Blueprint: Network Architecture

It�s All About Access -- A Comparison of Fiber vs Copper in 2008

by Piyush Sevalia, VP of Marketing

1/7/2008

Service providers today have one ultimate goal: build a broadband network that enables the delivery of a wide array of new revenue-enhancing voice, video and data services. These multi-play offerings allow a service provider to attract and retain customers during a tenuous period when their fixed line revenue is declining and they are reaching the saturation point in their mobile business.

For a service provider, success ultimately depends on the access network architecture it chooses to deploy. The approach a service provider takes in building its network can vary greatly: from a complete fiber overbuild to maximizing the investment in their existing copper infrastructure.

This article will examine the pros and cons of deploying fiber and copper, while providing an overview of the time, costs and performance associated with each architecture and the characteristics of standards in use today.

Gaining Access: Fiber vs. Copper

Fiber and copper both have distinct advantages � and disadvantages � when used in the access network. Fig.1 illustrates how both fiber and copper are utilized in the network architecture to serve individual homes and MDUs. As a newly deployed advanced infrastructure, fiber is capable of delivering extremely high bandwidth. As an optical technology, fiber gives a service provider more flexibility and scalability. In the future, new equipment is likely to be introduced that will utilize optical signals even more effectively, enabling greater bandwidth with little additional investment.

However, fiber is costly and time-consuming because � not unlike the construction of the public switched telephone network over a century ago � all new infrastructure has to be deployed. As an example, both Verizon and NTT have taken a long-term view for their infrastructure deployment. Both are upgrading most of their infrastructure to fiber � pushing fiber as close to the consumer as possible in order to ensure that they can deliver the most revenue-generating services well into the future. Both Verizon and NTT are deploying fiber to single family homes, where it can be installed relatively easily. In its newsletter detailing financial results for the third quarter of 2006, Verizon reports that its fiber to the home (FTTH) initiative costs $1,745 per home � $845 to pass a premise with fiber and another $900 to connect fiber to the home. In Japan, NTT's costs are slightly lower. In fiscal year 2006, the company reported that incremental FTTH investment per user was approximately 130,000 yen, or about US$1,070. As a result of the high price tag of fiber deployment, service providers must be patient to earn a return on their investment and consider the long-term benefits of PON.

While driving fiber directly to individual homes, Verizon and NTT are using a hybrid approach to delivering broadband services to multiple dwelling units (MDUs), such as apartment complexes or condominiums. In this scenario, they are using VDSL2 as the last mile technology because deploying fiber in restricted riser space is much more challenging.

Copper is the medium of choice in the majority of the world's telco communications networks. A service provider can maximize its existing assets by turbo-charging their copper network infrastructure with VDSL2 technology in order to deliver voice, data and video broadband services. Because they are not replacing their access network infrastructure, service providers can quickly and cost-effectively rollout revenue-enhancing triple play services and Internet protocol television (IPTV).

AT&T, for instance, is capitalizing on existing copper infrastructure for its U-Verse deployment. The company is building out fiber to the node (FTTN), but using VDSL2 to turbo-charge the existing copper loops entering homes. AT&T estimates that this architecture costs only about $360 per user to deploy � almost five times less than the cost of Verizon's all-fiber build.

Though it offers quick and easy deployment of advanced broadband services, telco copper is limited by the laws of physics and electrical engineering technology. The amount of bandwidth that a user can receive is limited by the distance of the user from the fiber-termination point, quality of the wire, and the amount of crosstalk on the line. To minimize the impact of noise and crosstalk, technology providers are developing leading-edge techniques such as rapid rate adaptation (RRA), repetitive impulse noise protection (REIN), micro-cut and far end crosstalk FEXT cancellation, which will potentially enhance the stability of the line and increase available bandwidth.

The Pay Off: An Equipment Cost Analysis

The basic cost of central office (CO) and customer premises equipment (CPE) for a fiber deployment is more than double that which is needed for a copper-based play. Note that this does not include installation costs which are significantly higher for laying new fiber, or time to market costs, which are also significantly higher for new fiber deployments.

For example, based on Ikanos' estimates, a service provider deploying an Ethernet Passive Optical Network (EPON)-based fiber network will have an average total equipment cost of about $250 per subscriber, assuming that there are 20 subscribers per optical line terminal (OLT) port.

In 2007, a VDSL2 equipment is forecasted to cost approximately $105 per subscriber � less than half that of an EPON network � according to the Dell'Oro Group's January 2007 publication, "Access Report: Five Year Forecast 2007-2011." This difference in equipment cost will need to be considered when the carrier makes its decision to go with an all-fiber infrastructure or a hybrid fiber-copper infrastructure.

