wireless mesh deployment using wi-fi -...

Wireless Mesh Deployment using Wi-Fi

2011. 07. 06.

Jae-Hyun Kim

Wireless Information aNd Network Engineering Research Lab.

School of Electrical and Computer Engineering

Ajou University, Korea

Wi-Fi 기술 방식 자문

Contents

WLAN Introduction

Coverage Extension

Directional Antenna

Carrier Sensing Problem

Wi-Fi Mesh Introduction

IEEE 802.11s

Throughput Enhancement

IEEE 802.11n

Conclusion

2

What is WiFi?

Definition of Wi-Fi

Informal : Wireless Fidelity (look like Hi-Fi)

Formal : never supposed to mean anything at all

Trademark of the Wi-Fi Alliance

Describe only a narrow range of connectivity technologies

including wireless local area network (WLAN) based on the IEEE

802.11 standards

3

What is Wi-Fi?What is IEEE

802.11 standard?

IEEE 802.11 Standard

Define one medium access control (MAC) and several physical layer (PHY) specifications for wireless connectivity for fixed, portable, and moving stations (STAs) within a local area

The base current version of the standard is IEEE 802.11-2007

Provide wireless connectivity to STAs that require rapid deployment

Describes the functions and services to operate within ad-hoc and infrastructure networks

Defines the MAC procedures to support the asynchronous MAC service data unit (MSDU) delivery

Defines several PHY signaling techniques and interface functions that are controlled by the IEEE 802.11 MAC

Defines mechanisms for dynamic frequency selection (DFS) and transmit power control (TPC)

Describes the requirements to provide data confidentiality of user information being transferred over the wireless medium (WM) and authentication

4

Major Task Groups in 802.11

5

PHY & Data Rates in IEEE 802.11

TGFrequency

(GHz)

Bandwidth

(MHz)

Data rate per stream

(Mbps)

MIMO

stream

Maximum data

rate(Mbps)Modulation

Range(m)

Indoor Outdoor

2.4 20 1,2 1 2DSSS,

FHSS20 100

a 5 206,9,12,18,24,36,4

8,541 54 OFDM 35 120

b 2.4 20 5.5, 11 1 11DSSS,

CCK38 140

g 2.4 206,9,12,18,24,36,4

8,541 54

DSSS,

CCK,

OFDM

38 140

n 2.4/5

207.2,14,21.7,28.9,

43.3,57.8,65,72.24 288

OFDM

CCK70 250

4015,30,45,60,90,1

20,135,1504 600

OFDM

CCK70 250

6

IEEE 802.11 (Layers and Functions)

MAC

Access mechanisms, fragmentation, encryption

MAC management

Synchronization, roaming, management information base (MIB), power management

7

Physical layer convergence protocol (PLCP)

Clear channel assessment (CCA) signal (carrier sense)

Physical medium dependent (PMD)

Modulation, coding

PHY management

Channel selection, MIB

Architecture in IEEE 802.11

Infrastructure

8

Ad-Hoc

Components in IEEE 802.11

Station (STA)

Terminal with access mechanisms to the wireless medium and radio contact to the access point

Access point (AP)

Station integrated into the wireless LAN and the distribution system

Basic service set (BSS)

A set of STAs that have successfully synchronized

Distribution system (DS)

A system used to interconnect a set of BSSs

Extended service set (ESS)

An ESS is the union of the BSSs connected by a DS

Not include the DS

The ESS network appears the same to an LLC layer as an IBSS network

STAs within an ESS may communicate and mobile STAs may move from one BSS to another (within the same ESS) transparently to LLC

9

Frequency Bands in IEEE 802.11

Industrial, Scientific and Medical (ISM) Bands

10

• UNLICENSED OPERATION GOVERNED BY FCC DOCUMENT 15.247, PART 15

• SPREAD SPECTRUM ALLOWED TO MINIMIZE INTERFERENCE

• 2.4GHz ISM BAND

- More Bandwidth to Support Higher Data Rates and Number of Channels

- Available Worldwide

- Good Balance of Equipment Performance and Cost Compared with 5.725GHz Band

- IEEE 802.11 Global WLAN Standard

1 2 3 4 5 6FREQUENCY (GHz)

