In a Cisco Unified Communications Manager (CUCM) and Cisco Unity Connection (CUC) integration using SCCP, CTI (Computer Telephony Integration) ports act as virtual endpoints for the voicemail system. These ports must register with CUCM's CTI Manager service to handle calls. If these ports are not registered, CUCM cannot route calls to the voicemail system (e.g., when a user dials the voicemail pilot number) or receive calls from it (e.g., for Message Waiting Indication - MWI). Therefore, a failure to route calls between the systems points directly to a CTI port registration issue, which is a fundamental connectivity requirement for the integration to function.

B. Verify OPTIONS Ping in the SIP trunk profile. This is incorrect because the problem explicitly states the integration uses SCCP (Skinny Client Control Protocol), not SIP. OPTIONS Ping is a keepalive mechanism for SIP trunks.
C. Verify voicemail SIP trunk in the route list. This is incorrect as the integration is SCCP-based. Call routing to voicemail in an SCCP integration uses a route pattern pointing to the voicemail ports, not a SIP trunk.
D. Verify Calling Search Space in the Directory Number setting. This is incorrect because the Calling Search Space (CSS) on the CTI ports' directory numbers primarily affects outbound calls from Unity Connection (e.g., MWI, call transfers), not the fundamental ability for CUCM to route calls to the voicemail system.

1. Cisco Unified Communications Manager Administration Guide

Release 12.5(1)SU1

"Device Menu" section

"Phone Configuration" chapter.

Reference: This guide details how to find and manage devices

including CTI Ports. The status page for any device

including a CTI port

will show its registration status with Cisco Unified CM. A status of "Unregistered" would confirm the issue. This is a primary troubleshooting step for device connectivity.

2. Integration Guide for Cisco Unity Connection Release 12.x

"Creating a Telephony Integration with Cisco Unified Communications Manager by Using SCCP" chapter.

Reference: This document outlines the creation of a "voice-mail port" in CUCM for the integration. It states

"For each voice-mail port

Cisco Unified CM creates a CTI port device." This confirms that CTI ports are the foundational element for call handling in an SCCP integration.

3. Cisco Unified Communications Manager System Guide

Release 12.5(1)SU1

"Cisco CTI Manager" chapter.

Reference: This guide explains

"Cisco CTI Manager... allows CTI applications to register and communicate with Cisco Unified Communications Manager." It clarifies that CTI ports

as CTI devices

depend on the CTI Manager service for registration and call control. A failure in this process prevents call routing.