ISDN Information Elements
Each type of message has Mandatory and Optional IEs associated with it. The
Information Element is identified with a single octet. Although a few single octet IEs
exist, most have multiple octets associated with them.
A study of all available IEs is beyond the scope of this book. However, commonly used
IEs are listed in Table 4-7. For further details, many public references are available on the
Internet. For this section, the cause, facility, progress, and display IEs are reviewed. They
represent the information most in demand in telephony systems and, therefore, most
important in the communications between the voice gateway and PBX or PSTN. Figure
4-9 illustrates the structure of common information elements.
200 Authorized Self-Study Guide: Cisco Voice over IP (CVOICE)
Length of the Cause Information
1 Class Value
Coding 0 Location
Standard
1
0 Cause IE (0x08)
8 7 6 5 4 3 2 1
The Cause IE for
Diagnosing Call Failure
Length of the Progress Information
1
Coding 0 Location
Standard
1
0 Progress IE (0x1E)
8 7 6 5 4 3 2 1
The Progress IE for
Tones and Prompts
Length of the Facility Information
Facility Description
Progress Description
Length of the Display Information
1
Coding 0 Location
Standard
1
0 Display IE (0x28)
8 7 6 5 4 3 2 1
The Display IE for the
Caller Name in Q.931
Display Description
1
Coding 0 Location
Standard
1
0 Facility IE (0x1C)
8 7 6 5 4 3 2 1
The Facility IE for the
Caller Name in QSIG
Figure 4-9 Common Information Elements