We consider the problem of providing network access to hosts whose physical location changes with time. Such hosts cannot depend on traditional forms of network connectivity and routing because their location, and hence the route to reach them, cannot be deduced from their network address. In this paper, we explore the concept of providing continuous network access to mobile computers, and present a set of IP-based protocols that achieve that goal. They are primarily targeted at supporting a campus environment with mobile computers, but also extend gracefully to accommodate hosts moving between different networks. The key feature is the dependence on ancillary machines, the Mobile Support Stations (MSSs), to track the location of the Mobile Hosts. Using a combination of caching, forwarding pointers, and timeouts, a minimal amount of state is kept in each MSS. The state information is kept in a distributed fashion; the system scales well, reacts quickly to changing topologies, and does ...

Traditionally, a transport protocol corrects errors in a computer communication network using a simple ARQ protocol. With the arrival of broadband networks, forward error correction is desirable as a complement to ARQ. This paper describes a simplified Reed-Solomon erasure correction coder architecture, adapted for congestion loss in a broadband network. Simulations predict it can both encode and decode at rates up to 1 gigabit per second in a custom 1 micron CMOS VLSI chip. 1. INTRODUCTION As part of a research effort to find a transport protocol (TP) suitable for broadband networks, this paper discusses the use of Forward Error Correction (FEC) for error control. While other TPs use Automatic Repeat ReQuest (ARQ) exclusively [01,02], our TP, known as TP++, is considering using FEC to complement ARQ. Section 2 introduces the different types of error control, while section 3 describes the nature of the errors on a broadband network. Section 4 shows that recent improvements in technolo...

In noncooperative networks users make control decisions that optimize their own performance measure. Focusing on routing, we devise two methodologies for architecting noncooperative networks, that improve the overall network performance. These methodologies are motivated by problem settings arising in the provisioning and the run time phases of the network. For either phase, Nash equilibria characterize the operating point of the network. The goal of the provisioning phase is to allocate link capacities that lead to systemwide efficient Nash equilibria. In general, the solution of such design problems is counterintuitive, since adding link capacity might lead to a degradation of user performance. We show that, for systems of parallel links, such paradoxes cannot occur and the optimal solution coincides with the solution in the single-user case. We derive some extensions to general network topologies. During the run time phase, a manager controls the routing of part of the network flow. The manager is aware of the noncooperative behavior of the users and makes its routing decisions based on this information while aiming at improving the overall system performance. We obtain necessary and sufficient conditions for enforcing an equilibrium that coincides with the global systemwide optimum, and indicate that these conditions are met in many cases of interest.

In noncooperative networks users make control decisions that optimize their individual performance objectives. Nash equilibria characterize the operating points of such networks. Nash equilibria are generically inefficient and exhibit suboptimal network performance. Focusing on routing, a methodology is devised for overcoming this deficiency, through the intervention of the network manager. The manager controls part of the network flow, is aware of the noncooperative behavior of the users and performs its routing aiming at improving the overall system performance. The existence of maximally efficient strategies for the manager, i.e., strategies that drive the system into the global network optimum, is investigated. A maximally efficient strategy of the manager not only optimizes the overall performance of the network, but also induces an operating point that is efficient with respect to the performance of the individual users (Pareto efficiency). Necessary and sufficient conditions for...

Abstract. The existence of Nash equilibria in noncooperative flow control in a general productform network shared by K users is investigated. The performance objective of each user is to maximize its average throughput subject to an upper bound on its average time-delay. Previous attempts to study existence of equilibria for this flow control model were not successful, partly because the time-delay constraints couple the strategy spaces of the individual users in a way that does not allow the application of standard equilibrmm existence theorems from the game theory literature. To overcome this difficulty, a more general approach to study the existence of Nash equilibria for decentralized control schemes is introduced. This approach is based on directly proving the existence of a fixed point of the best reply correspondence of the underlying game. For the investigated flow control model, the best reply correspondence is shown to be a function, implicitly defined by means of K interdependent linear programs. Employing an appropriate definition for continuity of the set of optimal solutions of parametrized linear programs, it is shown that, under appropriate conditions, the best reply function is continuous. Brouwer’s theorem implies, then, that the best reply function has a fixed point.

