Data Over Cable Service Interface Specification Research Articles

The behavior of TCP over DOCSIS-based CATV networks

This paper studies the impact of the data-over-cable service interface specification (DOCSIS) media-access control (MAC) protocol on the performance of the transmission control protocol (TCP) in hybrid fiber coax (HFC) broadband access networks. We find that the asymmetry ratio expressed in existing work cannot adequately explain the behavior of TCP in DOCSIS-based networks. To better capture the effect of DOCSIS on TCP, we express the asymmetry ratio (denoted by eta) in another way (denoted by k), considering the time-division multiple-access-like MAC layer operation of DOCSIS. When eta>1, TCP behaves as in a symmetric network, and when etales1, the system acts as in an asymmetric network, and the performance of TCP degrades. We find that the number of simultaneous TCP transfers significantly affects the asymmetry ratio. When the number of active transfers is below two times the maximum number of pending requests in a transmission period, the value of eta is larger than one, regardless of the value of k. However, when the number of active transfers becomes very large, the effect of DOCSIS on TCP becomes negligible, and the asymmetry ratio is determined by the bandwidth ratio of the channels times the length ratio of data and acknowledgement packets. Based on eta, we develop the round-trip delay of sending a data packet for both one-way and two-way transfers, and discuss the buffer requirement at the head end. The accuracy of the analytical model is validated by ns-2 simulations. The analytical result can provide useful guidelines in the design of slot allocation or scheduling mechanisms for any DOCSIS-based broadband access networks, including the emerging IEEE 802.16 WiMAX networks

DOCSIS Performance Analysis Under High Traffic Conditions in the HFC Networks

Hybrid Fiber Coaxial (HFC) networks provide a wide bandwidth and represent the solution of choice for many residential networks nowadays. The Data Over Cable Service Interface Specification (DOCSIS) protocol is an important standard for HFC networks and is supported by the majority of current vendors. This protocol uses the Truncated Binary Exponential Back-off (TBEB) algorithm to resolve collisions within the network by means of a back-off window. However, the performance of this algorithm tends to deteriorate when the network load is high. Consequently, the present study develops a novel mathematical model for the TBEB algorithm and then uses this model to identify the window size which yields the optimal system throughput and minimum delay time under high traffic conditions. The present numerical results confirm that the performance is improved when the window settings identified from the developed model are applied.

Full-duplex DOCSIS/WirelessDOCSIS fiber-radio network employing packaged AFPM-based base-stations

The simultaneous wireline (600 MHz) and wireless (5.5 GHz) transmission of data over cable service interface specification (DOCSIS) signals in a hybrid fiber-radio access network is presented. The DOCSIS signal wireless replica is generated by means of an optical harmonic up-conversion technique based on a dual-drive Mach-Zehnder modulator. The optical signal is fed to a base station (BS) where a packaged asymmetric Fabry-Pe/spl acute/rot modulator/detector acts simultaneously as a photodetector and an optical modulator. At the BS, the DOCSIS signals can be fed either to a wireline or a wireless access network, in a highly flexible approach. Full-duplex operation has been demonstrated for both access types, including indoor wireless transmission.

How DOCSIS Protocol Solves Asymmetric Bandwidth Issue in Cable Network

Since the high bandwidth and popular usage are the characteristics of cable network, it becomes one of the main solutions for residential network. The cable network is a kind of asymmetric bandwidth architecture, which generates certain performance issues. This article first discusses the issues stemmed from asymmetric bandwidth. It then briefly introduces Data over Cable Service Interface Specifications (DOCSIS) protocol, the most popular standard for cable network today. The rest of the article discusses the operations and mechanisms in DOCSIS protocol that solve those performance issues and other possible improvements in cable network.

