This paper proposes a method for optimizing bandwidth usage in Software Defined Networks (SDNs) based on OpenFlow. Flows of small packets presenting a high overhead, as the ones generated by emerging services, can be identified by the SDN controller, in order to remove header fields that are common to any packet in the flow, only during their way through the SDN. At the same time, several packets can be multiplexed together in the same frame, thus reducing the number of sent frames. Four kinds of small-packet traffic flows are considered (VoIP, UDP and TCP-based online games, and ACKs from TCP flows). Both IPv4 and IPv6 are tested, and significant bandwidth savings (up to 68 % for IPv4 and 78 % for IPv6) can be obtained for the considered kinds of traffic.

1. Optimization of Low-efficiency
Traffic in OpenFlow
Software Defined Networks
SPECTS 2014, International Symposium on Performance Evaluation of Computer and
Telecommunication Systems
July 6-10, 2014, Monterey, CA, USA
Jose Saldana, David de Hoz,
Julián Fernández-Navajas, José Ruiz-Mas
Fernando Pascual, Diego R. Lopez,
David Florez, Juan A. Castell,
Manuel Nuñez

2. SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
Index
1. Introduction
2. Proposed method
3. Results
4. Conclusions

3. SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
Index
1. Introduction
2. Proposed method
3. Results
4. Conclusions

4. Introduction
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 Software Defined Networks
 Separation of control and data planes
 Programmability of control plane
 Central control of the network as a whole
 Used in cloud computing: flexibility, efficiency
 Openflow: the most extended SDN standard

5. Introduction
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 Small-packets in the Internet
 Real-time services: High interactivity
VoIP
Online games (some of them use TCP)
 TCP ACKs. Downloads, videos, etc.

6. Introduction
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 High rates of small packets (high header-to-
payload ratio). Low efficiency:
 VoIP
 FPS game
 MMORPG game
 ACK

7. Introduction
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 Header compression can be used to reduce the
overhead:
 Many header fields are the same for every
packet in a flow: e.g., IP addresses, ports,
etc.
 These fields can be avoided, but:
 a context must be stored in both sides in order to
rebuild the packets
 Tunneling is necessary, since a packet with a
compressed header cannot be sent normally

8. Introduction
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 One solution: combining header compression
with multiplexing:
 The tunnel header is shared between a number of
packets
 A period is defined in order to gather a number of
packets
Period
. . .
. . .
Native game
traffic
Optimized
traffic
Period Period
. . .
. . .
. . .
. . .
. . .
. . .

9. Introduction
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 TCM (Tunneling Compressed Multiplexed
Traffic Flows) is a proposal for improving the
efficiency of these flows by:
 Header compression
 Multiplexing
 Tunneling
 30% to 55% saving
 Status: IETF draft
IP IP IP
No compr. / ROHC / IPHC / ECRTP
PPPMux / Other
GRE / L2TP / Other
IP
Compression layer
Multiplexing layer
Tunneling layer
Real-time traffic
Network Protocol
UDP
RTP
payload
UDPTCP
payloadpayload

10. Introduction
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 Tradeoff. Advantages:
 Bandwidth savings
 pps reduction (energy savings)
 At the cost of
Added processing requirements
Additional multiplexing delay
Five IPv4/UDP/RTP VoIP packets with two samples of 10 bytes
η=100/300=33%
savingOne IPv4 TCMTF Packet multiplexing five two sample packets
η=100/161=62%

11. Introduction
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 Objective of the present work: Proposal of an
equivalent optimization method, especially
focused on SDNs. Advantages:
 the tunneling layer is not necessary, since
the SDN provides it in a natural way
 the avoidance of the use of standard header
compression techniques
 multiplexing reduces the number of frames,
so a number of Ethernet fields (header, inter-
frame gap) are only sent once

12. SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
Index
1. Introduction
2. Proposed method
3. Results
4. Conclusions

13. Proposed method
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 In Openflow 1.0:
 all the switches are connected to a central
controller
 each packet is associated to a flow by means of a
12-field tuple, used for assigning the output port
SA,DA,Prot,ToS
In port
SA, DA, type
Ethernet IP TCP
Sport, DPortID, prio
VLAN

14. Proposed method
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 When a flow traverses a path, the IP and TCP tuple
fields of all the packets are the same for all the tables
of the switches of that path, and also in the
controller.
 Thus, the IP and TCP protocol fields already
included in the tuple are not necessary for switching
decisions but only for matching the packets with a
flow.