26MHz 83.5MHz 125MHz

2.400 to 2.4835GHz902 to 928MHz 5.725 to 5.850GHz

Spectrum Allocation in IEEE 802.11

Divided into 13 channels(14 channels in Japan) each of width

22 MHz

11

MAC Entity in IEEE 802.11

MAC Sublayer

12


Distributed coordination function (DCF)

Contention-based channel access

Carrier sense multiple access/collision avoidance (CSMA/CA)

Carrier sense

Physical carrier sense - CCA

Virtual carrier sense - Request to send/clear to send (RTS/CTS)

Point coordination function (PCF)

Polling-based channel access

Enhanced Distributed channel access (EDCA)

Support prioritized QoS

Differentiated by inter frame space (IFS), contention window (CW) size

HCF controlled channel access (HCCA)

Support parameterized(reservation-based) QoS

Allocate transmission opportunity (TxOP)

13


DCF

PCF

14

DIFS Contention Window

Slot time

Busy Medium

Defer Access

Backoff-Window Next Frame

Backoff slot reduced when channel is idle

SIFS

PIFSDIFS

Sense channel during DIFS

Beacon D1+Poll

NAV

SIFS

SIFS

U1+Ack

D2+Ack+Poll

SIFS

U2+Ack

SIFS

SIFS

CF-End

Uplink

Downlink

Contentio Free Period (CFP) for PCF

Contention

Period (CP)

for DCF

Contention Free Period Repetition Interval (CFPRI) or Superframe

Reset NAV

CF_MAX_DurationDx - downlink frame to STA x

Ux - uplink frame from STA x

PIFS


EDCA

HCCA

15

ACK RTS

CTS

SIFSSIFS

PIFS

AIFS[AC]=DIFS

SIFS

AIFS[AC]

AIFS[AC]

high priority AC

medium priority AC

low priority AC

defer access Contention Windows (counted in slots, 9us)

count down as long as medium is idle, Back off when medium gets bust again

CW=rand[1,CWi+1]

Contention Free Period, CFP(polling through HCF) Contention Period, CP (listen before talk and polling through HCF)

TXOP TXOP TXOPTBTT

QoS CF-PollQoS CF-PollCF-end

Beacon

Transmitted

by (Q)STAs

Transmitted

by HC

TBTTTime

RTS/CTS

Fragmented DATA/ACK

(polled by HC )

RTS/CTS/DATA/ACK

(after DIFS+backoff) RTS/CTS

Fragmented DATA/ACK

(polled by HC )

HC : Hybrid Coordinator AP , TBTT : Target Beacon Transmission Time

Consideration for Coverage Extension

Transmission power is limited in ISM band

Regulate equivalent isotropic radiated power (EIRP) in ISM band

by FCC 47 CFR part 15, subpart B Class B

16

<U.S. public safety transmit power levels by regulatory domain>

The amount of power that a theoretical isotropic antenna (which evenly

distributes power in all directions) would emit to produce the peak power

density observed in the direction of maximum antenna gain.

What is EIRP?

Regulatory Channel starting

frequency(GHz)

Channel spacing Channel set Transmit power limit(mW)

1 5 20 36,40,44,48 40

2 5 20 52,56,60,64 200

3 5 20 149,153,157,161 800

4 5 20 100,104,108,112,116,120,124 200

5 5 20 165 1000

6 4.9375 5 1,2,3,4,5,6,7,8,9,10 25


Directional Antenna

An antenna which radiates greater power in one or more directions

and reduced interference from unwanted sources

Commercially, increase about 20dBi(Yagi, Corner, Sector, Grid, etc)

Pros and Cons

Divert the RF energy in a particular direction to farther distances

• Increase range in near LOS(hallway, long corridor, isle)

Need to LOS environment

Cannot cover large area as the angular coverage is less

17


vender categoryGain

(dBi)

3dB beamwidth

(degree)

Max input

power (W)

Price

($)

GNS Wireless

Grid 27 7.5 100 295

Sector 20H : 120

V : 5300 500

Radio Labs

Yagi 12.5 30 150 57

Parabolic 23 10.5 100

18


Amplifier

Can amplify the receiver power, not the transmitter power

Amplify also the noise

19

Vendor AmplificationTemperature

rangePrice($)

RadioLabs

Tx : 26dBm(+2dB)

Rx : 30dBm(+1dB)

Rx Noise Figure:

3.5dBm

-30ºC~+70ºC 120

Tx : 30dBm(+2dB)

Rx : 10dBm(+1dB)

Rx Noise

Figure:3.5dBm

-40ºC~70ºC 300


Is it increase the coverage using the directional antenna and the amplifier?

