Evolving Ideas Computing, Communication and Networking Publish by Global Vision Publishing House Edited 517 by Jeetendra Pande Nihar Ranjan Pande Deep Chandra Joshi Unlicensed Mobile Access (UMA) Ravindranath Barathy 1, Dandavate Pushpak 2 and Das Bhumesh 3 ABSTRACT Unlicensed Mobile Access (UMA) technology enables access to GSM and GPRS mobile services over unlicensed spectrum, including Bluetooth and Wi-Fi. The idea of using unlicensed radio in mobile handsets for interconnecting with the core mobile network is interesting both technically and economically. The installed base of wireless access points has increased through the emergence of reasonable priced and easy to use WLAN equipment to accessing Internet with broadband connections. In addition to the convenience that the cordless devices provide, the use of unlicensed radio spectrums is expected to give economical benefits both for the end users and to operators. Based on a literature study, this paper depicts the current situation of UMA technology and its influence for businesses of operators and Telecomm vendors as well as the benefits for the users. INTRODUCTION Many users in India still have a fixed line telephone at home and in the office in addition to a mobile phone. Most of them would prefer just one mobile device, which could provide all needed communications services without needing to worry about what network is available. The unification of fixed and mobile devices as well as their services is often called with term fixed-mobile convergence (FMC). In this paper we look how UMA technology is enabling this kind of evolution. Also we briefly look the status of the other related standards. FMC is an important issue for many other stakeholders than end users. We discuss the influences of UMA for different players like operators and vendors. Descriptions of enabled end user services and a successful pilot are given. In the end of the paper we conclude how we see the situation of UMA today. 1 Sinhgad institute of Technology, Lonavala, Dept of Elec. &Telecomm. 2 Sinhgad institute of Technology, Lonavala, Dept of Elec. &Telecomm. 3 Sinhgad institute of Technology, Lonavala, Dept of Elec. &Telecomm.
518 Ravindranath Barathy, Dandavate Pushpak and Das Bhumesh TECHNOLOGY OVERVIEW Definition: UMA, also known as generic access network (GAN), is a telecommunication system that allows flawless combination of the cellular network with unlicensed wireless technologies. Unlicensed Mobile Access (UMA) is a technology that connects regular unlicensed wireless networks to GSM networks. The wireless networks are currently limited to Bluetooth and 802.11, but soon others will follow. UMA defines a UMA Network Controller, UNC, which connects to the mobile network using standard A/Gb connections, replacing GSM s Base Station Controller (BSC). All GSM services are tunnelled through the IP pipe, including GPRS. Of course, data transfer speeds are quite a lot faster than with cellular access (UMA Technology). Calls and data connections feature seamless handover between cellular and UMA, as well as roaming back to cellular if UMA isn t available. UMA enabled phones can use any standard 802.11 access point for connection, though naturally the AP must provide network access for the user. The network features multiple UNCs, one of which is a default one. The default UNC chooses another UNC for the mobile terminal if needed based on the network topology. The mobile terminal connects to the UNC via unlicensed wireless networks and fixed line, using pointto-point IPSec encryption. The UNC contains a security gateway (SGW), which takes care of the IPSec tunnel and IKEv2 authentication (Mobile Pipeline). The subscribers are identified by SIM credentials, and the SGW is connected to GSM s AAA service for subscriber authentication. Calls are transferred through IP bearers (RTP and UDP), using the same data flow as with VoIP networks. GPRS connections are carried by TCP using a lightweight UMA-RLC protocol, which is suitable for always-on broadband connections. (Mobile Pipeline). Right now, there are no phones implementing UMTS and UMA at the same time only handoff between GSM and UMA exists. At the moment, the UNC does not support all of the UMTS services, so development still goes on (InCode 2006). Fig. 1: UMA as compared to standard GSM HOW UMA WORKS? Under the GAN system, if the dual-mode phone detects the presence of a compatible unlicensed wireless spectrum, say a WLAN, then it establishes an Internet Protocol (IP) connection. Thus, Voice-over- IP (VoIP) calls can be placed and data can be transferred via the basic cheaper UMA technology.
