thamkhao 5 mac

8/9/2019 Thamkhao 5 MAC

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Hanoi University of Technology Faculty of Electronics and Telecommunications

07/08

Tham khoiu khin truy nhp ng truyn


07/08

Cc giao thc a truy nhp Gii quyt cc vn lin quan n mi

trng dng chung

Mt s loi: Contention protocols: gii quyt vn xung t

sau khi n xy ra.

Collision-free protocols (v d: bit-map protocol vbinary countdown) m bo xung t khng bao

gi xy ra


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Contention Protocols

Pure ALOHA Pht trin nm 1970 bi Hawaii University. Xc nhn vic truyn thnh cng qua nhn

c ACK ca pha nhn

Slotted ALOHA Ci tin: Thi gian c chia thnh nhiu

khe v khung ch c truyn ti thi imbt u ca mi khe


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CSMA (Carrier Sense Multiple Access)

Ci tin: Bt u truyn khi khng thy node no angtruyn

CSMA/CD (CSMA with Collision Detection)

Ci tin: Dng vic truyn nu xung t xy ra

CSMA/CA (CSMA with Collision Avoidance)

Ci tin:i khong thi gian ngu nhin v th li khing truyn khng bn (carrier is quiet). Nu vn vy th

truyn d liu CSMA/CA with ACK

CSMA/CA with RTS/CTS

Contention Protocols


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Pure ALOHA

Trong pure ALOHA, khung c truyn ti cc thi im tu


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Khi khung sn sng truyn, my phi i n thi im btu ca mt slot

Slotted ALOHA


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So snh thng lng

ALOHA


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CSMA

Thng lng ti a ca slotted ALOHA l0.368.

CSMA c nhiu ci tin so vi ALOHAbng cch lng nghe ung truyn trckhi truyn


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C ch xung t trong CSMA

1 2 3Time

Collision

4

Node 4 sense

Delay

5

Node 5 sense

Delay

Node 1 Packet

Node 2 Packet

Node 3 Packet


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Cc loi CSMA

CSMA

Nonpersistent CSMA

Persistent CSMA

Unslotted Nonpersistent CSMA

Unslotted persistent CSMA

Slotted Nonpersistent CSMA

Slotted persistent CSMA

1-persistent CSMA

p-persistent CSMA


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Nonpersistent/x-persistent CSMA Giao thc Nonpersistent CSMA:

Bc 1: Nu ng truyn ri, truyn ngay lp tcBc 2: Nu ng truyn bn, i mt khong thi gian

ngu nhin v lp li bc 1 Gi tr backoff ngu nhin lm gim xc xut xung t Nu backoffqu lp s lng ph thi gian ri

Giao thc1-persistent CSMA:

Bc 1: Nu ng truyn ri, truyn ngay lp tcBc 2 : Nu ng truyn bn, tip tc lng nghe n khi

ng truyn ri th mi truyn S xy ra hin tng xung t nu 2 node mun truyn li

(thng s dng vic truyn sau vi ln th)


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Giao thc p-persistent CSMA :Bc 1: Nu ng truyn ri, truyn vi xc sut p v ch

truyn trong khe thi gian tip theo (thi gian tr ng truynln nht cho mt gi tin) vi xc xut (1-p)

Bc 2: Nu ng truyn bn, tip tc lng nghe n khi ngtruyn ri th quay li bc 1

- Mt cch tho hip gia nonpersistent and 1-persistent CSMA

Nonpersistent/x-persistent CSMA


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La chn gi tr p nh th no

? Gi s N node mun gi tin v ng

truyn ang bn

Np c xem l s Node th truyn khing truyn bt u ri

Nu Np > 1, xung t c th xy ra

V vy phi m bo Np < 1 trnhxung t, trong N l s node hot ng

ln nht ti mt thi im


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Throughput

0 1 2 3 4 5 6 7 8 9

G

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

S

Aloha

Slotted Aloha

1-persistent CSMA

0.5-persistent CSMA

0.1-persistent CSMA

0.01-persistent CSMA

Nonpersistent CSMA


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CSMA/CD (CSMA with Collision Detection)

Trong CSMA, nu 2 node bt u gi khung ti cngthi im, mi node s vn truyn ton b khung mcd c xung t xy ra. >Lng ph thi gian cho vic truyn c khung tin.

CSMA/CD

Bc 1: Nu ng truyn ri, truyn khungtin

Bc 2: Nu ng truyn bn, tip tc lngnghe n khi ng truyn ri th truynBc 3: Nu xung t c pht hin trong

qu trnh truyn, ngng ngay vic truynBc 4: i mt khong thi gian ngu nhinv thc hin li thut ton trn


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CSMA/CD

A B

( is the propagation time)

T0 A begins transmission

A B

B begins transmission

Time

T0+-

A B

B detects collisionT0+

A B

A detects collision just

before end of transmission

T0+2 -


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CSMA/CA (CSMA with collision Avoidance)

Tt c cc node lng nghe ng truyn ging nh trongCSMA/CD. Node sn sng truyn s pht sng cm ng. Nu ng truyn bn, i n khi kt thc qu trnh vic truyn

hin ti N s tip tc i mt khong thi gian xc nh trc DIFS

(Distributed inter frame Space).

Nhn ly mt gi tr ngu nhin ca khe thi gian (gi tr khi uca b m backoff) trong mt contention window ch trc khitruyn 1 khung.

