Transport architecture evolution in UMTS/IMT‐2000 cellular networks

Mobile evolution from the second generation (2G) to the third generation (3G) raises several important questions for operators and manufacturers. How to ensure that the old and current investments can still be utilized in the future? What is the optimum architecture? ATM or IP? Voice or data? There is no single correct answer to these questions, as it all depends on individual cases. In this paper, we discuss the transport architecture evolution for the universal mobile telecommunications system (UMTS)/international mobile telecommunications—year 2000 (IMT‐2000), or 3G cellular networks and interworking aspects between 2G and 3G cellular networks. The interfaces between access nodes in a cellular network and the changes incorporated to support packet data services are described. Emerging services such as mobile data, virtual private networks (VPN) and location aware networking are described. Role of ATM and IP in this new transport architecture is presented. Control and data plane interworking issues between different transport technologies are described. The new ATM standard, ATM adaptation layer type 2 (AAL2) and its applicability for transporting compressed speech in an ATM based cellular network is described. A similar approach in IP, multiplexing in real‐time transport protocol (RTP) payload to transport compressed speech on selective interfaces of 3G network, is introduced. Transport network architecture evolution within four different scenarios is evaluated. Special interest is focused on the protocol stacks and flexible layered solutions that allow smooth migration from one transport technology to another. Copyright © 2000 John Wiley & Sons, Ltd.     

Broadband Network Delivery of Interactive Digital Video Using ATM

The integrated digital multimedia video service can be delivered via different network media such as Hybrid Fiber Coax (HFC) and Fiber to the Curb (FTTC). Asynchronous Transfer Mode (ATM) can be used as an effective transport mechanism for the digital video services, such as MPEG-2. Both the lower layer physical network topology/characteristics and network protocols impose special technical constraints on the overall digital video system design.The system issues on network delivery of digital video discussed in this paper include: (1) Overall network impact and system protocol stack for HFC and FTTC video delivery; (2) Interactivity of digital video and its signaling; (3) Quality of Service (QoS) impact on digital video coding algorithm.Finally, the future directions on the networked video field are discussed and implementation choice and migration strategy are briefly analyzed.     

QoS Provisioning in Wireless IP Networks

This paper deals with quality of service (QoS) provision in wireless IP networks. QoS provision is particularly challenging in wireless networks, where network resources are generally limited, variable over time and shared. In the design of possible measures to assure QoS one should consider that standardization is well established for the network layer Internet Protocol and for many underlying technologies of frequent use (e.g. IEEE 802.11, BLUETOOTH or HIPERLAN II). Therefore, as far as research on QoS is concerned, there is little room in both the IP and the link-layers for improved IP over wireless interfaces. In this paper we illustrate a solution in which an intermediate Wireless Adaptation Layer (WAL) is transparently interposed between the IP layer and specific link-layer technologies as a solution to provide QoS. The WAL addresses two main issues: (i) compensation for channel impairments in different platforms in order to enhance wireless channel reliability and (ii) implementation of traffic control and packet scheduling mechanisms to satisfy bandwidth and delay requirements, as well as to enforce a general principle of fairness among the IP associations contending for network resources and achieve optimal exploitation of transmission capacity. The WAL consists of a set of modules, each one in charge of a specific task, which can be enabled or disabled depending on the specific network environment. The novelty of the WAL approach is its capability of adapting itself to different wireless interfaces selecting performance enhancing modules for specific networks. This requires to modify the standard TCP/IP protocol stack by introducing an intermediate layer between the IP layer and the Data Link layer, with performance enhancement purposes. This paper focuses on two modules in particular, namely a traffic control module, which is in charge of performing congestion control and channel state dependent scheduling (CSD) packet scheduling, and a forward error correction (FEC) module, which compensates for channel impairments. This paper presents the proposed architecture provided with these modules and reports some measurements and simulations highlighting benefits resulting from the use of such modules.     

Challenges and opportunities of delivering IP-based residential television services

This article describes the main challenges of implementing an end-to-end architecture for delivery of high-quality, IP-based residential TV services to residential customers. The IP-based approach can be implemented with an IP multicast overlay network with traditional routers or use IP-multicast-aware ATM switching systems. Both approaches use IP multicast to transport MPEG-2 broadcast video and can work on any access architecture, especially on copper-based architectures (xDSL) such as ASDL and VDSL. The main challenges met while implementing the IP-based architecture are competitive positioning relative to traditional CATV architectures, overall architecture, head-end architecture and quality issues, traffic engineering for stringent QoS requirements, IP multicast requirements, and business case considerations. The IP-based approach described leverages Internet technology advancements and capitalizes on the impacts of Internet on interactive entertainment. Video channel manipulation at the head-end is dependent on access bandwidth and affects video quality. Video traffic management to meet stringent QoS requirements is challenging at the IP layer. High-capacity, responsive IP multicasting is essential to achieving high service quality. Cost-effective IP multicasting is a critical component of the business case.     

