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An Introduction to UMA (Unlicensed Mobile Access) technology

A new industry group, The UMA Consortium (www.umatechnology.org), tasked with bringing Unlicensed Mobile Access (UMA) technology to market describes it in these terms:

UMA provides access to GSM and GPRS mobile services over unlicensed spectrum technologies, including Bluetooth and 802.11, (and may be later to cover other unlicensed technologies, such WiMax or even UWB). By deploying UMA technology, service providers can enable subscribers to roam and handover between cellular networks and public and private unlicensed wireless networks using dual-mode mobile handsets.

One of the world’s leading independent experts on UMA, Monica Paolini of Senza Fili (means ‘without wires; in Italian) (http://www.senza-fili.com/) explains UMA technology as follows:

UMA enables GSM/GPRS handsets equipped with Wi-Fi or Bluetooth to access the GSM and General Packet Radio Service GPRS core networks using the unlicensed air interface when available (see Figure 1 below). As such, UMA represents an extension of the GSM/GPRS network for mobile operators, which can support voice services in homes, offices and hotspots both through the cellular and the WLAN networks.

Seamless delivery of mobile voice and data services over unlicensed wireless networks.
Provides the same mobile identity on Cellular RAN and unlicensed wireless networks.
Seamless transitions (roaming and handover) between Cellular RAN and unlicensed wireless networks.
Preserves investment in existing/future mobile core network infrastructure
Independent of underlying unlicensed spectrum technology (e.g. WiFi�, Bluetooth�)
Transparent to existing, standard CPE devices (e.g. access points, routers and modems)
Utilizes standard «always on» broadband IP access networks (e.g. DSL, Cable, T1/E1, Broadband Wireless, FTTH�)
Security equivalent to current GSM mobile networks
No impact to operations of Cellular RAN (e.g. spectrum engineering, cell planning,�)

A brief overview of the UMA Technology Architecture, Operation and Interoperability formed part of the initial announcement last September:

a) UMA Technology Architecture

Figure 1
Source: UMA Consortium

b) UMA Technology Operation

UMA technology provides alternative access to GSM and GPRS core network services via IP-based broadband connections. In order to deliver a seamless user experience, the specifications define a new network element (the UMA Network Controller, UNC) and associated protocols that provide for the secure transport of GSM/GPRS signalling and user plane traffic over IP. The UNC interfaces into the core network via existing 3GPP specified A/Gb interfaces.

An open test specification is under development that can be used to facilitate interoperability testing between implementations. The test specification is available here — http://www.umatechnology.org/specifications/index.htm. Companies planning to implement products based on the UMA specifications should seek bilateral compliancy testing agreements directly with other vendors.

In principle, the UMA specifications ensure interoperability similar to any other industry specifications, but the specifications may include options and parameters that have to be agreed bilaterally with other vendors. The UMA participating companies do not guarantee interoperability and the specifications may be upgraded without notice.

b) How did it come about?

In order to promote the widespread adoption of UMA technology, a number of leading companies within the wireless industry have jointly developed a set of open specifications.

Alcatel
British Telecom
Cingular
Ericsson
Kineto Wireless
Motorola
Nokia
Nortel Networks
O2
Research in Motion
Rogers Wireless
Siemens
Sony Ericsson
T-Mobile US

One of the first outputs of this new Consortium was the publication of specifications that set guidelines for mobile operators and handset manufacturers. These specifications also function as a blueprint for a future 3GPP standard. They are available at www.umatechnology.org. These important guidelines are available for use by vendors and carriers of wireless communications systems and applications in order to develop and deploy interoperable solutions.

Monica Paolini, (Senza Fili), who recently wrote the first authoritative assessment of UMA (http://www.senza-fili.com/UMAR_about.htm), declared that the spec is clearly designed by and for mobile operators, in order to allow them to manage both cellular and Wi-Fi traffic, and to integrate Wi-Fi voice services seamlessly with their GSM networks. With a Wi-Fi cellular phone, subscribers would be able to switch freely from the cellular network they use when away from home, to Wi-Fi when they enter their home network coverage, and vice versa.

UMA enables GSM/GPRS handsets equipped with Wi-Fi or Bluetooth to access the GSM and General Packet Radio Service GPRS core networks using the unlicensed air interface when available (see Figure 2 below). As such, UMA represents an extension of the GSM/GPRS network for mobile operators, which can support voice services in homes, offices and hotspots both through the cellular and the WLAN networks.

