Srinivas Vutukury

MDVA: a distance-vector multipath routing protocol

Routing protocols using the distributed Bellman-Ford (DBF) algorithm converge very slowly to the correct routes when link costs increase, and in the case when a set of link failures results in a network partition, DBF simply fails to converge, a problem which is commonly referred to as the count-to-infinity problem. We present the first distance-vector routing algorithm, MDVA, that uses a set of loop-free invariants to prevent the count-to-infinity problem. MDVA, in addition, computes multipaths that are loop-free at every instant. In our earlier work we shows how such loop-free multipaths can be used in traffic load-balancing and minimizing delays, which otherwise are impossible to perform in current single-path routing algorithms.

An algorithm for multipath computation using distance-vectors with predecessor information

Routing algorithms in the IP Internet provide a single path between each source-destination pair and where more than one path is provided, they are paths of equal length. Single-path routing is inherently slow in responding to congestion and temporary traffic bursts; multiple paths are better suited to handle congestion. Also the paths provided in RIP and OSPF are not free of loops during times of network transition, which can be debilitating to network performance. We present a distributed routing algorithm for computing multiple paths that need not have equal length between each source-destination pair in a computer network such that they are loop-free at every instant - in steady state as well as during network transitions. The algorithm is scalable to large networks as it uses only one-hop synchronization which is unlike diffusing computations that require internodal synchronization spanning multiple hops. The safety and liveness properties of the algorithm are proven and its complexity is analyzed.

A traffic engineering approach based on minimum-delay routing

Single-path routing provided by todays interior gateway protocols (IGP) make extremely inefficient usage of network bandwidth, and is evident in the large end-to-end delays flows experience in single-path routing as compared to minimum-delay routing. Enhancement to OSPF such as optimized multipath have not proved adequate to bridge this large delay gap. Practical implementations of minimum-delay routing, on the other hand, have been largely unsuccessful for reasons such as scalability, slow convergence and out-of-order packet delivery. This paper proposes a traffic engineering solution that adapts the minimum-delay routing for a given traffic matrix in a way that is practical and suitable to implement in the differentiated services framework. A simple and scalable packet forwarding technique is described that offers several improvements over OSPF-OMP.

MPATH: a loop-free multipath routing algorithm

Abstract We present a distributed routing algorithm for computing multiple paths between each source–destination pair in a computer network, such that the paths are loop-free at all times and are not necessarily of equal length. In this algorithm, routers exchange second-to-last hop on the shortest path to destinations in addition to shortest distances, which are used to prevent the well-know count-to-infinity problem. The safety and liveness properties of the algorithm are proved and its performance is analyzed.

Load-balanced anycast routing in computer networks

We present a practical approach to routing and anycasting with near-optimum delays taking into account the processing loads at routers and processing elements of a computer network. To accomplish this, the minimum-delay routing problem formulated by Gallager (1977) is generalized into the problem of minimum-delay routing with load-balancing to account for processing delays in network nodes (servers and routers). Gallagers theorem for necessary and sufficient conditions for minimum-delay routing is modified to include processing delays and changes of traffic levels at network nodes. The first distributed algorithm for load-balanced anycasting and routing in computer networks is presented. This algorithm, named MIDAS, provides approximate solutions to the modified necessary and sufficient conditions for minimum-delay routing. Simulations are use to compare the performance of the new algorithm with the performance of a traditional approach to sever load balancing.

A scalable architecture for providing deterministic guarantees

The Internet community has proposed the integrated services architecture (Intserv) and the signaling protocol RSVP to provide deterministic guarantees (bandwidth, delay and jitter) to individual flows. However, experience with practical systems has revealed the severe scalability problems of the Intserv model due to the amount of routing and reservation state that is required to he maintained in the routers. A natural approach to improving scalability of the Intserv architecture is through a reduction of the number of states in the routers by using aggregated flow state instead of per-flow state. We present a novel architecture that uses very few states in the routers, while still providing the deterministic guarantees of the Intserv model.

Simple MPLS-based flow aggregation scheme for providing scalable quality of service

Providing Quality of Service (QoS) capabilities in IP networks is the focus of much research in the Internet community today. The Intserv architecture proposed by IETF for supporting QoS in IP networks is known not to scale well to large networks due to the per-flow mechanisms it uses. While connection-less approach has been the central design paradigm of IP networks, many researches today believe connection-oriented mechanisms similar to virtual-circuits in ATM must be incorporated in IP networks in order to provide scalable QoS. Towards this end, the MPLS (Multi-Protocol Label Switching) technology has been put forward by the IETF. A crucial scaling issue with MPLS is that large number of LSPs (Label Switched Paths) may be required in the routers resulting in increase of state size in the routers. In this paper, we introduce the notion of Label-Switched Multipaths (LSMPs) and propose a simple technique for aggregating LSP into LSMPs such that the number of labels required in the routers is significantly reduced. Based on LSMPs we describe an architecture for providing deterministic guarantees that is far more scalable than architectures based on simple LSPs or those that use only multipoint-to-point LSP aggregation.

WiNN: an efficient method for routing short-lived flows

Delivering real-time streaming content requires finding paths with a minimum required bandwidth. Finding such paths when requested should be fast (low startup latency) and efficient (high call acceptance rates). However, current algorithms for finding such QoS paths are ineffective when the bulk of the flows are short-lived. First, these algorithms are computationally expensive to justify invoking them on a per-request basis, and they add substantial latency to the signaling process. Moreover, they rely on frequent advertisement of residual link bandwidth, which is prohibitively expensive to perform on a short time-scale. Considering these drawbacks, a simple heuristic WiNN (Widest Next-hop Neighbor) is proposed that has low startup latency and provides good call acceptance rates. The heuristic uses neither link state updates nor complex path selection algorithms.

A multipath framework architecture for integrated services

A major concern with the IETF proposed integrated services (Intserv) architecture for providing quality of service is that the amount of reservation state it stores in the routers and the RSVP protocol it uses to maintain the consistency of reservation state may not be scalable to high-speed backbone networks. Because of the large number of flows in the backbone network, the refresh messages associated with RSVPs soft-state mechanism, apart from consuming memory, bandwidth and computing power, can experience significant queuing delays and prevent correct functioning of the soft-state mechanism. For the refresh mechanism to scale, therefore, the reservation state size must be bounded so that delays of time-sensitive refresh messages can also be bounded through adequate bandwidth allocation. Vutukury and Garcia-Luna-Accves (see. Proc. of ICCCN, 1999) described the scalable multipath aggregated routing architecture (SMART) In which the reservation state size is a function of number of destinations rather than number of flows in the network. In this paper, we describe a reservation protocol (AGREE) to maintain this reservation state aggregated along the multipaths. The AGREE protocol, like RSVP, uses soft-states, but also ensures that the refresh messages experience bounded queuing delays. The SMART architecture combined with AGREE protocol is significantly more scalable compared to the Intserv/RSVP model.