Communications Engineering Services


To provide the equipment, support, and expertise necessary to operate the statewide emergency medical services communications systems.

Maryland’s emergency medical communications system is a complex network that provides communications among ambulances, med-evac helicopters, dispatch centers, hospital emergency departments, specialty referral centers, and trauma centers. Direction and control enable prehospital care clinicians to receive medical direction for the appropriate care and management of patients.

The MIEMSS EMS communications department has responsibility for designing, installing, operating the Emergency Medical Resource Centers (EMRCs) and Systems Communications (SYSCOM) center and maintaining the EMS communications system. Additional responsibilities include equipment purchasing, invoice payment, shipping, receiving, inventory control and telephone services.

The EMRCs are regional communications centers servicing the Baltimore and Washington metropolitan areas, EMS regions I,III, IV and V. Based on the most recent census information, the Region III and V EMRCs service approximately 90% of the population of Maryland. SYSCOM, located with the EMRCs at MIEMSS office in Baltimore, provides statewide voice and data communications for med-evac helicopter operations.

Access to PSAP via 911

The three digit number 911 is used to access the local Public Safety Answering Point (PSAP) in every jurisdiction within the state. By state law, access to 911 was implemented on July 1, 1985. Additionally, by law, enhanced 911 access was mandated by July 1, 1995. Implementation in Maryland of Wireless 911 that includes Automatic Location Information was somewhat slowed because of waivers that were granted by the FCC to the wireless industry. However, significant progress has been made over the past two years with focused efforts instituted by the State Emergency Numbers Board. Funding to support 911 services is through telephone subscriber fees administered by the State Emergency Numbers Board.


The EMS telephone network, EMSTEL, connects fire and ambulance dispatch centers, medevac helicopter bases, trauma centers, specialty referral centers, and other emergency resources to the EMRC/SYSCOM communications center. EMSTEL serves as a back-up to the public service dial telephone system. EMSTEL is used to 1) call SYSCOM to request and coordinate med-evac helicopter response; 2) arrange communications with hospitals in adjacent counties or other regions; and 3) coordinate inter-county mutual aid efforts. MIEMSS is currently deploying the next generation Voice-over-Internet Protocol (VOIP) replacement EMSTEL system.

Ambulance and EMS Dispatching and Communications

Each county is responsible for the dispatch of its ambulances, usually in response to a 911 call or request from another emergency services clinician. Ambulance dispatching is accomplished by a variety of means, such as manually or computer aided, and initial control is usually maintained by using a fire channel (VHF, UHF, or 800 MHz). All counties have implemented EMD programs to provide pre-arrival instructions to callers to assist in stabilizing patients prior to the arrival of medical assistance.

Once at the incident scene, the medical clinician can use existing medical protocols or may require medical direction depending on the patient’s condition. The clinician accesses the EMS communications system via a Call channel (in some states defined as a Hailing Channel) to obtain a medical channel for consultation with the hospital emergency department.

There are two types of EMS radio communications systems in use within Maryland: Regional (EMRCs) and local. There are currently four regional centers. The Region III EMRC is operated by MIEMSS and services Baltimore, Anne Arundel, Howard, Harford, Carroll, and Cecil counties and Baltimore City. MIEMSS also operates the Region V EMRC which services Frederick, Montgomery, Prince Georges, Calvert, Charles and St Marys counties. The Region 1 EMRC servicing Allegany and Garrett Counties with planned expansion to Washington County is operated by Allegany County in partnership with MIEMSS. The Region IV EMRC servicing the upper Eastern Shore is operated by Talbot County in partnership with MIEMSS. In remaining counties of the state the EMS communications service is provided by the local dispatch center using MIEMSS-provided communications equipment.

1. EMS Region III EMRC

The EMS Region III med-channel radio communications system is the most complex system in the state. This necessary complexity is due to the population density and the number of medical resources within the region.

EMS Region III comprises Baltimore City and the five surrounding counties. For communications purposes, however, Cecil County (part of region IV) is included in the region III EMRC. The region III EMRC is located in Baltimore at the MIEMSS building. Med-Channel communications is received at EMRC via one of 20 base station sites or through interfaces with local jurisdiction’s 800 MHz systems. EMRC is the central location for establishing medical consultation within the region. Whenever there is a need for medical consultation, the clinician contacts EMRC on Call 1. The EMRC operator directs the clinician to the appropriate med-channel and establishes a patch to the appropriate medical facility. Consultation facilities and multiple hospitals can be patched into a single consultation. The EMRC can also be accessed by local and 800 service dial telephone and a tie into the Region 3 EMRC provides access to all of the Region 3 area medical facilities.

A Trauma Line radio system is present at the R A Cowley Shock Trauma Center. RF radiating cables allow communications with the attending trauma physician via a portable radio on Med-Channel 5.5. This provides a means for field clinicians to receive medical consultation on trauma patients without the physician’s movements being restricted.

