Technical Considerations for CATV Open Access

Comments on the technical ability to implement open access provisioning via high-speed data over hybrid fiber-coaxial cable television systems in the United States. Prepared for the White House National Economic Council. Written in May, 1999.

By Mark Laubach

Copyright 1999 Mark Laubach, All rights reserved.
Non-commercial redistribution is allowed and encouraged.

1 Introduction

This white paper addresses the technical aspects of the question: What would be the level of pain felt by the United States cable industry if the government were to mandate open access for high-speed data broadband residential access cable television networks?

In this context, pain is directly related to actual or perceived lost money, revenues, or resources needed to implement open access given the state of today's broadband cable modem deployments. This paper attempts to stay close to technical viewpoints surrounding broadband residential access systems in general, with specific focus on cable television networks. It is not the intent of this paper to recommend policy, nor will it do diligence in assessing direct impact to the economics or business models of broadband access service providers or cable modem vendors. Any cost discussions are related to technical deployment and/or support costs.

2 Executive Summary

The U.S. Cable Industry, the DOCSIS standards it produced, and the compliant products produced by vendors, are not prepared to implement open access provisioning for high-speed data broadband access over cable television networks.

After securing cable industry commitment, at most three years lead-time is needed to produce open access ready DOCSIS-based cable modem products due to standards enhancement, vendor development, and successful certification of multiple vendors' products. For example, if U.S. policy were established that mandated open access provisioning by early year 2003, the U.S. cable industry would need to motivated and commit to begin standards enhancement in early year 2000. To deploy and enable open access provisioning, there would be substantial technical costs associated with updating and/or replacing previously deployed subscriber cable modems, updating or replacing CATV head-end high-speed data equipment, and enhancing cable operator backend net-works and support services for multiple service provider access.

This white paper presents a technical summary only and needs to be substantiated by a business and financial impact study.

3 Overview

• Open access provisioning is technically possible in all high-speed data broadband residential and commercial access networks:
• Cable television is not enabled and open access is difficult due to historical issues.
• Digital Subscriber Loop is enabled and exploiting open access provisioning now.

more. . .

4 Ideal Open Access Definition

For the purposes of this white paper, ideal open access provisioning for high-speed data broadband access networks is defined by a set of ideal technical requirements.

The requirements are labeled as R1 through R12 for reference later in the paper:

• R1: Provider Selection
• R2: Multiple Providers.
• R3: Ability to Provide
• R4: Bandwidth Allocation
• R5: Quality of Service
• R6: Subscriber Containment
• R7: Provider Containment
• R8: Link Privacy
• R9: User Content Preservation
• R10: Provider Address Management
• R11: Provider Subscriber Management
• R12: IP Dial Tone Service

These ideal requirements do not represent a consensus of definitions used by today's open access providers, nor are they meant to convey an official definition in use by the government or any regulatory agency. They are used here to illuminate and support comparisons of different open access provisioning methods that are discussed within this paper.

5 Summaries of Broadband Access Technologies

5.1 Digital Subscriber Line

5.2 Fiber to the Curb

5.3 Metropolitan Area Wireless

5.4 Broadband Satellite

5.5 Cable Television

6 Focus on DOCSIS RFI

This section discusses open access provisioning techniques using DOCSIS RFI based cable modem systems. The arrangement of this section is based on the ISO networking layer, starting with the physical RF layer up through applications.

6.1 Open Access: Layer 1 — Physical

Open access at Layer 1 is not workable.

6.2 Open Access: Layer 2 — Data Link / Media Access Control Protocol

6.3 Open Access: Layer 3 — Network: Internet Protocol Techniques

• DOCSIS RFI specifications at Layer 3 do not support ideal open access, due to the single provider architecture of the DOCSIS system and Layer 3 and Layer 2.
• DOCSIS RFI V1.1 does provide facilities that can be exploited for ideal open access solutions however, additional design work and requirements must be developed for ideal open access to be supported by the DOCSIS standard.
• There are specialized routing and tunneling techniques that support workable, but less than ideal open access solutions. These techniques could be exploited further, for more workable solutions however; additional enhancements are needed at Layer 2 for ideal open access.

