Network Coding vs. Erasure Coding: Reliable Multicast in MANETs

1. Network Coding vs. Erasure Coding:Reliable Multicast in MANETs • Atsushi Fujimura*, Soon Y. Oh, and Mario Gerla • *NEC Corporation • University of California, Los Angeles

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”

3. 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

4. Network Coding Example

5. 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

6. NC and EC Implementation

7. 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

8. Grid Topology Setting Grid Topology One source and three receivers Each node has rredundant paths (except the 1st hop) h: Number of hops from a source to receivers Source S r h Receivers R R R

9. 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

10. 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 variable packet drop rate, h=5 Packet delivery ratio for varying hop #

11. Analysis (Grid Topology) Single-hop models for NC (left) and EC (right) Different packets (NC) and duplicated packets (EC) S R R R S１ S２ S３ S f f f f f f 1-d 1-d R R Network coding case Erasure coding case

12. 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)

13. 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

14. 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

15. 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

16. Thanks