Wireless Bearers

Loosely speaking, a bearer can be defined as a wireless transport means. Anything that can transport information from one device to another is called a bearer, examples being GSM, AMPS, GPRS, Infrared (IrDA), and Bluetooth. As this book is published, there is much talk of a next-generation bearer called UMTS, and about whether it is worth the telecoms industry spending billions in UMTS licenses and infrastructure upgrades. However, these issues will be discussed later.

Bearers can be characterized as 2G, 2.5G, and 3G. 2G bearers are the so-called connection-oriented bearers, whereas 2.5G and 3G are packet-oriented.

Note 

G stands for "Generation".

Connection-Oriented versus Packet-Oriented

A connection-oriented bearer requires a sender of information to establish a network connection to a network service provider or ISP, before any data can be sent. This has two disadvantages for mobile applications. First, establishing a connection is a time-consuming process, as users of WAP-over-GSM have experienced. Second, it is not possible to "push" a notification to a mobile device without forcing the device to establish a network connection. With a connection-oriented bearer, users are typically charged for the whole time the connection is open, no matter whether data is transmitted through that connection or not.

On the other hand, with a packet-oriented bearer, a device can send and receive packets of information without the need to dial into a network service provider or ISP. Spontaneous networking and communication becomes a reality. The term "always-on communication" is often used to denote that a service can send a data packet to a device, and that the device can respond to the packet immediately by alerting the user, for example. With packet data, users will only pay for the amount of data they actually communicate, and not for idle time.

Important 

We can say that packet-oriented bearers are much better suited to the connectionless model of JMS, and that there is an "ideal fit" between the two technologies. This will be further motivated later in the chapter.

Second Generation (2G) Bearers

Second generation bearers are able to transport data reliably from one device to another, although at a rather low speed, examples being GSM, AMPS, and HSCSD. Also, 2G bearers are connection-oriented.

GSM

GSM (Global System for Mobile communication) offers data transmission speeds of up to 9,600 bps. It is a digital mobile telephone system that is widely used in Europe and other parts of the world, and uses a variation of time division multiple access (TDMA). It is currently the most widely used digital wireless telephone technology in the world. According to the GSM Association, GSM has over 120 million users worldwide and is available in 120 countries.

GSM digitizes and compresses data, then sends it down a channel with two other streams of user data, each in its own time slot. It operates at either the 900 MHz or 1,800 MHz frequency band. The choice of frequency is implemented in the mobile device's hardware.

Another interesting feature of GSM is that it includes the SMS wireless messaging solution, which is quickly growing in popularity.

AMPS/DAMPS

Digital-Advanced Mobile Phone Service (D-AMPS), sometimes spelled DAMPS, is a digital version of Advanced Mobile Phone Service, the original analog standard for cellular telephone service in the United States. Both DAMPS and AMPS are now used in many countries. Like GSM, DAMPS implements the TDMA standard.

Note 

For further information see Second Generation Mobile and Wireless Networks, Ulysses Black, Prentice Hall 1998, ISBN 0-136212-77-8.

HSCSD

High-Speed Circuit-Switched Data (HSCSD) is circuit-switched wireless data transmission for mobile user at data rates up to 38.4 kbps, four times faster than the standard data rates of GSM. HSCSD is comparable to the speed of many computer modems that communicate through today's fixed telephone networks.

2.5 Generation (2.5G) Bearers

It's still a long way to go until 3G bearers such as UMTS are both available and cheap. UMTS is not expected to become widely available until 2003. There is a risk that UMTS will not be successful due to the problems mentioned below. For this reason, 2.5G bearers such as GPRS and EDGE are being launched. Those bearers are packet-oriented and provide transmission speeds of up to a few hundred kilobits per second.

GPRS

General Packet Radio Service (GPRS) is a packet-based wireless communication service that, when available in 2001, promises data rates from 56 up to 114kbps and continuous connection to the Internet for mobile phone and computer users. GPRS directly supports the Internet Protocol (IP) and the CCITT X.25 protocol. A mobile GPRS application will typically use the TCP/IP or UDP protocol over GPRS.

Even though the transmission rate of GPRS is still much too low for multimedia and other traffic intensive applications, it provides an important new feature making it very appealing for JMS – GPRS is a packet oriented bearer, as opposed to GSM, AMPS/DAMPS, and HSCSD, which are connection-oriented bearers.

EDGE

Enhanced Data Rates for Global Evolution (EDGE), a faster version of the GSM wireless service, is designed to deliver data at rates up to 384 kbps and enables the delivery of multimedia and other broadband applications to mobile phone and computer users.