Abstract — I discuss connectivity between neuromorphic chips, which use the timing of fixed-height, fixed-width, pulses to encode information. Address-events—log2 (N)-bit packets that uniquely identify one of N neurons—are used to transmit these pulses in real-time on a random-access, time-multiplexed, communication channel. Activity is assumed to consist of neuronal ensembles—spikes clustered in space and in time. I quantify tradeoffs faced in allocating bandwidth, granting access, and queuing, as well as throughput requirements, and conclude that an arbitered channel design is the best choice. I implement the arbitered channel with a formal design methodology for asynchronous digital VLSI CMOS systems, after introducing the reader to this top-down synthesis technique. Following the evolution of three generations of designs, I show how the overhead of arbitrating, and encoding and decoding, can be reduced in area (from N to √ N) by organizing neurons into rows and columns, and reduced in time (from log2 (N) to 2) by exploiting locality in the arbiter tree and in the row–column architecture, and clustered activity. Throughput is boosted by pipelining and by reading spikes in parallel. Simple techniques that reduce crosstalk in these mixed analog–digital systems are described.

The capacity allocation problem in a network that is to be shared by noncooperative users is considered. Each user decides independently upon its routing strategy, so as to optimize its individual performance objective. The operating points of the network are the Nash equilibria of the underlying routing game. The network designer aims to allocate link capacities, so that the resulting Nash equilibria are efficient, according to some systemwide performance criterion. In general, the solution of such design problems is complex and at times counterintuitive, since adding link capacity might lead to degradation of user performance. For systems of parallel links, we show that such paradoxes do not occur and that the capacity allocation problem has a simple and intuitive optimal solution, that coincides with the solution in the single-user case.

Abstract—In this paper, we investigate the impact of variable-range transmission power control on the physical and network connectivity, on network capacity, and on power savings in wireless multihop networks. First, using previous work by Steele [18], we show that, for a path attenuation factor 2, the average range of links in a planar random network of Am2 having n nodes is c ffiffiffi p A n 1. We show that this average range is approximately half the range obtained when common-range transmission control is used. Combining this result and previous work by Gupta and Kumar [8], we derive an expression for the average traffic carrying capacity of variable-range-based multihop networks. For 2, we show that this capacity remains constant even when more nodes are added to the network. Second, we derive a model that approximates the signaling overhead of a routing protocol as a function of the transmission range and node mobility for both route discovery and route maintenance. We show that there is an optimum setting for the transmission range, not necessarily the minimum, which maximizes the capacity available to nodes in the presence of node mobility. The results presented in this paper highlight the need to design future MAC and routing protocols for wireless ad hoc and sensor networks based, not on common-range which is prevalent today, but on variable-range power control. Index Terms—Multihop networks, ad hoc networks, traffic capacity, network connectivity, power savings. Ç 1

Simple and robust engineering rules for dimensioning bandwidth for elastic data traffic are derived for a single bottleneck link via normal approximations for a closed-queueing-network (CQN) model in heavy traffic. Elastic data applications adapt to available bandwidth via a feedback control such as the Transmission Control Protocol (TCP) or the Available Bit Rate transfer capability in ATM. The dimensioning rules satisfy a performance objective based on the mean or tail-probability of the per-flow bandwidth. For the mean objective we obtain a simple expression for the effective bandwidth of an elastic source. We provide a new derivation of the normal approximation in CQNs using more accurate asymptotic expansions and give an explicit estimate of the error in the normal approximation. A CQN model was chosen to obtain the desirable property that the results depend on the distribution of the file sizes only via the mean, and not the heavy-tail characteristics. We view the exogenous "load...

We give a distributed algorithm to compute shortest paths in a network with changing topology. It does not suffer from the routing table looping behavior associated with the FordBellman distributed shortest path algorithm although it uses truly distributed processing. Its time and message complexities are evaluated. Pierre Humblet is with the Laboratory for Information and Decision Systems, Massachusetts Institute of Technology, Cambridge MA 02139. This research was supported in part by Codex Corporation and in part by the Army Research Office under Grant No. DAAL03-86-K-0171. 2 1) INTRODUCTION One of the oldest and best known problems in the field of distributed algorithms is to compute shortest paths between nodes in a network. This problem arises in the following context. We have a network of links and nodes (processors). Each link (I,J) is characterized by a direction dependent length LEN(I,J) that can change with time and can only be observed at node I. The nodes execute a distr...