HFC网络MAC协议及碰撞解决

ＨＦＣ网络（混合光纤同轴网）采用树状拓扑结构,分布于较广的匹配,有较大的延时,这使得ＨＦＣ网络中的ＭＡＣ（介质访问控制）协议的设计成为一个值得研究的问题。本文对ＨＦＣ网络中几种有影响的ＭＡＣ协议进行了综述,重点介绍了ＩＥＥＥ８０２．１４工作组的８０２．１４草案３。ＨＦＣ网络介质访问控制协议中最有特色的是碰撞解决算法,８０２．１４协 采用ｐ坚持算法结合ｎ叉树算法,前者用于预先避免碰撞而后者用于解决已     

A review of contention resolution algorithms for IEEE 802.14 networks

Bidirectional Cable TV networks using hybrid fiber coaxial (HFC) systems are good examples of broadcast environments where a contention resolution algorithm is needed in order to allocate the multiaccess medium (in this case the upstream link) among the various nodes. Recent activities of the IEEE 802.14 Working Group aimed at defining the physical and medium access control (MAC) layer protocols for HFC cable networks have focused on the study and evaluation of several contention resolution solutions for inclusion in the MAC protocol specifications. In this article several contention resolution algorithms considered by the IEEE 802.14 group are reviewed. Different implementations for several well known contention resolution algorithms such as tree-based and p-persistence are presented. Their performance is evaluated in the HFC context with respect to upstream channel allocation, roundtrip delay, various traffic types, and number of stations in the network. Simulation results for configurations and scenarios of interest are also presented.     

Allocation and scheduling algorithms for IEEE 802.14 and MCNS inhybrid 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     

On IEEE 802.14 medium access control protocol

In this article we present a comprehensive survey on the architecture, protocol issues, and standard of the hybrid fiber coaxial (HFC) networks which are evolving from the existing residential CATV networks. We first describe the HFC architecture and discuss the problems in providing two-way communication. Then, we identify three important medium access control (MAC) issues in designing the IEEE 802.14 standard; namely, synchronization, upstream channel access modes, and collision resolution. Resolutions adopted by the IEEE 802.14 Committee are illustrated after giving a protocol overview. Key resolutions include compensating round trip correction (RTC), interleaving minislots of data and request concurrently, and resolving collisions by multiple collision resolution engines, using the n-ary tree plus p-persistence algorithm with a first transmission rule. A comparative summary of some draft proposals that lead to the standard is given. Finally, we pinpoint two headend algorithms, minislot allocation and request scheduling, which are left open in the standard. They do not affect interoperability but may have a critical impact on performance.     

利用HFC接入Internet的MAC层协议设计与分析

分析了HFC网络实现双向数据传输的结构,分析比较了802.14/DOCSIS规范,提出使用扩频技术可以获得稳固的传输特性,就S＿CDMA多址接入方式和M＿ary CDMA方式分别设计了Internet接入的MAC层协议-竞争/冲突解决和轮询机制,分析表明该协议简单有效,易于实现。     

Architecture and performance of a MAC protocol for the HFC system

The IEEE 802.14 standard committee is currently working on a project to find a cost-effective means of providing access to integrated networks for people to enjoy multimedia programs and to work at home. An advanced system based on the cable TV system called hybrid fibre coax (HFC) is being studied. Since some properties of the HFC system preclude the possibility of directly using existing medium access control (MAC) protocols for its data link layer, a MAC scheme based on time division is discussed in this paper. This MAC scheme can be extended for wireless networks. © 1997 John Wiley & Sons, Ltd.     

