Tag Archives: Call via Work

#Skype4B: Call via work (Part IV)


This post is the IVth part of the Call via Work series and continuation of part III. In this blogpost, I am going to cover the limitations of Call via Work. However, CvW is a great feature of Skype for Business Server 2015 which can be implemented easily with a limited hardware configuration but it comes with its own limitations.

There are following limitation which comes with CvW:

  • CvW call back number doesn’t work directly. If a user has setup a call forwarding on CvW call back number and someone invites him through that number, in that situation call will fail because the invitation will not reach to the user. To avoid this situation, you should invite the user for meeting by clicking on his name, not by the number.
  • Following things cannot be used by CvW enabled user
    • Team Call
    • Response Group
    • Delegation
  • Following actions can’t be performed by CvW user through SfB:
    • Record a meeting
    • Mute or Unmute the call
    • Hold or Transfer the call
    • Call Parking
  • CvW can’t be used by user to access their PBX voicemail messages.
  • User of CvW can’t perform following things:
    • Add more users to a 2-person call.
    • Can’t escalate voice call to a collaborative meeting which includes other modalities such as video, PowerPoint etc.
  • No support for deskphone pairing or VDI plugin pairing.
  • Enhanced 911 capability and malicious call tracing are not available during Call Via Work calls.
  • If your PBX system does not support REFER with Replaces, the following behavior will happen. While on a Call Via Work call, if the user transfers the ongoing call from the PBX Phone, the call window will not disappear from their Skype for Business window. If the user then closes the call window, the call between the transfer target and the transferee will end.

Courtesry: Microsoft Technet

I hope you enjoyed the entire series of Call via Work. Please write your queries and feedback in the comment section.

Call via Work Part I

Call via Work Part II

Call via Work Part III

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#Skype4B: Call via work (Part III)


Part I and Part II of this blog post cover CvW fundamentals and how does it work. Now this part of the blogpost will cover CvW prerequisites and deployment process.

CvW is a cool feature of Skype for Business but it can only be configured in few scenarios. Below are the prerequisites and infrastructure should meet these requirements.

  • Unified Communication Web API (UCWA): Comes default with Skype for Business Server and installed automatically on all Skype for Business Front End Servers.
  • Mediations Server: Should be deployed standalone or part of the Front End server.
  • Direct Inward Dialing (DID): Each user should have DID on the PBX phone system for users who will be enabled for CvW and enabled for enterprise voice in SfB with the corresponding DID.
  • Automatic Configuration: CvW users must have Automatic configuration selected in their Advanced connections settings. The enables the client to discover the UCWA URLs.


  • Call forwarding and Simultaneous ring: CvW users must enable for call forwarding and simultaneous ring.
  • Dial-in and Dial-out conferencing: CvW users must enable for dial-in and dial-out conferencing which enable these users to get into and out of SfB conferences.


  • Delegation, team call, and response group: CvW users should be disabled for delegation, team call and response groups.

Deploy Call via Work: Now, let’s have a look into deployment part of the CvW.

  • Create a global phone number: for your deployment which Skype for Business displays on the PBX caller ID of users who are making Call Via Work calls.
         Set-CsRoutingConfiguration -CallViaWorkCallerId +<PhoneNumber>
  • Create one or more Call Via Work policies:
        New-CsCallViaWorkPolicy [-Identity] <XdsIdentity> [-Tenant <guid>] [-Enabled <bool>] [-UseAdminCallbackNumber <bool>] [-AdminCallbackNumber <string>] [-InMemory] [-Force] [-WhatIf] [-Confirm] [<CommonParameters>]
  • Assign a Call Via Work policy to each user who will be enabled for Call Via Work:
        Grant-CsCallViaWorkPolicy -Identity <UserName> -PolicyName Tag:<PolicyName>

Part IV of this article covers limitation in Call via Work.

#Skype4B: Call via work (Part II)


Part I of this blog post covers introduction of Call via work, differentiate remote call control and describe how does CvW work etc. Part II will cover different scenarios of call via work which takes place.

Outbound routing scenario has been covered in Part I. Now, let me describe inbound scenarios.

Skype for Business Server and PBX can be configured in two different ways for incoming traffic:

  1. Skype first in line
  2. PBX first in line

Case 1: User experience when external PSTN user makes an inbound call:

In this scenario, Skype First offers all the features such as Skype toast, missed call alert and voicemail while PBX first only offers voicemail.

