Information Technology Reference
In-Depth Information
4. MasterSlaveDeterminationAck
5. VendorIndentification
6. MultiplexEntrySend
7. MultiplexEntrySendAck
8. OpenLogicalChannel
9. OpenLogicalChannelAck
10. MiscellaneousCommand:VideoFastUpdatePicture
11. RoundTripDelayRequest
12. EndSessionCommand:disconnect
Here only messages 7 and 8 are dynamic because their content depends
on messages sent by remote terminals. Normally, message 1 to message
9 are only exchanged during call setup phase and message 10 and 11 are
used to maintain the call, and finally conversation is terminated using the
EndSessionCommand:disconnect command.
To present a clear idea about the details of a message and its submes-
sages, let's take TerminalCapabilitySet as an example. The message,
TerminalCapabilitySet is used by sending the terminal to inform the
receiving terminal about its multiplexer capabilities and also about its sup-
ported media codecs. An example of the hierarchical message structure of
TermnalCapabilitySet is shown in Figure 3.11. Here, we may observe that
most contents can be kept unchanged since they describe the capability of
a multimedia mobile terminal (as they are fixed for that specific terminal).
However, there is a field called “sequenceNumber,” which is used to label
instances of the TerminalCapabilitySet so that the corresponding response
can be identified. If there appear multiple instances of TerminalCapabilitySet
with the same content, then only the sequenceNumber field can easily be
changed dynamically.
Data structures
Parameters
Sequence number
Terminal capability set
Multiplex capability
Protocol identifier
H223 capability
Protocol identifier
. . .
Figure 3.11
Message structure of TerminalCapabilitySet. (From Fung Po Tso, Yufei Du, Weijia Jia, “Design
of an Efficient and Robust Multimedia Gateway for Pervasive Communication,” Wireless
Telecommunications Symposium, 2008. With permission.)
