Protokol Komunikasi @2012,Eko Didik Widianto Topologi ... · berefek pada satu node I Cocok untuk ﬁber optik ... I Rangkaian (digital) harus memberikan sinyal HI dan LO di jalur

Protokol Komunikasi

@2012,Eko DidikWidianto

Topologi Jaringan

Teknik Transmisi Data

Protokol Komunikasi

Lisensi

Prokotol KomunikasiKuliah#9 TSK-612 Sistem Embedded Terdistribusi - TA

2011/2012

Eko Didik Widianto

Teknik Sistem Komputer - Universitas Diponegoro

http://didik.blog.undip.ac.id/2012/03/06/kuliah-tsk-612-sistem-embedded-terdistribusi-2011/

Protokol Komunikasi


Topologi Jaringan


Protokol Komunikasi

Lisensi

Review Kuliah

I Sebelumnya telah dibahas tentang metodologi desainsistem embedded terdistribusi

I Marketing & Engineering SpecsI ArsitekturI Software SpecsI DesainI ImplementasiI Pengujian


Protokol Komunikasi


Topologi Jaringan


Protokol Komunikasi

Lisensi

Tentang Kuliah #9 Protokol Komunikasi

I Jika ingin membuat sistem embedded terdistribusiI Maka diperlukan jaringan

I Pokok Bahasan:I Sistem bus: jaringan embedded, multiplexing, busI Menempatkan bit ke jalur transmisi: antarmuka fisik,

enkoding bitI Klasifikasi protokol: operasi umum, trade-off (tidak ada

protokol yang ’terbaik’), wired vs wireless

I LinkI Website: http://didik.blog.undip.ac.id/2012/03/06/

kuliah-tsk-612-sistem-embedded-terdistribusi-2011/I Email: [email protected]

I Acknowledgement:I http://www.ece.cmu.edu/~ece649/[ECE649]




mailto:[email protected]

http://www.ece.cmu.edu/~ece649/

Protokol Komunikasi


Topologi Jaringan


Protokol Komunikasi

Lisensi

BahasanTopologi Jaringan

Topologi BusTopologi Star

Teknik Transmisi DataTransmisi Data (Bit)Noise ReductionProteksi Terhadap SpikeEnkoding (Channel)Message

Protokol KomunikasiCoordination: Bus Master ApproachCoordination: Transmit and Hope (CSMA)Coordination: Explicit TokensCoordination: Implicit TokensBinary Countdown (Bit Dominance)EmulationWireless Networks

Lisensi


Protokol Komunikasi


Topologi JaringanTopologi Bus

Topologi Star


Protokol Komunikasi

Lisensi

Topologi Jaringan

I Topologi jaringan sistemembedded

I Linear: busI satu jalur bus

digunakan secarabersama

I multiplexing aksesjalur

I StarI satu node menjadi

pusat


Protokol Komunikasi



Topologi Star


Protokol Komunikasi

Lisensi





Lisensi


Protokol Komunikasi



Topologi Star


Protokol Komunikasi

Lisensi

Topologi Bus

I Sistem jaringan busI Cocok untuk komunikasi berjarak jauh antar-subsistem

I Misalnya: elevator, jalur perakitanI Digunakan di sebagian besar sistem kontrol embedded

I Sistem jaringan desktop sebelumnya menggunakan busI Beragam opsi protokol dapat diimplementasikan (fleksibel)I Putusnya satu segmen kabel akan memisahkan busI Tidak cocok untuk jalur fiber optik karena masalah di splitting dan

mergingI Contoh:

I serial comm, CAN (Controller Area Network), Inter-IntegratedCircuit (I2C), Serial Peripheral Interface (SPI), Firewire (high speedserial bus IEEE 1394)


Protokol Komunikasi



Topologi Star


Protokol Komunikasi

Lisensi





Lisensi


Protokol Komunikasi



Topologi Star


Protokol Komunikasi

Lisensi

Topologi Star

I Sistem jaringan starI Dapat mengemulasikan

fungsi busI Mudah untuk mendeteksi

dan mengisolasi kegagalanI Terputusnya jalur hanya

berefek pada satu nodeI Cocok untuk fiber optik

I Memerlukan lebih banyak pengkabelanI Digunakan secara umum di sistem desktop

I Terputusnya hub (sebagai pusat jaringan) berakibat satu jaringanterputus

I Bisa digunakan untuk mengisolasi node yang membangkitkan terlalubanyak trafik

I Topologi star ini semakin populerI jaringan kontrol yang safety-critical menggunakan dual redundant

star (dua jaringan independen, tiap jaringan mempunyai topologistar)


