The IP edge for LMRs

   Internet Protocol has become the underlying technology for all forms of modern communication. Whether it's cellular operators delivering IP-based applications such as voice over IP (VoIP) and video telephony or 911 PSAPs, most everything in telecommunications today runs over IP at some point.

   Certainly the evolution to IP-centric communication has not been without considerable doubt. Some veteran radio techs still believe that IP networks are too unreliable to use for mission-critical public safety communications. The truth is, however, that IP networks are inherently resilient, and can be distributed across multiple sites by using a simple peer-to-peer architecture that has no single point of failure. The fault tolerance, adaptive routing, and disaster recovery capabilities of IP make it possible to route packets via a different path if the standard path goes down.

   Businesses, military and governments all rely on IP to transport mission-critical communications in the form of VoIP, video calling/conferencing, e-mails and text messages. Public safety agencies that depend on land mobile radio (LMR) systems for their mission-critical communication can also benefit significantly from IP. Newer state-of-the-art LMR systems take advantage of IP to provide operators with simplified network expansion, end-to-end digitized voice, improved alarm and performance monitoring, and remote access.

   Using an all-IP backhaul allows the use of commercial off-the-shelf components. An all-IP network, utilizing standard routers and switches, allows Ethernet to be used to connect the repeaters at a site to each other and to repeaters at other sites. Adding a repeater becomes as simple as ensuring that there are available connections on the antenna network and adding an Ethernet cable to the switch at the site.

   If you run out of positions on the existing switch, it can simply be replaced by a larger one. When switches are added or restored to the network, they and the existing switches at all the sites automatically discover each other and start working together. IP connectivity means that no proprietary switches are only available from a single source.

   An IP capable repeater is able to take the digitized voice stream out of the air and convert it to IP for connection directly to a switch. No analog audio is sent over the backhaul infrastructure. Digitized voice can be uncompressed, compressed and even encrypted. Digitized voice also means greater immunity from radio frequency interference and no loss of audio quality as the voice information is sent via the backhaul to another site or the console.

Alarm and monitoring

   The Simple Network Management Protocol (SNMP), a component of the IP Protocol Suite, can be used to monitor the status of the LMR network. SNMP agents expose management data on the site repeaters and other network components as variables. The managing system can request the data, or alarm traps can be used to send the data automatically if values vary from pre-defined parameters. The SNMP also permits active management tasks, such as modifying and applying a new configuration.

   There are a variety of SNMP Managers that run on standard computers and can be used to collect the data or receive alarm traps. These managers can generate e-mail messages to warn of alarm conditions.

   Operational statistics can indicate how often the equipment is used, providing information that can be used to determine if the system has sufficient capacity during busy times. The data collected can also be used to detect trends that show increased usage over a period of time, enabling an operator to anticipate needed expansion before the system becomes overloaded.

The 'native' IP difference

   It is important to note, however, that "native" IP implementations are absolutely critical for LMR operators to take full advantage of the performance, reliability and operational improvements that IP provides.

   Operators need to be certain that the system they are purchasing is fully IP from the consoles, through the radio network, right up to the repeaters. For systems that are IP by design, replicating the resilience of IP networks with a peer-to-peer communications architecture, and with network management built into each component, comes naturally.

   Watch out for systems using an IP Gateway to convert data from IP to a proprietary network backbone, as seen in Figure 1. The inherent complexity of retrofitting legacy circuit-switched systems adds reliability challenges, as well as complexity in design, implementation and operations. In addition, the expansion of such a system will be more difficult and require proprietary switches and equipment.

   A "native" IP architecture (Figure 2) has built-in autonomy and survivability, delivering a system that is reliable, highly available and doesn't have to involve additional cost or complexity.

   It would be in the best interest of any LMR professional to become proficient in the maintenance of IP networks, including switches and routers. People who are unfamiliar with IP networks will be at a significant disadvantage and potentially left behind as the industry moves to new, IP-capable LMR networks. Sticking with four-wire analog links with tone remote is not a solution for the future — the advantages are too great to ignore.

   Sherman Banks is a technical sales engineering support manager for EADS Secure Networks North America with more than 20 years of wireless communications experience.

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