Introduction to BT IUP


The British Telecom Interconnect User Part (BT IUP) feature offered by Cantata provides the signaling procedures, formats, and codes that are used to support standard customer services and network features at the point of interconnect between public networks in the United Kingdom using the C7 IUP protocol. The BT IUP feature was derived from the standards of the Public Network Operators - Interconnect Signaling Committee (PNO-ISC).

The common call control procedures are drawn upon as necessary to implement the various services provided in the BT IUP protocol. Cantata provides BT IUP as a variant of the TUP and L3P TUP modules of an SS7 protocol stack. Once configured, the host may issue messages to place outgoing calls and receive incoming calls.


This section describes the use of the BT IUP protocol, provides an example of a configuration file used to set up an SS7 protocol stack for BT-IUP and shows call flows for the BT IUP.

Message Processing

The Cantata implementation of the BT IUP protocol allows the host to issue any IUP message embedded with the BT IUP Parameters data ICB (0x23). This ICB is formatted from multiple Tag Length Value (TLV) elements. One TLV element that will always be present contains the "H0" and "H1" bytes. These bytes are listed in the H0/H1 Allocation Code tables of the PNO-ISC specifications. Additional TLV elements are used to specify any missing parameters in the underlying IUP message. The L3P BT IUP PPL component contains control logic and atomic functions to retrieve and validate TLVs as required, based upon the initial derived message type. That is, derived from the H0 H1 TLV. L3P BT IUP supplies default values to complete a message so that the message can be sent to a far-end CSP.

To further support off loading the host of routine message processing, the BT IUP Parameters data ICB may appear in Outseize Control messages. When the BT IUP Parameters data ICB is present in the message new activity may be undertaken within the L3P BT IUP PPL component on behalf of the host. The L3P BT IUP PPL has access to an atomic function which tests for the presence of this ICB and CSPs to user-desired PPL logic based upon the actual message type.

Important! This implementation is coded to the CSP for "standard" processing. Any user-desired processing may be added as desired.

Features Available

In addition to the basic features the host application may include:

Answer an incoming call, stimulate the host to place an outgoing call, and then connect both.

Place an outgoing call by forming the smallest message possible.

Place an outgoing call utilizing the BT IUP message of the host’s design.

Automate the typical host call processing by off-loading routine operations to the PPL (L3P IUP PPL).

Remove functionality from either of the PPLs and allow the host to perform as much of the protocol as desired.

Allow Cantata customers to receive and transmit every BT IUP message currently specified, or to be specified.

Support Call Failure Reporting to the host for both incoming and outgoing calls.

Support Circuit Group Out of Service

Support common Querying Messaging

Support Audit Logging

Support Error Alarms

Support Fault Logs

Support redundancy

Messages Not Supported

The following messages are not supported. These messages may be passed from the host to the network via PPL Event Requests, and may be passed from the network to the host in PPL Event Indications. Therefore, any processing required on their behalf are handled entirely by the host. All other messages listed in PNO-ISC/SPEC/006 Issue 3 May 1999 are supported.


Call Drop Back (CDB)

Enveloped ISUP Message (EIM)

Enveloped ISUP Segmented Message (EISM)

Nodal End-to-END Data (NEED)

Operator Condition Message (OCM)

Node-to-Node Message (OSS)

Protocol Negotiation Message (PNM)

User-to-User Data (UUD)

Congestion Control

Congestion control is supported for BT IUP. See Enabling Congestion Control for BT IUP for more details.