Thursday, August 20, 2009

Broadband data service

Both 3G and WiFi support broadband data service, although as noted earlier, the data rate offered by WiFi (11Mbps) is substantially higher than the couple of 100 Kbps expected from 3G services. Although future generations of wireless mobile technology will support higher speeds, this will also be the case for WLANs, and neither will be likely to compete with wireline15 speeds (except over quite short distances).

The key is that both will offer sufficient bandwidth to support a comparable array of services, including real-time voice, data, and streaming media, that are not currently easily supported over narrowband wireline services. (Of course, the quality of these services will be quite different as will be discussed further below.) In this sense,16 both will support "broadband" where we define this as "faster than what we had before."

Both services will also support "always on" connectivity which is another very important aspect of broadband service. Indeed, some analysts believe this is even more important than the raw throughput supported.

WiFi, 3G access

Both 3G and WiFi are access or edge-network technologies. This means they offer alternatives to the last-mile wireline network. Beyond the last- mile, both rely on similar network connections and transmission support infrastructure. For 3G, the wireless link is from the end- user device to the cell base station which may be at a distance of up to a few kilometers, and then dedicated wireline facilities to interconnect base stations to the carrier's backbone network and ultimately to the Internet cloud. The local backhaul infrastructure of the cell provider may be offered over facilities owned by the wireless provider (e.g., microwave links) or leased from the local wireline telephone service provider (i.e., usually the incumbent local exchange carrier or ILEC). Although 3G is conceived of as an end-to-end service, it is possible to view it as an access service.

For WiFi, the wireless link is a few hundred feet from the end-user device to the base station. The base station is then connected either into the wireline LAN or enterprise network infrastructure or to a wireline access line to a carrier's backbone network and then eventually to the Internet. For example, WiFi is increasingly finding application as a home LAN technology to enable sharing of DSL or cable modem residential broadband access services among multiple PCs in a home or to enable within-home mobility. WiFi is generally viewed as an access technology, not as an end-to-end service.

Because both technologies are access technologies, we must always consider the role of backbone wireline providers that provide connectivity to the rest of the Internet and support transport within the core of the network. These wireline providers may also offer competing wireline access solutions. For example, one could ask whether an ILEC might seek to offer WiFi access as a way to compete with a 3G provider; or a 3G provider might expand their offe rings (including integrating WiFi) to compete more directly with an ILEC. Of course, the incentives for such head-to-head competition are muted if the 3G provider and ILEC (or cable modem provider) share a common corporate parent (e.g., Verizon and Verizon Wireless or Telefonica and Telefonica Moviles).

Finally, focusing on the access-nature of 3G and WiFi allows us to abstract from the other elements of the value chain. Wireless services are part of an end-to-end value chain that includes, in its coarsest delineation at least (1) the Internet back bone (the cloud); (2) the second mile network providers (ILEC, mobile, cable, or a NextGen carrier); and, (3) the last mile access facilities (and, beyond them, the end-user devices). The backbone and the second mile may be wireless or wireline, but these are not principally a "wireless" challenge. It is in the last mile – the access network – that delivering mobility, bandwidth, and follow-me-anywhere/anytime services are most challenging.

WiFi , 3G wireless

Both technologies are wireless which (1) avoids need to install cable drops to
each device when compared to wireline alternatives; and (2) facilitates mobility. Avoiding the need to install or reconfigure local distribution cable plant can represent a significant cost savings, whether it is within a building, home, or in the last mile distribution plant of a wireline service provider. Moreover, many types of wireless infrastructure can provide scalable infrastructure when penetration will increase only slowly over time (e.g., when a new service is offered or in an overbuild scenario). New base stations are added as more users in the local area join the wireless network and cells are resized. Wireless infrastructure may be deployed more rapidly than wireline alternatives to respond to new market opportunities or changing demand. These aspects of wireless may make it attractive as an overbuild competitor to wireline local access, which has large sunk/fixed costs that vary more with the homes passed than the actual level of subscribership. The high upfront cost of installing new wireline last- mile facilities is one of the reasons why these may be a natural monopoly, at least in many locations.


