Online & On-Premise Enterprise Voice Deployment Options – Skype for Business (SfB)


Essentially, Skype for Business (SfB) can be used to offer telephony features (followings) to enterprise users what an IP-PBX or traditional PBX is capable of.

  • PSTN or SIP Trunk
  • Inbound and Outbound Calls
  • Call Parking Service
  • Call forwarding and Transfer
  • Simultaneous Ringing
  • Team Calling & Delegation
  • Common Area Phones
  • Caller ID Manipulation
  • Emergency Services
  • Voice Mail
  • Dial-In Conferencing

These telephony features and functionalities are made available by a right design of enterprise voice deployment. An enterprise may require additional hardware, server, and software to offer entire or partial set of telephony features to the end users.

This article would discuss deployment options to enable enterprise voice features for your users whether their accounts exist in Office 365 or in your on-premises Skype for Business Server deployment.

Enterprise Voice Deployment Models for On-Premise Users

This section of article focusses on options to enable enterprise voice features to on premise users.

Integration with IP-PBX

Enterprises migrating to Skype for Business (SfB) Enterprise Voice have an existing IP-PBXs deployment in place. You need to integrate IP-PBXs and SfB infrastructure to enable co-existence for following reasons;

  • Enterprise can gradually move the telephony features to SfB while retaining some of the features to IP-PBXs.
  • Depending on use cases, you can have users distributed across IP-PBXs and SfB setup. Enable calling between them.
  • Leverage the TDM telephony interfaces offered by the IP-PBX while move rest of the services to SfB.

Further manipulation in this design is possible to support other devices or features like contact centres.

Note: Mediation server can be either installed standalone or collocated with the Front End Server.

SIP Trunking with ISP Partners

This deployment model allows you to avail SIP Trunking services from the service provider using data connection. In a SIP Trunking deployment all calls entering and leaving the enterprise are carried as SIP packets across a data connection — there are no “phone lines” like there are in a TDM deployment. Enterprises availing SIP Trunk service don’t pay for T1 or E1 lines. Instead, they pay for the bandwidth.

This deployment model extends lot of flexibility and helps you save money. Ideal for a new branch but could be a final state of existing branch as well.

Note: Mediation server can be either installed standalone or collocated with the Front End Server.

Integration with SIP Trunk and TDM Devices

Merge above two topologies and you end up getting this one. SIP Trunk is the primary carrier of telephony features and PSTN connections exists for disaster recovery purposes. PSTN connections can also exist for the services which can't use data connection for some reason.

Call via Work

Remote Call Control was supported by previous versions of Lync server. RCC allowed you to control PBX phones using Lync clients. You needed to install SIP/CSTA gateway that can connect to both Lync Server and the PBX.

Skype for Business server no more supports Remote Call Control (RCC). Call via Work is an official replacement of Remote Call Control (RCC). Call via Work uses UCWA (instead of CSTA gateway) to connect Skype for Business Server and PBX deployment. UCWA is by default installed on the Front End servers. This feature is not supported for online users.

Enterprise Voice Deployment Models for Online Users

This section of article focusses on options to enable enterprise voice features to online users.

Cloud PBX with PSTN Calling Service

PSTN calling service lets online users make local or international calls. The PSTN infrastructure is managed by Microsoft on cloud. A customer can either port the existing numbers or get new ones from Microsoft. It involves zero on-premise infrastructure. Additional numbers can be obtained directly from Microsoft.

(Image courtesy – Microsoft)

Downside of this model is limited number of countries supported. As of now, Microsoft supports PSTN calling service in only selected regions. Also, It is important to note that this service is not available for on-premise users. It’s important to note that as of now Response Groups and Group Call Pickup features are not available under this model.

Cloud PBX with Skype for Business Cloud Connector

Enterprises can extend on-premise PSTN service to the online users. A recently released, Cloud Connector, helps enterprises to achieve this. Cloud Connector is a set of packaged Virtual Machines (VMs) that implement on-premises PSTN connectivity with Cloud PBX. This model is advisable if you don’t have Skype for Business (SfB) on premise infrastructure… and you want to extend on premise PSTN service to the online users.

(Image courtesy – Microsoft)

Cloud PBX with On Premise Skype for Business Deployment

An enterprise already have on-premise Enterprise Voice (Skype for Business) deployment, and is in the process to migrate to online service. Users are homed on Skype for Business online and still using PSTN connectivity through on-premise Enterprise Voice deployment. This is a classic case of hybrid topology. An enterprise can extend on-premise PSTN service to online and on-premise users.

(Image courtesy – Microsoft)

Overall Assessment

Advanced calling features such as Response Groups and Group Call Pickup are not supported by cloud PBX. Similarly there could be known limitations of every deployment model. It’s always advisable to assess the requirements efficiently before deciding a final deployment model for SfB users. In some cases, it could be combination of such models depending on regions\branches.

Note: Refer to

To know qualified IP-PBX, Gateways and SBCs for integration purpose.

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