Hitting the market now, 2.5G wireless data services-based on Wireless Access Protocol (WAP) and General Packet Radio Service (GPRS)-are driving system developers to look for new ways to integrate wireless data traffic into the broadband Internet backbone. But marrying cell networks, digital circuit-switched networks and packet-switched networks is a complex proposition. Although many holders of new third-generation (3G) spectrum licenses plan to build all-new digital networks from the ground up, existing network operators need solutions that combine wireline and wireless traffic, both circuit and packet, across a common backbone.
This week's Focus takes a look at the forces behind integrating wireless traffic onto the Internet backbone.
According to contributor Randall Fahey, vice president of marketing for chip maker Morphics Technology Inc. (Campbell, Calif.), there are two drivers at work pushing for integration: the exponential growth in demand for more capacity, and the fact that operators can no longer make a profit with voice-only networks. The average revenue per voice subscriber is falling faster than the average cost of the equipment to support that subscriber. "These trend lines are already crossing, so network operators are making a big push to find new value-added transactional or information services, which is driving any kind of data access over the wireless network," he said.
System designers are therefore focusing on data access at the edge of the core network, which is highly varied. Dial-up Internet access goes through the public switched telephone network (PSTN), as does cell-phone access; Internet service providers (ISPs) and corporate enterprise networks often use an on-site Internet Protocol switch or node; and cable access is growing.
"We're in the process of putting in all the plumbing for a wireless network that connects directly to the Internet, not just for cell users but for fixed and mobile users as well," said Fahey. "But that will happen in steps." In some parts of the edge there will be different types of access points, such as hybrid circuit-packet switches, traditional circuit access and ATM/IP interfaces. "So the edge of the network will get interesting because of these new access methods," he said. A key component of the 3G standardization process is to separate what the access networks must do and which types of core networks they have to hook up to, whether PSTN or Internet.
Meanwhile, packet data traffic has already exceeded voice traffic, according to Elda Rudd, director of marketing for wireless Internet solutions at Nortel Networks (Richardson, Texas). Carriers are making the conversion from circuit-switched to packet-switched networks via hybrid circuit/packet switches, which help preserve their existing investments. Over time, those systems will carry more packets and less voice traffic.
In the evolution toward a wireless Internet, Nortel Networks sees three different layers where these changes are occurring. The first layer is the basestation transceiver subsystem, the access point where subscribers can get onto the wireless Internet. Today, cell sites in this layer provide mostly voice access, but emerging 2.5G wireless services, such as Sprint's wireless Web service or AT&T's relaunched Digital PocketNet, are also providing data. "So these wireless packet data services are real," Rudd said. "We're on the cusp of seeing volumes increase tremendously in the next 12 months, as handsets and terminals become more widely available." The network build-out of digital data services throughout the entire coverage of service providers is the last stage of this development, and requires more work.
The second layer is the services-enabling layer, where specific system platforms will evolve as more data traffic comes onto the network, said Rudd. "These boxes will have to take on routing, quality of service and service provisioning functions. We are integrating these capabilities into that layer of our network, to start the transition from traditional circuit-switching into managed packet switching." This layer has traditionally been closed and proprietary, but the move into IP, has opened up into other programming languages and commercial-grade hardware, allowing open interfaces to be created so applications and services can be hooked into it.
Those applications and services comprise the third layer, which is just now beginning to change. "In the next two years, this area will explode, fueled by the capabilities that the Internet can provide, as well as by the other two supporting layers," said Rudd. "This is the layer that allows the highest speeds, and 'five-nines' reliability, making them cost-effective to operators, and sustainable."
A taste of 3G
But most of what is expected for the worldwide 3G mobile communications networks proposed by the International Telecommunications Union, through its International Mobile Telecommunications 2000 initiative, is already possible today, said Rudd. "The perception of what 3G does serviceswise that 2.5G can't is much higher bandwidth. But about 80 percent of the requirements of IMT-2000 are met today with 2.5G services." Where they fall short is in their data rates, which is the main enabler for graphics and the multimedia aspects of 3G. However, it will still require another year or so for 2.5G services to be rolled out completely so that coverage is ubiquitous. 3G network buildouts will begin toward the end of this year and increase at the beginning of 2001, aided by the expected increases in 2.5G-ready handsets.
GPRS-enabled Global System for Mobile Communications networks, are already creating a market for 3G services, said Roger Snyder, product marketing manager of Phone.com Inc. (Redwood City, Calif.). By the end of this year, GPRS networks will be rolled out around the world, beginning in Europe. "These networks will give users the first taste of what 3G will be like: an instant-on, packet-based service that will be able to scale up in bandwidth," he said.
In the first half of 2001, production-level quantities of handsets using the Wireless Markup Language, based on the Wireless Access Protocol (WAP), will be available, said Snyder. They will work with uplinks, or WAP gateways, installed in the operators' networks, and web servers equipped with Phone.com's developers kit.
One thorny issue in handset design is coping with the signal processing needs created by the exponential growth in transmission capacity. This signal processing explosion in broadband wireless is not unique, however, said Ravi Subramanian, Morphics' vice president of systems engineering. It has happened in previous data transmission technologies: the transition from voice-band data modems to DSL, the cable modem explosion, and digital video broadcasting.
In each of these cases, capacity demand has increased 10 times in about four years, while the signal-processing capabilities of traditional DSPs have only increased the same amount in six years. Access-specific, programmable signal processors with advanced digital modulation and coding schemes have been used to cope with the capacity demand. "That's not to say higher capacity can't be achieved with a traditional DSP, but the questions are, how much does it cost and how much power is required?" said Subramanian. "While broadband capacity requirements are pushing the needed performance up, consumer demands are pushing the cost and power down."
Ann R. Thryft, a frequent contributor to the EE Times supersection, is a freelance writer based in San Mateo, Calif.
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