rise sigificatly aroud 1-10 GHz oe importat exceptio is IR at aroud 100 THz very iexpesive Sigals above 100 GHz caot peetrate walls Most sigals below 300 GHz are regulated by the FCC Radio (RF) Microwaves Visible Ifrared (IR) Ultraviolet X-Rays Gamma Rays $ FCC Fre. (Hz) CSE/EE 474 Commuicatio 61 Speed Compoets iclude: Trasmitter (LED) ad paired receiver (photodiode) IrDA supports wide rage of speeds 2400 bps to 4 Mbps Exact physical-layer protocol used depeds o speed of IrDA coectio Uses highest speed available o both devices determied whe coectio is established Future promises eve higher speeds: Mbps is ot too far off Compariso to other wireless techologies: Low-power RF (e.g., Bluetooth) slightly slower (.5-2 Mbps max) Boud by walls, easy to cotrol, itetioal aspect Much lower-power tha high-speed RF (e.g., a at 50Mbps) CSE/EE 474 Commuicatio 62

32 Low-speed Modulatio Speed: 2400 bps kbps ( Serial Ifrared, or SIR) Oly 0 s reuire pulse (ad thus power) ; pulse < full bit time Stadard UART byte framig Pulse is costat 1.6 µs log (so duty cycle varies with speed) Average duty cycle: 9% Speed: 576 kbps - 1 Mbps similar to SIR (pulse oly for 0 s ; pulse < full bit time) pulse lasts 1/4 of bit time (so pulse varies with speed) Average duty cycle: 12.5% Speed: 4 Mbps ( Fast Ifrared, or FIR) uses four-pulse-positio-modulatio scheme (4PPM) pulse durig exactly 1/4 of each symbol boudary 4PPM makes sychroizatio easier to maitai Duty cycle: 25% (idepedet of data) Lowest power/bit CSE/EE 474 Commuicatio 63 Rage Liear: IrDA stadard reuires 0-1 m Realistically, some trasceivers work at up to 10 m Agular: Limited to a arrow coe (15 half-agle) Doe to help reduce iterferece betwee devices 0-1 m CSE/EE 474 Commuicatio 64

33 IrDA Protocol Stack Aalogous to the stadard layered etwork model Cosists of both reuired ad optioal compoets Applicatio Layer Trasport Layer Network Layer Data-lik Layer Physical Layer Stadard Network Model IrCOMM IrLAN IrOBEX TiyTP IrLMP IrLAP Physical Layer IrDA Protocol Stack Serial ad parallel port emulatio IrDA iterface acts as a local-area etwork IR Object Exchage trasfer of objects Segmetatio ad re-assembly automatically break-up large packets (ad put back together correctly) Per-chael flow cotrol Multiplexes several virtual coectios o a sigle IrLAP coectio (logical service access poits LSAPs) Hadle coectios/discoectios Implemet reliable trasfer CSE/EE 474 Commuicatio 65 Protocol Overhead Very simple model (poit-to-poit), so ca expect reduced protocol overhead For layers i IrDA protocol stack, overhead per packet/frame is: IrLAP = 2 bytes IrLMP = 2 bytes Total: 5 bytes TiyTP = 1 byte For perspective, compare to TCP/IP over Etheret: Etheret = 18 bytes miimum IP = 20 bytes Total: 58 bytes (miimum) TCP = 20 bytes IrDA takes advatage of its simpler model, ad keeps protocol overhead very low. CSE/EE 474 Commuicatio 66