Calling Party??™s Category This is also a mandatory parameter for the SS7 message. The
value is set to 0000 0000 Calling party??™s category unknown when converting from a SIP
INVITE to an SS7 IAM. If the call is an emergency call, this can be set to NS/EP Call or
Emergency Service Call, dependent on the operators??™ implementation.
Forward Call Indicators The Forward Call Indicators are found in the IAM and must
be set as follows:
Bit D Interworking indicator Interworking encountered 1
Bit F BICC/ISUP indicator BICC/ISUP used all the way 0
Bits HG BICC/ISUP preference indicator BICC/ISUP not required all the way 01
Bit I ISDN Access indicator Originating access non-ISDN 0
Bit M Ported number translation indicator Number not translated 0
Number translated 1
Hop Counter The Hop Counter is mapped to the MAX-FORWARDS header in the SIP
domain. If the call originated in the SS7 domain, the Hop Counter value is used for the
MAX-FORWARDS header, and decremented by one.
In the opposite direction, the MAX-FORWARDS header value is copied into the Hop
Counter parameter of the SS7 message and decremented by one.
Establishing a Session in the IMS 127
Nature of Connection Indicators There are a number of parameters within the SS7 IAM
that must be set in the SS7 direction if a SIP INVITE is received by the MGCF. These
parameters are:
Bits AB One satellite circuit in the connection 01
Bits DC Continuity check not required (ISUP) or No COT to be expected (BICC) 00
Continuity check performed on a previous circuit (ISUP) or COT to be expected
(BICC)
10
BIT E Outgoing echo control device included 1
Transit Network Selection The Carrier Identification Code (CIC) is derived from the
REQUEST-URI if available and used to identify the transiting carrier.
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