an fall well below what current analog modems can handle. Thus, the demand for speedy broadband technologies is on the rise.
ISDN's Wide Availability
ISDN is the most widely available technology of the high-bandwidth options. Most competing high-speed offerings are currently in various stages of research, testing, and deployment. None of them are as mature or as widespread as ISDN.
Even in the U.S., where ISDN is seen as a not-so-attractive technology, an increasing number of ISPs are now capable of handling ISDN. Once it's installed properly on the user end, this high-speed technology connects reliably at speeds of up to 128 Kbps and transfers data at speeds of up to 300 Kbps with compression.
There are two types of ISDN: Primary Rate Interface (PRI) and Basic Rate Interface (BRI). PRI ISDN is generally found in telephone switches, computer telephony, voice processing, and dial-up Internet acce
ss. Residential installations and small businesses chiefly use BRI ISDN. A BRI ISDN link provides two B channels for data and voice transmission, and a D channel for signaling functions, such as call setup. You can use either or both B channels for LAN-to-LAN access, Internet access, videoconferencing, or other applications that demand higher bandwidth than analog modems can provide.
To achieve an aggregate 128-Kbps throughput, all ISDN modems now support the multilink PPP channel-bonding technology, which lets two connecting units negotiate and combine two or multiple channels to serve as one larger pipe with expanded bandwidth. In addition, multilink PPP ensures interoperability with all carrier equipment. What's more, by incorporating a new technology called Always On/Dynamic ISDN (AO/DI), the D channel will soon be available to carry e-mail, news headlines, or other data -- without having to dial up an ISP or corporate network.
Therefore, ISDN users could speak on one voice channel, send files
into a corporate office on another, and get low-bandwidth data such as e-mail on a third. And because the D channel is always live between the ISDN subscriber and the phone company's central office, users save the cost of dialing up every time they want to get low-bandwidth data.
A Dead Technology?
Contrary to many phone companies' expectations, ISDN services did not take off as planned, especially in the U.S. Users complained that it was difficult to install, that the phone companies took forever to set up the lines, that technical support was inefficient, and that it was too expensive.
Also, ISDN's 64- or even 128-Kbps rate hardly spurred the interest of the business community, which handles many bandwidth-hungry communications applications such as shared CD-ROM access, shared live video catalogs, interactive movies, and real-time, downloadable videos and music.
"If such obstacles in getting ISDN service cannot be removed, users will turn to emerging new high-bandwidth technologi
es," says Thomas Huang, president of VersaNet Communications, an affiliate of Taiwan modem maker CIS Technology.
In fact, a handful of ISDN vendors have already predicted that ISDN may eventually be replaced by faster technologies such as ADSL or cable modems. However, "these data-only solutions are not likely to replace ISDN, but to coexist," according to Felix Jeng, R&D manager at Alpha Telecom, a professional customer premises equipment (CPE) manufacturer.
Jeng points out that cable-modem services don't cover switched voice traffic. Cable-modem service is based on a shared-network topology, which means that the amount of bandwidth that's available to a customer depends on how high the traffic volumes are at any given time. In addition, he says that the shared networks operate at a speed as fast as 10 Mbps. This should give customers at least as much bandwidth as BRI ISDN under normal traffic loads.
"At least for the next two years, cable modems and ADSL devices will not pose any threa
ts to ISDN," says Jim Hsieh, ISDN project leader for the communications product business division at CIS. ISDN is the best solution because users are able to manage phone calls, e-mail, and videoconferencing with one technology, Hsieh adds.
Cost Is a Big Factor
In spite of its slow takeoff in the U.S., ISDN has long been a standard for high-speed remote access in regions where the infrastructure is complete and the service is easy to come by. Europe and Japan have seen the greatest success in terms of ISDN proliferation. In Japan, it has the strong backing of the government. There will be nearly 1 million ISDN lines installed there by the end of the year.
This is why most Taiwanese ISDN product makers target Japan as their largest sales outlet. However, because Japan's NTT and NEC corporations dominate more than 80 percent of their home market, there is little room for market expansion in Japan.
Many modem and networking-product manufacturers in Taiwan are applying their mass-produc
tion strengths to volume ISDN service providers who need terminal adapters (TAs) and infrastructure equipment such as routers, bridges, and switches.
