Equal Cost Multipath Research Articles

Oblivious Routing in IP Networks

To optimize the flow of traffic in IP networks, operators do traffic engineering (TE), i.e., tune routing-protocol parameters in response to traffic demands. TE in IP networks typically involves configuring static link weights and splitting traffic between the resulting shortest-paths via the equal-cost-multipath (ECMP) mechanism. Unfortunately, ECMP is a notoriously cumbersome and indirect means for optimizing traffic flow, often leading to poor network performance. Also, obtaining accurate knowledge of traffic demands as the input to TE is a non-trivial task that may require additional monitoring infrastructure, and traffic conditions can be highly variable, further complicating TE. We leverage recently proposed schemes for increasing ECMP’s expressiveness via carefully disseminated bogus information (lies) to design COYOTE, a readily deployable TE scheme for robust and efficient network utilization. COYOTE leverages new algorithmic ideas to configure (static) traffic splitting ratios that are optimized with respect to all (even adversarial) traffic scenarios within the operator’s “uncertainty bounds”. Our experimental analyses show that COYOTE significantly outperforms today’s prevalent TE schemes in a manner that is robust to traffic uncertainty and variation. We discuss experiments with a prototype implementation of COYOTE.

Openflow Based Dynamic Flow Scheduling with Multipath for Data Center Networks

The routing mechanism in Data Center networks can affect network performance and latency significantly. Hash-based method, such as ECMP (Equal-Cost Multi-Path), has been widely used in Data Center networks to fulfill the req... | Find, read and cite all the research you need on Tech Science Press

Non-SPF routing algorithm based on ordered semi-group preference algebra

Layer 2 network technology is extending beyond its traditional local area implementation and finding wider acceptance in provider's metropolitan area networks and large-scale cloud data center networks. This is mainly due to its plug-and-play capability and native mobility support. Many efforts have been put to increase the bisection bandwidth in layer 2 network, which has been constrained by the spanning tree protocol (STP) that layer 2 network uses for preventing looping. The recent trend is to incorporate layer 3's routing approach into layer 2 network so that multiple paths can be used for forwarding traffic between any source-destination (S-D) node pair. Equal cost multipath (ECMP) is one such example. However, ECMP may still be limited in generating multiple paths due to its shortest path (lowest cost) requirement. In this paper, we consider a non-shortest-path routing approach, called equal preference multipath (EPMP) based on ordered semi group theory, which can generate more paths than ECMP. In EPMP routing, all the paths with different traditionally-defined costs, such as hops, bandwidth, etc., can be determined equally now and thus they become equal candidate paths. By the comparative tests with ECMP, EPMP routing not only generates more paths, provides 15% higher bisection bandwidth, but also identifies bottleneck links in a hierarchical network when different traffic patterns are applied. EPMP is more flexible in controlling the number and length of multipath generation. Simulation results indicate the effectiveness of the proposed algorithm. It is a good reference for non-blocking running of big datacenter networks.

Flow Optimization in Data Centers With Clos Networks in Support of Cloud Applications

The proliferation of cloud computing has forced data centers to support a large number of dynamic resources such as virtual machines and storage volumes from any physical location within the data center. This has led to highly volatile and unpredictable traffic patterns. The emergence of cloud applications that exchange large volumes of information have created large persistent flows that need to coexist with other types of traffic. As a result, a number of data center topologies have been proposed to support cloud applications. One of the topologies that has gained prominence is the Clos network. On one hand, Clos networks provide many nice properties, such as equidistant hops, bandwidth, and latency. On the other hand the routing of diverse traffic flows still remains an issue. Current routing methods such as equal-cost multi-path (ECMP) routing that rely on flow hashing over equal cost paths do not take into consideration traffic volume nor network state. In this paper, we investigate routing in Clos topologies. We formulate optimal flow routing in Clos networks as a binary multicommodity flow problem and present optimized flow re-routing, a modified version of the binary multicommodity flow problem that uses a heuristics approach to minimize hash collisions. We also propose FlowFit, a practical optimization method that uses network state to optimally re-assign flows to links. Our experimental and simulation results show a significant improvement in bisection bandwidth and flow completion time over ECMP.

