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MPLS Traffic Engineering Load Balance Algorithm Using Deviation Path

Fenglin Li

Department of Computer Science and Technology

Wuhan University of Science and Technology

Wuhan, China

e-mail: 15994207833@139.com

Jianxun Chen

School of Computer

Harbin Engineering University

Harbin, China

e-mail: cjxwh@wust.edu.cn

AbstractSince conventional routing algorithm is easily

leading to the problem that some segments of a network are

quite congested while other segments along alternative routes

are under utilized, this thesis proposed a new load balance

algorithm called load balance algorithm using deviation path.

Multiple Protocol Label Switching (MPLS) uses its explicit

routing technology to implement traffic engineering. The new

algorithm is based on this advantage of MPLS and is used to

achieve load balance of traffic engineering in MPLS network.

The simulation results of Network Simulator (NS2) showed

that this algorithm can effectively balance the workload

between different links and can improve the network

performances with lower delay, smaller loss rate and higher

throughput.

Keywords- MPLS; Traffic Engineering; Network Simulation;Deviation Path

I. INTRODUCTIONAlong with the multi-fold growth of the netizen

population, unceasing expansion of network scale, theexponential growth of network application and the explosiverising of network traffic, the existing network can hardlysatisfy the need of network application, accordingly lead tothe decrease of network performance and the increasingfrequency of network congestion. Congestion typicallymanifests under two scenarios: (1) When network resourcesare insufficient or inadequate to accommodate offered load.(2) When traffic streams are inefficiently mapped ontoavailable resources; causing subsets of network resources to

become over-utilized while others remain underutilized [1].The first type of congestion problem can be addressed by

expanding the capacity of the network. However, networkexpansion is extremely expensive and its not the majorcause. In fact, the primary cause of network congestion is theunbalanced distribution of network traffic. Therefore how to

balance the network traffic and improve the internet qualityof service is becoming the most crucial issue.

II. MPLSTRAFFIC ENGINEERINGA. Traditional routing algorithms

Traditional IP routing algorithm like OSPF and ISIS

compute the shortest way to the destination only based onthe destination address and it means that traffic fromdifferent sources passing through a router with the same

destination will be aggregated and sent through the samepath. Therefore these algorithms have two problems.

The shortest paths from different sources overlap atsome links, causing congestion on those links. And alink may be congested despite the existence ofunder-utilized link in the network.

The traffic from a source to a destination exceeds thecapacity of the shortest path, while a longer path

between these two routers is under-utilized.The main issue with conventional routing protocols is

that they dont take capacity constraints and trafficcharacteristics into account when routing decisions are made.So some segments of a network can be very congested whileother segments along alternative routes are under utilized. To

optimize the utilization of resources in a network, animportant network optimize technique Traffic Engineeringcame into being as required. Traffic Engineering is the

process of controlling how traffic flows through onesnetwork so as to optimize resource utilization and network

performance [2]. Minimizing congestion is a primary trafficand resource oriented performance objective.

In practice, there are many strategies that can be used fortraffic engineering like IP-over-ATM [3], constraint basedrouting [4] and others. MPLS (Multiple Protocol LabelSwitching) Traffic Engineering overcomes the limitations ofthese approaches by perfectly combining the flexibility oflayer 3 with the traffic management capability of layer 2 andis regarded as the key technique of next generation IP

backbone network. Its emergence provides strong technicalsupport for traffic engineering.

B. Load Balancing Algorithms in MPLS TrafficEngineering

Load balancing is an operation that distributes trafficflow rationally in the current network topology over multiple

paths. And the paths are not required to be the shortest paths.There are three types of load balancing algorithm in MPLS:

Topology-Based Static Load Balancing AlgorithmTSLB is improved on the basis of traditional shortest

path routing. In this algorithm, the shortest path in the set isexamined to see if it meets the bandwidth requirement. Ifyes, that path is selected, otherwise that path is deleted fromthe feasible set [5]. Comparing with the shortest path routing,

TSLB has effectively eased the congestion on the bottleneck.However since the algorithm is static, it wont be preempted.