Limited

IEEE 802.11 is basically operated by the slot

Slot Time : time granularity in IEEE 802.11 Slot Time : FHSS(50μs), DSSS(≤20μs), OFDM(≤9μs)

aCCATime : FHSS(27μs), DSSS(≤15μs), OFDM(≤4μs)

aRxTxTurnaroundTime : FHSS(20μs), DSSS(≤5μs), OFDM(≤2μs)

aAirPropagationTime : 1μs Distance < 300m

+aMACProcessingDelay : ≤2μs

20


aSlotTime이 증가할 경우

Propagation delay의 증가에 따른 성능의 변화

Contention Window가 Node의 수에 최적화되어 있을 경우

Basic DCF를 사용할 경우

21

참고문헌 G. Bianchi, “Performance Analysis of the IEEE 802.11 Distributed Coordination Function”,

IEEE Journal on Selected Area in Communications, Vol. 18, No. 3, pp. 535-547, Mar. 2000

max 1/

, /21 1

cK

s c

E PS K T

T K T K e

min 1

1/

1

1 1s c

K

D T TK e

minD

sT

cT

E P

maxS : maximum throughput

: minimum delay

: consumed time to successfully transmit

: consumed time by the collision

: average payload size

: propagation delay


성능 분석 결과

Throughput 감소

Propagation delay(σ)이 1μs증가하면 평균 1.1%의 throughput 감소

Delay는 점짂적으로 증가

Propagation delay(σ)이 1μs증가하면 평균 0.8us의 delay 증가

22

300 600 1000 2000 10000 1500010

15

20

25

30

35

40

45

50

Distance(m)

Thro

ughput(

Mbps)

300 600 1000 2000 10000 150009

9.05

9.1

9.15

9.2

9.25

9.3

9.35

9.4

9.45

9.5

Distance(m)

Del

ay(m

sec)


Need to wireless backhaul using PtP device

23

Vendor Data Rate Range Frequency Cost($)

Motorola105Mbps

(Ethernet)

LoS : 250km

Near LoS : 40km

NLoS : 10km

5.4GHz5,995

(w ant.)

300Mbps

(Ethernet)

LoS : 250km

Near LoS : 40km

NLoS : 10km

5.8GHz3,295

(w/o ant.)

Bridge

Wave

1.25Gbps

(Ethernet) Up to 11.5km 80GHz 33,000

Proxim

wireless125Mbps 1km 60GHz

Wi-Fi Mesh Network using IEEE 802.11s

It will provide an IEEE 802.11 Wireless DS that supports both

broadcast/multicast and unicast delivery at the MAC layer

using radio-aware metrics over self-configuring multi-hop

topologies.

The objectives

Increased range/coverage & flexibility in use

Reliable performance

Seamless security

Power efficient operation

Multimedia transport between devices

Backward compatibility

Interoperability for interworking

24

Network Architecture in IEEE 802.11s

Mesh point (MP)

Relay frames each other in a router-like hop-by-hop fashion

Mesh access point (MAP)

Mesh relaying + AP service for clients

Mesh portal point (MPP)

Acting as a bridge to other networks

25

MP

MPP

MP

MP

STAs

802.11s Mesh links

Legacy 802.11s links

MAP

` `

`

Multi Channel Operation in IEEE 802.11s

Single interface

Simple channel allocation

Share the resources for the client access, backhaul ingress, backhaul egress Increase the latency, Decrease the throughput

Low cost

Multiple interface

Advanced channel allocation

All radio on a device should use the same mode

WLAN mesh network is a layer 2 network

Each radio can operate on different band(Max. = 4 in OFDM)

26<Simple interface example> <Multiple interface example>

Key Functionality of Mesh Networks

Mesh Topology Creation

Self-configuring neighbor discovery

Channel selection

Link establishment with neighbor MPs (Authentication/Association)

L2 Routing

Mesh path selection and forwarding based on MAC addresses

Radio-aware metrics for routing

Hybrid wireless mesh protocol (HWMP)