A Simple Congestion-Aware Algorithm for Load Balancing in Datacenter Networks

We study the problem of load balancing in datacenter networks, namely, assigning the end-to-end data flows among the available paths in order to efficiently balance the load in the network. The solutions used today rely typically on an equal-cost multi path (ECMP) mechanism, which essentially attempts to balance the load in the network by hashing the flows to the available shortest paths. However, it is well-known that the ECMP performs poorly when there is asymmetry either in the network topology or the flow sizes, and thus, there has been much interest recently in alternative mechanisms to address these shortcomings. In this paper, we consider a general network topology where each link has a cost, which is a convex function of the link congestions. Flows among the various source–destination pairs are generated dynamically over time, each with a size (bandwidth requirement) and a duration. Once a flow is assigned to a path in the network, it consumes bandwidth equal to its size from all the links along its path for its duration. We consider low-complexity congestion-aware algorithms that assign the flows to the available paths in an online fashion and without splitting . Specifically, we propose a myopic algorithm that assigns every arriving flow to an available path with the minimum marginal cost (i.e., the path which yields the minimum increase in the network cost after assignment) and prove that it asymptotically minimizes the total network cost. Extensive simulation results are presented to verify the performance of the myopic algorithm under a wide range of traffic conditions and under different datacenter architectures. Furthermore, we propose randomized versions of our myopic algorithm, which have much lower complexity and empirically show that they can still perform very well in symmetric network topologies.

Flexible Interconnection of Scalable Systems Integrated Using Optical Networks (FISSION) Data-Center—Concepts and Demonstration

With Internet traffic doubling almost every other year, data-center (DC) scalability is destined to play a critical role in enabling future communications. While many DC architectures are proposed to tackle this issue by leveraging optics in DCs, most fail to scale efficiently. We demonstrate flexible interconnection of scalable systems integrated using optical networks (FISSION), which is a scalable, fault-tolerant DC architecture based on a switchless optical-bus backplane and carrier-class switches. The FISSION DC can scale to a large number of servers (even up to 1 million servers) using off-the-shelf optics and commodity electronics. Its backplane comprises multiple, concentric bus-based fiber rings to create a switch-less core. Sectors, which constitute top-of-the-rack switches along with server interconnection pods, are connected to this switchless backplane in a unique opto-electronic architectural framework to handle contention. The FISSION protocol uses segment-routing paradigms for use within the DC as well as an SDN-based standardized carrier-class protocol. In this paper, we highlight, through three use cases, a FISSION test-bed, and show its feasibility in a realistic setting. These use cases include communication within the FISSION DC, in situ addition deletion of servers at scale and equal-cost multipath (ECMP) provisioning.

Traffic Engineering With Equal-Cost-MultiPath: An Algorithmic Perspective

To efficiently exploit the network resources operators, do traffic engineering (TE), i.e., adapt the routing of traffic to the prevailing demands. TE in large IP networks typically relies on configuring static link weights and splitting traffic between the resulting shortest paths via the Equal-Cost-MultiPath (ECMP) mechanism. Yet, despite its vast popularity, crucial operational aspects of TE via ECMP are still little-understood from an algorithmic viewpoint. We embark upon a systematic algorithmic study of TE with ECMP. We consider the standard model of TE with ECMP and prove that, in general, even approximating the optimal link-weight configuration for ECMP within any constant ratio is an intractable feat, settling a long-standing open question. We establish, in contrast, that ECMP can provably achieve optimal traffic flow for the important category of Clos datacenter networks. We last consider a well-documented shortcoming of ECMP: suboptimal routing of large (“elephant”) flows. We present algorithms for scheduling “elephant” flows on top of ECMP (as in, e.g., Hedera) with provable approximation guarantees. Our results complement and shed new light on past experimental and empirical studies of the performance of TE with ECMP.

