1. Congestion Control in Software Define Data Center Network
Speaker : Cheng-Yu Chang
Advisor : Dr. Kai-Wei Ke
Date : Dec

2. Outline Software Define Network (SDN) TCP/IP Congestion Control
Data Center Network (DCN)
Methodology
Implementation
Future Directions
References

3. Software Define Network (SDN)
Traditional Architecture
SDN Architecture

4. TCP/IP Congestion Control

5. TCP/IP Congestion Control
Explicit Congestion Notification (ECN) in TCP/IP
Notify congestion to end nodes
Sender reduce sending rate
Operation of ECN with IP
TCP

6. Operation of ECN with IP
00 – Non ECN-Capable Transport, Non-ECT
10 – ECN Capable Transport, ECT(0)
01 – ECN Capable Transport, ECT(1)
11 – Congestion Encountered, CE.

7. Operation of ECN with TCP
ECE: TCP receiver echoes back this congestion indication
CWR: reduces its congestion window as for a packet drop

8. Example of ECN ECN=11, Congestion Encountered ECE, ECN-Echo
CWR, Congestion Windows Reduced

9. Data Center Network (DCN)
Topology
Elephant/Mice Flow
TCP Incast

10. Data Center Network - Topology
K-ary fat tree topology
Advantages: Low Cost, Full Bisection BW
K=4

11. Elephant vs Mice Flow Link Utilization Elephants (long-lived):
Large amount of data
Less concerned about latency
Can fill up network buffers
Mice (short-lived):
To be bursty
Latency-sensitve
Link Utilization

12. TCP Incast
Many to One communication pattern
Throughput collapse

13. Congestion Control Methodology
Detection Method
Control Method

14. Methodology Detection Method Control Method Congestion Packet in
Action
Low latency
Low packet loss
High throughput

15. Detection Method Purpose: Detect the network congestion
Method (per table/per flow/per port):
Queue size
Packet drop rate
Bandwidth
Link captaincy (Link load)

16. Control Method Purpose: Action to reduce congestion
Method 1: Modify the host
TCP Stack Modify - RWIN, ACK interval
Admission Control - Bandwidth allocation
Method 2: host no modify
Reroute - chose less congestion path, with DLBMP
Switch ECN setting modify

17. Implementation

18. Implementation Under TCP Congestion/Incast in Data Center Network
Architecture:
Congestion Detection
Target flow identification
Congestion Control modification

19. Congestion Detection TCP Incast in the DCN case throughput collapse
Detection Method:
The queue size more than threshold
Available bandwidth less than threshold
Port/Flow load more than link capacity threshold

20. Target flow identification
Use the DSCP for identification
Detect the Elephant/Mice use
rate and time
large segments
Elephant flow: more sensitive and commonly affected (Target)

21. Congestion Control modification - part 1
Method: use different queues/paths/congestion control
Example of different queues:
Elephant flow: queue 1
Mice flow: queue 2
Congestion  Different queues
No congestion  Same queue

22. Result of different queues

23. Result of different queues

24. Result of different queues

25. Congestion Control modification - part 2
Example of different congestion control:
Elephant flow: discard the CE code point (without CC)
Mice flow: TCP/IP congestion control
Elephant and Mice use same queue

26. Result - Mean Throughput
Proposed = Different ECN
Queue = Different Queue
50 mice flows
100 mice flows

27. Result - Goodput Goodput = application-level throughput 50 mice flows

28. * FCT = flow completion time
Result - Mice Flows
Traffic:
9 Elephant flows
50 Mice flows
Mice Flows
Different ECN
Queue
ECN
ECN off
Min FCT
0.003 s
0.014 s
0.002 s
0.013 s
Mean FCT
0.545 s
0.627 s
1.011 s
0.178 s
Max FCT
1.015 s
3.230 s
3.016 s
0.623 s
Avg. Throughput
7652 Mbps
1243 Mbps
8343 Mbps
3609 Mbps
* FCT = flow completion time

29. Result (Cont.) Elephant flow
Throughput: Different ECN > Queue > ECN > ECN off
Mice flow
Mean of FCT: ECN off > Different ECN > Queue > ECN
Average throughput: ECN > Different ECN > ECN off > Queue

30. Future Directions With QoS mechanism
Congestion Control and QoS use rerouting first.
If path load is full than:
Elephant flow with QoS without Congestion control
Mice flow with congestion control

31. References
Lee, Chunghan, et al. "Flow-Aware Congestion Control to Improve Throughput under TCP Incast in Datacenter Networks,“ in Computer Software and Applications Conference (COMPSAC), 2015, pp
Gholami, M., & Akbari, B. “Congestion Control in Software Defined Data Center Networks Through Flow Rerouting,” in rd Iranian Conference on Electrical Engineering (ICEE), 2015, pp
S.Fang, Y.Yu, C. H.Foh and K. M. M.Aung. “A loss-free multipathing solution for data center network using software-defined networking approach,” IEEE Trans. Magn., vol. 49, no. 6, pp , Jun., 2013.
M. F. Bari, S. R. Chowdhury, R. Ahmed, and R. Boutaba, “PolicyCop:An autonomic QoS policy enforcement framework for software defined networks,” in Proc. IEEE SDN Future Netw. Serv. (SDN4FNS), Nov. 2013, pp. 1–7

32. References
Open vSwitch and the Intelligent Edge,