In a modern Avaya Aura® Contact Centre (AACC) environment, agent desktops are typically SIP-based endpoints, such as Avaya Agent for Desktop. For these SIP agents, Application Enablement Services (AES) provides Computer Telephony Integration (CTI) by communicating with Avaya Aura® Session Manager, not directly with Communication Manager (CM) for call events. The standard-based protocol used for this communication between AES and Session Manager is TR/87, which specifies CSTA (Computer Supported Telecommunications Applications) over SIP. Session Manager then communicates with CM to control the call. Therefore, within the message flow for an AACC SIP agent, TR/87 is the essential CTI protocol used by AES.

A. WCF: Windows Communication Foundation (WCF) is a Microsoft programming framework and not a telephony signaling or CTI protocol used between Avaya Aura® core components.

B. ASAI/TSAPI: The ASAI (Adjunct/Switch Application Interface) protocol is used for the direct CTI link between AES and CM. However, this link is primarily for controlling non-SIP (e.g., H.323/DCP) endpoints, not for the modern AACC SIP agent architecture.

C. DMCC/TSAPI: DMCC (Device, Media, and Call Control) is a service used by AES for controlling endpoint devices and media streams, such as the AACC softphone client, but it is not the primary protocol for call-state event signaling.

1. Avaya Aura® Contact Center Solution Description (NN43001-109, Issue 11.0, July 2017):

Page 26, Section: Avaya Aura® Application Enablement Services: "For SIP agent support, Application Enablement Services uses the TR/87 protocol to communicate with Session Manager." This document explicitly states that TR/87 is the protocol used for SIP agents in an AACC context.

2. Avaya Aura® Application Enablement Services Overview and Specification (02-300360, Issue 11, May 2017):

Page 11, Section: CSTA Service: "The CSTA service provides an ECMA-323 CSTA Phase III XML interface that is compliant with the TR/87 standard from the SIP Forum... The CSTA service uses the TR/87 standard to communicate with Avaya Aura® Session Manager." This confirms AES uses TR/87 to communicate with Session Manager.

3. Application Notes for configuring Avaya Aura® Contact Center 7.0.2 with Avaya Aura® Communication Manager 7.1, Avaya Aura® Session Manager 7.1 and Avaya Aura® Application Enablement Services 7.1 (May 2017):

Page 4, Figure 1: Avaya Aura® Contact Center with Avaya Aura® - System Architecture: The system architecture diagram clearly illustrates a communication link labeled "TR87" between the Application Enablement Services server and the Session Manager. This visual evidence from an official configuration guide reinforces the protocol's role in the message flow.