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Walkthrough Wednesdays

Unity Connection Design FAQ






The document answers frequently asked questions on designing a Cisco Unity Connection based Voice Messaging Solution.

Cisco Unity Connection is a feature-rich voice messaging platform that runs on the same Linux-based Cisco Unified Communications Operating System that is used by Cisco Unified Communications Manager.



Q1. What are the different Voice Messaging Types available for an enterprise considering Cisco Unity Connection?



There are 3 types are voice message types available while deploying Cisco Unity Connection.

  • Voicemail Only: Refers to telephony voicemail integration where there is no access to the voicemail via any messaging client.
  • Integrated Messaging: Refers to voicemail with telephony access as well as voicemail-only access via a messaging client for example IMAP Client such as Cisco Jabber.
  • Unified Messaging: Refers to voicemail with telephony access as well as voicemail, email, and fax access via a messaging client for example Text to Speech & Single Inbox.



Q2: What are the different messaging deployment models supported with Cisco Unity Connection?



Cisco Unity Connection supports the following messaging deployment models

  • Single-site messaging
  • Multisite deployment with centralized messaging
  • Multisite deployment with distributed messaging

The below tables provides a glance at the combinations supported by Cisco Unity Connection solution when deployed with Cisco Unified Communications Manager (CUCM).


Table 1 Supported Combinations of Cisco Unity Connection and Unified CM Call Processing Deployment Models

Model Type

Cisco Unity Connection

Single-site messaging and single-site call processing


Centralized messaging and centralized call processing


Distributed messaging and centralized call processing


Centralized messaging and distributed call processing


Distributed messaging and distributed call processing


Centralized messaging with cluster over the WAN


Distributed messaging with cluster over the WAN



Q3: What is the typical Port to User ratio while sizing Voice Mail Ports?



There's no hard and fast rules to sizing a system for the number of users per port. Typically sizing should be based on the customer's previous voicemail system's traffic patterns. Ratios of 20/1 or 25/1 or 40/1 are commonly used, however it's really specific to the customer's traffic patterns. If previous traffic pattern reports aren't available from the previous voicemail system, one can always run with the port/user ratio given by the OVA template and then run the port usage analyzer tool to collect actual traffic patterns on the server and then adjust accordingly.


Q4: What are the elements that influence the scale and size of Unity Connection solution?



The key elements that can influence an organizations choice of hardware are listed below

  • Audio Codecs: Default is g711ulaw. Minimal transcoding impact when using g729a. Usage of iLBC and g722 places a significant load and has different impact on voice ports that can be provisioned.
  • Voice Ports: While sizing voice ports take into consideration the use of the Web Inbox web client, or the Cisco Unity Connection ViewMail for Microsoft Outlook client and Networking.
  • Voice Message Storage Capacity: The message storage is designed to handle between 20 minutes to 30 minutes of message storage (using the G.711 system recording codec) for each user configured according to the supported message platform. This equation changes in case faxes and email replies/forwards are also stored on box.
  • Users: Consider current and future expansion
  • Simultaneous TUI/VUI Sessions
  • Client Access: Various types of clients can access a Unity Connection server or cluster for voicemail retrieval and these include IMAP, RSS Reader, Visual Voicemail, Web Inbox etc.


Q5: What is the minimum and maximum number of users a Unity Connection solution can support?



Unity Connection server or server pair (Active/Active Cluster) supports a range of 100 to 20,000 users. For details on the different scalability options available for Cisco Unity Connection, please refer to Cisco Unity Connection 9.x Supported Platforms List





1. Deploying Cisco Unity Connection in a virtualized environment provides more flexibility to an organization as opposed to physical hardware option.

2. For organizations with up to 500 users, Cisco Unity Connection is available in Cisco Unified Communications Manager Business Edition (CMBE), a single-server solution that includes a co-resident Cisco Unified Communications Manager, which further simplifies installation, support, and maintenance.


Q6: Can a Cisco Unity Connection cluster be split into Virtual & physical hardware?



Yes. If you install a Cisco Unity Connection cluster on one virtual machine and one physical machine, it is recommended to configure the virtual machine to match the specifications of the physical server for CPU, memory, and disk space. If disk space on the physical server and virtual machine do not match, Cisco Unity Connection uses the smaller disk size to determine when the disk on which messages are stored has reached maximum capacity.


Q7: Does Cisco Unity Connection Cluster support Dual (Split) Data Center Architecture?



Yes. A Cisco Unity Connection cluster can be deployed across the WAN and a max RTT between the servers should be 80ms. For detailed list of requirements for splitting a Cisco Unity Connection cluster, please refer to

Cisco Unity Connection Cluster Requirements When the Servers Are in Separate Buildings or Sites section of System Requirements for Cisco Unity Connection


Q8: What are the load balancing best practices in a Cisco Unity Connection Cluster?



Leading load balancing best practices are listed below


  • Load Balance Calls: It is recommended to route most calls to the subscriber server.
  • Load Balance Clients: It is recommended to route most client access requests (IMAP, RSS, Web Inbox etc) to the publisher server.
  • Each Cisco Unity Connection server in a Connection cluster must have voice messaging ports designated for dial-out functions such as TRAP, Message Notification, MWI etc.


Q9: What are the user provisioning options available in Cisco Unity Connection?



