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To provide the public safety community with a better understanding of what to expect from new and emerging networking technologies, and accelerate the standardization and utilization of such technologies.
M. R. Souryal, J. Geissbuehler, L. E. Miller, and N. Moayeri, Real-Time Deployment of Multihop Relays for Range Extension

Evaluation of Project 25 Inter-RF Subsystem Interface Behavior

Simulation tool
NS-2 simulation model


There is a need for evaluating the performance of the P25 Inter-RF Subsystem Interface (ISSI) system in order to gain insights on the overall system performance including the audio quality and latency in set-up. As more testing and demonstration events are planned for testing ISSI prototypes and products, a simulation tool that models the behavior of the ISSI system may come in handy for planning these experiments, but also providing additional feedback on the system performance for various deployment configurations, parameters, and as ISSI is interfaced with other technologies. This is especially true for large deployment topologies where experimental set-ups and demonstrations may be too costly to realize.


Our objective is to help users gain insights on how the ISSI interface works, which should permit the users to simulate various deployment configurations and parameter settings without the need for procuring and setting up expensive testbeds and demonstrations.

Simulation Tool

We are developing a tool that models the P25 ISSI protocols and provides the user with a graphical user interface.
The ISSI network simulation tool consists of
  1. the Graphical user interface (GUI) , which permits the user to
  2. the ISSI simulation model, and
  3. the server.

Work flow of the tool

Work flow of the ISSI simulation tool


The GUI has various panels that show
  • the graphical topology of the network,
  • a palette of icons for creating a network, and
  • the topology and confirguration parameters.

    Sample of a screen of the Graphical User Interface

    A sample screen capture of the Graphical User Interface (GUI)

    It also has various panels to show the statistics gathered for the simulation of the scenario. The statistics can be used to evaluate capacity planning of the links interconnecting the Radio Frequency SubSystems (RFSSs); and delays and packet loses caused by the call's path, congestion, and elements within the network.

    Sample of a statistic screen

    A screen shot of a select statistic

    NS-2 simulation models

    We are developing a model for the ISSI as an extension to the NS-2 simulation platform. NS-2 is a discrete event simulator for networking research. NS-2 contains models for many of the existing network technologies and protocols upon which new protocols can be added or existing ones extended or modified. Some example protocols that already exist for NS-2 that can be used to support the P25 ISSI model are Ethernet, IPv4, User Data Protocol (UDP), Session Initiation Protocol (SIP) and the Real-time transport protocol (RTP).
    Our ISSI model (an NS-2 extension) includes the call control manager, mobility manager, and transmission control manager as specified in TIA-102.BACA-A, as well as extensions to existing NS-2 Session Initiation Protocol (SIP) models.
    - The call control manager enables the establishment and termination of talk group calls and subscriber unit to subscriber unit (SU-to-SU) calls, as well as the various configuration parameters (e.g., priority, availability check, emergency call/ non-emergency call).
    - The mobility manager handles the movement of the subscriber units (SU) from RFSS to RFSS.
    - The transmission control manager hanldes the transmission of the RTP (e.g., voice) packets.


    The server is based on Java. The server manages user authentication, retrieves the script file, launches the simulation, monitors the simulation's progress, and provides the result files.


    Presentation on modeling and network simulation, an introduction to the ISSI messages and procedures, and an example network scenario.


    Nada Golmie
    Emerging and Mobile Network Technologies Group