The EMRC operator maintains a computerized status of all hospitals in the region. The system is known as CHATS (County Hospital Alert Tracking System). The operator provides notification of changes to a hospital’s status to the affected jurisdictions. The CHATS information is also available via the internet from the MIEMSS website.

2. EMS Region V

Region V is served by the region V EMRC located with the region III EMRC at the MIEMSS building in Baltimore. Operation of the region V EMRC is similar to that described for Region III. It includes Maryland hospitals located within the region, as well as Washington, D.C. hospitals and Frederick County. The region V EMRC is accessed via Med-Channel Call 2. A tie into the Region 3 EMRC provides access to all of the Region 3 area medical facilities.

3. EMS Region IV (upper shore)

The upper Eastern Shore area of Maryland’s EMS Region IV (Caroline, Dorchester, Queen Anne’s, and Talbot counties) is served by a regional EMRC located in Easton. The operation is provided by Talbot County using equipment provided and supported by MIEMSS. Access is via Med-Channel Call 2. Several counties also utilize an interface with their 800 MHz radio systems for EMS communications via the EMRC. A tie line to the region III EMRC provides access to Baltimore and Washington area medical facilities.

4.  EMS Region I

Region 1 (Allegany and Garrett counties) is serviced by the newest EMRC operated by Allegany County, in partnership with MIEMSS, located in Cumberland. Access is via Med-Channel Call 1. Washington County will be incorporated into Region 1 EMRC in the near future. A tie line to the region V EMRC provides access to Baltimore and Washington area medical facilities.

5.  EMS Region IV (lower shore)

These EMS regions service the medical needs of somewhat less populated areas. In these areas, EMS communications are provided by the local dispatch centers using equipment provided by MIEMSS. In most of these jurisdictions there is only one hospital in the county. The medical clinician contacts the local dispatcher on Med-Channel Call 2 to request communications with the local hospital. The EMSTEL can be used to provide communications with facilities in other jurisdictions.

Existing Med-Channel Sites

There are presently over 95 med-channel base station sites within the state. The present system allows approximately 95% radio coverage 95% of the time. Voters are used for automated med channel site selection by the EMRCs.

Med-Evac Helicopter Communications System

1.  SYSCOM Helicopter Communications

By regulation, MIEMSS is responsible for med-evac helicopter communications. All med-evac helicopters transporting patients to or from medical facilities within Maryland are required to communicate with SYSCOM. For this reason, 10 VHF 44.74 MHz helicopter communications sites were installed across the state. These sites were strategically located to ensure radio coverage to and from helicopters as reliably available over approximately 95% of the state. The helicopter communications system uses a voter and transmitter steering device to select the correct site.

The Maryland State Police (MSP) Aviation duty officer, stationed in SYSCOM, has primary responsibility for the dispatching of MSP helicopters. In addition to MSP, U.S. Park Police helicopters may be utilized for med-evac operations. MIEMSS is working with commercial air ambulance services in Maryland to provide use of those services in the event that the MSP helicopters are unavailable or significantly delayed.

Medical communications from the helicopter to trauma centers and other medical facilities are provided by the Region III and Region V EMRCs located at MIEMSS using 47.66 MHz base stations at 7 locations throughout the state. Using the EMRC switches or EMSTEL, the helicopter medic can obtain medical direction or give reports on patient condition to any medical facility in the state.

2.  Flight Following System

A flight following system in SYSCOM provides visual awareness of the status and location of all MSP helicopters. The system utilizes the FAA’s newest tracking system known as Automatic Dependant Surveillance-Broadcast (ADS-B). MIEMSS has partnered with the FAA to increase the coverage area of ADS-B by utilizing the state’s tower sites and transport systems.

The system allows the MSP duty officer to locate and dispatch the nearest helicopter to the scene of an incident. In addition, the system provides an alarm feature which identifies helicopters that are out of communications with the system which allows helicopter emergencies to be quickly identified. Graphic and text displays can be used to locate emergencies, enabling fast responses when a helicopter may be down or in trouble.

3.  Statewide Infrastructure Project

Started in early 2000, MIEMSS is a key participant in Maryland’s statewide project to construct the necessary infrastructure to support a public safety 700 MHz communications network. A key component of this project is the replacement of the 25 year-old MIEMSS analog microwave system with new digital equipment.

The new microwave system is based on 28 T-1 point-to-point links between all of the usable existing and newly constructed communications towers. Connectivity to the county 9-1-1 Public Safety Answering Point (PSAP) centers is included. The system is divided into five separate backbone segments, northern, western, southern, eastern, and the Baltimore City hospital segment.

MIEMSS has provided all of the engineering services for the design of this network. Other allied State agencies have contributed to the installation of the equipment. Towers and microwave equipment are provided by both the State and the local Counties in a partnership arrangement. Monitoring of the network is primarily done by MIEMSS with access to the management system available to the county and state maintenance personnel.

Existing communications systems, including the MIEMSS UHF system, have benefited from access to the new towers and microwave service.


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