Hybrid Fiber Coaxial Networks Research Articles

A priority scheme for the IEEE 802.14 MAC protocol for hybrid fiber-coax networks

In order to support quality-of-service (QoS) for real-time data communications such as voice, video and interactive services, multiaccess networks must provide an effective priority mechanism. The context of this work is the IEEE 802.14 standard for hybrid fiber coaxial (HFC) networks which has a shared upstream channel for transmissions from stations to the headend. This work presents a multilevel priority collision resolution scheme, which separates and resolves collisions between stations in a priority order, thereby, achieving the capability for preemptive priorities. We present a set of simulation scenarios which show the robustness and efficiency of the scheme, such as its ability to isolate higher priority traffic from lower priorities and to provide quick access to high-priority requests. In March 1998, a framework for handling priorities in the collision resolution process, which adopts a semantics similar to the semantics of our scheme, was included in the 802.14 standard.

A simulation-based study of TCP dynamics over HFC networks

New broadband access technologies such as hybrid fiber coaxial (HFC) are likely to provide fast and cost effective support to a variety of applications including video on demand (VoD), inter-active computer games, and Internet-type applications such as Web browsing, ftp, e-mail, and telephony. Since most of these applications use TCP as the transport layer protocol, the key to their efficiency largely depends on TCP protocol performance. We investigate the performance of TCP in terms of effective throughput in an HFC network environment using different load conditions and network buffer sizes. We find that TCP experiences low throughput as a result of the well-known problem of ACK compression. An algorithm that controls ACK spacing is introduced to improve TCP performance.

In-service cable-monitoring technique for hybrid fiber/coaxial networks based on frequency domain analysis incorporated with optical time-domain reflectometer and fiber benders

An integrated on-line cable-monitoring technique for hybrid fiber/coaxial (HFC) networks is proposed and experimentally demon- strated. The in-service monitoring of fiber optic cable and coaxial cable is achieved simultaneously by an optical time-domain reflectometer (OTDR) and the frequency domain analysis (FDA) method, respectively, where the FDA results are encoded in the additional dummy fiber through digitally modulated fiber benders. This technique can be easily developed into an automated in-service surveillance system to provide real-time monitoring to enhance HFC network reliability. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)01002-3)

Using proxies to enhance TCP performance over hybrid fiber coaxial networks

Using cable modems that operate at several hundred times the speed of conventional telephone modems, many cable operators are beginning to offer World Wide Web access and other data services to residential subscribers. Initial experiences indicate that real-world hybrid fiber coaxial (HFC) networks are susceptible to a variety of radio-frequency impairments that significantly reduce the benefits of using high-speed cable modems. The effects of packet losses in the access network are particularly accentuated during subscriber accesses to remote servers on the Internet. The longer round-trip times in such accesses together with the high packet loss rate result in dramatic degradations in performance perceived by subscribers. This paper shows that by using proxy servers to handle all remote accesses from an HFC access network, the performance of remote accesses can be significantly enhanced even in cases when the proxy servers do not function as data caches. By handling packet losses that occur in the HFC network locally, at low latencies and without the remote server even being aware of the loss, a proxy server enables faster recovery from packet losses. Most importantly, since it controls data transmissions over the local HFC network, the proxy server's transmission control protocol (TCP) implementation can be optimized for the loss of characteristics of the HFC access network, enabling a significant increase in performance when the access network is lossy.

The feasibility study of transporting IS-95 CDMA signals over HFC networks

This letter studies the feasibility of transmitting IS-95 code-division multiple-access (CDMA) wireless signals in hybrid-fiber-coax (HFC) networks. Capacity estimation of an HFC optical node-based CDMA cellular systems using a return-path channel model is provided. In addition to multiple-access interference in IS-95 CDMA networks, the return-path channel model takes into account ingress noise, impulsive noise, and microreflections in a coaxial cable transmission system; and laser diode clipping-induced intermodulation noise in an optical fiber link.

