融合网络传输性能的优化
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摘要
随着电信网、广播电视网以及互联网三网融合的进一步推进,各大运营商的业务互相渗透,衍生出了更加复杂的新业务,对网络系统提出了新的需求。对于广电运行商,有线电视网的双向网改造的日益深入和下一代广播电视网战略的进一步实施,用户的双向交互数据业务需求日益增加,使得对带宽资源的竞争也日益激烈。如何有效地利用已有的资源,保证业务的QoS需求,提高系统的传输效率,创造最大化的价值,是目前急迫需要解决的问题。
本文主要的研究目标在于定位融合网络环境下传输性能的瓶颈和影响因素的同时,提出适用于融合网络的解决方法与技术,着重解决IP over DVB封装协议和调度算法、传输控制协议TCP以及网络层与传输层协议报头优化在融合网络中面临的问题,对应的主要贡献和创新点总结如下所示。
首先研究IP over DVB封装协议和调度算法的优化,主要包括以下两点：
1.针对现有IP over DVB封装协议存在的硬件支持不好或者封装效率低下的问题,提出了一种兼容DSM-CC段格式的,支持将多个IP数据包在同一个封装段中传输的封装协议(高效段封装协议)。通过理论与实验证明该封装协议在保证一定灵活性的同时,与多协议封装相比,在实际实验场景中的封装效率平均提高1.4%,特别针对小数据包,如100字节的IP数据包,封装效率最大可由53.2%提升至95.7%。
2.针对DVB-C2下传统调度算法时延特性差和系统吞吐率下降的问题,提出了一种考虑DVB-C2链路容量可变且其数据调度与系统的传输效率紧耦合特点的两级调度模型,并在该模型的基础上,提出了考虑DVB-C2系统传输效率以及业务类型的二级调度算法。该模型与算法具有良好的时延特性、公平性和复杂度,而且仿真实验表明该模型与算法适用于链路容量变化的场景,与WRR等传统调度算法相比,更好的保证了业务的时延需求,系统的吞吐率提升了10.7%。
其次,研究融合网络传输控制协议TCP优化,主要贡献和创新点如下：
3.针对融合网络下传输控制协议TCP吞吐率降低的问题,提出了一种适用于融合网络的,基于区分数据包类型的分裂连接方法,并在有线电视网端采用了定制的TCP拥塞控制算法。仿真实验与分析表明本文所提算法与传统算法相比,具有更高的系统吞吐率。
4.为进一步提升融合网络中有线电视网端TCP性能和能够更好的满足业务QoS需求,提出了应用于有线电视网的,基于业务感知的跨层传输层协议优化方法：根据预分配的带宽以及业务的QoS需求,统计最小拥塞窗口,初始慢启动阈值以及最大拥塞窗口等参数。实验与分析表明,在带宽预分配网络环境中,与传统的TCP协议相比,所提算法在吞吐率、公平性、以及稳定性方面均有明显的提升,同时能够更好的满足业务的QoS需求。
最后,研究和解决网络层与传输层协议报头优化在融合网络中面临的问题：
5.为了减少IP/UDP协议报头冗余信息带来的额外开销,提高带宽利用率,结合传统报头压缩技术和融合网络的特点,提出了一种应用于HFC的IP/UDP报文传输优化方法,利用IP over DVB封装协议中reserved、MAC等字段或者逻辑通道定位方法等方式来唯一标识报文,压缩IP/UDP全部报头字段而不引入其他字段,提高了系统的报头压缩增益、时延增益、带宽增益以及封装效率,同时考虑终端不还原UDP/IP头部的情形,为终端提供灵活的接收方式。
6.针对TCP的SACK选项冗余信息的问题,为提升TCP性能,特别是非对称融合网络下的性能,提出了修正的自适应调整SACK机制,让SACK块描述字段大小根据网络实时特性进行自适应调整,并通过MA-SACK-Filtering机制,减少不必要的上行MA-SACK,最后通过仿真实验,验证了算法的有效性,与SACK算法相比,系统吞吐率最多提升了78.1%。
As the convergence of telecommunication network, broadcast network and Internet accelerates, the services of different network operators penetrate mutually, which will bring much more complex new service forms and propose additional demand for network system. For television network operators, with the development of two-way cable television network transformation and further implementation of the Next Generation Broadcast networks, the need for two-way interactive service increases day by day which leads to more competing for bandwidth resource. How to guarantee the QoS of service, improve the transmission efficiency of the system and create maximum value is an emergency problem.
The goal of this paper is to analyse the bottleneck and factors of the transmission performance and propose methods and techniques for converged network, which focus on handling with the problems of encapsulation protocol and data scheduling of IP over DVB, transport control protocol and the network layer and the transport layer protocols header optimization. The contributions and innovations are shown as below.