Scenario 1: Skype first in line scenario for inbound PSTN call:

User Experience:

  1. PSTN user makes a call
  2. Skype for Business Server receives call
  3. User A client endpoints is alerted
  4. Since User A is enabled for CvW and Simulring, a ms-SkipRnl header is used to force a call out to user A desk phone

Scenario 2: PBX first in line scenario for inbound PSTN call:

User Experience:

  1. PSTN user makes a call
  2. PBX receives call
  3. Since User A has PBX desk phone, therefore user desk phone rings

Case 2: User experience when internal user makes an inbound call:

In this scenario, Skype for Business user (as a first party) offers all the features such as Skype toast, missed call alert and voicemail while PBX desk phone (as a first party) offers voicemail.

Scenario 1: Skype for business user scenario for inbound PSTN call:

User Experience:

  1. User B makes a call to User A from SfB Client
  2. Skype for Business Server receives call
  3. User A client endpoints is alerted
  4. Since User A is enabled for CvW and Simulring, a ms-SkipRnl header is used to force a call out to user A desk phone

Scenario 2: PBX user scenario for inbound PSTN call:

User Experience:

  1. User B makes a call from PSTN desk phone
  2. PBX receives call
  3. Since User A has PBX desk phone, therefore user desk phone rings

I hope, this post gives you clarification about inbound scenarios of CvW. If you have any comments or queries, please write in comments box. I’ll be happy to hear from you and resolve all your queries.

#Skype4B: Call via work (Part I)


Skype for Business Server 2015 introduced Call via Work (CvW) and replaced remote call control (RCC) which was available in previous versions of Lync server. It enables integration between Skype for Business and your PBX phone system. A SfB user enabled for CvW can initiate a PSTN call from SfB client and leverages PBX phone to have a call with another user within organization or outside the organization.

How is it different from Remote Call Control?

RCC is a replacement of CvW but doesn’t work in same way, you can understand it in this way: RCC required computer-supported telecommunications application (CSTA) gateway to integrate Lync Server with PBX system while CvW uses Unified Communication Web API (UCWA) as the back-to-back user agent (B2BUA) between Skype for Business Server and PBX systems. Therefore, CvW only work in case you have direct SIP between Skype for Business Server and PBX systems.

Call via Work offers the following for PBX phone users:

  • Click-to-call experience form Skype for Business client
  • IM, App and Desktop Sharing, File Transfer
  • One-click meeting join experience

How does it work?

The end user selects another end user in their Skype for Business client, and clicks the phone icon to call him. Or, during an IM conversation, the end user clicks to call another user they are having the session with. The PBX phone of the user who placed the call starts to ring. The caller ID for this phone shows a global phone number which you have set up to show in the caller ID of all users placing Call Via Work calls. This global phone number is not an actual phone number that corresponds to any one person’s phone. Instead, it is a visual signal to let a user know that this is their own outgoing call, and not an incoming call happening at the same time. When you deploy Call Via Work, you should educate those users about this global phone number and what it means. The user who placed the call picks up their PBX phone. Skype for Business then initiates the voice call to the callee. When the callee answers, the voice call begins. If the two users already had an IM session going, it can continue. Courtesy: Microsoft TechNet

Let’s take an outbound call scenario where Users A which is enabled for Call via Work initiates a call from SfB client to external PSTN number.

  1. User A initiates a call from SfB client.
  2. Skype for Business Server places call to user’s PBX phone.
  3. PBX System routes call and user answer that call.
  4. When Sfb server perceives that call has been answered by local user then it initiates a far-end call by using user A DID.
  5. PBX system routes a call out to PSTN with user’s DID.
  6. Far-end calls answers and call is established.

Once call has been initiated, media will directly flow between both the end points.

Let’s take an another outbound call scenario where Users A which is enabled for Call via Work initiates a call from SfB client to User B within same organization. Here, User B is enabled for call via work and Simulring.

  1. User A initiates a call from SfB client.
  2. Skype for Business Server places call to user’s PBX phone.
  3. PBX System routes call and user answer that call.
  4. When Sfb server perceives that call has been answered by local user then it initiates a call to user B.
  5. Since User B is internal user and enabled for call via work and set to simulring their own desk phone, a ms-skipRnl header is used on an outbound call to force another call out to user B desk phone
  6. User B answers call from either skype client or desk phone and call is established.

Once call has been initiated, media will directly flow between both the end points.

The above examples are simple scenarios but there are many other scenarios which take place when deploy call via work. Rest of the scenarios, I’ll coven in next part of this blog series.