by Sascha Lindecke, Director, Product Marketing, Infineon Technologies AG
Systems for high-speed wireline network access via DSL (digital subscriber line) and VoIP (voice over Internet protocol) have been available on the market for quite some time now. Nevertheless, only recent advances in semiconductors and in the employed algorithms have led to inexpensive, high-speed products that provide broadband access for consumers and business users. In the process, DSL— with an installed base of more that 75 million subscribers worldwide—has become synonymous with broadband access. New, highly integrated chips make it possible to meet the requirements for today’s DSL-based home gateways.
There are several variations of DSL in use. ADSL (asymmetric DSL) was standardized in the early ’90s; it offers data transmission rates between 1 and 8 megabits per second (Mbps) “downstream” and approximately 700 kilobits per second (kbps) for “upstream” communication. With ADSL, network operators and service providers can use existing copper wires to offer broadband data services, especially for Internet access. To date, more than 100 million ADSL chipsets have been shipped worldwide. Furthermore, by defining the more powerful ADSL2 and ADSL2+ standards, the ITU (International Telecommunication Union) has created a basis for continuing ADSL’s success story for the mass broadband market. In the meantime, the first chips have become available for these new ADSL standards.
SHDSL (single pair high bit rate DSL) supports symmetrical data transmission with data transmission rates of up to 2.3Mbps. The second generation of this standard, which was published at the end of 2003, permits data rates of up to 5.7Mbps. This DSL variation is configured for data applications in smaller business units.
VDSL (very high bit rate DSL) is the youngest member of the xDSL family; it permits data transmission rates of more than 100Mbps, but only for shorter ranges. At a “downstream” data rate of 54Mbps, the typical range is approximately 300m (1,000 feet). As early as June 2003, Infineon and Metalink reached data transmission rates of 150Mbps with VDSLPlus technology. The VDSL2 standard is currently being prepared; besides higher throughput rates and longer ranges, it is also intended to ensure interoperability with ADSL2 and ADSL2+. VDSL is—as is ADSL2/2+—predestined for the transmission of video, voice, and data services via standard telephone lines.
“Home gateways” and “office gateways” The G.992.3 (G.dmt.bis, Full-Rate) and G992.4 (G.Lite.bis) ADSL2 standards specified by the ITU expand the current ADSL standard to include new performance features and functions. To be more specific, this step makes longer ranges and higher data transmission rates possible, improves diagnostic capabilities, and reduces power consumption in “stand by” mode.
Theoretically, ADSL permits maximum data throughput rates of up to 8Mbps downstream and up to 1Mbps upstream. In practice, however, data rates between 1.5 and 6Mbps are being reached on downstream lines from the provider to the user. Upstream, values range between 16 and 750kbps on the lines to the access node. ADSL’s maximum range is about 5.5km (3.4 miles). For ADSL2, a special mode has been introduced for longer lines (RE-ADSL); it makes it possible to increase the data transmission rate by 50kbps over longer distances or increase the range by about 200m (650 feet). These improvements are made possible by, among other things, more efficient modulation. In addition to these enhancements, ADSL2 allows four dimensional, 1-bit QAM (quadrature amplitude modulation) with 16-state Trellis code. That makes it possible to achieve higher data transmission rates in conjunction with longer distances.
First-generation ADSL utilizes a fixed framing-overhead with which 32kbps of overhead per frame are “lost” to the payload data. With ADSL2, on the other hand, the overhead bits can be programmed in the range from 4 to 32kbps. This especially comes into play in association with long distances when the data throughput rate is relatively low. At a data transmission rate of 128kbps, 32kbps have to be “donated” for overhead when ADSL is used. That figure represents a sizeable chunk (25 percent) of the overall data rate. With ADSL2, on the other hand, overhead can be reduced to 4kbps, which makes an additional 28kbps available for services.
The fault diagnosis capabilities offered by ADSL systems have been and still are an important aspect for customer satisfaction, and ultimately for the technology’s success as well. For this reason, ADSL2 transceivers have been equipped with enhanced diagnostic capabilities. These diagnostic features include tools for handling errors during installation and operation, performance monitoring during service, and upgrade qualification. ADSL2 transceivers support the measurement of line noise, loop attenuation, and the SNR (signal-to-noise ratio) for both ends of the line.
ADSL2 also enables real-time performance monitoring that provides information on the line quality and noise on both ends of the line. Service providers can then use software to evaluate this information, which enables them to ensure a high quality of service (QoS).
First-generation ADSL transceivers always work with a full power supply, even when they are not currently active. Two power-management modes have been introduced with ADSL2. They reduce power consumption while still maintaining “always-on” functionality for the user. The L2 low-power mode engages in the central office (CO). There, the technology can quickly switch into and out of L2 mode depending on the amount of Internet data traffic being transmitted via the ADSL2 connection. L3 mode enables a general reduction of power consumption on both ends (CO and customer modem) by activating the sleep mode when the connection has been inactive for a defined amount of time. When the user returns to online mode, the ADSL2 transceiver only requires about three seconds to initialize and return to communications mode.
Downstream data transmission rates at twice the speed L2 mode is one of ADSL2’s most significant new features. The ADSL2 transceiver can switch into L2 mode and then back out depending on the amount of Internet traffic being transmitted via the ADSL connection. For instance, when large files are being downloaded, ADSL2 works in full power mode (L0) to reach top speeds. Nevertheless, when less data is being transmitted—for example, when the user is reading a text—the transceiver enters L2 mode and power consumption is reduced considerably. The mode change takes place in the blink of an eye without interruption of services and without bit errors.