Protokol Komunikasi


Topologi Jaringan

Teknik Transmisi DataTransmisi Data (Bit)

Noise Reduction

Proteksi Terhadap Spike

Enkoding (Channel)

Message

Protokol Komunikasi

Lisensi





Lisensi


Protokol Komunikasi


Topologi Jaringan


Noise Reduction


Enkoding (Channel)

Message

Protokol Komunikasi

Lisensi

Transmisi Data (Bit)

I Rangkaian (digital) harusmemberikan sinyal HI dan LO dijalur bus

I Contoh: HI = ’1’ = 5 volt danLO = ’0’ = 0 volt

I Titik referensi: GNDI Sistem embedded harus tahan

terhadap noise (noise immunity)I Isolasi noise di node tunggal

sebelum data ditransmisikanI Hindari noise di jaringan


Protokol Komunikasi


Topologi Jaringan


Noise Reduction


Enkoding (Channel)

Message

Protokol Komunikasi

Lisensi





Lisensi


Protokol Komunikasi


Topologi Jaringan


Noise Reduction


Enkoding (Channel)

Message

Protokol Komunikasi

Lisensi

Teknik untuk Mengurangi NoiseTeknik Differential Driver

I Mengirimkan nilai Data dan DataInversenya ke bus 2-jalur

I Contoh:Data: HI = ’1’ = 5 volt danLO = ’0’ = 0 voltInverse Data: HI = ’1’ = 0volt dan LO = ’0’ = 5 volt

I Titik referensi: GNDI Receiver mengurangi 2 nilai data

dataI Menghilangkan tegangan

bias common-modeI Menyisakan selisih noise

yang mempengaruhi jalur


Protokol Komunikasi


Topologi Jaringan


Noise Reduction


Enkoding (Channel)

Message

Protokol Komunikasi

Lisensi

RS-485 Multi-Master Bus

I Digunakan di jaringan kontrol industrial (seperti Modbus, Profibus)I RS-422 differential drivers: high-speed + jangkauan jauh (10Mbps

@12 meter)I Ditambahkan terminator untuk mengurangi noiseI Harus hanya satu sistem yang outputnya diaktifkan dalam satu

waktu (multiplexing access)I Sering disebut “master/slave” - satu sistem memerintahkan

sistem lain saat gilirannya tiba


Protokol Komunikasi


Topologi Jaringan


Noise Reduction


Enkoding (Channel)

Message

Protokol Komunikasi

Lisensi





Lisensi


Protokol Komunikasi


Topologi Jaringan


Noise Reduction


Enkoding (Channel)

Message

Protokol Komunikasi

Lisensi

Isolator Optik untuk Proteksi Tegangan SpikeI Tegangan spike dari noise yang besar dapat merusak node-node yang

terkoneksiI Diperlukan isolasi untuk mengatasi tegangan spike yang curam dan

besarI Isolator optik menyediakan gap udara secara fisik

I LED akan berpendar saat disediakan arusI Photo-transistor menghantar saat LED menyinarinya dengan IRI Dua set di tiap-tiap node

I Satu set untuk transmit, dan satu set untuk terimaI Menyediakan isolasi yang sangat baik

I Tanpa ada koneksi fisik, hanya photon yang melintasi gapI LED akan saturasi, jika diberikan arus yang berlebih (over-drive)I Masih mempunyai noiseI Jaringan harus mempunyai sumber daya sendiri

I Menyediakan bit dominanceI Namun, jika LED terpaku ke “on”, jaringan akan terganggu

Sumber: http://en.wikipedia.org/wiki/Opto-isolator


Transformer Coupling dan Stuck NodeI Stuck node merupakan masalah di sistem terdistribusi

I Jika sebuah node terpaku dengan mentransmisikan ’low’ atau’high’, seluruh jaringan akan mati

