An Initiating DAS and a Response DAS both provide life-safety critical coverage. One for civilians to communicate an emergency and the other to coordinate a response. These are two very different systems supporting different wireless networks, technologies, survivability requirements while being regulated by completely different stakeholders seeking different benefits. These are, logically, different systems when installed in a building. So far, installations are supporting this thesis. Comparatively few buildings have a combined Initiating and Response DAS for those exact reasons.

The Distributed Antenna System (DAS) world has bifurcated into two different installations; a Cellular/WiFi network for the occupants of the building and a first responder network for incident communications. Both systems serve critical life-safety functions at different stages of the incident response. At TowerIQ, we consider the Cellular/WiFi network to be the most critical initiation system in any building, Initiating systems are the services and devices that report an alarm and start the emergency response system. Alternatively the First Responder wireless network utilized during the response is as important as water for our First Responders.These networks have unique user expectations, operational requirements, and regulatory regimes.

Initiating DAS

Each year over 240 million calls are made to 911. With 60% of those calls originating from indoor cell phones, significantly more calls have been initiated from cell phones than from manual pull stations or automatic detection devices. These initiating calls from civilians to 911 operators primarily occur on one of four domestic wireless operators, with the user being oblivious to the massive and interwoven amounts of infrastructure required to support that call.  The caller is also unaware as to if their signal is being carried by an external cellular site, or through a distributed antenna system installed inside the building. What the caller does know, is they have cellular coverage within the building. They are able to call, stream, and ultimately report a public safety emergency by directly communicating with 911 operators.

Functionality and Installation

The operational use of the Initiating DAS creates its own unique requirements for capabilities and its actual construction. An Initiating DAS provides day-to-day cellular coverage to the occupants, while the “Macro Network” fails to penetrate through the glass, walls, appliances, etc. of the building. Inclusive of data, text messaging, and phone calls, the functionality extends to 911 calls as well as mass notifications such as amber alerts. 

Initiating DAS installations can vary greatly depending upon the size of the building and the expected capacity. For the smallest installations, this can simply be described as a “two-antenna” installation. One cellular capable antenna is installed on the roof (properly grounded, of course) and pointed towards to local cell site. A Bi-Directional Amplifier boosts the signal received from that antenna while a second antenna installed in the building radiates that signal to cell phones. With thoughtful engineering, additional antennas can be installed inside the building to further expand coverage without the requirements of an additional Bi-Directional Amplifier, or rooftop antennas. This is commonly referred to as a “Passive DAS.”

When the building is too large or its capacity demands are too high for a “Passive DAS”, the building then becomes its own cell site. In place of a rooftop antenna, a hardwire connection to the cell networks is used. Rather than only utilizing coaxial cable to distribute signal throughout the building, fiber optic cables distribute communications information between high capacity remote radio units throughout the building. Those remote radio units then each drive a “Passive DAS.” 

Both system types provide day-to-day cell coverage to the occupants of the building. They also will provide emergency cell coverage to those same occupants, should the need arise. Consider fire-alarm initiating and mass notification systems. In the case of a fire incident, those systems are expected to report, announce, and having performed their duty, cease operations as the building transitions into a response mode. These systems are required to maintain dormant functionality through a 24 hour blackout while still supporting 5 and 15 minutes of active operations, respectfully, before failing. Similarly, the Initiating DAS should consider this framing for its operations to ensure that at the start of an incident the occupants will have the ability to report to the 911 operator. While a cellular DAS does not have a standby state, the system is always amplifying cellular coverage, it is within reason to expect 15 minutes of backup power, that is, 15 minutes of expected operations at the start of an incident. 


Presently, initiating wireless network coverage is not considered to be a part of a building’s life safety package. Such coverage is not considered to be a part of a building’s Certificate of Occupancy requirements. However, cellular coverage can now be considered the “fourth utility” for a building; a critical marketing feature expected by the occupants of the building.

The most active regulator for initiating wireless networks is the Federal Communications Commission (FCC). The FCC controls the allocation of spectrum to the carriers, defines what devices are allowed to transmit on that spectrum, but it does not define coverage requirements, including indoors. However, the FCC has taken significant steps to simplify the process for buildings to voluntarily rectify poor cellular coverage with Bi-Directional Amplifier (BDA) distributed antenna systems. These installations can “borrow” signal from the external cellular sites and amplify into the structure. Their installation must be registered with the FCC via a web form, and must be installed by qualified individuals. The FCC does mandate enhanced 911 (e911) functionality is provided by the cellular network provider wherever coverage is provided. Within a few years, when a call is initiated from inside a building, the wireless carriers must be able to determine that callers location within 3 meters to enable effective first response.

