FL 4 Kommunikayionssystem
what is the purpose of automatic repeat request ARQ
• Purpose : to provide a service that delivers packets
– in order
– without errors
– without duplications
what are the basic elements of automatic repeat request ARQ
• Basic elements of ARQ:
– Error-detecting code with high error coverage, e.g., a Cyclic Redundancy Check (CRC) code
– Timeout mechanisms
– ACKs (positive acknowledgments)
– and sometimes NAKs (negative acknowledgments)
what is the first attempt in the transmitter for a ARQ protocal
Transmitter
1. Accept SDU from layer above
2. Create frame by adding header and error-detection bits
3. Transmit frame using the service of the layer below and start a timeout timer
4. If timer expires, retransmit frame (i.e., repeat step 3)
5. If ACK is received go to Step 1
first attempt for reciever for ARQ protocal
Receiver
1. Wait for new frame
2. Check received frame for errors
3. If no errors are detected:
– Deliver SDU to layer above
– Send ACK to transmitter
4. If errors are detected: discard frame
5. Go to Step 1
finite state machine(fsm) for First Attempt ARQ Protocol TRANSMITTER and RECIEVER
1.
SDU arrives from layer above
1. Create and store frame in memory. 2. Transmit frame 3. Start timer 4. Stop accepting new SDUs
2.
Timer expires 1. Retransmit frame. 2. Reset and start time
3.
Erroneous ACK arrives 1. Retransmit frame Error-free ACK arrives 2. Reset and start timer
4.
Error-free ACK arrives 1. Stop timer 2. Remove frame from memory 3. Start accepting new SDUs
and
reciever:
1. Error-free frame arrives. 1. Extract SDU and deliver to layer above 2. Send ACK
2. Erroneous frame arrives 1. Discard frame
what happends when you loose ACK
Lost ACKs lead to duplicate SDU delivery
how does short time look like
A too-short time-out leads to
– duplicate SDUs delivery
– possibly lost SDUs
what is the main idea between sequence numbers
Main idea
– Transmitter enumerates transmitted frames with sequence numbers
– Receiver includes the sequence number of received frames in the ACK frame
Both the transmitter and receiver maintains state variables to keep track of the transmitted and received frames
common example of state variables sequent number
– Transmitter state variable = sequence number of last frame that has been sent
– Receiver state variable = sequence number of the frame to be expected next
• In practice, sequence numbers must be reused to limit overhead, i.e., the sequence number should fit into a relative small number of bits
stop and wait state variables
The transmitter maintains a binary (1-bit) state variable
S last = sequence number of last transmitted frame
last transmitted information frame: Slast | SDU | CRC
stop and wait state variables
The receiver maintains a binary (1-bit) state variable
R next = sequence number of next expected frame=
1, last correct received frame had sequence number 0
= 0, last correct received frame had sequence number 1
ACK frame: Rnext | CRC = want frame Rnext = acknowledge frame with Slast = Rnext ⊕ 1
• The receiver accepts a frame with sequence number Slast only if Slast = Rnext
what is the ready state for stop and wait ARQ transmitter
Initialize sequence number Slast = 1 (first transmitted SDU has Slast = 0)
• Ready state
– Await SDU from upper layer
– Update sequence number Slast = Slast ⊕ 1
– Start timer, transmit frame with sequence number Slast
– Go to blocking state
what is the blocking state of stop and wait ARQ transmitter
Blocking state
– Do not accept new SDUs from upper layer
– If timer expires, reset timer and retransmit frame
– Upon reception of ACK frame
• if error detected or wrong sequence number (Rnext ≠ Slast ⊕ 1), ignore ACK
• if no errors detected and correct sequence number (Rnext = Slast ⊕ 1), go to ready state
stop and wait ARQ reciever
Initialize sequence number Rnext = 0
Ready state
• Await arrival of a frame
– if errors are detected, discard frame
– if no errors are detected, extract the sequence number Slast
• if sequence number is the expected one, i.e., Slast = Rnext
– deliver SDU to upper layer
– update sequence number Rnext = Rnext ⊕ 1
– send ACK with sequence number Rnext
• if sequence number is the not expected one, i.e., Slast ≠ Rnext
– discard frame
– retransmit ACK with sequence number Rnext
stop and wait fsm
SDU arrives from layer above
1. Set Slast = Slast ⊕ 1
2. Create and store frame with Slast
3. Start timer
4. Transmit frame
Timer expires
1. Retransmit frame
2. Reset and start timer
Arrival of error-free ACK
1. Stop timer
2. Remove frame from memory
Arrival of erroneous ACK or ACK with Rnext = Slast ⊕ 1 with Rnext ≠ Slast ⊕ 1
1. Retransmit frame
2. Reset and start timer
stop and wait fsm
Arrival of error-free frame with Slast = Rnext
1. Extract SDU and deliver to layer above
2. Set Rnext = Rnext ⊕ 1
3. Send ACK with Rnext
Arrival of erroneous frame or frame with Slast ≠ Rnext
1. Discard frame
2. Send ACK with Rnext
efficency of stop and wait
Consider an ARQ-protocol in Layer n
• Layer-n service provides error-free transmission of n-SDUs
• The effective data rate of the service, i.