网络融合的趋势分析和展望

下一代网络业务、控制、承载、接入分离的思想为未来网络融合提供了统一的架构。网络融合包括业务融合、核心网络融合、接入网络融合、终端融合、运维融合等多个方面。未来融合网络的发展趋势将是在核心控制层采用IP多媒体子系统(IMS),在核心承载层采用因特网协议/多协议标记交换(IP/MPLS)技术,在业务层采用统一开放的业务提供架构,在接入层支持固定、移动、窄带、宽带等多种接入技术,终端则呈现多模化和智能化的趋势,最终实现一个用户、一个号码、一个终端、一个账单、一个核心网络、随时随地享受的全业务模式。     

A New Transport Protocol for Broadcasting/Multicasting MPEG-2 Video Over Wireless ATM Access Networks

Because of the telecommunications de-regulation act and progress in wireless technologies, we will see the co-existence of heterogeneous broadband access infrastructures in the broadband video service industry in the near future. In this paper, we addressed the error control issue when transmitting MPEG-2 video streams over wireless access networks for broadband video broadcast or multicast services. An end-to-end transport protocol based on ATM and wireless ATM technologies is proposed. For video services, the underlying transport network should be transparent and quality should be maintained uniformly over all the segments whether wireline or wireless links. For network resources to be used efficiently, error control should be applied locally on the wireless segments so as to avoid the excessive overhead over the reliable wireline portions. Because a broadband video broadcast or multicast service is a one-to-multiple point service, FEC is the most prevalent error control mechanism. Due to the important role of MPEG-2 control information in the decoding process, priority MPEG-2 control information has to be differentiated from MPEG-2 data information, and excess error protection has to be allocated to it in order to achieve satisfactory QoS. Therefore, a header redundancy FEC (HRFEC) scheme for error control is applied at the local distribution centers before the MPEG-2 encoded video streams are transmitted over the wireless channels. HRFEC is an FEC-based selective protection scheme, which allocates extra error protection to important control information. Simulation results show that the quality of the reconstructed video sequence is vastly improved by using HRFEC, when the channel condition is poor.     

基于交互式抗误码技术的H.263编解码器

目前，在IP分组网中进行视频图像的传输正被日益广泛地应用。但是，由于IP分组网固有的特点，IP分组包丢失的现象不可避免并极大地影响了视频传输的服务质量。本文通过对一种使用连续更新来阻止差错传播（RESCU）的交互式抗误码技术进行改进，实现了一种新的交互式抗误码方法。同时，我们根据这种方法实现了一种具有良好差错恢复能力的H．263编解码器，从而改善了因分组包丢失对视频传输质量带来的影响。     

A Practical RTP Packetization Scheme for SVC Video Transport over IP Networks

Scalable video coding (SVC) has been standardized as an extension of the H.264/AVC standard. This paper proposes a practical real‐time transport protocol (RTP) packetization scheme to transport SVC video over IP networks. In combined scalability of SVC, a coded picture of a base or scalable enhancement layer is produced as one or more video layers consisting of network abstraction layer (NAL) units. The SVC NAL unit header contains a (DID, TID, QID) field to identify the association of each SVC NAL unit with its scalable enhancement layer without parsing the payload part of the SVC NAL unit. In this paper, we utilize the (DID, TID, QID) information to derive hierarchical spatio‐temporal relationship of the SVC NAL units. Based on the derivation using the (DID, TID, QID) field, we propose a practical RTP packetization scheme for generating single RTP sessions in unicast and multicast transport of SVC video. The experimental results indicate that the proposed packetization scheme can be efficiently applied to transport SVC video over IP networks with little induced delay, jitter, and computational load.     

Dissecting the performance of YouTube video streaming in mobile networks

Video streaming applications constitute a significant portion of the Internet traffic today, with mobile accounting for more than half of the online video views. The high share of video in the current Internet traffic mix has prompted many studies that examine video streaming through measurements. However, streaming performance depends on many different factors at different layers of the TCP/IP stack. For example, browser selection at the application layer or the choice of protocol in transport layer can have significant impact on the video performance. Furthermore, video performance heavily depends on the underlying network conditions (eg, network and link layers). For mobile networks, the conditions vary significantly, since each operator has a different deployment strategy and configuration. In this paper, we focus on YouTube and carry out a comprehensive study investigating the influence of different factors on streaming performance. Leveraging the Measuring Mobile Broadband Networks in Europe (MONROE) test bed that enables experimentation with 13 different network configurations in four countries, we collect more than 1800 measurement samples in operational mobile networks. With this campaign, our goal is to quantify the impact of parameters from different layers on YouTube's streaming quality of experience (QoE). More specifically, we analyze the role of the browser (eg, Firefox and Chrome), the impact of transport protocol (eg, TCP or QUIC), the influence of network bandwidth, and signal coverage on streaming QoE. Our analysis reveals that all these parameters need to be taken into account jointly for network management practices, in order to ensure a high end‐user experience.     

