外文翻译基于哈希模式的负载均衡性能研究.docx

1、外文翻译基于哈希模式的负载均衡性能研究中文5790字 毕业设计外文翻译专 业 网络工程 班 级 学生姓名 xx 学 号 xx 指导教师 Performance of Hashing-Based Schemes for Internet Load BalancingZhiruo Cao ,Zheng Wang ,Ellen ZeguraCollege of Computing Georgia Institute of Technology Atlanta, GA 30332-0280Bell Labs Lucent Technologies Holmdel , NJ 07733AbstractL

2、oad balancing is a key technique for improving Internet performance. Effective use of load balancing requires good traffic distribution schemes. We study the performance of several hashing schemes for distributing traffic over multiple links while preserving the order of packets within a ow. Althoug

3、h hashing-based load balancing schemes have been proposed in the past, this is the first comprehensive study of their performance using real traffic traces.We evaluate five direct hashing methods and one table-based hashing method. We find that hashing using a 16-bit CRC over the Five tuple gives ex

4、cellent load balancing performance. Further, load-adaptive table-based hashing using the exclusive OR of the source and destination IP addresses achieves comparable performance to the 16-bit CRC. Table-based hashing can also distribute traffic load according to unequal weights. We also report on fou

5、r other schemes with poor to moderate performance.KeywordsLoad sharing, hashing.I. INTRODUCTIONLoad balancing (also known as load sharing) is a key technique for improving the performance and scalability of the Internet. For example, many large enterprise networks are connected to multiple Internet

6、Service Providers (ISPs) to achieve redundant connectivity and to distribute traffic loading. Inside the Internet, the backbones are often engineered to have multiple parallel trunks between major Points of Presence to ensure high availability. Typically, these parallel trunks are congured as equal-

7、cost paths and allow load balancing over them.The parallel trunks may become even more ubiquitous when the promising Dense Wavelength Division Multiplexing (DWDM) technology is deployed in the future Internet back-bone. DWDM expands the capacity of communication trunks by allowing a greater number o

8、f channels to be carried on a single optical fiber. With potentially tens or even hundreds of DWDM channels between major points, load balancing is essential in best utilizing the multiple parallel channels.Parallel architectures have been used for packet processing for coping with exponential growt

9、h in Internet traffic, Instead of one processing engine, packets are dispatched to multiple parallel engines inside a router to increase the overall processing throughput. The same technique is also used in scaling web servers. Popular web servers often operate a farm of machines and the routers con

10、nected to them split the HTTP requests to different machines.For all of these examples, effective use of load balancing requires good schemes for splitting traffic over multiple links. In addition, since the majority of the traffic on the Internet is TCP-based 1, traffic splitting schemes need to av

11、oid packet misordering within a TCP ow, which can falsely trigger congestion control mechanisms and cause unnecessary throughput degradation 2, 3.In this paper, we propose and evaluate a class of hashing based traffic splitting algorithms which preserve per-ow packet ordering. We consider five hash

12、functions that are “direct,”meaning that the hash function produces a value in the range of 0.N-1, where N is the number of outgoing links. We also consider a table-based generalization that involves hashing to M bins, then assigning the M bins to the N outgoing links. Table based hashing requires m

13、ore state than direct hashing, but has the flexibility to support unequal load distribution and dynamic adaptation.Our results are obtained by simulating the performance of a trafc splitter, using packet traces taken from two trunks of a major Internet backbone provider. We nd that direct hashing wi

14、th the destination IP address causes signicant imbalance across two links. Using the Internet checksum or the exclusive OR of both the source IP address and destination IP address improves the performance considerably, though moderate imbalance persists. The more computationally complex 16-bit CRC o

15、f the ve-tuple (source address, destination address, source port,destination port and protocol id) gives excellent load balancing performance, keeping the load and queue lengths very similar on two links. Equally good load balancing can be achieved using table-based hashing with adaptation, which re

16、quires less computation than the CRC but necessitates monitoring the link loads and storing (and adjusting) the mapping from table bins to links.Table-based hashing has the additional advantage that it can distribute the load according to unequal weights. Further, an index-based version of this sche

