Modeling and analyzing the performance of adaptive hierarchical networks

Rapid development of optical communication techniques has made possible large scale wavelength routing optical networks. Nowadays, these networks are deployed worldwide. Large scale networks have natural hierarchies due to either geographical reasons or administrative consideration and are therefore managed in a hierarchical way correspondingly. That is, networks are composed of several subnetworks, which are themselves composed of other even smaller subnetworks. Erlang fixed point approximation (reduced load approximation) has been extensively used in performance evaluation of end to end call blocking probability in traditional circuit switching networks, which are also called loss networks. This method has also been extended for hierarchical loss networks. However, performance evaluation of call blocking probability in hierarchical wavelength routing optical networks has not yet been presented. In this paper, a kind of approximation method is developed for analyzing end to end call blocking probability in hierarchical wavelength routing optical networks. By iteratively running processes combining a top-down load distribution and a bottom-up calculation of node-pair blocking in the network hierarchy, a steady state will be reached and approximate end to end call blocking probability in hierarchical wavelength routing optical network is obtained. Both the link independent model and the link correlation model are used in our analysis. By comparing theoretical results derived from our approximation method and results obtained from discrete event simulation, we illustrate that our method gives reasonable estimate of end to end call blocking probability in hierarchical wavelength routing optical networks, with the correlation model giving much more accurate estimate than the independent model.

Analysis of adaptive cost functions for dynamic update policies for QoS routing in hierarchical networks

For reducing routing information to achieve scalability in large ATM networks, ATM private network-to-network interface (PNNI) adopts hierarchical routing. In order to provide efficient routing, a large ATM network is decomposed into subnetworks, called peer groups (PG), and peer groups will advertise aggregated routing information only. Because the aggregated information is not very precise, a call set up message may be rejected on a chosen route. When an ATM node discovers a call set up message cannot proceed due to insufficient resource, it initiates a back-tracking procedure called against call blocking. Although crankback reduces blocking probability, it also causes additional overhead, such as longer setup delay. Therefore, in this paper, we propose two approaches to reduce crankback overhead, The first approach adds additional information into the set up message, referred to as CIS (crankback information stack), to reduce crankback overhead. The other approach, referred to as CT (cost threshold), uses aggregated path cost and the cost information of a previously rejected call set up message to determine whether call setup on the next alternate path should be tried. Our simulation results show that both of the proposed approaches reduce crankback overhead significantly. Especially, the combination of CIS and CT approach achieves further improvement.

The purpose of this paper is to investigate the network throughput in ad hoc wireless networks (AHWN) under a cluster-based hierarchical routing scheme. Hierarchical routing has been known to handle the scalability issue in the AHWN. Such hierarchical routing protocols can reduce the routing overhead, as lesser nodes need to know topology information of an AHWN. Some works have studied the routing overhead of hierarchical base routing. However, there is little formal analysis that considers influence on the other network performance metric, e.g. throughput, incurred by these procedures. This paper provides a theoretical computation on the throughput of the AHWN under one hierarchical structure, i.e., cluster-based. It discusses the issue that the cluster head nodes may become the bottle neck for throughput, since the throughput of such AHWN is relatively smaller by a factor of O(N2/N1), N2 is the number of cluster-head nodes and N1 is the number of all the nodes in a network. Hence, there is a trade-off between the gain from routing overhead and loss from network throughput in the design of hierarchical routing for AHWN which need to be optimized.

In the future automated battle field communications will be supported in part by a hierarchical wireless network that includes: ad hoc ground radio subnets; point to point wireless long haul backbone, and; unmanned aerial vehicles (UAVs). In such a hierarchical network, nodes are generally partitioned into groups. Each group has one or more backbone nodes that provide access points to the backbone network and to UAVs. Communications between groups can thus utilize links at higher level. A critical protocol in the operation of such a large mobile network is routing. Previous research of UAV based systems has generally assumed the use of a hierarchical routing scheme, for example, extended hierarchical state routing (EHSR). However, a hierarchical scheme like EHSR has some limitations. In this paper, we extend landmark ad hoc routing (LANMAR) to a hierarchical structure with backbone nodes, high quality backbone links and UAVs. We show that the basic LANMAR scheme can be extended to incorporate backbone and UAV links. We will also show how backbone links and UAV links are automatically discovered by the LANMAR routing algorithm and are used effectively to reach remote destinations (thus reducing the hop distance). In other words, our scheme will combine the benefits of flat LANMAR routing and physical network hierarchy, without suffering of the intrinsic EHSR limitations.

An exact end-to-end blocking probability algorithm for multicast networks

In this paper we present a hierarchical routing protocol in a large wireless, mobile network such as found in the automated battlefield or in extensive disaster recovery operations. Conventional routing does not scale well to network size. Likewise, conventional hierarchical routing cannot handle mobility efficiently. We propose a novel soft state wireless hierarchical routing protocol-Hierarchical State Routing (HSR). We distinguish between the "physical" routing hierarchy (dictated by geographical relationships between nodes) and "logical" hierarchy of subnets in which the members move as a group (e.g., company, brigade, battalion in the battlefield). HSR keeps track of logical subnet movements using home agent concepts akin to Mobile IP. A group mobility model is introduced and the performance of the HSR is evaluated through a detailed wireless simulation model.