A dynamic control scheme for the IEEE 802.14 draft MAC protocolover CATV/HFC networks

We first describe the draft multiple/random access protocol for IEEE 802.14 over the cable TV/hybrid fiber coaxial (CATV/HFC) networks. To best fit this draft protocol into the target network, we propose a dynamic control scheme to adequately adjust the parameters. Simulations of the draft protocol are then presented to depict the effectiveness of the proposed scheme and further highlight the directions for the design of MAC protocols over the CATV/HFC networks     

MLAP: a MAC level access protocol for the HFC 802.14 network

Interactive residential broadband/multimedia services are expected to be the next main event in the cyberspace experience. The large excess bandwidth (well over 300 MHz) available in today's cable TV (CATV) hybrid fiber/coaxial (HFC) plants is an ideal candidate to provide the underlying communications infrastructure for interactive digital services to the home; cable operators that have not yet upgraded their all-coaxial plants to HFC are quickly moving in this direction. MLAP is a flexible ATM-friendly MAC protocol that is capable of supporting various types of traffic with diverse quality-of-service requirements. We introduce a very versatile MAC protocol for the HFC 802.14 network. MLAP can provide integrated broadband services to the home, internetwork easily with ATM wide area networks, support QoS constraints for various types of traffic, and operate over a variety of physical layer protocols. Our presentation is only an extended summary of our medium-sharing protocol proposal to the IEEE 802.14 WG. We consider only error-free system operation. MLAP provides for the use of timers for the recovery of error situations in the network. MLAP is also supported by a management suite of protocols for management of the overall system     

Performance evaluation of candidate MAC protocols for LMCS/LMDSnetworks

Broadband wireless access (BWA) offers attractive features such as ease and speed of deployment, fast realization of revenues, and low infrastructure cost. This paper focuses on medium access control (MAC) alternatives that can find application in an LMDS/LMCS network capable of supporting multimedia traffic. Multifrequency demand assignment TDMA-based schemes appear (at the moment) to be a suitable choice in this context. The selected protocol should be dynamically capable of providing multirate capabilities and quality-of-service guarantees. An obvious candidate for the aforementioned purpose is the LMDS-specific MAC proposal in the DAVIC 1.2 recommendation. For purposes of comparison, we also examine the evolving IEEE 802.14 MAC convergence protocol and MCNS (multimedia cable network system) DOCSIS (ITU J-112) MAC standard that are intended to support similar applications and services in an HFC (hybrid fiber coax) environment. The three protocols are examined under noiseless and noisy channel conditions. Previous results on LMDS channel characteristics are summarized and used for modeling noisy channel conditions. The candidate protocols are compared in terms of mean access delay, throughput, and collision multiplicity statistics, when contention of users is involved. The effect of dynamic slot allocation on the performance of the candidate protocols is also examined     

HFC网络中上行信道的MAC层协议性能分析

HFC(Hybrid Fiber Coaxial)作为一种主要接入网络,近年来受到了越来越深入的研究.HFC网络具有独特的树形-分支结构,其上、下行信道在频段上相互隔离,下行信道带宽较大,是一对多的广播信道,上行信道带宽较小,是多对一的共享信道.因此HFC网络的MAC(Medium Access Control)层协议设计重点,在于如何解决共享信道的接入冲突问题,以及如何提高上行信道的利用率和降低上行信道的接入延时.本文结合当前HFC网络中主要MAC层协议的设计思想,从本质上分析了影响协议性能的关键因素.通过对MCNS(The Multimedia Cable Network System)提出的MAC层协议——DOCSISv1.0(Data-Over-Cable Service Interface Specifications version 1.0进行仿真,有力证实了本文的分析结果,对我们进一步深入研究HFC网络接入技术具有很好的指导意义.     

Network architecture and medium access control for deploying third generation (3G) wireless systems over CATV networks

We propose a novel and cost‐effective approach for the deployment of third generation (3G) wireless systems over hybrid fiber coaxial (HFC) CATV networks. The main goal is to facilitate 3G deployment over the existing CATV plant and reduce the large cost required for building a dedicated last mile infrastructure for 3G access networks. Our proposal reduces the last mile cost by sharing the existing CATV network and using the standard equipment and protocols of data‐over‐cable systems interface specifications (DOCSIS). This allows rapid deployment of 3G wireless systems, facilitates convergence of wireless and wireline networks and paves the way towards all IP wireless networks. Enhancements to the DOCSIS medium access control (MAC) protocol must be implemented in order to support Quality of Service (QoS) guarantees for 3G data and signaling traffic. This paper presents the proposed 3G over CATV network architecture and DOCSIS medium access control (MAC) enhancements for enabling the support of QoS guarantees for 3G data and signaling traffic. The proposed MAC enhancements can reduce the access delay for delay‐sensitive traffic by 30 to 40% over existing DOCSIS MAC without compromising QoS guarantees for other traffic classes, or the DOCSIS channel utilization. Copyright © 2004 John Wiley & Sons, Ltd.     

