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Network Coding vs. Erasure Coding: Reliable Multicast in MANETs. Atsushi Fujimura*, Soon Y. Oh , and Mario Gerla *NEC Corporation University of California, Los Angeles. Motivation. Tactical networks require high reliability of multicast communications for effective mission accomplishment - PowerPoint PPT Presentation
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Network Coding vs. Erasure Coding:Reliable Multicast in MANETs
Atsushi Fujimura*, Soon Y. Oh, and Mario Gerla
*NEC Corporation University of California, Los Angeles
Page 2
Motivation
Tactical networks require high reliability of multicast communications for effective mission accomplishment
Both Network coding (NC) and erasure coding (EC) can increase reliability in lossy networks
Which coding scheme is more reliable and efficient for MANETs?
“The jury is still out”
Page 4
NC and ECImplementation Both randomly and linearly encode:
– Block coding: stream of packets is split into blocks and encoded
– Coefficients are randomly drawn from a finite field– Receivers reconstruct original data
Erasure Coding Example
Page 5
Network Coding Example
Page 6
NC and EC Implementation Probabilistic Forwarding:
– In both NC and EC each intermediate nodes forwards with probability f
Forwarder generates random number x
Compare x and drop rate d
If (x < d) forwarding received packet
Otherwise drop packet
Packet Drop
Page 7
NC and EC Implementation
Network Coding Erasure Coding
Coding at Source
( Rate c = k/n )
Coding rate c = 1.A source does not generate redundant packets
k original packets are encoded into n > k source encoded packets, c < 1
Encoding at Intermediate
NodesYes No
Buffering and Forwarding
Intermediate nodes enqueue innovative packets for re-encoding
Intermediate nodes forward only non-duplicated packets
Page 8
Simulation Settings
Qualnet implementation– Random linear coding– 2Mbps channel bandwidth, 376m radio range– 802.11b MAC and PHY– 1KB/s traffic
Two topologies– Grid topology– Random topology
Performance Metrics– Packet Delivery Ratio (PDR)– Normalized Packet Overhead
Page 9
Grid Topology Setting
Grid Topology– One source and three
receivers– Each node has r
redundant paths (except the 1st hop)
– h: Number of hops from a source to receivers
Receivers
R
S
R R
h
Source
r
Page 10
Simulation (Grid Topology)
EC coding rate ranges between c=1 and c=1/6 EC requires twice as much line overhead to
achieve the same delivery ratio as NC
Packet delivery ratio when h =5 Overhead in term of h when f =1
Page 11
Simulation (Grid Topology)
EC Delivery ratio is very sensitive to hop number (while NC holds its performance variation smaller)
Packet drop probability on a link (d) has more impact on NC achievable delivery ratio
Packet delivery ratio for varying hop # Packet delivery ratio for variable packet drop rate, h=5
Page 12
Analysis (Grid Topology)
Single-hop models for NC (left) and EC (right) Different packets (NC) and duplicated packets (EC)
f f f
S 2
R
1-d
f f f
S
R
1-d
S 1 S 3
R
S
R R
Network coding case Erasure coding case
Page 15
Random Topology
50 nodes including one source and 10 multicast members
Nodes are randomly distributed in a square field
Node density = average number of nodes within the transmission range (376m)
0
200
400
600
800
1000
1200
1400
0 200 400 600 800 1000 1200 1400
(m)
(m)
Page 16
Simulation (Random Topology)
EC suffers much more overhead (similar to the results in Grid Topology)
As for grid topology, EC delivery ratio equals NC delivery ratio between c =1/3 and c=1/2
Packet delivery ratio and overhead when the node density is 12
Page 18
Simulation (Random Topology)
Packet Drop decreases delivery ratio, but more significant in NC than EC
Node mobility helps both NC and EC recover from high packet drop rate
Packet drop probability (d) = 0.4
Packet delivery ratio with drip rate and mobility when node density is 12
Page 19
Summary
Compared NC and EC in MANETs NC can achieve high delivery ratio with much less overhead
Future Work Implementation of joint EC and NC scheme Extension to vehicular applications
Page 20
Thanks