Analysis on topological features of deterministic hierarchical complex network

This paper presents two mobile location management algorithms for ATM (asynchronous transfer mode) networks based on the PNNI (private network-to-network interface) standard. The first solution is called the mobile PNNI scheme because it builds on the PNNI routing protocol. It uses limited-scope (characterized by a parameter S) reachability updates, forwarding pointers, and a route optimization procedure. The second solution is called the LR (location registers) scheme because it introduces location registers (such as the cellular home and visitor location registers) into the PNNI standards-based hierarchical networks. This scheme uses a hierarchical arrangement of location registers with the hierarchy limited to a certain level S. Analytical models are set up to compare the average move, search, and total costs per move of these two schemes for different values of the CMR (call-to-mobility ratio), and to provide guidelines for selecting parameters of the algorithms. Results show that at low CMRs (CMR<0.025), the LR scheme performs better than the mobile PNNI scheme. We also observe that the two schemes show a contrasting behavior in terms of the value to be used for the parameter S to achieve the least average total cost. At low CMRs, the parameter S should be high for the mobile PNNI scheme, but low for the LR scheme, and vice versa for high CMRs.

The authors compare the performance of a mobile packet radio network with a hierarchical structure with one which is fully distributed. The network end-to-end throughput is used as the performance measure. The authors define the performance of network end-to-end throughput to be the number of network nodes times the inverse of the average end-to-end transmission delay for anode. It can be interpreted as the average number of packets successfully arriving at destinations per unit time in the network. To analyze the performance of the hierarchical network, first, a local-access algorithm is proposed. The local access scheme is designed for low cost nodes, which are required to provide the basic functions of receiving and transmitting packets with a fixed power radius. The authors show that the hierarchical network outperforms the fully distributed network for most scenarios due to the significant decrease in the average number of hops and increase in frequency reuse. >

This paper studies the blocking performance of optical burst switching (OBS) networks using a sequential office control (SOC) state-independent deflection routing policy. We show that unprotected deflection routing may destabilize OBS resulting in higher blocking probabilities than if bursts were not deflected but simply blocked. This study was motivated by the well-known destabilizing effect that alternative routing has on circuit switching in classical telephony networks. We propose two forms of protection to guard against destabilization: 1) wavelength reservation, which is analogous to trunk reservation in circuit switching; and, 2) preemptive priority, which is a new form of protection where bursts that have not been deflected are given preemptive priority over bursts that have been deflected. Our main contribution is a one-moment reduced-load approximation to evaluate the blocking performance of OBS networks using deflection routing protected by either wavelength reservation or preemptive priority. Our reduced-load approximation relies on the usual assumptions of link independence and Poisson distributed link arrivals. We quantify the error admitted in making these two assumptions via simulation. Using our reduced-load approximation, we evaluate the blocking performance of protected and unprotected deflection routing in several randomly generated networks. The chief conclusion of our study is that deflection routing in OBS should be given some form of protection to avoid destabilization resulting from upward load variations, and in terms of blocking performance, preemptive priority is the best form of protection for OBS. We use simulation to verify that our conclusions remain valid for a realistic traffic scenario.

Wireless sensor networks (WSNs) nodes are commonly designed to work with limited resources of memory, energy and processing. The routing protocol is one of the key components of WSNs and its features impact network performance significantly. We present an efficient Multi-Parent Hierarchical (MPH) routing protocol for wireless sensor networks; its main goal is to achieve reliable delivery of data in a single sink scenario while keeping low overhead, reduced latency and low energy consumption. The main features of MPH are self-configuration, hierarchical topology, persistence according to link quality, and source routing from sink to nodes. Network performance simulations of the MPH routing protocol are carried out and compared with two popular protocols, AODV, DSR and with the well-known algorithm ZTR (Zigbee Tree Routing). Results show that for the single sink scenario, the MPH protocol has an energy saving of 35% against AODV and DSR protocols and 8% compared with ZTR. MPH has 27% less overhead compared with AODV and DSR. And MPH presents a 10% increase in packet delivery compared with AODV, DSR and ZTR. Finally, we present a real WSN built based on the MPH protocol, which works satisfactorily, providing an experimental demonstration of the capabilities of the protocol.

Stochastic performance evaluation of hierarchical routing for large networks

Multicast connections have a bandwidth saving nature. This means that a multicast connection --- in taking the form of a tree with streams merging at the nodes --- requires much less capacity from the network links than a bunch of separate point-to-point connections providing the same connectivity. In this paper, we consider dynamic multicast connections that can be used to model, for example, TV or radio delivery on a telecommunications network, such as an ATM network with virtual circuits. We show how to calculate the blocking probabilities of requests to join such a tree. First, we consider the blocking probabilities occurring in a single link. The resulting model is able to capture heterogeneous capacity requirements for different multicast channels. Then we extend the results to a whole network using the reduced load approximation. The accuracy of the approximation method is studied by simulations.

A social network is composed of social individuals and their relationships. In many real-world applications, such a network will evolve dynamically over time and events. A social network can be naturally viewed as a multiagent system if considering locally-interacting social individuals as autonomous agents. In this paper, we present an Autonomy-Oriented Computing (AOC) based model of a social network, and study the dynamics of the network based on this model. In the AOC model, the profile of agents, service-based interactions, and the evolution of the network are defined, and the autonomy of the agents is emphasized. The model can reveal dynamic relationships among global performance, local interaction (partner selection) strategies, and network topology. The experimental results show that the agent network forms a community with a high clustering coefficient, and the performance of the network is dynamically changing along with the formation of the network and the local interaction strategies of the agents. In this paper, the performance and topology of the agent network are analyzed, and the factors that affect the performance and evolution of the agent network are examined.