This paper outlines the development of the Institute of Electrical and Electronics Engineers (IEEE) Project 802.14. This working group is chartered to develop standards for the medium access and physical layers for hybrid fiber-coax cable-TV systems that will deliver integrated multiple services (data, audio and video) to the home. Also discussed are the technical challenges, the standard development process and an update on its status as of September 1995.

Described here is an adaptive MAC-layer protocol that supports multiservice (STM and ATM) applications in the context of subscriber access to tree and branch (e.g., fiber-coaxial cable) networks. The protocol adapts to changing demands for a mix of circuit and cell mode applications, and efficiently allocates upstream and downstream bandwidth to a variety of bursty and isochronous traffic sources. In the case of a hybrid fiber-coaxial (HFC) network the protocol resides in customer premises equipment and a common head-end controller. A medium-access control (MAC) processor provides for dividing the time domain for a given digital bitstream into successive frames, each with multiple STM and ATM time slots. Within the STM region of a frame, variable length time slots are allocated to calls (e.g., telephony, video telephony) requiring different amounts of bandwidth. A contention access signaling channel is also provided in this region for call control and set-up requests. Within the ATM region fixed-length time slots accommodate one individual ATM cell. These ATM time slots may be reserved for a user for the duration of a call or burst of successive ATM cells, or shared via a contention process. At least one contention time slot is available for signaling messages related to ATM call control and set-up requests. Further, the fixed-length ATM time slots may be reserved by a user for the duration of a call, or shared through a contention process. This paper describes the MAC-layer protocol, its relation to circuit- and ATM- amenable applications, and its performance with respect to signaling throughput and latency, and bandwidth efficiency for several service scenarios.

Cable TV companies and regional Bell operating companies, e.g. PacBell, are preparing for the future by installing or rebuilding existing all-coaxial cable plants into hybrid-fiber coaxial plants and by offering a wide range of interactive services which they feel will be most attractive to their subscriber base. These new-to-cable services span a wide range of performance attributes, each placing its own demands on the capabilities of the broadband bearer service system. These services include, but are not limited to: video-on-demand, digital video, video telephony, voice telephony, and a suite of interactive digital data services ranging from traditional Internet and information service access (e.g., Compuserve and Prodigy) to multi-player gaming. The future broadband infrastructure challenge can be met by developing a novel family of integrated bearer service products which communicate using asynchronous transfer mode protocols over the cable TV network. This paper summarizes the ATM over HFC definition work taking place in the ATM Forum's Residential Broadband Working Group and the standards progress in the IEEE P802.14 Cable TV Media Access Control and Physical Protocol Working Group. Finally, an example of bridging Ethernet packets over ATM over HFC is discussed. This paper focuses on the aspects of ATM and the MAC layer and does not detail the rf or physical environment.

Hybrid fiber-coax technology allows one network to deliver both traditional telephony as well as a host of broadband services including broadcast TV, cable TV, interactive TV, video-on- demand, enhanced pay-per-view, etc. This paper presents an overview of hybrid fiber-coax architecture including discussion of the components for transmission of telephony and broadband services from the headend/central office to the home. The components and architecture of an HFC system are compared to traditional telephony. An HFC system can be broken into 4 major sections: headend/central office and interoffice network, a feeder system, a distribution system, and a customer interface. The components within each of these sections include: local digital switches, host digital terminals, broadband and narrowband optical transmitters and receivers, optical nodes, power nodes, network interface units, set top terminals and several types of passives. The function of these components is reviewed as are spectrum allocation, and signal flow.

