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Call Control Internal Interfaces

The interfaces within Call Control include the following:

Channel Management (CH) to Connection Management (CM)

Connection Management (CM) to Physical Connection Management (PC)

Channel Management (CH) to Router (RTR)

CH to CM

Through the CH/CM interface, requests are from CH to CM, while indications are from CM to CH.

The CH component reports the following to the CM:

Incoming channel events, such as Layer 3 alerting and answer

Service requests such as one to make a call association with another channel

The CM reports to the CH appropriate incoming events from a remote CM, such as remote alerting, answer, or call request indications.

CM to PC

Through the CM/PC interface, the CM communicates changes in connection requests from both the local and remote CMs. PC uses these events to determine if PCM connections should be made or broken.

CM to RTR

The CM/RTR interface manages access to a distributed call router that gives the internal call routing capabilities. The purpose of this interface is to allow the Call Control layer to query whether routing information is available for an incoming call that it is trying to service.

To satisfy many applications, the CM component provides both blocking and non-blocking versions of the router atomic functions. This arrangement provides application developers greater control in handling call routing errors. Primitives are provided not only to request and acknowledge a router service, but also to communicate a channels availability as a resource group member. Because the call router is distributed, calls cannot be queued if an entire resource group is busy.

A successful route is acknowledged by the CM component that terminates the route.

Call Control External Interfaces

Components within Call Control interface to the following software modules:

Local CM (Channel A) to Remote CM (Channel B)

Local Router (Channel A) to Remote Router (Channel B)

Signaling Layer (Layer 3)

Host (Layer 5)

DSP Manager

Switching Driver

Local CM to Remote CM

The Call Manager (CM) component of Call Control handles associations between channels (Call setup and teardown). CM manages the associations by sending messages between the PPL components on each side of the association. The messages use atomic functions in the CM state machine that are received as PPL events.

When channels are associated, call processing events are passed between them, such as Alerting, Answer, and requests for voice path connections. Information is also passed about each channel's PCM format, logical address, and physical address.

Local Router to Remote Router

Initiation of an internal router operation requires instantiation of a Router (RTR) component state machine for the channel requesting the route. For calls spanning multiple nodes, the local router initiates a router on the remote node, which continues processing the route on the remote node.

Interface to the Signaling Layer

The main call processing interface within the CSP is between Call Control and Signaling. Signaling resides on the line cards.

A protocol similar to Q.931 abstracts the network signaling layer from Call Control. It is used to accept incoming calls, make outgoing calls, answer, and release channels.

The CH component manages the Signaling interface. All events to and from the Signaling module are sent and received by the CH component. Events from Signaling are sent as PPL events into CH. Events from CH are sent to Signaling with PPL atomic functions in the CH state machine.

Interface to the Host

The Call Control interface to the host (Layer 5) communicates call processing events from the CSP to the host and allows the host to drive the call processing actions of the CSP. The host interface can be used to accept incoming calls, make outgoing calls, answer, and release channels from the host.

You customize the host interface using PPL. You can change the format of established API messages and add new messages using the PPL Event Request and PPL Event Indication messages. You can transfer new data to and from the host using the PPL Generic API feature. Call Control provides these features, which allow the host to create new call models with the CSP and to implement them using PPL.

By default, all host interface management within Call Control takes place in the CH component by default. The Router (RTR) component can terminate the Route Control message to perform certain host-initiated routing operations. The other components have a limited interface to the host, by which they can send and receive PPL events with the PPL Event Request and PPL Event Indication messages.

The following is a list of API messages used between the host and Call Control:

Host to CH

Connect

Connect Wait

Release Channel

Outseize Control

Inseize Control

Connect Tone Pattern

Connect With Pad

Disconnect Tone Pattern

Collect Digit String

DSP Service Cancel

Generate Call Processing Event

Park Channel

Connect With Data

Release Channel With Data

CPC Detection

Connect To Conference

Request For Service Response

Outpulse Digits

Connect One-Way Forced

Recorded Announcement Connect

Recorded Announcement Disconnect

DSP Service Request

PPL Event Request

Route Control

CH to Host

Message Acknowledgment (a response to any of the host-initiated message listed above)

Request For Service

Request For Service With Data

Channel Released

DS0 Status Change

Call Processing Event

Release Request

Channel Released With Data

Call Progress Analysis Result

PPL Event Indication

Interface to DSP Services

Call Control has an interface to the DSP Services module. The DSP Services module receives from various software modules requests for DSP services. DSP Services allocates DSP resources from a pool of available resources. The results of the DSP services (for example: collected digits, completion of outpulse) are reported to the requesting module.

The DSP Services module processes host-initiated DSP service requests and also initiates DSP service requests itself as a part of PPL modification. The CH state machine makes the full range of DSP services available to Call Control.

To satisfy many applications, CH provides both blocking and non-blocking versions of DSP feature requests through PPL atomic functions. This arrangement gives application developers greater control in handling errors in DSP allocation, including call failures caused by waiting for DSP service.

If a DSP resource allocation error occurs, the blocking versions automatically purge. The non-blocking versions allow the PPL to process the error.

Interface to the Switching Driver

The CSP contains a hardware/software switching subsystem that makes PCM connections between timeslots. The subsystem handles PCM connection issues such as PCM format conversion and power level (dB) output padding. Call Control simplifies this normally complex operation. The PC component controls when PCM connections are made and broken during the processing of a call.

The interface to the switching driver consists of three primitives that are accessed through atomic functions in the PC state machine. These primitives extract information from databases about the local and remote channel. Because the CSP is distributed, the PC state machine manages only half of a connection. To establish a full duplex connection, both channels must activate their default PC state machines.

Setting up, monitoring, and tearing down calls.
Protocol layer of the CSP.
See Pulse Code Modulation.
A computer, attached to the Excel platform through an RS-232 or Ethernet link, from which you run the telecommunications application that controls the Excel platform.
Application layer of the CSP.
Digital Signal Processor
See Programmable Protocol Language.
Call signaling protocol for setup and termination of calls.
A condition that, when met, drives a state machine from one state to another. A condition that drives a Component out of its current state by invoking an associated primitive.
Outgoing call setup during real-time call processing on a specific channel.
RFS. A Status Message indicating that some entity is requesting service from the Excel platform.