Excerpts

Preface When ADSL hit the market in the late 90s, the residential broadband market started to really heat up. Dial-up Internet access, while being a well-understood and reliable service, could not keep pace with the demands of having homes connected at broadband speeds. Cable networks, with their hybrid fiber and coax networks, were also competing for similar customers as traditional Telcos. Thanks to cable operators, Triple Play services had already gained a foothold in the customer conscience as a service bundle that can be provided by a single company. This eased the way for Telcos to also deliver their own Triple Play service bundles over a single copper pair--the same copper pair that was used for many years as a simple telephone line. A Triple Play package is a bundle of an Internet, video, and VoIP service. Video services almost always have two components: a Video on Demand, and an IP Television (IPTV). IPTV takes traditional terrestrial and satellite channels and delivers them over an IP network to the customer premises. Multi-Play services are an extension of this concept and divide Internet access in to more sophisticated services with specialized Quality of Service handling. Until the early to mid part of this decade, apart from some early-adopters, service providers were not given to broadening their residential data portfolio past Internet access. This mindset is rapidly changing and the market is diverging into two segments. The first segment is the commodity ISPs, who provide a cheap and fast Internet service. The cost-barrier to entry is lower due to the lower service overhead; the competition here is fierce. The second is to whom this book is aimed--those providers in, or looking at, getting into the Triple- and Multi-Play service market. Several reasons drive the diversification. From a political perspective, many Telcos with wired access are finding their traditional revenues being eroded due to regulatory pressures. Triple- and Multi-service bundles are an ideal way to maintain some service margin in an increasingly competitive market. For access seekers, regulatory intervention is a much cheaper way to expand network coverage compared to an expensive copper or fiber access network rollout. For both wholesalers and access seekers, there was a major drawback to video service deployment: ADSL does not have much bandwidth to play with. ADSL2+ pushes up the downstream limit to over 24Mbps, giving ample headroom for high-definition IPTV channels, while not making a severe impact on Internet performance. This book is the perfect companion for anyone in the networking industry. If you are a journalist or analyst who wants more inside, in-depth information about next-generation broadband access networks, you will find it here. Or if you work at a vendor or service provider, the architectures and configurations enhance your technical understanding with practical applications of protocols and hardware. ATM-based DSL networks are well understood and have been in the marketplace for many years. There already one or two books on these broadband networks. However, this book fills the gap in the market for a leading-edge architecture guide of next-generation, Ethernet-based DSL networks and Triple- and Multi-Play services. Because this book is more about architectures than focusing exclusively on technology, this book appeals to a wider audience than just technicians. Planners, financial controllers, managers, and network architects will also find useful information. The designs and techniques described in this book apply to many markets around the world. The intent of this book is to inform the reader of best practices in the industry and where there is still contention, the pros and cons of each alternative are laid out. For example, North American providers generally choose to go with a customer-specific VLAN architecture, whereas European providers prefer to use a service VLAN. Explanations of these terms and the advantages and disadvantages of each are two examples of the flexible approach that this book attempts to provide. Many readers already in the industry will be familiar with the topics in each chapter, but the concepts in the latter parts of each chapter are not intended for beginners. For example, many of the MPLS concepts in Chapter 3, "Designing a Triple Play Backbone," are not intended for those whose exposure to MPLS is for the first time. The description for each of the 12 chapters listed in the next section tells the reader the intended technical level along with any recommended reading titles. What You Will Learn After reading this book, the reader will have enough knowledge to work through the issues and challenges involved with designing and deploying a triple- and multi-play network. There may be times where there is not enough detail in a particular section. The intention has been to cover at least the basics, so the reader at least knows what issues are involved if they need to do more research. Most of the IETF RFC-based technologies have been referenced by URL for further investigation. Although Wikipedia might not be 100% accurate, for technical information, it is a reliable and useful resource for unfamiliar topics. As of January 2007, PDFs of in-force ITU-T specifications are freely downloadable. These are quite specific in nature and are good when needing to delve deep in to specific aspects of a DSL modulation or Ethernet protocol. Chapters of This Book Chapter 1, "A History of Broadband Networks," describes the beginnings of broadband access networks, starting with the advent of the DSL family of technologies--CAP and DMT--and how this had an effect on deployment throughout the world. This tells the story of technology development