Setting the Standards

Technology standards are important factors that a service provider must consider when deciding which type of technology to deploy. Fig. 2 outlines the characteristics of two common standards for both fiber and copper deployments.

For fiber architectures, the two common standards include EPON and gigabit PON (GPON). EPON is popular in the Japanese market and is making inroads in other Asian countries, including China and Korea. EPON is based on Ethernet technology and the IEEE standard P802.3ah. EPON can deliver data streams of up to 1 Gbps and operates at a distance of up to 20 km between the OLT and optical network terminal (ONT). EPON OLTs support up to 32 individual users on each PON port. Multi-vendor deployment is still an issue in markets like Japan and China due to certain proprietary security frameworks adopted by carriers. Silicon vendors are effectively forced to incorporate custom security blocks into their solutions, resulting in a lack of wide spread interoperability among different vendors' products. Broad-based deployments will likely be hampered as a result, and original equipment manufacturers (OEMs) will be faced with continued hire costs due to lack of choice on supply chain.

GPON � based on ITU-T standards G.984.1, G.984.2, G.984.3, G.983.4 and G.983.5 � is being deployed worldwide and is expected to be the FTTH technology of choice in Europe and North America. It is based on generic frame protocol (GFP), which offers an open interface for more efficient transport of a variety of protocols. GPON delivers symmetrical and asymmetrical combinations of speeds up to 2.5 Gbps and operates at distances of up to 37 km between OLT and ONT. GPON can support up to 64 individual users per PON port. Newly approved standards G.983.4 and G.983.5 offer, respectively, a specified dynamic bandwidth assignment (DBA) mechanism and protection options that enhance survivability. GPON becomes the access technology of choice for carriers that plan to future proof their last mile access networks and avoid any major infrastructure changes. One of the advantages with GPON technology is the fact that it is driven by large OEM and carrier participation in Europe and North America. The Full Service Access Network (FSAN) consortium is the driving force behind this industry cooperation. Early participation by many North American and European carriers in FSAN helped derive a common technical specification, which has lessened the complexities associated with multi-vendor interoperability efforts.

VDSL2 and ADSL are the two most common technologies used in copper-based deployments today. VDSL2 is a physical layer technology for access networks that uses discrete multitone technique (DMT) modulation to offer high bandwidth to the consumer. It has eight profiles defined for a variety of applications, ranging from short loops to very long loops, and therefore, is a universal technology for access deployment. New VDSL2 products are supporting a variety of new features, such as integrated Quality of Service (QoS), enhanced impulse noise protection (INM), seamless rate adaptation (SRA), RRA and channel bonding. Another key benefit of VDSL2 is that it supports end-to-end IP transmission, which is the technology of choice for all new access deployments. As carriers push fiber closer to the consumer, VDSL2 enables them to deliver revenue-enhancing, value-added services quickly and cost-effectively. VDSL2 is in use today in Asia, by carriers in Japan, Korea and Taiwan, as well as in European countries, such as Belgium, Germany and Switzerland.

The various flavors of ADSL technology cannot support data rates as high as VDSL2. ADSL is an excellent technology for providing data-only services at longer loops (2 to 5 km). Data rates max out at 25 Mbps, as detailed in Fig. 2. Most of the ADSLx deployments to date have used asynchronous transfer mode (ATM) technology, and will continue to do so for compatibility reasons. ADSL has been in use worldwide for more than seven years.

