Page E-4
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.
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：无人机系统路线图 Unmanned Aircraft Systems Roadmap(151)