Wireless technologies also facilitate mobility. This includes both (1) the ability to
move devices around without having to move cables and furniture; and (2) the ability to stay continuously connected over wider serving areas. We refer to the first as local mobility and this is one of the key advantages of WLANs over traditional wireline LANs. The second type of mobility is one of the key advantages of mobile systems such as 3G. WLANs trade the range of coverage for higher bandwidth, making them more suitable for "local hot spot" service. In contrast, 3G offers much narrower bandwidth but over a wider calling area and with more support for rapid movement between base stations. Although it is possible to cover a wide area with WiFi, it is most commonly deployed in a local area with one or a few base stations being managed as a separate WLAN. In contrast, a 3G network would include a large number of base stations operating over a wide area as an integrated wireless network to enable load sharing and uninterrupted hand-offs when subscribers move between base stations at high speeds.


This has implications for the magnitude of initial investment required to bring up WLAN or 3G wireless service and for the network management and operations support services required to operate the networks. However, it is unclear at this time13 which type of network might be lower cost for equivalent scale deployments, either in terms of upfront capital costs (ignoring spectrum costs for now) or on-going network management costs.

WiFi vs 3G


From the preceding discussion, it might appear that 3G and WiFi address completely different user needs in quite distinct markets that do not overlap. While this was certainly more true about earlier generations of mobile services when compared with wired LANs or earlier versions of WLANs, it is increasingly not the case. The end- user does not care what technology is used to support his service. What matters is that both of these technologies are providing platforms for wireless access to the Internet and other communication services.

In this section we focus on the ways in which the two technologies may be thought of as similar, while in the next section we will focus on the many differences between the two.

WiFi

WiFi is the popular name for the wireless Ethernet 802.11b standard for WLANs. Wireline local area networks (LANs) emerged in the early 1980s as a way to allow collections of PCs, terminals, and other distributed computing devices to share resources and peripherals such as printers, access servers, or shared storage devices. One of the most popular LAN technologies was Ethernet. Over the years, the IEEE has approved a succession of Ethernet standards to support higher capacity LANs over a diverse array of media. The 802.11x family of Ethernet standards are for wireless LANs.

WiFi LANs operate using unlicensed spectrum in the 2.4GHz band. The current generation of WLANs support up to 11Mbps data rates within 300 feet of the base station. Most typically, WLANs are deployed in a distributed way to offer last-fewhundred- feet connectivity to a wireline backbone corporate or campus network. Typically, the WLANs are implemented as part of a private network. The base station.

equipment is owned and operated by the end-user community as part of the corporate enterprise network, campus or government network. In most cases, use of the network is free to end-users (subsidized by the community as a cost of doing business, like corporate phones).

Although each base station can support connections only over a range of a few hundred feet, it is possible to provide contiguous coverage over a wider area by using multiple base stations. A number of corporate business and university campuses havedeployed such contiguous WLANs. Still, the WLAN technology was not designed to support high-speed hand-off associated with users moving between base station coverage areas (i.e., the problem addressed by mobile systems).

In the last two years, we have seen the emergence of a number of service providers that are offering WiFi services for a fee in selected local areas such as hotels, airport lounges, and coffee shops.12 Mobilestar, which declared bankruptcy during the latter half of 2001, was one of the leaders in this area. In addition, there is a growing movement of so-called "FreeNets" where individuals or organizations are providing open access to subsidized WiFi networks.

In contrast to mobile, WLANs were principally focused on supporting data communications. However, with the growing interest in supporting real-time services such as voice and video over IP networks, it is possible to support voice telephony services over WLANs.

