MOSA, or the Modular Open Systems Approach, is a Department of Defense business and technical strategy for building systems that can change over time. It uses modular design and open interfaces so components can be added, replaced, or upgraded without redesigning the full system.
MOSA can make it easier to introduce new technology into a defense system, but adding a new radio, compute module, waveform, or application does not automatically make it communicate with everything already in the field. That is a real challenge at the tactical edge, where military units often operate a mix of legacy analog radios, software-defined radios, IP networks, MANET systems, SIP endpoints, tactical applications, and other communications equipment.
REDCOM Sigma helps connect those environments by providing a common command-and-control communications layer and bridging legacy analog radios with modern IP-based communications. MOSA makes it easier to change what is inside the architecture. Our role at REDCOM is to help make sure the communications systems within that architecture can still communicate together.
What is Modular Open Systems Approach (MOSA)?
The DoD uses MOSA to support competition, reduce vendor lock-in, improve interoperability, and make technology upgrades easier.
The basic idea is simple: changing one part of a system should not force a program to replace everything connected to it.
The DoD currently organizes MOSA around five primary pillars:
- Employ a modular design
- Designate modular interfaces
- Leverage consensus-based open standards
- Establish enabling environments
- Certify conformance
It is more than an engineering preference. For major defense acquisition programs, MOSA is also required under Title 10 U.S.C. § 4401.
Is MOSA a technical standard?
No. MOSA is an acquisition and system design approach, not a single technical standard or certification.
That distinction matters because MOSA is often discussed alongside CMOSS, SOSA, VICTORY, FACE, MORA, and OMS/UCI. Those standards and architectures can help programs implement MOSA, but they are not interchangeable with MOSA itself.
So when evaluating a product for a MOSA environment, the better question is not simply, “Is it MOSA?” Programs should look at whether it supports modularity, open interfaces, interoperability, and future technology insertion.
The Army’s CMOSS Mounted Form Factor (CMFF) is a useful example. Instead of installing separate purpose-built boxes for every capability inside a vehicle, CMFF is designed around common infrastructure into which capabilities can be integrated as modular cards. The Army says the approach is intended to reduce size, weight, power, and cost (SWaP-C) while making it easier to introduce new capabilities as technology changes.
- CMOSS provides a suite of standards for converging C5ISR/EW hardware and software resources.
- SOSA establishes common hardware and software approaches for sensor processing systems.
- VICTORY defines interfaces intended to improve integration of C5ISR/EW equipment on military vehicles.
- FACE establishes an open software environment for military aviation.
- MORA addresses modularity and interoperability of radio-frequency resources.
Why MOSA matters for tactical communications
Tactical communications rarely come from one vendor or one generation of technology. A unit may use legacy analog radios, software-defined radios, MANET networks, SIP devices, SATCOM, and tactical applications during the same mission. Joint and coalition operations can add even more systems to that mix, and many of those existing systems may remain in service long after new capabilities are introduced.
MOSA gives programs more flexibility to introduce or replace technology without rebuilding the entire architecture around it. But modular hardware and open interfaces do not automatically solve the communications problem. A new radio, waveform, network, or application still needs to communicate with other systems in the field, including older equipment that continues to meet the mission requirement.
For tactical C2, keeping those systems connected is an important part of making a modular architecture useful in actual operations. Interoperability is paramount.
MOSA keeps the architecture open. Interoperability makes that openness operationally useful.
Where REDCOM Sigma Fits in a MOSA Communications Architecture
REDCOM Sigma is a software-based C2 communications platform designed to bring different communications resources into a common operational environment. Sigma supports voice, video, chat, radio interoperability, and C2 control within the same software platform.
We do not require every component in the architecture to come from REDCOM. Our goal is to give operators a way to communicate across the equipment and networks already available to them, which matters in an environment where a program may choose one vendor for radios, another for tactical compute, and another for networking.
Sigma uses established standards and protocols such as SIP, RTP, MLPP, and XMPP. It operates at the application layer and can use IP-based networks for transport. We build the interoperability and C2 layer that helps connect the radios, networks, and endpoints selected for the mission which aligns with the Modular Open Systems Approach vision.
Connecting legacy and modern systems without rip-and-replace
One of the benefits of MOSA is the ability to introduce new technology without redesigning an entire system every time something changes. We take a similar approach to tactical communications by focusing on how new capabilities can work with equipment that is already fielded.
A new requirement should not automatically trigger replacement of the entire communications stack. In many cases, the better answer is to connect the new capability to what already works rather than forcing a full replacement.
Legacy analog radios are a good example. They may still meet the mission requirement and remain in use while the rest of the network moves toward IP-based or software-defined systems.
Sigma is designed around that reality. We can bring legacy and next-generation communications into the same C2 environment, so programs have more flexibility in when and how they replace equipment. Specifically, the REDCOM Sigma XRI can connect analog tactical radios with IP-based communications systems, SIP endpoints, IP radios, PTT applications, and other C2 resources. The platform is agnostic to radio make, model, encryption, and waveform.
This can be especially useful during long modernization cycles because not every unit, platform, or echelon receives new technology at the same time. For a MOSA-based system, this gives programs another option besides rip-and-replace. New capabilities can be introduced while older systems remain connected to the mission.
