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¡.2 Dynamic mode switching (see Figure 3)
'he mode switching procedure makes use of the frame structure specifíed in 4 and of the sequences defíned in 5. It
hould be noted that all terminal receivers musí remain in frame search throughout the cali.
Vhen the terminal ís receiving ín a framed mode, that is, it ís capable of decoding bit A, mode switching should be
lelayed if the A bit is set to 1; eventually the mode mismatch recovery procedure as described in 6.4 míght be used.
Vhen the terminal X wishing to make a mode switch is receiving unframed signáis, the capability exchange sequence
nay be used fírst to forcé the other terminal Y to a framed mode; henee terminal X can check for incoming A — 0. This
ise of sequence A Ís particularly necessary if X was previously transmítting unframed signáis, since Y would not be in
i posítion to deal wíth a mode change from X until it had regaíned frame alignment (see 6.2.3). If X had previously
leen transmitting framed signáis, the capability exchange sequence may be omitted on the assumption that if Y had
tnexpectedly lost frame alignment it would already have attempted a recovery procedure (see 7),
[.2.1 Dynamic mode switching from a framed mode to another framed mode
'he basic sequence mode switching described Ín 5.2 is used.
U the transmitting terminal, if a BAS command is transmitted to sígnal a new mode, the transmitter must opérate in
he appropriate mode from the first octet of the next sub-multiframe.
¡imilarly, at the receiving terminal, if the received BAS signáis a new mode, the receiver must opérate in the
ppropriate rnode from the first octet of the next sub-multiframe.
1.2.2 Dynamic mode switching from a framed mode to an unframed mode
^.s in 6.2.1, the basíc sequence mode switching described in 5.2 is used.
íowever, as the BAS for sígnalling an unframed mode is transmitted for a single sub-multiframe, a mode mismatch
nay occur in drastic error condítions. Optionally, a method may be used to improve the reliability of the switching: the
iew BAS valué Ín the basic sequence mode switching is repeated three times; this WÍ11 cause a temporary corruption of
Ele least significant bit of the received ínformation.
1.2.3 Dynamic mode switching from an unframed mode to another mode (framed or unframed)
?he basic sequences frame reínstatement and mode switching are sequentially transmitted, the former including
apabilíty exchange if necessary.
1.3 Mode O forcing procedure
¡ee Figure 4
>.3.1 Single channel
Vhere ít is necessary to ensure that both termináis are operating in mode O (for ínstance before cali transfer), tras
irocedure is used.
'he forcing terminal uses dynamic mode switching (see 6.2) with BAS audio command to switch to mode OF, followed
ly sequence A using BAS (100) indicating only G.711 audio capability. The valué [1 or 2] appropriate to the terminal"s
iwn región Ís used in case.the cali is to be transferred to a local G.725 type-0 terminal. On receipt of this, the remote
erminal Ís obliged to switch to mode OF also using the indicated law for its encoder and decoder. The procedure is
omplete when the forcing terminal detects incomíng mode OF. Changes of network configuraron can now be
mplemented (see 8).