Figure 2: A Comparison of Fiber and Copper Standards

EPON ¹	GPON ¹	VDSL	ADSL
Up to 1 Gbps data streams	Symmetrical and asymmetrical combinations of the following speeds: Downstream � 1.2 Gbps and 2.5 Gbps Upstream � 155 Mbps, 622 Mbps, 1.2 Gbps and 2.5 Gbps	VDSL1 (G.933.1) VDSL2 (G.993.2), scalable symmetrical and asymmetrical data rates. 8 profiles defined for different services. 30a profile. Aggregate data rate of 200 Mbps DS/US: 100/100 Mbps Application: MxU/FTTB 17a: DS/US 100/50Mbps Application: /FTTN/FTTR 12a/b profile DS/US: 60/30 Mbps. Application: FTTR/FTTEx 8a/b/c/d profiles. Aggregate data rate 50 Mbps Application: FTTR/FTTEx	ADSL (G.992.1), DS/US: 8 Mbps/800 kbps ADSL2 (G.992.3), DS/US: 12 Mbps/1 Mbps an annex with extended upstream � US < 3 Mbps an annex with for extended reach � up to 5 km ADSL2-RE (G.992.3), DS/US: 8 Mbps/1 Mbps ADSL2+ (G.992.5), DS � 25 Mbps US � 1.2 Mbps
Broadcast downstream and TDM upstream	Broadcast downstream using TDM; TDMA utilized for upstream	Discrete multi-tone (DMT) modulation, FDD for downstream and upstream	DMT-based modulation. FDD (ADSLx) and EC (HDSL)
Supports 32 individual users per single PON port	Supports 32 (possible 64) individual users per PON port	1:1 connection between CO and CPE. CO line cards typically support 48 ports.	1:1 connection between CO and CPE. CO line cards typically support 48-72 ports
Can operate at distances of up to 20 km between OLT and ONT	Can operate at distances of up to 37 km between OLT and ONT	Can operate at distances up to 6-7 km, though is most effective in shorter loops	Can operate at distances of up to 6-7 km
3 wavelengths supported: Voice & data: 1490 nm downstream and 1310 nm upstream Video � 1550 nm downstream	3 wavelengths supported: Voice & data: 1490 nm downstream and 1310 nm upstream Video � 1550 nm downstream	Support for a variety of services: Integrated QoS: Dual-latency for triple play services. Data that must be protected uses the interleaved path while data that is sensitive to delay can use the path without interleaving (or with only a minimum of interleaving). ATM/IP Channel bonding for extended reach/rate Support for POTS/ISDN services	Support for a variety of services: Primarily ATM, though newer ADSL2+ standard supports IP Channel bonding for extended reach/rate Support for POTS/ISDN services
	Specified Dynamic Bandwidth Assignment (DBA) mechanism	Optional Dynamic Spectral Management (DSM I/II/III) mechanism to improve compatibility and reduce cross-talk. Enhanced rate/reach and immunity to interference	Optional Dynamic Spectral Management (DSM I/II/III) mechanism to improve compatibility and reduce cross-talk. Enhanced rate/reach and immunity to interference
	Protection options that enhance survivability	Support for spectral compatibility and enhanced stability provided: Spectral shaping U/DPBO (US/DS power backoff) Impulse noise protection (INP) Pre-emption Bitswap Seamless Rate Adaptation (SRA)	Support for spectral compatibility provided: Spectral shaping UPBO (US power backoff) Bitswap Seamless Rate Adaptation (SRA)
		Loop Diagnostic mode Power management � power modes	Loop Diagnostic mode Power management - power modes

^{1 � Information
provided by Dell'Oro Group, in "Access Report: Five Year Forecast
2007-2011."}

The Ultimate Decision

When determining the proper choice of access technology, a service provider must consider several factors:

How quickly do you want to begin offering services and reach profitability?
Do you have the capital and time for a long-term buildout?
Do you want to make radical changes to futureproof your network or would less costly, incremental changes serve your customers needs?
Do you want to deploy advanced voice, video and data services over a widespread area or do controlled rollouts in specific markets.

How a service provider answers these questions may determine which access network upgrade path they take. Fiber, which is costly and time-consuming, will offer the maximum amount of flexibility for adapting to new, higher bandwidth services long into the future. Using DSL, however, enables a service provider to maximize its investment in copper infrastructure while efficiently deploying the bandwidth necessary to capably handle voice, video and data applications.

About the Author

Piyush Sevalia is the vice president of Marketing for the Access Products Group at Ikanos Communications. In this position, he is responsible for creating and executing the group's vision and strategy. He also holds responsibility for all corporate and marketing communications. Since September 2000, Sevalia has brought to market multiple generations of VDSL and FTTx solutions, contributing to significant growth in the company's revenues and profits. His leadership has helped Ikanos achieve and maintain its No. 1 market share position for four successive years and resulted in the company's successful primary and secondary public offerings.

Prior to Ikanos, Sevalia spent more than nine years at Cypress Semiconductor in various senior marketing management and applications engineering roles. His contributions resulted in several multi-million dollar acquisitions and the creation of several $100 million products. He also developed and successfully executed a strategy to triple the revenues of the Clocks Products Group in two years.

Sevalia earned a B.E. in electrical engineering from the University of Bombay in India, an M.S. in electrical engineering from the University of Michigan, Ann Arbor, and an MBA from the University of California, Berkeley. He holds four patents, has authored several technology and business articles, and frequently speaks at industry conferences.

About Ikanos

Ikanos Communications, Inc. (NASDAQ: IKAN) develops chipsets that enable carriers to offer Fiber Fast� bandwidth and Gigabit network processing for enhanced triple play services. Ikanos' multi-mode VDSL2/ADSLx and network processor solutions power access infrastructure and customer premises equipment for many of the world's leading network equipment manufacturers. Ikanos' solutions enable fast and cost-effective carrier rollouts of interactive broadband services, including IPTV. For more information, visit www.ikanos.com.

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