This blog entry is part four in my mini series of looking at the different Voice over IP systems (VoIP) that can be used over wireless networks such as UMTS or CDMA 1xEV-DO. Part 1 focused on UMA, part 2 on SIP, part 3 on IMS, and this part will take a look on the use of Skype over wireless.
UMA, SIP and IMS are all centralized systems. That means that they use a centralized server which is responsible for authenticating users, for establishing connections between users for voice, video, instant messaging or any other kind of media transfer, and also for billing. Skype uses a fundamentally different architecture as it does not rely on a centralized server for most of these tasks. Skype is a Peer to Peer network in which end points of the network help out each other to establish and maintain a connection.
A peer to peer network has a number of advantages over a centralized approach:
- Centralized servers are costly to buy, maintain and operate. The more people use the service the bigger the server has to become. In a peer to peer network such as Skype, however, signaling load at a central point does not increase in the same way as in centralized systems.
- Individual peers help out each other to establish a connection. This is especially important as many users are behind firewalls or network address translation (NAT) routers typically used at home. Thus, they can not communicate directly with each other. Skype peers that have no such restrictions help out peers that do and forward traffic between such users. This is the main reason why Skype is so easy to set up on PCs and other devices compared to other technologies like for example SIP. For those of you who would like to find out more about Skype, here’s a link to an analysis of how Skype works which has been published by Philippe Biondi and Fabrice Desclaux of EADS.
While most other VoIP systems use legacy voice codecs to transport the media stream over IP, Skype uses its own resource efficient codecs which which on top even have a superior voice quality. Thus, Skype works quite well over UMTS and I use it on a regular basis when traveling. It should also work quite well over EV-DO as well, as bandwidth is also sufficient. Personally I’ve never tried so this is just a speculation.
Many operators (carriers) are scared of Skype and other VoIP systems as they are afraid that such services will decrease their revenue on traditional voice minutes. I think there is no such risk in the near future as there is still a PC required to run Skype over a wireless link. However there are first signs that Skype is also moving to mobile devices. A beta client for Windows Mobile is already available and a non official beta of Skype on a Nokia S60 6680 has also been spotted by the author (see picture above). So operators should hurry up and develop strategies to integrate such innovative applications into their concepts. Some have already done so, like for example E-Plus in Germany. They even offer a UMTS flatrate together with the Skype software and a headset. An interesting first step, certainly not made too soon as new devices such as the Nokia N80 with built in WLAN will spur the interest of a wider audience to cheap VoIP over wireless.
At this point I close my wireless VoIP mini series for now. Four different VoIP systems, four different basic ideas and four ways for every one in the industry and of course the users to benefit. I think it will still take several years before Wireless VoIP becomes mainstream but the first signs are already here.