Nu hin ang c mt qu trnh truyn tin bi mt node khc trongchu k thi gian ny (backoff time), node s gi nguyn gi tr bm.

Tip tc m li sau khi node khc kt thc vic truyn + DIFS.Node c th bt u vic truyn khi b m n 0


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CSMA/CA

Time

Node As frame

Nodes B & C sense

the medium

Nodes B resenses the medium

and transmits its frame.

Node C freezes its counter.

Node Bs frame

Nodes C starts

transmitting.

Delay: BDelay: C

Nodes C resenses the

medium and starts

decrementing its counter.

Node Cs frame


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07/08 CSMA/CA/ACK

DIFS

Next Frame

ACK

Data

Other

Source

Destination

DIFS

SIFS

Contention window

Defer access Backoff after defer

SIFS Short Inter Frame Spacing

Time


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CSMA/CA with RTS/CTS Pha gi s gi bn tin RTS (request to send) sau

khi ng truyn ri sau khong thi gian ln hnDIFS.

Pha nhn tr li bng bn tin CTS (clear to send)sau khi ng truyn ri mt khong thi gian SIFS.

Sau d liu c truyn. RTS/CTS c s dng cho vic t ch ung

truyn v vy xung t chxy r a vi cc bn tin iukhin.


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CSMA/CA with RTS/CTSDIFS

Next Frame

CTS

RTS

Other

Source

Destination

DIFS

SIFS

Contention window

Defer accessBackoff after defer

SIFS

Data

SIFS

ACK

Time


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RTS/CTS

RTS

CTS

Data

ACK

Node A Node B

Tr truyn lan


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Wireless LAN Protocols

A wireless LAN. (a) A transmitting. (b) B transmitting.


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The MACA protocol.

(a) A sending an RTS to B.

(b) B responding with a CTS to A.

Wireless LAN Protocols


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Ethernet Ethernet Cabling

Manchester Encoding

Lp con MAC Ethernet Hiu sut ca mng Ethernet Fast Ethernet

Gigabit Ethernet

IEEE 802.2: Logical Link Control


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Ethernet Cabling

Cc loi cp ph bin s dng trong cng ngh Ethernet


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(a) 10Base5, (b) 10Base2, (c) 10Base-T.

Ethernet Cabling


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(a) Binary encoding, (b) Manchester encoding,(c) Differential Manchester encoding.

Ethernet Cabling


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Lp con MAC

nh dng khung (a) DIX Ethernet, (b) IEEE 802.3.


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Ethernet MAC Sublayer Protocol

Xung t c pht hin sau khong thi gian 2

Lp con MAC


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Hiu sut mng Ethernet

Hiu sut mng Ethernet tc 10 Mbps vi 512-bitslot times.


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Fast Ethernet

Mt s loi cp dng trong mng Fast Ethernet


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multi-level transmit-3 levels

100BASE-TX (like 100BASE-FX) uses 4B/5B encoding which is thenscrambled and converted to multi-level transmit-3 levels or MLT-3.

Any Transition = binary 1.

No transition = binary 0.

Long strings of zeros

would give a DCcomponent but because ofthe 4B/5B encoding this

can never happen.


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100BASE-FX (like 100BASE-TX) uses 4B/5B encoding which is thenscrambled and converted to Non Return to Zero, Inverted.

Non Return to Zero, Inverted

Any Transition = binary 1.

No transition = binary 0.

Long strings of zeros

would give a DCcomponent but because ofthe 4B/5B encoding this

can never happen.

Fiber cannot use the 3 level MLT3 because thelight source has only two levels, ON and OFF.


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Gigabit Ethernet

(a) A two-station Ethernet. (b) A multistation Ethernet.


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Mt s loi cp dng trong mng Gigabit Ethernet

Gigabit Ethernet


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IEEE 802.2: Logical Link Control

(a) V tr lp con LLC. (b) nh dng giao thc


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Wireless LANs

Protocol Stack 802.11

Lp vt l ca 802.11 Lp con MAC Cu trc khung 802.11


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802.11 Protocol Stack


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Lp con MAC trong 802.11

(a) Hidden station problem.

(b) Exposed station problem.


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B C DA BA C D

- A ang truyn d liu sang B

- C nm ngoi tm sng ca trm A

- C cng mun truyn d liu sang B

- C a ra kt lun sai v trm B

- C vn truyn d liu sang trm B

- B ang truyn d liu sang A

- C nm trong tm sng ca trm B

- C mun truyn d liu sang D

- C a ra kt lun sai v mi trng

truyn thng- C khng truyn d liu sang D

S 1 S 2


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CSMA/CA.

The 802.11 MAC Sublayer ProtocolLp con MAC trong 802.11


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Mt cm mnh



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Khong cch lin frame trong 802.11



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Cu trc khung 802.11


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Broadband Wireless

So snh 802.11 and 802.16


Lp vt l trong 802.16

Cu trc khung 802.16


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Lp vt l 802.16


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Khung tin v cc khe thi gian

Lp vt l 802.16


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Cu trc khung 802.16

(a) generic frame. (b) bandwidth request frame.


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Bluetooth

ng dng ca Bluetooth

Bluetooth Protocol Stack

Cu trc khung Bluetooth


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ng dng ca Bluetooth


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Bluetooth Protocol Stack

The 802.15 version of the Bluetooth protocolarchitecture.


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Cu trc khung Bluetooth

Khung d liu Bluetooth


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- Nguyn Vn Hong T8

- Chu c dng DT8

- Nguyn c ThnhT8

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