This paper proposes three different approaches to providing integrated digital services to small businesses and residential customers over modern hybrid fiber and coaxial (HFC) access networks. The target delivery system is one that is flexible and forms a multiservice, service- independent platform capable of providing a wide range of services (voice, video, data, and multimedia). The merits and limitations of the three approaches are explored. In the first approach, the common facilities of an HFC access network may be shared by the frequency partitioning of the coaxial plant's radio frequency spectrum. video, data, and telephony services each use different portions of this spectrum -- a service-dependent network. In the second approach, asynchronous transfer mode (ATM) transmission is used as the information delivery vehicle all the way to the home or small business, creating a more flexible delivery system. The ATM-based architecture is expected to support any service or service mix -- a service-independent network. In the third approach, a common transport protocol composed of both asynchronous and synchronous transfer modes (ATM/STM) is used. Such an approach could (1) provide a common interface between home/small business premises equipment and both the circuit and ATM switching networks; (2) meet a wide range of delay and throughput requirements; and (3) allow for many network migration scenarios.

Since 1990 there has been a rapid increase in the demand for communication services, especially local and wide area network (LAN/WAN) oriented services. With the introduction of the DFB laser transmitter, hybrid-fiber-coax (HFC) cable plant designs, ATM transport technologies and rf modems, new LAN/WAN services can now be defined and marketed to residential and business customers over existing cable TV systems. The term metropolitan area network (MAN) can be used to describe this overall network. This paper discusses the technical components needed to provision these services as well as provides some perspectives on integration issues. Architecture at the headend and in the backbone is discussed, as well as specific service definitions and the technology issues associated with each. The TCP/IP protocol is suggested as a primary protocol to be used throughout the MAN.

The push to reduce system operating cost and increase performance in a traditional cable television tree-and-branch architecture has led system designers to pursue the hybrid fiber- coaxial (HFC) architecture as a viable solution. This solution, which joins the photonic world with radio frequency (rf) transmission, yields favorable results with respect to transporting analog video services. As a result, system operating enhancements such as improved carrier- to-noise ratios, improved carrier-to-distortion measurements, and fewer active components in cascade are possible. In addition, an enabling platform for the deployment of other two-way interactive services, facilitating duplex transmission, is successfully accomplished. In order to realize this network, there are some acute operational issues that need to be addressed. The picture quality problems of the past have been minimized. However, the thought of transporting telephony and other digitally formatted signals gives rise to other technical operating concerns. The adverse effects of impulse noise and ingress in the down and upstream paths of the HFC plant on digital signals and ancillary data services are described in this paper. Experimental data shows how these impairments affect network reliability from a technical operational context.

Offering interactive services and data in a hybrid fiber/coax cable system requires the coordination of a host of operations and business support systems. New service offerings and network growth and evolution create never-ending changes in the network infrastructure. Agent-based enterprise models provide a flexible mechanism for systems integration of service and support systems. Agent models also provide a mechanism to decouple interactive services from network architecture. By using the Java programming language, agents may be made safe, portable, and intelligent. This paper investigates the application of the Object Management Group's Common Object Request Brokering Architecture to the integration of a multiple services metropolitan area network.

Hybrid fiber-coax (HFC) systems have been developed to efficiently deliver television and other broadband services along with voice-grade services to the subscriber's premises. The efficiency of an HFC system, from both a call processing and an economic point of view, is enhanced by providing an integrated interface into the local digital switch (LDS) for the voice- grade services. Two interfaces in the public domain that can be used to provide the integrated voice-grade interface to the LDS are known as the TR-08 Interface, defined in Bellcore's Technical Reference document TR-NWT-000008, and the TR-303 Interface, defined in Bellcore's Technical Reference document TR-NWT-000303. This paper presents a brief overview of the TR-08 and TR-303 interfaces to LDSs. The advantages of using the TR-303 Interface for an HFC system's voice-grade interface to the LDS are discussed for the operations, administration, maintenance, and provisioning (OAM&P) functions. Also discussed are the economic considerations of providing plain old telephone service (POTS) and integrated services digital network circuits in HFC systems via TR-08 and TR-303 interfaces to the LDS.

