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motion imagery and other data collected by manned and unmanned sensor platforms has become
increasingly important to the war fighter, the proliferation of sensors and platforms that use CDL has
raised the military Services’ interest in assuring interoperability.
1 “CDL” denotes a family of full-duplex, jam-resistant, point-to-point microwave communication links developed by
the US Government and used in imagery and signals intelligence (SIGINT) collection systems. CDL is defined by
the Common Data Link Waveform Specification, Revision F, November 2002. In a 1996 affordability initiative to
broaden potential CDL applications, the Defense Airborne Reconnaissance Office (DARO) and the Defense
Advanced Research Projects Agency (DARPA) developed a narrow-band version of CDL (at that time limited to
data rates up to 10.71 Mbps), which was designated Tactical Common Data Link (TCDL). TCDL is evolving into a
full-bandwidth (up to 274 Mbps) technology that is light-weight and relatively low-cost, is fully compliant with the
CDL specifications, but may not be as feature-rich or environmentally capable as traditional CDL systems.
2 ASD (C3I) Memorandum, Common Data Link (CDL) Policy, 18 October 1994.
3 ASD(C3I) Memorandum, Common Data Link (CDL) Policy, 19 June 2001
UAS ROADMAP 2005
APPENDIX E – INTEROPERABILITY STANDARDS
Page E-5
The family of standard CDL waveforms4 provides an exceptional range of features that allow CDL to be
tailored to meet many program, platform, and operational needs. Because of this flexibility, a transmitting
terminal and an associated receiving terminal may both be compliant with the CDL Waveform
Specification, but may not be interoperable because they are designed or configured to conform to
different parts of the specification. The need to standardize the user systems interface to the
communications system has resulted in the approval of Annex B of the CDL specification. The following
section describes the key parts of Annex B.
STANAG 7085 (Interoperable Data Links for Imaging Systems)
The CDL specification has been made available to NATO in the form of STANAG 7085. STANAG
7085 is currently based on Revision E of the CDL Specification. Release of the newer Revision F to
NATO is in progress.
CDL Terminal Interoperability
In the OSI reference model, the physical layer (layer 1) provides the physical means for transmitting
digital data from one computer to another and regulates the transmission of the stream of data over a
physical medium. In CDL terms, the physical layer is composed of a pair of radio terminals (e.g., an
airborne terminal and a surface terminal, or two airborne terminals) and the complex radio waveform that
establishes the link between the two terminals. Interoperability profile compliant systems will use the
CDL Spec Annex B to define the physical layer. In addition, compliant systems will implement one or
more external IEEE 802.3 100BaseTX Ethernet ports for interconnection with external Ethernet-based
local area networks.
Data Signal Framing
The OSI reference model data link layer (layer 2) establishes the procedures and protocols for
transmitting data over the physical layer. Among these functions is packaging the bits into packets, cells,
or frames for transmission, and for recovering the data at the receiving terminal. Layer 2 protocols have
means for detecting and correcting errors that may occur during transmission. In the CDL context, layer 2
also provides a means for the receiving terminal to identify the beginning of a frame of data in the
unbroken stream of bits received over the link. CDL layer 2 networking protocols are specified in
appendix II and annexes A, B, C, and D of the CDL waveform specifications. Annex A details the
ATM/CTFF framing procedure used by some CDL systems. Annex B details the Ethernet/GFP framing
procedure.
No changes are required in the Ethernet or GPF protocols (Layer 2) to support either IPv4 or IPv6 (Layer
3). Only the IPv4 Header Compression (Layer 3) feature will have to be turned off or updated to support
the new IPv6 header compression scheme if desired.
Data framing with Ethernet
Interoperability profile compliant systems will, as a minimum, implement layer 2 framing of data using
IEEE 802.3 100BaseTX Ethernet (up to 100 Mbps), as defined in the CDL waveform specifications,
appendix II, annex B. Further, interoperability profile compliant systems will implement the specific
Ethernet datagram structure defined in annex C. These requirements, however, do not preclude system
architectures from implementing additional layer 2 framing procedures.
Generic Framing Procedure (GFP)
Standards Profile compliant systems will as a minimum implement international telecommunications
　
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