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link establishment (or handoft). is no longer viable.
Explicit subnetwork connection maintenance. The process by
which an aircraft DTE maintains a subnetwork connection
with a ground DTE with which it has a subnetwork
connection only after completing the link handoff.
Frame. The link layer frame is composed of a sequence of
address, control, FCS and information fields, bracketed by
opening and closing flag sequences. A valid frame is at
least 11 octets in length and contains an address field
(8 octets), a link control field (1 octet) and a frame check
sequence (2 octets). A frame may or may not include a
variable-length information field.
Initiated handoff. The transmission process by which a station
initiates link handoff.
Internetworking protocol. A protocol that transfers data
packets between intermediate systems and end systems
interconnected by subnetworks and that is supported by the
routing protocols and addressing plan.
Link. A link connects an aircraft DLE and a ground DLE and
is uniquely specified by the combination of aircraft DLS
address and the ground DLS address. A different subnetwork
entity resides above every link endpoint.
Link establishment. The process by which an aircraft and a
ground LME discover each other, determine to communicate
with each other, decide upon the communication
parameters, create a link and initialize its state before
beginning communications.
Link handoff. The process by which peer LMEs, already in
communication with each other, create a link between an
aircraft and a new ground station before disconnccting the
old link between the aircraft and the current ground
station.
Link layer. The layer that lies immediately above the physical
layer in the Open Systems Interconnection protocol model.
The link layer provides for the reliable transfer of information
across the physical media. It is subdivided into the
data link sub-laycr and the media access control sub-layer.
Link lnanagement entity. A protocol state machine capable of
acquiring, establishing, and maintaining a connection to a
single peer system. An LME establishes data 1,ink and subnetwork
connections, "hands-off" those connections, and
manages the media access control sub-layer and physical
layer. An aircraft LME tracks how well it can communicate
with the ground stations of a single ground system.
Media access control {MAC). The sub-layer that acquires the
data path and controls the movement of bits over the data
path.
Multicast. A transmission intended to be received by multiple
stations.
Network layer. The layer that provides the upper layers with
independence from the data transmission and routing
functions used to connect systems. The network layer is
responsible for routing and relaying functions both within
any subnetwork and throughout the aeronautical internetworking
domain.
New link (or new ground station). After successful completion
of handoff (or link establishment), the new
"current" link.
N(r). The receive sequence number at the link layer, which
indicates the sequence number of the next expected hame
(and explicitly acknowledges all lesser numbered frames).
N(s). The send sequence number at the link layer, which
indicates the sequence number associated with a transmitted
frame.
Old link (or OM ground station). Following link establishment
during a handoff, the link that was previously the "current"
link becomcs the "old" link.
Physical layer. The lowest level layer in the Open Systems
Interconnection protocol model. The physical layer is
concerned with the transmission of binary information-over
the physical medium (e.g. VHF radio).
Private parameters. The parameters that are contained in
exchange identity (XTD) frames and that are unique to the
VHF digital link environment.
Proposed link (or proposed ground station). The link being
negotiated (in a handoff) to replace the current link.
Quality of service. The information relating to data transfer
characteristics used by various communication protocols to
achieve various levels of performance for network users.
Requested handofJ The one-transmission process by which a
station requests its peer entity to initiate a link handoff.
Service primitives. The status and control information that
must be available to the receiving entity to properly
6111W7
No. 72
Part I Annex 10 - Aeronautical Telecommunications
process incoming information. A service primitive may
contain parameters. If parameters exist, they describe
information that is defined either as mandatory (M) or
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