R eff = number of bits in one SDU / avergare bme to transmit one SDU
| Quiz |
|---|
| cyber security 1-3 |
| HIZTEGIA HARD |
| HIZTEGIA |
| PigsPigs |
| Wordly Wise 3000 lesson 1vocabulary |
| Teeth |
| HT (Context) |
| marketing chapter 9 |
| BHV-Toets |
| home services pricing |
| Genetics midterm 1 |
| Anthro week 3 flashcards |
| Antho week 4 quiz |
| emprical studies introbasics - central tendency, spread |
| ak se3thema water en bevolking en ruimte |
| biology B6 |
| unit 6 bio |
| WC Reading Quiz #2 |
| Study-HOSA |
| Supply Chain |
| psychometry |
| trophosphere geographylol |
| chemieorganische verbindingsklassen en monofunctionele verbindingsklassen |
| geography atmosphere |
| Biologi 5.2 Energi och materia + 5.3 |
| Pathologie orthopedie breuken |
| spainsh unit 2 b |
| AP1 |
| Revalida |
| scince test flash cardsstudyy |
| French Vocab Test |
| songbirds and snakes vocab |
| Spanska glosor |
| geo110 |
| french |
| LobstersLobsters |
| Social Terms Jan-Feb |
| Pathologie orthopedie bovenste extremiteit |
| KNSS 307 ( development of human locomotions |
| KNSS 307( Early Motor Development |
| Modern studies testmy test |
| The limbic systemCharlotte |
| English vocabulary |
| Pathology unit 1 |
| History quiz 4 |
| Respiritory system |
| GTF + De taktiska grundprinciperna |
| Fondamentaux Biologie |
| Sampling |
| FL 3 Kommunikationssystem |
| Films test |
| Unit 4 |
| NO |
| geología chuletillas |
| Capitals |
| Économie S4 |
| politics essayessay |
| week 1.2 Term and Lesions |
| Week 2 - Skin Care 2 Assignment - Emollients and Eve Taylor Lotions, Moisturizer |
| week 1.2- Extended Health screening |
| Vocabulary |
| Japanese Phrases Unit 2 |
| Japanese Phrases Unit 1 |
| geologia |
| Sharks |
| months and order numbers |
| Spanska läxa v.5 |
| spanish 2 2A and 2B |
| phyics 10P1 |
| Réviser les pronoms et les déterminants 5e |
| georaphymap skills key words |
| Japanese PhrasesSo I don't look like a dumb tourist |
| cree |
| show me tell me motorbikeeee |
| CELLScan you answer the questions |
| Geometryanswer these |
| Forensic science review |
| Réviser les pronoms et les déterminants 6e |
| Svenska adjektiv mm A |
| mineralen |
| 1) Humble 2) Serendipity 3) Tedious 4) Riposte 5) Outlandish 6) Benevolent 7) Ba |
| english exam gr 10 |
| loayمشهور طالب نشيط |
| Population Vocab |
| vitamines |
| Biology/Nask flashcardsVerrie prittie vlesjkarts meet bij Kirsten for bijoloodjie ent nask prodject |
| E-nummers |
| Spierskeletsysteem2 -KTY2 |
| Maths |
| perception: intro- what is perception
- the eye
- prisoners ?
- evolution
-examples
-sensation vs perecption
-camera model
- experimental study |
| Inför fysik-prov (kapitel 6) |
| main practice |
| german 15 |
| multiplying |
| science |
| science plants test unit 3 |
| Business test |
| masu form |
| C1 Level vocabulary |
| Unit 1 Animal Diversity |
| homeworkexam de finance chapitre credit |
| les genresla hierarchie des genres |
| englisch chapter 2 |
| gsJa |
| electronics |
| los verbos |
| science studying |
| matte |
| light reflection |
| physicss |
| combined higher, quantitative chemistry, GCSE flashcardsidk |
| substances - chemistry |
| men and women in the family |
| contraception in islam |
| Anglais: native americans |
| IT Management chapters 1-3 |
| latijn |
| pneumatics and hydraulics |
| Divorce in islam |
| History quiz THREE!!!! |
| Tableau Periodique |
| frankie capuano biopsychology |
| gsce japanese words |
| Organisatiekunde hoofdstuk 10 |
| Albania |
| te form - JPN |
| Special dates |
| Koine Greek Ch. 20-22 |
| enthalpy change |
| Biology topic 5 and 6Communicable diseases, vaccinations, antibiotics and painkillers, investigating antibiotics, discovering drugs, developing new drugs, |
| Les dates de la seconde guerre mondiale |
| sight words |
| ge se3 |
| geschiedenis |
| Organisatiekunde hoofdstuk 9 |
| frenchtbh idk |
| Character Profiles |
| emergency drill |
| CricketsCrickets |
| Examain final sciences |
| HT (dystopian themes and examples)-themes in every dystopian novels
-with examples from HT |
| Words & Phrases 2 |
| Semaine 4 |
| Santé motricité physio cardio vasculaire |
| Exambio |
| Myndigheterden trista delen |
| cosmetology |
| Engelska 2 |
| BiologyIn this biology quiz you will have 60s to answer each question , the questions and answers are ranzomized.
