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Cisco Unity port sizing

Viewing 6 posts - 1 through 6 (of 6 total)
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  • #27179 Reply
    Sijbren Beukenkamp

    Not sure if this is right place to ask this question, so please forgive if it isn’t.

    A customer in Europe is migrating towards IP Telephony and Unified Messaging from Cisco. They did not have VM or UM in the legacy environment.

    Are there any guidelines of how many ports I need to design for the Unity servers based on the number of users.

    What also might help if there is some indication from other deployments.

    Thanks in advance

    #27180 Reply
    Andrew Zhilenko

    Check the PortaSIP/PortaUM solutions from Porta Software ( They are open source and do not have any per-port limitations.

    #27181 Reply
    Sijbren Beukenkamp

    Haven’t read the full documentation, but is seems to be a interesting product to keep in mind.
    Some questions:
    1. Does it scale to 10000 users.
    2. Does it support a distributed architecture.
    3. Does it need the E1 interface for incoming voice calls or only for DSP resources, as the UM must coexist with Cisco CallManager.

    #27182 Reply
    Andrew Zhilenko

    1) Yes
    2) You can have multiple UM gateways, but normally one IMAP server (I will have to check if Cyrus IMAP supports distributed message storage)
    3) Yes, because of the Cisco limitations for the IVR on the VoIP call leg – you need to pass all the incoming calls to voicemail through E1/T1. If you can forward the calls from CCM to PortaUM, it can process them.

    #27183 Reply
    Sijbren Beukenkamp


    I see that you are quite a fan of the product. It is interesting and I will keep it mind.
    The customer is already on the Cisco track and also needs a tight integration with Exchange 2003 and Active directory.
    So my main question still remains:
    Are there guidelines for sizing Cisco Unity (UM) ports, when the customer did not have UM before.

    #27184 Reply

    The general rule for port sizing is approximately 25 users per port. However, this depends on how you will be using automated-attendant and if users will be listening to their messages from the desktop (Outlook). For more information about Cisco Unity, you should visit

    There is a customer forum and tons of cool tools there.

Viewing 6 posts - 1 through 6 (of 6 total)
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