Mino – The UC Guy

Microsoft Unified Communications Blog

How to implement Enterprise Voice in a non-DID scenario?

Posted by Mino on October 7, 2008

When implementing Enterprise Voice in OCS 2007 the assumption is that each user homed on OCS will have his/her own dedicated phone number directly reachable from the PSTN, a so called Direct Inward Dialing (DID) or Direct Dial-In (DDI). It is the DID defined for the user in E.164/RFC 3966 format in the msRTCSIP-Line attribute, i.e. tel:+4544890101. Some customers might not have a DID for each user. In stead they have 1 DID for the company, i.e. the main number, and all recipients have a unique extension assigned. An Interactive Voice Response (IVR) system or a switch board operator answers the main number and redirect the calls to the recipient.

So how could you implement Enterprise Voice in such a scenario? In a non-DID scenario you will have to define the msRTCSIP-Line attribute for each user in the format tel:+<main number in E.164>;ext=<extension>, i.e. tel:+4544890101;ext=200.

When implementing this type of solution you need to make sure that your PSTN Gateway/PBX  can understand this format. Why? It needs to be able to understand the components of the string and work with them. On outgoing calls from OCS to the PBX they need to be able to extract the extension from the Calling Line Id and present only the extension to the PBX (i.e. strip “tel:+<main number in E.164>;ext=”). On  incoming calls to OCS from the PBX they need to generate the format for Calling Line Id and Called Line Id.


2 Responses to “How to implement Enterprise Voice in a non-DID scenario?”

  1. Bogdan Barbulescu said

    We have a mixture of DID and NonDid on the Cisco side and we do not wnat to use the CUCU-MOC.
    We also do not want to have different numbers for the MOC and Cisco IP Phones (single number)
    Can I use the tel:+;ext=, i.e. tel:+4544890101;ext=4540101
    The DN for the IP Phone is 4540101 for DID number
    and tel:+4544895555;ext=4543101 for a NON DID the DN for the IP Phone is 4543101

    is the Cisco CUCM 7.x capable to understand the format
    Is this configuration possibe ?
    Should I get DID’s for each user ?

  2. Mino said

    Hey Bogdan,

    well to answer your question we must agree on the cisco version that you are using whether it is 7.x or earlier versions.
    ok if you are using earlier versions like 6.x then it will also be able to understand however the call signal will only come to one end point which is the Office communicator . and the call flow will be PSTN to Cisco , then Cisco SIP trunk to Mediation , then mediation to front end which will enderstand that the LINE URI of the user.
    what is diffirent in version 7.x is the dual forking , however this is a feature that is not yet tested by Microsoft side and it is claimed by cisco that it is working and that it sends the signal to both the cisco end point and the office communicator.

    to answer you question in specific , yes you can have the OCS in non DID by using the extension where the caller will first dial the Pilot number of the company and then enter the extension of the user and this will alow the call to come to OCS , however it will either come to OCS or Cisco end point and you can not send the signal to both end points unless you try the dual forking option of CUCM 7 which is not yet confirmed by Microsoft

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