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Access To Contact Header

Overview

For an endpoint to endpoint call, one endpoint receives an INVITE message (in this case the CSP) and returns a 200OK response. The endpoint that sent the INVITE message uses the Contact information from the 200OK response to send the ACK message to the CSP and subsequent messages such as BYE.
Likewise, the endpoint that receives the INVITE (in this case the CSP) uses the Contact header to send future requests such as BYE. Final responses to INVITE message have to be routed back the same path.

This feature allows the host read and write access to the following fields in the contact header in the 200OK response for an INVITE message:

• Contact Display Name

• Contact Username

• Contact Parameters

Note that the host portion cannot be changed b ecause if it is changed, the remote end point would not be able to route future requests to the CSP correctly.

Pertinent Specification

RFC 2543/3261

API Messages Used

• PPL Event Request (0x0044)

• PPL Event Indication (0x0043)

• Connect with Data (0x0005)

Description

Write Access to Contact Header

The write access to the display name, username, and parameter in the Contact header involves the outbound 200OK response for the INVITE message received and outbound REFER message.

The SIP stack allows the host to fill in the Display Name, Username, and Parameter in the Contact header using the following NPDI TLVs:

• 0x292B - NPDI SIP Contact Display Name

• 0x292C - NPDI SIP Contact Parameters

• 0x292D - NPDI SIP Contact Username

To modify the Contact header fields in the 200OK response for the INVITE message, the host includes the TLVs either of the following:

• PPL Event Request for answer in Layer 4 (Component 0x61, Event 0xC9)

• Connect with Data (0x0005) message

Important! For coupled Call Agent Mode enabled calls, where the host has provided the physical span/channel, the CSP will ignore the above TLVs unless the host continues to provide the coupled span/channel.

Read Access to Contact Header

The read access to the Contact Header fields involves the inbound 200OK response for the INVITE message sent and the inbound REFER message.

The SIP stack reports to the host the Display Name, Username and Parameters in the Contact header with the following NPDI TLVs.

• 0x292B - NPDI SIP Contact Display Name

• 0x292C - NPDI SIP Contact Parameters

• 0x292D - NPDI SIP Contact Username

Configuring the CSP to Report Contact Header

The SIP stack reports the Contact Header as follows:

• For Remote End Answered messages- PPL Event Indication (Component 0x00A7, Event 0x0020)

• For Inbound REFER messages- PPL Event Indication (Component 0x00A7, Event 0x0020)

This feature is disabled by default. You can enable this feature with the EXS API as follows.

To enable this feature, set bit 13 in the SIP Message Information Mask (0x027F) TLV in the VoIP Protocol Configure (0x00EE) message.

Refer to Configuring SIP in the Converged Services Administrator User’s Guide to configure with SwitchKit CSA.

Positive acknowledgment to a message
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.
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.
Network Protocol Data Intelligence. Also called “Interworking,” it is a software product that operates within Excel’s Call Control (Layer 4) and Services (Layer 5) call processing layers. NPDI is meant to enhance Excel’s call processing product offering by allowing call processing layers (specifically Layers 4 and 5) to perform advanced analysis, generation, and conversion of Network Signaling (NS) Layer 3 information.
Call processing layer of the CSP.
Tag-Length-Value block. A standardized block that allows data to inserted in a standard way into API messages.
Voice over Internet Protocol. The delivery of voice information in digital form in discrete packets rather than in the traditional circuit-committed protocols of the public-switched telephone network (PSTN).
CSA. GUI-based tool used to configure, provision and monitor a Excel platform related to, for example, SIP, H.323, and VDAC Resouce Attributes.
See Converged Services Administrator.