Navid Nikaein
Mobile Communication Department
Mobile Advanced Networks
Broadcasting
1
This work is licensed under a CC attribution Share-Alike 3.0 Unported license.
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]
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Flooding
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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
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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
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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
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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
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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
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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
©Navid Nikaein 2012 9
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
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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
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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?
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Source
Relay
Discussion
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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)
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Broadcasting Techniques
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
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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 ?
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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]);
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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
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Study 1: Algorithm Efficiency Static Network without MAC
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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
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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
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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
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Three parameters are changed simultaneously
Study 4: Combined Network
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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)
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Broadcasting Techniques
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
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Path Offset
Relative Distance Estimation
How the RDE can be improved? path_offset= d x path_mobility x elapsed time
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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
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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 ?
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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
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Broadcast With MAC Support
Allowing two non-interfering radio to transmit at the same time
Exploiting spatial concurrency Scheduling Smart antenna
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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
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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
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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
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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
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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
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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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