A New Carrier Recovery Loop for High-Order Quadrature Amplitude Modulation

In this paper, we present a new all-digital carrier recovery loop for high-order quadrature amplitude modulation (QAM) signal constellations. The proposed approach is a blind phase-frequency detector structure that consists of a phase detector, a phase offset estimator, a frequency offset estimator, and a digital control oscillator. Compared to previous related approaches, the proposed algorithm provides a wider acquisition range and a more accurate estimation of frequency and phase offsets. These features are demonstrated by simulation results of the DOCSIS (Data-Over-Cable Service Interface Specifications) cable modem system.

VoIP services with embedded CAC over cable modem systems

VoIP (voice over Internet protocol) technology has rapidly been growing up recently, which transmits voice packets by using the user datagram protocol (UDP). VoIP quality is difficult to expect because it is hard to predict the influence of packet delay, packet lose, packet error, etc. This paper proposes an embedded call admission control (CAC) mechanism by applying real-time transfer protocol (RTP) and the real-time control protocol (RTCP) for VoIP services over hybrid fiber/coaxial (HFC) networks. The proposed CAC mechanism is evaluated by the impact of the various traffic load in cable modem termination system (CMTS), which estimates how VoIP quality satisfies the user's requirements under different constrains on cable networks. We discuss VoIP CAC mechanism for the upstream channel according to the data over cable service interface specifications (DOCSIS) version 1.1 and particularly consider G.723.1 voice packets at the transmission rate of 6.3 kbps. The performance measurement of the proposed embedded CAC mechanism is obtained by simulation experiments under various network constrains, which includes throughput, packet dropping ratio and call blocking ratio. Obviously this paper provides an efficiency and fast method for CMTS to decide how many calls can be accepted.

Scheduling Delay Minimization for Non-UGS Data in Multi-Channel HFC Network

SUMMARY The multi-channel Hybrid Fiber Coaxial (HFC) network is essentially a shared medium with multi-channels. Its operation requires the use of a scheduling algorithm to manage the data transmission within each channel. The Data-Over-Cable Service Interface Specification (DOCSIS) protocol is an important standard for HFC networks. Since this protocol does not explicitly specify the scheduling algorithm to be used, many alternative algorithms have been proposed. However, none of these algorithms are applicable to the scheduling of non-Unsolicited Grant Service (UGS) data in multi-channel HFC networks. Accordingly, the present study develops a multi-channel scheduling algorithm which optimizes the scheduling delay time of each transmitted non-UGS request. This algorithm manages the amount of data transmission in each upstream channel according to the overall network load and the bandwidth available in each channel. This study constructs a mathematical model of the algorithm and then uses this model as the basis for a series of simulations in which the performance of the scheduling algorithm is evaluated.

객체지향 모델링을 이용한 케이블 데이터 가입자 망관리 시스템의 설계 및 구현

가입자 망에는 ADSL(Asymmetric Digital Subscriber Line), VDSL(Very high-bit rate Digital Subscriber Line), DOCSIS(Data Over Cable Service Interface Specifications) 등이 있으며, 다양한 형태가 있다. 다양한 종류의 접속방식과 이 기종의 장비를 이용하여 가입자에게 단일 형태의 초고속 인터넷 서비스를 제공하고 있다. 이러한 여러 가지 분산된 가입자 망을 효율적으로 관리하기 위해서는 다양한 형태의 접속방식을 지원하는 이 기종 장비 및 단말들의 상위 개념으로서 추상적이며 개념적인 객체 관리모델이 필요하다. 본 논문은 통합된 계층적 망 관리를 가능하게 하는 인터넷 가입자 망에 대한 모델링 구조를 RM-ODP를 이용하여 제시하였다. 그리고 가입자 망의 예로서 UML을 이용한 객체지향 방법론을 채택하여 DOCSIS의 HFC 가입자망에 대한 관리 시스템을 설계하고 구현하였다. There exist several types of distributed subscriber networks using Asymmetric Digital Subscriber Line(ADSL), Very high -bit rate Digital subscriber Line(VDSL), and Data Oner Cable Service Interface Specifications(DOCSIS). The efficient and concentrated network management of those several distributed subscribers networks and resources requires the general management information model of network, which has abstract and conceptual managed objects of the heterogeneous networks and its equipment to manage the integrated subscriber network. This paper presents the general Internet subscribers network modeling framework using RM-ODP to manage that network in the form of integrated hierarchy. This paper adopts the object-oriented development methodology with UML and designs and implements the HFC network of DOCSIS as an example of the subscriber network.

