Link-16 Data Exchange

Link-16 Data Exchange Link-16 transmits data serially using 70 bit data words. During the transmit time slot, either three, six, or 12 data words can be transmitted. The number of words transmitted depends on whether the standard, packed-2, or packed-4 data packing structure is used. The number of words that composes a Link-16 message is variable but is normally 1, 2, or 3 words. There are three types of messages: fixed format, free text, and variable format. The fixed format messages are called J-series messages and are used to exchange tactical information. Free text messages are used for voice communications, while the variable format messages are user defined in length and content. Variable format messages are not used by the Navy. JTIDS Architecture There are several features of the JTIDS architecture that have resulted in improved communications of the Link-16 system. These features include the following: Nodelessness Security Network participation groups NODELESSNESS. —A node is a unit required to maintain communications of a data link. In Link-11, the NCS is a node. If the NCS goes down, the entire net is inoperative. Link-16 does not need a dedicated station. When the Link-16 net is established, a single JU transmits a Network Time Reference (NTR). The time established by this unit is the network system time. All other units in the net use the NTR message to synchronize with the network. Once the NTR and the network have been established, the network can continue to operate regardless of the participation of any particular unit. SECURITY. —The security of the Link-16 system is vastly improved over that of the Link-11 system. In Link-16, both the data and the transmissions are encrypted. Data is encrypted by a cryptovariable for message security. The security of the data transmission is provided by the use of a second cryptovariable that controls the transmitted waveform. Frequency hopping to prevent jamming is one of the features of the security system. The transmission security also provides for the introduction of jitter and a pseudo-random noise to be added to the waveform. The addition of jitter and noise, along with the frequency hopping, makes the transmitted signal extremely difficult to detect and jam. N E T W O R K P A R T I C I P A T I O N GROUPS. —The time slots of a Link-16 network can be broken down into separate Network Participation Groups (NPGs). An NPG is defined by its function and determines the types of messages that are transmitted on it. Some of the NPGs used by the Navy are as follows: Surveillance Electronic Warfare Mission Management Weapons Coordination Air Control Fighter-to-Fighter Secure Voice Precise Participant Location and Identification (PPLI) and Status By dividing the net into NPGs, each JU can participate on only the groups that support the mission of the unit. Most Navy Command and Control (C²) units, both ships and aircraft, operate on all the defined NPGs except the Fighter-to-Fighter NPG. Link-16 New Capabilities The increased size of the Link-16 enables the reporting of up to three times as much tactical information as was available under the Link-11 7 -6