ISUP:Information element usage

Within every notification or request message (other than a configuration message), the host application will have to read or insert data structures called “information elements” (or IEs). These data structures contain mandatory or optional information required by the ISUP layer and/or the remote ISUP layer to properly process the required operation (such as issuing a voice call).

The SS7 ISUP specifications define approximately one hundred different IEs that are used differently according to the variant or type of message. As a common example, the “called party number” IE contains the phone number of the party the host application wants to connect to. Therefore, this IE is inserted in the IAM message to inform the remote ISUP layer about the targeted end-user.

NOTE: ITU-T information elements are described more in detail in specification document Q.763.

NOTE: IE encoding, although similar between specifications (i.e. ANSI and ITU), may still differ slightly and requires that the user have access to the specification documents he plans to use. Since those are copyright-protected documents, TelcoBridges cannot make those directly available.

IE inclusion in different messages

Depending on which messages are sent to / received from the SS7 network, the host application should expect specific IEs to be inserted or processed. The following two tables show in which messages IEs can be used or are to be expected. Some IEs are mandatory, which means that a request toward the stack will fail if they are not present. On the other hand, it does mean that optional IEs are not required but that it may depend on the variant that is being used or on the local network implementation. This is why the host application designer needs to verify with national or international authority for the proper IEs.