Mobile Advanced Networks Broadcasting - Accueil | …nikaeinn/lectures/mobadv/chapter02...Navid Nikaein Mobile Communication Department Mobile Advanced Networks Broadcasting 1 This

Navid Nikaein

Mobile Communication Department

Mobile Advanced Networks

Broadcasting

1

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Broadcasting

Common operation in many applications Paging, alarm and warning system

Building block to solve many network layer problems Broadcasting of control information in Routing Data dissemination

Network wide broadcasting is called Flooding A process in which one node sends a message to all other nodes in

the networks (one-to-all type of comm.) Rebroadcast a copy of the same received message to all its

neighbors for all interfaces except the one from which it received the message

Requires processes and techniques to dump redundant and duplicate packet generation [2] [3]

©Navid Nikaein 2012 2

htpp://www.eurecom.fr/

Flooding


I

G

C

F

B

A M

N

J

D K

L

V

W

U

Z

T

X H

S

Represents source and destination nodes Represents the network nodes

Represents the network connectivity

R


Flooding


I

G

C

F

B

A M

N

J

D K

L

V

W

U

Z

T

X H

S

Represents a node that receives packet P for the first time

Represents transmission of packet P

R


Flooding


I

G

C

F

B

A M

N

J

D K

L

V

W

U

Z

T

X H

S

Nodes that already received the packet P - Potentially generates collision under random access channel, e.g. at node H, - Note that I & J do not see each other. It is said that they are hidden from each other

R


Flooding


I

G

C

F

B

A M

N

J

D K

L

V

W

U

Z

T

X H

S

- Generate redundant & unnecessary information, e.g. node G and H receive multiple copies of the same message - Note that node H does not forward the packet P again due to SN - Transmission may collide at D: Packet P may not be delivered to the destination

R


Flooding


I

G

C

F

B

A M

N

J

D K

L

V

W

U

Z

T

X H

S

R

D does not forward the packet Flooding is omni-directional (blind) e.g. node A & B receive the packet P - Flooding may not converge to the shortest path (hop #) e.g. P<s,d>=(S, J, L, N, D) instead of P<s,d>=(S, J, K, D)


Flooding


I

G

C

F

B

A M

N

J

D K

L

V

W

U

Z

T

X H

S

R

Flooding range is network diameter (TTL) e.g. node T receives the packet P - It’s difficult to keep track of the network diameter - Unreachable nodes (e.g. Z) or nodes for which destination is the only upstream node (e.g. R) do not receive the packet P


Discussion

Observations High overhead Unreliable packet delivery Route diversity

Parameters Angle: omni directional Scope: network diameter

Scalability as the ability to maintain the network performance when limiting factors grow Mobility rate Traffic load Number of nodes Network density


broadcast storm problem


Discussion

Flooding is key component of (many proposed ) algorithms and protocols for mobile ad hoc networks

At least flooding should be Scalable : maintain the performance as the limiting factors

grow Efficient : minimum number of rebroadcasting Reliable : guarantee of the packet delivery



Discussion

Expected additional coverage (EAC) Node “A” sends a broadcast message Additional area that can benefit from node “B” rebroadcast Observation: this decreases as the number of transmissions heard

increase [3] Results: rebroadcasting can provide only 0-61πr2 EAC


B A r r

d

rddxxrdINTC

dINTCrSSSr

d

BABAB

≤≤−=

−=−=

∫

∩−

0,4)(

)(

2/

22

2π0

10

20

30

40

50

1 2 3 5 7 9 11Expe

cted

Cov

erag

e(%

)

No. of transmissions heard

EAC Avg. EAC= 0-41πr2

K≥ 4 EAC=0.05%


Discussion

Optimal broadcasting Relay selection problem?


Source

Relay


Discussion


24 retransmissions to diffuse a message up to 3 hops

Retransmission node

11 retransmission to diffuse a message up to 3 hops

Retransmission node - MPR


Broadcasting Techniques

Determine a small set of forwarding nodes to ensure coverage Localized techniques: are based only on the information from all

nodes within a constant hop distance Globalized techniques: are based on the knowledge of the whole

network

Network topology information (long lived) Periodic “hello” message K-hop neighborhood information (k=2 or 3)

Broadcast state information (short lived) Snooped: snoop the activities of its neighbors Piggybacked: attach H most-recently visited node information

(including designated forward neighbors)




Many methods have been proposed to improve the efficiency of the broadcasting [2][3] Probability-based

