基于LZSS的SIP压缩算法改进研究

3GPP在R5版本中首次提出了IP多媒体子系统（IMS）的概念,SIP协议被选择为呼叫会话控制协议。由于SIP是基于文本的协议,在会话过程中需要重传大量的数据,导致在会话建立过程中时延的增加。文中在分析现有的SIP信令压缩算法的基础上,提出了一种带有预处理的LZSS与算术编码相结合的改进算法。首先对消息进行预编码,然后进行LZSS压缩,压缩完后与算术编码相结合,这种改进后的算法减少了信令传输延迟。文中运用典型的SIP会话环境进行仿真实验,其结果验证了改进算法能够有效地提高性能,缩短消息长度和减小传输时延。     

一种新的基于IMS的SIP重传机制

目前,IP多媒体子系统（IMS）中基于会话初始化协议（SIP）的会话建立时间受到无线信道约束带宽、帧错误率（FER）值的影响,交换的消息数量、消息长度以及重传机制对于会话建立的时延有很大的影响,延长了会话建立的时间。将基于SIP的会话建立与无线信道的性能结合,提出一种新的SIP自适应重传机制。实验结果表明,该重传机制缩短了会话建立的时间,对IMS端到端的服务质量（QoS）性能有明显的改善。     

IMS中基于LZSS的SIP信令压缩算法研究

3GPP在R5核心网引入了IMS结构，并选择会话初始协议（SIP）作为呼叫/会话的控制信令。但在无线环境下消息过长成为SIP在IMS中的应用瓶颈。在SigComp框架下，对各种压缩算法进行了比较，并根据SIP消息特点选择LZSS算法作为SIP信令压缩的基本算法。为了进一步提高SIP信令的压缩比，提出了LZSS＋Huffman的压缩算法及其实现流程，并对算法的压缩效果进行了仿真分析。     

SIP协议在IMS中的应用研究

基于SIP协议的IMS系统是未来3G时代实现多媒体应用的关键组成部分,与之相关的标准已经成为通信和网络界的研究热点。本文在介绍IMS系统架构和SIP信令协议的基础上,分析了IMS系统和SIP协议的实体对应关系,最终提出了一套基于IMS系统,两个用户终端如何通过SIP信令机制建立多媒体通信的解决方案。通过该方案可以实现全IP网络架构下的从终端注册,到会话建立,最终拆除会话完整的多媒体业务流程。     

基于SigComp的会话初始化协议压缩算法

独立媒体服务(IMS)是第三代合作伙伴计划(3GPP)在版本5中提出的支持IP多媒体业务的子系统,而基于文本的SIP消息过大成为其在IMS无线环境应用下的瓶颈,因此采用会话初始化协议（SIP）来建立和维护多媒体会话。在SigComp框架下,将改进后的LZSS算法与算术编码相结合对SIP信令进行压缩。实验表明新的算法有较高的压缩率,对改善IMS的SIP会话建立延时有一定的参考价值。     

SIP协议在IMS中建立实体会话的应用研究

首先简要介绍了IMS和SIP协议,通过分析IMS系统中多实体会话建立的信令流程,阐述了SIP在IMS系统中的应用,并对现有SIP消息的结构进行扩展,解决终端之间提供/应答的不匹配情况.     

IMS中一种新的SIP压缩机制

3G IP多媒体子系统（IMS）中采用会话发起协议（SIP）建立和维护多媒体会话,然而,SIP是基于文本的协议,在会话建立过程中需要传输大量的数据,导致会话建立时延的增加。对经典的LZW算法进行改进,将LZW与HUFFMAN算法和静态字典相结合,提出S-LZW-HUFFMAN算法实现对SIP消息的压缩。仿真结果表明,新算法比目前标准化组织建议采用的压缩算法具有更高的压缩效率,能够有效降低传输时延,缩短IMS中基于SIP的会话建立时延。     

IMS网络应用SIP协议的时延改进策略研究

介绍了IMS网络系统与SIP协议在IMS网络中的应用,在设定的网络仿真环境前提下,设计并且建立了IMS网络会话的仿真模型以及会话流程.通过采用OPNET网络仿真软件仿真指出IMS网络应用SIP协议呼叫时延的产生原因,通过设计引入"前提"的概念来改进时延,并且利用OPNET网络仿真工具通过仿真比较验证了该方案的有效性和正确性.     

