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
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