Unlicensed Mobile Access (UMA) 519 Fig. 2: Concept of UMA When a compatible UMA technology is not available, the phone functions in the carrier s specific cellular network. The UMA technology exhibits all the fundamental characteristics of a persistent technology. It is a decentralized, diverse, seamless connection, and simple for the user. Sr. no Modes of Operation 1 cellular network only 2 cellular network where available and Wi-Fi otherwise 3 Wi-Fi where available and cellular network otherwise 4 Wi-Fi only HISTORY AND EVOLUTION The UMAC worked with the 3GPP (Third Generation Partnership Project), established in 1998 through a collaboration agreement between different telecommunication standards bodies, they created the formal standard for UMA. They published the initial specifications for UMA in the year 2004(September), it explains the functioning of the same device over a: Licensed radio spectrum connection (GSM), when users are outside the UMA coverage. Unlicensed radio spectrum (Bluetooth or Wi-Fi), when being inside the UMA coverage. 3GPP defined UMA as a part of 3GPP release 6 (3GPP TS 43.318) under the name of GAN (generic access network). UMA defines a parallel Radio access network (RAN) called as the UMAN that interfaces with the mobile cellular core network using existing GSM-defined standard interfaces. This solution uses the IP tunnelling technique, which transparently extend mobile voice, data, and IP multimedia subsystem (IMS) services to mobile users through enabling service delivery to mobile phones over any WLAN Access Point (including Wi-Fi and Bluetooth). For faultless integration between existing mobile networks and unlicensed spectrum networks, a UMA-enabled handset is defined with dual-mode operation capable of connecting within both networks.
520 Ravindranath Barathy, Dandavate Pushpak and Das Bhumesh BENEFITS OF UMA FOR MOBILE OPERATORS AND SERVICE PROVIDERS Recently, a number of market trends and industry developments have joint to make a practical business proposition for UMA. Subscribers and service providers can thus exploit the rollout of broadband data connections and WLANs to offer a single user device for both cellular and fixed-line connectivity. UMA technology can allow mobile operators and service providers to make the most of their revenue potential and improve subscriber retention by increased use of mobile phones. The following benefits for mobile operators, service providers, as well as clients could hence be achieved: Improving the use of GSM radio network resources by using an alternative cost efficient and highbandwidth access network. Reduction in the capital and operational expenditure on radio networks by use of an alternative low-cost access network. Providing advanced and steady services over both fixed and mobile networks. Offering bundled fixed and mobile services, making the mobile handset the customer s only phone, thereby increasing their share of the customer s total expenditure. Considerably increasing the use of mobile voice and data services in locations where usage was discouraged due to cost or network coverage. Delivering enhanced reach as well as better voice quality. Bringing increased usage and allowing new services to be offered, thus delivering broadband data rates to the handsets. Since service providers have a lower cost to provide the service, they will be able in the near future to achieve higher margins and offer more aggressive pricing to their subscribers. Users have the advantage of using the same handset everywhere (inside home and outside). Users benefit from economical (special pricing) and technical advantages (radio coverage at their homes and offices). Delivery of mobile voice and data services over unlicensed wireless networks. Provides the same mobile identity on Cellular RAN and unlicensed wireless networks. Mobile Station FUNCTIONAL ENTITIES The MS shall include dual mode (GSM and unlicensed) radios and the capability to switch between them. The MS supports either Bluetooth (using the Bluetooth PAN profile) or 802.11. The MS supports an IP interface to the access point. In other words, the IP connection from the UNC extends all the way to the MS. Access Point The Access Point (AP) provides the radio link towards the mobile station using unlicensed spectrum. It connects through the broadband IP network to the UNC. The AP does not provide any UMA-specific gateway functions, and any generic AP can be used to interconnect the MS to the UNC via the broadband IP network.
Unlicensed Mobile Access (UMA) 521 UNC A UNC connects to a unique MSC and SGSN via the A-interface and GB interface respectively. The UNC provides functions equivalent to that of a GERAN base station controller. It connects via an IP transport connection to an AP. The UNC interfaces to the MS using the Up interface. It maintains end-toend communication with the MS and relays GERAN signalling to the A/Gb interface towards the Core Network. Specifically, the functions supported by the UNC include: Up user plane data services: Inter-working data transport channels over the Up interface to packet flows over the GB interface. Registration for UMA service access Set-up of UMA bearer paths for CS and PS services. These include participation in establishment, management, and tear down of secure signalling and user plane bearers between the MS and the UNC. UMA functions equivalent to GSM RR and GPRS RLC such as for paging and handovers. MS and AP addressing parameters are: Fig. 3: Blocks of UNC IDENTIFIERS IN UMA 1. The IMSI associated with the SIM in the terminal: The MS provides the identifiers to the UNC when it registers to a UNC. The UNC maintains a record for each registered MS.