On-demand and proactive routing

MAC Enhancement

for supporting QoS(basically EDCA), and increasing the network

throughput

Security

27

MAC Enhancement in IEEE 802.11s

EDCA as the basis for the .11s media access mechanism

Re-use of latest MAC enhancement from 802.11

Compatibility with legacy devices

Interaction of forwarding and BSS traffic

Handling of multi-hop mesh traffic and single-hop BSS traffic within

one device impacts network performance

Dependent on system fairness and prioritization policies

Treated as an implementation choice

MAC enhancement for mesh

Intra-mesh congestion control

Simple hop-by-hop congestion control mechanism implemented at

each MP

Common channel framework (Optional)

Support for multi-channel MAC operation

28

Need for Congestion Control

Mesh characteristics

Heterogeneous link capacities along the path of a flow

Traffic aggregation: Multi-hop flows sharing intermediate links

Issues with the 11/11e MAC for mesh:

Nodes blindly transmit as many packets as possible, regardless of

how many reach the destination

Results in throughput degradation and performance inefficiency

29

2

1

7

6

3

High capacity linkLow capacity link

Flow

4

5

Intra-Mesh Congestion Control Mechanisms

Local congestion monitoring

Each node actively monitors local channel utilization

If congestion detected, notifies previous-hop neighbors and/or the neighborhood

Congestion control signaling

Congestion control request (unicast)

Congestion control response (unicast)

Neighborhood congestion announcement (broadcast)

Local rate control

Each node that receives either a unicast or broadcast congestion notification message should adjust its traffic generation rate accordingly

Rate control (and signaling) on per-AC basis – e.g., data traffic rate may be adjusted without affecting voice traffic

Example: MAPs may adjust BSS EDCA parameters to alleviate congestion due to associated STAs

30

CCF for Multi-Channel MAC Operation

A framework that enables single and multi-channel MAC

operation for devices with single and multiple radios

Common channel is:

Unified Channel Graph on which MPs and MAPs operate

The channel from which MPs switch to a destination channel and

return back

MPs with multiple radios may use a separate common channel for

each interface

CCF supports optional channel switching in different forms

After RTX/CTX exchange on common channel, MP pairs switch to a

destination channel and then switch back

Groups of MPs may switch to a negotiated destination channel

Neighbors discover support for CCF during association.

Using the Mesh Capability IE in the beacon

31

Multi-Channel CCF for Single Radio: Channel Switching

32

RTX

MP1

MP2

MP3

MP4

Common

Channel

Data

Channel n

Data

Channel m

CTX

SIFS

CTX

SIFS

RTX

DIFS

DIFS

DATA

Switching

Delay

ACK

SIFS CTX

SIFS

RTX

DIFS

Switching

Delay

DATA

Switching

DelayDIFS

ACK

SIFS

Network Topology

MP boot sequence

Neighbor discovery

A MP performs passive or active scanning

Classify the node‟s physical neighbor according the profile

• Ignore node, Neighbor MP, Candidate peer

Channel selection

The channel of a MP is set to the highest channel precedence value

Link establishment

Determine the directionality

Link state measurement

The superordinate node of the link measures the bit rate and packet

error rate

Path selection and forwarding

Using airtime cost

AP initialization (optional)

33

Network Participation

34

57

12

6

4

3

Mesh Identifier:WLANMesh_Home

Mesh Profile:(link state, airtime

metric)

X

Capabilities:Path Selection: distance vector, link

state

Metrics: airtime, latency

1. Mesh Point X discovers

Mesh (WLANMesh_Home)

with Profile (link state,

airtime metric)

2. Mesh Point X associates /

authenticates with

neighbors in the mesh,

since it is capable of

supporting the Profile

3. Mesh Point X begins

participating in link state

path selection and data

forwarding protocol

One active protocol/metric in one mesh, but allow for alternative protocols/ metrics in different meshes

8

Hybrid Wireless Mesh Protocol

Extensible framework

Default metric

Airtime cost

Default protocol

Radio metric ad-hoc on demand distance vector (RM-AODV)

Optional protocol

Radio aware optimized link state routing (RA-OLSR)

Different meshes may have different active path selection

protocols

Path selection messages

Transported at the link layer

Using IEEE 802.11 management frames

35

Airtime Link Metric Function

Airtime cost

The amount of channel resources consumed by transmitting the

frame over a particular link.

