Information Technology Reference
In-Depth Information
A
terminal
receiving
EndSessionCommand
without
first
having
transmitted it shall
•
If the initiating terminal's EndSessionCommand message indicated
“disconnect line,” optionally follow process above, then proceed to
phase E.
Otherwise, follow process above, then proceed to phase E. If possible,
•
the responding terminal should proceed to the new mode indicated
in the initiating terminal's EndSessionCommand message.
3.2.1.3.5 Supplementary Services and Call Clearing
If the terminal arrived at supplementary services and call clearing by invol-
untary disconnection, it shall disconnect or revert to analog telephony,
depending on a predetermined configuration.
A terminal wishing to terminate a call shall first initiate the session end
procedure described in phase endsession.
In supplementary services and call clearing, the terminal should proceed
as it indicated in the EndSessionCommand message. If it indicates a change
to another digital communication mode, it shall begin the new mode at the
equivalent of Initialization; otherwise, it shall initiate the cleardown proce-
dures defined in V.34.
3.2.2 introduction of H.245
H.245 provides a number of different services, some of which are expected to
be applicable to all terminals that use it and some are more specific to particu-
lar ones. In H.245, these services are named as Signaling Entities (SE). Each
SE defines a series of procedures to handle with corresponding messages.
Procedures are defined to allow the exchange of audiovisual and data capabili-
ties; to request the transmission of a particular audiovisual and data mode; to
manage the logical channels to transport audiovisual and data information; to
establish what terminal is the master terminal and what is the slave terminal
for the purposes of managing logical channels; to carry various control and
indication signals; to control the bit rate of individual logical channels and the
whole multiplex; and to measure the round trip delay, from one terminal to the
other and back. These procedures are explained in more details below.
3.2.2.1 Master-Slave Determination Signaling Entity
Conflicts may arise when two terminals involved in a call initiate simi-
lar events simultaneously and only one such event is possible or desired.
For example, conflicts may arise when resources are available for only one
occurrence of the event. To resolve the conflict, one terminal shall act as the
master and the other terminal shall act as a slave terminal. Rules specify
how the master and slave terminal shall respond at times of conflict.
