ISUP:Information element usage

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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.


Note: In the following two tables, mandatory items are denoted by 'M' while optional items are denoted by 'O'.



ISUP mandatory/optional IEs (ITU)

Information elements IAM SAM IN IN COT ACM CO CP ANM FOT RE RL CC BLO BLA SU CF CG CGB CQ CQ FAA FR FAC ID IR NR SG PAM US UPA
RS UBL UBA RE CG CGU GR FAR UP
LPA OL UCI GR
Access delivery information O O O O O
Access transport O O O O O O O O O
Automatic congestion level O
Backward call indicators M M O O
Call diversion information O O
Call history information O O
Call reference O O O O O O O O O O
Called party number M
Calling party number O O O
Calling party’s category M O
Cause indicators O O M O M M
Circuit group supervision message type ind. M M
Circuit state indicator M
CUG interlock code O
Connected number O O
Connection request O O O
Continuity indicators M
Echo control information O O O O
Event information O O O O O O O O O O O O O O O O O O O O O O
Facility indicator M
Forward call indicator M
Generic digit O O
Generic notification ind. O O O O O O
Generic number O O O O O
Generic reference O
Information indicators M
Information request indicators M
Location number O
Message compatibility information O O O O O
MCID response indicator O
MCID request indicators O
MLPP precedence O
Nature of connection indicators M
Network specific facility O O O O O O O O
Optional backward call indicators O O O O
Optional forward call indicators O
Original called number O
Originating ISC point code O
Parameter compatibility information O O O O O O O O O O O O O O
Propagation delay counter O
Range and status M M M M
Redirection information O O
Redirecting number O
Redirection number O O O O O
Redirection number restricted O O O O O
Remote operations O O O O O O
Service activation O O O O O O
Signaling point code O
Subsequent number M
Suspend/resume indicators M
Transit network selection O
Transmission medium requirement M
Transmission medium requirement prime O
Transmission medium used O O O O
User service information O
User service information prime O
User-to-User indicators O O O O O O O O
User-to-user information O O O O O O O M



ISUP mandatory/optional IEs (ANSI)

Information elements IAM INR INF CRA CRM COT ACM EXM ANM CPG FOT REL CFN CVR CVT CCR BLO BLA SUS CGB CGBA GRS CQR FAC
RLC RSC UBL UBA RES CGU CGUA GRA
LPA UCIC CQM
Access transport O O O O O O
Automatic congestion level O
Backward call indicators M O O
Business group O O O O O
Call reference O O O O O O O O O
Called party number M
Changed number O O O
Calling party number O O
Calling party’s category M O
Carrier identification O
Carrier selection information O
Cause indicators O O M
Circuit group assignment map O O
Circuit group characteristic indicators M
Circuit group supervision message type ind. M M
Circuit identification name O
Circuit state indicator M
Circuit validation response ind. M
CLLI code O
Connection request O O O O O
Continuity indicators M
Egress service O
Event information M
Forward call indicator M
Generic address O O
Generic digits O
Generic name O
Hop counter O
Information indicators M O O O
Information request indicators O M
Justification indicators O
Nature of connection indicators M M
Network transport O O O O O
Notification indicator O O
Original called number O
Operator services information O
Optional backward call indicators O O O
Originating line information O O
Outgoing trunk group number O
Precedence O
Range and status M M M M
Redirection information O O O
Redirecting number O O
Remote operations O O O O O
Service activation O O O O O O
Service code O
Special processing request O
Suspend/resume indicators M
Transaction request O
Transit network selection O
Transmission medium used O O O
User service information
User service information prime O
User-to-User indicators O O O
User-to-user information O O O O O O

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