I Solusi: menggunakan current-mode transformercoupling

I Komponen AC dari sisi bit akanmenyeberang transformer

I Komponen DC dari node yang stuckdiabaikan

I Induktansi transformer memproteksitegangan spike

I Operasi current-mode akan meningkatkannoise rejection

I Umumnya digunakan di kontrol penerbanganI misalnya: MIL-STD-1553 (defines

mechanical, electrical, and functionalcharacteristics of a serial data bus),sistem avionics

I Tapi mempunyai keterbatasanI TIdak dapat melakukan bit dominanceI Deteksi collision sangat sulitI Sinyal harus DC balanced (energi sinyal high dan low sama)

Protokol Komunikasi


Topologi Jaringan


Noise Reduction


Enkoding (Channel)

Message

Protokol Komunikasi

Lisensi





Lisensi


Protokol Komunikasi


Topologi Jaringan


Noise Reduction


Enkoding (Channel)

Message

Protokol Komunikasi

Lisensi

Jenis Enkoding Kanal

I RZ – Return to Zero encodingI Encoding memastikan sinyal kembali ke “zero” sesering

mungkinI Memaksa transisi setiap satu atau dua bit dengan aturan

enkoding sederhanaI Memudahkan mensinkronisasi bit stream di sisi penerimaI Memudahkan penggunaan coupling transformer

I NRZ – Non-Return to Zero encodingI Ditujukan untuk meningkatkan efisiensi hanya dengan

mengirimkan nilai bit walaupun tanpa transisiI Tapi kurangnya transisi menyulitkan untuk mensinkronisasi bit

stream

Kode RZ Kode NRZ


Manchester Coding

I Manchester EncodingI Data dienkode dengan transisi dari

high-to-low (transisi turun) ataulow-to-high (transisi naik)

I Pasti terdapat transisi di tiap bitI Bandwidth terbesar adalah 2 transisi

perbit

I Kalau terjadi error, dikoreksi denganmenginversikan pasangan bit fisikterbesar

I Contoh: 11010001

Enkoding NRZ

I Send a Zero as LO; send One as HII Kasus terburuk: message mempunyai

semua ZERO atau semua ONEI Tidak ada transisi di data

I Solusiya: membatasi panjang data menjadi 8bit

I SYNC dan END mempunyai nilai yangberlawanan, memastikan ada 2 sisi permessage

I Teknik ini digunakan di port serialUART

I Bandwidthnya satu transisi perbit

I Contoh: 11010001

Protokol Komunikasi


Topologi Jaringan


Noise Reduction


Enkoding (Channel)

Message

Protokol Komunikasi

Lisensi





Lisensi


Protokol Komunikasi


Topologi Jaringan


Noise Reduction


Enkoding (Channel)

Message

Protokol Komunikasi

Lisensi

Message

I SyncI Designates start of a message and lets receiver sync to

incoming bits

I HeaderI Global priority information (which message gets on bus

first?)I Routing information (source, destination)

I DataI Application- or high-level-standard defined data fields (often

only 1-8 bytes)

I Error detectionI Detects corrupted data (e.g., using a CRC)

I EndI Designates end of message


Protokol Komunikasi


Topologi Jaringan


Noise Reduction


Enkoding (Channel)

Message

Protokol Komunikasi

Lisensi

Prioritas Message

I Local priorityI Each node transmits its highest priority message when it

gets a turn on the busI Or, it can implement some form of round-robin message

transmission, etc.

I Global priorityI Which node gets the next turn on the bus?

I Could be a function of round-robin selection of nodesI Could be a function of the node’s inherent priorityI Could be a function of the priority of the highest message on

the node

I Fundamental tension: latency vs fairnessI Reducing latency for high-priority nodes/messages vs

Ensuring fairness/no starvation for low-prioritynodes/messages


Protokol Komunikasi


Topologi Jaringan


Protokol KomunikasiCoordination: Bus MasterApproach

Coordination: Transmit andHope (CSMA)

Coordination: ExplicitTokens

Coordination: ImplicitTokens

Binary Countdown (BitDominance)

Emulation

Wireless Networks

Lisensi

Protokol Komunikasi Embedded


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Message Coordination

I Message coordination:I Bus Master AppoarchI Transmit and Hope (CSMA, Carrier Sense Multiple Access)I Explicit tokenI Implicit tokensI Binary countdown (bit dominance)


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi





Lisensi


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Coordination: Bus Master Approach

I Bus Master can poll for messages & wait for responseI Problem: missing/slow slave

