GSM over Ethernet


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GSM over Ethernet

  1. 1. DATA CABLING GSM over Ethernet Roger Dettmer reports on how a UK company– with a little help from Category 5 cabling–is helping to realise the commercial potential of the GSM pico base station SM is, far and away, the world’s most improve employee efficiency, and it can G successful mobile phone system. It has two-thirds of the world market, is available in more than 150 countries and boasts around 650 million subscribers. A key feature of the system’s design is the negotiate a special tariff to limit the cost of all mobile calls originating within in-office cells. With all these attractions, the obvious question is why does office telephony remain overwhelmingly dominated by conventional capability to handle mobile users travelling at handsets linked to PABXs by fixed wiring? The high speed. Reflecting the performance of answer lies in the technical and financial European high-speed trains, notably the French barriers that have traditionally prevented the TGV, GSM can provide acceptable speech quality deployment of an effective GSM infrastructure and inter-cell hand-offs for users travelling at up within the office environment. to 250 km/h. In engineering terms this is truly impressive; in practice it’s almost wholly Macro, micro and pico irrelevant to the vast majority of users. The GSM standard defines a three-layer Although GSM was designed for outdoor hierarchy of base stations. The macro base mobile use, in many countries the bulk of station, at the top of the hierarchy, provides the 1 With a footprint mobile calls are made within buildings by overlay network for fast-moving subscribers. smaller than a notebook callers whose maximum speed is unlikely ever Next down the ranking is the micro base PC, the nanoBTS can be mounted easily and to exceed the 7 km/hr or so attainable in a very station, typically providing coverage to people unobtrusively on a wall brisk walk between offices.The popularity of in- moving between large buildings, e.g. on a or ceiling office mobile use is not hard to fathom. User attractions include no more missed calls when you’re away from your desk, the convenience of a single phone with a single number (instead of two or more), and access to a rich, familiar feature set, including a built-in telephone directory, mailbox and messaging. The benefits to the operator can be equally compelling. In general, office callers tend to be high ARPU (average revenue per user) customers, and the operator has a vested interest in keeping them happy. Suppose mobile operator Y agrees to deploy a number of new base stations specifically to improve coverage within the offices of company X. All eligible employees get an operator Y handset, which they use within the office and, as like as not, everywhere else. The net result is that ARPU will go up, while, churn – the tendency to switch operators – will go down, delivering a win-win situation for the operator. Company X will also benefit. Wireless communications should IEE REVIEW MARCH 2002 37
  2. 2. DATA CABLING Power over Ethernet Traditional office phones derive their power directly from a There are currently two basic approaches to deploying centralised source, invariably equipped with battery backup to power over Ethernet: first, directly from an end-span device, provide protection in the event of a power failure. Replicating i.e. the Ethernet switch; secondly, from a mid-span device–an this level of security for IP phones connected to an Ethernet independent powering device sitting between the data switch LAN involves either providing every phone with an individual and the patch panel. End-span devices can deliver power via uninterruptible power supply (expensive and impractical), or either the spare or the data pair, while mid-span devices are limited to using the spare pair. The current market for power over Ethernet products is dominated by PowerDsine, an Israeli company, specialising in fast Ethernet switch products supporting power 110/220 V AC 100 Mbit/s or 48 V DC delivery over telecom and UPS converged voice-data mid-span unit networks, and switch manufacturer Cisco. RJ45 PowerDsine claims to be wall outlet the originator of the power 100 Mbit/s over Ethernet concept, and 48 V DC which, according to Amir RJ45 Lehr, the company’s Vice web camera wall outlet President of Marketing, RJ45 wall outlet originated with a market research study late in 1998 identifying the power data supply problems of IP wireless LAN access point phones as a potential business opportunity. The company started with a demonstration mid-span IP phone unit, based on its off-the- shelf xDSL powering modules and using the data pair for power transmission. Power over Ethernet means that terminal devices require only a single connection to the network Then, in 1999, it introduced for data and power the first commercially available product for spare devising some means of distributing power over the Category and data pairs, and initiated the IEEE call for interest in order 5 cabling system (in principle, relatively straightforward). to work towards an industry standard. PowerDsine currently There are eight wires on Category 5 cabling. Pins 1,2,3 and 6 dominates the mid-span market, with a range of 6, 12 and 24 are used for data (configured as two twisted pairs), and pins port units. 