Most countries considering digitisation experiment with datasharing at all battlefield levels. At the highest levels, commercial equipment provides a network that can be hardwired into buildings or fixed operations centres for a nominal cost. At the static brigade and division level, usually there is a trunk system that can be modified to handle data to be shared at higher levels. This leaves only the tactical level to be connected.

This level presents the most difficult problem. Stations to be connected are mobile in battle so a wireless solution is necessary to make connection between vehicles and HQ. Radios that connect vehicles properly at the lowest levels with data throughputs approaching those of standard network speed, are still not fielded, so how do you create a tactical internet using low-bandwidth VHF radios?

The US has approached the bandwidth issue as a hardware problem. The US Army develops modems and radios to help solve the limited bandwidth problem but other countries cannot afford dozens of hardware iterations before fielding a properly functioning system.

Computing Devices has approached the problem with a combination of software, hardware and network topology called battleWEB that works well under almost any bandwidth limitations. The design and topology described is the result of years of research aimed at creating a fully functional, combat-capable tactical internet for the lowest possible cost that can be made using existing digital or analogue radios regardless of age.

The first issue when creating a budget tactical internet is to decide on the network topology. This is the basic design of the network and is critical. There are two ways of connecting nodes, or vehicles, together: client-server and peer-to-peer. Using client-server topology some vehicles are clients that get their information routed to them through another vehicle acting as a server. When a message is to be sent the information has to go through the server. In the peer-to-peer network, every vehicle is its own server. When a message is sent it uses connectivity provided through surrounding vehicles to get information out.

A two-fold problem

The problem with client-server networks on the battlefield is two-fold. First, vehicles move about and may lose connectivity with the server. Careful planning can mitigate this, clients and servers are grouped so that during routine military operations they remain connected. If a platoon commander is the server and the rest of the platoon become clients, they should stay together so the system works. If the server is removed, clients become orphans. However if the platoon commander's vehicle is blown up the rest of the platoon is disconnected and left out of the information battle. Now, imagine the servers for the battalion were destroyed! It is easy to see that the client-server topology would have a hard time surviving contact unless measures were taken to ensure connectivity or the ability to promote a client-to-server status instantly existed.

Peer-to-peer networks are less vulnerable because no one is the server; there is no specific weakness in the system. The problem is these networks can seem disorganised, but there are ways around these issues. First, if the tactical internet were a single, giant peer-to-peer network, it would be extremely disorganised so we use radios to connect the network. If we structure a peer-to-peer internet around the existing hierarchy used for tactical radio communications, we bring organisation to the network. The tactical internet becomes a series of peer-to-peer inter-connected radio networks.

To know who is out there, we can institute a method of self discovery. When a computer is turned on it broadcasts a personalised hello and everyone on the network instantly knows who it is and how they are connected. Stations broadcast any message so the computer can listen in and add that station to the address book. This self-discovery can be coupled with a messaging system with fixed addresses that overcomes the problem of being unable to communicate unless you have heard from someone first. So basic problems with peer-to-peer connectivity can be overcome with clever programming and by using existing communications hierarchy.

Peer-to-peer networks also have an advantage during re-organisation. In a client-server system, someone has to re-programme the server and routers to accept new clients. The peer-to-peer system needs only a change in the radio channel and a "hello" to join the new network, a better fit with the dynamic nature of military operation.

Also peer-to-peer systems can be programmed to help when two stations are out of communication. A third station can overhear a message and re-broadcast it automatically to the station out of contact and also forward an acknowledgement.

The final issue with network topology is band- width. In a normal client-server system the network transmits messages using transport control protocol/ internet protocol (TCP/IP). While this is flexible enough to define any computer on Earth from any other, it consumes a large amount of bandwidth. Each packet of data comes with a huge header full of information that tells data where to go and who it came from. Although adding robustness to a hard-wired system, it is unworkable on anything less than a premium data radio.

A low-budget tactical internet will have to find a way of communicating without transmitting the enormous overhead of TCP/IP over old VHF analogue radios. A simple solution is to use software to strip the TCP/IP information of data before it goes through the thin pipe of the VHF radio and attach a simple radio address in its place. The connectivity remains the same, but only a fraction of the bandwidth is used.

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