MOSA and vendor lock-in
Vendor lock-in is one of the problems MOSA is intended to reduce. Proprietary interfaces can turn a simple component change into a much larger integration effort. Over time, a program may stay with an incumbent vendor because replacing one part of the system creates too much cost, risk, or engineering work.
REDCOM takes a different approach to tactical communications. Sigma does not require every radio, endpoint, or network to come from the same vendor. Its role is to connect the communications technology a program already uses or plans to field.
That fits the intent behind MOSA. Programs can choose technologies based on mission requirements instead of staying inside one proprietary communications ecosystem.
Why MOSA also matters in DDIL environments
MOSA becomes even more useful when communications are operating in denied, degraded, intermittent, or limited (DDIL) environments.
At the tactical edge, the preferred communications path may not always be available, so a unit may need to move between tactical radio, MANET, SATCOM, cellular, wired IP, or another available network as conditions change. A communications architecture that can use different networks and generations of equipment gives operators more ways to stay connected.
Sigma brings IP and RF communications into a common C2 environment, so operators have more options when network conditions change. In a DDIL environment, that flexibility has a direct operational purpose. When one path becomes unavailable, communications need another way through.
What should programs look for in a communications solution built on MOSA principles?
When evaluating communications technology for a MOSA-based program, a few practical questions matter more than a general “open architecture” claim.
Programs should ask whether a radio, application, or network can be changed without redesigning the rest of the communications system. They should also look at whether systems from different vendors can work together, whether important interfaces use documented standards, and whether new technology can still communicate with legacy equipment that must remain in service.
Deployment flexibility matters too. A communications capability that can work across different compute platforms and form factors gives integrators more room to adapt as requirements change.
Questions to consider:
- Can a radio, application, or network be replaced without redesigning the entire communications architecture?
- Are important interfaces based on documented and widely supported standards?
- Can equipment from multiple vendors operate within the same C2 environment?
- Can new technology interoperate with legacy systems that still need to remain in service?
- Can the communications capability be deployed across different compute platforms and form factors?
- Can operators manage those disparate systems without adding another layer of operational complexity?
- Does the architecture preserve multiple communications paths when operating in DDIL conditions?
Building communications for what comes next
No program manager knows exactly what tactical communications will look like ten years from now, nor should systems being fielded today require us to know.
MOSA gives defense programs a way to introduce new technology without rebuilding the entire system around it. Open standards reduce integration barriers. Modular design makes technology refresh easier. Interoperability helps make sure the new capability can still communicate with what is already there.
REDCOM Sigma supports that approach at the C2 communications layer. It connects legacy and modern systems, works across different networks, and gives programs a standards-based way to manage communications without tying the architecture to one vendor.
For REDCOM, that is where MOSA and tactical interoperability meet: add what comes next without losing what already works.
Frequently Asked Questions About MOSA
What does MOSA stand for?
MOSA stands for Modular Open Systems Approach. It is a Department of Defense business and technical strategy for designing systems with modular components and open interfaces so they can be updated, replaced, or expanded over time without redesigning the entire system.
Is MOSA a technical standard?
No. MOSA is an acquisition and system design approach, not a single technical standard or certification. Standards and architectures such as CMOSS, SOSA, VICTORY, FACE, MORA, and OMS/UCI can help defense programs implement MOSA principles.
Is MOSA required by the Department of Defense?
Yes. 10 U.S.C. § 4401 requires applicable major defense acquisition programs, and directs other defense acquisition programs to the maximum extent practicable, to use a Modular Open Systems Approach to support incremental development, competition, innovation, and interoperability.
Why does the DoD use MOSA?
The DoD uses MOSA to make defense systems easier to upgrade and sustain over their full life cycle. It can help reduce vendor lock-in, support competition, improve interoperability, and make it easier to introduce new technology without replacing an entire system.
What is the difference between MOSA and CMOSS?
MOSA is the broader business and technical approach. CMOSS, or C5ISR/EW Modular Open Suite of Standards, is a suite of standards that supports MOSA implementation for C5ISR/EW systems. CMOSS uses standards such as VICTORY, OpenVPX, MORA, and FACE to support modular hardware, software, and network architectures.
How does MOSA help tactical communications?
MOSA helps tactical communications systems accommodate new radios, networks, applications, and other technologies without forcing a complete redesign. Open interfaces and standards also make it easier for equipment from different vendors and generations to work within the same C2 environment.
How does REDCOM Sigma support MOSA principles?
REDCOM Sigma® uses standards-based communications and is designed to work across different networks, radios, endpoints, and compute platforms. Sigma and Sigma XRI can connect legacy analog systems with modern IP-based communications, giving programs a way to add new capabilities without replacing equipment that still works.
Can MOSA help reduce vendor lock-in?
Yes. One of the goals of MOSA is to make it easier to replace or upgrade individual components without being tied to one proprietary system. REDCOM supports that approach by allowing Sigma to work with communications technology from different vendors instead of requiring a closed REDCOM ecosystem.
Can legacy systems still be used in a MOSA architecture?
Yes. A MOSA-based architecture does not require every older system to be replaced. If a legacy capability still meets the mission requirement, standards-based gateways and interoperability tools can help connect it to newer systems. This is especially important in tactical communications, where analog radios and newer IP-based systems often operate side by side.
