https://www.dialogic.com/webhelp/msp1010/10.2.3/webhelp/MSP_DG/ISUP/Introduction_to2.htm

Introduction to ISUP

The Integrated Services Digital Network User Part (ISUP) is used for
establishment of wired connections between exchanges. It includes
messages associated with the connection and disconnection of calls.
ISUP is the protocol used to support the signaling necessary to
provide voice and non-voice services in telephone communications. It
is an extension of SS7, used as the interface protocol for voice and
data within, and for ingression or egression to/from the Public
Switched Telephone Network (PSTN.)

Advantages of ISUP

There are numerous advantages to using ISUP for call processing and
trunk group maintenance/management functions. These advantages
include the following:

  * Faster call setup

  * Conservation of network resources

  * Improved customer feature support as well as enhanced features

  * Improved/Automated trunk management procedures

ISUP requires that the exchange be digital and support SS7. This does
not mean that the exchange cannot interface with non-SS7 capable
devices or exchanges. All that is required is that the exchange be
able to interwork with other signaling types such as TUP, R2, R1,
DTMF and/or SS7.

Definition

The ISDN User Part defines the protocol which is used to support the
signaling functions required for both a) Non-ISDN voice/data
communications and b) ISDN voice/data communications in North
America, and for ISDN functionalities throughout the rest of the
world. ISUP can also be used to support dedicated/private
telecommunications systems consisting of either digital or analog or
mixed networks. The data from ISDN messages is transferred to ISUP
messages for call processing or data transfer. They are two separate
protocols that function together. ISDN can be thought of as a
user-side and network-side protocol while ISUP is strictly network
side. ISDN may also be used between exchanges, but that is not the
primary intent of the protocol. There is enough flexibility and spare
capacity within the protocol to support present application
requirements as well as, any foreseeable future requirements.

Currently the ISDN User Part is designed to use the services of the
SS7 Message Transfer Part (MTP). The use of the SS7 Signaling
Communication Control Part Network has been provided for in the
specification but, at present, no procedures exist that require the
use of the SCCP for ISUP. ISUP connects to the SS7 MTP as User Part
5. Because ISUP exists as a User Part, all Layer 4, 5, 6, and 7
functions are handled within the software that comprises ISUP.

Inter-Exchange Signaling

ISUP is used for the exchange of data between exchanges. Data is
passed in messages between exchanges for call processing,
maintenance, and circuit management. These messages are in the
standard SS7 format of the MSU. The actual ISUP data is carried
within the SIF.

An understanding of these messages is important as it allows you to
know what type of data is being transferred between exchanges at any
given moment in time.   There are many messages defined in the ITU
and ANSI standards. However, very few exchanges, if any, support all
of them. It is a good idea to be familiar with the various messages
even if they are not supported by your exchange. It is possible that
one of these unsupported messages may be received at your exchange,
and it is important to know how to deal with it.

ISUP Call Control and Circuit Management API

The host manages ISUP call control and circuit management through the
following mechanisms:

  * Common Call Control API message (for example Outseize Control,
    Request for Service with Data), using SS7 Parameter (ISUP) to
    pass data.

  * Channel State

DS0 Status Change messages notify the host of service state changes
and channel purges. The Service State Configure message allows the
host to bring channels in and out-of-service.

  * The PPL Event Indication and PPL Event Request messages allow the
    host to send and receive messages to and from PPL components.

The MSP 1010 sends PPL Event Indication (0x0043) messages to the host
in response to various SS7-related call processing events, such as
reception of an ACM, ANM, or CON (for ITU only) for ISUP.

Data is included in the SS7 Parameter ICB (ISUP). If you do not
require this information, ACK the message and then ignore it.

The host can generate SS7-related call processing or management
events using the PPL Event Request (0x0043) message.

You can modify the default call model to have the Called and Calling
Party Numbers passed to the host as BCD encoded digits.

Related Topic

Example Configuration for SS7 Voice Circuits.

                                   

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