Electric utilities are in the midst of a communications renaissance.
Legacy networks built on SONET, frame relay and carrier-leased circuits are being replaced with newer, packet-based telecommunications networks similar to those found on public carrier networks. Utilities have multiple network technologies to choose from: Standard IP routing, MPLS with Traffic Engineering (MPLS-TE), MPLS Transport Protocol (MPLS-TP), Carrier Ethernet and software defined networking (SD-WAN) are the most common. How do you know which one is right for your utility?
As a telecommunications engineer with Burns & McDonnell, I have spent the past 17 years working in communications, the last six with these technologies. In this blog series, I’ll look at each one, pointing out the features that could make it an attractive solution for a utility. But first, let’s take a quick look at the current state of utility communications and the challenges new packet networks are called to address.
Back in the 1980s, many utilities began implementing time division multiplexed (TDM) communications to transport SCADA data and transmission line teleprotection information between substations and from substations back to their control centers. Many either leased or installed their own fiber and built SONET networks with fiber backbones capable of communication speeds in the low hundreds of megabits per second order of magnitude.
These systems dedicate capacity to each circuit and don’t share capacity dynamically. A 64-kbps circuit always reserves this capacity for a single device, regardless of whether it is transmitting data.
In the past decade or so, AT&T, Verizon and other members of the carrier industry shifted from TDM-based equipment to packet-based technologies. Communications equipment vendors followed suit. With carriers eliminating or raising prices on copper-based DS0 and T1 services, many utilities started looking at building packet-based networks themselves.
I am not here to pronounce the end of SONET, but the shift toward packet-based technologies has begun.
Utilities Making the Switch
Several utilities started the movement to packet networks by installing routers in substations for card readers, video and other security-related equipment. Other applications, including metering, digital fault recording, voice over IP (VoIP) and transform monitoring, also began using IP services. The next logical question: Is a standard IP-routed network suitable for SCADA and teleprotection?
By standard IP routing, I am talking about rather simple interconnected routers that run an interior gateway protocol (IGP), such as open shortest path first (OSPF) or intermediate system-intermediate system (IS-IS). To isolate IGP segments and protocol chatter, larger networks might be further segmented and run an exterior gateway protocol (EGP), such as Border Gateway Protocol (BGP).
Networks use these protocols to update a routing table that indicates the networks that are reachable via various router interfaces. It’s possible, for example, to set up virtual private networks (VPNs) and isolate the data types to keep metering and security separate from SCADA. It’s also possible to use layer 2 VLANs and IP header information to mark traffic and perform basic network quality of service.
Standard IP routing, however, falls short if all host devices cannot be replaced with Ethernet-capable devices. In that case, a utility is left supporting both TDM and IP networks until every device in the system is Ethernet-capable. While serial-to-IP converters can help bridge the gap, some protection and SCADA protocols such as IEEE C37.94 and frequency shifted tone protection cannot be reliably converted to Ethernet.
Many of the technologies we’ll discuss in upcoming blog posts are designed to support existing TDM communications while upgrading to a packet network, allowing a smooth migration.
Next up: We’ll take a closer look at MPLS-based technologies and how they add capabilities to a standard IP-routed network to support utility applications.
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