First, we study the improvement of encapsulation protocol and data scheduling of IP over DVB, mainly including following two aspects:
1. For badly hardware support or inefficient encapsulation problems of encapsulation protocol for IP over DVB, an encapsulation protocol called Effective Section Encapsulation(ESE), which is compatible with DSM-CC, is proposed. Multiple IP packets are allowed to be encapsulated in one section through ESE. As the simulation result shows, this new encapsulation method not only keeps flexibility, but also has higher encapsulation efficiency than MPE, especially for small packets, encapsulation efficiency can be improved from53%to95.7%when the length of IP packet is100B.
2. For the problems of traditional scheduling algorithm over DVB-C2, which include bad delay characteristics and decline in system throughput, a two-level scheduling model and corresponding adaptive scheduling algorithm against the characteristics of DVB-C2are proposed. The algorithm considers the transmission efficiency and types of service. Theoretical analysis and simulation shows that the model and algorithm has good delay characteristic, fairness and complexity, suitable for the scene that link capacity is volatile. What's more, it provides a better guarantee of delay requirement and throughput of the system (10.7%improvement) than the traditional scheduling algorithm, like WRR.
Then, the improvement of TCP over the converged network is studied:
3. For the problem that the throughput of TCP declines over the converged network, a split algorithm base on distinguishing packet type is proposed and a tailored TCP algorithm called controlledTCP for HFC which is single-hop route and controllable is proposed. Compared with customary algorithm, the proposed algorithm has a better throughput.
4. To improve the performance of TCP over the converged network and meet the QoS requirements of service, a cross-layer TCP optimization method base on service awareness is proposed. According to the pre-allocated bandwidth and QoS requirements, the minimum congestion window, the initial slow start threshold and the maximum congestion window are calculated. Theoretical analysis and simulation shows that compared with the traditional TCP algorithm, the proposed algorithm not only has a better performance in throughput, fairness and stability, but also meet the QoS requirements of service better.
Last, we focus on the problems that the network layer and the transport layer protocols header optimization over the converged network:
5. To save bandwidth and improve the utilization of bandwidth, an UDP/IP header compression method for HFC is proposed. The method utilizes the field in encapsulating protocol of IP over DVB like the reserved field and MAC field or the method to locate logical channel to identify the packet. The method compresses the entire head of IP/UDP by the information of the bottom layer protocol, and it provides a flexible receive mode for the terminal by considering the situation of no need to restore the UDP/IP head. The simulation shows that this method is more flexible and provides a better header compression, delay and bandwidth gain than other methods.
6. For the problem of TCP SACK option redundant information, in order to improve the performance of TCP, especially over the asymmetric converged network, a scheme called Modified Adaptive SACK Filtering is proposed, which adjusts the size of the block information in SACK option according to the real-time characteristics of network. Furthermore, the scheme decreases some useless MA-SACK packet to alleviate the process pressure of router. Based on the simulation results, the effectiveness is verified:compared with SACK, the throughput is promoted by78.1%at most.
本文主要的研究目标在于定位融合网络环境下传输性能的瓶颈和影响因素的同时,提出适用于融合网络的解决方法与技术,着重解决IP over DVB封装协议和调度算法、传输控制协议TCP以及网络层与传输层协议报头优化在融合网络中面临的问题,对应的主要贡献和创新点总结如下所示。
首先研究IP over DVB封装协议和调度算法的优化,主要包括以下两点：
1.针对现有IP over DVB封装协议存在的硬件支持不好或者封装效率低下的问题,提出了一种兼容DSM-CC段格式的,支持将多个IP数据包在同一个封装段中传输的封装协议(高效段封装协议)。通过理论与实验证明该封装协议在保证一定灵活性的同时,与多协议封装相比,在实际实验场景中的封装效率平均提高1.4%,特别针对小数据包,如100字节的IP数据包,封装效率最大可由53.2%提升至95.7%。
2.针对DVB-C2下传统调度算法时延特性差和系统吞吐率下降的问题,提出了一种考虑DVB-C2链路容量可变且其数据调度与系统的传输效率紧耦合特点的两级调度模型,并在该模型的基础上,提出了考虑DVB-C2系统传输效率以及业务类型的二级调度算法。该模型与算法具有良好的时延特性、公平性和复杂度,而且仿真实验表明该模型与算法适用于链路容量变化的场景,与WRR等传统调度算法相比,更好的保证了业务的时延需求,系统的吞吐率提升了10.7%。
其次,研究融合网络传输控制协议TCP优化,主要贡献和创新点如下：
3.针对融合网络下传输控制协议TCP吞吐率降低的问题,提出了一种适用于融合网络的,基于区分数据包类型的分裂连接方法,并在有线电视网端采用了定制的TCP拥塞控制算法。仿真实验与分析表明本文所提算法与传统算法相比,具有更高的系统吞吐率。
4.为进一步提升融合网络中有线电视网端TCP性能和能够更好的满足业务QoS需求,提出了应用于有线电视网的,基于业务感知的跨层传输层协议优化方法：根据预分配的带宽以及业务的QoS需求,统计最小拥塞窗口,初始慢启动阈值以及最大拥塞窗口等参数。实验与分析表明,在带宽预分配网络环境中,与传统的TCP协议相比,所提算法在吞吐率、公平性、以及稳定性方面均有明显的提升,同时能够更好的满足业务的QoS需求。
最后,研究和解决网络层与传输层协议报头优化在融合网络中面临的问题：
5.为了减少IP/UDP协议报头冗余信息带来的额外开销,提高带宽利用率,结合传统报头压缩技术和融合网络的特点,提出了一种应用于HFC的IP/UDP报文传输优化方法,利用IP over DVB封装协议中reserved、MAC等字段或者逻辑通道定位方法等方式来唯一标识报文,压缩IP/UDP全部报头字段而不引入其他字段,提高了系统的报头压缩增益、时延增益、带宽增益以及封装效率,同时考虑终端不还原UDP/IP头部的情形,为终端提供灵活的接收方式。
