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Garzillo.Net solution for Radio Over IP

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We are working with new business partners from “Solutions IP” on innovative projects. A solution was created integrating multiple UHF and VHF repeaters in the Thetford Mines region for Land Mobile Radios (LMR), covering a large area in central Quebec.

In typical land mobile systems, a central dispatch console or the base station control communications to the disparate handheld or mobile units in the field. The systems might also employ repeaters to extend the range of communications for the mobile users. LMR systems can be as simple as two handheld units communicating between themselves and a base station over preset channels. Or, they can be quite complex, consisting of hundreds of remote units, multiple dispatch consoles, dynamic channel allocation, and other elements.

A Land Mobile Radio (LMR) system is a collection of portable and stationary radio units designed to communicate with each other over predefined frequencies. They are deployed wherever organizations need to have instant communication between geographically dispersed and mobile personnel. Typical LMR system users include public safety organizations such as police departments, fire departments, and medical personnel. However, LMR systems also find use in the private sector for activities like construction, building maintenance, and site security.

These repeaters are used in a commercial communications network, and work using DMR standard for voice communications, which ensures not only excellent audio quality as well as some extra features such as telemetry, private calls between stations and telephone system and SMS messages.

DMR stands for Digital Mobile Radio, it is an open digital mobile radio standard defined by the European Telecommunications Standards Institute (ETSI) Standard TS 102 361 parts 1–4[1] and used in commercial products around the world. DMR, along with P25 phase II and NXDN are the main competitor technologies in achieving 6.25 kHz equivalent bandwidth using the proprietary AMBE+2 vocoder. DMR and P25 II both use two-slot TDMA in a 12.5 kHz channel, while NXDN uses discrete 6.25 kHz channels using frequency division.

DMR was designed with three tiers. DMR tiers I and II (conventional) were first published in 2005, and DMR III (Trunked version) was published in 2012, with manufacturers producing products within a few years of each publication.

However, for allowing the multiple repeaters to function as an integrated network, the interconnection of repeaters is required.

The main difficulty was the direct visibility of the repeaters for establishing the wireless links, and given budget limitations of the network operator, the rental of dedicated voice lines for this exclusive purpose was also discarded, and in this way, an IP integration was made ideal for the customer, given most of the sites had access in some manner to an internet connection.

The topology bellow was proposed to the client:

Fig.1: Network Topology for Land Mobile Radio with nodes on multiple locations and interconnected by the Internet

The “LMR gateways” were created using Mikrotik-RB951Ui-2HnD as hardware, which, in addition to being cost-effective, already has all the necessary software resources for this project.

 

The VPN Tunnels were created among the routers to ensure that IP packet traffic and routing is done in, ensuring the security and privacy of the network on the Internet.

In addition, QoS rules were created to prioritize the traffic of the audio packets of the repeaters inside the tunnel, since in some cases we were forced to share the tunnel band with other local network applications that were already in operation, enforcing network isolation with firewall rules.

The internet connections used are provided by cable modem or by xDSL, which ensures the cost effective for the data links of this network, which in the Point of Presence were shown with a high SLA figure.

The repeaters used at these sites were manufactured by Hytera Model-RD982. Currently this client is trying out some dispatch solutions to be used on this voice network and added value features of the network.

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