UK ISUP Signaling Sub-field Descriptions

Sub-Field 1

Protocol Variant (always UK-ISUP)

Sub-Field 2

Presentation Number Nature of Address
3 decimal characters, 000-999.

Sub-Field 3

Presentation Number Address Restriction Indicator
1 decimal character, 0-3.

Sub-Field 4

Presentation Number Screening Indicator
1 decimal character, 0-3.

Sub-Field 5

Presentation Number Digits
Variable length string, up to 30 decimal characters.

Sub-Field 6

The Partial Calling Line Identification Digits (fixed length string of 18 decimal characters).
The Partial Calling Line Identification is generated when the actual Calling Line Identification is not available or can not be obtained. Each switch within the Network is assigned a unique Partial Calling Line Identification, which is obtained from the Official Telecommunication body (OFTEL).
For example, a Partial Calling Line Identification of 123456789045450000 is interpreted as:

• 12 – Type of Switch
• 345 – PNO Identify
• 678 – Switch Number
• Remaining Digits – Bilaterally Agreed Digits (with trailing zeroes inserted to fill subfield)

Sub-Field 7

The Release Reason (3 decimal characters, 0-255).
The IUP specific Release Reason used to terminate the Call. The value is encoded per the PNO 6 specification, Section 2.4.24, Release Reason.

Sub-Field 8

Malicious Call Trace (variable length string of up to 3 characters). Valid values are:

• "" – No trace on this call.
• "MCT" – A Malicious Call Trace (MCT) is being performed on this call. This will help tracing the call through the network.

Sub-Field 9

Service Information (3 decimal character enumeration or empty)
This field contains service related information associated with the call. This field was initially added to carry the DPNSS Ring Back When Free service information.
Valid values for this field are:

• empty – An ordinary call with no service information.
• 1 – CPC_SVC_INFO_DPNSS_REAL (a real call established for ring back when free).
• 2 – CPC_SVC_INFO_DPNSS_VIRTUAL (virtual call established for ringback when free)