36

pt

tpcaa

er

BOOc

1

1

Parameter Description 802.11a 802.11b

Oca Channel access overhead 75μs 335μs

Op Protocol overhead 110μs 364μs

Bt Number of bits in test frame 8224 8224

r Transmission bit rate for Bt

ept Error rate for Bt

Radio Metric AODV

Basic features

Source node broadcasts a RREQ message flooded by all nodes

When a RREQ is received, the node creates a reverse path to the source

The forward path is established when a RREP is received

Difference

RREQ for multiple destinations are aggregated in same message

Path select algorithm select the interface with highest available capacity

Airtime-cost

To adapt channel fluctuation

Periodically refresh routes to maintain the route

Keep the candidate route (secondary path)

Intermediate nodes does not generate a RREP even if they have a route to the destination

37

A

S

C

B

E

D

AODV

A

C

B

E

D

RMAODV

S

HWMP Example #1: No Root, Destination Inside the Mesh

38

Example: MP 4 wants to communicate with MP 9

1. MP 4 first checks its local forwarding table for

an active forwarding entry to MP 9

2. If no active path exists, MP 4 sends a RREQ to

discover the best path to MP 9

3. MP 9 replies to the RREQ with a RREP to

establish a bi-directional path for data

forwarding

4. MP 4 begins data communication with MP 9

59

710

6

4

3

2

1

8

X

On-demand path

HWMP Example #2: Non-Root Portal, Destination Outside the Mesh

39

Example: MP 4 wants to communicate with X

1. MP 4 first checks its local forwarding table for an active forwarding entry to X

2. If no active path exists, MP 4 sends a RREQ to discover the best path to X

3. When no RREP received, MP 4 assumes X is outside the mesh and sends messages destined to X to Mesh Portal(s) for interworking

Learned via IE in beacons, probe response

4. MP 1 forwards messages to other LAN segments according to locally implemented interworking

59

710

6

4

3

2

1

8

X

On-demand path

HWMP Example #3: Root Portal, Destination Outside the Mesh

40

Example: MP 4 wants to communicate with X

1. MP 4 first checks its local forwarding tablefor an active forwarding entry to X

2. If no active path exists, MP 4 mayimmediately forward the message on theproactive path toward the Root MP 1

3. When MP 1 receives the message, if it doesnot have an active forwarding entry to X itmay assume the destination is outside themesh and forward on other LAN segmentsaccording to locally implementedinterworking

Note: No broadcast discovery required whendestination is outside of the mesh

59

710

6

4

3

2

1

8

X

Proactive path

Root

HWMP Example #4: With Root, Destination Inside the Mesh

41

Example: MP 4 wants to communicate with MP 9

1. MP 4 first checks its local forwarding table for an active forwarding entry to MP 9

2. If no active path exists, MP 4 mayimmediately forward the message on the proactive path toward the Root MP 1

3. When MP 1 receives the message, it flags the message as “intra-mesh” and forwards on the proactive path to MP 9

4. When MP 9 receives the message, it mayissue an on-demand RREQ to MP 4 to establish the best intra-mesh MP-to-MP path for future messages

59

710

6

4

3

2

1

8

X

Proactive path

Root

On-demand path

Reference Model for 802.11s Interworking

42

802.11sMeshPoint

802.11sMeshPoint

802.11sMeshPoint

802.11sMeshPoint

802.11sMeshPoint

802.11sMeshPoint

802.11sMeshPoint

802.11sMeshPoint

802.11s

MAC802

MAC

Bridge

802.11s

MAC802

MAC

BridgeMesh Portal Mesh Portal

L3 Router L3 Router

The 802.11s MAC entity appears as a single port to an 802.1 bridging relay or L3 router.

802.11s mesh portals expose the WLAN mesh behavior as an 802-style LAN segment

(appears as a single loop-free broadcast LAN segment to the 802.1 bridge relay and higher

layers).

Achieving 802 LAN Segment Behavior

43

Bridge Protocol

Bridge

Relay 802.11s

MAC(including

L2 routing)

802 MAC

1

11

59

710

6

2

4

3

13

14

12

Support for connecting an 802.11s mesh to an 802.1D bridged LAN• Broadcast LAN (transparent forwarding)

• Overhearing of packets (bridge learning)

• Support for bridge-to-bridge communications

802 LAN

802 LAN

Layer-2 Mesh

Broadcast LAN

• Unicast delivery

• Broadcast delivery

• Multicast delivery

Interworking: Packet Forwarding

44Abr

ah

1

11

59

710

6

2

4

3

13

14

12A.1

15

A.2

A.3

B.1 B.2

Destination

inside or outside

the Mesh?

