Skype began, in 2003, as a peer to peer communications system, meaning that each user ran software to power the service on their own computers. When Microsoft acquired the service in 2011, it began work to move away from peer to peer, first moving to a system of Linux based "supernodes," but now, according to a blog post on the Skype Garage blog and a conversation we had with Microsoft's Skype Corporate Vice President Gurdeep Pall, a conversion to the cloud using a pure Azure backend is just about complete.
In the past months, Microsoft has been working with a "dual stack" architecture, building out cloud services on Azure while still maintaining the earlier systems, a situation that hasn't always worked perfectly. Messages have sometimes not synced, or notifications have not been delivered, sometimes due to the switchoff from one system to another, but now Skype is nearly ready to run fully on Azure. But moving to the cloud has its advantages, and will be well worth it in the end. According to the blog post:
Recently, we have been focused on transitioning Skype from a peer-to- peer architecture to a modern, mobile friendly cloud infrastructure. By moving to the cloud we have been able to significantly improve existing features like file sharing and video messaging, and launch new features like mobile group video calling, Skype Translator and Skype Bots to name just a few.
Microsoft is also planning to trim some of the devices and operating systems it supports, but will still support XP, Vista, and Windows 7 on, Yosemite on Mac, iOS 8 and Android 4.03. Skype just announced its latest UWP client for Windows 10 Mobile, and has worked to support ORTC and WebRTC to be able to run on Linux and Chromebooks.
One additional change Gurdeep Pall explained to me in our discussion is that all Skype accounts are now Microsoft accounts on the back end. This means that the accounts can be recovered more easily, using the same password recovery system that you would use for your Outlook.com account. Many Skype users in the past, unable to recover their passwords or account names, would simply give up and create new accounts, and the new system will help.
Microsoft has been on a fairly long journey to basically rebuild the entire back end of a system used every day by hundreds of millions of users, a transition that hasn't always been easy, but now with a move to Azure almost complete, Microsoft should be ready to build on the Skype platform.