Call flow with Cloud Connector Edition

Cloud Connector Edition is an option for those customers who are new to Microsoft Real Time Communication and directly adopting Skype for Business Online (Office 365) for real time communication. At present to find an organization without any telephony system is almost impossible. When customers are looking for best RTC solution and adopting SfB online, it is crucial for them to leverage existing telephony investment while maintaining seamless user experience across all RTC modalities. Microsoft is committed to provide seamless PSTN calling experience through Cloud Connector Edition to those users who are accessing all the SfB modalities except PSTN calling form SfB online infrastructure.

Let’s discuss more about PSTN calling. In Skype for Business each conversation is divided into two pieces i.e. signaling and media. When you are using CCE all media traffic for PSTN calling will be managed by CCE and PSTN Gateway while signaling will be managed by CCE and SfB online infrastructure.

Whenever, we talk about telephony communication, it could be either inbound or outbound.

Outbound Calling: If a user place a call from internal network:

  1. Users dial an external PSTN number in E.164 format
  2. SIP traffic routes to Skype for Business online infrastructure
  3. SfB online performs a reverse number lookup for the dialed number
  4. The RNL fails because it is an external number and doesn’t belongs to any SfB user
  5. The call is routed to the Edge component of CCE
  6. If the PSTN routes exist Edge Server relays the traffic through Mediation component of CCE
  7. Mediation component sends the traffic to the PSTN gateway and establish a connection between the user end point and PSTN Gateway through Mediation component for media flow

Inbound Calling: If an internal user receive a call from PSTN network:

  1. PSTN Gateway receives a call from external PSTN number for a SfB online user who is in internal network as of now
  2. Gateway routes the SIP traffic to Mediation component of CCE
  3. Traffic goes out from Mediation component to SfB Online through Edge component of CCE
  4. SfB online performs a reverse number lookup
  5. The RNL passes and SfB online finds that this number belongs to the SfB online user
  6. SIP signaling goes to all the point of presence of that user
  7. Finally, Media traffic will be established between PSTN gateway and Mediation component and between Mediation component and the user end point for media flow

These are the features which are available through CCE as of now.

There are many limitation if you will compare it with Skype for Business on-premises or hybrid. Below are the list of limitations:

  1. No call via work or remote call control
  2. No media bypass
  3. No response group
  4. Active call can’t be transferred to the cell phone which is registered in your Active Directory by picking it from a list of suggested phones in the transfer menu. You can transfer to any other number.
  5. Call between SfB user and PSTN number can’t be escalated as conference call
  6. Users must use full number in E.164 format only
  7. Only specific series of Polycom phones are supported as of now
  8. No integration available with contact centers
  9. Private lines and common area phones are also not supported

I tried to cover most of the stuffs but there is no guarantee if you face any other limitation.


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