下一代网络多媒体会话中H.248与SIP之间协议协作的研究

H.248和SIP是下一代电信网络的两个核心协议,通过H.248和SIP之间的协作来完成多媒体会话的建立、调整和删除是在下一代网络中实现多媒体业务需面临的重要问题。文章在深入研究H.248和SIP协议的基础上针对协议协作的应用环境抽象了一个协作模型。依据此模型,对两方多媒体会话和多方多媒体会话中各信令交互阶段H.248和SIP之间的协作进行了详细阐述。对H.248和SIP协议之间协作的研究可以应用到下一代电信网络的工程技术领域。     

基于SIP协议的WebRTC信令研究与应用

在近年来随着用户对音视频通话质量要求的提高,WebRTC以其强大的多媒体处理能力得到了广泛的应用.然而WebRTC提供的JSEP是一种弱信令,在企业级的融合通信应用中必须将WebRTC与实际的信令协议相结合.SIP是IMS的核心技术,对多媒体会话的控制起着非常重要的作用.本文介绍了WebRTC和SIP协议融合的已有方案,研究了WebRTC和SIP协议互通需要解决的问题,提出了一种WebRTC的PeerConnection层和SIP协议在客户端的融合方案,并和其他方案对比,得出该方案的优缺点.     

A Cross-Layer Analysis of Session Setup Delay in IP Multimedia Subsystem (IMS) With EV-DO Wireless Transmission

This paper analyzes the session setup delay in the IP multimedia subsystem (IMS) with the CDMA2000 evolution data only rev. A (EV-DO rev. A) standard for wireless transmission. Session setup delay is particularly critical for interactive multimedia applications, such as gaming, push-to-X and voice over IP (VoIP), as it directly translates in user perception of service quality. Keeping signaling delay low, however, is a challenge in IMS due to the text-based nature of the session initiation protocol (SIP) for signaling, and, more significantly, due to the lossy and capacity constrained wireless links. To address this challenge, we analyze the session setup delay end-to-end, by taking into account key system properties across all layers, ranging from radio links to IMS signaling architecture. We present a model for cross-layer performance analysis and simulation, which includes the statistical properties of the EV-DO (rev. A) wireless channel, and also takes into consideration the properties of transport protocols (TCP, UDP) and SIP signaling (message size and compression). By means of analysis and simulations, we study the setup delay performance of a generic, multi-operator IMS communication scenario between two mobile users. We describe how session setup delay can be estimated and reduced in realistic IMS settings and we propose architecture alternatives to the basic IMS scenario. The results derived from this study show that the proposed methods can incrementally lead to a lower setup delay and less sensitivity to the radio transmission quality and frame error rate compared to the base IMS scenario     

基于服务质量的多媒体通信初始路由建立算法的研究

基于服务质量的路由选择机制是从根本上提供分布式多媒体应用所需的服务质量保证的重要手段之一。该文提出了两种基于服务质量的多媒体通信初始路由建立算法。一种算法支持在两个通信方之间建立基于服务质量的初始路由,既可以作为点对点多媒体通信的基于服务质量的路由选择／初始路由建立算法,也可以作为初始成员为两个的多媒体动态组通信的基于服务质量的初始路由建立算法,另一种算法支持在多个通信方之间建立基于服务质量的初始路由,既可以作为多媒体静态组通信的基于服务质量的路由选择／初始路由建立算法,也可以作为初始成员为多个的多媒体动态组通信的基于服务质量的初始路由建立算法,文中还探讨了这两种算法的正确性。     

基于服务质量的多媒体组通信目的节点加入与退出算法的研究

路由选择机制是分布多式媒体系统中的重要研究方向。其中,基于服务质量的多媒体通信目的节点加入与退出算法是关键组成部分。该文在基于服务质量的多媒体通信初始路由建立算法的基础上,基于资源共享原则,提出支持成员动态加入与退出多媒体组通信的目的节点加入与退出算法,以增加使用费用最小为目标在满足服务质量约束的条件下完成目的节点加入,在不影响多媒体组通信服务质量的前提下,在完成目的节点退出的同时最大限度地释放已占用资源。文中还探讨了这些算法的有效性。它们和基于服务质量的多媒体通信初始路由建立算法相结合,可以提供对分布式多毁体组应用服务质量保证的支持。     

Interworking of heterogeneous access networks and QoS provisioning via IP multimedia core networks

Moving towards packet networks, where IP will have a prominent role, constitutes nowadays a widely accepted perception of future communications, the first instance of which has begun to materialise with the IP multimedia core network subsystem (IMS). By specification, IMS is the first implementation towards reaching converged communications which allows users to communicate with video, audio and multimedia content, via any fixed, mobile and wireless access network type, with controllable QoS. To enable IMS communications across heterogeneous networks, incorporating UMTS, WLAN and fixed IP access points, 3GPP and ETSI’s TISPAN currently work on schemes for controlling bandwidth allocation at the service level by employing logical interfaces that carry SIP messages. This article analyzes how interconnection between such heterogeneous networks may be performed on real platforms. In this effort, special attention is paid to the way the various interconnection possibilities can affect end-to-end QoS provisioning.     

