Home' RTCA Documents for Review : C2 Link Systems MASPS_Draft Contents Appendix E
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Connections Over Point-to-Point Links Versus Over Networked Links
Before discussing how Connections and Switchovers between different types of links may
be executed, it is instructive to describe the layers of the International Organization for
Standards (ISO) Open Systems Interconnection (OSI) layered protocol model for data link
communications that are involved in the establishment and delivery of data over just Point -
to-Point links versus over links that include mobile air/ground networks. Those layers will
then be used to establish a common framework for the description and safety analysis of
C2 Link System Switchovers.
When the C2 Link Connection between UA and CS is established over a Point-to-Point
terrestrial link or a Point-to-Point SATCOM link, the C2 Link System functionality
that supports the exchange of C2 Link User Data and Control Messages between the
UA and CS will be allocated among the following protocol layers of the OSI model:
Physical Layer (L1) functionality including modulation and forward error
correction functions that enable power and bandwidth efficient delivery of data
over each of the links that provide a Connection between the UA and CS. This
functionality resides in the Terrestrial GRS and SATCOM GES and the UA’s
Terrestrial ARS and SATCOM AES.
Data Link Layer (L2) functionality consisting of:
RF Link) Access Control (MAC) including RF
frequency/channel selection and Time Division Duplex (TDD) functionality
for simultaneous transmit and receive operation over a terrestrial link that uses
the same frequency assignment for transmit and receive; or transmit and
receive frequency selection for simultaneous transmit and receive operation
using Frequency Division Duplex (FDD) over a SATCOM link that requires
separate channel assignments for transmit and receive.
Link Connection Control including (1) message source and destination
addressing, (2) the functionality associated with the establishment,
maintenance and termination of the connections between CS and UA C2 Link
Management Systems, (3) providing for data integrity and security, and (4) the
switching of the connectivity between terrestrial and SATCOM Point -to-Point
links. All the Link Connection Control functions are assumed to be performed
by the functionality within the CS and UA C2 Link Management Systems.
The choice of appropriate addresses to control the exchange of data between
the CS and UA over each Point-to-Point link may be managed by the UAS
operator. Unique addresses are required to prevent unauthorized use of the
link frequency/channel assignment(s).
When the C2 Link System Connection between UA and CS is established over a
Terrestrial Wireless Network or a SATCOM Network, the CS will connect to the UA
via a Terrestrial Wireless Network gateway or SATCOM Network gateway operated
by a Communications Service Provider (CSP). In general, the CS will not be co-
located with the Terrestrial Wireless Network or the SATCOM Network gateway. The
connection between the CS and the remote Terrestrial Wireless Network gateway or
SATCOM Network gateway may be a direct leased line connection or via a ground
network such as the Internet.
The C2 Link System functionality that supports the exchange of C2 Link User Data
and Control Messages between the UA and CS via a mobile air/ground network
consists of additional functionality than that required for information exchanges over
just Point-to-Point links. The functionality required to exchange data over mobile
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