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What is Skype for Business Server 2015?

We take a look under the hood at the Skype for Business on-premises engine

Skype for Business logoWhen Skype became part of the Microsoft empire in 2011, plenty in the telecoms industry suspected that the purchase was driven by more than just a desire to own a popular consumer comms brand.

Sure enough, some four years later, Microsoft finally revealed its hand. The Skype name was transposed onto a brand new business UC platform, Skype for Business. Far more comprehensive and feature rich than its free-to-use consumer cousin, the name was nonetheless a statement of intent.

It was a statement that said, in the eyes of the one of the world’s true tech giants, the future of business communications lay in integrated voice, video and IM, in simple-to-use apps with a focus on user experience (UX), and in the Cloud. All brand values integral to the success of Skype.

However, although Microsoft did signal these intentions by making Skype for Business part of its Office 365 cloud application suite, it also recognised the importance of maintaining continuity with the traditions of business UC. And so, alongside Skype for Business Online, it also launched an on-premises software edition – Skype for Business Server 2015.

But what exactly does the Skype for Business Server edition do, how does it work, and why was Microsoft so keen to create an on-premises version?

Skype for Business Server 2015 Basics

Skype for Business Server 2015 is a business UC software platform designed to run in a company’s own data centre. It was a direct replacement for Microsoft’s previous on-premises UC product, Lync. It is available in two editions, Standard and Enterprise.

In terms of features, it does all of the things you would expect from a enterprise-class UC solution. It provides secure IM with both internal and external contacts, along with a full contacts directory and real-time presence information so users can see who is online and available.

It also provides video and voice communication, both one-to-one and conferencing. These are supplemented with collaboration features such as the ability to share files or screens, and there is in-built scheduling for virtual meetings.

Skype for Business Server 2015
Skype for Business Server 2015 is the on-premises engine which runs Skype for Business clients across different platforms.

Crucially, and a key departure from the original Skype, Skype for Business also acts as a VoIP telephone system, linking to external telephone lines and offering full PBX call management features. Like many modern business telephone systems, it supports remote and mobile connections, meaning home workers, branch offices and field staff on their mobiles can use the office system features, such as directories and phone numbers.

The word ‘server’ is important. Skype for Business Server 2015 is technically not the part you use to make a call or IM a colleague, the user interface. That is the Skype for Business Client App. Clearly, you need to run both for Skype for Business to be useful, but the server specifically refers to the part that sits in your data centre and powers everything else. A bit like the engine in a car compared to the gears and wheel you drive with, if you like.

Skype for Business Server 2015 is deployed in what is known as a distributed architecture – it is actually run across two separate servers in your data centre. The front-end server handles things like application delivery, contact directories and user authentication, while a back-end server contains databases of all the programs that drive the front-end server.

Skype For Business Server
This split model helps improve availability through redundancy. If, for example, the front-end server goes down, you still have the back-end data saved to get up and running again quickly, rather than the whole lot failing. Skype for Business Server 2015 Standard edition can run on a single front-end and back-end server combination, while the Enterprise edition is intended for between 3 and 12 front-end server pools for deployment across large organisations.

Skype for Business Enterprise Voice

Despite the arrival of the cloud, UC, online collaboration and more, the king of business communications is still the telephone. To create a truly comprehensive enterprise UC offering out of Skype, Microsoft knew that it would have to make it work as a VoIP solution, with connections to telephone endpoints, external telephone lines and PBX controls.

It was also aware that many businesses of all sizes still prefer to run their VoIP systems on-premises, despite the emergence of cloud PBX.

Skype for Business Enterprise Voice drives both telephony and audio conferencing. It is made up of three basic ingredients. First of all, it allows businesses to connect to external telephone services and make calls to any telephone user in the world via VoIP or landline. That means Skype for Business users are not restricted to only calling other Skype users, as was the case with the original app.

Skype for Business 2015 deployment
Skype for Business Server 2015 is deployed using a distributed server architecture for improved redundancy and availability.

It does this by using the Session Initiation Protocol (SIP) for real-time communications. SIP allows a wide range of communications media, such as voice, video and IM, to be used at once, but it also allows for external telephony connections, either via SIP trunks or PSTN.

The second key ingredient in Skype for Business Enterprise Voice is full PBX call handling features. Businesses need more than just the ability to make and answer calls. With multiple users and high in-coming traffic volumes, you need features like call waiting, extension dialling, voicemail and auto attendant. Skype for Business Enterprise Voice provides them all.

The final ingredient is the ability to connect remote and mobile users to the on-premises network. To do this, businesses have to deploy what are known as edge servers, which manage the external connections and provide security features such as firewalls. This allows people to benefit from office phone system features such as call handling even when they are off site, without compromising security.

Enterprise Voice offers one of the most compelling reasons for running Skype for Business Server 2015. Without it, you could connect with other Skype for Business users with voice, video and IM, set up meetings and collaborate – fine for internal communications, certainly. But it would be completely separate to your telephone system, and would only deliver functions that you could run more easily, cheaply and with greater flexibility using Skype for Business Online.

The VoIP PBX platform built into Skype for Business Server 2015 makes it a viable option for external communications, too, turning it into a full end-to-end UC solution. And although cloud PBX functionality is now included on the highest Office 365 subscription tiers for Skype for Business online, many businesses still like the level of control running their own telephone system on-premise gives them.

Skype for Business / Microsoft Teams Series Sponsors

Enghouse Interactive

A leader in customer communications with integrated solutions such as multi-channel contact centre, self-serve, attendant operator consoles & call handling.


Nuvias Group is a pan-EMEA ICT distribution business incorporating brands such as Wick Hill, Zycko and Siphon.


Plantronics is a global headset manufacturer producing audio communications equipment for business and consumers.


Polycom are a video conferencing provider and manufacturer of SIP phones, headquartered in the USA.

Sennheiser logo

Sennheiser is a German privately-held audio company specialising in the design and production of a wide range of headsets for business and personal use.

Swoop Datacom

Complete IP endpoint eco-system provisioning and management platform with secure capability and real world template support.


Global cloud video conferencing & collaboration solution provider headquartered in Norway.

West Unified Communications

Global unified communications and contact centre vendor headquartered in Chicago, USA

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Written by Paul Newham

Paul Newham

Hi I'm Paul, I specialise in technology, covering telecoms, cloud and IT infrastructure and digital marketing.