Portal(s)

forward

the message

Use path

to the

destination

Interworking: MP view

1. Determine if the destination is inside or

outside of the Mesh

a. Leverage layer-2 mesh path discovery

2. For a destination inside the Mesh,

a. Use layer-2 mesh path discovery/forwarding

3. For a destination outside the Mesh,

a. Identify the “right” portal, and deliver packets via

unicast

b. If not known, deliver to all mesh portals

45

Interworking support

Each MP maintains a layer-2 forwarding table, and there are

three kinds of format to present next hop field

The MAC address : the destination is inside the Mesh

The identity of the MPP : the destination is outside the Mesh

A broadcast address : the destination is outside the Mesh and we

don‟t know what the correct MPP is

46

New components in IEEE 802.11n

PHY enhancements

High modulation : OFDM modulation with additional coding

methods, preambles, multiple streams and beam-forming

Multiple input multiple output (MIMO) : spatial multiplexing

Channel aggregation : two adjacent 20 MHz channels are

combined to create a single 40 MHz channel

MAC Enhancements

Frame aggregation : aggregation in MAC or PHY to efficiently pack

smaller packets into a single MPDU

Block acknowledgement : A performance optimization in which an

IEEE 802.11 ACK frame need not follow every unicast frame and

combined acknowledgements may be sent at a later point in time

47

PHY enhancements

Multiple Input Multiple Output (MIMO)

Transmit and receive with multiple radios simultaneously in same

spectrum

Compare to traditional single input single output radio (with

optional receive diversity)

48

channelRadio

Radio

D

S

P

Bits

TX

Radio

Radio

Radio

D

S

P

Bits

Radio

RX

channelRadioDSPBits

TXRadio DSP Bits

RX

MIMO Method

Spatial multiplexing (SM) throughput ↑

Space-time block coding (STBC) diversity ↑

Transmit beamforming (TxBF) directivity ↑, overall throughput ↑

49

A

B

A

B

A

B

Spatial Division Multiplexing

Multiple independent data streams are sent between the

transmit and receive antennas to deliver more bits in the

specified bandwidth

Cross-paths between antennas are automatically decoded by

the receiver, assuming sufficient “richness” in the propagation

environment

50

Radio

Radio

D

S

P

More Bits

TX

Radio

Radio

Radio

D

S

P

More Bits

Radio

RX

MAC Enhancement

The basic MAC Exchange

Block ACK

With block ACK, we don‟t need to ACK each MPDU

Frame Aggregation

With frame aggregation, multiple MAC frames are assembled into

a single PHY frame

Provides a Latency vs. Throughput tradeoff

51

RTS

CTS

MPDU

ACK

MPDU

ACK

RTS

CTS

MPDU MPDU

BACK

RTS

CTS

A-MPDU

BACK

Frame Aggregation

MAC service data unit aggregation (A-MSDU)

Group logical link control packets (MSDUs) with the same 802.11e

Quality of Service, independent of source or destination

MAC protocol data unit aggregation (A-MPDU)

occurs later, after MAC headers are added to each MSDU

52

MAC

Proce-

ssing

F1

F2

F3

MAC

header

F1

F2

F3

MAC

Proce-

ssing

F1

F2

F3

MAC

header

F1

F2

F3

MAC

header

MAC

header

A-MSDU A-MPDU

Backward compatibility

Backward compatibility to a/b/g & Coexistence

802.11n supports three compatibility modes

Non-HT mode (Legacy mode)

- Compatible with 802.11a/b/g

HT-mixed mode

- For high throughput operation and coexistence

HT-Greenfield mode

- For high throughput operation but not detectible by legacy devices

The new PHYs require enhanced protection mechanisms to avoid

interfering with existing older station (i.e. a/b/g)

53

Consideration for Throughput Enhancement

Random Network

Source-destination의 방향성이 없는 네트워크

Theoretical upper limit of the per node throughput capacity

Theoretically achievable capacity to ever node in a random static

wireless ad hoc network

Assumed by Ideal global scheduling and routing

With the use of real MAC, routing, and transport protocols and

a realistic traffic pattern, the achievable capacity in a WMN, in

practice, is much less than the theoretical upper limit

54

1/O n

<참고문헌>

P. Gupta and P.R. Kumar, „„The Capacity of Wireless Networks.‟‟ IEEE Transactions on Information Theory, vol. 46, no. 2, pp.