This presentation is a report of the testing activities of the CableLabs Network Integrity Working Group. The working group consisted of several CableLabs member companies which conducted rf analog and digital bit-error testing at five CATV networks in the U.S. and Canada. The purpose of the working group was to measure the reliability and availability of the contemporary CATV network as specified by traditional switched access telephony performance parameters. Transmission data was collected for both forward and reverse (sub- split) paths of the rf broadband network, in both traditional and hybrid fiber/coax architectures, and for baseline and controlled variation events. The basic premise of this testing was to ascertain which cable television network elements adversely affected transmission of a 'generic' digital communications system and how they can be managed or controlled. The digital transmission utilized in the test was a QPSK modulated, T-1 rate (1.544 Mbit/second), modem without error correction. The intent was not to derive the necessary modulation technique and error correction scheme to properly operate in every cable television system, but rather to determine the principal sources of impairments existing in these networks and deduce corrective measures. The full report of the Network Integrity Working Group is published by CableLabs, Inc., and is titled, 'Two-Way Cable Television System Characterization -- Final Report', April 1995.

This paper presents a comparison of the two most common modulation systems for downstream digital transmission on hybrid fiber/coax: quadrature amplitude modulation (QAM), and vestigial sideband modulation (VSB). Both modulations use multiple signal levels to send multiple bits per Hertz with similar bandwidth efficiency. Detailed calculations of QAM and VSB performance on hybrid fiber/coax are reported here. It is shown that, since VSB has a higher symbol rate, it has at most one-half dB less received SNR than QAM because of dispersion and jitter. This difference is negligible. Proposals for VSB recover the carrier with a pilot tone and a PLL, and proposals for QAM use all-digital data-directed carrier recovery. Simulations reported here show that QAM and VSB have very similar carrier recovery performance. It is concluded that, for hybrid fiber/coax, the performance and inherent cost of QAM and VSB are very similar, although the two systems have many implementation differences and are incompatible.

Digital transport capabilities to a home served by a fiber-to-the-curb network are limited by the transmission characteristics of the twisted-pair drop cable. However, advanced digital signal processing techniques can substantially increase the data transmission capability over the relatively short lengths of these metallic sections. The purpose of this study is to estimate the maximum achievable information rate versus drop cable length (between 100 to 500 meters), when very high rate asymmetric digital subscriber line (VADSL) modems, with a QAM modulation technique, are used. Different QAM constellations have been analyzed and two types of disturbances have been considered: far-end crosstalk (FEXT) and additive white Gaussian noise (AWGN). Simulation results show that FEXT is a greater impairment than AWGN, and that a 16-QAM constellation outperforms any other number.

This paper examines the evolutionary potential of hybrid fiber coaxial systems for new services. It is shown that the cost of building dual (or 'overlay') cable TV and telecom networks is higher than adding telephony to a cable TV network on the hybrid fiber coax principle. It is shown that other services including Ethernet access to the Internet can also be added at low incremental cost. The potential of modems carrying ATM traffic to carry an even wider range of services is also considered.

Cable operators in the U.K. enjoy unprecedented license to construct networks and operate cable TV and telecommunications services within their franchise areas. In general, operators have built hybrid-fiber-coax (HFC) networks for cable TV in parallel with fiber-copper-pair networks for telephony. The commonly used network architectures are reviewed, together with their present and future capacities. Despite this dual-technology approach, there is considerable interest in the integration of telephony services onto the HFC network and the development of new interactive services for which HFC may be more suitable than copper pairs. Certain technological and commercial developments may have considerable significance for HFC networks and their operators. These include the digitalization of TV distribution and the rising demand for high-rate digital access lines. Possible scenarios are discussed.

We report a test of MPEG1 compressed video. Each of twelve short standard test scenes was processed through seven versions of MPEG1 and through four comparison systems, yielding a total of 132 processed scenes. The MPEG1 versions were at bit rates of 0.9, 1.2, and 1.8 Mb/s. The comparison systems included VHS VCR and simulated cable TV. Consumers judged the quality of each of the 132 scenes in a laboratory viewing room, using high quality playback equipment, and according to standard procedures of the international standards community. Consumers rated the quality of MPEG1 at 1.8 Mb/s as perceptibly different from a standard unprocessed signal but not annoying. However, MPEG1 at 1.8 Mb/s was also judged to be somewhat less good than VHS. Varying the bit rate in the range 0.9 Mb/s to 1.8 Mb/s for MPEG1 coding had a substantial effect on consumers' judgments of video quality: the higher the bit rate the better the judged quality. The 12 test scenes from the ISO MPEG committee differ in their ability to discriminate codecs when judged by consumers. Demographic differences among consumers did not affect the quality ratings.