Physical layer characterization of hybrid fibre coax (HFC) networks

This paper reviews the future prospects of cable television networks through their evolution towards HFC topology. This upgrade will allow cable operators to provide full broadband bi-directional communications (image, data and voice) and generate new revenues from their existing network. This article focuses on: what is an HFC topology, what are the relevant parameters to characterize its physical layer, what are the technological key issues and future trends?

ATM traffic control in hybrid fiber–coax networks – problems and solutions

The IEEE 802.14 working group is currently standardizing a new media access control (MAC) protocol for the emerging Hybrid Fiber–Coax (HFC) networks. Crucial for the success of 802.14 will be its ability to support higher layer traffic services, namely, ATM Constant Bit Rate (CBR), Variable Bit Rate (VBR) and Available Bit Rate (ABR) traffic classes. In this study, we investigate the inter-operation of the MAC protocol, defined by 802.14, with ABR transmissions. An important finding of our study is that the bandwidth contention on the upstream channel in the HFC network may interfere with the feedback congestion control mechanisms of ABR traffic control. This interference can result in unfairness between ABR sources and decreased utilization of the upstream HFC channel. As a solution to the problem we propose a scheme whereby the headend station of the HFC network returns congestion information contained in resource management (RM) cells to the ABR sources. The proposed mechanism can be incorporated into the ABR rate control scheme without modifying the current traffic management specifications. Numerous simulation scenarios are presented to illustrate our findings. Parts of the results have been presented to the IEEE 802.14 standardization committee.

A new network architecture with intelligent node (IN) to enhance IEEE 802.14 HFC networks

In the hybrid fiber/coax (HFC) architecture, a number of 500-2000 subscribers in the CATV (community antenna TV) network may cause serious collisions during the request phase. In this paper, we propose a new network architecture which using an intelligent node (IN) to stand for a group of subscribers to request the demand resources. The intelligent node has the ability to reduce the collision probability as well as the collision resolving period. The simulation results shown that the throughput and average buffer delay obtained by the proposed architecture is better than that of the standard architecture.

Hybrid fiber coax networks: a viable option for telemedicine.

Cable companies have improved their networks to the degree that they are viable alternatives to currently deployed networks. A detailed look at these cable networks shows them to be superior in bandwidth (capacity), speed, flexibility, and ubiquity. The services that can be provided by these networks are ideal to numerous advanced applications, including telemedicine.

Applications of Chaotic Digital Code-Division Multiple Access (CDMA) to Cable Communication Systems

In this paper the technical details of chaotic digital code-division multiple access ((CD)2MA) communication systems used in cable communication systems are presented. The cable communication system may be a pure coaxial RF cable network, a hybrid fiber-coax network, or a pure optical fibre network for high-capacity data link. As an example of its many potential applications in cable communication systems, (CD)2MA is used to support the upstream digital data communications in cable TV systems occupying the very noisy 5–40 MHz portion of spectrum. Although the (CD)2MA proposed in this paper is only used to support current Internet services via cable TV networks, it can also be used to support the high-speed data-link provided in the 550–750 MHz band in hybrid fiber-coax networks. (CD)2MA is a new communication framework which uses band-limited chaotic carriers insted of linear ones. For the purpose of generality, in this paper the band-limited chaotic carriers are approximated by groups of linear sub-carriers, which distribute within the same bandwidth with a fixed amplitude, random phases and uniformly distributed frequencies. The theoretical result of the performance of (CD)2MA is given. We also provide the simulation results of the bit-error-rate (BER) performances of a synchronous (CD)2MA used in cable communication systems. The results show that the (CD)2MA system has a better performance than the synchronous CDMA system proposed for the same cable communication system. Technical details of (CD)2MA are also presented for the future design of prototype systems. We present the framework of the whole (CD)2MA system including carrier syncronization, timing recovery and the details of nonlinear carrier generators.