The UMA Consortium have provided a simple graphic and text explanation of how UMA works — as well as making available a 240 page — set of specifications (that can be downloaded from here — http://www.umatechnology.org/specifications/index.htm)
Figure 2
Source: UMA Consortium

A mobile subscriber with a UMA-enabled, dual-mode handset moves within range of an unlicensed wireless network to which the handset is allowed to connect.
Upon connecting, the handset contacts the UMA Network Controller (UNC) over the broadband IP access network to be authenticated and authorized to access GSM voice and GPRS data services via the unlicensed wireless network.
If approved, the subscriber’s current location information stored in the core network is updated, and from that point on all mobile voice and data traffic is routed to the handset via the Unlicensed Mobile Access Network (UMAN) rather than the cellular radio access network (RAN).
ROAMING: When a UMA-enabled subscriber moves outside the range of an unlicensed wireless network to which they are connected, the UNC and handset facilitate roaming back to the licensed outdoor network. This roaming process is completely transparent to the subscriber.
HANDOVER: If a subscriber is on an active GSM voice call or GPRS data session when they come within range (or out of range) of an unlicensed wireless network, that voice call or data session can automatically handover between access networks with no discernable service interruption. Handovers are completely transparent to the subscriber.

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Further narrative on how the technology will work in practice is provided by Monica Paolini of Senza Fili:

Unlike other convergence solutions, UMA is tightly linked to the mobile core network, which is used for routing, authentication and billing. Regardless of the air interface used, the handset or mobile station (MS) is connected to a 2G or 3G core network. A call initiated using the Wi-Fi interface reaches the 2G core network through the UMA Network (UMAN). The MS accesses the UMA network through a Wi-Fi Access Point (AP) and an IP broadband connection. While the AP and the broadband connections are necessary, the UMA specifications do not mandate their particular requirements. The WLAN infrastructure and broadband connection have to be managed by the user (or the mobile operator, if it so decides). Any Wi-Fi AP and broadband connection are expected to work in an UMA environment. The UMA Network Controller (UNC) provides the interface to the cellular core network. The UNC performs the same function as the GERAN base station and, at the core level, traffic from the two systems (GERAN and UMAN) is treated equally. UMA specifications recommend that the UNC is able to route calls through the 3G core network as well.

d) What do operators stand to gain?

In brief, UMA has been described as a way to use unlicensed Wi-Fi and Bluetooth spectrum to carry voice through a gateway to the existing GSM networks. GSM operators can then leverage their huge investment and better serve existing and new customers with better pricing and service. It was noted that UMA will be relatively simple and inexpensive to deploy at the core network level, as no substantial changes are required. The UNCs (and links to the core network) are the only key new infrastructure elements that need to be introduced into the access network.

Industry analysts also note that operators can increase their appeal by bundling in calls across free spectrum, especially if it fills in gaps in their coverage. Also a guaranteed cheap home connection through Wi-Fi could make mobile price plans more attractive, while fixed line providers could use UMA services to add mobile services (through virtual operator deals).

e) How might end users benefit?

Lower Calling Charges when on WiFi
Simultaneous Ringing of Mobile and Fixed when at Home and Office
A second, «UMA-only» telephone number for the Mobile (that looks and acts like a fixed number to callers)
A «Vonage-like» VoIP service from the core mobile network
Lower priced downloads for new generation MP3 phones

f) The current state of play

What next? In addition to developing and maintaining the initial specifications, the companies that support UMA are working closely with the 3GPP standards organisation to use the specifications as the basis for the development of a formal standard. So with UMA passing through the 3GPP on the path to official standardisation, it may not be long before a seamless cellular and WiFi roaming experience will be arriving on handsets sometime in the not so distant future.

The guidelines seem to be aimed mainly, but not exclusively, at proposed services for consumer or small businesses. An early beneficiary of the UMA mindset is likely to be one of UMA group’s founding members, British Telecom, with its Bluephone project.

The Unlicensed Mobile Access (UMA) standard that is driving converged devices and services also got a major boost in June 2005 when equipment vendors Nokia and Alcatel announced initiatives to drive the specification at Supercomm in Chicago.

Alcatel said it would integrate UMA control functionality into its Spatial Wireless softswitch and server range. The move means Alcatel will have to make tweaks to its mobile architecture since the UMA add-on will obviate the need for a separate management element in the network. (More on this here — http://www.home.alcatel.com/vpr/vpr.nsf/DateKey/07062005_2uk).

Nokia demonstrated at Supercomm an upgraded version of its MSC network controller to support UMA and said Finnish operator Saunalahti is already using this in trials of handsets capable of handling both cellular and Wi-Fi calls. (More on this here — http://press.nokia.com/PR/200506/997555_5.html)

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