Smart Grid Communications Networks: The Public or Private Debate
The public vs. private networks debate has been raging for some time now. Why would utilities prefer either privately-owned or public carrier networks for their communications needs? Could the most optimal network be conceivably a combination of both? We spoke at length with Narasimha Chari, CTO and co-founder of Tropos Networks, who put in his two cents on the subject.
Q: What factors determine the choice of using a private or public network?
A: It really depends on which applications are most critical to the utility. Seven factors were outlined by the UTC's response to a DOE RFI on smart grid communications needs: they are availability, survivability, coverage, latency, security, control as well as life cycle. I believe that private networks can fulfill almost all the requirements laid out by utilities and cities better than public networks, but that doesn’t mean that public networks do not have a role to play.
Q: In terms of availability, why would a utility or city prefer private over public networks, or vice versa?
A: Availability essentially means how reliably a system performs over time. Mission critical communications require network availability of 99.999% or more, or less than 5 minutes of downtime a year. Private wireless networks can typically be engineered to much higher levels of reliability than public networks, through a combination of wireless technologies and architectures. For example, mesh architectures afford a high degree of resiliency through being able to leverage multiple redundant communication pathways. With a private network, utilities can also ensure that mission-critical traffic is properly prioritized and reliably delivered, something that is hard to ensure over public wireless networks, especially during emergencies and natural disasters when public networks can degrade significantly due to traffic congestion.
Q: And how about survivability? Do public and private networks have the same resiliency?
A: Networks need to be environmentally hardened to withstand adverse conditions, as well as have access to backup power during outages. Private wireless networks can leverage multiple technologies to meet these challenges; in particular, Tropos’ networks utilize multiple spectrum bands, and resilient mesh network architectures employing sophisticated algorithms for channel selection, power control and interference mitigation, but public carrier networks have a mixed record in that regard.
To use a real-life example, Southern Company, a utility with 4.4 million customers, noted in a February filing with the FCC that they had to rely on their private network to aid in power restoration after an extended weather-related outage - due to the lack of redundancy, weather-hardened facilities, and routine maintenance for the networks – as the public network service is often unavailable and cannot be restored until after electric utility service has been restored. When it is restored, it can quickly become over-congested.
Q: So in terms of survivability and availability, private networks appear to be pulling ahead in the race with public networks. How about measuring them in terms of their network coverage?
A: Well, the ideal goal for coverage within a target area is of course the holy grail of 100%. Given that utilities typically do not operate specifically in one type of geographical environment (urban, surburban and rural) but have a mix of all types, the coverage goal is quite the challenge, for both private and public networks. To meet this challenge, private networks typically utilize a combination of wireless technologies to achieve their coverage goals. Commercial public carriers have an additional challenge in providing ubiquitous uniform coverage, as their business model and systems are optimized around providing coverage and capacity to the largest concentrations of consumers possible, versus being designed to ubiquitously cover an entire service territory. This means that unserved or underserved areas are often not economical for a public carrier to cover. At the same time however, I believe that there will be areas within a service territory where private networks are not feasible or cost-effective to deploy, and where public networks will have an important role to play.
Q: The last four factors you mentioned were latency, security, life-cycle and control. What would you say are the key takeaways in comparing private and public networks using these factors as measurements?
A: I would say that once again, these depend on the particular applications which are needed by different utilities and cities. For example, with utilities, mission critical applications such as distribution automation and wide-area monitoring and control have very stringent low-latency requirements, whereas others such as advanced metering infrastructure (AMI) are less demanding. In general, private networks have lower latencies (10-100 millisecond range) compared to public cellular networks, which are deployed in the 100-1000 millisecond range.
The same can be said for security and control—it depends on how secure the utility or city needs it to be, and how much control they require over their networks. Private networks are specifically designed for the utility to exercise control over desired levels of coverage and performance and the kinds of technology to deploy. Additionally, utilities operate critical infrastructures that are also subject to regulatory oversight and while public carrier networks can provide secure VPN connections, private networks provide utilities with a much greater degree of control over security, enabling them to demonstrate compliance with reliability and security mandates from Federal agencies such as NERC. Obviously, having a fully owned and controlled private network comes with certain associated costs (capital as well as operational) and those need to be traded off against the benefits of the approaches, and in some cases public networks may be the better choice for a utility.
Life cycle is also a cost issue. Cellular timescales for upgrades can be short, often 2-4 years, whereas utilities typically have longer investment depreciation timelines. Implementing cellular technology means that upgrades have to be ongoing or assets may become obsolete and “stranded.” This can be extremely cost-prohibitive for utilities and cities, especially if they have to think about upgrading millions of deployed meters, for example.
Q: So to sum up: can a utility have its needs fulfilled by just one type of network, or the other?
A: I believe that most communications needs will be fulfilled by private networks, but public cellular networks, will still have an important role to play – to provide coverage in difficult areas and to cost-effectively and quickly provision connectivity to certain non-mission-critical utility applications. I’m not alone in my opinion: In their filing with the DOE, the UTC also determined that the majority of utility applications will be enabled by private networks, although commercial carriers will be able to support some of their applications . A recent report entitled Smart Grid Networking and Communications from Pike Research noted that “grid applications with strict performance requirements, high reliability requirements, or high cost sensitivity tend toward utility-owned (private) and operated infrastructure. Other applications, such as AMI backhaul applications, will often use public infrastructure.” Given the wide diversity of utility service territories, the regulatory requirements and their specific communications needs, it is probably safe to say that both public and private networks have important roles to play in enabling smart grid communications. |