388–404, March 2000.

J. Li, C. Blake, D.S.J. De Couto, H.I. Lee, and R. Morris, „„Capacity of Ad Hoc Wireless Networks,‟‟ Proceedings of ACM

Mobicom 2001, pp. 61–69, July 2001.

1/ logO n n


CSMA/CA based MAC protocol

Due to the exposed node problem

String topology

55

String topology 1 hop 2 hop 3 hop 4 hop 5 hop >5 hop

Normalized throughput 1 0.47 0.32 0.23 0.15 0.14

1/hop 1 0.5 0.33 0.25 0.2 0.16

<exposed node problem>

1/1/ dO n


Theoretically achievable capacity

56

2 4 6 8 10 12 14 16 18 200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Number of Client

No

mal

ized

Th

rou

gh

pu

t

Capacity Upperbound

Ideal case, String topology

CSMA, String topology

CSMA, 2dimensional topology

•Branch의 수가 증가할 수록 throughput 감소 증가•Network topology를 최대한 정방형으로 설계•패킷의 크기가 클수록 throughput 감소가 작음(채널에러가 없는경우)


Arbitrary network

Arbitrary의 의미 „임의로 결정되어 변하지 않는‟의 뜻으로 매 전송마다 동일한 시작 및 목

적지 노드, 전송률, 전송 전력 을 가지는 네트워크로 정의

시스템 모델은 Nc개의 client가 균일하게 분포

Nr개의 mesh router가 존재

Client는 자싞과 가장 가까운 라우터와만 직접 통싞

Capacity upper-bound

MP의 수가 적을 때:

• Per-client throughput: 이 증가할수록 증가

MP의 수가 많을 때:

• Per-client throughput: 이 증가할수록 감소

57

/ log ,r c c g rN O N N N O N

r

c

c

NC

N

rN

/ log ,r c c g rN N N N O N

1

logc

r c

CN N

rN

<참고문헌>

P. Zhou, X. Wang, and R. Rao, “Asymptotic Capacity of Infrastructure Wireless Mesh Networks,” IEEE Transactions on

Mobile Computing, Vol. 7, No. 8, Aug. 2008


Performance

Network topology

Theoretical per node throughput

58

0 10 20 30 40 500.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

0.11

Number of router

No

mal

ized

th

rou

gh

pu

t

50 client

100 client

25 client

STA의 수가 결정되면 최적의MAP(MP)의 수와 MPP의 수가

결정됨

Throughput Enhancement

Multi-radio system (여러 개의 NIC, 최대 4개) 으로 구현

IEEE 802.11n 사용

Frame aggregation, Block ACK, MIMO

상용 장비

BelAir, Cisco, Nortal, SkyPilot

Multi-Hop QoS

Can provide using EDCA, not guarantee

59

IP layer

802.11n

(40MHz)

802.11n

(20MHz)

802.11n

(20MHz)

Upper branch

or gateway

Lower

branchAccess


60


Vendor Model Feature Price($)

BelAir

Network

BelAir200

Wireless Multi-

Service Switch

Router

• Modular architecture

• Supports Wi-Fi,WiMAX and Cellular

• IEEE 802.1p prioritization with 4 queue

• 1-port Ethernet interface

• 4x T1 interface

• IEEE 802.1D MAC bridging

• 802.1x(RADIUS) ,EAP and AES

• MIC2003-13 approvals

4000~9000

(Depending on

the number of

radio module)

Cisco Cisco Aironet

3500 Series

Access Point

• IEEE802.11n

• Dual-band controller-based 802.11a/g/n

• 2x3 multiple-input multiple-output

• Frame aggregation


• 802.11i, Wi-Fi Protected Access 2 (WPA2),

WPA

2600

SkyPilot SkyPilot®

Connector

DualBand

• IEEE 802.11b/g

• Up to 7.5 miles / 12 kilometers

• AES-128 encryption


Conclusion

Wi-Fi Mesh using IEEE 802 based technology

Coverage can be extended by directional antenna and amplifier

However, it may limited by the slot size

More than several km Need to point-to-point equipment

In Mesh network, throughput can be reduced in proportion to

the number of node

Multi-Radio system and IEEE 802.11n required

61

Thank you !