522 Ravindranath Barathy, Dandavate Pushpak and Das Bhumesh 2. Public IP Address of the MS: The Public IP address of MS is the source IP available in the outermost IP header of packets received from the MS by the UNC-SGW. If available, this identifier may be used by the UNC to support locations services and fraud recognition. 3. The Access Point (AP) ID: The AP-ID is the MAC address of the unlicensed mode access point through which the MS is accessing UMA service. This identifier is provided by the MS (obtained via broadcast from the AP) to the UNC via the Up interface, when it requests UMA service. The AP-ID may be used by the UNC to support location services. Cell Identifiers for UMA A single UNC correspond to a single cell, and referred to as UMA cell, for the purpose of handover from GERAN to UMAN. The cell is recognized by a Cell Global Identity (CGI), which is the concatenation of an LAI and CI. The CGI allocated to the UNC is config.d as the target handover cell in all neighbouring GERAN cells. Neighbouring GERAN cells are those whose service area overlaps the UNC service area, for the purpose of handover. For example, neighbour cells are: - All GERAN cells attached to the same MSC as the UNC - All GERAN cells attached to a different MSC but that can handover to the MSC to which the UNC is joined. For purposes of providing location services and emergency services an operator may create cell identification contexts locally to a UNC. These cell recognition contexts are not visible to the MS. These cell IDs are extra to the one assigned to the UNC for handover purposes. NOTE: The location area (or routing area) assigned to the UNC may be different from, or the same as, the location area (or routing area) of the overlapping GERAN cells. The GERAN-to-UMAN handover method makes use of an RF channel number (ARFCN) and base station identity code (BSIC) parameters to identify the UMA target cell. Selection of ARFCN should follow the following guidelines: 1. The ARFCN should not be allocated from the operator s existing BCCH pool so that a scarce BCCH is not used. 2. The ARFCN is desired to be the same unique number across the whole operator network so that the BSS configuration effort can be minimized. Available options for the selection of the ARFCN: 1. Ideally, the UMAN is assigned an ARFCN value which is not in the frequency bands currently used by the operator. 2. Typically, different PLMNs in the same country have disjoint frequency allocations. For each PLMN, some of the frequencies are reserved for BCCH beacon; BCCH will be transmitted with constant max power on time slot 0. Other frequencies are dedicated as traffic channels. The UMAN ARFCN could use any non-bcch frequency from the carrier s existing frequency pool. Standard GSM MSs will be able to tune onto this channel but will not be able to find the FCCH burst. 3. Alternatively, in a PCS-only (1900 MHz) network, ARFCN can be any value falling within the GSM (900 MHz) or DCS (1800 MHz) band. MS operates in one of following two modes: - GSM mode MODE SELECTION
Unlicensed Mobile Access (UMA) 523 - GSM RR is the serving RR entity - UMA mode: - UMA RR is the serving RR entity. On power up, the MS starts in GSM mode and performs the normal GSM power-up sequence. After that, it might switch into UMA mode based on mode selection choice determined by user preferences and service provider configuration [UMA R]. Emergency calling actions have some exceptions. - GERAN-only: - The MS shall stay in GSM mode and never switch to UMA mode. - GERAN-preferred: - The MS shall continue in GSM mode, as long as a PLMN is available via GERAN (per TS 23.122). If no PLMN is available via GERAN, the MS may look for UMA coverage, and if it is identified, shall perform the registration procedure, thereby switching to UMA mode. At any time, when in UMA mode, if a GSM PLMN becomes accessible or MS leaves UMA coverage, the MS shall perform the rove-out procedure. (Whichever is applicable), thereby switching to GSM mode. - UMAN-preferred: - At any time, when in GSM mode and PLMN search (due to no GSM cell available) is not in progress, if UMA coverage becomes accessible, the MS shall perform the rove-in procedure per sub- or switch to UMAN procedure. - UMAN-only: - The MS shall continue in UMA mode (switching after the initial power-up sequence in GSM mode is completed) and never switch to GSM mode. UMAN DISCOVERY AND REGISTRATION PROCEDURE The Discovery process is carry out by the MS when first trying to obtain UMA facility in order to verify the identity of the Default UNC which may also serve as the serving UNC for that connection. The UMA registration process is performed between the MS and UNC. It serves the following objects: It informs the UNC that