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Investigation of a Packet-Switched Inter-System Interface for Land Mobile Radio SystemsTsiakkouris, Stavros A. 01 August 2002 (has links)
Traditionally, and up to this date, Land Mobile Radio (LMR) systems have been interconnected via leased lines and microwave links across circuit-switched networks. With the recent deployment of digital LMR standards such as the Association of Public and Communications Officials (APCO) Project 25 and the Terrestrial Trunked Radio (TETRA), traffic exchange has become more bursty and non-uniform, and as such, less suitable for circuit-switched networks.
This thesis proposes a framework for a packet-switched Inter-System Interface (ISI) for LMR systems. Packet-switched networks have the advantage of supporting traffic integration, utilize capacity efficiently, scale easily and seamlessly, and eliminate single points of failure by providing a distributed architecture. Session Initiation Protocol (SIP) signaling messages are defined for setting up and tearing down unit-to-unit calls across the ISI. The Session Description Protocol (SDP) is used to describe how the voice calls are encoded. Voice packets are exchanged between LMR users using the Real-Time Transport Protocol (RTP).
Based on the proposed framework, we develop a simulation model to investigate the performance of the ISI when different numbers of LMR users try to establish unit-to-unit calls across the packet-switched ISI. Three packet transport technologies providing Wide Area Network (WAN) connectivity are considered, IP, ATM, and Frame Relay. The results indicate that a packet-switched ISI can take advantage of statistical multiplexing techniques to distribute network resources more efficiently. Quantitative results are obtained for throughput and link utilization. When using an access link providing T1 service, we show that the End-To-End (ETE) delay, and delay variation can be controlled at levels capable of supporting the timely delivery of real-time voice packets. Assuming link utilization is maintained below 100%, the maximum ETE delay experienced in all three packet transport technologies considered is 58 ms and the maximum call setup time is less than 300 ms.
An ATM WAN provides the best performance for all time-dependent metrics considered, i.e., ETE delay, delay variation, and call setup time. An IP WAN provides the highest bandwidth efficiency. Selecting the appropriate packet transport technology for the WAN is a tradeoff between the delay that can be tolerated by the voice packets traversing the LMR network and the cost of bandwidth on the access link. / Master of Science
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Security in Packet-Switched Land Mobile Radio Backbone NetworksThomschutz, Hans Olaf Rutger 18 August 2005 (has links)
Spurred by change in government regulations and to leverage lower-cost technology and services, many land mobile radio (LMR) operators have begun transitioning from circuit-switched to packet-switched backbone networks to handle their future communication needs. Due to the unique demands of packet-switched backbone networks for LMR, it may not be wise to carry over the previously implemented security methods used with circuit-switch systems or to treat an LMR backbone as a regular packet-switched network. This thesis investigates security in packet-switched LMR backbone networks to identify security issues in packet-switched LMR networks and provide possible solutions for them. Security solutions that are examined include different types of virtual private networks (VPNs), various encryption and keying procedures for safe communication, and logic behind how and where to implement security functions within the network. Specific schemes examined include IP Security (IPSec), OpenVPN, Virtual Tunnel (VTun), and Zebedee. I also present a quantitative analysis of the effects that the solutions have on packet-switched networks, in terms of link utilization, and on voice traffic, in terms of delay and delay jitter. In addition, I evaluate, in general terms, the additional cost or complexity that is introduced by the different security solutions.
Simulation with OPNET Modeler was used to evaluate how the various security schemes affect voice communication and network performance as a whole. Since OPNET Modeler does not provide models of security functions, the source code of the transceiver system models was modified to introduce additional overhead that is representative of the various security solutions. Through experimentation, simulation, and analysis of the security schemes considered, it was found that the most effective security scheme overall for a packet-switched LMR backbone network would either be IPSec or OpenVPN implemented at the base stations and end-hosts. Both security schemes provide strong encryption, flexibility, and are actively supported. However, if bandwidth is scarce and flexibility is less important, then a security solution with less overhead, such as VTun, should be considered. Thus, one has to balance performance with security to choose the most effective security solution for a particular application. / Master of Science
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