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
Protokol Komunikasi
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
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]
Protokol Komunikasi
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
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
@2012,Eko DidikWidianto
Topologi JaringanTopologi Bus
Topologi Star
Teknik Transmisi Data
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
@2012,Eko DidikWidianto
Topologi JaringanTopologi Bus
Topologi Star
Teknik Transmisi Data
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
@2012,Eko DidikWidianto
Topologi JaringanTopologi Bus
Topologi Star
Teknik Transmisi Data
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
@2012,Eko DidikWidianto
Topologi JaringanTopologi Bus
Topologi Star
Teknik Transmisi Data
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
@2012,Eko DidikWidianto
Topologi JaringanTopologi Bus
Topologi Star
Teknik Transmisi Data
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi DataTransmisi Data (Bit)
Noise Reduction
Proteksi Terhadap Spike
Enkoding (Channel)
Message
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi DataTransmisi Data (Bit)
Noise Reduction
Proteksi Terhadap Spike
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi DataTransmisi Data (Bit)
Noise Reduction
Proteksi Terhadap Spike
Enkoding (Channel)
Message
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi DataTransmisi Data (Bit)
Noise Reduction
Proteksi Terhadap Spike
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi DataTransmisi Data (Bit)
Noise Reduction
Proteksi Terhadap Spike
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi DataTransmisi Data (Bit)
Noise Reduction
Proteksi Terhadap Spike
Enkoding (Channel)
Message
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi DataTransmisi Data (Bit)
Noise Reduction
Proteksi Terhadap Spike
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi DataTransmisi Data (Bit)
Noise Reduction
Proteksi Terhadap Spike
Enkoding (Channel)
Message
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi DataTransmisi Data (Bit)
Noise Reduction
Proteksi Terhadap Spike
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi DataTransmisi Data (Bit)
Noise Reduction
Proteksi Terhadap Spike
Enkoding (Channel)
Message
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi DataTransmisi Data (Bit)
Noise Reduction
Proteksi Terhadap Spike
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi DataTransmisi Data (Bit)
Noise Reduction
Proteksi Terhadap Spike
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
Emulation
Wireless Networks
Lisensi
Protokol Komunikasi Embedded
Protokol Komunikasi
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
Emulation
Wireless Networks
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
Emulation
Wireless Networks
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
Emulation
Wireless Networks
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
Emulation
Wireless Networks
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
Emulation
Wireless Networks
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
Emulation
Wireless Networks
Lisensi
Contoh Bit Dominance
Protokol Komunikasi
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
Emulation
Wireless Networks
Lisensi
Before CAN
Protokol Komunikasi
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
Emulation
Wireless Networks
Lisensi
After CAN
Protokol Komunikasi
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
Emulation
Wireless Networks
Lisensi
CAN is Central of Automotive Networks
Protokol Komunikasi
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
Emulation
Wireless Networks
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
Emulation
Wireless Networks
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol KomunikasiCoordination: Bus MasterApproach
Coordination: Transmit andHope (CSMA)
Coordination: ExplicitTokens
Coordination: ImplicitTokens
Binary Countdown (BitDominance)
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
@2012,Eko DidikWidianto
Topologi Jaringan
Teknik Transmisi Data
Protokol Komunikasi
Lisensi
Lisensi
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