• Army soldiers check the setup up of an antenna for voice and data tactical communications in Port-au-Prince, Haiti. While the responsibilities between the Cyber and Signal branches are still evolving, a seven-layer model may be helpful in defining the divide. U.S. Navy photo by Chief Petty Officer Robert J. Fluegel
     Army soldiers check the setup up of an antenna for voice and data tactical communications in Port-au-Prince, Haiti. While the responsibilities between the Cyber and Signal branches are still evolving, a seven-layer model may be helpful in defining the divide. U.S. Navy photo by Chief Petty Officer Robert J. Fluegel

Separating the Signal and Cyber Branches

The Cyber Edge
May 4, 2020
By 1st Lt. Cory Mullikin, USA


The seven-layer model divides branch responsibilities.


The rising prominence of the Cyber branch in the U.S. military, and namely the Army, begs the question “What will the Cyber branch be used for?” Citing the Defense Department’s plan for the Cyber branch, as well as the Signal branch’s shifting roles in the realm of cyberspace, the responsibilities of both branches are becoming clear. It is evident that as time goes on, the Cyber branch will become focused mainly on the defense of the military domain and cyberspace.

The majority of the department’s cyber goals are focused directly in defense. The Defense Department’s cyber strategy outlines the goals as, “Defend the DOD information network, secure DOD data and mitigate risks to DOD mission; Be prepared to defend the U.S. homeland and U.S. vital interests from disruptive or destructive cyber attacks of significant consequence; Build and maintain robust international alliances and partnerships to deter shared threats and increase international security and stability.”

Historically, all things relating to the Non-Secure Internet Protocol Router (NIPR) domain were encompassed by the Signal Corps. Even to this day, the Signal branch is intertwined in all seven layers of the open systems interconnection (OSI) model.

The OSI model is a seven-layer model that allows digital products to operate and communicate with other communication devices. The first layer, the physical layer, includes electricity, cabling and other physical world attributes. Layer two, the data link, is where most switches operate to transfer data. Layer three, the network, is where most router use exists and forwards packets to their destination. The fourth layer, transport, transfers data from user end systems to hosts. Layer five, is the session layer and generates so-called sessions when devices need to communicate to each other. The penultimate layer, the presentation layer, is where the network language is translated to the application language and then “presents” the packet. The final layer, application, is the layer that the user sees and works different applications on, such as a web browser This model helps to define where the Signal and Cyber branches work respectively.

In the past, the role of Signal was not only to provide the network, but also to defend it from any intruders, hackers or attackers of the Department of Defense Information Network, and the NIPR or the Secure Internet Protocol Router (SIPR) domain.

Since both the Signal branch and Cyber branch are concerned with defense of the networks owned by the department, where is the line of responsibility drawn? The answer is where they operate in the OSI model. The Cyber branch’s main areas of concern are layers three, four, and five, so naturally their defense concern would be those three. Some could argue the use of cyber in layers six and seven; however, these would fall more into the offensive use of the Cyber branch. While this is a possibility, the Cyber branch, so far at least, is not shaping up to be an offensive branch.

The Signal branch operates through all of the layers of the OSI model, from the physical layer all the way to the application layer. This provides redundancy on the layers protected by cyber, but this is slowly becoming less of the focus of the Signal branch. Some become intimidated by this notion, but the Signal branch’s role is switching to solely providing the cyber network and communications. Signal will continue to be actively employed though. As mentioned earlier, Cyber operates in three layers of the OSI model.

As time goes on, and Cyber becomes more prominent as a branch of the Army, Signal will be solely tasked with providing the NIPR and SIPR domain and the Department of Defense Information Network. Areas such as satellite communications, line-of-sight communications, cabling and all physical layer aspects of the OSI model will still fall well into the realm of the Signal branch.

In conclusion, the Signal branch and Cyber branches, while very similar now and even redundant in some respects, are drifting apart. This will leave the realm of defense and cybersecurity to the Cyber branch. All physical aspects, as well as network maintenance, will be the responsibility of the Signal branch. Signal will also be in charge of aspects of communications discussed. Like in the past the Signal branch will give birth to this new branch of the Army and still remain relevant to the active warfighter.

1st Lt. Cory Mullikin, USA, is a native of Jackson, Tennessee, and graduate of the University of Memphis. He is a Signal officer currently stationed with the 25th Infantry Division at Schofield Barracks, Hawaii.

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