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ISUP Call Processing

The ISDN User Part (ISUP) is an application layer of SS7 stack. ISUP was originally designed to implement sophisticated signaling schemes for ISDN. Even though ISDN had limited success in the marketplace, ISUP has become the de-facto standard for signaling between digital exchanges.

Xenon has digital trunk connectivity with other exchanges in the network. SS7/ISUP protocols are used for signaling. The following is a list of components constituting ISUP call processing module along with a brief description.

ISUP Call

ISUP Call task in Xenon is designed to handle both incoming and outgoing ISUP calls. It creates the Incoming ISUP Call object for handling incoming ISUP calls. Outgoing ISUP Call object is created to handle outgoing ISUP calls.

Refer to message sequence chart documents under the section EventStudio Documents for message signaling details. The ISUP Call object in these documents covers both outgoing and incoming cases.

Incoming ISUP Call Object

The Incoming ISUP Call object is a state machine that handles the incoming call on digital trunk circuit. The states of the Incoming ISUP Call contain all the message protocol sequence for ISUP at incoming end under different scenarios.

The ISUP Call object for an incoming call is created on receipt of IAM i.e. Initial Address Message in ISUP signaling. It is deleted once the REL i.e. Release - RLC i.e. Release Complete sequence is completed with the previous exchange and all the call resources have been released. It performs the following actions.

  • It receives ISUP messages from the SS7 message handler.
  • It sends ISUP messages to the SS7 message handler.
  • It gets the Path resource allocated from Space Slot Manager.
  • It maintains ISUP signaling timers while awaiting ANS i.e. Answer Message and RLC i.e. Release Complete Message.
  • It gets the Path resource de-allocated from the Space Slot Manager when the call ends.

Outgoing ISUP Call Object

The Outgoing ISUP Call object is a state machine that handles the outgoing call on digital trunk circuit. The states of the Outgoing ISUP Call contain all the message protocol sequence for ISUP at outgoing end under different scenarios.

The ISUP Call object for an outgoing call is created on receipt of Call Request Message from the originating or incoming XEN once the call routing is done . It is deleted once the REL i.e. Release - RLC i.e.Release Complete sequence is completed with the next exchange. It performs the following actions.

  • It receives ISUP messages from the SS7 message handler.
  • It sends ISUP messages to the SS7 message handler.
  • It maintains ISUP signaling timers while awaiting ACM i.e. Address Complete Message and RLC i.e. Release Complete Message.

ISUP Call Manager

The ISUP Call Manager manages all the Incoming ISUP Call objects and Outgoing ISUP Call objects on a XEN. It creates Incoming ISUP Call object on receipt of IAM i.e Initial Address Message on an incoming trunk.It creates a outgoing ISUP Call when the call routing results in call outgoing on ISUP circuit. It deletes the Incoming or Outgoing ISUP Call object once the Call is over.