Emergency Communications 101: Part II

Often public safety telecommunication personnel are left out of the loop as technology becomes more and more complicated. In Part I, basic radio component were described. In Part II, I discuss some of the terms and changes facing telecommunicators today...


Last month, I went over a few basics to help public safety communications center managers understand some of the technological language involved in the work we do every day. I’m sure I’m not alone in wishing that all we needed to know is that when we put our foot down on the pedal somehow magically our voice is transmitted out to our officers and when they hit a little button they get to talk to us. Of course in this fantasy world, there are never dropped or garbled transmissions. And definitely never, never those weird alien voices and sounds. But along with desire that things would magically happen and always work, most telecommunications professionals also have an insatiable appetite to know things. Some view this as nosey, but I see it as an asset for someone who asks really personal questions for a living. With this need for understanding for how things work and the necessity to bring communications through today’s evolutional environment, we desire basics. This column will be part two of a series designed to provide a bit of this understanding.

Land Mobile Radio (LMR)

Cassidian Communications, one of the leading manufacturers of military and public safety hardware, defines LMR as “a broad term that encompasses all licensed two-way ‘push-to-talk’ mobile radio communications.” Terrestrial users in vehicles (mobiles) and on foot (portables) depress a button and hold it down the entire time they are talking. With LMR only one speaker can be on an audio channel at a time. Two types exist within LMR-Conventional and Trunked. Conventional systems use a dedicated frequency (channel) for each group of users. Trunking uses a pool of channels which can be used by different groups of uses (talkgroups). A trunked system basically shares all the frequencies while a computer controls where a transmission goes looking for the next open channel. These LMR trunked systems are similar to the trunked lines of 9-1-1. LMRs can be either analog or digital.

Project 25 (P25) Standards

P25 is a suite of standards for digital radio communications developed by the Association of Public Safety Communications Officials (APCO) and administered by the Telecommunications Industry Association (TIA). Cassidian explains, “The P25 suite of standards was developed to address a number of spectrum and interoperability issues related to LMR communications.” Some of the issues included the Federal Communications Commission’s (FCC) mandates reference radio efficiency, improvement of voice quality, earlier LMR restrictions on component interoperability and completion and the growing emphasis on encryption and data. P25 standards are designed to assist in the transition between analog and digital systems. When a radio or system is designated P25-compliant it means it follows these standards.

Legacy vs. Enterprise

In general, legacy equipment denotes the old-style analog radios. They were designed to work only within their manufacturer and are not interoperable with other products or manufacturers. Much of the push towards interoperability stems from incidents where diverse agencies utilized different legacy radio systems and were unable to talk to each other even if they were just in another room or on the other side of the building. Enterprise systems are defined as the new analog or digital radio systems that are designed to be compatible.

Next Generation 9-1-1 (NG9-1-1)

Historically, 9-1-1 systems were only able to collect data through land-based telephone systems. NG9-1-1 is an initiative designed to bring public safety telecommunications up to speed with the technology being used by the community. This initiative is aimed at upgrading the infrastructure so that Public Safety Answering Points (PSAP) can receive and transmit not only voice, but images, text, video and data to a variety of sources including mobile data terminals (MDT) and other wireless devices, such as cell phones, tablets and laptops. Spearheaded by the National Emergency Number Association (NENA), work towards implementing NG9-1-1 began in 2003. Currently, there are several PSAPS in various stages and the impact of the new technology is being compiled and studied.

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