The number of voice messaging ports to install depends on numerous factors, including:

• The number of calls Unity Connection answers when call traffic is at its peak.

• The expected length of each message that callers record and that users listen to.

• The number of users.

• The number of ports that are set to dial out only.

• The number of calls made for message notification.

• The number of MWIs that are activated when call traffic is at its peak.

• The number of TRAP connections needed when call traffic is at its peak. (TRAP connections are used by Unity Connection web applications to play back and record over the phone.)

• The number of calls that use the automated attendant and call handlers when call traffic is at its peak.

• Whether a Unity Connection cluster is configured. For considerations, see the “Considerations for a Unity Connection Cluster” section .

It is best to install only the number of voice messaging ports that are needed so that system resources are not allocated to unused ports.

The calls that the voice messaging ports answer can be incoming calls from unidentified callers or from users. Typically, the voice messaging ports that answer calls are the busiest.

You can set voice messaging ports to both answer calls and to dial out (for example, to send message notifications). However, when the voice messaging ports perform more than one function and are very active (for example, answering many calls), the other functions may be delayed until the voice messaging port is free (for example, message notifications cannot be sent until there are fewer calls to answer). For best performance, dedicate certain voice messaging ports to answer incoming calls, and dedicate other ports for dialing out. Separating these port functions eliminates the possibility of a collision, in which an incoming call arrives on a port at the same time that Unity Connection takes the port off-hook to dial out.

If your system is configured for a Unity Connection cluster, see the “Considerations for a Unity Connection Cluster” section on page 2-3.

Ports that only dial out and do not answer calls can do one or more of the following:

• Notify users by phone, pager, or email of messages that have arrived.

• Turn MWIs on and off for user extensions.

• Make a TRAP connection so that users can use the phone as a recording and playback device in Unity Connection web applications.

Typically, these voice messaging ports are the least busy ports.

If your system is configured for a Cisco Unity Connection cluster, see the “Considerations for a Unity Connection Cluster” section on page 2-3.

Caution

In programming the phone system, do not send calls to voice messaging ports in Cisco Unity Connection that cannot answer calls (voice messaging ports that are not set to Answer Calls). For example, if a voice messaging port is set only to Send MWI Requests, do not send calls to it.

• A hunt group is configured to send incoming calls first to the subscriber server, then to the publisher server if no answering ports are available on the subscriber server.

• Both Unity Connection servers are active and handle voice messaging traffic for the system.

• In Cisco Unity Connection Administration, the voice messaging ports are configured so that an equal number of voice messaging ports are assigned to each Unity Connection server. This guide directs you to assign the voice messaging ports to their specific server at the applicable time.

• The number of voice messaging ports that are assigned to one Unity Connection server must be sufficient to handle all of the voice messaging traffic for the system (answering calls and dialing out) when the other Unity Connection server stops functioning.

If both Unity Connection servers must be functioning to handle the voice messaging traffic, the system does not have sufficient capacity when one of the servers stops functioning.

• Each Unity Connection server is assigned half the total number of voice messaging ports.

If all the voice messaging ports are assigned to one Unity Connection server, the other Unity Connection server is not able to answer calls or to dial out.

• Each Unity Connection server must have voice messaging ports that answer calls and that can dial out (for example, to set MWIs).

• The hunt group on the phone system sends all calls to the functioning Unity Connection server.

• The functioning Unity Connection server receives all voice messaging traffic for the system.

• The number of voice messaging ports that are assigned to the functioning Unity Connection server must be sufficient to handle all of the voice messaging traffic for the system (answering calls and dialing out).

• The functioning Unity Connection server must have voice messaging ports that answer calls and that can dial out (for example, to set MWIs).

If the functioning Unity Connection server does not have voice messaging ports for answering calls, the system cannot answer incoming calls. Similarly, if the functioning Unity Connection server does not have voice messaging ports for dialing out, the system cannot dial out (for example, to set MWIs).