Faisal Aslam

Interdomain path computation: Challenges and Solutions for Label Switched Networks

For label switched networks, such as MPLS and GMPLS, most existing traffic engineering solutions work in a single routing domain. These solutions do not work when a route from the ingress node to the egress node leaves the routing area or autonomous system of the ingress node. In such cases, the path computation problem becomes complicated because of the unavailability of the complete routing information throughout the network. This is because service providers usually choose not to leak routing information beyond the routing area or AS for scalability constraints and confidentiality concerns. This article serves two purposes. First, it provides a description of the existing and ongoing work in interdomain TE within the IETF. This information is currently found in various Internet drafts and has not yet been collectively presented in a single document. To this end, a summary of both existing path computation architectures - PCE-based and per-domain - is provided. Second, it compares two per-domain path computation schemes in terms of the total number of LSPs successfully placed and average number of domains crossed, without assuming availability of complete topology information. We notice that the two per-domain path computation schemes, proposed in [1, 2], have comparable path computation complexities and setup latencies.

Introducing TakaTuka: a Java virtualmachine for motes

We present TakaTuka, a tiny Java Virtual Machine (JVM) for wireless sensor motes. TakaTukas preliminary version successfully runs on Crossbows mica2 motes. Furthermore, TakaTuka also runs on Windows and Unix.

Optimized java binary and virtual machine for tiny motes

We have developed TakaTuka, a Java Virtual Machine optimized for tiny embedded devices such as wireless sensor motes. TakaTuka requires very little memory and processing power from the host device. This has been verified by successfully running TakaTuka on four different mote platforms. The focus of this paper is TakaTuka’s optimization of program memory usage. In addition, it also gives an overview of TakaTuka’s linkage with TinyOS and power management. TakaTuka optimizes storage requirements for the Java classfiles as well as for the JVM interpreter, both of which are expected to be stored on the embedded devices. These optimizations are performed on the desktop computer during the linking phase, before transferring the Java binary and the corresponding JVM interpreter onto a mote and thus without burdening its memory or computation resources. We have compared TakaTuka with the Sentilla, Darjeeling and Squawk JVMs.

Online routing of bandwidth guaranteed paths with local restoration using optimized aggregate usage information

We investigate the problem of distributed online routing of bandwidth guaranteed paths with local restoration. A unified model is proposed that captures the bandwidth sharing characteristic of backup paths that provision local restoration, corresponding to different fault models. We apply the model to describe bandwidth sharing on backup paths for varying degrees of network state information. The extent of backup bandwidth sharing depends on the amount of network state information made available through routing protocols. A key design criterion for traffic engineering schemes is to maximize the sharing between backup paths, while minimizing this protocol overhead. M.S. Kodialam and T.V. Lakshman (see Proc. Infocom, p.376-85, 2001) demonstrated that propagating a constant amount of aggregated information per link leads to cost effective bandwidth sharing. We propose oAIS, a new aggregate information scenario, in which we judiciously select the propagated information, such that the protocol overhead is identical to that of Kodialam and Lakshman. Simulations show that oAIS outperforms other information scenarios with comparable protocol overheads.

Inter-Domain Path Computation using Improved Crankback Signaling in Label Switched Networks

For label switched networks, such as MPLS and GMPLS, most existing traffic engineering (TE) solutions work in a single routing domain. These solutions do not work when a route from the ingress node to the egress node leaves the routing area or the autonomous system (AS) of the ingress node. In such cases, the path computation problem becomes complicated because of the unavailability of the complete routing information throughout the network. We present CWS (computation while switching), a new inter-domain path computation scheme which tries to compute a near-optimal path without assuming the availability of complete topology information. We provide a detailed comparison of the CWS scheme with another per-domain path computation scheme given in J.-P. Vasseur et al. (2006). Unlike the standard per-domain path computation scheme (Vasseur et al., 2006), the CWS scheme continues the quest for a better path instead of terminating the search at the first available path, resulting a significant improvement in terms of path optimality. In particular, CWS guarantees that, for a given network state, a computed inter-domain path will traverse a minimum number of domains. This improvement in path computation directly impacts the amount of traffic that can be allowed on the network. For example, for the COST266 topology with 28 domains and 37 bidirectional inter-domain links, CWS places 960 of the requested 2000 paths as compared to 683 paths placed by existing schemes. Finally, the path setup latency of the CWS scheme remains comparable to that of existing schemes, by allowing the data flow as soon as the first feasible path is found.