15. Proposed method
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 First step: we can remove the fields included in the
tuple and substitute them by a flow identifier (FID),
so the packet can travel in an optimized manner
within the SDN (e.g. TCP/IP: 13 bytes saved, and 3
bytes added for the FID. Total 10 bytes):
PayloadNative
headers
Payload
Compressed
headers
FID
SDN controller
Ingress
EgressIP TCP TCPIP IP TCPTCPIP
Optimization within SDN

16. Proposed method
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 Openflow 1.1 allows switches and controllers to agree on
different flow matching syntaxes
 Second step: The inclusion in the tuple of other
NOCHANGE fields of Transport and Network layers.
 These fields are not required for identifying the flow
 But including them in the tuple would make it possible to
remove them from all the packets, thus allowing even
higher header compression ratios
 Counterpart: slight increase of the storage requirements of
the switches and the controller (about 40 bytes per flow)
 We can also include in the tuple application-layer fields
(e.g. RTP), obtaining more savings

17. Proposed method
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 Third step: the SDN controller can match groups of flows
sharing a common path segment within the SDN.
 Packets belonging to different flows can be multiplexed
together and sent as a single Eth frame.
 We need a Multiplexing protocol (e.g. PPPMux).
E
E
IPv4 header: 20 bytes
TCP header: 20 bytes Inter-frame gap: 12 bytes
PPP Common header: 1 byte
PPPMux header: 2 bytes
T
IP
Payload
IPTwo Eth/IPv4/TCP
frames with
P=20bytes:
T P E IP T P
T P IP T P GIP F
G
F GF
One Eth PPP frame including the two packets:
E Eth header: 26 bytes*
G
FID: 3 bytes
F Eth FCS: 4 bytes
P
PH
M
FID
M
FID
M
PH
FID
* The Eth header includes 4 bytes of VLAN 802.1Q

18. SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
Index
1. Introduction
2. Proposed method
3. Results
4. Conclusions

19. Results
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 Four traffic patterns have been tested:
 a) VoIP using IP/UDP/RTP (40 bytes header for
IPv4 and 60 for IPv6) and G.729 codec with 2
samples per packet (20 bytes payload) every 20 ms.
 b) Client-to-server flows of a UDP-based online
game (28 or 48 bytes header), with 24.65 packets per
second, and an average payload of 41.09 bytes.
 c) Client-to-server flows of a TCP-based online game
(40 or 60 bytes header) of 9.51 packets per second
with an average payload of 8.74 bytes.
 d) IP/TCP ACKs of 40 or 60 bytes

20. Results
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 Fields considered as NOCHANGE:
IPv4 IPv6 TCP/UDP RTP
Version Version Source Port Version
IHL Traffic Class Dest. Port P
DSCP Flow Label Data Offset X
ECN Next Header Reserved CC
Time To Live Hop Limit Urgent Pointer M
Protocol Source Address PT
Source Address Dest. Address SSRC id
Dest. Address

21. Results
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 Maximum savings for each pattern
(asymptote if the number of multiplexed
packets is high):
VoIP UDP game TCP game TCP ACKs
IPv4 62.75% 52.21% 65.02% 72.62%
IPv6 72.13% 62.55% 74.95% 81.37%

22. Results
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 Savings as a function of the number of multiplexed packets
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Bandwidthsavingpercentage
number of packets
Bandwidth savings IPv4
VoIP
UDP game
TCP game
ACKs

23. Results
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 Savings as a function of the number of multiplexed packets
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Bandwidthsavingpercentage
number of packets
Bandwidth savings IPv6
VoIP
UDP game
TCP game
ACKs

24. SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
Index
1. Introduction
2. Proposed method
3. Results
4. Conclusions

25. Conclusions
SPECTS 2014 Optimization of Low-efficiency Traffic in OpenFlow SDNs
 The SDN controller can find a number of flows
sharing a common path
 The flows that are constant can be avoided, using an
identifier
 With this method we can save bandwidth and reduce
the number of pps: 68% for IPv4 and 78% for IPv6
 Counterpart: additional latency. It can be kept under
tolerable limits for services sending high packet rates

26. Thank you very much!
Jose Saldana, David de Hoz,
Julián Fernández-Navajas, José Ruiz-Mas
Fernando Pascual, Diego R. Lopez,
David Florez, Juan A. Castell,
Manuel Nuñez