基于HFC-CATV网的媒体访问控制协议

通过引入“组群 (cluster)”的概念 ,提出一种适用于HFC CATV网络的媒体访问控制 (MAC)协议的新结构模型 ,并分析该协议的工作原理和实现机制。     

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$etaleqq 1$, 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.     

基于DOCSIS的CM和CMTS的设计与实现

HFC（Hybrid Fiber Coax)为多媒体和宽带业务提供了一种宽带接入方式。本文论述了HFC接入网的结构和频谱安排,并结合HFC接入网的双向改造,对媒体接入层（MAC）和物理层（PHY）进行了具体分析,同时给出DOCSIS（Data-Over-Cable Service Interface Specification)规范中MAC协议解决上行信道分配问题的实现方法以及物理层的方案;最后,给出了符合DOCSIS规范的CM（Cable Modem）和CMTS（Cable Modem Terminal System)的软件和硬件实现方案。     

PCUP: pipelined cyclic upstream protocol over hybrid fiber coax

In order to bring the NII (National Information Infrastructure) into the home, the community cable TV networks have to be reengineered to support two-way interactive services. The authors propose the PCUP (pipelined cyclic upstream protocol) as the upstream MAC (medium access control) protocol for the HFC (hybrid fiber coax) community access network. The PCUP is designed with the intention of pipelining the upstream channel. This is achieved by proper station positioning, which measures the station propagation offset from the headend, and transmission scheduling which assigns each station a transmission starting time and duration in a cycle. By taking into account the propagation offsets and transmission lines, transmitted cells can appear back-to-back (i.e., pipelined) at the headend. Since only the active stations are scheduled to transmit in a cycle, a membership control mechanism, which runs a contention-based tree walk algorithm, is executed periodically to allow the stations to join or leave. The authors also compare the PCUP with various schemes proposed to the IEEE 802.14 committee     

A priority scheme for the IEEE 802.14 MAC protocol for hybridfiber-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     

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.     

HFC网络安全与加密机制的研究

增强型基线保密性接口（BPI＋）是一种基于DOCSIS标准的数据保密访问共享媒体的接口标准,利用BPI＋定义的多种密钥及管理协议可以在媒体访问控制层（MAC）解决HFC网络的数据安全问题。这种技术对开展HFC网络数据业务是十分重要的。     

Increasing fairness and efficiency using the MadMac protocol in ad hoc networks

The IEEE 802.11 MAC layer is known for its unfairness behavior in ad hoc networks. Introducing fairness in the 802.11 MAC protocol may lead to a global throughput decrease. It is still a real challenge to design a fair MAC protocol for ad hoc networks that is distributed, topology independent, that relies on no explicit information exchanges and that is efficient, i.e. that achieves a good aggregate throughput. The MadMac protocol deals with fairness and throughput by maximizing aggregate throughput when unfairness is solved. Fairness provided by MadMac is only based on information provided by the 802.11 MAC layer. MadMac has been tested in many configurations that are known to be unfair and compared with three protocols (IEEE 802.11 and two fair MAC protocols). In these configurations, MadMac provides a good aggregate throughput while solving the fairness issues.     

Performance issues with IEEE 802.11 in ad hoc networking

Although 802.11 is initially designed for infrastructure-based networks, the distributed coordination function allows mobiles to access the radio medium without the need for a base station. Thus, studies in wireless multihop networks, also called ad hoc networks, often rely on the use of IEEE 802.11 for the physical and MAC layers. However, for a couple of years the use of 802.11 in ad hoc networks has been discussed. Different scenarios show serious performance issues. The performance offered by 802.11 is often low and directly impacts the performance of higher-layer protocols. In this article we provide a summary of the different performance issues extracted so far. We classify basic situations according to the main effects. We then present a quick survey of the possible solutions to these problems. This classification is intended to help design appropriate MAC protocols dedicated to ad hoc networks.