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V5.2 Call Processing

The following half call matrix summarizes the different types on calls supported by Xenon. Xenon uses this matrix to classify every call into two half calls. We will be discussing V5.2 half calls in this section. ISUP half calls will be discussed in the ISUP Design section.

Half Call Types Terminating V5.2 Outgoing ISUP
Originating V5.2 This call has originated in this exchange and the called subscriber also resides in this exchange. This call originates in this exchange but the called subscriber resides in some other exchange. An ISUP trunk is used to route the call towards the destination exchange.
Incoming ISUP This call originated in some other exchange and is destined for a subscriber residing in this exchange. This is a transit call. The call was originated in some other exchange and the called subscriber resides in another exchange. This exchange is a part of the route towards the destination exchange.

V5.2

V5.2 protocol defines the interface between Local Exchange (LE) and Access Network (AN). Xenon implements the Local Exchange for V5.2. The V5.2 Call Processing module defines all the actions and resources involved in voice calls originating from or terminating on V5.2 subscribers. The following is a list of the components constituting this module along with a brief description.

V5.2 Call

The object V5.2 Call is a state machine that represents the V5.2 originating and terminating call handling on XEN processor in Xenon. The following diagram shows the basic sequence of state transitions during a V5.2 subscriber originating call and V5.2 terminating call. States associated with a timer are shown with a small clock on the left side of the state. These states are called timed states.

V5.2 state machine

Here is a high level description of the various states of V5.2 Call. For details refer to EventStudio Documents.

Idle This represents the state where no call is active on port.
Allocating This represents the condition where E1 slot is being allocated towards V5.2 subscriber. It is a timed state awaiting Allocation Complete message.
Collecting Digits This state represents the condition where the calling V5.2 subscriber is being fed dial tone and the call is collecting the called party digits dialed by the calling subscriber. It runs the timer based on Inter digit timeout more than once to collect all the digits.
Switching Path This state represents the condition where the path resource is being allocated for the call. It involves time-space-time switching for the call. The calling subscriber is being fed call routing tone at this time. It is a timed state awaiting on path resource response message from Space Slot Manager. It should be noted that Space Slot Manager gets the call routing done by Routing Manager before performing the path switching.
Awaiting Status This state represents a condition where the call routing and path resource information is being informed to the terminating XEN. It is a timed state awaiting on called subscriber's free-busy status as response. On receipt of the free-busy status, calling subscriber is either fed ring back tone or busy tone.
Ringing This state represents the condition where the called V5.2 subscriber is being rung. It is a timed state awaiting on called subscriber answer.
Originating Conversation This state represents the condition where the call is in conversation and the port is the calling subscriber in the call. The call metering is performed in this state.
Terminating Conversation This state represents the condition where the call is in conversation and the port is the called subscriber in the call. It performs the called subscriber hold(CSH) timeout if called subscriber on-hook is received.
Releasing This state represents a condition where the call is being released and the path allocated for call is being released. The reason for call release may be calling subscriber has gone on-hook, called subscriber is busy or congestion encountered on a outgoing call. It is a timed state awaiting path release response message from Space Slot Manager.
Awaiting On-hook This state represents a condition where the V5.2 subscriber, calling or called is being fed some tone indicating the call status. It is a timed state awaiting subscriber on-hook.

V5.2 Manager

The V5.2 Manager manages all the V5.2 Interfaces on a XEN processor. In turn, each V5.2 Interface manages all the V5.2 Call objects for that Interface. The V5.2 Manager performs the following functions.

  • It creates and deletes V5.2 Interface objects on OMC commands.
  • It is involved in the V5.2 Interface startup signaling with the Access Network.
  • It creates and deletes V5.2 subscribers on receipt of OMC commands.
  • It maintains the free-busy status of all the V5.2 subscribers on the V5.2 Interface.
  • It creates a V5.2 Call Object as soon as a V5.2 subscriber goes off-hook or a terminating call is received for a V5.2 subscriber.
  • It deletes V5.2 Call Object when the originating or terminating call is over.

E1 Manager

The E1 Manager manages the E1 links associated with the XEN. The E1 links are created when the V5.2 Interface is created. The E1 Manager performs the following functions:

  • It manages and allocates V5.2 E1 ports for all the E1 links in an Interface.
  • It allocates E1 slot towards calling or called V5.2 subscriber on request.
  • It de-allocates E1 slot towards calling or called V5.2 subscriber on request.

Tone Manager

The Tone Manager resides on the XEN and performs the following actions.

  • It switches the specified tone or announcement towards the given V5.2 subscriber on request.
  • It stops feeding the specified tone or announcement towards the given V5.2 subscriber on request.

DSP Manager

The DSP Manager controls the DTMF receivers for DTMF dialing subscribers on the XEN. It performs the following functions.

  • It allocates a DTMF receiver for collecting called subscriber digits dialed by the calling DTMF subscriber.
  • It de-allocates the DTMF receiver once the digit collection is over.