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211 1/00
No. 75
Part Z Annex 10 - Aeronautical Telecommunications
6.5.3.4.4 Timer T4 (muximum delay between transmissions).
Timer T4 shall be set to the maximum delay
between transmissions (T4). Timer T4 shall bc started or
restarted on en-queuing a framc for transmission. Timer T4
shall never be cancelled. If a DLE does not receive a fraine
before Timer T4 expires, it shall send a command frame (P=l)
to ensure a response from the peer DLE. When in the ABM,
the DLE shall send an KR; when in the SRM, the DLE shall
send an SREJ; when in the FRM, the DLE shall send a FRMR.
The value of amer T4 shall be at least two minutes longer for
a ground DLE than for the peer aircraft DLE. The command
frame shall be transmitted using normal Timer TI procedures
up to N2 times. If no response is received, the DLE shall
assume that the link is disconnected and that site recovey
procedures shall be invoked.
Note 1.- Kmer T4 is used to verifi the continued existence
of the link.
Note 2.- There is one Emer T4 per a DLE.
6.5.3.4.4.1 Recommendation.- A DLE in the ABM or
SRM should send lrny outstanding frames with the P bit of the
last INFO frame set to I.
6.5.3.4.5 Parameter M (maximum number of bits of any
frame). The parameter N1 defines the maximum number of
bits in any frame (excluding flags and zero bits inserted for
transparency) that a DLS shall accept.
6.5.3.4.6 Counter N2 (maximum number of
transmissions). Counter N2 defines the maximum number of
transmissi,ons that the DLS shall attempt to transmit any
outstanding XID-CMD frame. A Counter N2 shall be set to
zero when a new frame is ready for transmission. Counter N2
shall be incremented after each transmission of the frame. The
counter shall be cleared after its associated frame is
acknowledged. When Tirner T1 expires, a DLE shall invoke
the retransmission procedures of 6.5.3.4.1 up to N2 - 1 times.
When Emer T3 expires, a DLE shall invoke the retransmission
procedures of 6.5.3.4.3 up to N2 - 1 times. When Counter N2
reaches the maximum number of attempts (value of parameter
N2) the LME shall be informed and the frame shall not be
transmitted.
Note 1.- There is one Counter N2 per unacknowledged
franze.
Note 2.- The value of the ground N2 parameter may be
different from the value of the aircraft N2 pammeter:
6.5.3.4.7 Paranieter k (window size). Parameter k shall be
set to the maximum number of outstanding sequentially
numbered INFO frames that may be transmitted before an
acknowledgement is required.
Note.- The val~ie of the ground k parameter may be
different from the value of the aircru. k parameter:
6.5.3.5 Description of procedures. Except as noted in
6.5.3.6 through 6.5.3.11.6, the standard procedures described
in IS0 4335 and IS0 7809 shall be followed.
6.5.3.6 Modes of operation. The only modes of operation
that a DLE shall support are those detailed below.
6.5.3.6.1 Operational mode. The operational mode shall
be asynchronous balanced mode (ABM).
6.5.3.6.2 Non-operational mode. The non-operational
mode shall be asynchronous disconnected mode (ADM).
Note.- Among the reasons a DLE or LME enters nonoperational
mode includes issuing or receiving any of the
following frames: DISC, XID-CMD-LCR, DM or
XID_RSP-LCR (abbreviated frame names are defined in
Tables 6-11 and 6-17).
6.5.3.6.2.1 DISC frame. If a DLE is unable to continue to
receive, it shall transmit a DISC to terminate the current link.
The P bit shall be set to 0 in DISC commands. A DLE shall
treat all received DISCS (regardless of the P bit) as a DISC
(F=O).
Note.- The use of a DISC command m y result in the loss
of unacknowledged data.
6.5.3.6.2.2 DM frame. If a DLS receives any valid
unicasted frame, exckpt for an XID or TEST frame,-from a
DLS with which it does not have a link, it shall respond with
a DM frame. All DM frames shall be transmitted with the F bit
set to 0. An aircraft transmitting or receiving a DM frame shall
initiate link establishment on one LME if no links remain. A
DLE shall treat all received DMs (regardless of the F bit) as a
DM (F=O).
Note I.- ff an LME is iit the process of executing n
handofl it will retrunsmit the XID-CMD-HO (P=l) and wait
for Timer T3 to expire.
Note 2.- A station receiving an itavalid frame may choose
to discard the frame insteud of resportding with u DM.
Note 3.- The procedures for an LME receivirlg a unicasted
XID*frorn an LME with which it does not have a link are fourrd
in 6.5.4.4.
6.5.3.6.3 Frame reject tnode. When in ABM or SRM, and
after transmitting a FKMR command, the DLE shaII enter the
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