from vendors and deployment milestones by service providers. There are also discussions of broadband access devices, access protocols, and the most common authentication and accounting protocol--RADIUS. The technical knowledge needed to understand this chapter is low. Chapter 2, "Next-Generation Triple-Play Services," is an introduction to what triple- and multi-play services really mean. What does a video service actually entail? What are the components of a triple-play network, from a high-level perspective? How is VoIP integrated into the network? These questions are all answered in this chapter. There is also a section on business connectivity, describing how services such as Layer 3 and Layer 2 VPNs are being deployed with DSL access. The technical knowledge in this section is medium due to heavy use of jargon and some of the more complex topics in each subsection. Chapter 3, "Designing a Triple-Play Backbone," looks at how operators are implementing backbones that can carry triple-play services. The chapter begins with an overview of the most popular type of protocol on provider backbones: Multi-Protocol Label Switching (MPLS). The discussion quickly moves to describing a common service that providers have implemented--Layer 3 VPNs. MPLS networks are also used for their traffic engineering properties, and may not use any Layer 3 VPNs except for business services. Included are many examples of how IP multicast services can be integrated into these networks. The discussion starts from a common example of multicast and Protocol Independent Multicast (PIM) and how traffic and protocols flow. There are many optimizations and enhancements possible with this model, such as using source-specific multicast and redundant rendezvous points, which are described here. An efficient way to transport multicast on an MPLS network using point-to-multipoint LSPs are explained in detail here. Also included is a look to the future of next-generation backbone IPTV delivery using VPLS with point-to-multipoint trees. The Broadband Network Gateway (BNG), often called a Broadband Remote Access Server (B-RAS), is an important point for service definition. The focus moves to integrating BNGs in to the network for triple-play services. This covers multicast protocols on the BNG, such as IGMP and additional features for PIM. Finally, implementing a highly available core network is a hallmark of any service provider, so there are protocols and strategies, such as BFD fast-reroute, that can be added to a network for added robustness. The technical knowledge required for this chapter is medium to advanced because many of the principles described assume some prior experience with MPLS networks and multicast protocols. Chapter 4, "Designing a Triple-Play Access Network," covers one of the most important aspects of a next-generation DSL network--the access network. There are two major components to this critical piece of infrastructure: the DSLAM, and the network between the DSLAM and the BNG, also called the aggregation network. DSLAM deployment architectures such as hub-and-spoke, daisy-chained are shown here. Designing the aggregation network is an important task. Examples described in Chapter 4 are using an MPLS network to transport customer traffic from DSLAMs to the BNG. Layer 2 tunneling technologies, such as VPLS, Martini or Kompella VPNs. Extensive deployment scenarios of these technologies is also shown as more traditional transport, such as CWDM, DWDM, or dark fiber. The second part to the chapter is the lively discussion as to the type of VLAN architecture to run between the DSLAM and the BNG: Should it be a 1:1, VLAN-per-customer model, or a service-per-VLAN model? The type of model chosen has important implications and should be designed correctly from the start. This chapter contains important information to enable the reader to make an informed decision for their VLAN architecture. Medium-level technical knowledge of MPLS protocols is also recommended for this chapter. Chapter 5, "Choosing the Right Access Protocol," covers an equally lively debate in the industry--whether to use PPP or DHCP as the protocol between the BNG and the customer. Jargon and protocols, deployment scenarios are explained here. As with any architectural choice in this book that does not have a clear answer, there are pros and cons of both approaches. Despite being quite narrow in focus, a low to medium level technical knowledge of PPP and DHCP is needed for this chapter. Chapter 6, "Evolutions in Last-Mile Broadband Access," is a chapter for those who like to get deep into technical details on transport networks. This chapter takes a tour of the evolution of DSL networks, from the first ADSL deployments using Carrierless Amplitude/Phase Modulation to the standard Discrete Multi-Tone (DMT) in use today. Topics commonly associated with DSL lines--spectrum usage, cross-talk, special protocol features, and data rates--are explained in detail in this chapter. Line-level protocols that are covered include ADSL, ADSL2, ADSL2+, VDSL, VDSL2+, and SHDSL. This chapter is appropriate for anyone with a medium-level knowledge of transport protocols. Chapter 7, "Wholesale Broadband Networks," covers what wholesale providers and access seekers need to know when working in a wholesale, unbundled environment. An unbundled environment is one where a local authority has mandated that an incumbent provide access to customers connected to the local loop. Types of unbundled services range from a simple Layer 3 IP wholesale service to a full unbundled copper service, which are two such examples that are covered. Some additional attributes and protocols associated with L2TP, such as tunnel fragmentation and proxy LCP, are also covered