Using “D” Messages for Layer 3 • 8-5 •
The H.110 Basic Rate ISDN Board
8.3 Information Elements
Information elements are used to encode information that may be required
to handle a call. In “D” messages on the H.110 BRI Board, these
elements are represented by single argument characters. Only those
elements that are needed are included in the messages. Elements that are
unambiguous or constant are encoded by the board in the Q.931 messages
but are not part of the “D” messages. Some elements that are rarely used
such as sub-addresses are not part of the “D” message scheme. Details on
which arguments are used in which specific message can be found in
Section 5.4.
8.3.1 Bearer Capability
Bearer capability is used to describe the type of call being placed. This
argument is present in both SETUP commands and responses. The four
options for bearer capability are:
A 3.1 kHz audio, 64 kbps, circuit mode, Mu-Law
D Unrestricted digital information, 64 kbps, circuit mode
R Rate adaption from 56 kbps, 64 kbps, circuit mode
S Speech, 64 kbps, circuit mode, Mu-Law
8.3.2 Cause
The Cause element is present in a number of different messages. Its
purpose is to give a reason why a particular message such as a DISConnect
was issued. Some causes such as Normal Clearing are part of a normal
call while other causes may indicate an error condition. The cause element
is quite lengthy, and therefore the argument is represented by a two digit
hexadecimal number in “D” messages. The first digit of the cause serves
to divide the causes into different classes, i.e. a ‘0’ indicates a cause related
to dialing. The list of causes are:
01 Unallocated Number
02 No route to specified transit network
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