Design of a video-server complex for interactive television

This paper describes the architecture and implementation of a scalable video server for interactive television services, which has been used in several video-on-demand projects in Japan. This server supports a large number of users with the delivery of high-quality video and provides many types of interactive multimedia applications. The server, using the IBM RISC System/6000® and RISC System/6000 Scalable POWERparallel Systems®, permits full interactive operation with clients. It also can deliver a large number of streams when it is expanded from a single-processor system to a multi-processor system, without any change of the server architecture. In this paper, we describe the end-to-end architecture, the design considerations regarding scalability of the delivery scheme for MPEG-2 transport streams, and the management mechanism for interactive applications. This paper also addresses the implementation of quality of service for digital services through a hybrid fiber-coax network infrastructure, and protocols for interactive television services.

Using proxies to enhance TCP performance over hybrid fiber coaxial networks

Using cable modems that operate at several hundred times the speed of conventional telephone modems, many cable operators are beginning to offer World Wide Web access and other data services to residential subscribers. Initial experiences indicate that real-world hybrid fiber coaxial (HFC) networks are susceptible to a variety of radio-frequency impairments that significantly reduce the benefits of using high-speed cable modems. The effects of packet losses in the access network are particularly accentuated during subscriber accesses to remote servers on the Internet. The longer round-trip times in such accesses together with the high packet loss rate result in dramatic degradations in performance perceived by subscribers. This paper shows that by using proxy servers to handle all remote accesses from an HFC access network, the performance of remote accesses can be significantly enhanced even in cases when the proxy servers do not function as data caches. By handling packet losses that occur in the HFC network locally, at low latencies and without the remote server even being aware of the loss, a proxy server enables faster recovery from packet losses. Most importantly, since it controls data transmissions over the local HFC network, the proxy server's transmission control protocol (TCP) implementation can be optimized for the loss of characteristics of the HFC access network, enabling a significant increase in performance when the access network is lossy.

Allocation and scheduling algorithms for IEEE 802.14 and MCNS in hybrid fiber coaxial networks

IEEE 802.14 and MCNS (multimedia cable network system) are two standards developed for the hybrid fiber coaxial (HFC) CATV networks. Both standards model an upstream channel as a stream of minislots. But their philosophies on resolving collisions in the shared upstream channel are rather different, where IEEE 802.14 adopts the priority+FIFO first-transmission rule and the n-ary tree retransmission rule, and MCNS adopts the binary exponential backoff algorithm with adjustable window sizes. Both provide reservation access, while IEEE 802.14 and MCNS also support isochronous access and immediate access, respectively. In this paper, we try to prepare a suggestion list for vendors on how to allocate minislots for reservation access and immediate access and how to schedule the reserved bandwidth, which greatly affect the performance of a cable network and are left open by the standards.

Enhanced throughput efficiency by use of dynamically variable request minislots in MAC protocols for HFC and wireless access networks

We consider Medium Access Control (MAC) protocols in which minislots are used to request permission to transmit packets of information (voice, data, video, or multi?media) in the upstream channels, and the information is subsequently transmitted in packet time?slots allocated by a central controller. Such MAC protocols are currently being considered for Hybrid Fiber?Coax (HFC) as well as wireless access networks. In this paper, we compare MAC protocols for three cases with regard to request minislots: (1) with no minislots (in this case, the first of a batch of information packets from a station is transmitted in contention mode and also carries with it a reservation request for the remainder of packets in that batch), (2) with fixed number of minislots per frame, and (3) with dynamically variable number of minislots per frame. There is transmission overhead associated with minislots, but there are potential throughput efficiency benefits under a range of traffic mix scenarios. This paper also proposes an algorithm for dynamically varying the number of minislots as a function of the traffic mix. Results based on analytical performance models are presented to compare throughput efficiencies for the three cases stated above. The results show that a MAC protocol with dynamically variable minislots has the highest throughput efficiency amongst the different alternatives mentioned above.