62

Q & A

Backup slides

MP boot sequence

63

Neighbor discovery

A MP performs passive or active scanning to discover

neighboring MPs

Add nodes of the same profile into MP’s neighbor table

Node’s physical neighbors can be classified to ignore node,

Neighbor MP and Candidate peer

Ignore node: a node that can‟t be communicated with (different

profile nodes)

Neighbor MP: a node that is a neighbor in the Mesh network, but

can‟t setup a link with it (the same profile nodes)

Candidate peer: a node that is a neighbor MP and can setup a link

in the Mesh network, (the same profile nodes)

64

Neighbor discovery

65

802.11 beacon OFDM Mesh ID WLAN mesh capability Neighbor list DTIM Mesh Portal reachability

Beacon

ID

Version

Active protocol ID

Active metric ID

Peer capacity

Power save capability

Channel precedence

A

B

C

DProfile : 1Version: 1

Active protocol ID: 1

Active metric ID: 2

Profile : 2Version: 1


Active metric ID: 3



Active metric ID: 3

Beacons



Active metric ID: 2



Active metric ID: 1

Neighbor discovery

66

Neighbor table

MAC adr. Primary

MAC adr.

State Directionality Operating

channel #

Channel

precedence

Bit rate PER RSS

B’s adr #1 #1 Neighbor 1 1 5dp

C’s adr #1 #1 Neighbor 1 1 4dp

A

B

C

DProfile : 1Version: 1


Active metric ID: 2



Active metric ID: 3



Active metric ID: 3

Beacons



Active metric ID: 2

Neighbor discovery

67

Neighbor table

MAC adr. Primary

MAC adr.


channel #

Channel

precedence

Bit rate PER RSS

B’s adr #1 #1 Candidate

Peer

1 1 5dp

C’s adr #1 #1 Neighbor 1 1 4dp

A

B

C

D

Peer capacity: # of additional MP

peers that the device can

accommodate

Beacons

Channel Selection

Channel selection mode

Simple unification mode

Single channel unification mode

Advanced mode

Beyond the scope of spec.

Single channel unification mode

The channel of a MP is set to the highest channel precedence

value of candidate peer

68

Channel Selection

69

A‟ Neighbor table

MAC adr. Primary

MAC adr.


channel #

Channel

precedence

Bit rate PER RSS

B’s adr #1 #1 Candidate

Peer

1 1 5dp

C’s adr #1 #1 Candidate

Peer

6 3 4dp

A

B

C

3>1

As a result, A‟s channel is 6

Backup slides

RM-AODV

70

Radio Metric AODV

71

A

S

C

B

E

D{S,D,0}

{S,D,0}

2

3

3

1

3

5

2

2

S S 2

S S 3

Radio Metric AODV

72

A

S

C

B

E

D

2

3

3

1

3

5

2

2

S S 2S A 5

S C 6S S 3

{S,D,2}

{S,D,3}

Radio Metric AODV

73

A

S

C

B

E

D

2

3

3

1

3

5

2

2

S S 2S C 4

S C 6S S 3

Radio Metric AODV

74

A

S

C

B

E

D

2

3

3

1

3

5

2

2

S S 2S C 4

S C 6

S E 8

S S 3

Radio Metric AODV

75

A

S

C

B

E

D

{D,S,5}

2

3

3

1

3

5

2

2

S S 2S C 4

S C 6

D D 2

S E 8

S S 3

E E 3

D E 5

C C 3

D C 8

{D,S,2}

Radio Metric AODV

76

A

S

C

B

E

D

2

3

3

1

3

5

2

2

S S 2S C 4

S C 6

D D 2

S B 6

S S 3

E E 3

D E 5

C C 3

D C 8

Radio Metric AODV

The selected path is S C B D

77

A

S

C

B

E

D

{D,S,3}

2

3

3

1

3

5

2

2

S S 2S C 4

D D 2

S C 6

D D 2

S B 6

S S 3

E E 3

D B 3

B B 1

C C 3

D C 7

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