A Bandwidth Allocation Scheme to Improve Fairness inData Center Networks

Yusuke ItoUniversity of Kitakyushu,

Kitakyushu, Japanwash000i@net.is.env.

kitakyu-u.ac.jp

Hiroyuki KogaUniversity of Kitakyushu,

Kitakyushu, Japanh.koga@kitakyu-u.ac.jp

Katsuyoshi IidaTokyo Institute of Technology,

Tokyo, Japaniida@gsic.titech.ac.jp

ABSTRACTThe development of various Internet technologies has en-abled users to connect to the Internet through a wide vari-ety of access networks and communication terminals. Thishas brought a great demand for cloud computing which al-lows users to enjoy various Internet services provided bydata centers (DCs) anytime, anywhere. In cloud comput-ing, though, users more distant from DCs receive a poorerquality of service in terms of transmission rates because ofthe TCP RTT-unfairness problem. Therefore, we propose abandwidth allocation scheme based on collectable informa-tion in DC networks to enable fair communication serviceto each user. We have confirmed the effectiveness of thisapproach through simulation evaluations.

Categories and Subject DescriptorsC.2.1 [Computer-Communication Networks]: NetworkArchitecture and Design

KeywordsBandwidth Allocation, TCP, Data Center

1. INTRODUCTIONUsers can now connect to the Internet through a wide vari-ety of access networks and communication terminals such assmart phones or PCs. This has created a great demand forcloud computing which allows users to enjoy various Internetservices provided by data centers (DCs) [1] anytime, any-where. Major services available through cloud computinginclude file sharing or transaction services which commonlyuse TCP as a reliable data transmission protocol.

In cloud computing, a user’s quality of service in terms oftransmission rate depends on the distances from DCs. Thisproblem is caused by how TCP controls congestion. TCPcannot exactly identify the conditions of other flows, so itestimates an available bandwidth based on packet losses.Since congestion control is applied according to round-trip

http://dx.doi.org/10.1145/2680821.2680834.

time (RTT), the transmission rate for a user with a shortRTT is effectively increased compared with that of a userhaving a long RTT. Fairness in terms of throughput amongflows with different RTTs needs to be improved.

To improve fairness among flows, CHOKeW [2] has beenproposed as one of the active queue management (AQM)technologies applied on routers. This approach adjusts thepacket dropping rate per flow based on service classes andnetwork conditions. It realizes fair communication amongflows by preferentially discarding packets which belong toa high rate flow. However, the processing cost on routersincreases enormously as the number of flows increases.

In this study, we propose a bandwidth allocation schemebased on collectable information in DC networks to providefair communication service to each user. This scheme col-lects flow information including the bandwidth of each link,the number of competing flows, and the RTT of each flowfrom routers and servers in DC networks and then fairlyallocates transmission rates among flows based on the col-lected information. We show the effectiveness of this ap-proach through simulation evaluations.

2. PROPOSED SCHEMEThe proposed scheme fairly allocates transmission ratesamong flows based on collectable information in DC net-works as shown in Fig. 1. Flow information such as the band-width of each link, the number of competing flows, and theRTT of each flow is collected by a Unified Congestion Con-trol Architecture (UCCA) [3], which uniformly manages thecongestion information in the networks. Routers in DC net-works periodically inform servers of the number of existingflows, which can be measured by extending the OpenFlowarchitecture. The servers identify bottleneck links based onthe information about the number of flows received from therouters and the bandwidth of each link, and calculate thetransmission rate which should be allocated to each flow bydividing the bandwidth of the bottleneck link by the numberof competing flows.

For down direction communication from a server to a client,the server can simply allocate the calculated transmissionrates to each flow. On the other hand, for up direction com-munication from a client to a server, the server needs toinform the client of the allocated transmission rate. Ourscheme uses TCP’s advertised window size to notify theclient of the transmission rate. The server calculates the

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Notification of

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Measurement of RTT

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Figure 1: Proposed Scheme

bandwidth delay product of each flow as the advertised win-dow size based on the bandwidth which should be allocatedand the RTT of each flow. That is, the advertised windowsize of a flow having a long RTT is larger than that of ashort RTT flow. The RTT of each flow is measured by theserver’s TCP. If the server does not send any data to theclient, it periodically sends probe packets to measure RTT.This bandwidth allocation should enable fair communica-tion among flows which have different RTTs. However, thenumber of competing flows and the RTT of each flow varydynamically in an actual environment. Therefore, the accu-racy of the bandwidth allocation is likely to depend on theinterval time needed to collect the flow information.

3. PERFORMANCE EVALUATIONTo investigate the efficiency of our scheme, we evaluated itthrough simulation using Network Simulator ns-3 after itsimplementation. In the simulation, we used a tree topologyto focus on the basic characteristics of the scheme. A serverconnected two edge routers through a core router. Each edgerouter connected five clients separately. Thus, there weretwo client groups and these had access links with differentdelay times: 2 and 7 ms. Other links had a delay time of 1ms. The bandwidth of all links was 100 Mb/s. One clientof each group started to send 100 MB of data to the serverevery 10 seconds, so two flows were joined every 10 seconds.The TCP algorithm was NewReno. The interval time tonotify the flow information varied from 0.05 to 10 s. Weevaluated Jain’s fairness index and total throughput for theproposed scheme and conventional TCP.

Figures 2(a) and 2(b) show the fairness index and totalthroughput of the proposed and conventional schemes whenthe notification interval time varied from 0.05 to 10 s. Theproposed scheme provided higher fairness and throughputthan the conventional scheme regardless of the notificationinterval time. This was because the proposed scheme al-locates an adequate advertised window size to each flowaccording to RTT. In addition, the proposed scheme sup-presses packet drops on routers through bandwidth alloca-tion, thus improving throughput.

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Figure 2: Effect of notification interval time

4. CONCLUSIONOur proposed bandwidth allocation scheme uses collectableinformation in DC networks to provide fair communicationservice to each user. Simulation evaluations show that thisscheme enables higher fairness and throughput than can beachieved with conventional TCP. In our future work, wewill consider the most effective way to fairly allocate linkbandwidth in DC networks to each user even when accessnetworks are bottlenecks.

5. ACKNOWLEDGMENTSThis work was supported in part by JSPS KAKENHI GrantNumber 25280028.

6. REFERENCES[1] J. Zhang, F. Ren, and C. Lin, “Survey on transport

control in data center networks,” IEEE NetworkMagazine, vol. 27, no. 4, pp. 22–26, July/August 2013.

[2] S. Wen, Y. Fang, and H. Sun, “Differentiatedbandwidth allocation with TCP protection in corerouters,” IEEE Transactions on Parallel and DistributedSystems, vol. 20, no. 1, pp. 34–47, January 2009.

[3] K. Kusuhata, I. Kaneko, K. Iida, H. Koga, andM. Shimamura, “A unified congestion controlarchitecture design to improve heterogeneous wirelessnetwork efficiency and accommodate traffic by variousrich applications,” Proc. IFIP HET-NETs2013, p. 5,November 2013.

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