Most ISDN TAs that Taiwanese companies make are 16-bit ISA cards with Windows 95 Plug and Play support. These internal cards sport common features as they all use solutions provided by chip makers. Cutthroat competition among ISDN vendors has largely brought card prices down, resulting in decreasing profit margins.
Lately, vendors in Taiwan are moving more upscale by adding external ISDN TAs to their product lineups. While they earmark internal cards for the European market, stand-alone models are in large demand in Japan.
Finding ways to make ISDN TAs more suitable for use with portable computers, active, self-powered adapter cards that have their own processors, memory, and drivers are currently under development. E-tech will soon launch an active-type ISDN adapter that features a 32-bit CPU, at least 256 KB of static RAM (SRAM), and 8 KB of
dual-port RAM for ISDN protocols and driver software. This will allow it to operate without host PC resources.
Full support for ISDN APIs such as WinISDN, Winsock with PPP, multilink PPP, Common API (CAPI) 2.0, and Telephony API (TAPI) is important to ensure a TA's operability. It lets ISDN TAs run most existing communications software and all commercially available applications.
Standards Support
European users, especially those in Germany, require the use of CAPI 2.0, because it eliminates the need for COM-port emulation. Auto-detection for the 1TR6, 1TR7, 1TR12, E-DDS1, and NT-1 protocols, as well as the Network Driver Interface Specification (NDIS) interface for raw-HDLC (high-level data-link control), Cisco-HDLC, PPP, and MLPPP supports, are included in most Taiwanese products.
Additionally, these units conform to the ISDN-1, 5ESS, DMS-100, European Telecommunications Standards Institute (ETSI), and INS Net 64 standards for ISDN communications. Some of these models also come wi
th bundled applications, such as Internet, videotext, file transfer, fax, voice, mail, and terminal-emulation software.
For the high-end corporate segment, Taiwanese manufacturers are making more routers that enable multiple users on a LAN to access the Internet at high speeds. ISDN routers, like other routers, let users build anything from complex switched-circuit networks to simple peer-to-peer dial-in connections. Users can also fine-tune their line usage, which can reduce ISDN fees.
Many ISDN routers are equipped with some combination of a standard Ethernet port, multiple plain old telephone service (POTS) ports, and a built-in fax modem. Some of the routers even have a built-in Ethernet hub. This bundling obviates the need for extra analog lines for the user's office and additional equipment. The Prestige 2864I, from ZyXel Communications, for instance, has an option of a five-port external Ethernet hub.
The standard for compression in ISDN routers is Stac LZS, which offers up to 4-to-1
and 5-to-1 data-compression ratios. However, though many router vendors implement Stac LZS and most implementations work together, some vendors support Microsoft's Stac compression, which may not work with other Stac-based compression. Many vendors support both types, but a few support only one.
Another unique feature that's supported by ISDN routers is IP-address sharing. With this feature, each remote workstation has its own local IP addresses, but all outbound packets from the remote workstations share a single IP address, which is attached at the router. Inbound packets destined for those machines are sorted by the router and readdressed to those specific remote workstations. Because dial-in ISPs typically charge by the IP address, this can save on operating costs and effort.
At the CeBIT show in Hannover, Germany, this year, ZyXel demonstrated its Prestige 100, which lets up to four users access the Internet at the same time, supporting IP routing. Another model, the Prestige 128, supports bo
th IP and IPX routing, as well as bridging. A single-user account feature lets multiple users on a corporate LAN access the Internet simultaneously using a single IP address from an ISP.
ADSL on the Rise
ADSL links designed to give high-speed, inexpensive remote access to corporate LANs and the Internet over standard phone lines are the next big thing on the high-bandwidth horizon. The performance benefits are clear: The technology supports typical downstream rates of 1.5 to 8 Mbps and upstream links as fast as 640 Kbps. That makes it potentially more than 10 times speedier than ISDN without the requirement to install an expensive new medium.
But while a new infrastructure is not required, high equipment cost is keeping ADSL from significant growth in the consumer market for the time being. CIS's Hsieh speculates that wide-scale ADSL deployment will not begin until 1999. All major telecom operators are doing trials in some areas.
In the meantime, some Taiwan companies are offering h
igh-bit-rate digital subscriber line (HDSL) systems. Providing the same fast data throughput in a symmetric and full-duplex format, HDSL is now being considered as a viable data-access option for the mass market. Alpha's HDSL systems have been marketed and accepted in Japan.
