Packet reassembly during cell loss

Asynchronous transfer mode (ATM) is a packet switched data transport system based on short, fixed length cells. Each cell carries a virtual channel indicator (VCI) and virtual path indicator (VPI) in its header. Essential to the services offered by the ATM networks is the ATM adaptation layer (AAL), an ITU-TSS defined layer that adapts the cell-based ATM physical layer to packet, datagram, or bit-stream-oriented higher layers. Failure modes causing cell loss along a virtual connection are examined, and the ways AALs cope are analyzed. The sources of cell loss and their effects on AAL3/4 or AAL5 type of service are described. The usefulness of the ability of AAL3/4 to pass fragments of corrupted data up to higher layer protocols is discussed, and the implementation of selective cell discarding within switching nodes is considered, and the limitations imposed by each AAL are examined     

B-ISDN and the OSI protocol reference model

The evolution of public telecommunication networks toward broadband integrated services digital networks (B-ISDNs) is presented. The asynchronous transfer mode (ATM), which supports B-ISDNs, and the B-ISDN protocol reference model are discussed. It is shown that the service offered by the ATM layer in the B-ISDN protocol reference model is equivalent to the service offered by the OSI physical layer. It is also shown that the service offered by the ATM adaptation layer (AAL) type 3/4 is similar to an OSI data link service. The emergence of the metropolitan area network (MAN) standard as an intermediate support for broadband services and the similarities between the DQDB MAC and the AAL type 3/4 in its connectionless mode are discussed     

Quality of service in telecommunications .II. Translation of QoSparameters into ATM performance parameters in B-ISDN

The main goal of this article is to present the translation of quality of service (QoS) parameters between layers. The QoS parameters in the ATM layer and AAL are defined. This translation concept came from the QoS framework in which the influence of the protocol stack on the QoS should be considered. As an example, we concentrate on the translation from the AAL to the ATM layer, as the AAL must be designed to be service-dependent and specific. Translation, both taking the transport protocol into account as well as between application and transport QoS, needs further study. However, our study shows that the QoS translation is a possible and good approach in end-to-end QoS guarantees in the broadband integrated services digital network (B-ISDN). As far as the end-to-end QoS guarantee issue is concerned, the transport QoS requirements are specified in terms of bounds on transport QoS parameters. The bounds on transport QoS parameters will be translated into the bounds on ATM layer QoS parameters. The ATM-layer QoS parameters resulting from the translation will be the performance requirements on a connection basis for the ATM network, but are basically the end-to-end parameters, including the network and the end systems. Therefore, the QoS translation finally results in the network performance parameters in the ATM network. We define QoS parameters in the AAL and ATM layer. Case studies in which the translation method is applied to a constant bit rate (CBR) video service and data service, respectively, are also presented     

宽带ISDN与ATM交换技术第二讲B－ISDN用户－网络接口和协议（下）

宽带ＩＳＤＮ与ＡＴＭ交换技术第二讲Ｂ－ＩＳＤＮ用户－网络接口和协议（下）刘斌（清华大学计算机系北京１０００８４）３ＡＴＭ层前面在介绍ＡＴＭ的基本概念和ＡＴＭ层功能时，已涉及许多有关ＡＴＭ层的内容，这里对一些细节再作补充。简单地讲，ＡＴＭ层的任务就是为...     

Error detection and correction options for data services in B-ISDN

The authors investigate error detection and correction options for data services in the broadband integrated services digital network (B-ISDN). They discuss and analyze different options for error detection and correction by considering the various alternatives ranging from no error protection to only error detection. Based on the analysis and results presented, a per-cell cyclic redundancy check (CRC) has been adopted in the adaptation layer for all data services. The authors focus on the ATM (asynchronous transfer mode) adaptation layer (AAL) error protection alternatives available within the framework of a per-cell CRC. The ATM cell header and AAL fields are described. A 4 bit cell sequence number for detecting cell misordering is analyzed. Based on the analysis, it is concluded that the 4 bit sequence number provides a powerful capability for detection of cell misordering     

适应多媒体业务的ATM适配层AAL2

介绍了ＩＴＵ Ｔ建议Ｉ．３６３．２中定义的新型ＡＴＭ适配层ＡＡＬ２,包括协议的细节及ＡＡＬ２的应用实例。与其他ＡＡＬ协议相比,ＡＡＬ２的优点在于更强的业务适应能力和高效的频带利用率,因此是传输多媒体业务的较佳ＡＴＭ适配类型。     

