efficient network coded data transmission in dtn
DESCRIPTION
Efficient Network Coded Data Transmission in DTN. - Paper By Yunfeng Lin, Baochun Li, Ben Liang. Outline. Motivation Constraints in DTN Network coding Vs Replication Binary Spraying Vs Epidemic routing Protocol Principle Assumptions Description Example Performance - PowerPoint PPT PresentationTRANSCRIPT
- Paper By Yunfeng Lin, Baochun Li, Ben Liang
OutlineMotivation
Constraints in DTN Network coding Vs Replication Binary Spraying Vs Epidemic routing
Protocol Principle Assumptions Description Example
Performance Average transmission / relay Transmission delay Relay buffer size Optimal Maximal Spray count Vs Identical Maximal spray
count
Motivation – Constraints in DTNOpportunistic connections between nodesNodes have limited transmission capabilitiesBuffer space limitationsBattery power limitedNodes might be mobileDelay in packet delivery will be largeNode density is sparse
Motivation – NC Vs ReplicationReplication – Transmitting copies of a packet.Network coding – combining packets and transmitting the resultant packet
Example:
K = 3, K – Number of source packets, namely, A, B and C.
Number of encoded packets, K’ = 3
Buffer Space of each relay, BS = 2
Number of nodes = 4, which includes one source, one destination. Number of relays is two.
Motivation – Replication Example
A
B
C
A
B
A
B
R1
R2
DESTINATION
Motivation – Replication ExampleR1
R2
A
B
C
A
C Replaces B
A
Here also C replaces B
DESTINATION
ONLY A AND C ARE RETRIEVED. FOR, B MORE DELAY IS
INCURRED
Motivation – NC Example
A + B + C
A + 2B + 3C
2A + 2B + C
A + B + C
A + 2B + 3C
A + B + C
A + 2B + 3C
R1
R2
DESTINATION
Motivation – NC ExampleR1
R2
A + B + C
A + 2B + 3C
2A + 2B + C
3A +3B +2C, x = 1
3A + 4B + 4C, x = 1
5A + 5B + 3C, x = 2
5A + 6B + 5C, x = 2
DESTINATION
ANY THREE PACKETS CAN HELP RETRIEVE A, B AND C
Motivation – Binary Spraying Vs ER
S, K = 2
R1
R2
R3
R4
D
Epidemic routing
Binary spraying
S, K = 2, L = 2
R1, L = 1
R2, L = 1
R3
D
R4R5
Protocol - PrincipleThis protocol called the E-NCR, is a combination of
Network coding and Binary spraying.
NCER Binary Spraying
E-NCR
ER
NCER – Network Coding based Epidemic routingER – Epidemic RoutingE-NCR - Efficient Network coding based routing
Protocol - AssumptionsThere is once source with ‘K’ packets to be transmitted, ‘n’
relay nodes and a destinationFor every opportunistic contact, only one packet can be
transmitted.The source ‘S’ and the Destination ‘D’ have enough buffer
space to hold all ‘K’ packets. But relay nodes have buffer space B, defined as 1 <= B <= K
While a packet transmission is made, no other back-ground traffic exists.
A packet in the buffer in an node is purged as soon as a ACK is received from ‘D’ or Time-to-live field is zero.
Protocol - DescriptionSOURCE-RELAY:
K' = K + some more encoded packets L = c * log k, where c is some constanti = 0;S = K';do{ if(detect any node and <i,l> not already there with that node) { send an encoded packet <i, L, co-efficients, packet>
i++; }
}while(S != i);
Protocol - DescriptionRELAY-RELAY, SENDER SIDE:
do{ if(detect any node X) {
get spray list of X; //list element is a tuple <i, l>,where i is index of packet, ‘l’ is the //remaining spray count
do {
compare this->spraylist with x->spraylist;if(any this->spraylist-><i, l> such that l >=0 and i does not exist in x->spraylist)
{send encoded packet <i, floor(l/2)> to node x;update tuple <i, l> to <i, ceil(l/2)>;}
}while(end of x->spraylist); }}while(true);
Protocol - DescriptionDESTINATION:
do{
if(got a packet){
add to packet listtry to decode list of
packets;if(decode possible){ exit loop;}
}
}while(true);
RELAY-RELAY, RECEIVER SIDE:
if(packet received){
if(buffer size == max_buffer_size){encode incoming packet with all packets in list;}else{place packet in free slot;}add <i,l> of incoming packet to spray list;
}
Protocol - ExampleIn the following example,
There are 7 nodes. One Source, One destination and 5 relays
The buffer space is 1 for the relay nodes and 3 for the source and destination
Number of packets to be transmitted from source is k = 3
L, the maximal spray count is set to log2(k) which is approximately 2 and the threshold is T = 1.
In the first level, l, the spray count reduces to L/2 which is 1. Since, this is the threshold, all future transmissions are one per packet.
Protocol - Example
E1, E2, E3
E2,
L = 2
E2
E3
E1,
L = 2
E1
E1 + (X) E2
L = 1
E3 + (Y) E1
L = 1
E1 + (X) E2 E3 + (Y) E1
E3 + (Z) E2
E3,
L = 2
Performance - Avg transmission per relay
Performance - Transmission delay
Performance - Relay buffer size
Performance – Optimal Vs Identical Maximal spray count
Some LimitationsDestination has to wait till minimum of ‘K’
encoded packets have to be receivedSome packets which have linear dependence
could arise during encoding at relays.
AcknowledgementsMy Audience for your comments, time and
patience.Prof. Chan Mun ChoonDr. A. V. BabuManjunathChen Bin BinThe Authors of the paper