Application Notes:

Analog radio system redesign utilizes TDM and IP backhaul

Overview

An East coast county emergency network was faced with retiring 4-wire E&M leased circuits by their local carrier. These circuits were utilized as the primary connectivity for their mission critical radio system between dispatch and 4 fire stations.

Challenge

The benefits of upgrading to Ethernet/IP included a more feature rich and easily maintained system, but the cost and training associated with an end-to-end system upgrade was a challenge. Although the county was confident they could deploy fiber to some of their stations, leased T1 backhaul was the only option for sites where deploying fiber was not cost effective. In addition, audio fidelity when transitioning from analog to digital was a concern so the equipment selected would need to maintain audio quality while integrating their existing voters, receivers and radios. The solution would need to accommodate T1 and IP backhaul, resulting in a mixed IP/TDM network solution.

Solution

The county preferred a single vendor to simplify support, maintenance, and training for their staff. After careful consideration TC Communications was selected. The JumboSwitch TC3846-6 was selected for the IP backhaul where the county was able to install private fiber to their stations. The Mini Channel Bank TC8614 was selected for stations with leased T1 backhaul.

The county was particularly considerate in selection of the analog to IP conversion equipment for this solution. To satisfy these requirements the TC3846-6 was selected for its unique design and ability to provide linear audio frequency response at audio ranges from 300Hz to 3000Hz. Many radio over IP solutions are session initiated protocol (SIP) based; SIP and voice over IP (VoIP) can cause audio compression and have difficulty handling variation in latency, resulting in poor audio quality. See this write up for a more in-depth discussion on audio fidelity in 4-Wire E&M to Ethernet conversion. The TC3846-6 maintains high audio quality over leased, fiber and microwave backhaul and provided high audio quality for the county's radio system. In addition, the TC8614 allowed them to accommodate leased T1 backhaul utilizing equipment from a single vendor proven in other deployments.

Benefit

The county's ability to maintain their existing voters, radios and receivers resulted in significant cost savings when compared to an end-to-end upgrade. The solution proposed by TC Communications was simple, quick and flexible allowing for a speedy migration completed without interfering with daily operations.

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