1. TCP+Network Coding
Li Shushi

2. Outline
Introduction TCP/NC
Detail about TCP/NC
Redundancy factor R 2

3. TCP has poor perfomance in wireless network
Introduction
TCP has poor perfomance in
wireless network
TCP interprete packet loss as a
congestion signal
But in wireless network,
congestion is not the main
reason for packet loss 3

4. Network coding improve throughput example
Introduction
Network coding improve throughput
example 4

5. Network coding improve throughput example
Introduction
Network coding improve throughput
example 5

6. Send linear combination of packets
TCP/NC
Send linear combination of packets
The message is split into a stream of packets P1,P2,...
code these packets, Fq
mk=min(nk,Wen)
nk:packet number in buffer
Wen:coding window size 6

7. definition TCP/NC seen packet:if the node can compute a
linear combination of the form (Pk+q),
then the packet Pk is seen
q is a linear combination involving packets
with indices larger than k.
Redundancy factor R:For every packet that arrives from TCP,R(>= 1)linear combinations are sent to the IP layer on average 7

8. obtained by performing
TCP/NC
definition
decode matrix:a matrix in reduced echelon form
obtained by performing
Gauss-Jordan elimination
on the coefficient matrix
number of seen packets=Rank of matrix 8

9. TCP/NC
lemma
Let SA and SB be the set of packets seen by two node A and B.Assume SA\SB is not empty.Suppose A sends a random linear combination of its witnesses of packets in SA,and B receive it successfully.The probability that this transmission causes B to see the oldest packet in SA\SB is 1-1/q.
q is the field size. 9

10. TCP/NC Network coding layer
we embed the network coding layer below TCP and above IP on the source and receive side 10

11. Source side TCP/NC source side has to do two type of things:
(1)generate a random linear combination of the packets in the coding window
(2)remove the acknowledged packet from the coding buffer and hand over the ACK to the TCP sender 11

12. receiver side TCP/NC receiver side responds to two types of events:
arrival of packet from
source and ACKs from
TCP sink 12

13. coding header structure
TCP/NC
coding header structure 13

14. receiver buffer management
TCP/NC
receiver buffer management
store packets that have not been decoded and delivered to TCP receiver,and the packets that have been delivered but not been dropped by encoder.drop the packets whose last bytes is smaller than base. 14

15. Redundancy factor R Redundancy Factor R
too little redundancy,the data rate reaching the receiver will not match the sending rate because of losses,the losses are not effectively masked from TCP layer;
too much redundancy is also bad,sending too much linear combinations can congest the network,and the transmission rate may limited by the rate of code itself. 15

16. Self-adaptive Scheme to Adjust Redundancy
Redundancy Factor R
Self-adaptive Scheme to Adjust Redundancy
In TCP/NC,we set redundancy factor R a constant,but under different channel,the optimal values are different,we want to adapt R based on the characteristics of the underlying channel.
we use a self-adaptive scheme to dynamically adjust R based on the collective feedback information of ACKs. 16

17. Four state of segment in receiver buffer
Redundancy Factor R
Four state of segment in receiver buffer
we define the difference between first_byte_unseen and first_byte_uninvolved
is the "Gap",we add the variable gap to the ACK header.we adjust R based on the value of gap 17

18. Redundancy Factor R 18

19. I use mathematic model to simulate
Redundency Factor R
Mathematic model
I use mathematic model to simulate
TCP/NC and prove that TCP/NC performs better than TCP in wireless lossy network.
you can see more details in[1]]Jitendra Padhye. Modeling TCP Reno Performmance: A Simple Model and ItsEmpirical Validation[J]. IEEE/ACM Transactions on Networking, 2009: 1-9. 19

20. Mathematic Model
TCP/NC VS TCP 20

21. Future Work Future Work build a more accurate model to study
TCP/NC performance
Find a suitable way to adjust redundency
factor dynamically
simulate TCP/NC by NS2,and compare with TCP 21

22. Thank you !