Алгоритмы канального уровня

axel@wl.unn.ruhttp://www.wl.unn.ru

:http://www.sumkino.com/wsn/course

WSN

( , Ethernet ..) , .

(MAC) .

CordlessheadsetBluetoothAccessPoint 802.11Zigbee/802.15.4

MAC MAC FDMATDMACSMA

MAC

: ALOHA (Pure and Slotted), CSMA

: FDMA, TDMA, CDMA

MAC MAC

. MAC .

MAC .

.

MAC .

. Goodput.

.

, .

MAC . :

.

, .

Overhearing .

Control Packet Overhead goodput.

.

(overhearing)

(Voice).

QoS

Time Division Multiply Access: TDMA .

Time Division Multiply Access: TDMA TDMA , .

:

. - (FDMA, CDMA).

.

.

Bluetooth (piconets).

master 7 slave .

Master (poll) .

Scatternet

ALOHA :packet radio networkssend when ready18-35% channel utilization

CSMA (Carrier Sense Multiple Access):listen before talk50-80% channel utilization

CSMA - .CBADCBAD

MACA MACA (Ethernet) .

RTS-CTS-DATA .

CTS, . RTS, CTS.

MACAW (Wireless) .

RTS-CTS-DATA-ACK .

ACK, .

802.11CFABEDRTSRTS = Request-to-Send

802.11CFABEDRTSRTS = Request-to-SendNAV = 10NAV =

802.11CFABEDCTSCTS = Clear-to-Send

802.11CFABEDCTSCTS = Clear-to-SendNAV = 8

802.11CFABEDDATA DATA CTS. ACK.

802.11CFABEDACK

CSMA/CA .

CSMA/CA: . : , . : RTS CTS . , .

CSMA/CA .

NAV (Network Allocation Vector )

NAV (overhead) RTS/CTS/DATA/ACK.

(/)

Backoff .

Backoff Interval , backoff [0,MaxBackoff]. MaxBackoff- , .

backoff () . , .

backoff 0 RTS .

Backoff Interval: MaxBackoff=31B1-backoff 1B2-backoff 2

Backoff Interval Backoff MAC . MaxBackoff . MaxBackoff .

backoff . IEEE 802.11 DCF: backoff MaxBackoff .

Backoff Interval

CTS RTS, MaxBackoffMaxBackoff ( )

, MaxBackoff .

MaxBackoff .

WSN

CSMA vs TDMA

CSMA vs TDMA

MAC WSNMAC WSN

2000 2004 16

.

MAC WSN

MAC WSN

MAC WSN .

? (Control Packet Overhead) (Overhearing unnecessary traffic)

.

MAC MAC

. , .

} WSN

S-MAC: Co-ordinated Adaptive Sleeping

Ye, Heidemann (USC), Estrin (UCLA)

S-MAC: Co-ordinated Adaptive Sleeping (TDMA) (CSMA).

. , ,

. , CSMA/CA.

S-MAC: Co-ordinated Adaptive Sleeping : / .

S-MAC : . RTS/CTSOverhearing , .

: .

: .

duty cycle ~10%

.

: . , . (SYNCHRONIZER) , . (FOLOWER) .

.

(SYNC) .

, , .

:

: multi-hop .

: .4123listen .

S-MAC

IEEE 802.11 ad hoc mode

backoff

RTS/CTS

RTS/CTS/DATA/ACK

: .

: , .

?

?

S-MAC: Mica Motes (UC Berkeley) 8-bit CPU at 4MHz,128KB flash, 4KB RAM20Kbps radio at 433MHzTinyOS S-MAC duty cycle duty cycle ( )

S-MAC: 11 , . S-MAC .

.* Wei Ye, John Heidemann Medium Access Control in WSN

S-MAC: , .Latency under highest traffic loadNumber of hopsAverage message latency (S)10% duty cycle withoutadaptive listen 10% duty cycle with adaptive listen No sleep cycles Latency under lowest traffic loadNumber of hopsAverage message latency (S)10% duty cycle withoutadaptive listen 10% duty cycle withadaptive listen No sleep cycles * Wei Ye, John Heidemann Medium Access Control in WSN

S-MAC: .Effective data throughput under highest traffic loadNumber of hopsEffective data throughput (Byte/S)No sleep cycles 10% duty cycle with adaptive listen 10% duty cycle without adaptive listen .* Wei Ye, John Heidemann Medium Access Control in WSN

S-MAC: CSMA/CA .

() , RTS/CTS MAC , .

B-MAC: Versatile Low-power medium access for sensor networks

Joe Polastre, Jason Hill, David Culler(U.C. Berkeley)

B-MAC , .

(Unscheduled sleep)

. , .

(Unscheduled wakeup)

CSMA/CA app-specific .

B-MACBMACsetMode (Listening/Transmit)setPreambleLengthsetCheckIntervalRTS/CTS MACTree-optimizedMACEvent-responseoptimizedMACBMAC (link-layer reliability) RTS/CTS ( )

B-MACLong PreambleData transmissionSenderReceiverReceive dataCarrier sense , carrier sense .

RTS/CTS .

B-MACLong PreambleData transmissionSenderReceiverReceive dataCheck intervalCarrier sense CheckInterval , .

carrier sense , .

B-MAC

B-MAC

B-MAC

WSN

Medium Access Control in Wireless Sensor Networks Wei Ye and John Heidemann

Energy-Efficient Medium Access Control Koen Langendoen and Gertjan Halkes

An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks Tijs van Dam,Koen Langendoen, Sensys 2003

Medium Access Control with Co-ordinated Adaptive Sleeping for Wireless Sensor Networks W. Ye, J. Heidemann, D. Estrin, IEEE/ACM Transactions on Networking, 2004.

The End

Design Discussion: MAC layer for event detectionGiven:1 High-powered camera sensorMany (20) low-power camera sensorsRequirement:Low-power cameras are periodically sensingTrigger high-power camera when low-power ones detect motion within time Delta.Discuss appropriate choice of MAC layer (TDMA/FDMA/CDMA/CSMA) forSingle hop vs multihopLarge vs Small DeltaScheduled vs unscheduled sleep