Wireless VoIP Demystified – Part 4: Skype

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.

2 thoughts on “Wireless VoIP Demystified – Part 4: Skype”

  1. Martin,

    Thanks for this fine series on wireless VoIP. You’ve done an excellent job of presenting the alternatives for VoIP from a carrier network perspective.

    And as an engineer, I appreciate the elegance of a P2P solution like Skype. It’s essentially a walkie-talkie that works on any network type.

    From the enterprise perspective, SIP and IMS retain their appeal long after the IT departments have shut down Skype. The reason for this is twofold.

    First, there is the issue of client software. In large IT environments, the overhead of installing the Skype client on thousands of devices adds significant management cost. Even though Skype has done an excellent job of making their client easy to download and install, it’s still a concern, especially given the frequent updates Skype makes to the client.

    Secondly, the Skype user license gives Skype the authority to update the software at any point in time and to run executable files on user devices. IT management likes the stability that comes from predictable product lifecycles and the ability to test new software before it goes into production. From an IT perspective, the Skype client is a sanctioned virus with an unknown product lifecycle.

    Keep in mind that these same IT managers readily admit that Microsoft Outlook is the most dangerous virus in their network.

    There are constraints other than technology. I don’t mean to imply that enterprise requirements will dominate carrier-network architectures. Instead, the object example here is that there are constraints that determine which technologies get deployed and in what ways.

    For example, in the carrier network, we’ve been talking about “converged billing” for over a decade. It still hasn’t happened, even though everyone agrees that it’s “the best way.” The conclusion to which I’ve arrived is that there must be another set of constraints dictating the way billing platforms are deployed within carrier environments.

    So if Skype succeeds or fails, it won’t be because it’s the best technology or the right architecture. Chances are that we’ll get a sub-optimal technology for an altogether different set of reasons…over which we’ll have little control.

  2. Thanks very much for this article.I found a lot of useful information about the VOIP system and what it’s all about it because I wasn’t very accustomed with it.

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