NPP: a facility based computation framework for restoration routing using aggregate link usage information

We present NPP – a new framework for online routing of bandwidth guaranteed paths with local restoration. NPP relies on the propagation of only aggregate link usage information [2,9] through routing protocols. The key advantage of NPP is that it delivers the bandwidth sharing performance achieved by propagating complete per path link usage information [9], while incurring significantly reduced routing protocol overhead. We specify precise implementation models for the restoration routing frameworks presented in [1] and [2] and compare their traffic placement characteristics with those of NPP. Simulation results show that NPP performs significantly better in terms of number of LSPs accepted and total bandwidth placed on the network. For 1000 randomly selected LSP requests on a 20-node homogenous ISP network [8], NPP accepts 775 requests on average compared to 573 requests accepted by the framework of [2] and 693 requests accepted by the framework of [1]. Experiments with different sets of LSP requests and on other networks indicate that NPP results in similar performance gains.

Improving geometric distance estimation for sensor networks and unit disk graphs

Distance measurement between nodes in wireless sensor networks is a prerequisite for a variety of applications and algorithms. However, special hardware allowing such measurements is expensive, especially if dealing with hundreds or thousands of nodes. Fekete et al. presented an approach on distance estimation based on only the neighborhood information available to all nodes in the network. We improve this algorithm, such that it does no longer rely on uniformly distributed nodes. For our approach, it is sufficient that the second derivative of the probability distribution function is a constant.

Bandwidth Sharing with Primary Paths for Protection Routing in an MPLS Network

In label-switched networks such as MPLS, protection routing involves computing and setting up the backup paths at the same time when the primary paths are routed. It has previously been shown that two or more backup paths may share bandwidth along common links if such backup paths will never be activated simultaneously. Such sharing between the backup paths leads to reduced bandwidth reservations and, hence improved performance in terms of number of path requests that can be accommodated on the network (Aslam et al., 2005). We present a novel idea that backup paths may also share bandwidth with certain primary paths, thereby further reducing the overall bandwidth reservations on the network. This results in even more path requests being accommodated on the network. Sharing with primary paths is possible with any protection routing framework. To demonstrate this sharing, we use the NPP protection routing framework as an example (Aslam et al., 2005). We provide the enhancements to the NPP framework needed to exploit sharing with the primary paths. For the enhanced NPP framework, simulation results on various networks confirm that sharing with primary paths indeed results in better network utilization. This increased performance is achieved with bounded local state information and without requiring any additional routing or signaling overhead.

Offline GC: trashing reachable objects on tiny devices

The ability of tiny embedded devices to run large and feature-rich Java programs is typically constrained by the amount of memory installed on those devices. Furthermore, the useful operation of such devices in a wireless sensor application is limited by their battery life. We propose a garbage collection (GC) scheme called Offline GC which alleviates both these limitations. Our approach defies the current practice in which an object may be deallocated only if it is unreachable. Offline GC allows freeing an object that is still reachable but is guaranteed not to be used again in the program. Furthermore, it may deallocate an object inside a function, a loop or a block where it is last used, even if that object is assigned to a global field. This leads to a larger amount of memory available to a program. Based on an inter-procedural and field-sensitive data flow analysis we identify, during program compilation, the point at which an object can safely be deallocated at runtime. We have designed three algorithms for the purpose of making these offline deallocation decisions. Our implementation of Offline GC indicates a significant reduction in the amount of RAM and the number of CPU cycles needed to run a variety of benchmark programs. Offline GC is shown to increase the average amount of RAM available to a program by up to 82% compared to a typical online garbage collector. Furthermore, the number of CPU cycles consumed in freeing the memory is reduced by up to 94% when Offline GC is used.

Recovery, routing and load balancing strategy for an IP/MPLS network

The paper considers a problem of routing, protection and load balancing in the IP/MPLS network. A network design problem combining all these aspects is presented. Proportionally fair distribution of residual bandwidths on links is used for load balancing, and protection is achieved with failure-dependent backup paths. The efficiency of the proposed approach is tested by combining optimization and simulation tools. Numerical experiments show that using the proposed load balancing and protection mechanisms decreases the number of disrupted LSPs in case of failures, as compared to other recovery options considered.