Broadband Access

Wireline and Wireless - Alternatives for Internet Services

Steven Gorshe, Arvind Raghavan, Thomas Starr, Stefano Galli

• Publisher: Wiley
• Year: 2014
• ISBN:
  9781118878798
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Written by experts in the field, this book provides an overview of all forms of broadband subscriber access networks and technology, including fiber optics, DSL for phone lines, DOCSIS for coax, power line carrier, and wireless. Each technology is described in depth, with a discussion of key concepts, historical development, and industry standards. The book contains comprehensive coverage of all broadband access technologies, with a section each devoted to fiber-based technologies, non-fiber wired technologies, and wireless technologies. The four co-authors' breadth of knowledge is featured in the chapters comparing the relative strengths, weaknesses, and prognosis for the competing technologies.

Key Features:

• Covers the physical and medium access layers (OSI Layer 1 and 2), with emphasis on access transmission technology
• Compares and contrasts all recent and emerging wired and wireless standards for broadband access in a single reference
• Illustrates the technology that is currently being deployed by network providers, and also the technology that has recently been or will soon be standardized for deployment in the coming years, including vectoring, wavelength division multiple access, CDMA, OFDMA, and MIMO
• Contains detailed discussion on the following standards: 10G-EPON, G-PON, XG-PON, VDSL2, DOCSIS 3.0, DOCSIS Protocol over EPON, power line carrier, IEEE 802.11 WLAN/WiFi, UMTS/HSPA, LTE, and LTE-Advanced

1
Introduction to Broadband Access Networks and Technologies

1.1 Introduction

In the mid-1990s, there were many doubts about the future of broadband access. No one was sure if the mass market needed or wanted more than 100 kbit/s; what applications would drive that need; what broadband access would cost to deploy and operate; what customers were willing to pay; whether the technology could provide reliable service in the real world; or which access technology would “win.” Government regulation in many countries made it unclear if investment in broadband would yield profits. It seemed that broadband access would be available only to wealthy businesses. Fortunately, there were some people who had a vision of a broadband world and who also had the faith to carry on despite the doubts.

We now live in a world where broadband access is the norm and households without it are the exception. No one asks today why the average household would need broadband access. The answer is obvious: we need internet access, with its ever-growing number of applications, and VOD (video on demand). With more than 600 million customers connected to broadband networks, no one asks if the technology works or whether it can meet the customer's willingness to pay.

Furthermore, a growing application of broadband access is the support of femtocells, and small cells in general. Resorting to small cells has today become the most promising trend pursued for increasing wireless spectral efficiency, and the key to its success is the availability of a high capacity wired line to the home. Also, a growing fraction of cellular data is today generated indoors. In addition, it has become clear that no single broadband access technology will win the entire market, and that the market shares of the different technologies will change over time.

Each access technology has its strengths and weaknesses. A common constraint is that we can have it fast, low cost, and everywhere – but not all at the same time. In many cases, the choice of broadband access technology is driven by the legacy network infrastructure of the network provider. In other cases, national regulatory considerations are a significant factor. As a result, each access technology has its areas of dominance in terms of geography, applications, and political domains.

The book is divided into three sections:

• The chapters in the first section of the book cover technologies and standard protocols for broadband access over fiber-based access networks.
• The chapters in the second section cover technologies and standards associated with non-fiber, non-wireless broadband access.
• The chapters in the final section of the book address wireless broadband access technology and standards. Some of these technologies have been widely deployed, while others are anticipated to see deployment soon.

1.2 A Brief History of the Access Network

The traditional access network consisted of point-to-point wireline connections between telephone subscribers and an electronic multiplexing or switching system. The early access network used a dedicated pair of wires (referred to as a copper line or “loop”) between the subscriber and the central office (CO) switch.¹ As the cost of multiplexing technology decreased, it became more economical in many cases to connect subscribers to a remotely located terminal. This remote terminal (RT) would multiplex calls from multiple subscribers onto a smaller number of wires for the connection to the CO. Network cost was reduced by having far fewer pairs of wires from the CO to the remote areas. As the technology evolved from analog frequency domain multiplexing (FDM) to digital time domain multiplexing (TDM), the RT systems became known as digital loop carrier (DLC) systems.