The latest ADSL standard from the ITU—ADSL2+—doubles ADSL2’s bandwidth again. While ADSL2 with G.992.3 and G.992.4 specifies a downstream frequency of 1.1MHz or 552kHz, the downstream frequency for ADSL2+ (G.992.5) has been raised to 2.2MHz. In this way, it is possible to reach data rates of up to 25Mbps across shorter telephone lines (less than 900m or approx. 3,000 feet). Beyond that, ADSL2+ offers special functions for reducing crosstalk.
Within the ADSL2 and ADSL2+ standards, there are also additional appendices (Annex A-L) that, among other things, specify sub-carriers or tone frequencies with their corresponding downstream and upstream transmission performance. Annex L, which covers the specific performance enhancements for ADSL2 and ADSL2+ is particularly interesting. This annex is also referred to as Reach- Extended ADSL2 (RE-ADSL2). It describes the implementation of a new mask for power spectral density. The mask makes it possible to boost the reach of an ADSL2 link by up to 600m (approx. 2,000 feet). For ADSL2, Annex M describes an additional mode that can be used to double the upstream data rate in a POTS environment.
ADSL2 and ADSL2+ will bring an additional increase to ADSL’s market penetration, since their new functions and enhanced performance capabilities offer benefits (in terms of user friendliness) to both customers and operators. The new ADSL standards are supported by leading chip manufacturers, but also by DLC/DSLAM providers. Infineon has already made the first chips available that support the ADSL2/ADSL2+ standards on the CPE side (“Amazon”) as well as in CO applications (“GEMINAX MAX”).
In many cases, DSL transmission supplements existing baseband voice services. This means that there are two separate networks available for transmitting voice and data, and that is associated with corresponding limitations in terms of cost and overhead. In order to overcome these problems, Infineon has developed IVD systems (integrated voice and data) that make it possible to transmit voice and operate the DSL function on one line. Thus, a single IVD line card offers a range of functions that until now required separate cards for voice, data (DSL), and the voice splitter. This makes it possible to install DSL services by replacing existing voice line cards with IVD line cards.
The IVD line cards support both older analog voice services and VoIP. VoIP uses an Internet Protocol to convert voice into data information. In the network, voice calls are treated like data, which is why packet oriented voice services offer functions such as advanced messaging or automatic call forwarding to different terminals. Reduced telephone costs are one of VoIP’s primary advantages, because every call is a local call. Infineon offers all the required components for a completely integrated IVD line card with the “Geminax MAX” ADSL2+ chip (which does not require a splitter) together with the “Vinetic” high-power, eight channel voice processor for POTS (plain old telephone service) and VoIP.
Complete ADSL2/2+ home gateways On the CPE side, these “tripleplay” applications can be put together as needed. In this way, the “Amazon” single-chip solution—which is equipped with an ADSL2/2+ engine, an analog front end (AFE), a line driver, a high-performance MIPS processor, two 10/100 Ethernet interfaces (MAC and PHY), PCI, and other connectivity interfaces—permits high-speed, wireline data transfer from a wide area network (WAN) into a local area network (LAN). Combined with the high data throughput rates that are made possible by the ADSL2+ standard and fixed-line support of the quality of service (QoS), the “Amazon” chip is ideally suited for triple-play applications that transmit voice, video, and data via a single home gateway. “Amazon” completes Infineon’s end-to-end ADSL2/2+ product portfolio. This product range also includes the “Geminax MAX” family, which was specially developed for optimizing communication with high data throughput rates on the CO end. The “Amazon” single-chip solution is particularly well suited for configuring ADSL2+ modems with one or more ports as well as for CPE gateways with additional functions, such as multiple Ethernet switches, VoIP, WLAN, etc.
This system can be expanded to include the inexpensive “WildCard” 802.11a/b/g WLAN chip that integrates a WLAN MAC (media access control) and a baseband processor. With the integrated PCI interface, “WildCard” offers 32-bit processing and PCI bus-master capabilities. The “WildCard” chip is fully compatible with 802.11a/b/g and with the “WiFi WPA” (WiFi protected access) security standard. In this way, the “WildCard” chip makes it possible to build a wireless Ethernet network with throughput rates up to 54Mbps. For modem manufacturers, there is a development system available that makes it possible to design a system at low cost and with optimized performance.
The “Amazon” chip for ADSL2/2+ and the “WildCard” chip for 802.11a/b/g WLAN make it possible to develop inexpensive settop boxes, DSL modems and routers, and home gateways that permit broadband transfer of data, voice, and video. Overall, there is a large range of CPE products available for realizing broadband access systems that support WLAN and VoIP: from a simple Ethernet bridge to highly developed ADSL gateways. The market for broadband CPEs that also make it possible to build a home network is expected to grow by 35 percent each year for the next five years and reach shipments of 22.5 million units per year by 2008. An extensive portfolio of chips from a single source is available for developing broadband home gateways. The spectrum includes high-performance communications processors, standard xDSL transceivers, and scalable voice products. The company has developed a modular and flexible family of products that also makes VoIP applications possible on the same hardware and software platform. The comprehensive line up of CPE devices, whether wireline or wireless, stand alone modems, or network interface cards (NICs), secures significant cost and performance advantages for the user.
