====== Dial VIA Office ======
  * New in CUCMv7
  * Used by Smart Phones
  * Allows users to place calls from [[cucm-cumc|Cisco Unified Mobile Communicator (CUMC)]]
  * Similar to [[cucm-mva|Mobile Voice Access]] on remote phones
  * Calls made via Dial VIA Office will show corporate caller ID
  * User can dial internal extension numbers and PSTN destinations
  * The audio channel of the call, using the mobile voice network, can be set up by CUCM (like a reverse dialing)
    * User has the ability to choose any number to be used for reverse call (e.g. initiate a call from CUMC and select hotel number to be used for setting up the audio channel from CUCM to user)
    * Potential savings on toll charges and roaming charges
  * The signaling uses GPRS for the data channel

===== Forward Dialing =====
  * Dial-via-office with **forward dialing**
    * Mobile call is setup by mobile phone.
    * CUMC uses mobile data network to signal call.
    * CUMC user invokes dial-via-office feature on smart phone and calls directory number 2000.
    * Smart phone sends the call setup message over the mobile data network (GPRS)
    * CUCM informs the smart phone what PSTN number to dial to get dial-via-office access.
    * CUMC places the PSTN call over mobile voice network to dial-via-office number.
    * CUCM connects this incoming call to the target number (directory number 2000).
    * CUMC uses mobile data network (GPRS) to signal call.
  * If the CUCM does not receive a PSTN call from mobile phone within 30s, the CUCM will send SIP Service unavailable to CUMC over data connection.
{{cucm-dvia-off1.png|}}

  * SIP Invite from CUMC to CUCM over the data network
  * Tell CUCM that forward dialing will be used
<code>
SDP parameter "a=setup:active"
</code>

  * SIP Responds from CUCM to CUMC
  * Indicates the number to be used for Dial-via-office access
<code>
SDP parameter "c=PSTN E164 5766711"
</code>

===== Reverse Dialing =====
  * Dial-via-office with **reverse dialing**
    * Call to mobile phone is set up by CUCM.
    * CUMC uses mobile data network to signal call.
    * CUMC user invokes dial-via-offce feature on smart phone and calls directory number 2000.
    * Smart phone sends call setup message over mobile data network and requests reverse dialing to its mobile PSTN number
    * CUCM places outgoing call to PSTN number of the smart phone.
    * When answered, CUCM connects the call to the target number (directory number 2000).
{{cucm-dvia-off2.png|}}

  * SIP Invite from CUMC to CUCM over the data network
  * First SDP tells CUCM that reverse dialing is requested
  * Second SDP indicates the callback number to be used
<code>
SDP parameter "a=setup:passive"
SDP parameter "c=PSTN E164 4085551234"
</code>

  * CUMC allows callback number to be set manually per call
    * Not limited to mobile PSTN of smart phone
    * Can be set to home landline number, hotel number, etc.
    * Call control (with enterprise features) is on CUMC, audio is on specified callback phone.