Making sense of IP for public safety
Public-safety communications have seen many changes in the past 30 years. Lately the integration of IP into public-safety networks has generated much interest. At the same time, IP seems to be greatly misunderstood. Armed with the proper information, however, it is possible to accurately evaluate these systems.
In the beginning, IP was mainly associated with non-voice traffic such as e-mails and computer files. A few years ago, some systems started to use digitized voice that could be sent in packets over the same wired IP data networks; this was called voice over IP (VoIP). VoIP is now starting to appear at 911 public-safety answering points as trunk lines.
Radio over IP (RoIP) refers to the use of IP networks as the backbone to carry the voice traffic (VoIP) between radio base stations and console equipment. Today, IP networks can carry both voice and data for public safety. But because voice is so important to public safety, we can focus primarily on voice systems using RoIP.
Why consider RoIP? First, the interconnections among base stations, consoles and other infrastructure can be made more reliable because of the ring and mesh configurations common with IP networks. These configurations are inherently resistant to single or multiple points of failure. Second, existing private IP LAN or WAN network assets that a city, county or state may have can be used to carry the connections that formerly required special leased lines to the base stations.
Third, the equipment in the IP network (routers, hubs, computers) is commercial-off-the-shelf (COTS) and can be sourced from other manufacturers besides the radio vendor, leveraging the decreasing costs of the digital Moore’s Law curve. Fourth, IT personnel from the data or CIO department can maintain the IP network, allowing the radio technicians to focus on the radio side.
Unfortunately, there has been some misunderstanding regarding the use of IP for mission-critical communications. First, the public Internet is subject to hackers and other security risks. Second, VoIP had an inauspicious start in Internet telephony some years ago. Those early VoIP systems suffered from delays in the voice (latency), poor fidelity and other problems. Let’s try to demystify IP so we can better assess its use in public safety.
VoIP is just one of several forms of digital voice communication to which we have become accustomed. In the 1960s, the public telephone systems in the U.S. began to digitize some of their infrastructure in an attempt to simplify telephone trunk engineering.
Those early systems set the standard for digitization at 64,000 b/s. Those data rates were high because the voice coders (vocoders) used to digitize the voice were relatively primitive, and telephone customers demanded high voice quality.
In the late 1980s, APCO saw that digital radio was becoming an affordable technology with many advantages and, through Project 25, they standardized the digital formats for public-safety communications (see related story page 30). These formats defined the type of vocoder (IMBE, after a long period of testing), the feature set (ID, emergency, encryption, etc.) and the handshake protocols for either conventional or trunking operation that would allow a radio of brand X to talk to brand Y.
VoIP is the next logical progression — taking the digitized voice and instead of sending it as a continuous data stream, breaking it into packets that can be sent over an IP packet-switched (as opposed to circuit-switched) backbone network. VoIP has, in fact, been used for mission-critical (but not life-safety-critical) applications over wired networks in the financial services industry. Wall Street, which stands to lose millions of dollars in revenues if the trading systems used by brokers were to malfunction for even a minute, has found that VoIP is reliable, and they are increasingly adopting such systems.
However, systems for public safety have unique needs, including priority/emergency, security/control, reliability and extensive use of the mobile radio environment, which experiences fading conditions. Next month, we’ll examine these issues in depth.
John Facella is the director for public-safety markets at M/A-COM. Prior to joining M/A-Com, he spent 20 years at Motorola in public-safety wireless communications.