3G


3G is a technology for mobile service providers. Mobile services are provided by service providers that own and operate their own wireless networks and sell mobile services to end-users, usually on a monthly subscription basis. Mobile service providers7 use licensed spectrum to provide wireless telephone coverage over some relatively large contiguous geographic serving area. Historically, this might have included a metropolitan
area. Today it may include the entire country. From a users perspective, the key feature of mobile service is that it offers (near) ubiquitous and continuous coverage. That is, a consumer can carry on a telephone conversation while driving along a highway at 100
Km/hour. To support this service, mobile operators maintain a network of interconnected and overlapping mobile base stations that hand-off customers as those customers move
among adjacent cells. Each mobile base station may support users up to several kilometers away. The cell towers are connected to each other by a backhaul network that also provides interconnection to the wireline Public Switched Telecommunications Network (PSTN) and other services. The mobile system operator owns the end-to-end network from the base stations to the backhaul network to the point of interconnection to the PSTN (and, perhaps, parts thereof).

The first mobile services were analog. Although mobile services began to emerge in the 1940s, the first mass market mobile services in the U.S. were based on the AMPS (Advanced Mobile Phone Service) technology. This is what is commonly referred to as first generation wireless. The FCC licensed two operators in each market to offer AMPS service in the 800-900MHz band. In the 1990s, mobile services based on digital mobile technologies us hered in the second generation (2G) of wireless services that we have today. In the U.S., these were referred to as Personal Communication Systems (PCS)8 and used technologies such as TDMA (Time Division Multiple Access), CDMA (Code Division Multiple Access) and GSM (Global System for Mobile Communications). From 1995 to 1997, the FCC auctioned off PCS spectrum licenses in the 1850 to 1990 MHz band. CDMA and TDMA were deployed in the various parts of the U.S., while GSM was deployed as the common standard in Europe.9 The next or Third Generation (3G) mobile
technologies will support higher bandwidth digital communications and are expected to
be based on one of the several standards included under the ITU's IMT-2000 umbrella of
3G standards.

The chief focus of wireless mobile services has been voice telephony. However, in recent years there has been growing interest in data services as well. While data services are available over AMPS systems, these are limited to quite low data rates (<10Kbps). Higher speed data and other advanced telephone services are more readily supported over the digital mobile 2G systems. The 2G systems also support larger numbers of subscribers and so helped alleviate capacity problems faced by older AMPS systems in more congested environments. Nevertheless, the data rates supportable over 2G systems are still quite limited, offering only between 10-20Kbps. To expand the range and capability of data services that can be supported by digital mobile systems, service providers will have to upgrade their networks to one of the 3G technologies. These can support data rates of from 384Kbps up to 2Mbps, although most commercial deployments are expected to offer data rates closer to 100Kbps in practice. While this is substantially below the rates supported by the current generation of wireline broadband access services such as DSL or cable modems, it is expected that future upgrades to the 3G or the transition to 4G mobile services will offer substantially higher bandwidths. Although wireline systems are likely to always exceed the capacity of wireless ones, it remains unclear precisely how much bandwidth will be demanded by the typical consumer and whether 3G services will offer enough to meet the needs of most consumers.

Auctions for 3G spectrum licenses occurred in a number of countries in 2000 and the first commercial offerings of 3G services began in Japan in October 2001. More recently, Verizon Wireless has announced "3G" service in portions of its serving territory(although this is not true-3G service).

Compare 3G wifi



The two most important phenomena impacting telecommunications over the past decade have been the explosive parallel growth of both the Internet and mobile telephone services. The Internet brought the benefits of data communications to the masses with email, the Web, and eCommerce; while mobile service has enabled "follow-meanywhere/ always on" telephony. The Internet helped accelerate the trend from voicecentric to data-centric networking. Data already exceeds voice traffic and the data share continues to grow. Now, these two worlds are converging. This convergence offers the benefits of new interactive multimedia services coupled to the flexibility and mobility of wireless. To realize the full potential of this convergence, however, we need broadband access connections. What precisely constitutes "broadband" is, of course, a moving target, but at a minimum, it should support data rates in the hundreds of kilobits per second as opposed to the 50Kbps enjoyed by 80% of the Internet users in the US who still rely on dial-up modems over wireline circuits, or the even more anemic 10-20Kbps typically supported by the current generation of available mobile data services. While the need for broadband wireless Internet access is widely accepted, there remains great uncertainty and disagreement as to how the wireless Internet future will evolve.