DQRAP (distributed queuing random access protocol), is a multiple access protocol that offers a throughput equal to the offered traffic up to a load of one with a lesser delay than any other multiple access protocol. DQRAP utilizes three control minislots and two distributed queues: transmission and collision resolution, to provide this performance for all values of 'a', i.e., the size of the network is immaterial. This paper describes: (a) how DQRAP can act as the switching fabric for a distributed ATM switch serving an HFC (hybrid fiber-coax) network; and (b) how CBR (constant bit rate) traffic is supported on our distributed ATM switch, i.e., a DQRAP/ATM switch. Simulation results representing the operation of a DQRAP/ATM switch operating in two modes: (a) the control minislots in dataslots allocated to CBR traffic are utilized in the reservation process; and (b) the control minislot capacity in those slots is allocated to CBR data.

A discrete wavelet multitone (DWMT) system for communications over hybrid fiber coax (HFC) networks is described. DWMT is a high performance multicarrier modulation technique that provides robust, efficient communications in the presence of the types of channel impairments encountered on the HFC plant. This multicarrier technique, based on a wavelet transform, provides spectral efficiency and achieves significant advantages in the presence of narrowband interference to meet the challenges of providing telecommunication services on HFC networks.

Discrete multitone (DMT) has been accepted as a very effective modulation technique for point-to-point transmission on a channel whose SNR is highly frequency-dependent, and it has been adopted by ANSI as the standard for ADSL [up to 7 Mbit/s on unshielded twisted- pair (UTP)]. Synchronized DMT (SDMT), a variation of DMT for multipoint-to-point transmission, will be proposed to the ATIS committee T1E1.4 for VDSL (up to 51.8 Mbit/s on hybrid fiber/UTP), and to the IEEE committee 802.14 for the upstream channel of an HFC system. This paper describes the method of synchronization, which allows the efficient combination of signals from multiple transmitters without the use of guard bands in either the frequency- or time-domain. It also describes a protocol for controlling access to the shared channel by these transmitters, which may have widely varying needs for data rates and formats.

For an expeditious and successful penetration of broadband services to residential and other small traffic subscribers, cost-efficiency by means of investment sharing and partial re-use of existing infrastructure are imperative. Employment of passive optical technology to feed subscriber clusters while maintaining the copper in the last drop is a promising strategy. To achieve traffic concentration and high utilization, a MAC protocol designed for low CDV is essential. A TDMA protocol based on ATM cells suitable for upgrading both twisted pair and coaxial based access networks creating hybrid solutions is presented. This protocol offers a dynamic response at cell level to the bursty traffic expected in B-ISDN using the reservation method to sample by periodic requests the arrival rate. No resort to signalling related information is required. Differentiating the handling between delay tolerant and non-tolerant traffic can offer significantly higher exploitation and a cost effective solution for the local loop.

Fundamental limits in a fiber optic network can dictate the number of video and data channels that can be multiplexed into a cable television network. The most prominent distortions are relative intensity noise (RIN) in the laser diode, nonlinear distortions (NLD) such as those characteristic of the laser diode, and photodiode detector shot noise. According to several researchers, there is a basic limit to the number of cable video channels and the depth of modulation that can be put on a laser diode before impairments distort the video to such an extent as to be unacceptable. This distortion is seen in the form of composite second order (CSO) and composite triple beat (CTB) impairments, as well as clipping noise. This paper shows the development of a laser diode clipping model used to determine and simulate the clipping effect in a laser diode. This model allows a clearer understanding of the affects of clipping in analog and digital carrier networks.