Users can be provisioned in Cisco Unity Connection using one of the following options


  • Manually Provisioning
  • Bulk Provisioning using Cisco Unity Connection Bulk Administration Tool
  • Import Users via AVVID XML Layer (AXL) from CUCM
  • Import Users via LDAP from an existing user directory for example Microsoft Active Directory


Q10: What does LDAP support in Cisco Unity Connection include?



LDAP support in Cisco Unity Connection includes the following

  • Synchronization of user information from corporate directory.
  • Authentication of Cisco Unity Connection Web Applications through LDAP.
  • Cisco Unity Connection Multi-Forest LDAP Synchronization: Supported by using Active Directory Lightweight Directory Services (AD LDS) as a single forest view integrating with the multiple disparate forests. For more details, please refer to How to Configure Unified Communications Manager Directory Integration in a Multi-Forest Environment
  • LDAP Filtering
  • LDAPv3
  • LDAP over SSL (LDAPS)





Voicemail Password/PIN is still locally maintained.

Q11: What mechanisms are available to scale Cisco Unity Connection messaging solution beyond 20,000 users ?



A Cisco Unity Connection system can be scaled to 100,000 users by making using of networking options i.e. Digital Networking & VPIM networking. For more details on networking and how it can help solve scalability concerns an of an organization, refer to the Networking Guide for Cisco Unity Connection





The URL redirects to Cisco Unity Connection – Maintain & Operate Guides. Please select the Networking Guide for Cisco Unity Connection document pertinent to the release you’re deploying.

Q12: Which digital networking link to choose while designing Cisco Unity Connection Networking?



The below table can be used as a cheat sheet for deciding which digital networking link suites best to your organizations needs


Table 2 Intrasite Networking Vs Intersite Networking


Intrasite Networking

Intersite Networking






  • Easier to administer:


  • System distribution list membership is replicated throughout the site, so you do not have to decide which site should home a list.
  • For each remote messaging server that you connect to via VPIM, you only have to configure VPIM location details once.
  • The message recall feature works across all locations in the site.
  • You can mix Cisco Unity Connection release 7.x, 8.x, and 9.x servers.
  • You have the flexibility to add an intersite link to a Cisco Unity Digital Network or to another Cisco Unity Connection site in the future. 
    • Supports up to 20 locations (in combination with intrasite networking).


  • Requires less bandwidth than intrasite networking for replication traffic over the intersite link, particularly if there are many locations on each side of the link.
  • Data is replicated once between the gateways over the link rather than being replicated directly to all nodes in the network.
  • System distribution list membership is not replicated across the link.
  • Replication can be scheduled to occur only during off-hours.
  • The intersite link uses a synchronous protocol that is more bandwidth-efficient than SMTP.




  • Requires higher bandwidth for replication than intersite networking.


  • Supports only up to 10 locations. 
    • Requires more administrative overhead, especially when both sites must be configured for VPIM locations.
    • Message recall does not work between sites.
    • All locations must be running Connection release 9.x.
    • Does not allow for linking to a Cisco Unity Digital Network.


Q13: Does Cisco Unity Connection offer SRST equivalent for voicemail in a centralized messaging with centralized call processing deployment model?



Yes. Cisco Unity Connection offers a feature named Survivable Remote Site Voicemail (SRSV) which allows a remote site user to access voicemail when the IP connectivity/WAN to Central site is down. Cisco Unity Connection 9.1(1) now offers native SRSV which allows voicemails to be synched when the WAN/IP Connectivity is restored. This eliminates the need for Unified Messaging Gateway (UMG) which was required to achieve SRSV previously. For more details on Native SRSV support on Cisco Unity Connection 9.1(1), please click here.


Q14: Are there any special considerations for Single Inbox feature for Cisco Unity Connection?



Yes. Single inbox has special requirements especially related to bandwidth when separated by WAN. See a pictorial view explaining the requirements.




For more detailed requirements for Single Inbox, please refer to my Ask the Expert: Designing, Configuring & Monitoring of Cisco Unity Connection


Q15: How many types of integrations does Cisco Unity Connection support and what is the maximum number of integrations it can support?



Cisco Unity Connection supports unlimited number of integrations; however the number of integrations is dependent on the available ports.

  • Integration with CUCM using SCCP & SIP
  • Integration with CUCME using SCCP & SIP
  • Integration with CUCM Business Edition Using SCCP Only
  • Integration via PIMG
  • Integration via TIMG
  • Integration via ISR to QSIG enabled Phone System


Q16: What VMWare features are supported by Cisco Unity Connection?



Cisco Unity Connection supports a limited set of VMWare features offered by VMWare vSphere. For a detailed list of supported features, please refer to VMware Feature Support for Messaging and Presence 8.0(2) through 9.x



Q17: Does Cisco Unity Connection support SNMP for monitoring?



Yes. Cisco Unity Connection supports SNMP v1, 2c and 3 for monitoring. Use the Cisco Unified Serviceability Portal to configure SNMP support.

Related Information

Cisco Unity Connection 9.x Supported Platforms List

Cisco Voice Messaging - Cisco Unified Communications System 9.x SRND

Design Guide for Cisco Unity Connection 9.x

System Requirements for Cisco Unity Connection Release 9.x


Also refer to the Q&A for my Ask the Expert: Designing, Configuring & Monitoring of Cisco Unity Connection