Those carriers are, in effect, an additional regulator for the initiating DAS. As the license holder of the spectrum, they have the power to stop any Bi-Directional Amplifier from transmitting when it interferes with the operations of their wireless networks. If a Bi-Directional Amplifier is transmitting noise, if it is too strong, or if it is using too much capacity, the carriers have every right to show up to the property to demand the Initiating DAS be shut down and repairs affected.

Response DAS

After the initiating call has been made,whether by cell phone, pull station, or smoke detector, the communications responsibility now falls on the Responder DAS. A relatively new fire-alarm subsystem, the Responder DAS enables first responders to have reliable two-way radio communications inside of a building and during an incident. Incidents ranging from medical, fire, and terrorist attacks have all demonstrated the need for first responder voice communications. 80% of first responders have reported dead zones while communicating and coordinating their response. These dead zones can have devastating consequences for civilians and first responders alike, first responders need to coordinate their response.

Functionality and Installation

Experiencing the same signal impediment as your cell phone, a first responders two-way radio coverage will suffer if a building’s mass blocks their signal. First responders typically operate on a dedicated two-way radio network exclusively for their use, which is owned and maintained at the local level. First responders now expect for the two-way radio that they carry to communicate back to dispatch and other responders just as if they were outside the building with clear line of sight to the radio tower. A Response DAS can be viewed as a remediation effort. When the building was constructed, it impeded the two-way radio signal for local first responders and the obligation is on the building to fix it.

Coverage amplification for the Responder DAS has traditionally been provided with a Bi-Directional Amplifier and a passive DAS, similar to the “two antenna installation” described for the Initiating DAS. One spectrum specific antenna is installed on the roof, grounded, and directed to the first responder’s radio system’s transmission tower. That signal is then amplified through a Bi-Directional Amplifier and retransmitted through the second antenna(s) installed inside the building. 

A consequence of local control and operations is the sheer variation in two-way radio channels, each locality having their own technological requirements compared to the relative simplicity of the big four cellular carriers. A result of operating on different frequencies is a lack of interoperability. A firefighter from Miami will not be able to enter a building in New York City and have two-way radio coverage. A responder in Hollywood, Florida will not be able to enter a building in Miami and expect two-way radio coverage. This variation in wireless networks does affect the equipment utilized to provide coverage in the building, whereas the firefighter jacks they replaced where universal, the radio equipment is customized to the specific jurisdiction.. 

Despite the lack of wireless network uniformity, there are universal construction and operational rules that are applicable. Presume the Response DAS infrastructure will be exposed to both extreme heat and water at the same time and the building has also lost power. The Response DAS needs to operate through those conditions while first responders are on scene and relying on their two-way radios for command and control. These operational realities dictate several specific requirements, including waterproofing, fire resistant construction techniques, and significant emergency power requirement.


There are two distinct chains of regulatory responsibility for a Responder DAS. One deriving authority from fire code requirements and the other from FCC requirements. 

First responder wireless coverage requirements have been clearly defined in national fire code references for several years now. States and local jurisdictions adopt and modify those references to suit their local application, incorporating them into their local building codes. This chain of implementation squarely places enforcement authority in the hands of the local fire marshal. The entity that has the authority to grant a building its certificate of occupancy also has the obligation to ensure first responders have two-way radio coverage at the completion of construction and also throughout the building’s operational lifespan. The code requirements are for coverage inside the building and not necessarily a requirement for the installation of a Response DAS. While some jurisdictions may require a Response DAS because of special use cases, the majority of jurisdictions only require signal amplification when the natural coverage from the local radio system is deficient inside the building. When a system is required, it is the fire marshal’s authority that will also enforce construction standards, making sure the Responder DASis both reliable and survivable.

Parallel to fire code regulations are FCC responsibilities, with legal rights assigned by the FCC via licenses to organizations and individuals. The rights conveyed include the ability to transmit on certain frequencies, at certain power levels, from certain locations. Further, the FCC has granted those same license holders the ability to enable signal boosting devices, the Response DAS. However, the fire marshal is typically not the government entity charged with maintaining the responsibilities assigned by that FCC license that burden will often fall upon the first responder organization or a governmental IT department. If a Response DAS goes awry and pollutes the spectrum, the affected license holders, all the way to the FCC, have a legal right to step in.

Two Different Systems

An Initiating DAS and a Response DAS both provide life-safety critical coverage. One for civilians to communicate an emergency and the other to coordinate a response. These are two very different systems supporting different wireless networks, technologies, survivability requirements while being regulated by completely different stakeholders seeking different benefits. These are, logically, different systems when installed in a building. So far, installations are supporting this thesis. Comparatively few buildings have a combined Initiating and Response DAS for those exact reasons. 

At TowerIQ, we believe that because of the specialized use cases of these two DAS types, the hardware and systems utilized in these installations will continue to diverge. Initiating DAS will continue with rapid technological advancement towards increased bandwidth, while Response DAS will continue to develop in regard to scale and survivability.

Back to Latest News