This paper investigates the affects of upstream channel distortion in HFC networks for serving areas of different size, rf channel bandwidth, modulation scheme, and operating frequency. Experimental characterization of the reverse upstream channel as well as digital transmission performance simulation for a variety of cases are presented. Upstream channel availability results based on a minimum BER performance of 10^-8 with and without the use of equalization are presented as well.

The CATV system delivers analog video signals from a centralized headend through a tree- and-branch fiber/coax network. That architecture is very cost effective for delivering broadcast video channels to a vast area. The introduction of interactive TV, data and telephony services requires an upstream link from customers to the headend. Although equipment for upstream transmission is available, CATV systems are primarily engineered for the delivery of one way analog broadcast TV programs. In this paper, issues related to two-way digital transmission through the coaxial cable distribution plant are examined. The objective is to establish a reliable computer modeling environment for the study and simulation of general and advanced transmission systems over the coaxial cable distribution plant. The discussions are focused on three general topics: the coaxial cable distribution plant transmission channel, the corresponding noise environment, and applicable transmission system architectures. Two- port network models are developed for the components (coaxial cable, taps, etc.) of the coaxial cable distribution plant. A realistic distribution plant channel model can be constructed based on these component models. The distribution plant noise level is analyzed based on thermal noise level, amplifier noise figure, and the funneling effect. The upstream ingress noise model is also developed. Three advanced transmission systems, adaptive transmitter, frame based equalization, and discrete multitone (DMT), are presented. End to end computer simulation results are presented using QPSK upstream.

Although the vision for the future Integrated Broadband Communication Network (IBCN) is an all optical network, it is certain that for a long period to come, the network will remain very heterogeneous, with a mixture of different physical media (fiber, coax and twisted pair), transmission systems (PDH, SDH, ADSL) and transport protocols (TCP/IP, AAL/ATM, frame relay). In the current work towards the IBCN, the ATM concept is considered the generic network protocol for both public and private network, with the ability to use different underlying transmission protocols and, through adaptation protocols, provide the appropriate services (old as well as new) to the customer. One of the major difficulties of heterogeneous network is the restriction that is usually given by the lowest common denominator, e.g. in terms of single channel capacity. A possible way to overcome these limitations is by extending the ATM concept with a multilink capability, that allows us to use separate resources as one common. The improved flexibility obtained by this protocol extension further allows a real time optimization of network and call configuration, without any impact on the quality of service seen from the user. This paper describes an example of an ATM based multilink protocol that has been experimentally implemented within the RACE project 'STRATOSPHERIC'. The paper outlines the complexity of introducing an extra network functionality compared with the added value, such as an improved ability to recover an error due to a malfunctioning network component.

This paper presents key results from hybrid fiber-coax (HFC) network reliability modeling. The primary objectives are to provide in-depth evaluation of HFC reliability, analyze impacts from individual network elements, and discuss the implications of the results. The scope of the study includes traditional CATV, telephony/data, and video dial tone (VDT) services on HFC.

This paper provides a high-level overview of an object-oriented simulation tool developed to model the HFC-2000^TM broadband access network of AT&T. One objective of this tool is to help estimate the traffic capacity of fiber nodes and to explore various alternatives in architecture and design. Another objective is to provide guidelines for the use of different time slot assignment algorithms and for capacity planning. To achieve these goals, salient operational and serving features of the HFC-2000^TM have been incorporated into the tool. Specifically, the tool models the traffic and serving characteristics of an entire fiber node with multiple coaxes, each carrying traffic both upstream and downstream. To facilitate the evaluation of performance under different traffic scenarios, the simulator allows traffic characteristics to be specified on a per-port basis in terms of a large variety of service types. A finite-source quasi-random input process is used to model the call arrivals from the different ports, with each port being considered an independent traffic source. A mixture of lognormal distributions is used for the call holding time distributions of various call types. The traffic from any given port is characterized by a service profile which specifies the probabilities for the different call types to be generated by the port. The traffic loading offered by a given port is specified by the hourly CCS (hundred call seconds) for that port. The tool is built using the object-oriented feature of C++. Different objects are used to implement the various features of the different types of network interface units, upstream and downstream channels, and the various types of call events.