Research of a SDN Traffic Scheduling Technology Based on Ant Colony Algorithm

SDN decouples network control plane and data plane, makes the controller gain the global network topology view using logically centralized control, and appropriate scheduling of the network traffic conducted by north bound interface. For the controller of distributed routing multipath and the dynamic characteristics, the ant colony algorithm mechanism routing is adopted and compared with the traditional Equal Cost Multipath Routing (ECMP) algorithm by the experimental simulation. The results show that the ant colony algorithm reduces a link or node congestion in the network, and improves the network link’s utilization rate effectively.

DiFS: Distributed Flow Scheduling for adaptive switching in FatTree data center networks

Data center networks leverage multiple parallel paths connecting end host pairs to offer high bisection bandwidth for cluster computing applications. However, the state-of-the-art routing protocols such as Equal Cost Multipath (ECMP) is load-oblivious due to the static flow-to-link assignment. They may cause bandwidth loss due to flow collisions. Recently proposed centralized scheduling algorithm or host based adaptive routing that requires network-wide state information may suffer from scalability problems. In this paper, we present Distributed Flow Scheduling (DiFS), a new adaptive switching method, for FatTree data center networks, which is a localized and switch-only solution. DiFS allows switches to cooperate to avoid over-utilized links and find available paths without centralized control. DiFS is scalable and can react quickly to dynamic traffic because it is independently executed on switches and requires no synchronization. DiFS provides global bounds of flow balance based on local optimization. Extensive simulations show that the aggregate throughput of DiFS using various traffic patterns is much better than that of ECMP, and is similar to or higher than those of two representative protocols that use network-wide optimization.

IP Fast Rerouting and Disjoint Multipath Routing With Three Edge-Independent Spanning Trees

We develop approaches for disjoint multipath routing and fast recovery in IP networks that guarantee recovery from arbitrary two link failures. We achieve this by developing the first known algorithm to construct three edge-independent spanning trees, which has a running time complexity of $O(V^2)$ . The property of these trees is that the paths from a source to the destination on the trees are mutually link-disjoint. We illustrate how the three edge-independent trees rooted at a destination may be employed to achieve multipath routing and IP fast recovery. We discuss different ways of employing the trees. The routing of packets is based on the destination address and the input interface over which the packet was received. If the trees are employed exclusively for multipath routing, then no packet overhead is required. If the trees are employed for failure recovery, then the overhead bits will range from 0 to 2 bits depending on the flexibility sought in routing. We evaluate the performance of the trees in fast recovery by comparing the path lengths provided under single- and dual-link failures with an earlier approach based on tunneling. We also evaluate the performance of the trees when used for multipath routing and compare it to equal-cost multipaths (ECMP).

Equal Preference Multi-Path Routing for L2 Hierarchical Networks

The layer 2 network technology is extending beyond its traditional local area implementation and finding wider acceptance in provider’s metropolitan area networks and large-scale cloud data center networks. This is mainly due to its plug-and-play capability and native mobility support. Many efforts have been put to increase the bisection bandwidth in a layer 2 network, which has been constrained by the spanning tree protocol that a layer 2 network uses for preventing looping. The recent trend is to incorporate layer 3’s routing approach into a layer 2 network so that multiple paths can be used for forwarding traffic between any source-destination (S-D) node pair. ECMP (equal cost multipath) is one such example. However, ECMP may still be limited in generating multiple paths due to its shortest path (lowest cost) requirement. In this paper, we consider a non-shortest-path routing approach, called EPMP (Equal Preference Multi-Path) that can generate more paths than ECMP. The EPMP is based on the ordered semi-group algebra. In the EPMP routing, paths that differ in traditionally-defined costs, such as hops, bandwidth, etc., can be made equally preferred and thus become candidate paths. We found that, in comparison with ECMP, EPMP routing not only generates more paths, provides higher bisection bandwidth, but also allows bottleneck links in a hierarchical network to be identified when different traffic patterns are applied. EPMP is also versatile in that it can use various ways of path preference calculations to control the number and the length of paths, making it flexible (like policy-based routing) but also objective (like shortest path first routing) in calculating preferred paths.