Improved priority access, bandwidth allocation and traffic scheduling for docsis cable networks

The Data Over Cable Service Interface Specifications (DOCSIS) is intended to support IP flows over HFC (hybrid fiber/coax) networks with significantly higher data rates than analog modems and Integrated Service Digital Network (ISDN) links for high quality audio, video and interactive services. To support quality-of-service (QoS) for such applications, it is important for HFC networks to provide effective media access and traffic scheduling mechanisms. In this paper, we first present a multilevel priority collision resolution scheme with adaptive contention window adjustment. The proposed collision resolution scheme separates and resolves collisions for different traffic priority classes (such as delay-sensitive and best effort streams), thus achieving the capability for preemptive priorities. Second, a novel MAC (media access control) scheduling mechanism and a new bandwidth allocation scheme are proposed to support multimedia traffic over DOCSIS-compliant cable networks. It is shown through simulation results that throughput and delay performance have been improved for the transmission of real-time VBR (variable bit rate) traffic as compared to current DOCSIS specifications.

Packet acquisition in upstream transmission of the DOCSIS standard

In upstream transmission of the DOCSIS (data over cable service interface specification) 1.0/1.1 and the TDMA mode of DOCSIS 2.0 standard, a packet begins with a preamble, the length and value of which are programmable by the headend. The acquisition process includes packet detection, symbol timing estimation, carrier frequency offset estimation and carrier phase estimation by means of the preamble so that the following information packet can be correctly demodulated. Methods to solve these tasks are not subject to standardization and are left to the system designer. However, they have a great impact on the system performance and thus are key elements for implementation. We present dedicated algorithms. A specific preamble is created and the corresponding scheme for packet acquisition is described in some detail. The packet detecting algorithm is independent of the carrier and symbol timing. The symbol timing estimate is obtained by using the minimum mean square algorithm regardless of the carrier frequency deviation and carrier phase. Algorithms for estimating the carrier frequency offset and carrier phase are proposed. Computer simulation results are given for all algorithms presented.

An Analytical Model for the Performance of the DOCSIS CATV Network

The Data Over Cable Service Interface Specification (DOCSIS) is established as the primary cable network data communication standard inNorth America and is the first specification having reached international standard level. It is therefore appropriate to determine its performance. Previous works on performance analysis of the DOCSIS Community Antenna Television network have been carried out using computer simulations. In this paper, we propose a model for mini-slot allocation with two priority classes of traffic which supports a real-time Constant Bit Rate (CBR) service and a non-real-time data service. Real-time CBR traffic has pre-emptive high-over-line priority over non-real-time data traffic. The service discipline is First Come First Served. Two critical characteristics, average delay and throughput, are analysed. Finally, numerical results are presented. The results demonstrate that the delay requirement of real-time CBR traffic can be easily met at the expense of the delay of non-real-time data traffic.

A novel mechanism for providing service differentiation over CATV network

With the emersion of new types of applications on the Internet, the need of broadband access is unavoidable. It also makes the differentiation of services provided by the network necessary. One of the most competitive broadband access solutions is Cable TV network since it is a network now in widespread use with enough bandwidth. Among the protocols of digital data-over-cable, Multimedia Cable Network System (MCNS) Data-Over-Cable Service Interface Specifications (DOCSIS) is the most popular standard nowadays. Based on this standard, we proposed a novel mechanism that can provide service differentiation over cable network. We explain the detail operation and interaction of each part of the system in this paper. Simulation is used to find out the performance on two subjects. First, MAC protocol configurations and parameters are discussed. Second, we compare various scheduling methods for providing service differentiation in the headend. From the results, the proposed mechanism is applicable and the characteristics of key parameters are found.