Resource-Based Static Load Balancing Algorithm

2012 International Conference on Computer Science and Service System

978-0-7695-4719-0/12 $26.00 2012 IEEE

DOI 10.1109/CSSS.2012.155

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RSLB pre-computes the feasible set of paths the sameway as TSLB, but it examines the paths to find the one withthe lowest available bandwidth that can afford the need forthe new arrival traffic. But when there are only few low-rateflows are sent during a long time, links with large capacity inthe Internet will be idle for quite some time.

Dynamic Load-Balancing Algorithm (DLB)As a dynamic algorithm, DLB overcomes the restriction

of RSLB and TSLB. It not only pay attention to the networktopology, but also take traffic bandwidth requirement,network resource engrossing and traffic characteristics intoaccount. DLB reroutes the existing traffic flows to find a

path for the new flow if the resource-based algorithm fails tofind a path for the new flow.

III. LOAD BALANCING ALGORITHM USING DEVIATIONPATH (LBDP)

Although we can use explicit routing technology tochoose a path that steer clear of the hotspot when a LSP isestablished. But as we all know, network traffic can be veryabruptly, thus the chance of congestion is still quite high.

Therefore adaptive adjustment capability of a network is stillvery essential.

A. General Terminology in LBDPG=(V,E) is a MPLS network topology graph, where

V={v1, v2,, vn} is the set of vertices in G and E is the set ofedges in G. Use e(i,j) to refer to the link between node vi andnode vj.

Isoline: a line on a network topology map connectingnodes with equal distance value to the destination of a certainflow.

As seen from the spanning-tree in Fig. 1, for the certainflow from source node v0 to the destination node v13, nodesv8, v9, v11 and v12 have the equal distance value to v13,that means they are on the same isoline.

Deviation Path [7]: For a given network topology G thereis a path from node vi to node vj called p1, p1= vi,v1,v2,,vk,, vj . And another path from node vi to node vj called p2is existed too, p2= vi,v1

,v2,, vk

,, vj . If vi,v1,v2,, vk=vi,v1

,v2,, vk

and vk+1 vk+1, then node vk+1

is called thedeviation node of node vk+1 and p2 is the deviation path of p1against node vk+1.

For example, as shown in Fig. 1, there is a path fromnode v0 to node v13 called p1, p1=v0,v6,v8,v13. Andanother path from v0 to v13 is p2=v0,v6,v9,v13. So v9 is thedeviation node of v8, and p2 is the deviation path of p1against v8.

Figure 1. Network topology and its spanning-tree.

B. LBDP ModelThe general idea of deviation path load balancing

algorithm is as follows: first of all, when a new flow isgenerated, creating its spanning-tree and get the isolines;secondly, when a congestion is about to happen, select aswitch flow from the link; thirdly, search for available pathsand choose the optimal one to relocate the selected switch

flow; finally, switch the chosen flow to balance the load.Fig. 2 is the process of LBDP.

IV. THE IMPLEMENTATION OF LBDPA. Create Spanning-tree and get isolines

When a new flow is generated, use breadth-first search tocreate its spanning-tree and get the isolines. The informationwe gathered from this section can be quite useful for theimplementation of the algorithm, especially for the pathsearching and selecting part.

B. Monitoring and Flow selectionEach LSR in the MPLS network periodically checks its

outcome links. They recompute the bandwidth utilizationrate of the links after each interval and if the value of acertain link e(i,j) exceed the predetermined threshold we

set, it indicates that a congestion is about to happen. Andwhat we need to do now is to select a proper flow and switchit onto another path that doesnt use link e(i,j).

We can get the minimum bandwidth we must relocate bythe following formula ,then select the flow with a minimum

bandwidth that no less than disB in (1).

),()(1

jiBkflowdisBnk

=

(1)

C. Path SearchingNow presume that link e(i,j) is the congested link.

According to the monitoring and flow selection part, wehave selected flow[f] as the switch flow and we can easilyget the current path it goes.

Figure 2. LBDP flow chart

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Assume that nowpath= Vs,,Vi,Vj,, Vd, if we can finda deviation path of nowpath called bpath that uses Vj as thedeviation node, namely bpath= Vs,,Vi,Vj

,, Vd, then wecan use it as the path for flow switching since its a path thatsteer clear of congested link (Vi,Vj). The same rule applies tonodes Vs,,Vi, so our searching nodes would besnode(0)=Vj, snode(1)= Vi,, snode(k)= Vs. As for the rest

nodes Vj+1,, Vd, their deviation paths are pointless for usdue to their use of link e(i,j). Once the searching nodes aresettled, what we must do now is to search their qualifieddeviation paths and select the best one.