Data access to the telephone network began with the introduction of voiceband modems that could transmit the data as a modulated signal within the nominally 4 kHz voiceband pass-band frequency. The shorter lines (loops) allowed by DLCs made increasingly efficient modulation technologies practical. However, as explained in Appendix 1.A, the maximum data capacity of voiceband modems was limited to 33.6 kbit/s, or 56 kbit/s under special circumstances. Modems and their evolution are also discussed briefly in Appendix 1.A.

As a result, out-of-band technologies were introduced that transmitted signals over the copper line at frequencies outside the voiceband. Since these technologies sent digital information in the out-of-band signals, they became known collectively as digital subscriber line (DSL) technology. DSL is discussed further in Section 1.3 and Chapter 7–10.

Since the subscriber lines are implemented with twisted wire pairs, with multiple lines sharing the same cable without being shielded from each other, there are limits on the bandwidth that is achievable with DSL. For this reason, network providers became interested in alternatives to the subscriber line for providing broadband access. The three main contending technologies are coaxial cable, fiber optic cable, and wireless radio frequency connections. Each of these technologies is reviewed in later chapters of this book.

Coaxial cable networks were deployed by community access cable television (CATV) companies to provide broadcast video distribution. Due to the high bandwidth capabilities of coaxial cables, they had the potential for offering broadband services to their subscribers. In order to offer broadband data services, CATV companies evolved their networks to support upstream data transmission, and introduced fiber optic cables for higher performance in the feeder portion of their networks. As discussed below and in Chapter 11, coaxial networks have their own challenges as well as advantages.

Telephone network providers responded to the potential broadband advantages of the CATV companies by deploying additional fiber in their access networks. Telephone companies have deployed fiber directly to each subscriber's premises in some areas. Others are deploying fiber to terminals near enough to the subscribers' premises that broadband services can be provided by the latest very high-speed DSL technologies. The most attractive aspect to fiber is its virtually unlimited bandwidth capability. The primary drawback has been the relatively high cost of the network and its associated optical components.

Wireless access had not originally been a significant contending technology for residential broadband access. However, as wireless mobile networks have become widely deployed, and new technologies and protocols have been developed, wireless broadband access has become increasingly important. It is especially attractive in regions that lacked a legacy wireline infrastructure capable of evolution to broadband services. Examples of such regions include developing nations and rural areas. It also offers the very significant advantage of allowing mobile, ubiquitous service rather than being restricted to service at the subscriber's premises.

Since a limited amount of spectrum is available for use in broadband services, the networks to support it have become increasingly complex. For spectrum efficiency, wireless networks use grids of antenna, where each subscriber only needs enough signal power to reach the nearest antenna. The region covered by each antenna is referred to as a cell. The result is that the same frequencies can be used by subscribers in non-adjacent cells, since their signals should not propagate far enough to interfere with each other. The signal formats have been optimized in the latest protocols to approach the Shannon limit for data bits transmitted per Hertz of transmission channel bandwidth. Capacity is further increased by re-use of the spectrum through smaller cells and smart antenna technologies. Both add cost, and radio signals are always more vulnerable to various types of interference than wireline technologies. Wireless technologies are discussed further in Section 1.6 below, and in detail in Chapter 14–17.