Unified transport layer support for data striping and host mobility

Data striping across multiple network interfaces and its applications to mobile environments was recently investigated (Phatak and Goff, 2002). Therein, a network-layer Internet protocol (IP)-in-IP encapsulation mechanism was proposed to aggregate the bandwidth of multiple network paths by striping a single transport layer [transmission control protocol (TCP)] connection across them. The analysis and experimental results from that study demonstrated fundamental limitations to TCPs performance in such scenarios. In this paper, we therefore propose a method of overcoming these limitations by striping data at the transport layer. For a proof-of-concept demonstration we use a substantially enhanced version of the stream control transmission protocol (SCTP). Our analytical results and experimental data illustrate that there are significant advantages to using a transport protocol with native support for the simultaneous use of multiple network interfaces, as opposed to stretching TCP to a point where it is no longer effective. This work naturally leads to another fundamental issue of end-to-end support for host mobility at the transport layer. Our analysis and results demonstrate that transport layer support for multiple network (IP) interfaces, together with the capability to dynamically add or delete IP addresses can yield the following advantages: higher bandwidth, load balancing, and increased fairness, enhanced reliability, and end-to-end support for host mobility. This is independent of the underlying network-layer and, hence, is applicable to static/wired, as well as wireless/ad hoc environments. The proposed protocol offers a unified solution to both data striping across multiple networks interfaces, as well as end-to-end mobility support.     

OMAC: A new access control architecture for overlay multicast communications

Multicast communications concern the transfer of data among multiple users. Multicast communications can be provided at the network layer—an example is IP multicast—or at the application layer, also called overlay multicast. An important issue in multicast communications is to control how different users—senders, receivers, and delivery nodes—access the transmitted data as well as the network resources. Many researchers have proposed solutions addressing access control in IP multicast. However, little attention has been paid to overlay multicast. In this paper, we investigate the access control issues in overlay multicast and present OMAC: a new solution to address these issues. OMAC provides access control for senders, receivers, and delivery nodes in overlay multicast. The proposed architecture, which is based on symmetric key cryptosystem, centralizes the authentication process in one server whereas it distributes the authorization process among the delivery nodes. Moreover, delivery nodes are utilized as a buffer zone between end systems and the authentication server, making it less exposed to malicious end systems. To evaluate our work, we have used simulation to compare the performance of OMAC against previous solutions. Results of the simulation show that OMAC outperforms previous multicast access control schemes. Copyright © 2010 John Wiley & Sons, Ltd.     

Scalable video coding over RTP and MPEG-2 transport stream in broadcast and IPTV channels - seamless content delivery in the future mobile internet

The ITU-T and ISO/IEC standard for scalable video coding was recently finalized. SVC allows for scalability of the video bitstream in the temporal, spatial, or fidelity domain, or any combination of those. Video scalability may be used for different purposes, such as saving bandwidth when the same media content is required to be sent simultaneously on a broadcast medium at different resolutions to support heterogeneous devices, when unequal error protection shall be used for coverage extension in wireless broadcasting, as well as for rate shaping in IPTV environments. Furthermore, it may also be useful in layered multicast transmission over the Internet or peer-to-peer networks, or in any transmission scenario where prioritized transmission for network flows is meaningful. In order to make usage of SVC in the aforementioned use cases, standards for defining the transport format and procedure are required. Therefore, we give a detailed overview of the recently finished SVC standards on transport over IP/RTP and the MPEG-2 transport stream. Both standards are important for IPTV and video on demand, where the first is important for SVC transport over mobile broadcast/multicast channels, and the latter is also important for SVC transport over traditional digital broadcast channels.     

Wireless video applications in 3G and beyond

This article surveys wireless video applications that have been commercialized recently or are expected to go to market in 3G (and beyond) mobile networks, mainly covering error control technologies in view of "wireless video." We introduce several related 3GPP standards including circuit-switched multimedia telephony, end-to-end packet-switched streaming, multimedia messaging service, and multimedia broadcast /multimedia service. We also review the supporting technologies for those four applications. The article concludes with a discussion of error control and rate control adaptability to network QoS variation, which is distinct from wired networks and critical to wireless networks. With respect to MBMS, we point out that required cell transmission power is crucial when realizing meaningful multicast coverage, and suggest a system that integrates different unicast and multicast networks, application-layer data repair, and transmission scheduling.     