The goal of this article is to compare and contrast two technologies that are likely to play important roles: Third Generation mobile ("3G") and Wireless Local Area Networks ("WLAN"). Specifically, we will focus on 3G as embodied by the IMT-2000 family of standards2 versus the WLAN technology embodied by the WiFi or 802.11b standard, which is the most popular and widely deployed of the WLAN technologies. We use these technologies as reference points to span what we believe are two fundamentally different philosophies for how wireless Internet access might evolve. The former represents a natural evolution and extension of the business models of existing mobile providers. These providers have already invested billions of dollars purchasing the spectrum licenses to support advanced data services and equipment makers have been gearing up to produce the base stations and handsets for wide-scale deployments of 3G services. In contrast, the WiFi approach would leverage the large installed base of
WLAN infrastructure already in place.

In focusing on 3G and WiFi, we are ignoring many other technologies that are likely to be important in the wireless Internet such as satellite services, LMDS, MMDS, or other fixed wireless alternatives. We also ignore technologies such as BlueTooth or HomeRF which have at times been touted as potential rivals to WiFi, at least in home networking environments.4 Moreover, we will not discuss the relationship between various transitional, or "2.5G" mobile technologies such as GPRS or EDGE, nor will we discuss the myriad possibilities for "4G" mobile technologies.5 While all of these are interesting, we have only limited space and our goal is to tease out what we believe are important themes/trends/forces shaping the industry structure for next generation wireless services, rather than to focus on the technologies themselves. We use 3G and WiFi as shorthand for broad classes of related technologies that have two quite distinct industry origins and histories.

Speaking broadly, 3G offers a vertically- integrated, top-down, service-provider approach to delivering wireless Internet access; while WiFi offers (at least potentially) an end-user-centric, decentralized approach to service provisioning. Although there is nothing intrinsic to the technologies that dictates that one may be associated with one type of industry structure or another, we use these two technologies to focus our speculations on the potential tensions between these two alternative world views.

We believe that the wireless future will include a mix of heterogeneous wireless access technologies. Moreover, we expect that the two worldviews will converge such that vertically-integrated service providers will integrate WiFi or other WLAN technologies into their 3G or wireline infrastructure when this makes sense. We are, perhaps, less optimistic about the prospects for decentralized, bottom-up networks – however, it is interesting to consider what some of the roadblocks are to the emergence of such a world. The latter sort of industry structure is attractive because it is likely to be quite competitive, whereas the top-down vertically- integrated service-provider model may – but need not be -- less so. The multiplicity of potential wireless access technologies and/or business models provides some hope that we may be able to realize robust facilities-based competition for broadband local access services. If this occurs, it would help solve the "last mile" competition problem that has bedeviled
telecommunications policy.

UMTS




The Universal Mobile Telecommunications System, UMTS, will take the personal communications user into the Information Society of the 21st century. It will deliver advanced information directly to people and provide them with access to new and innovative services.

The fundamental difference between GPRS and UMTS resides in the support of high bit rate bearer services with the notion of negotiated traffic and QoS characteristics. This shall allow UMTS to support single- and multi-media N-ISDN applications and single- and multimedia IP applications. In the final stage UMTS supports packet switched data service capabilities of at least 2 Mbps peak bit rate per user in urban areas and 384 kbps in wider areas along with Point-to-Multipoint communication. Moreover, the core network allows one mobile terminal to handle more than one bearer service simultaneously and to have bearer services of different connection modes. It is nevertheless expected that the terminal and network capabilities will put some limitations on the number of bearer services that can be handled simultaneously. Each connection has independent traffic and performance characteristics in the sense of throughput, delay and packet loss. The core network is IP based while the network between SGSN and RNC is ATM based. Standardization will have been finished in fall 1999 and the first releases are expected on the marked by summer 2000. Licensing is under progress and Japan might be the first country ready to introduce UMTS.