Supports Three Channels
The ADSL technology supports three channels: downstream (simplex), upstream plus control (full-duplex), and POTS. As always, POTS occupies the lowest end of the bottom 4 kHz and is split off from the digital data by a passive low-pass filter, ensuring uninterrupted voice service even if the ADSL connection fails. Both the downstream and full-duplex channels can carry more than one bearer channel. Moreover, the digital portion of the connection never reaches the service provider's switching system, thereby offsetting network overload on the central switch.
In Taiwan, CCL/ITRI is a government-sponsored R&D organization. Chen Yun, manager of its transmission system department, says ADSL's chan
nel-splitting capability makes the technology appealing to
phone companies
in the U.S. and elsewhere in the hope that they will be able to fend off competition from high-bandwidth data services offered by cable modems.
To take advantage of the technology, you need a special ADSL modem, and telecommunications operators must install special switches and equipment to provide service. Because most of the necessary switch upgrades are not in place, it will take some time to bring ADSL within reach of everyone.
Foreseeing a rosy future for ADSL as the most widespread high-bandwidth solution for connecting home computers to the Internet, modem manufacturers are revving up product development for the new ADSL technology.
CCL/ITRI heads an ADSL alliance with more than 10 modem and telecom companies, including Askey, DBTEL, GVC, Hitron, Tainet, Taiwan Telecom, Tecom, UFOC, U-King, and ZyXel. The first product produced by the alliance is a remote- site product: ADSL Remote Bridge
and POTS splitter. The interface between each site is connected by an HDLC/ADSL interface. The service between each site uses a 10Base-T Ethernet interface. The frame- based media access control (MAC) encapsulation is implemented for ADSL router-based network access.
DMT or CAP?
For now, CCL/ITRI has yet to choose between two types of ADSL: discrete multitone (DMT) or carrierless amplitude and phase modulation (CAP). Both are designed to modulate bits that are sent though the line.
According to Chen, DMT is expected to become the industry standard in the future. The technology brings transmission speeds closer to the theoretical limits allowed by ADSL, because it is more robust against difficult line conditions and impulse noise. Another major benefit offered by DMT is support for interoperability between equipment from different vendors.
Another advantage of DMT is that line coding divides available transmission bandwidth into 256 independent subchannels. Interference to the signal
in one frequency range does not have as great an impact as it would with the unified channel structure of CAP.
CCL/ITRI is currently caught between the two standards. While DMT offers more performance benefits, CAP is more widely used than DMT. Besides, CCL/ITRI officials worry that the price for DMT's chip set will remain too expensive and difficult to implement without the pressure of competition from CAP technology.
Reduced Cost
Recent developments that are aimed at reducing the cost of the ADSL technology are mainly directed toward increasing highly integrated, low-cost, high-performance chip sets. Leading suppliers for this market are Motorola, SGS-Thomson, Alcatel, Texas Instruments, and Analog Devices.
Originally, CCL/ITRI's ADSL alliance agreed to use Motorola's single-chip CopperGold ADSL transceiver, which guarantees the highest board reliability, according to Chen. CCL/ITRI is also Motorola's alpha-site test-bed for the solution. Nevertheless, Motorola is finding it diff
icult to increase its yield, according to sources in the alliance, making the alliance turn to alternative solutions from Alcatel or SGS-Thomson.
IC vendors from Taiwan such as Winbond Electronics and Macronix International have also announced development projects for ADSL chip sets. The move will help hardware makers to substantially reduce their costs.
Furthermore, CCL/ITRI plans to develop ATM-based (asynchronous transfer mode) ADSL technology in hopes that the technology will be competitive with cable modems without requiring telephone companies to overhaul vast portions of their existing phone network.
In 1998, the ADSL alliance will introduce the HLA system, which includes remote- and central-site products, ADSL Remote Bridge and POTS splitter and DSL Access Mux (DSLAM) and Central POTS splitter. The interface between each site is connected by an ATM/ADSL interface. The service at the remote site uses a 10Base-T Ethernet interface, and the service interface at the central site uses an
ATM interface to connect the ATM public data network.
Where to Find
Alpha Telecom, Inc.
Hsinchu, Taiwan
Phone: +886 3 578 5717
Fax: +886 3 578 5817
E-mail:
atti@shts.seed.net.tw
Internet:
http://www.alpha-tele.com
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