here. Low to medium level knowledge of L2TP and prior reading of Chapter 4 are sufficient for this chapter. Chapter 8, "Deploying Quality of Service." Not a day goes by in discussions of next-generation DSL services without mentioning Quality of Service. This substantial topic is all about how to effectively deliver multiple services in a bandwidth-constrained environment. This covers the history of QoS in an IP environment, showing how IP precedence and Differentiated Services have had an important impact in helping to define a prioritization architecture. Uses of these mechanisms with QoS features, such as rate-limiting, shaping, RED and W-RED, and strict priority scheduling are a few of the features explained in this chapter. The concepts in this chapter do not require much prior knowledge and a low to medium level of understanding of access architectures in Chapter 4. Chapter 9, "The Future of Wireless Broadband," presents a survey of the wireless technologies that complement today's traditionally wireline-based multi-service networks. With advances in 3G wireless technologies such as growing data rates, advanced in service control, security & quality of service, it's becoming possible to deliver comparable services wirelessly as it is over wireline triple & quad-play architectures. The chapter covers the history of wireless data, from the ETSI GSM and early CDMA days, through Wideband CDMA & UMTS, through today's evolving wireless broadband architectures, such as IMS, SIP, and non-SIP based fixed mobile convergence and wireless video. The chapter contains a survey of the different technologies, network architectures behind them, and evolving wireless broadband standards. Chapter 10, "Managing IP Addressing," takes a look at one of the simpler tasks of a BNG--assigning an IP address. This chapter explains all the options available to a network operator, for both PPP- and DHCP-based networks. Whether this involves simple static address assigned via RADISU or a more complex approach using dynamically signaled on-demand address pools (ODAP), many common approaches are described in this chapter. Keeping with the forward thinking trend of this book, there is also a section on the implications of IP address management in an IPv6 access network. The concepts in this chapter are of a low to medium technical complexity. Chapter 11, "Dynamic User Session Control," is an overview of subscriber session management. It describes through the major platforms that work behind the scenes to manage things like billing, provisioning, RADIUS, and the user database. There are two types of provisioning changes--basic, which has been the typical way to manage the network; or the service provider making manual or semi-automatic changes to network elements based on a request from a customer. This chapter also describes how advanced dynamic service provisioning can reduce the opex overhead of subscriber management, with such techniques as customer self-care web portals and automated service provisioning engines. Chapter 12, "Security in Broadband Networks," presents some of the concerns carriers face when operating broadband subscriber networks. Subtopics include Denial of Service against infrastructure, and security of VoIP. The basic premise of the chapter is to present ideas around demarcation of levels of trust, and to discuss the problems that can occur when resources are exhausted or anomalous packets are received by systems. The reader should have a basic understanding of VoIP technologies when reading through the security concepts pertaining to VoIP. The majority of the chapter is of a low to medium technical nature. Multivendor Routing We have tried throughout this book to give an independent rendering of broadband network architectures. Because all of us are currently employed by Juniper Networks, the reader may see some emphasis given to Juniper's routing technologies and protocols as opposed to Cisco Systems. This is not intentional but merely a fact of life that we all live and breathe one routing set of equipment. Where appropriate, we have posted listings throughout the book that show both Juniper and Cisco configurations whenever they differ large enough to draw attention to themselves. Because the focus of this book is on architectures, the basic principles do not change depending on what vendor supplies your routing equipment. Often one vendor will be stronger in one area over another. For example, their system might be better at handling DHCP over PPP, or might have a limited VLAN capacity, so prefers the N:1 over the 1:1 approach. Therefore, vendors differ in their recommendations for broadband network architectures; this is normal. This book has tried to present neutral, but smart network choices; and where there is still contention in the market place, present as much information as possible. So, armed with the right information, the reader can make the best choices for their network. Terms We use a lot of terms that have originated in the field as broadband network architectures are being created and designed. We have created a short glossary at the end of this book to accommodate the reader and to give you an advantage the next time you are invited to a cocktail party attended by network engineers. This is intended to supplement individual definition tables listed in various chapters. (c) Copyright Pearson Education. All rights reserved. Excerpted from Broadband Network Architectures: Designing and Deploying Triple-Play Services by Chris Hellberg, Truman Boyes, Dylan Greene All rights reserved by the original copyright owners. Excerpts are provided for display purposes only and may not be reproduced, reprinted or distributed without the written permission of the publisher.