Advances in network-supported media delivery in next-generation mobile systems

This article presents new concepts for network-supported media delivery in mobile networks. Automatic composition and merging of networks are central parts of these concepts. Media delivery is no longer an end-to-end service that only uses the network as an IP transport. Instead, these concepts create a service-aware network and provide customized delivery support through per-service overlay networks. They also integrate specialized processing nodes as part of the delivery topology, which include transcoders but also more complex processors, such as localized program insertions or personalized spam control. This article describes the underlying concepts and how these new network capabilities for media delivery services are requested, invoked, and managed.     

基于IP网络的视频会议系统关键技术

随着Internet的迅猛发展和多媒体技术的进步,在IP网络上开展视频会议受到了人们的广泛重视.本文分析了基于IP网络的视频会议系统的特点,详细讨论了在IP网络中实现视频会议系统所需要解决的3个关键问题:会议系统可以采用的不同结构和标准,不同的呼叫控制实现方式,传输的协议选择和QoS保障.     

Flexible Network Support for Mobile Hosts

Fueled by the large number of powerful light-weight portable computers, the expanding availability of wireless networks, and the popularity of the Internet, there is an increasing demand to connect portable computers to the Internet at any time and in any place. However, the dynamic nature of a mobile host's connectivity and its use of multiple network interfaces require more flexible network support than has typically been available for stationary workstations.This paper introduces two flow-oriented mechanisms, in the context of Mobile IP , to ensure a mobile host's robust and efficient communication with other hosts in a changing environment. One mechanism supports multiple packet delivery methods (such as regular IP or Mobile IP) and adaptively selects the most appropriate one to use according to the characteristics of each traffic flow. The other mechanism enables a mobile host to make use of multiple network interfaces simultaneously and to control the selection of the most desirable network interfaces for both outgoing and incoming packets for different traffic flows. We demonstrate the usefulness of these two network layer mechanisms and describe their implementation and performance.     

A survey of inter-domain peering and provisioning solutions for the next generation optical networks

The emergence of carrier grade transport technologies has led to a paradigm shift in inter-domain routing which became an important feature of the transport layer based on optical transmission and switching. While the new technologies have capabilities to provide end-to-end guaranteed quality of service (QoS), the lack of inter-operability between different technologies, administrative areas and control planes makes interdomain peering and provisioning below the conventional Internet Protocol (IP) layer a challenge. In this survey, we analyze various multi-domain routing models for emerging Layer 2 and WDM switched networks which have been proposed till date, and based on that survey, we highlight some open issues and future challenges pertaining to scalability, reliability, multi-domain QoS, control plane interworking and dynamic peering.     

End-to-end optimized TCP-friendly rate control for real-time video streaming over wireless multi-hop networks

Rate control is an important issue in video streaming applications. The most popular rate control scheme over wired networks is TCP-Friendly Rate Control (TFRC), which is designed to provide optimal transport service for unicast multimedia delivery based on the TCP Reno’s throughput equation. It assumes perfect link quality, treating network congestion as the only reason for packet losses. Therefore, when used in wireless environment, it suffers significant performance degradation because of packet losses arising from time-varying link quality. Most current research focuses on enhancing the TFRC protocol itself, ignoring the tightly coupled relation between the transport layer and other network layers. In this paper, we propose a new approach to address this problem, integrating TFRC with the application layer and the physical layer to form a holistic design for real-time video streaming over wireless multi-hop networks. The proposed approach can achieve the best user-perceived video quality by jointly optimizing system parameters residing in different network layers, including real-time video coding parameters at the application layer, packet sending rate at the transport layer, and modulation and coding scheme at the physical layer. The problem is formulated and solved as to find the optimal combination of parameters to minimize the end-to-end expected video distortion constrained by a given video playback delay, or to minimize the video playback delay constrained by a given end-to-end video distortion. Experimental results have validated 2–4 dB PSNR performance gain of the proposed approach in wireless multi-hop networks by using H.264/AVC and NS-2.     

多层网络中的生存性策略

多种不同层次技术的融合是现代通信网络的一大特点,同时也它带来了多层网络中故障恢复机制的协调问题。首先对多层网络中涉及到的各种生存性问题进行了概述,然后在IP/optical网络结构下,详细介绍分析了多层网络中的各种生存性策略。最后,给出了在多层网络中如何选择相应的生存性策略的指导方针。