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InfoMagic Standards 1994 January
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1991-12-31
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1 LAPB has entered a disconnected -------------------------------- 0
phase ------->
(i.e. Conrol <TERM>, see Note 3)
3 LAPB has entered a disconnected -------------------------------- 0
phase ------->
(i.e. Conrol <TERM>, see Note 3)
Any Physical level has no circuit to -------------------------------- 0
a remote DTE ------->
Note 1 - Status <OP-T> indicates to LAPB that the sending of frames is enabled.
Note 2 - Status <INOP-T> indicates to LAPB that the sending of frames is
inhibited.
Note 3 - Control <TERM> indicates that LPAB has entered the disconnected phase
(equivalent to ADM of HDLC).
Note 4 - HDTM uses the idle data link channel state indication (at least 15
contiguous 1's) for requesting that the remote DTE enter the half-duplex sending
state.
Fascicle VII.5 - Rec. T.71 PAGE1
TABLE 2/T.71
Description of state transitions in terms of the V.26 bis modem interface
Present Event Action New
state state
0 Calling DTE: Circuit 107 ON Turn circuit 105 0N 4
Connect LAPB to circuit 103
0 Called DTE: Circuit 107 ON Start timer T 2
4 Circuit 106 ON Enable sending of LAPB frames 1
(see Note 1)
1 Transmission concluded (see Note Inhibit sending of LAPB frames
2) Disconnect LAPB from circuit 103
Hold circuit 103 in the binary 1 2
condition
Turn circuit 105 OFF (see Note
3)
Start timer T
2 Reception of a flag Stop timer T 3
2 Expiry of timer T Turn circuit 105 ON
Release circuit 103 from binary 4
1 condition
Connect LAPB to circuit 103
3 Reception of 15 contiguous 1 Turn circuit 105 ON
bits (see Notes 4 and 5) Release circuit 103 from binary
1 condition
Connect LAPB to circuit 103
PAGE6 Fascicle VII.5 - Rec. T.71
4
1 LAPB has entered a disconnected Turn circuit 105 0FF 0
phase
3 LAPB has entered a disconnected -------------------------------- 0
phase ------->
Any Circuit 107 OFF Turn circuit 105 OFF 0
Note 1 - It is necessary to ensure that at least one full flag is transmitted
after circuit 106 comes ON. This flag may be the opening flag of the first frame.
co
concluded by either of the following:
V counting a sequence of contiguous flags on circuit 103 while in state 1,
V a timeVout, T,
V a signal from another source, e.g., from a higher level.
However, if no frame is transmitted while in state 1, not less than five
contiguous flags shall be sent in state 1 before entry into state 2.
Note 3 V It is recommended that circuit 105 not be turned OFF until 15 bit times
after the binary 1 condition is established on circuit 103. This will assure
transmission of an idle sequence to the remote DTE.
Note 4 V It is recognized that whether or not an idle sequence is sent by the
remote DTE, the DTE will detect an idle sequence after circuit 109 goes OFF,
since according to Recommendation V.26 bis, this will hold circuit 104 in the
binary 1 condition.
Note 5 V It is understood that circuit 109 will go OFF. Entry into state 4 may be
made dependent on this OFF condition, as an implementation option.
Fascicle VII.5 - Rec. T.71 PAGE1
ANNEX A
(to Recommendation T.71)
Additional rules making for greater efficiency in half-duplex transmission
A.1 General considerations
- Greater efficiency is obtained in recovery situations.
- The application of these rules is optional.
- The application of these rules does not imply any incompatibility or
entail any amendment of DTEs (or DCEs) which observe the procedures
described in Recommendation T.71.
A.2 Rules of operation
1) Before the DTE (or DCE) gives the turn b
that it has acknowledged all the frames received and
accepted before it received the turn.
2) If the DTE (or DCE) receives or takes the turn, it will
always first retransmit all the I-frames which have not
been acknowledged.
3) The DTE (or DCE) must replace the last RR frame in each
turn, if any, by an REJ frame carrying the appropriate
N(R).
PAGE6 Fascicle VII.5 - Rec. T.71