Wireless VoIP demystified

Nokia has managed quite successfully to bring UMA (Unlicensed Mobile Access), it’s preferred Wireless Voice over IP variant to the attention of the big press during the recent 3GSM congress in Barcelona. Most journalists, however, haven’t really understood what UMA is about as it is just one of at least four very different flavors of Wireless VoIP, each with its advantages, disadvantages, usage scenarios, and proponents that push the solution. To fill this gap and to show the benefits and drawbacks of the different flavors of Wireless VoIP for the user, I’ve decided to write a couple of blog entries in the days to come to compare the following technologies:

  • UMA (Unlicensed Mobile Access)
  • SIP (Session Initiation Protocol) implementations on mobile phones
  • IMS (IP Multimedia Subsystem) clients
  • Non standard Wireless VoIP systems such as Skype

First on the list is UMA, a 3GPP standard like GSM and UMTS, loved and feared alike by mobile operators (or carriers as you say in the U.S.). The principle of UMA is simple: It replaces the GSM radio technology on the lower protocol layers of the mobile phone with Wireless LAN. A call is then tunneled via a Wifi Access Point connected to a DSL/cable modem via the Internet and a gateway to the Mobile Switching Center (MSC) of a mobile network operator. The gateway between the Internet and the network of the mobile operator is called a UMA Network Controller and one of the companies developing such a network node is Kineto Wireless.

For me, UMA is a semi-VoIP service, as a call is only transported over IP on the link between the mobile phone and the UMA Network Controller. After the gateway, a traditional Mobile Switching Center (MSC) and a circuit switched connection is used to connect the call to the destination.

By always traversing the core network and an MSC of a mobile operator, UMA binds a mobile subscriber to his mobile network operator. This is the part mobile operators like most about UMA. What mobile operators don’t like about UMA in many cases is the fact that the DSL or cable connection is usually in the hands of other companies. In many cases users pay their DSL fees to an incumbent fixed line operator or cable company. Thus, in most cases UMA only makes sense if a mobile operator offers the service together with the fixed line operator that controls the DSL or cable access.

As described above, UMA replaces one radio technology with another and otherwise leaves the rest of the system as it is. This makes it difficult to price incoming calls differently for a caller while the called party is at home and using his (cheaper) Wifi/DSL/cable connection compared to calls the called party receives while roaming in the cellular network. This is due to the fact that mobile operators in Europe use special national destination codes in order to be able to charge a caller a different tariff for calls to a mobile phone user. In the U.S. charging incoming calls to a UMA user differently might be less of an issue as mobile networks use the same national destination codes as fixed line operators. There is no additional charge for the caller as the mobile phone user gets charged for incoming calls. As the mobile network is aware that the user is currently in his (cheaper) home Wifi cell, incoming calls can be charged accordingly.

Outgoing calls made via the Wifi access point and a DSL or cable connection are also under the control of the mobile operator. It is unlikely that mobile operators will offer outgoing calls for free as is usually the case for connections between two VoIP subscribers as the call will always be routed through a mobile switching center and a circuit switched connection instead of being transported via IP end to end. Consequently I think it’s going to be difficult for an operator to price the service competitively.

Last point on the downside for the user: As UMA is not an end to end VoIP technology there is no presence information and built in instant messaging capabilities as in other systems.

On the positive side, UMA offers a seamless experience for the user. From an application point of view UMA it is transparent to the user on the mobile as the same graphical user interface is used for both cellular and Wifi calls. The standard even offers seamless roaming between the two access technologies for ongoing calls, i.e. a call is handed over from Wifi to the cellular network when a user leaves the coverage area of a Wifi access point.

UMA also tunnels GPRS services into the core network of the mobile operator. Data speeds are much higher though, again producing a seamless or even better experience for the user while in a UMA Wifi cell, e.g. for web browsing on the phone, operator portal access, music downloads, etc.

Two other important positive sides of the technology are the use of the same phone number regardless of whether the phone is connected via the cellular network or Wifi and the fact that indoor coverage can be improved by deploying Wifi access points instead of more expensive cellular micro base stations.

As has been shown, UMA offers a lot to users. If operators figure out a way to offer the service at a competitive price users will surely like it.

In the next blog entry in this series I will give an overview of mobile SIP and how this end-to-end VoIP technology compares to UMA.

One thought on “Wireless VoIP demystified”

  1. hi reading this article on uma ,,,

    what happens if the call is a pure data / internet call then u will use the gb interface which we are usiing ips on to the sgsn -> ggsn -> internet

    for a voice call i grant u would go via the msc – thus not always ip … however the msc is having less + less control when soft switches come out then will be all ip ?? via via gateways .,,,

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