a MS is now joined through a unique AP and is accessible at a unique IP address. The UNC keeps track of this information for the purposes of providing service, for e.g. mobileterminated calls. It provides the MS with the operating parameters related with the UMA service. The GSM System Information message information that is applicable in UMA mode is delivered to the MS during the UMA registration process. These procedures are applicable for the following circumstances and mode selection preferences: - UMAN-only - UMAN-preferred - GERAN-preferred, and no GSM PLMN available Discovery and Registration When an MS supporting UMA first tries to unite to a UNC based on a UMA subscription, it needs to recognize the Serving UNC. In order to do this it first connects to a Provisioning UNC and then discovers a Default UNC, which in turn can redirect the MS to a Serving UNC. A MS supporting UMA may be provisioned (e.g. on the SIM) with the Fully Qualified Domain Name (FQDN) or IP address of the Provisioning UNC and the associated Security Gateway (SGW). In case the
524 Ravindranath Barathy, Dandavate Pushpak and Das Bhumesh SIM is not provisioned with the FQDN or IP address, the MS shall derive a FQDN for the Provisioning UNC and the secure gateway, based on its IMSI. The FQDN shall comply with the following format: Provisioning SGW: sgw.uma.mncnnn.mccmmm.3gppnetwork.org Provisioning UNC: punc.uma.mncnnn.mccmmm.3gppnetwork.org Where nnn and mmm are restored with the IMSI MNC and MCC information in the SIM. The MS shall set up a secure tunnel using the provisioned or derived address, and connect to the Provisioning UNC.The Default UNC serves as the primary registration destination address for the MS when it not succeeds to register on an alternate Serving UNC. These alternate Serving UNC addresses are accumulated in the MS and associated with previously connected WLAN APs if there is no GSM coverage or with GSM cell identities if there is GSM coverage. Following the invention procedure the MS shall set up a secure tunnel with the secure gateway of the default UNC and try to register with the Default UNC. The Default UNC network may also serve as the Serving UNC for that connection. The procedure may result in the MS getting re-directed to a different Serving UNC. UNC redirection refers to the capability of a UNC to redirect an MS to a UNC distinct from the one it initially requests access to based on MS provided information and operator chosen policy. For example, the appropriate serving UNC is the UNC whose UMA service area overlaps the MS s umbrella GSM coverage. The right serving UNC could be joined to the identical MSC as the GSM BSC to which the umbrella GSM cell belongs. The correct serving UNC could be joined to a dissimilar MSC that can handover to the MSC, which provides umbrella GSM coverage to the MS. If no GSM coverage is accessible when an MS connects to the UNC for UMA service, then the UNC cannot necessarily decide the position of the MS for the purposes of assigning the MS to the accurate serving UNC (to allow handover and location-based services). The UNC shall permit the operator to establish the service policy in this case; e.g., the operator could provide service to the user with certain limitations (possibly with a user interface indication on the MS). Serving UNC information shall be linked with the GSM CGI. The stored Serving UNC information is, - Serving SGW FQDN or IP address following successful registration; - Serving UNC FQDN or IP address following successful registration; The number of such entries to be accumulated in the MS is implementation specific. For a particular AP or GSM cell, only the last successfully registered UNC association shall be stored. The MS shall remove from its stored list the address of the Serving UNC on receiving a registration reject. If the MS does not receive a response to the Registration Request sent to the Serving UNC (and which is not the Default UNC), it shall effort to register with the Default UNC in order to obtain a new Serving UNC for the connected AP. If the MS does not receive a answer to the registration request sent to the Default UNC, it shall try the discovery procedure with the Provisioning UNC in order to attain a new Default UNC. When the MS joins a WLAN, for which it does not have a stored Serving UNC in its memory, it shall effort to register with the Default UNC. The Discovery and Registration procedures consist of the following steps:
Unlicensed Mobile Access (UMA) 525 Connecting a WLAN Discovery of Default UNC, through the Provisioning UNC Registration with the Default UNC Potential redirection to a Serving UNC or refusal. Registration with a Serving UNC Through the Registration process the MS may get re-directed to another Serving UNC. This could be based on the following, among other reasons: Current location signalled through the overlapping GERAN Cell Global uniqueness or other location attributes. Signal of joined AP Load balancing in the NW Operator Policy Roaming agreements in case of a roaming MS A successful registration process results in the UNC establishing a context for the MS. The MS obtains the necessary system information for the UMAN it has registered on and can trigger a usual Location/Routing Area Update procedure with the CN. Fig. 4: Discovery and Registration
526 Ravindranath Barathy, Dandavate Pushpak and Das Bhumesh DE-REGISTRATION The UMA De-Registration procedure allows the MS to inform the UNC that it is disconnecting UMA mode, permitting the UNC to free resources that it allocated to the MS. The UNC may also implicitly deregister the MS when the TCP connection to the MS is abruptly lost. Fig. 5: De-Registration initiated by MS Fig. 6: De-Registration initiated by UNC The UNC sends the URR DEREGISTER to the MS. The Deregistration procedure can also be initiated by the Serving UNC. Fig. 7: Investment structure CONSUMER BENEFITS Cost advantages Utilisation advantages Service advantages (1) Get more benefits at low price (1) Get more broadband speed (1) A particular provider. with multiplay bundles. (2) Calls at low rate. (2) Better indoor coverage (2) An unique customer service
Unlicensed Mobile Access (UMA) 527 VENDOR STRATEGIES The initial aim for the vendors of UMA forum was to establish standardized technology to ensure cooperation in commercialization stage of the technology, because it was crucial to provide compatibility between all manufacturers products and prevent the emergence of multiple competing standards (Schilling 2005). Telecomm vendors eagerly market their FMC solutions for operators. Handset vendors tend to build support for multi-radio and multi-access terminals enabling different access methods including WLAN. For example Nokia has announced that it will aim supporting both UMA and what they call Native IP access to be used with IMS (Nokia Corporation 2005). Some vendors develop their own network equipment to support UMA while some others have made strategic decision to offer them trough a collaboration partner Vendor Alcatel Ericsson Kineto Wireless Motorola Nokia UMA solution Together with Spatial Own UNC Own UNC Kineto s software, possibly own hardware Resells Kineto s UNC CONCLUSION UMA enabled handsets will be available in greater numbers very soon, complete with a very low power consuming 802.11g WLAN chips. It is unlikely to see any reasonable growth for the UMA Bluetooth markets, since the range is limited and access points aren t available (Philips 2005). Still, it is not clear whether UMA will be a big hit or not. The operators need to have enough customers with UMA enabled handsets so that their investments to the network side would be profitable. In some countries, such as the United States, UMA is more attractive than in others, due to the worse existing cell coverage. Also, the pricing point is critical for the customers, so that they are willing to buy a UMA enabled mobile handset as well as have the additional radios switched on, sacrificing some standby time. We estimate that UMA in its current form will be properly in use, if it ever will, in around 2 years. UMA technology seems to suite well for regular mobile network operators in their long-term mobile network evolution and it has a significant time-to-market advantage over VCC some new fixed-line operators such as cable-tv and VoIP providers are likely to target to IMS directly without UMA. Since IMS with VCC provides a substitute for UMA, the technology choice of operators plays a key role in how UMA is diffused. We believe that all related standard technologies will be used side by side within future mobile networks, though analyzing the overlaps between UMA and I-WLAN would need separate studies and knowledge about anticipated convergence between VCC and the most advanced scenarios of I-WLAN (In Code 2006).
528 Ravindranath Barathy, Dandavate Pushpak and Das Bhumesh 1 3GPP, Rel-4: Network Architecture. 2 3GPP, Rel-4: Handover procedures. REFERENCES 3 3GPP, Rel-5: Intra-domain connection of Radio Access Network (RAN) nodes to multiple Core Network (CN) nodes. 4 3GPP, Rel-4: Mobile radio interface layer 3 specification. 5 3GPP, Rel-4: Security related network functions. 6 3GPP, Rel-4: Functional Stage 2 Description of Location Services in GERAN. 7 www.umatoday.com/uma overview 8 www.umatoday.com/uma history 9 Unlicensed Mobile Access (UMA) User Perspective (Stage 1) 10 Unlicensed Mobile Access (UMA) Architecture (Stage 2). 11 Unlicensed Mobile Access (UMA) Protocols (Stage 3)