7 Technical Observations

It is not the argument that cable system cannot technically support ideal open access provisioning.

7.1 Technical Cost Considerations

. . . Therefore it is apparent that a revenue exchange similar to DSL would be needed where service providers pay their way for connection to a head-end and for sup-port of subscribers. Specifics of any business models for future open access economics require further study. Such models are beyond the scope of this paper.

8 Summary

A definition for ideal open access provisioning was presented.

A high level review was performed discussing the technical abilities of the current DOCSIS cable modem specifications to meet the ideal open access requirements in the U.S. Cable TV Broadband Access environment.

Various approaches and alternatives were discussed. A short-term mandate for open access provisioning over cable systems would cause immediate technical and cost pain for U.S. cable operators: the existing and upcoming DOCSIS RFI specifications do not support open access directly, however DOCSIS RFI Version 1.1 does provide fundamental facilities that would be exploited for open access.

Most cable operators' high-speed data over cable and backend servers and networks have been designed and optimized for a single ISP. Forcing these systems to support open access provisioning would incur unforeseen technical costs for new capital equipment and support. There are techniques being used by some cable operators to provide workable but, less than ideal open access provisioning, via specialized routing and tunneling techniques. Some of the capability needed for this support may rely on customized software from select vendors and may not be generally available. These techniques are being applied to cable modem systems and are independent of the cable modem system, e.g. DOCSIS versus proprietary. In some cases, a vendor's cable modem may need a software or hardware update to work. Tunneling techniques also have merit, but impact the cable modem directly, and will take time to put into place. Either solution can be developed to better couple with upcoming bandwidth allocation and QoS abilities of DOCSIS V1.1 systems.

A longer-term mandate, such as three to five years, should give sufficient time for the U.S. cable industry and associated vendors to develop and upgrade the DOCSIS specifications and products to support ideal open access. However, all cable modem systems deployed between now and then would not support ideal open access. There is significant cost associated with the manner in which legacy technology is upgraded to desired technology. However, given sufficient planning, open access capable cable modems could be deployed on the same upgraded CMTS's that support legacy cable modems. The cost impact is beyond the scope of this paper. There are other broadband access network methods being used in the U.S., with some methods in place today: (e.g. DSL) and some under development or just beginning deployment: wireless, satellite, FTTC. The wireless and satellite methods are lacking open access provisioning requirements and standards. It is observed that all broadband access systems could potentially share the same ideal open access provisioning goals, thereby providing a consistent service offering potential to subscribers, regardless of broadband access method.

9 About the Author

MARK LAUBACH holds a Bachelors of Electrical Engineering and a Master of Science in Computer Science from the University of Delaware (thesis advisor is David J. Farber). He is currently an independent consultant. He is a co-founder and past Vice President and Chief Technology Officer at Com21, Inc. in Milpitas, California where he was responsible from 1994 to 1999 for directing the end-to-end systems architecture, protocol design, performance, and technology of the Com21 ATM-based cable TV network telecommunications products. He has participated in many cable TV standards activities (IEEE, IETF, ATM Forum, SCTE, and CableLabs' DOCSIS). He has made numerous presentations at Cable TV industry conferences and events. He is an instructor for cable modem systems and protocols at Networld+Interop. He is a principle co-inventor of a patent with Paul Baran, and a principle co-inventor on several additional patent filings with Com21 and other companies. Prior to Com21, he was with the Hewlett-Packard Company for 14.5 years. Mark is past chair of the IP-over-ATM Working Group. He is the author of the RFC1577/2225 Classical IP and ARP Over ATM (IPOA) standard. He is a past member of the CSNET Executive Committee. He is a senior member of IEEE (Institute for Electrical and Electronic Engineers), a member of ACM (Association for Computing Machinery), and a member of SCTE (Society of Cable Telecommunications Engineers).