4,5,7 and 8 are spare, and thus freely available for power Cisco entered the market as a consequence of its delivery. Because the power current has a much lower commercial interest in IP telephony. It introduced its first frequency than the data transmission, it’s also possible to range of products in May 2000, including a number of power- send power over the data pair. enabled Ethernet switches and a single mid-span unit. To Unfortunately, this encouraging picture is seriously date, Cisco claims to have sold the equivalent of over 6 million undermined by the fact that the low-cost terminations used Ethernet power points. on the majority of today’s Ethernet devices are unable to Pending the ratification of the IEEE standard all power over tolerate even modest power levels, necessitating a suitable Ethernet products are proprietary, so that any terminal device, detection scheme to ensure that power is only supplied to IP phone, wireless LAN access point, security sensor, pico those LAN-connected devices where it is required and which base station etc, will only work with a mid or end-span unit are equipped with suitable terminations. The IEEE 802.3 employing a matching supplier-specific device detection Working Group, which is responsible for the Ethernet protocol, algorithm. Ratification should significantly increase market has established a Task Force, 802.3af, to establish a standard volume by providing a basis for interoperability between the for supplying power over Ethernet and detecting power-using products of all compliant vendors. Amir Lehr believes that devices. The Task Force has targeted mid-2002 for completion within three to five years, over 75% of new Ethernet edge of its technical work and early 2003 for a ratified standard. switch ports will feature power over Ethernet. 38 IEE REVIEW MARCH 2002
  3. 3. DATA CABLING university campus. Finally, at the bottom of the GSM handset market, providing software and stack, the pico base station is intended to chip set designs for more than 15% of the provide in-building coverage, e.g. serving the world’s handsets. Today, ip.access is the supplier lobby of a hotel or a section of a large open-plan of the world’s smallest GSM base station, the office. Power levels fall as you move down the nanoBTS (base station transceiver), measuring a hierarchy, but the broad functionality of the mere 210 mm by 280 mm (Fig. 1). It’s fully different base station types is the same. compatible with the ETSI pico base station In practice, the market for pico base stations is standard, and has a range of over 500 m in an little better than embryonic, with a dearth of uncluttered environment, while the in-building suppliers and high costs preventing significant range is of the order of 50 m, depending on the deployment. As a consequence, dedicated in- building construction materials. building GSM coverage has generally been The nanoBTS has been engineered specifically limited to relatively large public areas, e.g. to overcome the financial barriers that are shopping malls and airport departure lounges, currently inhibiting the deployment of pico served by micro base stations supported by a base stations, driving down the lifetime cost system of distributed antennas.The great bulk of of ownership by minimising the capital, in-office mobile users are thus left solely reliant installation, and system management costs.Tight on the technically inappropriate overlay control over manufacturing costs comes from network, where signal attenuation – from solid making maximum use of the mass-market walls and argon-filled or metallised double hardware and software components originally glazing – significantly increases the incidence of developed by TTP Communications for GSM blocked and dropped calls. The net result is the handsets. Low installation costs are attributable, commercial paradox of a wireless system in in part, to the unit’s small size – allowing it to be which the majority of high-value calls are made mounted on a wall or ceiling – but, more in the place where the network is at its weakest. significantly, to the technology used to back All this could be about to change. haul wireless traffic from base stations to the GSM base station controller (BSC). Small is beautiful The traditional approach to deploying in- 2 System architecture. ip.access is a Cambridge technology start-up building GSM coverage, using micro base Voice traffic is confined created specifically to address the potential of stations and a distributed antenna system, within the office LAN; the GSM pico base station market. The company involves lengthy cell and frequency planning, signalling information is routed to the mobile was formed in December 1999 as a wholly coupled with a significant disruption of the switching centre (MSC) owned subsidiary of TTP Communications – a workplace from the need to install extensive co- in the external main major source of intellectual property for the axial and fibre cable runs. Increasingly, however, operator site wireless office 30 to 10 000 staff main operator site nanoBTS feature PABX server PSTN media local and OMC gateway signalling ATM, frame relay, SDH gateway public MPLS, Ethernet Extension mobile switched router router MSC network hub nanoBSC other SGSN Internet wireless offices IEE REVIEW MARCH 2002 39
