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Outbound SIP Call with Call Agent Mode

Overview

With this feature, the CSP has the bearer on/off switching capability for outbound call legs too.

This capability is needed when the media services in the CSP (like DSP-2 card) or media transit path (like external TDM IVR or operator) is required for the called party.

Description

Call Agent Mode (CAM) in the CSP provides dynamic switching of media streams on or off the CSP RTP channels with a minimal amount of SIP messages.

Inbound Calls

Prior to this feature, the CSP supported bearer on/off switching of Call Agent Mode for inbound calls only. The CSP can connect the inbound leg of a SIP call to a TDM network or to a DSP media service.

This functionality allows the caller to be connected to an operator in a PSTN network. It also allows the application of DSP services such as playing announcements to the calling (inbound) leg.

Bearer switching is based on a coupling and decoupling mechanism. Coupling associates a physical timeslot with a virtual timeslot to enable bearer-switched service. Decoupling dissociates a physical timeslot from a virtual timeslot to enable bearer-free switched service.

The bearer switching takes place whenever required with minimal interaction from the host.

Outbound Calls

With this feature, the CSP has the bearer on/off switching capability for outbound call legs too.

This capability is needed when the media services in the CSP (like DSP-2 card) or media transit path (like external TDM IVR or operator) is required for the called party.

Example: A directory assistance operator is located behind a TDM switch. The initial conversation between the operator and called party is bearer-switched through the CSP. Later, the operator drops out of the call flow while connecting the calling party and the called party bypassing the bearer path from the CSP.

PPL Event Request to Generate RE-INVITE message - PPL Event Request (0x0024)

The PPL Event Request (0x0024) is used to generate a
RE-INVITE message to the SIP endpoint connected to the channel indicated in the channel AIB.

This PPL Event Request will work only if the call is in bearer-free mode or else it will NACK with 0x130C (Call is not in bearer-free mode.)

The PPL Event Request is added to the SIP UA (0x00A7) component. When the PPL Event Request generates a RE-INVITE message, the 200 OK SIP message received from the other end having the SDP information will be reported to the host using the PPL Event Indication (0x0020) by the SIP UA component.

The data in the PPL Event Indication could be used within the subsequent Connect with Data (0x0005) message. The received PPL Event Request is ACKED if the data is valid.

Generic PPL ICB in Outseize Control (0x002C) message

The Outseize Control (0x002C) message is enhanced to support the following two TLVs within the Generic PPL ICB (0x001E):

• Channel Service TLV (0x0116)

• Call Agent Physical Channel ID TLV (0x011A)

0x001E Generic PPL

ICB Type | 0x03 (Extended Data)
ICB ID | 0x001E
Data Length (2 bytes) | Variable
Number of TLVs (2bytes) | Variable
Tag | TLV 1 Tag
Length | TLV 1 Length
Value | TLV 1 Value
: | TLV n Tag
: | TLV n Length
: | TLV n Value
TLVs | 0x0116 Channel Service 0x011A Call Agent Physical Channel ID

NACK

Value | Description | Corrective User Action
--- | --- | ---
0x130C | Call not in bearer-free mode | Be sure call is in bearer-free mode.

API Messages Used

The following messages are used by this feature. Refer to the API Reference for the formats.

• PPL Event Request (0x0044) message

• Outseize Control (0x002E) message

PPL Information

PPL Component 0x00A7:

• Event Request 0x0024 - Generate RE-INVITE message

• Event Indication 0x0020 - Answer on B-Side

Digital Signal Processor
See Time Division Multiplexing.
See Integrated Voice Response.
Real-Time Transport Protocol. Supports transport of real-time data like interactive voice and video over packet-switched networks.
Session-Initiation Protocol. A signaling protocol used for establishing sessions in an IP network. A session could be a simple, two-way telephone call, or it could be a collaborative multi-media conference session.
Public Switched Telephone Network
See Programmable Protocol Language.
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.
See Address Information Block.
Negative acknowledgement to a message.
See Information Control Block.
Outgoing call setup during real-time call processing on a specific channel.
Tag-Length-Value block. A standardized block that allows data to inserted in a standard way into API messages.
A programmable software component that uses PPL state machines that can be modified with the PPL Tool.