“What’s the Edge Server do?”

One of our team members fielded this question while on-site the other day. He’d just finished describing the Skype for Business topology we proposed for the customer’s business (hybrid deployment, across 3 offices). One of the users piped up right afterward.

Now to his credit, my co-worker answered the question immediately, and (from his impressions) to the user’s satisfaction. He’d mentioned it to me only in passing. But, me being me, I seized on it as a good post idea.

We’re all about educating users here. In case another user at that customer site, or a future customer’s, still has questions? Let’s take a detailed look at what goes into an Edge Server.

(Please note: We will not discuss Reverse Proxies or Load Balancers in this post. If you want to hear more about these, I’m happy to dedicate a post to each. Please comment if so.)

The Edge Server’s Primary Role

The Edge Server grants Skype for Business access to users outside the internal network. These are mobile users, remote users, federated users (e.g. partners, vendors), and sometimes even customers.

Without the Edge Server, these external users can’t send or receive IM, take phone calls, or join in Online Meetings.

How does it do that? Essentially, by acting as an IP intermediary. It translates external IP addresses into internal IP addresses to facilitate the external user connections. As such, the Edge will need routable public IPs assigned to it (or non-routable private IPs, if you use NAT).

Skype for Business Servers
That’s our Edge Server right there. No, that one.

Main Components of an Edge Server

Each Edge Server runs four main services.

  1. Access Edge. This service gives users a trusted connection for inbound & outbound SIP traffic. Like a private road through the Internet.
  2. Web Conferencing Edge. This service allows an external user to join Online Meetings running on your Skype for Business Server. A virtual “ticket to the show,” as it were.
  3. A/V Edge. This service enables audio/video, application sharing, and file transfer for external users while in said Meetings. That way you’re not missing out on any parts of the conversation.
  4. XMPP Proxy. Finally, this service sends & receives XMPP messages (eXtensible Messaging and Presence Protocol) from federated partners. It makes sure external users can still talk with federated users.
    • NOTE: This is not required for all Edge Servers. You may need an XMPP gateway running on the Front End as well.

Other Servers Edge Communicates With

Front End. Obviously, the Edge Server will communicate the most with the Front End (Standard or Enterprise Edition). Otherwise external user connections would just vanish!

Office 365 Cloud. If you’re running a hybrid configuration, the Edge Server will have to communicate with Office 365 servers. Edge will treat the Office 365 tenant as a federated partner, so make sure SIP Federation is enabled.

Exchange UM Server. Edge must communicate with Unified Messaging, in order for external users to get their voicemails.

Persistent Chat Server. For topologies supporting Persistent Chat, the Edge Server will need to communicate with its server. Access Edge needs to facilitate external users joining chats.

Reverse Proxy, Firewall, Load Balancer. Together with the Edge Server, these servers/tools create the “perimeter network.” They protect your network from unauthorized access (e.g. malware), while letting authenticated users through.

Edge Server Functionality
A Microsoft diagram illustrating some of the Edge Server’s functions. It keeps busy. Image courtesy of Microsoft.com.

Is One Edge Server Enough?

For most offices, yes. One Edge Server can handle 12,000 concurrent users. But for high-availability topologies, you can collocate Edge Servers.

Reminder: Don’t Forget about Mobile User Access

When configuring an Edge Server, make sure you’ve addressed mobile users. We’ve had to reconfigure Edge Servers which were set up properly for most remote users…but mobile apps didn’t have access the moment they left the office.

Every Time You Use Skype for Business on the Road, Thank Your Edge Server

Among our customers, IM is the most-used Skype for Business tool benefiting from the Edge Server. But inviting customers or vendors into an Online Meeting is the most valued benefit.

“You mean they can actually join the meeting too? Just like each of us?” Yes, they sure can! Thanks to the Edge Server. Show it a little love.

(I’m not actually sure how you’d do that. Do servers appreciate it when you clean their fans?)

Did you have a question about what Edge Servers do, or how they do it? Please comment or email your thoughts.

How the Edge Server Fits into Skype for Business

9 thoughts on “How the Edge Server Fits into Skype for Business

  • November 24, 2017 at 2:48 am

    Great post.
    Yes please. Would love to hear the same about Reverse Proxy’s and Load Balancer’s 🙂

    • November 29, 2017 at 10:01 am

      Thanks for the comment. You got it. I’ve got both on the calendar for future posts. Probably get to those in January, so check back!

  • November 30, 2017 at 2:48 am

    great article
    quick one for ya:)

    our sfb 2015 onprem was working a treat . federated im, video, conferencing etc etc

    now we see we cannot do video calls with a federated partner but we can with public skype users.

    any tips 🙂

    • December 6, 2017 at 10:39 am

      Hi Carl,
      Thanks for the comment. Let me ask you two questions:
      1. Did you make any updates? To the Skype for Business server, the Windows Servers on which it runs, or the network hardware?
      2. Are you unable to do video calls with only one federated partner, or all of them?

      My guess is you have a blocked port range, or a bandwidth limitation. If you did make updates, you may have blocked some of the ports Skype for Business needs open at the edge. If you can’t use video with only one partner, one of you may have a bandwidth limitation holding up video.

      Hope this helps!

  • October 9, 2018 at 4:36 am

    Did you ever get to the reverse proxy post?

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  • March 28, 2020 at 7:52 am

    Is it possible to run skype for business without edge server on a vps on internet? I deployed SfB without edge server but only Instant Messaging works and users cannot call each other or even the Audio Test Service. all the firewalls are off and servers are in a one-to-one NAT environment.

    • April 15, 2020 at 8:11 am

      Thanks for the comment Alireza, No, it’s not possible to run without an Edge Server if you want to communicate outside your network. This sounds more like an issue with the Mediation Server, or Reverse Proxy. If you’d like troubleshooting help, our IT consultants can do that. Please contact me directly.


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