© 2008 OPNET Technologies, Inc.
Title: Link Failure Monitoring Using Network Coding
In network tomography, we seek to infer link parameters (such as delay) inside a network through end-to-end measurements at (external) boundary nodes. As can be expected, such approaches suffer from identifiability problems; i.e., even with the maximum volume of data obtainable from such end-to-end probes, a large number of the network topologies are not identifiable. A basic result characterizing network topologies which are not identifiable is first derived. Then, we introduce an innovative approach based on linear network coding that overcomes this problem, given an appropriate choice of network code coefficients. OPNET was used to confirm the validity of the claims. For that, we implemented Network Coding scheme in OPNET and based on that our link failure method got tested. More information about OPNET implementation is available at our homepage.
Title: End-to-End delay measurements using unicast probe sending (Simulation)
Measurement and analysis of the network behavior are crucial to understanding the Internet performance and designing appropriate control mechanisms for better performance. End-to-end measurement is a common tool for network performance diagnosis, primarily because it can reflect user experience and typically requires minimal support from intervening network elements. This project aims to determine delay of each link in a network by just sending probes from boundary nodes. Probes should be sent out in a way to have minimum (ideally none) effect on the others. In other words, probing too frequently, even when traffic is minimal, causes the delay along the network varies based on the other probes currently within the network. In some cases it could results in non-symmetric delay measurement. We used OPNET to simulate end-to-end probe sending method in networks with different sizes (10 nodes – 40 nodes) in order to analyze networks behavior.
Title: Research on Wireless Mesh Networks
802.11 wireless LANs for broadband wireless access constitute a growing success story. Their deployment in single-cell (i.e. single AP) scenarios (homes, small business and hotspots) is well-supported by current .11 technology. However scaling such networks to the enterprise environment to serve a large number of simultaneous users with voice and data services while providing coverage remains a challenge. A promising architectural solution consists of a two-tier multi-cellular, multi-hop approach to WLAN network design whereby an AP mesh provides the infrastructure for communication between mobile clients. Implicit in this is a direct wireless inter-connection between mesh nodes which all route traffic (only some of which are APs with associated clients, and a very small fraction act as gateways to the wired Internet).
Our research seeks to advance the state-of-art of such .11 based multi-hop mesh networks by undertaking an integrated cross-layer approach to innovations at Layers 1-3 (joint PHY/MAC/Network). Optimizing of such networks will require on-line tuning of key protocol parameters at various layers (hence leading to an Adaptive Mesh). Currently we are investigating
* The impact of Physical Carrier Sensing (determined by carrier sensing and/or receiver sensitivity threshold) on MAC performance as a function of network topology
* The impact of Multi-radio/node on MESH network performance, particularly the new degrees of freedom that it offers for joint channel assignment and link-aware routing as components of an optimized .11 AP mesh.
We have developed several modifications to the default OPNET 802.11 models to support our research, and continue to use OPNET as the base for simulation experiments supporting the above research topics. Among other modifications/updates, we expect to add in support for channel-aware routing protocols.
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