I Master uses worst-case timeout waiting for responseI If slave gets confused/is late, protocol fails

I Problem: broken master

I Master can send a time tick – TDMAI Other nodes select response time from that time tickI Then becomes a form of time slice/time slot protocols


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Polling

I OperationI Centrally assigned Master polls the other nodes (slaves)I Non-master nodes transmit messages when they are

polledI Inter-slave communication through the master

I ExamplesI MIL-STD-1553B, 1773, Profibus, Bacnet, AN192


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Polling Tradeoff

I AdvantagesI • Simple protocol to implement

I historically very popularI Bounded latency for real-time applications

I DisadvantagesI Single point of failure from centralized masterI Polling consumes bandwidthI Network size fixed during installation (not robust)

I Or, master must discover nodes during reconfiguration

I Prioritization is local to each nodeI But, can use centralized load balancingI Polling need not be in strict order; it could be, for example: 1,

2, 1, 3, 4, 1, 5, 1, 3, 1, 6, ...(repeats)


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

TDMA - Time Division Multiplexed Access

I OperationI Master node sends out a frame sync to synchronize clocksI Each node transmits during its unique time slot

I ExamplesI Satellite Networks, static portion of FlexRay


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

TDMA Tradeoff

I AdvantagesI Simple protocol to implementI Deterministic response timeI No wasted time for Master polling messages

I DisadvantagesI Single point of failure from the bus masterI Wasted bandwidth when some nodes are idleI Requires stable clocksI Network size fixed during installation (not robust)I Prioritization is local to each node

I can use centralized load balancingI Variation: Variable Length TDMA

I Unused time slices are truncated to save timeI More efficient use of bandwidthI Used in FlexRay Dynamic Segment

(http://en.wikipedia.org/wiki/FlexRay)


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi





Lisensi


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Coordination: Transmit and Hope (CSMA)Carrier Sense Multiple Access

I Send a message and hope it made itI Useful for satellites & systems with no collision detectionI Vulnerable for entire time a message is transmittingI No direct way to know if message was delivered

successfully

I IMPLICIT collision detectionI Response might not make it even if message makes itI Iterate until some node pair gets lucky twice in a row


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Transmit And Collide (CSMA/CD)I Transmit message

I If you get lucky network transitions to activeI But If you get unlucky, you get a collision eventI Vulnerability window is about 2 tpd

I Two propagation delays along length of networkI The time during which the receiver hears nothing, but a frame

from another transmitter is already in-flight

I After collision, back off a certain timeI Amount of time to back off should vary with network loadI Repeated collisions result in increasing backoff times


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Transmit And Collide (CSMA/CD)Carrier Sense Multiple Access / Collision Detection

I OperationI A node waits for an idle channel before transmittingI Collisions can occur if two or more nodes transmit

simultaneouslyI If a collision is detected, the nodes stop transmitting

I Resolve contention using random backoff algorithm (2xlonger interval each retry)

I ExamplesI Ethernet (IEEE 802.3 LAN), Bacnet, CAB, CEBus


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

CSMA/CD Tradeoffs

I AdvantagesI Small latency for low traffic loadI Network initialization/configuration is not requiredI Node can enter or leave the network without any

interruptionI Supports many nodesI Probabilistic global prioritization is possible

I DisadvantagesI Designed for aperiodic traffic - not ideal for synchronized

control loopsI Collision detection is an analog process which is not

always practicalI Unbounded individual message latencyI Poor efficiency under heavy loads


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi





Lisensi


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Coordination: Explicit TokensI Token value says which node is transmitting and/or should transmit next

I Token holder = OWNER; only the owner may transmitI Master/slave polling is a special form where token is passed by

master and returned to master by slaveI Problems: Lost token / Duplicated token(s) / Who starts?

