Plan for UM

Applies to: Office 365 for enterprises

If you plan to deploy Exchange Unified Messaging (UM), or to integrate an existing on-premises UM deployment with cloud-based UM, make sure you've prepared by reading the following:

  • Understand how UM coexistence works
  • Estimate your capacity needs
  • Prepare your infrastructure for a cloud UM deployment
  • Prepare to deploy UM in the cloud
  • Plan to migrate UM-enabled mailboxes to the cloud
  • Plan for UM auto attendants in the cloud
  • When you're ready to deploy

Understand how UM coexistence works

UM coexistence means you’re deploying UM both on-premises and in the cloud. To support UM coexistence, you need to do two separate deployments: one on-premises and one in the cloud. The only point at which the two deployments could intersect is at the PBX, and only if you’re splitting the traffic on a PBX to both on-premises mailboxes and cloud-based mailboxes.

If you’re planning to migrate your UM mailboxes to the cloud or to set up your organization to support UM coexistence, you need to understand the differences between an on-premises deployment of UM and UM deployment in the cloud. For more information, see Differences Between an On-Premises Deployment of UM and UM Deployment in the Cloud.

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Estimate the capacity you need

For UM deployments that don’t use Lync, each call handled by UM for an organization must pass through the organization’s session border controller (SBC). An SBC is a SIP-aware firewall that allows your PBX to communicate with the UM service in the cloud without exposing your corporate network or telephony infrastructure to the public network. Before you can determine the capacity required for your SBC to handle the UM traffic for your organization, you need to determine the number of concurrent calls that must be handled by the SBC.

When selecting an SBC, consider the following:

  1. How many UM-enabled users must be supported.
  2. What additional call handling capacity should be provisioned to cover periods of high caller demand and possible growth of the user base.

The following chart shows an estimate of the number of UM-enabled users who can be supported, based on the number of concurrent calls for a small system (up to 25 concurrent calls).

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The next chart shows an estimate of the number of UM-enabled users who can be supported, based on the number of concurrent calls for larger systems (up to 50,000 concurrent calls). You can estimate the number of users who can be supported for a larger organization by extending the lines in this chart above 50,000 concurrent calls.

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The more concurrent calls to UM that your SBC can handle, the greater the number of users that it can support. However, the actual number of users who can be supported depends on your organization’s use of UM.

  • Light usage   Represented by the upper two lines in the charts, light usage is calculated for systems in which the average user receives fewer than 4 voice messages per day and calls in to Outlook Voice Access at most once a day, for about a minute, to listen to voice messages. This model allows for an automated attendant. The two light usage lines represent different levels of tolerance for callers receiving a busy signal. That is, the lines indicate whether a caller trying to use the system at its busiest times has a 1 percent or 5 percent chance of hearing a busy signal because all available phone lines available in the SBC are already in use. The difference between the two lines is relatively small, but it can have an impact in your capacity planning.
  • Heavy usage   Represented by the lower two lines in the charts, heavy usage is calculated for systems in which the average user receives 10 voice messages per day and calls in to Outlook Voice Access for 6-7 minutes per day. This model allows for several automated attendants. As in the light usage profile, there are two lines showing different levels of tolerance for callers receiving a busy signal.

The usage in most organizations is likely to be somewhere between light and heavy, though light voice mail usage is becoming more common now that there are so many ways of contacting users. Users often review UM voice messages with an e-mail client rather than dialing in to Outlook Voice Access.

Here are examples to illustrate possible scenarios.

  • Small System, Heavy Usage   Contoso has 200 Exchange users who will be UM enabled in Office 365. They use voice mail heavily. The Contoso administrator wants to ensure that the chance of a caller receiving a busy signal when they’re trying to access or leave voice mail in the busiest part of the day is no more than 1 percent. On the Small System Capacity Planning chart, the administrator reads across from the point at which 200 is marked on the vertical axis, and determines that 15 concurrent calls should be more than enough to meet the requirements, but 10 may not be enough.
  • Large System, Light Usage   Fabrikam has 1600 Exchange users who will be UM enabled in Office 365. They’re light users of voice mail: the Fabrikam administrator estimates that an average user only receives 1 or 2 voice messages per day. The Fabrikam administrator wants to ensure that the chance of a caller receiving a busy signal when they’re trying to access or leave voice mail in the busiest part of the day is no more than 1 percent. On the Large System Capacity Planning chart, the administrator reads across from the point at which 1600 is marked on the vertical axis, and determines that 25 concurrent calls should be more than enough to meet the requirements, but 20 may not be enough.