  4. 4. DATA CABLING modern offices, along with many commercial units, providing the network operator with buildings, are permeated by a ready-made information on local frequency usage to assist in cabling infrastructure in the form of Category 5 allocating frequencies and power levels to the structured cabling providing the physical layer individual nanoBTSs. It works because the pico for an Ethernet-based local area network (LAN). cell is physically small, so that a measurement of The nanoBTS overcomes the need to install a the radio environment made at the base station dedicated cabling infrastructure by plugging itself is reasonably representative of conditions directly into existing LAN sockets, requiring just across the cell. This would not be the case for a matter of minutes to mount and configure. micro and macro base stations, with their This overlay network is then patched to a significantly larger cell sizes. separate LAN hub connected to a BSC. The base stations don’t just use the physical Marketing infrastructure represented by the existing The wireless office is the most obvious high- Category 5 wiring; they also use standard volume application for pico base stations, and Ethernet as a transport protocol for GSM traffic. ip.access is currently working with a large This last feature – unique to the nanoBTS, systems integrator in this area. There are, according to Neil Piercy, Systems Architect for however, additional market sectors where ip.acess – has a number of important advantages. the technology has considerable commercial First, it avoids the need to switch intra-office potential. The most obvious of these is public calls within the external GSM mobile switching infill, with the nanoBTS providing a more centre (MSC). Signalling information is passed ‘directed’ and cost-effective alternative to the out to the MSC, but voice traffic is routed across traditional use of micro base stations and the office LAN, just like any other IP packets, distributed antennas. In a particularly thereby virtually eliminating transmission costs spectacular example of an infill application, for intra-office calls (Fig. 2). Secondly, it ip.access is working with an operator holding a simplifies the installation of nanoBTSs on the GSM licence covering a public underground network. They’re Ethernet devices and, as such, system with around a million passengers a day. use standard Ethernet configuration protocols to Spot infill in busy city centres could also be very acquire a valid IP address. Finally, it allows important, using pico base stations installed in the LAN and back-haul infrastructure to be public payphones. Large apartment blocks, colocated with the existing LAN/WAN especially in the Asia-Pacific region, are also infrastructure in a communications hub room. seen as a significant potential market. In general, size and power requirements dictate Looking a little more to the future, ip.access is that an in-building micro base station needs a investigating the possible use of its base station totally separate physical location. In this case, technology in the retail sector. Imagine a new cable runs (possibly using Category 5 supermarket that installs pico base stations in its cabling in the case of active antenna systems) stores and issues its customers with compatible would almost certainly have to be installed to handsets, possibly as part of a deal with an link the base station to the distributed antennas. existing network operator, or with the store Using Category 5 cabling has a further chain acting as a mobile virtual network potential advantage. When the IEEE power over operator. The customer walks into the store and Ethernet standard, 802.3af, is finalised (see is detected and recognised by the network, panel), it will be possible to meet the nanoBTS’s which updates the handset display with a list of 15 W maximum power requirements directly customer-specific special offers. The customer from the Category 5 cabling. Feedback from selects an item of particular interest, ‘drinks’ say, ip.access’s prospective customers suggests this and is presented with details of the current wine is, potentially, a very attractive feature.‘It means,’ promotions and their location within the store, says Neil Piercy, ‘the difference between getting with the option of calling a ‘customer helpline’ someone to lay low-voltage, inherently safe to obtain recorded advice on suitable Category 5 cabling, and getting a qualified complementary menu choices from a well- electrician to lay Category 5 plus a mains spur, know TV wine pundit. Finally, at the checkout, disrupting the existing office electricity supply.’ the customer is rewarded with a money-off Low installation costs and low system voucher, again delivered electronically over the management costs are further supported by local GSM network. It would, to say the least, be nanoBTS’s unique Network Listen feature.This is a significant technical advance on the lowly essentially an in-built mobile receiver which loyalty card. monitors emissions from other base stations, including any overlying macro and micro © IEE: 2002 40 IEE REVIEW MARCH 2002