Probabilistic scheme Counter-based scheme

Area-based Distance based scheme Location-based scheme

Neighbor knowledge Self pruning Scalable broadcast algorithm (SBA) Ad hoc broadcast protocol (AHBP) Multipoint relay (MPR)

Clustering Topology Control



Pseduo Code: counter-based scheme pkt=receive_pkt(); For all i

If (p[i] != pkt) { p[i+1] = pkt; cnt[i+1]=0; }

else j = i;// index of already received pkt

If (p[i+1]){ // new pkt cnt[i+1]++; RAD[i+1]=uniform_rand(0, Tmax); }

else {// old pkt if (RAD[j]--)

cnt[j]++; else // RAD expires

if (cnt[j] < Threshold) • Rebroadcast (p[j])

else • drop p[j] }

Adaptability to local topologies

In dense net?

In sparse net?

What about delay ?



Pseduo Code: location-based scheme

Pkt[i]=receive_pkt();

AC[i]= 𝜋𝑟2 − 4∫ 𝑟2 − 𝑥2𝑟𝑑/2 𝑑𝑥; (see the broadcast storm paper, section 3.5)

If (pkt[i]) // new pkt Tmax[i] = (collision_probaility > .5 || num_pkt_s > 40 ) ? uniform_rand( 0.05 , 0.1) ; uniform_rand(

0, 0.001) ; // adaptive rad, values are in second, see the paper broadcast techniques

If ( (AC[pkt(i)] >= AC_THREASHOLD) && pkt [i]) RAD[i]=uniform_rand(0, Tmax);

else { Drop(pkt(i)); RAD[i]=0; }

AC[i]= 𝜋𝑟2 − 4∫ 𝑟2 − 𝑥2𝑟𝑑/2 𝑑𝑥;

if (RAD[i]--) If ( (AC[pkt(i)] < AC_THREASHOLD) && pkt [i]))

Drop (pkt(i));

else // RAD expires Send (pkt[i]);



SIMULATION RESULTS OF BROADCASTING TECHNIQUES [2]



Simulation Parameters

Simulator: NS2 Network Area: 350m2

Transmit range: 100m Packet Size: 64 bytes IFQ Length: 50 Simulation Time: 100S Number of Trials: 10 Confidence Interval: 95% Random Assessment Delay: 0.01S Hello Interval: 1S



Study 1: Algorithm Efficiency Static Network without MAC


Performance of the algorithms from a sparse network to a dense network

Neighbor knowledge techniques outperform other techniques

traffic: CBR 10 pkt/s


Study 2: Congested Network Contention Scheme: 802.11MAC


To improve the performance, RAD needs to be adaptive

Performance of the algorithms by varying the congestion rate

Traffic: VBR 1-80 pkt/s Num nodes = 60


Study 3: Mobile Network with null MAC Random Way Point: Zero Pause Time


Performance of the algorithms by varying the mobility rate

Neighbor knowledge techniques are sensitive to mobility rate

Traffic: CBR 10 pkt/s Num nodes = 60 Mobility = RWP, 0 PT


Study 4: Combined Network


Three parameters are changed simultaneously


Study 4: Combined Network


Three parameters are changed simultaneously


Discussion

Reliable Broadcasting is expensive in wireless environments Despite these local optimizations, broadcasting is only efficient

when Network is small and dense Network traffic load is low-medium Network mobility is low-medium

Use simple flooding for small packets e.g. route generation process

Or, apply some global optimizations for more adaptive and dynamic techniques History of a node to limit the angle and/or scope of broadcasting Our assumption “each layer can be optimized independently” may not

always be true Exploit novel techniques at different layers (cross-layering)




How to limit the scope of the flooding? Query localization technique [Castenada99] Relative distance estimation RDMAR [Aggelou99] Expanding ring search [hassan04]

How to reduce the angle of the flooding? Location aided routing LAR [ko00] Distance routing effect algorithm for mobility [basagni98] Relative movement estimation RME [nikaein03]

How to reduce the redundancy ? Broadcast storm problem [ni99] Broadcasting techniques [camp02] Topology control [rajaraman02] Network Coding



Path Offset

Relative Distance Estimation

How the RDE can be improved? path_offset= d x path_mobility x elapsed time


SRC DST

Src Offset

Dst Offset

RD_Offset

H x R

…

Offset= mobility x elapsed time TTL=(Src_Offset+Dst_offset)/R + H


Expanding Ring Search

Broadcasting Scope: Scope increment and threshold

TTL(0) = TTL_START If TTL(i-1) + TTL_INCREMENT <

TTL_THRESHOLD then TTL(i)= TTL(i-1) + TTL_INCREMENT

else TTL(i) = NET_DIAMETER

If a NEW route for the same destination is required then TTL(0) = Hop_Count + TTL_INCREMENT


