Rethinking combined voice and data networks for utilities

Making the case for DMR as the platform of choice for utilities that are considering a multiuse distribution automation investment.

Traditionally, a common wide-area LMR networking scenario has been to deploy separate networks for voice and data, accepting the resulting duplication of infrastructure and operational costs.

Unfortunately, when these combined voice and data networks were deployed, they struggled to deliver the QoS demanded for mission-critical voice and data services; system resources were often locked out by either voice or data to the detriment of the other service.

This is unacceptable for real-time, mission-critical applications.

Trunked DMR Tier 3 is an all-digital standard that reignites the opportunity to rethink wide-area PMR voice and data solutions that deliver combined networks without those limitations.

The catalyst for the rethink is the well-documented channel capacity doubling of DMR’s two-slot TDMA technology, and when combined with resource-management facilities of trunking, DMR Tier 3 offers a fresh perspective on combined voice and data networking.

It’s all about trunking

The trunking capability of DMR Tier 3 offers call management and network resource optimisation without any human intervention, while central infrastructure equipment redundancy and base stations can support either control or traffic capabilities to deliver mission-critical level service.

Centralised configuration of users means operators can manage and monitor the network efficiently, supported by extensive status and capacity reporting. This, in turn, provides invaluable network visibility, making it simpler to optimise the network, easily adding or moving capacity as needs always change.

DMR Tier 3’s greatest strength is possibly its reliable delivery of mission-critical voice and SCADA over a common network, with each receiving its guaranteed quality of service.

The trunked network operator has many options to define how the network behaves, such as:

• ability to prioritise network resources for voice or SCADA traffic,
• reserving traffic channel resource allocations for voice, or SCADA so that dynamic network loading does not impact QoS,
• concatenated logical channels that can deliver higher data rates, especially if resources are idle,
• call pre-emption and queuing based on call priority and network loading,
• efficient support for SCADA signalling via the control channel, for sites with low SCADA device counts while still offering uninterrupted voice call support.

How does this make a tangible difference for network providers and users?

Let’s consider a distribution utility’s wide-area communication challenge: dependable, mission-critical voice and data communications across the entire network.

Mobile field workers rely on voice-based, workgroup-centric, dispatch services for a safe and efficient work environment under all conditions - from BAU to black start.

Over the same coverage area, remote devices along distribution lines monitor and control the distribution grid. These devices provide line visibility and management to deliver required grid reliability metrics. A SCADA control room application polls for, and responds to, remote event notifications from the remote devices.

SCADA protocols such as DNP3 or IEC 60870-5-10x, used by remote devices, provide robust communication over narrowband PMR networks. However, while SCADA messaging is typically only 50-300 bytes in size, message timeouts and latency will generate retries and alarm conditions in 10 seconds, should they be delayed or fail.

This is where trunked DMR’s flexible, centrally managed timeslot allocation becomes useful. One or more timeslots can be permanently allocated to regular, time-critical, SCADA polling activities, with the remaining site resources available on demand for voice and other data traffic.

This effectively means you have two independent network services, deployed over common infrastructure, but realising the benefits of a single-vendor, simpler ROI, and a single network to design, deploy, maintain, harden and secure.

This article originally appeared in issue 4 of Tait Communications’ Connection Magazine.