In order to search the deviation paths of searching nodesnode(p), a simple and efficient way is to search the isolinewhere snode(p+1) located and its two neighbor isolines ifthey are existed. And the searching of other isolines are notnecessary as the nodes on them are not in the neighbor set ofsnode(p+1). The specific steps are as follows:

Search the nodes on isoline Tm-1: Assume thatsnode(p+1) is on isoline Tm, so Tm-1 is the isoline

before Tm and its also the isoline where snode(p) islocated. If theres a node snode(p)

on isoline Tm-1

and e(snode(p), snode(p+1))E, then its the nodewe are looking for. A qualified deviation againstsnode(p) is found while no loop is existed andavailable bandwidth is wide enough.

Search the nodes on isoline Tm: the method is thesame as the previous step.

If Tm+1 is existed, then search the nodes on isolineTm+1. Until now the research part is over.

The specific procedures are as follows:INPUT: network topology G, source node Vs and destinationnode Vd, Tsd=(TWX,ZDL), SS/*SS={snode(p)|p=0,1,k}. Tsd is consists of isolines: TWXand shortest path of each node: ZDL. */OUTPUT: LSPProcedure SSlsp(G, nowpath, Vi, Vj, Vs, Vd)

BEGINFind the isolines of each searching nodes, like the isolineof snode(p) is st(q);For (m=1;m=

B(flow[k]) THEN

BEGIN //minlsp is the shortest qualified path so far

IF var minlsp doesnt exist, THEN minlsp templsp;ELSE //minlsp exists

BEGIN

IF templsp.length< minlsp.length THEN

minlsp templsp;ELSE IF templsp.length=minlsp.length &&templsp.abw

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no packet is dropped ever since LBDP avoided the congestedpath. As to LBAR, the dropped packets is reduced at first,but quickly increased due to the second congestion. In Fig. 8,we can see that LBDP has increased the throughput of thenetwork pretty well but it turns out not to be as good asLBDP. And Fig. 9 is about the network delay. As the figureillustrated, LBDP has smaller delay than the average

standard of SPF, meanwhile LBAR is quite time consuming.After all, based on the analysis and evaluation above we

can tell that LBDP can significantly increase bandwidthutilization ratio and throughput, and reduces both delay and

packet losses. We can conclude from the comparison of threealgorithms that the proposed algorithm can obviouslyimprove the network performance.

Figure 3. SPF

Figure 4. LBAR 1st balance

Figure 5. LBAR 2nd congestion

Figure 6. LBDP

Figure 7. packet loss

Figure 8. throughput

Figure 9. delay

VI. CONCLUSIONIn this paper, we first discuss the general issues of

traditional routing algorithms. We then present the MPLS TEtechnique and three load balancing algorithms of MPLS TE.After that, based on our study, a new load balancingalgorithm called LBDP is proposed. Finally, the simulationresults of NS2 showed that LBDP can effectively balance theworkload between different links and can improve thenetwork performances. Also, the feasibility and the validityof this algorithm are proved.

ACKNOWLEDGMENT

We are grateful for helpful comments from Zhang Kai,

and the anonymous reviewers. We would also like to thankYuan Shuai and Xiang Shuangshuang for helpful discussions.

REFERENCES

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[3] C. Semeria, Traffic Engineering For The New Public Network,Juniper Networks Whitepaper, September 2000.

[4] B.Fortz, J.Rexford, and M.Thorup, Traffic Engineering WithTraditional IP Routing Protocols, IEEE Communication Magazine,October 2002.

[5] Keping Long, Zhongshan Zhang and Shiduan Cheng, Loadbalancing algorithms in MPLS traffic engineering, In 2001 IEEEWorkshop on High Performance Switching and Routing, 2001,

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[6] Chen Janxun, Zhang Yong and Ma Chengguang, Load Balance bySideway Algorithm for MPLS Traffic Engineering, Computer andDigital Engineering, 2006.

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