I Token passed as node number or other similar valueI May be tacked on to end of data-bearing messageI Can be either node# that has token or node# that gets token

nextI Null messages with tokens must be passed to prevent network

from going idle


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Token Bus

I OperationI A token signal is passed from a node to node on a bus

(virtual ring)I Only the token holder has permission to access the media

I ExamplesI IEEE 802.4, Arcnet, AN192, MAP, Profibus


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Token Bus Tradeoffs

I AdvantagesI Bounded latency for real-time control applicationsI High throughput during heavy trafficI On-the-fly reconfiguration

I DisadvantagesI Token passing latencies under light traffic conditionsI Prioritization local to each nodeI Lengthy reconfiguration processI Token initialization, loss, and duplication recovery overheadI Collisions may occur during initialization and

reconfigurationI Complex protocol (especially at MAC sublayer)I Token bus was popular for a while, but is used less often

now


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi





Lisensi


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Coordination: Implicit TokensI Length of waiting period is used as a time-domain

implicit “token”I Owner of bus determined by what time it is instead of

explicit token messageI Time slices – waiting period is a whole message long

I TDMA

I Time slots – waiting period is as short as possible ~ 2tpdI CSMA/CA (collision avoidance)


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

CSMA/CA (Implicit Token)

I OperationI IDLE: Active station transmits immediatelyI After each message, reserve S slots for N nodes

I Slots are normally idle – they are time intervals, not signals!

I BUSY: Transmit during your assigned slotI If S=N, no collisions - known as Reservation CSMAI If S<N, statistical collision avoidance

I ExampleI Echelon LONTalk


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

CSMA/CA Tradeoffs

I AdvantagesI Small latency for light trafficI Good throughput under heavy trafficI Global prioritization through fixed slots

I prioritized implicit token passes

I Bounded latency through rotating slotsI non-prioritized implicit token passes

I DisadvantagesI Restarting time slots from an idle bus can be difficult

I Send dummy messages to avoid idle state

I Collisions can occurI Node complexity in mapping Sth slot to Nth node


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi





Lisensi


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Binary Countdown (Bit Dominance)

I OperationI Each node is assigned a unique identification numberI All nodes wishing to transmit compete for the channel by

transmitting a binary signal based on their identificationvalue

I A node drops out the competition if it detects a dominantstate while transmitting a passive state

I Thus, the node with the LOWEST identification value wins

I ExamplesI CAN, SAE J1850


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Contoh Bit Dominance


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Binary Countdown Tradeoffs

I AdvantagesI High throughput under light loadsI Local and global prioritization possibleI Arbitration is part of the message - low overhead

I DisadvantagesI Propagation delay limits bus length (2 tpd bit length)I Unfair access - node with a high priority can "hog" the

networkI Poor latency for low priority nodes


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Before CAN


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

After CAN


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

CAN is Central of Automotive Networks


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi





Lisensi


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Emulation

I You can use one protocol to emulate anotherI Use Ethernet (CSMA/CD) to emulate:

I Master/slave pollingI slaves only respond when polled

I Token bus – use explicit token messagesI application only transmits when it has the token

I TDMAI slaves measure time from message from master and transmit

appropriately

I But, there is costI “Slot” time involves round-trip through OSI “Slice” time must account for CPU/OS jitter, not just HW

oscillator drift


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Emulation CapabilityI Protocols higher in picture can emulate protocols lower in

pictureI Example: you can pass a token around on a CAN network

in software


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi





Lisensi


Protokol Komunikasi


Topologi Jaringan







Emulation

Wireless Networks

Lisensi

Wireless NetworkI Strength is installation flexibility

I No wiring harnesses to install (except for power)I Can make/break networks without physical connectionsI Can have overlapping/interacting/hierarchical networks

(e.g., Bluetooth)I Weakness is potential unreliability for critical operations

I Geometry may introduce standing waves/fadingI Conflicts with other wireless systems (EMC =

ElectroMagnetic Compatibility)I Interference from RF emitters (EMI = ElectroMagnetic

Interference)I Limited spectrum spaceI Where does a wireless node get its power – who changes

the batteries?I In general, unsuitable for use in critical applications that

aren’t fail-safe!I Also, cost

I Bluetooth is getting cheap enough to be in consumerelectronics

I But has to be able to beat a piece of copper and a plasticconnector

I And that cost has to include power supply strategy


Protokol Komunikasi


Topologi Jaringan


Protokol Komunikasi

Lisensi

Lisensi

Creative Common Attribution-ShareAlike 3.0 Unported (CCBY-SA 3.0)

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Documents

Protokol Komunikasi @2012,Eko Didik Widianto Topologi ... · berefek pada satu node I Cocok untuk ﬁber optik ... I Rangkaian (digital) harus memberikan sinyal HI dan LO di jalur