Home > Articles > Cisco Unified Communications Manager Deployment Models

Cisco Unified Communications Manager Deployment Models

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Mar 10, 2017.

Chapter Description

In this chapter from Implementing Cisco IP Telephony and Video, Part 1 (CIPTV1) Foundation Learning Guide (CCNP Collaboration Exam 300-070 CIPTV1), 3rd Edition, the author team introduces Cisco Unified Communications Manager (CUCM) and explores different redundancy models.

CUCM Call-Processing Redundancy

A cluster is a set of networked servers that can be configured to provide specific services per server. Some cluster servers can be configured to provide CUCM services while other servers can provide Computer Telephony Integration (CTI), Trivial File Transfer Protocol (TFTP), and other media services such as conferencing or music on hold (MOH) These services can be provided by the subscribers and the publisher and can be shared by all servers.

Clustering provides several benefits. It allows the network to scale to up to 40,000 endpoints, provides redundancy in case of network or server failures, and provides a central point of administration. CUCM also supports clusters for load sharing. Database redundancy is provided by sharing a common database, whereas call-processing redundancy is provided by CUCM groups.

A cluster consists of one publisher and a total maximum of 20 servers (nodes) running various services, including TFTP, media resources, conferencing, and call processing. You can have a maximum of eight nodes for call processing (running the Cisco CallManager service).

For a quick recap, a CUCM cluster has a CUCM publisher server that is responsible for replicating the database to the other subscriber nodes in the cluster. The publisher stores the call detail records, and is typically used to make most of configuration change, except starting with CUCM 8.0 where database modifications for user facing call processing features are made on the subscriber servers. The subscriber servers replicate the publisher’s database to maintain configuration consistency across the members of the cluster and facilitate spatial redundancy of the database.

To process calls correctly, CUCM needs to retrieve configuration settings for all devices. These settings are stored in a database using an IBM Informix Dynamic Server (IDS). The database is the repository for information such as service parameters, features, device configurations, and the dial plan.

The database replicates nearly all information in a star topology (one publisher, many subscribers). However, CUCM nodes also use a second communication method to replicate run-time data in a mesh topology as shown in Figure 2-9 (every node updates every other node). This type of communication is used for dynamic information that changes more frequently than database changes. The primary use of this replication is to communicate newly registered phones, gateways, and DSP resources, so that optimum routing of calls between members of the cluster and the associated gateways occurs.

Figure 2-9

Figure 2-9 Cisco Unified Communications Manager Database Replication Overview

Database replication is fully meshed between all servers within a cluster. Static configuration data, because it is created through moves, adds, and changes, is always stored on the publisher and replicated one way from the publisher to each subscriber in the cluster. However, user-facing feature data, for example, Cisco Extension Mobility features, is writeable on a subscriber and are replicated from an updated subscriber to all other servers. All nonuser-facing feature data can be written only to the publisher database and is replicated from the publisher to all subscribers.

User-facing features are typically characterized by the fact that a user can enable or disable the feature directly on their phone by pressing one or more buttons, as opposed to changing a feature through a web-based GUI.

As illustrated in Figure 2-10, user-facing features that are listed below do not rely on the availability of the publisher. The dynamic user-facing feature data can be written to the subscribers to which the device is registered. The data is then replicated to all other servers within the cluster. By allowing the data to be written to the subscriber, the user-facing features can continue to function in the event of a publisher failure.

Figure 2-10

Figure 2-10 User-Facing Feature Processing

User-facing features are any features that can be enabled or disabled by pressing buttons on the phone and include the following:

  • Call Forward All (CFA)

  • Message Waiting Indicator (MWI)

  • Privacy Enable/Disable

  • Do Not Disturb (DND) Enable/Disable

  • Cisco Extension Mobility Login

  • Hunt-Group Logout

  • Device Mobility

  • CTI CAPF status for end users and application users

Therefore, most data (all nonuser-facing feature data) is still replicated in hub-and-spoke style (publisher to subscribers), while user-facing feature data is replicated bidirectionally between all servers.

Cisco Unified Communications Manager Groups: 1:1 Design

A 1:1 CUCM redundancy deployment design, as illustrated in Figure 2-11, guarantees that Cisco IP phone registrations never overwhelm the backup servers, even if multiple primary servers fail concurrently. This design provides high availability and simplifies the configuration. However, the 1:1 redundancy design has an increased server count compared with other redundancy designs and may not be cost-effective.

Figure 2-11

Figure 2-11 1:1 Redundancy Design

The other services (dedicated database publisher, dedicated TFTP server, or MOH servers) and media-streaming applications (conference bridge or MTP) may also be enabled on a separate server that registers with the cluster.

Each cluster must also provide the TFTP service, which is responsible for delivering IP phone configuration files to telephones, along with streamed media files, such as MOH and ring files. Therefore, the server that is running the TFTP service can experience a considerable network and processor load.

Depending on the number of devices that a server supports, you can run the TFTP service on a dedicated server, on the database publisher server, or on any other server in the cluster.

In Figure 2-11, an Open Virtualization Archive (OVA) template with the maximum number of users functions as the dedicated database publisher and TFTP server. In addition, there are two call-processing servers supporting a maximum of 10,000 Cisco IP phones. One of these two servers is the primary server; the other server is a dedicated backup server. The function of the database publisher and the TFTP server can be provided by the primary or secondary call-processing server in a smaller IP telephony deployment (fewer than 1000 IP phones). In this case, only two servers are needed in total.

When you increase the number of IP phones, you must increase the number of CUCM servers to support the IP phones. Some network engineers may consider the 1:1 redundancy design excessive because a well-designed network is unlikely to lose more than one primary server at a time. With the low possibility of server loss and the increased server cost, many network engineers choose a 2:1 redundancy design that is explained in the following section.

Cisco Unified Communications Manager Groups: 2:1 Design

Figure 2-12 shows a basic 2:1 redundancy design. While the 2:1 redundancy design offers some redundancy, there is the risk of overwhelming the backup server if multiple primary servers fail. In addition, upgrading the CUCM servers can cause a temporary loss of some services, such as TFTP or DHCP, because a reboot of the CUCM servers is needed after the upgrade is complete.

Figure 2-12

Figure 2-12 2:1 Redundancy Design

Network engineers use this 2:1 redundancy model in most IP telephony deployments because of the reduced server costs. If a virtual machine with the largest OVA template is used (shown in Figure 2-11), the server is equipped with redundant, hot-swappable power supplies and hard drives, and it is properly connected and configured, it is unlikely that multiple primary servers will fail at the same time, which makes the 2:1 redundancy model a viable option for most businesses.

As shown in the first scenario in Figure 2-12, when no more than 10,000 IP phones are used, there are no savings in the 2:1 redundancy design compared with the 1:1 redundancy design, simply because there is only a single primary server.

In the scenario with up to 20,000 IP phones, there are two primary servers (each serving 10,000 IP phones) and one secondary server. As long as only one primary server fails, the backup server can provide complete support. If both primary servers failed, the backup server would be able to serve only half of the IP phones.

The third scenario shows a deployment with 40,000 IP phones. Four primary servers are required to facilitate this number of IP phones. For each pair of primary servers, there is one backup server. As long as no more than two servers fail, the backup servers can provide complete support, and all IP phones will operate normally.

9. Cisco Voice Gateways and Cisco Unified Border Element | Next Section Previous Section

Cisco Press Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Cisco Press and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Cisco Press products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@ciscopress.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by Cisco Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.ciscopress.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020