Systems Summary 2


Here we can compare the characteristics of some of the circuit switched systems.

The GSM standard was completed in 1990 with the first networks in operation in 1991. The
maximum user bit-rate for GSM is 9.6 kbps. As GSM is primarily a voice based digital system then no data interface is specified. Remember that because GSM is circuit switched a call setup is required before data is transmitted - this can take up to 40 seconds.

The High-Speed Circuit Switched Data standard was completed in 1997 and Ericsson’s
product is on the market. HSCSD offers higher speeds than GSM by utilizing several timeslots simultaneously; using all 8 timeslots in a single frame means a net bitrate of about 64 kbps. It's envisaged that the market for HSCSD will be quite small. Essentially, HSCSD makes several GSM calls simultaneously which means that a single user can hog a large portion of the air interface. Add that to the fact that making multiple GSM telephone call simultaneously is not a cheap pastime and it is easy to see that HSCSD is likely to be a niche market.

The Universal Mobile Telephone System is scheduled to be specified by 1999. The channel separation is undecided as of yet, but the channel access method will be Wideband-CDMA. The planned net bit-rate is between 144 kbps to 2 Mbps, depending on the users location. Remote areas with lower coverage should offer the minimum bit-rates, while urban areas with higher coverage should provide the higher bit-rates. The plan is to have UMTS in operation by the year 2002. To achieve this ambitious goal and to protect current network operators from capital dis-investment it is likely that UMTS will utilize the existing GSM infrastructure in some way.

First generation

The first generation cellular telephone systems were introduced up to the mid-80's and they are analogue systems. These include NMT450 and 900, AMPS and TACS.

The second generation of cellular systems came in the beginning of the 90's, they are digital systems and they behave almost identically. These systems include GSM and PDC.

Future systems, also called the third generation, will have to cope with very high demands on voice traffic and data rates much higher than today's systems are able to handle. Furthermore, it must be easy to introduce new services, and the cellular phones must be cheap and consume very little energy. It is likely that they will also have to handle roaming between traditional ground-based cellular systems and satellite-based PCS (Personal Communication Systems).

In a few years we could have this scenario: your car breaks down in a desolate area, you call your local garage and ask for help. You put on your Virtual Reality-helmet, and a repairman can, using real-time audio and video, guide you through the whole repair. The pictures may show what bolt to unscrew, what tools you need in different stages, etc. This puts high demands on the transmitting capacity of the cellular system and is only one example of what kind of situation the third generation of cellular systems would have to handle.

Systems Summary 1

In this table you can compare the different packet based wireless WAN systems.

The first commercially available Mobitex services offered a bitrate of 1.2 kbps. This was available in 1986 - a long way ahead of it's current competitors. A new Mobitex standard appeared in 1990 offering a gross bit-rate of 8 kbps.

Of the packet data systems that build on mobile telephone infrastructures, CDPD was the first to be standardized in 1993.

The gross bit-rate is 19.2 kbps and the net bitrate is approximately 10 kbps. Although the CDPD standard specifies both an IP and a CLNP interface, Ericsson's CDPD product offers only the IP version. The first CDPD networks went into operation in 1994. Ericsson's first CDPD network went into operation in 1997 in New Zealand.

PPDC was standardized in 1997. It offers a net bit-rate of between 9 and 26 kbps. This flexibility derives from the ability to utilize more than a single time-slot. The PPDC standard specifies an IP interface. The first PPDC networks was in operation in 1996 - before the standard was officially complete!

The GPRS standard will be the last to be completed with phase 1 standardized in spring of 1998 and phase 2 standardization ongoing. The net bit-rate offered is between 9 and 168 kbps, depending on the number of timeslots used. Phase 1 of the standard calls for both an IP and an X.25 interface, phase 2 may specify others.