Achieving Optimal Traffic Engineering Using a Generalized Routing Framework

The open shortest path first (OSPF) protocol has been widely applied to intra-domain routing in today’s Internet. Since a router running OSPF distributes traffic uniformly over equal-cost multi-path (ECMP), the OSPF-based optimal traffic engineering (TE) problem (i.e., deriving optimal link weights for a given traffic demand) is computationally intractable for large-scale networks. Therefore, many studies resort to multi-protocol label switching (MPLS) based approaches to solve the optimal TE problem. In this paper we present a generalized routing framework to realize the optimal TE, which can be potentially implemented via OSPF- or MPLS-based approaches. We start with viewing the conventional optimal TE problem in a fresh way, i.e., optimally allocating the residual capacity to every link. Then we make a generalization of network utility maximization (NUM) to close this problem, where the network operator is associated with a utility function of the residual capacity to be maximized. We demonstrate that under this framework, the optimal routes resulting from the optimal TE are also the shortest paths in terms of a set of non-negative link weights that are explicitly determined by the optimal residual capacity and the objective function. The network entropy maximization theory is employed to enable routers to exponentially, instead of uniformly, split traffic over ECMP. The shortest-path penalizing exponential flow-splitting (SPEF) is designed as a link-state protocol with hop-by-hop forwarding to implement our theoretical findings. An alternative MPLS-based implementation is also discussed here. Numerical simulation results have demonstrated the effectiveness of the proposed framework as well as SPEF.

Dynamic distributed flow scheduling for effective link utilization in data center networks

Current static flow scheduling techniques such as Equal Cost Multi Path (ECMP) and Valiant Load Balancing (VLB) use randomization and hash based techniques to schedule the flow in Data Center Networks (DCN). In such flow scheduling techniques, the probability of allotment of the same path for different flows at a time is high. This causes collision of flows and at times can lead to unfair link utilization. On other hand, Dynamic flow scheduling techniques such as Global first fit use a centralized mechanism to schedule flows. Global first fit can introduce the problem of unfair link utilization and also vulnerable to a single point of failure. Effective flow scheduling is the key problem in fat-tree topology based DCNs mainly due to the bandwidth over-subscription ratio and bursty nature of traffic. In this paper, we propose a dynamic distributed flow scheduling mechanism for effective link utilization and load balancing. Moreover our proposed mechanism prevents the core switch saturation scenario by taking flow scheduling decisions at lower layers. Load measurement performed on aggregate switches for various data center traffic flow patterns reveals that the load factors across all the aggregate switches vary by at most 0.11 when dynamic distributed flow scheduling is applied without flowlet splitting. Further with flowlet splitting our dynamic distributed flow scheduling mechanism improved the load factor variation to 0.08. The load factor values signify there is considerable improvement in link utilization and the switches are fairly load balanced. The experiment scenario is simulated using Colored Petri Nets.

Enhanced MENTOR Algorithm with ECMP Routing Enable

MENTOR (Mesh Network Topological Optimization and Routing) is an efficient heuristic design algorithm network that assigns traffic flow while selecting links to be installed. MENTOR is suitable to design networks categorized as virtual circuit packet switching such as Frame Relay, ATM and MPLS networks. However, MENTOR cannot be directly applied to datagram packet switching networks such as purely IP router network. This is because the traffic flows determined by original MENTOR are not always the shortest path routing based on IP link weight assignment. To solve this problem, Cahn proposed a modified version of MENTOR called MENTOR-II in which appropriate link weights are assigned to the installed links such that the traffic always route on the path with minimum distance. However, it should be noted that the traffic flows assigned by MENTOR-II are limited to a single path routing. This study proposed a new modified version of MENTOR called Enhance-MENTOR, or EMENTOR, which is able to assign traffic with the Equal Cost Multi-Path (ECMP) routing. Three options of E-MENTOR are considered, i.e. E-MENTOR with single path routing only, E-MENTOR with ECMP routing only and E-MENTOR that consider ECMP routing if benefit. The three options of E-MENTOR are evaluated in term of installation cost, routing cost and reliability for 729 network design conditions. The design results are compared with those of original MENTOR and MENTOR-II.