17、me can alter the weight distribution with minimal disruption to existing ows . Our results conrm that the index-based hashing can accurately achieve a weighted distribution when adaptation is also used.The rest of this paper is organized as follows. In Section II we discuss related work in trafc spl

18、itting and load balancing. Section III describes the behavior of an ideal trafc splitter, explains the requirements for a practical system, and denes the performance metrics that will be used to assess various hashing-based schemes. The set of schemes that we consider are described in Section IV. Th

19、e results of our study are described in Section V, and include analysis of the randomness inherent in the trace data (Section V-A). We conclude and mention areas for future work in Section VI.II. RELATED WORKLoad balancing has been used in telecommunication networks in the form of inverse multiplexi

20、ng 4. Inverse multiplexing allows service providers to offer wideband channels by combining multiple narrowband 56 kbps and 64 kbps trunks 5. The load balancing in inverse multiplexing is typically based on round robin distribution of packets or bytes 6, 7.Our work differs from inverse multiplexing

21、in two important dimensions. First, inverse multiplexing is designed for use over point-to-point links; its techniques are not typically applicable for network layer load balancing. Internet load balancing, however, makes use of the natural redundancy in the network topology. The paths for load bala

22、ncing, for example, equal-cost multi-paths, are discovered dynamically by routing protocols, such as OSPF 8, rather than through configuration. Second, in order to maintain synchronization and per-flow FIFO packet ordering in inverse multiplexing, it is necessary to add extra packet headers with seq

23、uence numbers or to keep state at both ends of the channel. But, implementing these additional mechanisms for network load balancing requires a new network protocol. In comparison, the hashing-based schemes can maintain per-flow packet ordering and can be implemented without requiring any additional

24、 protocol support.Hashing has been widely used in indexing and searching 9.In the networking context, hashing-based algorithms for address lookup 10, ow identication 11 and packet demultiplexing 12 have been proposed in the past. The use of hashing for network load balancing is not new. Some commerc

25、ial router products have implemented simple hashing over the IP destination address to distribute trafc 13. In the OSPF Optimized Multipath protocol (OSPF-OMP) 14, a number of possible approaches for load balancing over multiple paths are mentioned , including per-packet round robin, dividing destin

26、ation prexes among available next hops in the forwarding table, and dividing trafc according to a hash function applied to the source and destination pair. However, the proposed schemes are not evaluated with simulation or real network measurement. In the study of load balancing with OSPF-OMP, perfe

27、ct hashing is assumed15. A trafc splitting scheme using random numbers is proposed in 16. It applies the name-based mappings approach to load balancing 17. In this scheme, each next-hop is assigned with a weight based on a simple pseudo-random number function seeded with the ow identier and the next

28、-hop identier. When a packet arrives, the weights are generated, and the next-hop receiving the highest weight is used for forwarding. The scheme is approximately times as expensive as a hashing-based scheme, where is the number of outgoing links. Again, no performance study on the proposed scheme i

29、s presented.It is clear that although hashing-based schemes for trafc splitting have been proposed in the past, and some simple schemes have even been implemented in commercial products, the performance of such schemes has not been adequately evaluated .This paper presents the rst comprehensive perf

30、ormance study on a wide range of hashing-based schemes, using real packet traces from backbone networks.III. FRAMEWORKIn this section, we describe the behavior of an ideal trafc splitter, explain the requirements for a practical system, and dene the performance metrics for assessing various schemes.

31、A. Reference ModelA load balancing system typically comprises a trafc splitter and multiple outgoing links as shown in Figure 1. In such a system, the trafc splitter receives an incoming packet from a higher-speed link and forwards it to one of the lower-speed outgoing links. A good load balancing s

32、ystem should be able to split the trafc to the multiple outgoing links evenly or by some pre-dened proportion. In 7, it has been observed that there is a close relationship between fair queuing and load balancing. We now extend their observation to a mathematical model to obtain the constraints for ideal trafc splitting.Let us rst look at an ideal uid model where the trafc isinnitely divisible. Suppose that there are out going links in the load balancing system, and the capacity of link I is ui . Let Si(T,t) be