EDGE is a packet-oriented bearer delivering much higher speed than GPRS, anticipating the speed advances of UMTS. Also, EDGE does not incur high license cost and does not require a new network infrastructure. It might not be as fast as UMTS, but could well turn out much cheaper.

The EDGE standard is built on the existing GSM standard, using the same frame structure and cell arrangements. Ericsson notes that, when available, its base stations can be updated purely with software, without the need to exchange hardware components. Wireless data services based on EDGE are expected to become widely available during 2002.

Note 

See Ericsson's website for more details on EDGE's capabilities: http://www.ericsson.com/wireless/products/mobsys/gsm/subpages/umts_and_3g/edge.shtml

Third Generation (3G) Bearers

Third generation bearers are also packet-oriented but provide data speeds of more than 1 mbps. This makes those bearers appealing for multimedia applications, video conferencing, high-quality real audio, and so forth.

UMTS

Universal Mobile Telecommunications System (UMTS) is the most talked about and controversial broadband bearer. UMTS transmits text, digitized voice, video, and multimedia at data rates up to and possibly higher than 2 megabits per second, offering a consistent set of services to mobile computer and phone users no matter where they are located in the world. UMTS is geared to provide a fast and direct packet switched IP service to the end user.

Endorsed by major standards bodies and manufacturers, UMTS is planned to be the world standard for mobile connectivity by 2003. Once UMTS is fully implemented, mobile computer and phone users can be constantly connected to the Internet as they travel. However, the following concerns are being voiced in respect to the deployment of UMTS:

• High cost of licenses
  European governments are selling UMTS licenses to the highest bidders, through an auctioning mechanism. Some carriers have spent billions acquiring UMTS licenses. The question is: how will the carriers make this investment profitable?

• High cost of infrastructure
  UMTS requires new network infrastructure. The investment costs can be several billion dollars, in addition to the already paid license fees. Again, we should ask about the business model, and about how the telecoms industry are working on making that investment profitable, given that UMTS itself will eventually be replaced by an even faster technology.

• Resistance
  Rolling out new base stations is not easy, as the population is becoming more concerned about health risks imposed by electromagnetic radiation. Lawsuits could impose a considerable delay on the rollout of UMTS infrastructure.

• Transmission rates lower than advertised
  UMTS is poised to provide transmission rates higher than 1 mbps. But in reality, such transmission rates will be achieved only in the ideal – and rare – situation where your UMTS base station is underutilized, located nearby, and when you are standing still. Initially, UMTS transmission rates could be as low as 100 kbps, leading to disappointment and maybe even rejection of UMTS technology.

Other Bearers

Wireless LANs have the potential of providing high-speed interconnectivity in metropolitan areas or in buildings, at a low cost. Another bearer to watch is Bluetooth, which provides high-speed wireless connections between a variety of devices (phone, headset, PDA, printer) over distances of a few meters.

An intelligent combination of EDGE, wireless LAN technology, and Bluetooth might result in an appealing and cost-effective alternative to UMTS. For example, railway stations, airports, restaurants and other public locations could be equipped with a Wireless LAN or Bluetooth technology. This allows fast Internet access for travelers, as well as mobile access to business data through Virtual Private Networks (VPNs). Outside those locations, EDGE provides the mobile user with sufficient bandwidth for Web surfing and e-mail access.

Wireless LANs, Bluetooth, and EDGE incur much lower license and infrastructure cost than UMTS. Nevertheless, bandwidth of more than 10 megabits per seconds (Wireless LAN) can be offered in airports and other frequently visited locations.

Availability of Wireless Bearers

The following table summarizes the main characteristics of current- and next-generation wireless bearers:

Bearer	Availability	Where	Speed	Features
GSM	Early 1990s	Europe, Asia	9.6 kbps	Connection-oriented, incorporates wireless messaging (SMS)
DAMPS	Early 1990s	USA	13 kbps	Connection-oriented
HSCSD	1999	Europe	38.4 kbps	Connection-oriented, based on GSM
Bearer	Availability	Where	Speed	Features
GPRS	2000/2001	Europe, Asia, USA	115 kbps	Packet-oriented, based on GSM
EDGE	2001/2002	Europe, Asia, USA	384 kbps	Packet-oriented, based on GSM
UMTS	2003 (?)	Worldwide	2 mbps	Packet-oriented, requires new network infrastructure

Note 

For further sources in this area, please see Winning in Mobile eMarkets, Market study by TIMElabs Research Center, 2000, http://www.timelabs.de.