6.针对TCP的SACK选项冗余信息的问题,为提升TCP性能,特别是非对称融合网络下的性能,提出了修正的自适应调整SACK机制,让SACK块描述字段大小根据网络实时特性进行自适应调整,并通过MA-SACK-Filtering机制,减少不必要的上行MA-SACK,最后通过仿真实验,验证了算法的有效性,与SACK算法相比,系统吞吐率最多提升了78.1%。
As the convergence of telecommunication network, broadcast network and Internet accelerates, the services of different network operators penetrate mutually, which will bring much more complex new service forms and propose additional demand for network system. For television network operators, with the development of two-way cable television network transformation and further implementation of the Next Generation Broadcast networks, the need for two-way interactive service increases day by day which leads to more competing for bandwidth resource. How to guarantee the QoS of service, improve the transmission efficiency of the system and create maximum value is an emergency problem.
The goal of this paper is to analyse the bottleneck and factors of the transmission performance and propose methods and techniques for converged network, which focus on handling with the problems of encapsulation protocol and data scheduling of IP over DVB, transport control protocol and the network layer and the transport layer protocols header optimization. The contributions and innovations are shown as below.
First, we study the improvement of encapsulation protocol and data scheduling of IP over DVB, mainly including following two aspects:
1. For badly hardware support or inefficient encapsulation problems of encapsulation protocol for IP over DVB, an encapsulation protocol called Effective Section Encapsulation(ESE), which is compatible with DSM-CC, is proposed. Multiple IP packets are allowed to be encapsulated in one section through ESE. As the simulation result shows, this new encapsulation method not only keeps flexibility, but also has higher encapsulation efficiency than MPE, especially for small packets, encapsulation efficiency can be improved from53%to95.7%when the length of IP packet is100B.
2. For the problems of traditional scheduling algorithm over DVB-C2, which include bad delay characteristics and decline in system throughput, a two-level scheduling model and corresponding adaptive scheduling algorithm against the characteristics of DVB-C2are proposed. The algorithm considers the transmission efficiency and types of service. Theoretical analysis and simulation shows that the model and algorithm has good delay characteristic, fairness and complexity, suitable for the scene that link capacity is volatile. What's more, it provides a better guarantee of delay requirement and throughput of the system (10.7%improvement) than the traditional scheduling algorithm, like WRR.
Then, the improvement of TCP over the converged network is studied:
3. For the problem that the throughput of TCP declines over the converged network, a split algorithm base on distinguishing packet type is proposed and a tailored TCP algorithm called controlledTCP for HFC which is single-hop route and controllable is proposed. Compared with customary algorithm, the proposed algorithm has a better throughput.
4. To improve the performance of TCP over the converged network and meet the QoS requirements of service, a cross-layer TCP optimization method base on service awareness is proposed. According to the pre-allocated bandwidth and QoS requirements, the minimum congestion window, the initial slow start threshold and the maximum congestion window are calculated. Theoretical analysis and simulation shows that compared with the traditional TCP algorithm, the proposed algorithm not only has a better performance in throughput, fairness and stability, but also meet the QoS requirements of service better.
Last, we focus on the problems that the network layer and the transport layer protocols header optimization over the converged network:
5. To save bandwidth and improve the utilization of bandwidth, an UDP/IP header compression method for HFC is proposed. The method utilizes the field in encapsulating protocol of IP over DVB like the reserved field and MAC field or the method to locate logical channel to identify the packet. The method compresses the entire head of IP/UDP by the information of the bottom layer protocol, and it provides a flexible receive mode for the terminal by considering the situation of no need to restore the UDP/IP head. The simulation shows that this method is more flexible and provides a better header compression, delay and bandwidth gain than other methods.
6. For the problem of TCP SACK option redundant information, in order to improve the performance of TCP, especially over the asymmetric converged network, a scheme called Modified Adaptive SACK Filtering is proposed, which adjusts the size of the block information in SACK option according to the real-time characteristics of network. Furthermore, the scheme decreases some useless MA-SACK packet to alleviate the process pressure of router. Based on the simulation results, the effectiveness is verified:compared with SACK, the throughput is promoted by78.1%at most.
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