Cellular Digital

Cellular Digital Packet Data is a packet switched computer communication network built on top of the AMPS-system. The system offers a gross bit-rate of 19.2 kbps over 30 kHz channels. The standard was arrived at by a committee made up of several Bell-companies, IBM and other data communication players. The standard was ready in 1993, and the construction of CDPD is ongoing in the US, but the coverage is still inadequate.

The interest in CDPD has become an important selling point for AMPS. Vendors use the existence of CDPD solutions to push AMPS networks. Ericsson has had a CDPD product since the end of 1996, and several other suppliers also offer CDPD solutions, the earliest of which were introduced in 1994.

The CDPD standard defines both an IP and a ConnectionLess Network Protocol (CLNP) interface. (CLNP is the OSI equivalence of IP.) Ericsson has no CLNP service in the system, and has no intention to introduce it. The mobility solution is similar to that found in Mobile- IP. There is a base node that controls all it's subscribers' location, i.e. which Serving Node they are under. The Serving Node knows only which subscriber is under it for the moment.

PPDC


Packet Personal Digital Cellular is a standard for packet switched data in PDC. The gross bit-rate is 14-42 kbps depending on the number of time slots available. A maximum of three can be allocated to a single user. The carrier width is 25 kHz. The standardized interfaces are the radio interface and interface towards other nets. The radio interface standard was ready in the beginning of 1997, and the other standard (towards other networks) was also ready during 1997.

Mobitex

Mobitex is a well established, widely deployed dedicated, packet switched system. It is a narrow-band network offering a gross bit-rate of 8 kbps on 12.5 kHz channels. Note that several users may have to share this available bandwidth. Ericsson is the only supplier of network equipment for Mobitex, but radio modems, software and network add-ons are available from third party vendors.

The specification for 8 kbps was ready in 1990. In Sweden and Nigeria the systems are run on an older specification from 1986, which only offers 1.2 kbps. Because of this low bitrate, you don't hear so much about Mobitex in Sweden. The biggest network, run by RAM Mobile Data in the US, consists of about 1200 base stations with 93 % coverage of the urban business population.

The interface towards the net is specified in an open specification, developed by Telia, and nowadays administrated by the Mobitex Operators Association (MOA). The network layer is specially adapted to mobile computer communication, making it possible to develop applications for the vertical market. For the horizontal market, where you would rather use standard protocols and standard APIs, a specially adapted network layer is a disadvantage, but standard protocols can be run over the Mobitex network layer. These solutions are not specified in the interface specification. A number of products to solve the problem of standard protocol communication have emerged on the market.

To make connections to the X.25 environment easier, a network integrated X.25 gateway has
been developed, and an integrated IP solution is under development. The network architecture is hierarchic. There are two levels of switches, main switch and area switch. For large networks a subdivision in subnets, inter-connected with a backbone, can be used. On the backbone, TCP/IP is used, leaving the Mobitex provider free to choose the backbone supplier.

GPRS, General Packet Radio Services

GPRS, General Packet Radio Services, is a standard for packet switched data in GSM. The gross bit-rate is 33-270 kbps, depending on the number of time slots used. The standardization is ongoing under the management of ETSI, with the Point-to-Point service standard fixed in spring of 1998. The biggest news is that you don't establish a connection, but only use the channels when data is transmitted. It's possible to use more than one time slot to increase the users bit-rate. The great advantage with GPRS compared to circuit switched computer communication is that the data communication will be cheaper for the user, and at the same time more profitable for the network operator. Today the GSM computer communication is debited for the time the connection is established. If several users share the channel, a lower price could be given to each user, based on the amount of data transmitted. The network operator can earn more money from the packet switched channel than from a circuit switched computer communication.

The intention of the GPRS was that it should support all the possible network protocols like IP, X.25, etc. In phase one of the standardization only X.25 and IP are supported. For the support of GPRS, two new switching nodes are introduced: a "Serving Node", called SGSN, and a "Gateway Node", called GGSN. The terms SGSN and GGSN have already been explained in the lesson "GSM and GPRS". Even though the GPRS standardization procedure is not complete, Ericsson has started work on the implementation of these nodes.

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