After you’ve established your call capacity requirements, consult with your SBC manufacturer for information about how to order, license, and purchase an SBC with the required capacity. Note that some SBCs are more suitable for smaller installations, and call capacity can be licensed up to 25 concurrent calls, in multiples of 5. Other SBCs scale to larger capacities, and the licensing is in correspondingly larger increments. You may want to consider future needs when you select an SBC.

As your organization changes, continue to keep these requirements in mind. You can use the UM Call Statistics report to track the trends in call volume over time. For more information, see Review the UM Calls for Your Organization.

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Prepare your infrastructure

Make sure you have sufficient bandwidth and the necessary hardware for UM in the cloud.

Bandwidth

Verify that your organization’s network and your on-premises hardware support a cloud-based UM deployment and coexistence:

  • Analyze the voice mail traffic and usage pattern on your PBX to understand the maximum number of concurrent voice mail calls that’s typical in your organization.
  • Use the information about your maximum concurrent voice mail calls and the codec used to encode the media traffic to determine your required network bandwidth for cloud-based UM. You may find that you need more than one UM IP gateway.

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Install additional hardware

To support secure Voice over IP (VoIP) communication over the public network, you may need to install an SBC and a VoIP gateway.

The following diagram shows the infrastructure required to support UM for a system with a PBX that doesn’t support IP.

Connecting a Traditional PBX to Exchange Online UM

For checklists that help you set up UM with your telephone system, including IP PBX and Lync Server deployments, see Integrate UM with a Telephone System.

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Prepare to deploy UM in the cloud

Before you deploy UM in the cloud, the following planning steps will make the deployment go more smoothly:

  1. PBX traffic   Decide how you’re going to divide the traffic from your existing PBX. You need a unique pilot number for each UM dial plan in your cloud-based deployment.
  2. PBX used for cloud-based UM   Ensure that the PBX you want to use for integration with cloud-based UM has sufficient resources. These resources, which include a voice mail pilot number and voice channels for hunt groups, must be able to support the maximum number of concurrent calls you plan to support for your pilot users. If you’re using one PBX for both cloud-based and on-premises UM, you have to create separate hunt groups for voice mail on the PBX, and you have to have at least two pilot numbers: one for cloud-based mailboxes and another for on-premises mailboxes.
  3. SBC certificate   Obtain a digital certificate signed by a certification authority (CA) for your SBC. VoIP traffic between your SBC and cloud-based UM must use SIP over TLS and secure RTP (SRTP). SIP over TLS is different from SIP over TCP in that it uses encryption at the transport layer to secure the signaling. SRTP encrypts the audio payload. For more information, see the documentation for your SBC. For more information, see Get a Certificate for Exchange UM Online.

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Plan to migrate UM-enabled mailboxes to the cloud

When you decide which UM mailboxes you want to move to the cloud, consider the following differences in how UM works.

Feature Supported in cloud-based UM? Supported in on-premises UM?

Language support

All languages are supported

Varies depending on which language packs are installed

Speech access to the directory search feature

No

Yes

Speech-enabled auto attendants

No

Yes

Speech access to Outlook Voice Access

Yes

Yes

For more information about how to migrate UM mailboxes to the cloud, see Plan to Migrate UM-Enabled Mailboxes.

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Plan for auto attendants in the cloud

When you plan whether to move UM auto attendants to the cloud or keep them on-premises, consider the following:

  • Language support   Cloud UM automatically supports all languages that Exchange Online is localized for. For on-premises UM, you must install each language pack you want to use. For more information, see Language Support for Outlook Web App, the Exchange Control Panel, Unified Messaging, and Exchange Server 2010.
  • Speech-enabled directory search   Cloud UM doesn't support speech-enabled directory search. On-premises UM fully supports it.
  • Voice mail greetings   A UM auto attendant deployed in the cloud can retrieve the voice mail greetings for mailboxes in the cloud only. And on-premises UM auto attendants can retrieve voice mail greetings for mailboxes hosted on premises only.

If you're ready to create an auto attendant in the cloud, here’s how: Set Up and Manage a Unified Messaging Auto Attendant

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When you're ready to deploy UM

See Set Up Unified Messaging or Set Up Unified Messaging in a Hybrid Deployment. For additional help in setting up Exchange Unified Messaging with your PBX and an SBC, or with Lync Server 2010, see the following checklists:

For help troubleshooting your deployment, see the Unified Messaging Troubleshooting Tool.

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