1.3 Digital Subscriber Lines (DSL)

1.3.1 DSL Technologies and Their Evolution

DSL operates over a copper line at frequencies outside the voiceband, sending digital data directly from the subscriber, and thus avoiding the need for an analog to digital conversion. Since the telephone lines were designed to provide good quality for voiceband signals, they are often not particularly well suited for higher rate data signals. Reflections become a significant problem in the electrical domain at rates beyond the voiceband. One of the worst sources of reflections in North American networks is bridge taps. When the feeder cables are installed from the CO into the loop area, they go to splice boxes where the wires going to the subscribers are connected. When service is disconnected to a subscriber (e.g., due to the homeowner moving), a second pair of wires may be connected to the feeder cable to serve a different subscriber without removing the other line. The result is a bridge tap, and it is possible to have bridge taps at more than one location along the connection to a subscriber. The unterminated end of the unused line(s) causes electrical reflections of the DSL signals, and these reflections can cause destructive interference for certain frequencies (any impedance mismatch along the copper connection to the CO to the subscriber can cause harmful reflections, but the bridge taps are especially bad).

The first widely deployed services using a digital subscriber line were the Digital Data Service (DDS) from AT&T. DDS used baseband signals over the line and offered data rates including 2400, 4800 and 9600 bits/s, and 56 kbit/s. The lower rate signals were sometimes converted to analog signals at the CO and then mapped into a voiceband channel, thus avoiding any noise or distortion from the subscriber line. DDS required the end-to-end service be synchronized to a common atomic clock. DDS circuits also usually required that the line be groomed to remove impairments such as bridge taps. While DDS circuits were very valuable for some customers (e.g., banks using them for connections to ATM machines), they were too expensive to deploy to residential subscribers or even to many business subscribers.

The first serious attempt to provide higher data rates to subscribers was the basic rate interface of the Integrated Services Digital Network (ISDN-BRI). ISDN-BRI used baseband signals² over the subscriber line to offer bidirectional data rates of 144 kbit/s. ISDN-BRI was designed to operate over most subscriber lines of up to 18 000 feet without having to remove impairments such as bridge taps from the lines. The 144 kbit/s signal was typically divided into two 64 kbit/s bearer (B) channels and a 16 kbit/s data (D) channel. The B channels could be used for voice or data, while the D channel carried the connection signaling information, with its leftover bandwidth available to carry subscriber data packets. It was also possible to merge the two B channels or merge the Bs and D channel into a single 144 kbit/s channel. The cost of ISDN-BRI was relatively expensive, however, and there were no driving subscriber applications to generate high demand. ISDN also required that the connection signaling protocol be processed by the CO switch, which meant a major upgrade to the switches. By the time that Internet connectivity became a driving application, much higher rates were practical for DSL.³ In effect, ISDN BRI provided too little bandwidth, too late, with too much ne...

Table of contents

• Cover
• Title Page
• Copyright
• Dedication
• About the Authors
• Acknowledgments
• List of Abbreviations and Acronyms
• Chapter 1: Introduction to Broadband Access Networks and Technologies
• Chapter 2: Introduction to Fiber Optic Broadband Access Networks and Technologies
• Chapter 3: IEEE Passive Optical Networks
• Chapter 4: ITU-T/FSAN PON Protocols
• Chapter 5: Optical Domain PON Technologies
• Chapter 6: Hybrid Fiber Access Technologies
• Chapter 7: DSL Technology – Broadband via Telephone Lines
• Chapter 8: The Family of DSL Technologies
• Chapter 9: Advanced DSL Techniques and Home Networking
• Chapter 10: DSL Standards
• Chapter 11: The DOCSIS (Data-Over-Cable Service Interface Specification) Protocol
• Chapter 12: Broadband in Gas Line (BIG)
• Chapter 13: Power Line Communications
• Chapter 14: Wireless Broadband Access: Air Interface Fundamentals
• Chapter 15: WiFi: IEEE 802.11 Wireless LAN
• Chapter 16: UMTS: W-CDMA and HSPA
• Chapter 17: Fourth Generation Systems: LTE and LTE-Advanced
• Chapter 18: Conclusions Regarding Broadband Access Networks and Technologies
• Index
• End User License Agreement