Skype Changes From P2P to Client-Server Model

How Skype will carry your voice and data over the Net

Mature couple traveling, video chatting on table
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Skype doesn’t require you to know what's inside the box or how their communication mechanism works technically. It just gives more than a billion people a nice interface to communicate quite efficiently — and for free. But curious minds don’t want to remain totally clueless about the nerdy stuff involved, and in fact, it's not quite so techie if you have some basic network knowledge. Let’s see how your voice travels when you talk on Skype, and the changes the company has made to its model along the way.

Skype and P2P

P2P stands for peer-to-peer and is a means of transferring data over the Internet using the computers and devices of Skype users (technically referred to as nodes) as resources for temporarily storing and forwarding data to other users. Skype started based on its own decentralized P2P protocol, which leverages on each user’s device as a resource for data transfer on the network.

Skype identified certain nodes as ‘supernodes’ that would serve for indexing and as networking address translation (NAT) nodes. These nodes are selected from among the different users, of course without them knowing, by an algorithm which did the selecting based on their uptime, they are not being restricted by their operating systems or firewalls, and on the update of the P2P protocol.

Why P2P?

P2P offers several advantages, especially for VoIP. It allows the service to harness the power behind already existing and yet untapped resources on the network. This saves Skype from having to set up and maintain centralized servers for the control and forwarding of voice and video data over the Internet. The time taken for searching and location nodes and servers is also considerably decreased through P2P. The user base is therefore in an international decentralized directory. Each new user that connects to the network represents a node with its loads of juice like bandwidth and hardware infrastructure, and potentially a supernode.

Why Skype Changed to Client-Server and Cloud Model

The client-server model is simple — each user is a client that connects to a Skype-controlled server to request the service. Clients connect to servers like this in a one-to-many fashion. And many here means a really huge amount.

These servers are owned by Skype, that they call ‘dedicated supernodes’, that they control and whose parameters they can handle, like the volume of connecting clients, data protection and so on. Back in 2012, Skype already had ten thousand dedicated company-hosted supernodes, and it was already not possible for any user’s device to be promoted or selected as a decentralized supernode.

What was wrong with P2P? With the increasing number of connected users at any point in time, with numbers near 50 million, the efficiency of P2P has been questioned, especially after two serious outages caused by its inability to cope with the situation. The high volume of user nodes requesting service required more and more complex algorithms.

Skype saw a drastic increase in the number of users from different and recently-unserviced platforms like iOS and Android. Now, this diversity in platforms and algorithm implementations rendered P2P trickier increasing the possibility of failures.

Another reason advanced by Skype for moving away from P2P is battery efficiency on mobile devices. These recent years have seen a surge in the number of mobile users relying on their batteries for communication. With P2P, these mobile devices would have to very frequently be in power-hungry communication activity, as they would all act as active nodes. This would also require them to use more of their 3G or 4G data, thereby consuming not only battery juice but also often expensive data. Mobile Skype users, especially those with many contacts and lots of instant messaging conversations, would see their devices warm their hands and their battery drain quickly. The client-server and cloud-computing model is expected to solve this.

However, after the problems and interrogations arose from NSA revelations relating to wiretapping of Skype communication, many users and analysts have raised their eyebrows over the change from P2P to Skype-controlled client-server mode. Could the change have had other motivations behind? Is Skype users' data more secure now or less so? The answers to these questions still remain to be seen.