UMA (Unlicensed Mobile Access)

UMA (Unlicensed Mobile Access) is an industry collaboration to extend GSM and GPRS services nto customer sites by utilizing unlicensed radio technologies such as Wi-Fi (Wireless Fidelity) and Bluetooth®. This is achieved by tunnelling GSM and GPRS protocols through a broadband IP network towards the Access Point situated in the customer site and across the unlicensed radio link to the mobile device.

Thus UMA provides an additional access network to the existing GERAN (GSM EDGE Radio Access Network) and UTRAN (UMTS Terrestrial Radio Access Network).

Unlicensed Mobile Access (UMA) technology enables access to GSM and GPRS mobile services over unlicensed spectrum, including Bluetooth™ and WiFi™. Highlights of UMA Technology:

• 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,…)

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.

UMA Interoperability

An open test specification is under development that can be used to facilitate interoperability testing between implementations. The test specification will be available through this web site. 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.

1. 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.
2. 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.
3. 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).
4. 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.
5. 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.

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 from the UMA Consortium at above right). 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. Subscribers using UMA can take advantage of improved indoor coverage and higher data rates, when accessing the local WLAN.

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).

It is important to keep in mind that UMA is not a SIP-based VoIP technology, as the core network is still old-fashioned, circuit-switched GSM. VoIP is employed to carry the signal from the MS to the UNC, over the WLAN and the broadband connection, but once transferred to the core GSM network it is indistinguishable from the rest of the cellular traffic.

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. However, performance may be impacted when using APs or broadband connections that lack QoS functionality.

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.

UMA promises seamless mobility between the WLAN and the cellular network. A call initiated within the cellular network can be transferred to a WLAN network and vice versa as the subscriber moves to areas with or without WLAN coverage. During the handoff, the MS needs to be able to maintain a connection with both networks, as it is a make-before-break connection. As a result, the subscriber will not notice delays or other changes in the quality of the call.

Different security mechanism operate at different levels:

• MS to AP – UMA does not mandate any security mechanism, but can coexist with those available, such WPA, WPA2, or WEP.
• MS to UNC – The UNC includes a security gateway that provides mutual authentication and encryption for the traffic across the WLAN and the broadband connection.
• MS to core mobile network – The encryption and authentication methods used by the MS when using the GERAN are also used to protect UMA connections.
• MS to application server – An additional end-to-end data application mechanism (for example, HTTPS) may be used if needed.

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.

In its basic form—that is without QoS mechanisms in the WLAN—UMA does not require any change to the WLAN network either. Any AP is expected to work with UMA, although we expect that mobile operators will encourage APs that support QoS. This is because the throughput available in the WLAN and in the broadband connection should make it provide toll voice quality if no other application contends for the same bandwidth. If there is contention, however, UMA cannot guarantee the quality of a voice call or the throughput of a data connection and traffic prioritization with QoS can significantly improve performance, especially in a residential environment where traffic is likely to be less heavy than in the enterprise.

The most expensive and technologically challenging component of UMA solution is the Wi-Fi and cellular handset, because of battery-life limitations, cost, and size. To be UMA-enabled, a Wi-Fi and cellular phone requires client software to communicate with the UNC. While it may be possible to load the UMA software in any Wi-Fi and cellular phone, mobile operators are currently working on, and are more likely to market, handsets developed specifically for UMA access. Any UMA-enabled MS includes a Wi-Fi radio, which will give it access to any IP network and VoIP services (such as those from Skype or Vonage for instance). However mobile operators may decide to block this functionality, especially if they decide to subsidize the phones.