Recovery analysis of the DOCSIS protocol after service disruption

Wide scale power outages can cause serious disruptions to digital services over community antenna television (CATV) networks. This can result in long service recovery times for some or all of the cable modems (CMs). In this paper, the recovery mechanisms of the Data Over Cable Service Interface Specification (DOCSIS) protocol, due to service disruption, are studied. We propose a new scheme for the ranging of modems, namely persistent ranging algorithm (PRA) and two different simulation models have been developed for this purpose. The simulation results show that the static nature of the registration and initialization parameters can introduce an excessive delay in the recovery time of the system. Minimum recovery times of 820 s and 975 s (two ranging opportunities/second) for network architectures with 400 CMs and 500 CMs, respectively, on a single upstream channel were obtained. In order to validate the accuracy of the simulation models a set of experiments was performed on a CATV network testbed. The testbed results revealed that the simulation models produced are realistic and offer reliable estimates of large-scale network topologies. Extensions to the DOCSIS MAC protocol in which the status of the system prior to disruption is used have reported a decrease of up to 42% in the recovery time of the system.

An investigation into HFC MAC protocols: Mechanisms, implementation, and research issues

This study comprehensively reviews two HFC MAC protocols: Data-Over-Cable Service Interface Specifications (DOCSIS) and IEEE 802.14a. DOCSIS was approved by the ITU as a standard and is supported by many vendors. However, IEEE 802.14a remains a draft due to the delayed standardization process. After briefly introducing the features of HFC networks, the basic operations and mechanisms of these two MAC protocols are then examined. Both standards view an upstream channel as a stream of minislots and have similar mechanisms for upstream bandwidth management, virtual queue, downstream in MPEG-2 format, data-linklayer security, and ranging. However, the standards adopt different mechanisms for upstream access modes, QoS support, and collision resolution. Moreover, the implementation issues over hardware and software design for DOCSIS networks are investigated. This work also identifies the research issues in HFC MAC protocols, particularly allocation and scheduling issues.

Performance characterisation of the MCNS DOCSIS 1.0 CATV protocol with prioritised first come first served scheduling

The Multimedia Cable Networks Systems (MCNS) Data Over Cable Service Interface Specifications (DOCSIS) is established as the primary cable network data communications standard. The head-end scheduling algorithm is not defined within the standard but it is the key function for providing the required performance capability. Computer simulation, using the Common Simulation Framework (CSF) 12 version of the CableLabs DOCSIS 1.0 computer model, has been used to predict the upstream system throughput and mean access delay. A prioritised first come first served scheduling algorithm has been considered to provide a baseline reference set of performance statistics against which other algorithms can be compared. The simulations, with theoretical confirmation, have shown that the maximum sustainable system throughput is 1965 kbps for a channel capacity of 2560 kbps and a packet size of 1500 octets, whereas for packet size of 100 octets the maximum sustainable throughput is only 1550 kbps. The mean access delay is found to vary between 10-900 ms depending on the offered load and assuming that the offered load does not exceed the capacity of the channel. Excess offered load causes service starvation according to the assigned priority.

Erroneous MPEG packet synchronization in the MCNS/SCTE/ITU-T J.83 Annex B standard

This paper presents a phenomenon with repeating data packets sent according to the MCNS (multimedia cable network system) DOCSIS (data over cable service interface specification)/SCTE (Society of Cable Telecommunication Engineers)/ITU-T 5.83 Annex B standard. When repeating packets are received by a receiver, the receiver may erroneously lock onto the bit stream and produces incorrect MPEG packets. Repeating packets are usually not generated in practical systems. They are, however, easy to generate and preferred in a testing environment during product development. A system vendor may unknowingly encounter this phenomenon and incur delays in product designs in trying to solve this apparent error. This paper presents the mathematical background on the cause of this phenomenon.