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OPNET Technologies © 2010 OPNET Technologies, Inc. |
Research: Title: QoS and Channel-Aware Packet Bundling for Capacity Improvement in Cellular Networks, IEEE Transactions on Vehicular Technology, vol.59, no.8, pp.3886-3901, Oct. 2010. Baek-Young Choi, Jung Hwan Kim, Cory Beard. We propose a novel quality-of-service (QoS) and channel-aware packet bundling algorithm that takes advantage of adaptive modulation and coding. We show that optimal algorithms are nondeterministic polynomial time (NP)-complete, recommend heuristic approaches, and use analytical performance modeling to show the gains in capacity that can be achieved from our packet bundling algorithms. We show that channel utilization can be significantly increased by slightly delaying some real-time packets within their QoS requirements while bundling those packets with like channel conditions. We validate this paper through extensive OPNET simulations with a complete evolution-data optimized (EV-DO) implementation. Title: On the Accuracy of Poisson Approximation of Multiplexed Voice Traffic, O. Gusak, N. Oliver, K. Sohraby In order to reduce the time complexity of the model of a large communication system where the traffic consists of many individual packetized voice flows, we approximate the traffic by a single equivalent flow whose effects in the model are similar within specified confidence bounds but whose time complexity in the running model is greatly reduced. We demonstrate that an aggregation of 300+ voice flows, each modeled by an on-off model of talk and silence and a constant packet interarrival time in the “on” state, is quite accurately modeled by a single Poisson-distributed equivalent flow. Title: A Simulation Study of 802.16 MAC Layer on a Large-Scale Example, O. Gusak, N. Oliver, K. Sohraby In this work we investigate performance of the medium access control layer of an 802.16 wireless network consisting of 100 subscriber stations (SSs) and a single base station (BS). Experimental results show that the average packet queuing delay was virtually the same for weighted round robin and weighted fair queuing scheduling algorithms. Another interesting finding is that adapting the uplink/downlink ratio plays a crucial role in performance as the network load increases and channel conditions change. On the other hand, experiments show that for a higher network load, segmentation of large packets is a necessity in order to achieve performance and QoS conformance. We also observed a smaller average queuing delay for smaller values of frame duration. Title: A Flexible Representation of Input Parameters for Large-Scale OPNET Simulation Models, O. Gusak, N. Oliver, K. Sohraby This paper describes a modeling approach which allows simplifying the process of changing the structure of input parameters. The structure of the proposed model allows model variables associated with input parameters to be loosely coupled with their input methods. The loose coupling is abstracted by a module in each node of the modeled network. Thus, the module which is called “database” provides an interface for reading input parameters for all other processes of a given node. Under this organization, a change in the input method of a parameter leads to a modification in the code of the database module only, while all other modules are not affected. Along with the proposed approach, we also discuss different ways by which parameters of the database can be organized and accessed by other processes. Title: Modeling Signaling Traffic of an IP Multimedia Subsystem Using OPNET Custom Application Model, O. Gusak, N. Oliver, K. Sohraby In this paper we consider a simulation model of an IP multimedia subsystem (IMS). The main purpose of an IMS system is to initialize and support connections between user equipments (UEs). Hence, the key performance variable of an IMS system is control traffic flowing between UEs and IMS servers. To model this traffic, we use OPNET custom applications which provide a flexible mechanism to mimic data exchange between network nodes and require zero programming during implementation. We discuss difficulties and limitations of using custom applications for modeling signaling traffic in the model. As a remedy for these difficulties, we modify the simulation model by implementing an application model using the API for OPNET custom application model. We compare the two implemented models using the results of test simulation runs with the models. Title: API of OPNET Custom Applications as a Convenient Tool in High-Level System Modeling, O. Gusak, N. Oliver, K. Sohraby For a systems architect, modeling a system is a necessary task at every stage of its development. In early stages, engineers frequently need a high-level simulation model that captures major system concepts yet can be prototyped rapidly. This is where OPNET custom applications API can be helpful. It provides full flexibility to the model developer in capturing system interactions, while hiding unimportant protocol stack details. In this work, we present a model of a high-performance computing architecture designed using the custom applications API. We describe the system architecture, the simulation model structure and logic, and provide test simulation results. Title: QoS and Channel Aware Packet Bundling for VoIP Traffic in Cellular Networks, 21st International Teletraffic Congress (ITC), Paris, France, Sep. 2009, J. H. Kim, B.-Y. Choi, C. Beard.
We study the problem of multiple packet
bundling to improve spectral efficiency in cellular networks. The packet
size of real-time data, such as VoIP, is often very small. However, the
use of time division multiplexing (TDM) limits the number of VoIP users
supported, because a packet has to wait until it Title: Performance Analysis of IMS Control Plane over WiMAX Access Network, OPNETWORK 2010, Washington DC, O. Gusak Recent widespread introduction of 802.16 broadband wireless networks laid foundation for extensive deployment of IP multimedia services for mobile users. In this work, we focus on the performance of a wireless access network versus the performance of an IP multimedia subsystem (IMS) network that facilitates multimedia services for the users. Using OPNET Modeler, we simulate IMS registration and session setup transactions sourced from and terminated in a WiMAX access network. Analysis of simulation results show that the delay the signaling packets experience in the IMS network grows much faster with the growth of the volume of the signaling traffic than the delay experienced by the packets in the wireless segment. Results also show that the core IMS network delay is highly sensitive to the service rate of the signaling packets in individual IMS network nodes. Thus, with a slight decrease in the service rate of the packets in the core IMS network nodes, the IMS network may become the bottleneck for the signaling traffic. Teaching: CS 5520 Network Architecture-I (Instructors: Dr. Baek-Young Choi and Dr. Ken Mitchell) CS 5521 Network Architecture-II (Instructor: Dr. Deep Medhi) CS 5526 Network Routing (Instructor: Dr. Deep Medhi) ECE 5590WC Wireless Communications (Instructor: Dr. Cory Beard) OPNET Technologies, Inc. is a leading provider of solutions for managing networks and applications. OPNET's best-in-class solutions address application troubleshooting, application monitoring, network monitoring, network configuration management, network planning , and network simulation. OPNET’s solutions have been operationally proven in thousands of customer environments worldwide, including corporate and government enterprises, government and defense agencies, network service providers, and network equipment manufacturers. For more information about OPNET and its products, visit www.opnet.com. |
