Random-Walk Based Analysis of Virtual Backbone in MANETs

Service discovery architectures and cluster-assisted routing protocols in mobile ad-hoc networks (MANETs) heavily rely on formation and maintenance of a virtual backbone (VB). We present a novel analytic model for VB stability in MANETs. The model employs the dynamics of node movements, where link creation/failure is modeled via a random walk with probabilistic state-transition matrix. The backbone formation algorithm gives preference to the nodes with the smaller number of link changes and the higher degree. Therefore, the link arrivals and departures approximate the probability (and thus the expected time) for a mobile node to leave, join, or remain in the backbone, i.e., the stability of a dynamic structure of VB nodes

Analytical Model of a Virtual Backbone Stability in Mobile Environment

We present a probabilistic model of the stability of a virtual backbone in ad hoc networks. The model allows the computation of several metrics characterizing the dynamics of a node's random movement: (1) average time for the number of link changes of the node (i.e., instances of link creation and failure) or just failures to either drop below or exceed a given threshold, and, analogously, (2) average time for the number of active links of the node to either drop below or exceed a given threshold. The former defines the stability of the node's links and the latter is the node's degree (the number of active neighbors). Besides the stability of a virtual backbone, our model will help analyze the performance of various paradigms that rely on such link-based mobility metrics including some backbone- or clusterassisted routing protocols and service discovery architectures

Performance Study of Reliable Server Pooling +

The reliable server pooling allows redundant information sources to be viewed as a single transport endpoint, and therefore is able to provide persistent connections and balanced traffic. The IETF RSerPool Working Group has proposed an architecture to implement the reliable server pooling. We conducted a number of simulation experiments with the current definitions of the RSerPool protocols to quantify their performance in both wired and wireless environments. The simulation results show that the RSerPool works well in fixed and relatively reliable environments, but its performance worsens rapidly as the networks become more unreliable or mobile. The issues we identified in wireless mobile ad-hoc networks include network partitioning, high signaling overhead, and excessive aggressiveness in handling failures. These problems are partly due to the heavy reliance of the RSerPool architecture on the reliability of the underlying network, which is unlikely to be guaranteed in a wireless mobile ad-hoc environment

SCTP Subflows for Survivable FCS Applications

The Stream Control Transmission Protocol (SCTP), a general-purpose transport layer protocol by the IETF, has been a promising candidate to join UDP and TCP as a core protocol. The new SCTP services such as multi-homing, multi-streaming, message boundary preservation, no head-of-line delivery blocking, and enhanced security features can significantly enhance performance of FCS applications. SCTP congestion control mechanism in networks with path diversity or QoS enhancements to support differentiated services, can jeopardized performance due to the socalled false sharing. We propose to modify the current SCTP such that an association is divided into several subflows based on their Differentiated Services Codepoints (DSCPs). Each sub-flow inside the SCTP association shall have its own congestion control parameters. We derived analytic models for the SCTP with the proposed modification for differentiated services environment with both DropTail and RED queues. Our simulation experiments show that our proposed solution prevents false sharing and achieves a better throughput in a differentiated services network. The simulation experiment results also verify that the analytical models accurately reflect the SCTP behavior

Preferential treatment of SCTP subflows: Analysis and simulation

The current SCTP specification is not aware of QoS provided by a network. As a result, it is unable to support preferential treatment of the individual streams. We introduce the concept of dividing an association into subflows (SFs) so that the modified SCTP can support different levels of QoS. We define the necessary modifications to the current SCTP for this capability: namely, new data and SACK chunk formats to implement congestion control for each SF. To avoid the problem of false sharing, we modify SCTP such that each SF has its own congestion control mechanism. Using analytic models, we show that the modified SCTP is expected to perform better than the original SCTP. We verify these results through simulation experiments, where we observed that modified SCTP is able to take advantage of the diff-serv network and provides a better throughput

Reliable Server Pooling in Highly Mobile Wireless Networks

The reliable server pooling is a framework to handle session failures and increase the system's availability by providing several reliability services: from simple server selection to a full session-failover capability. In the IETF RSerPool, servers with equivalent functionality are pooled together; when a particular server becomes unavailable, a client application can transparently switchover to another server in the pool. Extensive simulation experiments identified two main shortcomings of the RSerPool in wireless mobile networks: the inaccuracy of the failure-detection mechanism for pooled servers, and high overhead of finding name servers. We introduce and evaluate alternative mechanisms that tackle these problems

Performance Evaluation of Subflow Capable SCTP

With its new features such as multi-homing, multi-streaming, and enhanced security, the Stream Control Transmission Protocol (SCTP) has become a promising candidate to join UDP and TCP as a general-purpose transport layer protocol. Multiple streams in an SCTP association provide an aggregation mechanism to accommodate heterogeneous objects, which belong to the same application but may require di#erent types of QoS from the network. However, the current SCTP specification lacks an internal mechanism to support the preferential treatment among its streams. Our earlier work introduced the concept of grouping SCTP streams into subflows based on their required QoS. We proposed to modify the current SCTP to implement subflows, each with its own flow and congestion mechanism to prevent the so-called false sharing. In this paper, performance evaluation of subflow capable SCTP (SF-SCTP) is studied through a set of extensive simulation experiments. The results show that the proposed SF-SCTP design is able to support QoS among the SCTP streams and that false sharing is avoided. The results also reveal SF-SCTP's significant benefits in improving the utilization of a bottleneck network

Metrics for Quantifying Benefits and Cost of Session Switchovers

To persistently maintain client-server connections in mobile ad-hoc networks, we investigate the reliable server pooling (RSP), where servers that can provide equivalent functionality are pooled together. The RSP is meant to increase the availability and survivability of the battlefield infrastructure by allowing clients to access a pool of redundant information sources. As a result, some failed sessions are going to be prolonged through a series of transparent switchovers beyond the time of the first failure. However, both the prolonged sessions and the RSP infrastructure itself will put additional stress on the network and server resources. This paper introduces a classification of switchovers and sessions (sustained, lost, and inconclusive), and then defines several metrics that quantify the aggregate benefit and cost of RSP in a system: session sustainability throughput, gain, and cost, as well as switchover efficiency. A set of simulation experiments are run to better illustrate the meaning and practical application of the defined metrics