A algorithm of dynamically assigning upstream bandwidth of hybrid fiber-coax networks

The contradiction between the upstream bandwidth of hybrid fiber-coax networks and a large number of services to be transmitted, is very sharp. Specially, a part of the bandwidth assigned to real-time variable bit rate (rt-VBR) services, is redundant. Thus, the algorithm of assigning upstream bandwidth must have high bandwidth multiplexing. The algorithm described here is based on ATM traffic descriptor parameters and the quality of service (QoS) parameters, and is designed for rt-VBR services. The algorithm utilizes the bursts and cell loss rate of rt-VBR services to multiplex bandwidth. The algorithm also has call admission control.

Risk analysis of residential broadband upgrade in a competitive and changing market

The article presents risk and techno-economic analyses of broadband access network upgrade strategies for public network operators and cable operators in a competitive environment in the residential and small business market. The effect of uncertainties in predictions of critical parameters such as demand forecasts and market shares are analyzed. The assessed technology options include broadband twisted pair modem, hybrid fiber coax networks, and ATM-based passive optical networks.

AN ECONOMIC FEASIBILITY STUDY FOR HYBRID FIBRE-COAX (HFC) NETWORKS

This paper presents the cost analyses required to ascertain the economic viability of hybrid fibre-coax (HFC) networks from the perspective of telephone service providers. The cost model for an HFC network delivering video is presented first in order for the installed first cost (IFC) for video to be computed. The IFC was found to be very sensitive to the service subscription rate or market penetration rate. Therefore, the economic viability of HFC networks depends on how much market share the telephone companies attain in the near future. Using this HFC network as an infrastructure, the cost model for an HFC network with a telephone overlay is developed, and the incremental cost (IC) analysis for telephony is presented. The cost analysis found that the network interface unit (NIU) is the single major cost component in the IC computation, and that, compared to the IFC for video, the IC for telephony is relatively insensitive to the service subscription rate. © 1997 by John Wiley & Sons, Ltd.

Ms START: A random access algorithm for the IEEE 802.14 HFC network

In this paper we introduce the n-ary Multi-slot Stack Random Access Algorithm (msSTART) for use in an IEEE 802.14 hybrid fiber/coaxial (HFC) network. The msSTART random access algorithm (RAA) is an evolution of the stack-based START algorithm. It is an easy to implement, high-efficiency, free-access, robust, stable RAA optimized to operate in an environment where contention slots could dynamically change. Through a series of simulation studies, we demonstrate the performance advantages of msSTART by comparing its throughput/delay characteristics to those of other popular RAAs, including ALOHA and tree-search RAAs. For the latter RAAs, we also provide a unified stack representation of their operation.

The effect of analog video modulation on laser clipping noise in optical video-distribution networks

Laser clipping distortion has been shown to cause potentially severe bit-error-rate (BER) floors in hybrid fiber/coax (HFC) networks carrying a combination of analog and digital video signals. Previous experimental investigations have generally used unmodulated analog carriers to quantify the effects of laser clipping. This paper provides experimental measurements of clipping noise and BER performance when the analog carriers are modulated, as they would be in actual systems. Comparisons with the case of unmodulated carriers are also given. Dramatic reductions in clipping-related degradation are observed once the carriers are modulated, suggesting that laser clipping will not pose a significant impediment to digital transmission in future HFC networks.

Cable access beyond the hype: on residential broadband data services over HFC networks

Current efforts in digital data transmission over hybrid fiber coaxial (HFC) networks will provide an efficient data transport mechanism for the "last mile" to residential users and will enable a very large number of services to the home. Provision of these services requires a complete end-to-end network architecture that provides an efficient connection between the server and the end user. Thus, it is necessary for the currently isolated HFC islands to gradually evolve into an efficient, highly connected, high-speed network. In this article, the authors review HFC networks and establish that they provide a more attractive and promising solution than the alternatives for "last mile" connectivity to the home, such as telephone connections. A list of broadband services are listed that are enabled by the high-speed data capabilities of HFC networks, and the necessary end-to-end infrastructure to support these applications is described, as well as possible evolution and migration paths for developing these end-to-end network architectures.