Dialogic 6.2 - Manual (Page 107)

BSMI Debugging
November 2009 107
Interpreting Information Elements
For Q.931 call control messages, the first Information Element (IE)
starts at byte offset 9 in the hexadecimal string. Each message can
contain several IEs of either fixed (single byte) or variable length.
Figure 8 on page 108 compares the general IE format against the
first IE contained in the example SETUP message, and illustrates
the following points:
„ A value of 0 in the shaded bit position indicates a variable-length
IE; a value of 1 in that position indicates a single byte IE.
Note:
Single byte IEs are commonly used for locking codeset shifts.
Locking shift IEs appear only after all variable-length IEs
within the message. Refer to the Bellcore Technical Reference
TR-TSY-000268 for more information on the structure and use
of single byte IEs and codeset shifts.
„ The IE identifier value 0x04 indicates a Bearer Capability IE;
refer to Table 4 on page 108 for possible IE identifier values. IEs
appear in messages in ascending order according to their
identifier number.
„ The 2-byte length of the IE value indicates that it contains only
the required structures for a Bearer Capability IE.
„ The IE contents indicate an information transfer capability of
unrestricted digital information (0x88) and a transfer rate/mode
equal to 64 kbps/circuit mode (0x90).
0 1 1 1 1 0 1 1 7B Information
0 1 1 0 1 1 1 0 6E Notify
0 1 1 1 1 1 0 1 7D Status
0 1 1 1 0 1 0 1 75 Status Enquiry
Table 3. Q.931 Message Types (Continued)
Message Type Bits Hex Message
IEs
00C10000080101050 4028890 180181 2C0735353532303030
03 278D Xmit 00 60 0 Setup 00 00 0 0018