A 1 3 – 1 9 1
040 7448 329657 (04.97) PC-SW 4.5
A N N E X E 4 : I N V E R S E M U L T I P L E X E R ( I S O / I E C 1 3 8 7 1 )
A13.1.3
Function of ISO/IEC CD 13871
Mode 1 (implemented in TITAN) has the following features:
– An initial channel is set up from the calling terminal (CT) to the answering
terminal (AT).
– This initial channel is used to exchange messages in which the CT provi-
des information to the AT on the preferred mode and the required data rate
n (n*64kbit/s or b*56kbit/s). In the event of discrepancies, the AT can at this
stage make alternative suggestions. The CT can accept the alternative or
reject it, in which case the connection is terminated.
– If a common mode has been agreed on, the CT requests further telephone
numbers from the AT (in accordance with the agreed data rate). Once all
required numbers have been exchanged (by handshake procedure), the
CT sets up the additional channels.
– When all the channels have been set up, each of these channels is used
to transmit a frame structure which allows the receiving terminal to carry
out delay equalisation. This delay equalisation is made necessary by the
possibly different channel routings which means that transparency cannot
be assured.
– The CT and AT calculate the delays between the individual channels and
then switch the channels transparently, i.e. no frame structure is transmit-
ted and the transmission capacity of the individual channels can be used
fully for user data (payload). Switching off the frame structure has a disad-
vantage, however: a change in the delay in one or more of the channels
(due to a changed routing in an exchange, for example) cannot be detec-
ted and corrected.
A13.1.4
Use of ISO/IEC CD 13871 with audiovisual (AV) terminals
ISO/IEC CD 13871 is used by AV terminals that realise connections over se-
veral ISDN channels and transmit the H.221 structure in only one channel, or
(e.g. due to insufficient processor capacity) are not in a position to process the
H.221 structure in each channel. These AV terminals use ISO/IEC CD 13871
for delay equalisation, otherwise also possible with the H.221 frame structure.
Since some of these AV terminals do not have ISO/IEC CD 13871 implemen-
ted, the provision of an additional unit to carry out inverse multiplexing beco-
mes necessary.
A13.1.5
Realisation of ISO/IEC CD 13871 (BONDING)
Inverse multiplex units that have BONDING mode 1 implemented are provi-
ded by various manufacturers (e.g. ASCEND, Newbridge). These terminals
have, depending on the respective configuration, an RS449 interface on the
host side, for example (used to exchange data between the AV terminal and
the network), and as network interface, a certain number of S
0
interfaces.
A13.1.6
Relationship between ISO/IEC CD 13871 and H.221
The H.244 specification describes the interoperation of H.221 and ISO/IEC
CD 13871. It specifies how the a switchover (in particular the frame search
with the corresponding timeouts) between H.221 and ISO/IEC CD 13871 must
take place.
Содержание Titan
Страница 1: ...TITAN Videocodec ISDN Videocodec Operator Manual ...
Страница 2: ...T I T A N V I D E O C O D E C I S D N V I D E O C O D E C O P E R A T O R M A N U A L ...
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Страница 147: ...8 153 040 7448 329657 04 97 PC SW 4 5 C H A P T E R 8 F A C T O R Y S E T T I N G S ...
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Страница 183: ...A12 189 040 7448 329657 04 97 PC SW 4 5 A N N E X E 3 O N S C R E E N D I S P L A Y O S D O P T I O N ...
Страница 187: ...A13 193 040 7448 329657 04 97 PC SW 4 5 A N N E X E 4 I N V E R S E M U L T I P L E X E R I S O I E C 1 3 8 7 1 ...
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