S D Intermediate Nodes

TTL=1

TTL=2

TTL=3 1st ring 2nd ring 3rd ring

S D Intermediate Nodes

TTL=1

TTL=1

TTL=1 1st ring 2nd ring 3rd ring


Example

Node “1“ wants to send message “A” to node “7” Best strategy can achieve in 4 transmissions

Strategy I: Retransmit each received packets Endless transmissions instead of 4 Tx /Txopt = 0

Strategy II: Retransmit each packet exactly once 6 transmissions instead of 4 Tx /Txopt = 0.67

Is there any alternative ?


1 1

3 2

7

6

5

4

1

2 3

5

3

6

6 4

2

4

A


Novel Techniques

Cross layering and joint design [4] Mac layer in support of broadcast Network coding Directional Antenna Location information

Precautions [5] It is about optimizing the performance through increasing

layer interactions, and sharing the information among different layers

Not a replacement for a layered architecture Be aware, optimization processes at different layers could go

in opposite directions



Broadcast With MAC Support

Allowing two non-interfering radio to transmit at the same time

Exploiting spatial concurrency Scheduling Smart antenna


1

3 2

7

6

5

4

• Example: 1 sends A to 7 -Performance depends on how MAC handles

the channel access (e.g. random access is unreliable)

- 5 transmissions is used instead of 4 - Tx /Txopt = 0.8%

• Are further improvements possible?

A

1st Tx

2nd Tx 3rd Tx

3rd Tx

4th Tx

5th Tx


Network Coding Concept


Source: C. Fragouli EPFL

PHY Network Coding


Network Coding Concept

If transmitting one packet costs 1 time unit, how many time units do we need to transmit message “A” and message “B” from 1 to 4 and 6


A

1

3 2

7

6

5

4

A B

A B

B

A+B A+B A+B

A B A B

•Store and forward a message or instead wait and process messages before forwarding?


Broadcast With Network Coding

Information theory and coding theory [6] Max-flow min-cut theorem in a directed graph [7]

maximum amount of flow is equal to the capacity of a minimal cut

Strategy III: Instead of repeating the same packet, combine the received or created

packets into one or several outgoing packets


A

1

3 2

7

6

5

4

A B

A B

B

A+B A+B A+B

A B A B

•Example: 1 sends A and B to 4 and 6 - Max-flow value is achievable and routing can’t achieve this - 6 transmissions for 2 messages are used instead of 8 -Tx /Txopt = 1.33

•Is this achievable in general ?


Application of Network Coding

Robust to collision and contention

Avoid bottleneck in some cases

Security: Extracting useful information becomes harder


Source: C. Fragouli EPFL


Conclusion

Broadcasting Problem Statement

Basic Broadcasting Techniques

Angle and scope are the key broadcasting parameters

Simulation results

Impact of network density, traffic load and mobility rate on the performance of the broadcasting techniques

Novel techniques for broadcasting



References

[1] : Routing in Communications Networks, M. Steenstrup, Prentice Hall, 1995 [2] : Comparison of Broadcasting Techniques for Mobile Ad Hoc Networks, B.

Williams, T. Camp, Mobihoc 2002 [3] : The Broadcast Storm Problem in a Mobile Ad Hoc Network, S.-Y Ni, Y.-C. Tseng,

Y.-S. Chen, J.-P Sheu, MobiCom, 1999 [4] : Wireless Ad Hoc and Sensor Networks: A Cross-Layer Design Perspective, R.

Jurdak, Springer, 2007 [5] : A Cautionary Perspective on Cross-layer Design, V. Kawadia, P.R. Kumar, IEEE

Wireless Communication, 2005 [6] : Network Flows: Theory, Algorithms, and Applications, R. K. Ahuja, T. L. Magnati,

J. B. Orlin, Prentice Hall, 1993 [7] : Handbook of Graph Theory, J. L. Gross, J. Yellen, CRC press, 2003 [8] : GPS-less Low-Cost Outdoor Localization for Very Small Devices, JN.Bulusu,

J.Heidemann, D. Estrin, IEEE Personal Communication, 2000



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Mobile Advanced Networks Broadcasting - Accueil | …nikaeinn/lectures/mobadv/chapter02...Navid Nikaein Mobile Communication Department Mobile Advanced Networks Broadcasting 1 This