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Project: ALERT-2 Protocol Development

The ALERT-2 project laid the foundation for the development of a next-generation suite of wireless network protocols for hydrologic warning systems (HWS). The project documented the requirements for next-generation wireless protocols for HWS networks and outlined a technical approach to meeting those requirements.

Hydrologic warning systems, (also called automated flood warning systems, AFWS), are wide-area, wireless sensor networks that collect hydrologic sensor data from large, often remote, areas. These systems support rain gauges, stream gauges, and to a lesser extent meteorological and other environmental sensors. The data collected by these systems are used to generate flood predictions and warnings. Because flash floods can develop quickly in some terrains, these data must be collected and made available to forecasters in near-real-time. These systems have been deployed in the U.S. and elsewhere since the 1970s. Many of these systems use the ALERT (Automated Local Evaluation in Real Time) protocol. The ALERT-2 protocols were intended to replace the original ALERT protocol.

The ALERT-2 Requirements Specification created as part of this project describes the limitations of the original ALERT protocol, documents the functional requirements for new protocols for HWS networks, and derived technical requirements from the functional requirements. This document was the result of numerous discussions HWS vendors, HWS operators, those who rely upon the sensor data collected by these systems, and federal, state, and local officials.

The original ALERT protocol (which the ALERT-2 protocols were intended to replace) transmits fixed-format, four-byte message at 300 bits-per-second (bps). The ALERT protocol is inefficient, unreliable, and difficult to extend. ALERT is a one-way, transmit-only protocol: remote stations transmit messages containing hydrologic sensor data towards the base station, which collects sensor data from the remote stations and forwards the data to applications and users. However, the protocol contains no provision for remote stations to receive messages. ALERT stations transmit messages without any coordination with other stations. As a result, two or more ALERT stations may transmit messages at the same time, which is likely to cause a "collision", interference that results in one or both of the messages being lost. Collisions occur more often as the network becomes more heavily loaded – ALERT networks perform most poorly when they are needed most, namely during major rain events.

The Requirements Specification generated considerable discussion within the HWS community. While there was widespread recognition of the benefits of a two-way network protocol, such as the ability to manage nodes remotely over the network, the community was divided over whether next-generation HWS networks ought to support two-way communications.

The draft ALERT-2 Protocol Specification outlines a layered network architecture for next-generation hydrologic warning systems. This specification suggests the development of a time-slotted Medium Access Control (MAC) protocol (often called a time-division, multiple-access or TDMA protocol) to minimize collisions and the resulting packet loss. (A MAC protocol controls when a station is permitted to transmit.) The network layer protocol is a variant of the Internet Protocol that is optimized for the very low bandwidth that is available in HWS networks. Three transport layer protocols would offer best-effort datagram service (similar to the Internet UDP protocol and the original ALERT protocol), reliable datagram service (a datagram service that tries to recover packets that are lost during transmission) and a reliable file transfer protocol (similar to the Internet TCP protocol). The best-effort datagram service would be useful for transmitting sensor data; the reliable datagram service might be used to activate devices located at remote nodes, and the reliable file transfer protocol would be useful for transmitting log files, configuration information, or software updates. This document suggested that application protocols use a type/length/value (TLV) structure so that the protocols could be easily extended to support new sensors or capabilities.

The ALERT-2 Requirements Specification, the ALERT-2 Protocol Specification, and other documents that were produced by this project are available online; links to these documents are included below.

It is important to note that the ALERT-2 (with a hyphen) project performed by SaloITS in unrelated to the ALERT2 (no hyphen) project of the National Hydrologic Warning Council (NHWC). While the ALERT-2 and the ALERT2 projects have similar names and both seek to develop a successor to the original, outdated ALERT protocol, the two projects offer dramatically different capabilities and solutions. Some, however, have observed that the ALERT2 (NHWC) project has integrated a number of technologies that were first highlighted by the ALERT-2 (SaloITS) project.

The ALERT-2 Protocol Development project was funded by the Department of Commerce under a Phase I SBIR contract, which was effective July 16, 2007 – January 15, 2008. Any opinions, findings, conclusions or recommendations expressed in this web page and these publications are those of the author and do not necessarily reflect the views of the Department of Commerce.

The work on the ALERT-2 protocols was subsumed by SaloITS' Wide-area Environmental Sensing and alerTing network (WESTnet) project. WESTnets are intended to provide general-purpose, wide-area, wireless network services that support both large-scale environmental monitoring and near-real-time alerting.

NOAA SBIR Solicitation

The ALERT-2 project was funded under the NOAA FY 2007 SBIR Solicitation. The solicitation included subtopic 8.3.10 W-W "Development of Open Source Initiative (OSI) Model Application Layer for Hydrologic Radio Telemetry Data". This subtopic solicited proposals to develop a new application-layer protocol to replace the existing ALERT protocol, which is currently used in hydrologic warning systems.

ALERT-2 Protocol Development Proposal

Salo IT Solutions submitted a successful proposal, "Alert-2 Protocol Development", in response to the NOAA FY 2007 SBIR solicitation. The proposal abstract offers a brief summary of the proposed work. The technical portion of the proposal details the proposed activities. It also enumerates some of the limitations of the existing ALERT protocol that the new ALERT-2 protocols address.

ALERT-2 Protocol Development Project Overview

A one-page overview summarizes the ALERT-2 Protocol Development project.

ALERT-2 Requirements Specification

The ALERT-2 Requirements Specification document identifies the functional requirements for a next-generation suite of wireless network protocols for hydrologic warning systems and derives technical requirements from those functional requirements.

ALERT-2 Protocol Specification

The ALERT-2 Protocol Specification outlines the development of a protocol suite that would provide Internet-like services for hydrologic warning systems.

ALERT-2 Protocol Development Project Phase I Final Report

The ALERT-2 Protocol Development Project Phase I Final Report summarizes the accomplishments of the project.

ALERT-2 Presentations

The principal investigator coordinated workshops with members of the hydrologic warning system community to discuss the requirements for a next-generation suite of protocols for hydrologic warning systems, and technologies that would be meet those requirements. He also presented the results of those workshops and of the project to the broader HWS community.
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