Algorithms for delay-constrained low-cost multicast tree construction

With the proliferation of multimedia group applications, the construction of multicast trees satisfying quality of service (QoS) requirements is becoming a problem of prime importance. Multicast groups are usually classified as sparse or pervasive groups depending on the physical distribution of group members. They are also classified based on the temporal characteristics of group membership into static and dynamic groups. In this paper, we propose two algorithms for constructing multicast trees for multimedia group communication in which the members are sparse and static. The proposed algorithms use a constrained distributed unicast routing algorithm for generating low-cost, bandwidth and delay constrained multicast trees. These algorithms have lower message complexity and call setup time due to their nature of iteratively adding paths, rather than edges, to partially constructed trees. We study the performance (in terms of call acceptance rate, call setup time and multicast tree cost) of these algorithms through simulation by comparing them with that of a recently proposed algorithm (V. Kompella, J.C. Pasquale, G.C. Polyzos, Two distributed algorithms for the constrained Steiner tree problem, in: Proc. Comp. Comm. Networking, San Diego, CA, June 1993) for the same problem. The simulation results indicate that the proposed algorithms provide larger call acceptance rates, lower setup times and comparable tree costs.     

QoS Control for NGN: A Survey of Techniques

This article presents an overview of standards and a survey of recent work on quality of service (QoS) control of next generation networks (NGNs). We outline primarily standardized QoS control architectures with respect to the service and transport strata of NGN. In the service stratum, QoS parameter negotiation using core IP multimedia subsystem (IMS) procedures is described. In the transport stratum, the resource control and admission schemes of IMS (3GPP), resource admission control function (ITU-T), and resource access control system (ETSI/TISPAN) are explained and compared with each other in terms of QoS coverage and number of required signaling messages. In addition, we give a survey of papers on QoS control architectures, which further strengthen existing standards by adaptively managing QoS modification according to user’s QoS changes and consistent QoS support for mobile users. Finally, we conclude this article with a discussion of further work of the QoS control for NGN.     

IMS 中基于策略QoS 管理模型

IMS（IP多媒体子系统）给客户带来丰富的多媒体体验的同时,也对服务质量（QoS）管理提出了更高的要求,即针对不同用户定制的不同服务,网络运营商应该制定差异化的策略进行QoS管理。3GPP定义了基于策略的QoS管理框架,但这个框架只是逻辑上的架构,没有定义具体物理实施的方案。对基于策略QoS管理模型进行了分析,在参照3GPP定义的标准基础上,提出了一种管理模型的实现方案,设计并实现了该模型中两个关键服务器策略决策服务器（PDF）和策略执行服务器（PEP）。经过测试,两个服务器能互相配合,正确完成查询策略信息,做出策略决策,执行带宽请求预留、QoS等级协商功能,为网络运营商提供了参考。     

Dynamic bandwidth allocation for 3G wireless systems—A fuzzy approach

3G Wireless systems are to support multiple classes of traffic with widely different characteristics and quality of service (QoS) requirements. A major challenge in this system is to guarantee the promised QoS for the admitted users, while maximizing the resource allocation through dynamic resource sharing. In the case of multimedia call, each of the services has its own distinct QoS requirements concerning probability of blocking (P_B), service access delay (SAD), and access delay variation (ADV). The 3G wireless system attempts to deliver the required QoS by allocating appropriate resources (e.g. bandwidth, buffers), and bandwidth allocation is a key in achieving this. Dynamic bandwidth allocation policies reported so far in the literature deal with audio source only. They do not consider QoS requirements. In this work, a fuzzy logic (FL)-based dynamic bandwidth allocation algorithm for multimedia services with multiple QoS (P_B, SAD, ADV, and the arrival rate) requirements are presented and analyzed. Here, each service can declare a range of acceptable QoS levels (e.g. high, medium, and low). As QoS demand varies, the proposed algorithm allocates the best possible bandwidth to each of the services. This maximizes the utilization and fair distribution of resources. The proposed allocation method is validated in a variety of scenarios. The results show that the required QoS can be obtained by appropriately tuning the fuzzy logic controller (FLC).