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Transition of Broadband Access Devices
to Residential Gateways

Amit Dhir

Xilinx Corporation

Introduction

In the past few years, the Internet has grown to become an integral tool and resource for an ever-growing population of corporate users. As this population continues to grow and expands to remote corporate users, or telecommuters, the need for access speeds equivalent to those found in the corporate environments has increased in importance as it impacts user productivity directly. The growing reliance on the Internet and the need for greater bandwidth is driving consumers to move away from traditional analog-based modem technology in favor of higher speed broadband access technologies. Broadband not only delivers faster Internet access to the home, but it also serves as the catalyst for the growth of the new home networking market.

Demand for high-speed Internet access solutions has fueled the proliferation of a number of rival technologies such as DSL, cable, satellite, wireless, power-line, and ISDN. This access is provided by digital modems. With the evolution of home networking, the digital modems are evolving into the residential gateway. Similar to the broadband access and residential gateway markets, programmable logic will play a key role in accelerating the growth and deployment of home-networking applications and technologies.

This article focuses on some of the broadband access technologies, the evolution of digital modems into residential gateways, and the need for programmable-logic solutions in this market.

What is Broadband?

Broadband access describes a high-bandwidth, digital-communication link that provides access speeds that are typically greater than 128 kbps. Broadband access not only provides significantly faster access times than older analog technologies (greater than 100 times), but it is also a conduit that is better suited for some of the newer, high-bandwidth Internet applications. These applications include streaming video, on-line shopping, MP3 music, voice over IP, viewing of high-resolution images, and online gaming.

Broadband service is delivered to the home using a variety of different technologies that include cable, DSL, satellite, wireless, power lines, and ISDN. While each technology has its own set of benefits and drawbacks, in most cases, the existing home-wiring infrastructure and the availability of the service itself usually plays the biggest role in determining the consumer's choice of broadband technology. The consumer's appetite for high-speed access is almost insatiable—market analysts estimate that there will be over 15 million broadband subscribers worldwide in 2001, growing to 40 million in 2003.

Some key market drivers for broadband access penetration include:

Increasing popularity of the Internet.

Internet applications increasingly include voice, video, and data in applications such as streaming video, Web browsing (online shopping using high-resolution images), e-mail, MP3 files, voice over IP, digitized photographs, and online gaming. These multimedia and interactive applications require high-speed Internet access.

Decreasing prices of broadband services.

Growth in telecommuters and day extenders using Virtual Private Networking.

Small offices, home offices (SOHO), and home businesses.

Home networking and the invasion of information appliances and multiple PCs.

Types of Digital Modems

Digital modems provide broadband access to the home. There are several types of broadband access technologies and hence, several digital modems.

Cable Modems

Cable companies that offer TV services to their customers are moving into offering services such as high-speed Internet access, free e-mail accounts, and are hosting e-commerce sites and IP-based voice applications.

The cable-network architecture is based on a network configuration of fiber-optic and coaxial cable, also known as hybrid fiber-coax (HFC). HFC networks can transmit broadband analog and digital services simultaneously, and are ideal for handling next-generation communication services. Additionally, HFC meets the expandable capacity and reliability requirements of new digital data services, and allows cable companies to add services incrementally without major changes to the overall network. HFC is a "pay as you go" architecture that matches infrastructure investment with new revenue streams, operational savings, and reliability enhancements. The HFC architecture comprises fiber transmitters, optical nodes, coaxial cables, and distribution hubs. HFC networks are two-way systems that are capable of communicating with a home network at over 40 Mbps. The customer-service area ranges between 500 and 2000 home networks. For cable companies, the combination of HFC with home-networking technologies is expected to generate new revenue streams.

Cable modems are client devices that provide high-speed, always-on, two-way communication over the ordinary cable TV network. Cable modems connect one port to the TV outlet on the wall and the other to the home network. The cable modem communicates over the cable network to a device called a CMTS (Cable Modem Termination System), which is a central device for connecting the cable TV network to a data network (the Internet).

The cable-modem speeds depend on the traffic levels and the overall network architecture. Theoretically, cable modems are capable of receiving and processing multimedia content at 30 Mbps. However, subscribers can expect to download information at 1.5 Mbps, as multiple users in the neighborhood share the bandwidth. Operators define a portion of the frequency spectrum to carry the data. The downstream path (head end to home network) lies between 50 MHz and 750 MHz. The 5 MHz to 42 MHz frequency range transmits information from the home network to the head end. Cable modems receive and transmit TCP/IP traffic, including multimedia content and Internet access.

The tuner in the cable modem receives a digital signal from the network and isolates a particular channel that contains the Internet data. It then converts the signal from RF levels back to baseband. The baseband output signal from the tuner is then forwarded to a demodulator. The demodulator samples the signal and converts it to a digital bitstream. The bitstream contains video, audio, and IP data. Once the bitstream is recovered, it is forwarded to a forward-error correction (FEC) unit and is checked for problems. The signal is then passed into the control unit and further to the home network using one of the high-speed data-port interfaces.

(Click here for larger view)
Figure 1 - Cable-Modem-Based Gateway

In a cable-modem-based gateway (Figure 1), programmable-logic solutions provide system interfacing (PCI, UART, DMA), encryption, interfacing to several home-networking technologies (Ethernet, USB 2.0, HomePNA), ASSP functionality (such as cable MAC), and glue logic.

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