In Cisco's Intelligent Contact Management (ICM) solution, a label is a string of characters or digits that is used to route calls to specific destinations or play specific prompts to the caller. When ICM sends back a label of 91919191, it is an invalid or non-existent label and the caller will hear an error message. This error message could be a pre-recorded message or a system generated message such as "The dialed number is not in service" or "Invalid extension, please try again".
It's important to note that MoH (Music on Hold) is a feature that plays music or pre-recorded announcements to callers while they are on hold, Ringing is the sound that a caller hears when the call is being connected and Audio is a general term that refers to the sound or voice that is played to the caller.

The signed certificate that is less administration in environments with many servers, such as CCE, is the Certificate Authority (CA) signed certificate. This type of certificate is signed by a trusted Certificate Authority (CA), which eliminates the need to manually manage each server's certificate. The CA signed certificate is also more secure than a self-signed or third-party signed certificate, as the CA has verified the identity of the certificate's owner and can revoke it if necessary. Security Authority (SA) signed certificates are not commonly used in CCE environments.

The call is assigned to a call type in the PCCE system when the call is first post-routed from Cisco Unified Customer Voice Portal (Unified CVP). The call type is determined by the data in the Cisco TCD table [1]. The call type is then used to guide the call routing scripts and determine how the call is routed to an agent [2].
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cust_contact/contact_center/icm_enterprise/icm_enterprise_12_6_1/design/guide/ucce_b_ucce_soldg-for-unified-cce-1261/rcct_b_ucce_soldg-for-unified-cce-1261_chapter_011.html
1. Solution Design Guide for Cisco Unified Contact Center Enterprise ...
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cust_contact/contact_center/icm_enterprise/icm_enterprise_12_6_1/design/guide/ucce_b_ucce_soldg-for-unified-cce-1261/rcct_b_ucce_soldg-for-unified-cce-1261_chapter_011.html
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cust_contact/contact_center/pcce/pcce_11_5_1/maintenance/Guide/PCCE_BK_P5FE2CBD_00_pcce-features-guide-11-5.pdf
2. Cisco Packaged Contact Center Enterprise Features Guide Release ...
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cust_contact/contact_center/pcce/pcce_11_5_1/maintenance/Guide/PCCE_BK_P5F

Two considerations for Active Directory (AD) are that Read-Only Domain Controllers (RODC) are supported and that it supports multi-domain, single AD Forest topology. RODC are used to provide secure access to AD data in remote locations, and the multi-domain, single AD Forest topology allows multiple domains to be managed from a single AD forest. Additionally, global catalogs are required at each AD site to enable efficient searches across the entire AD forest. AD does not provide a user interface, but Remote Access Control is available for software that is used to manage and administer the AD environment.