You can see your rank in the leaderboard after each question. |
| OKO |
| kwalitatief onderzoek OKO pb1612 |
| kwalitatief onderzoek |
| anatomie 2 |
| j-ljudet |
| english exam |
| Biology |
| physics |
| social studies |
| SHS - Transformation des organisations et impact sur le travail |
| SHS - Psychologie |
| SHS - Sociologie générale |
| SHS - epistemologie |
| TKAM final vocab |
| Spanish Irregular Preterite Verbs |
| Pathologie orthopedie onderste extremiteit |
| driving test |
| Koine Greek Prepositions |
| Organisatiekunde hoofdstuk 8 |
| nask |
| WHITECHAPLE |
| LT - Natural law (CHAPTER 1) |
| Bio Exam |
| LT - The legal order (CHAPTER 0) |
| LT - Law as a rational system (CHAPTER 1) |
| 5 glosor |
| koine greek ειμί |
| FL 2 Kommunikationssystem |
| maatschappijleer. |
| SOom första världskriget |
| English Literature |
| kemi 1 syror & baser begrepp |
| Ethiek periode 2 |
| Drug tables |
| general science |
| Chemistryok |
| Work |
| Engelska 1 |
| bio se3thema 6,7,10 & 11 |
| Spanska 4 |
| un mundo de fiestas |
| chem exam |
| Automotive |
| how to improve french vocabulary |
| types of houses in french |
| very hard french words |
| Koine Greek Ch. 18 & 19 |
| french words you will see in french books |
| various french house terms |
| parts of the bathroom in french |
| parts of the bedroom in french |
| french |
| The Lung Channel of Hand Taiyin |
| Anatomy and Physiology |
| tyska kap 3bräcka till |
| nl |
| physics flashcards |
| TYSKA FERIEN MAL ANDERS |
| romeo and juliet |
| Nederlands poëzie begrippenAlle begrippen van de poëzie les Nederlands. |
| PKG stoornissen jaar 1 |
| PKG jaar 1 |
| nederlands (lezen) hoofdstuk 1,2 en 3 theorie |
| anglais |
| Historia Källkritikfkn dö |
| An inspector calls |
| Geology |
| Ireland, the green island |
| leverspe |
| Organisatiekunde Hoofdstuk 7 |
| text sobre a Barbie |
| palavras mais usadas |
| FL1 Kommunikationssystemtermer inom kommunikationssystem |
| Grieks 4.1De Ring van Gyges |
| Busnissmodel |
| Politiek en economische handel |
| BMC |
| English Exam |
| Staatsrecht 1 |
| The brain & Limbic system |
| limbic system |
| art definitions and paintings |
| french - |
| french |
| histoireallo |
| ee |
| poets |
| duits 47 tot 52 4 |
| French speaking mock |
| b |
| Psykologi prov |
| Engels Unit 2 |
| duits 47 tot 52 3 |
| HistoryAbolition of slavery |
| Natural Disasters |
| Secu |
| bio test |
| Spanska NP Muntligt |
| spanish |
| Element 3 |
| Edodontic instruments |
| duits 47 tot 52 2 |
| duits 47 tot 52 |
| Frans A+B |
| Grieks 2.2Diotima |
| Spanish Words & Phrases |
| vocabulary |
| pharm |
| Pharmacie Semester 2 |
| scene 5a |
| Examin Géo |
| interior design vocab 2 |
| engels woordjes 2.1 t/m 2.4 |
| Grieks 2.1Aristophanus - Symposium |
| Physique Chimie Chap 10/11/12 |
| a level human geography |
| MU AW 2 |
| Ordförråd Substantiv B |
| Biologi 1 genetik |
| Economie |
| KA 4 |
| socials exam 10 |
| History 2 |
| Hinduism terms |
| Dugga - Iskunskap |
| spanish verbs |
| KA3 |
| BIO 112L EYE |
| Idas teknik begreppstest |
| toefl c1 |
| nederlands |
| Glosor kap 11 |
| Le passe compose - the perfect tense ( french ) |
| El begrepp |
| science summary sheets |
| 2.1. Mon identité |