On the efficacy of fine-grained traffic splitting protocolsin data center networks

Multi-rooted tree topologies are commonly used to construct high-bandwidth data center network fabrics. In these networks, switches typically rely on equal-cost multipath (ECMP) routing techniques to split traffic across multiple paths, such that packets within a flow traverse the same end-to-end path. Unfortunately, since ECMP splits traffic based on flow-granularity, it can cause load imbalance across paths resulting in poor utilization of network resources. More fine-grained traffic splitting techniques are typically not preferred because they can cause packet reordering that can, according to conventional wisdom, lead to severe TCP throughput degradation. In this work, we revisit this fact in the context of regular data center topologies such as fat-tree architectures. We argue that packet-level traffic splitting, where packets of a flow are sprayed through all available paths, would lead to a better load-balanced network, which in turn leads to significantly more balanced queues and much higher throughput compared to ECMP.

Revisiting next-hop selection in multipath networks

Multipath routing strategies such as Equal-Cost MultiPath (ECMP) are widely used in IP and data-center networks. Most current methods to balance packets over the multiple next hops toward the destination base their decision on a hash computed over selected fields of the packet headers. Because of the non-invertible nature of hash functions, it is hard to determine the values of those fields so as to make the packet follow a specific path in the network. However, several applications might benefit from being able to choose such a path. Therefore, we propose a novel next-hop selection method based on an invertible function. By encoding the selection of successive routers into common fields of packet headers, the proposed method enables end hosts to force their packets to follow a specific path.

An efficient algorithm to enable path diversity in link state routing networks

Multipath routing allows for load balancing and fast re-routing in order to improve the reliability and the efficiency of the network. Current IP routers only support Equal Cost MultiPath (ECMP) which guarantees that the forwarding paths do not contain loops. However, ECMP provides limited path diversity. In this paper, we present an efficient algorithm that allows routers to enable more path diversity: our algorithm let all routers compute at least the two best first hop distinct paths towards each destination and achieves a good tradeoff between path diversity and overhead. In addition, we propose a multipath routing scheme whose goal is to combine fast re-routing and load balancing loop-free routes. The low overhead of our scheme (no additional signaling messages and low complexity) and the nature of its loop-free rules allow to incrementally deploy it on current IP routers. Using actual, inferred, and generated topologies, we compare our algorithm to existing solutions.

Traffic distribution over equal-cost-multi-paths

To effectively manage the traffic distribution inside a network, traffic splitting is needed for load sharing over a set of equal-cost-multi-paths (ECMPs). In this paper, a new traffic splitting algorithm, called Table-based Hashing with Reassignments (THR), is proposed. Based on the load sharing statistics collected, THR selectively reassigns some active flows from the over-utilized paths to under-utilized paths. The reassignment process takes place in such a way that the packet out-of-order problem is less severe. Simulations show that THR provides close-to-optimal load balancing performance but suffers about 5% of packets arrived out-of-order. Although additional traffic monitoring function is needed by THR, we show that the extra complexity incurred is marginal.

A simulation study of the OSPF-OMP routing algorithm

Open shortest path first (OSPF) is the most widely used internal gateway routing protocol on the Internet. However, one shortcoming is that it does not take advantage of the existence of multiple equal-cost paths between source and destination nodes. A well-known variation of OSPF, OSPF-ECMP (ECMP, equal-cost multipath), does exploit the presence of multiple equal-cost paths, but only on a static basis. A variation of OSPF, OSPF-OMP (OMP, optimized multipath), attempts to dynamically determine the optimal allocation of traffic among multiple equal-cost paths based on the exchange of special traffic-load control messages. This paper briefly describes the OSPF-OMP algorithm and the design of a discrete event simulator that models its behavior. We then use this simulator to carry out three experiments that compare the performance of OSPF, OSPF-ECMP, and OSPF-OMP under a range of traffic loads and distributions. Our results show that OSPF-OMP produces improvements in both delivery time and the number of lost messages when compared with the other two protocols.