A new ATM adaptation layer for TCP/IP over wireless ATM networks

This paper describes the design and performance of a new ATM adaptation layer protocol (AAL‐T) for improving TCP performance over wireless ATM networks. The wireless links are characterized by higher error rates and burstier error patterns in comparison with the fiber links for which ATM was introduced in the beginning. Since the low performance of TCP over wireless ATM networks is mainly due to the fact that TCP always responds to all packet losses by congestion control, the key idea in the design is to push the error control portion of TCP to the AAL layer so that TCP is only responsible for congestion control. The AAL‐T is based on a novel and reliable ARQ mechanism to support quality‐critical TCP traffic over wireless ATM networks. The proposed AAL protocol has been validated using the OPNET tool with the simulated wireless ATM network. The simulation results show that the AAL‐T provides higher throughput for TCP over wireless ATM networks compared to the existing approach of TCP with AAL 5. This revised version was published online in July 2006 with corrections to the Cover Date.     

AAL2—一种新的ATM适配技术

由于支持短分组网络业务的需要，促使人们发展新的ＡＴＭ适配技术。文章论述了一个新的ＡＴＭ适配技术ＡＡＬ２的背景、适配技术的基本要求和实现的基本原理，并把ＡＡＬ２的适配能力与其它适配技术相比较，论证了ＡＡＬ２在支持短分组业务中不可替代的优势。     

Cell-loss concealment techniques for layered video codecs in an ATMnetwork

A layered video coding scheme with its inherent cell loss resilience has been considered as a means for transporting reliably integrated video services over an asynchronous transfer mode (ATM) based network such as the broadband-ISDN. This paper presents some data concealment techniques that can be implemented in the coding of video data at the encoder, in the ATM adaptation layer (AAL) functionality of network realization and at the decoder to improve the performance of a layered codec under different conditions of video packet loss. The performance of these techniques are verified by software simulations.     

1MPC8280的AAL2适配与DMA通道驱动软件的实现

在TD-SCDMA网络中,ATM适配层采用AAL5和AAL2处理ATM数据。由于目前大部分网络处理器都只支持AAL5的适配,不适合TD网络测试仪的应用。本文介绍了TD-SCDMA网络测试仪中基于PowerPC8280的ATM数据采集与DMA传输的实现方案,重点说明了AAL2适配以及利用PCI的DMA传输完成上层应用与底层硬件的数据交互。实际应用表明,文中提出的数据采集卡能够正确处理ATM协议的AAL2适配和DMA传输。     

A novel delineation mechanism for the ATM adaptation layer 2 over wireless ATM networks

The ATM adaptation layer 2 (AAL2) has been standardized by the ITU‐T for the support of low data rate and delay‐sensitive applications, such as voice, over ATM networks. One of the main characteristics of the AAL2 standard is the support for multiplexing information at the expense of introducing a new frame structure inside the payload of the ATM cells. The AAL2 standard introduces a mechanism for the delineation of the AAL2 packets and it has been found that the delineation mechanism reduces the performance of AAL2 in the presence of channels with high bit error rates. In this paper, a novel delineation mechanism is proposed for AAL2 to be used over highly error‐prone channels, such as wireless links. The proposed mechanism improves the performance (i.e. reduces packet loss) of the AAL2 standard in the presence of bit errors and in some cases reduces the overhead required for the delineation of the AAL2 packets. Copyright © 2002 John Wiley & Sons, Ltd.     

QoS guarantees for multimedia services on a TDMA-based satellitenetwork

This article describes a proposed network architecture for both the ground and space segments of a satellite network supporting multimedia services with quality of service (QoS) guarantees. The space segment proposal is geared toward a TDMA-based satellite network comprising many nongeostationary satellites, while the ground segment proposal does not put any restriction an the satellite network. The ground segment proposal is based on the new ATM adaptation layer 2 (AAL2) which we consider to have a major role to play in offering an efficient way to provide multimedia services over ATM networks. Indeed, it allows easy encapsulation of the complete set of media component sessions which forms a multimedia transaction into a single ATM virtual channel connection. An additional advantage of AAL2 is that it can run over any arbitrary slotted access system independent of the ATM format (i.e., without transporting the ATM cell headers). This is important for efficient interfacing of the ground and space segments. The space segment proposal aims at providing a robust, easily managed and controlled architecture to guarantee QoS by using a combination of connectionless and connection-oriented techniques. This is achieved by: defining a fixed logical network architecture (i.e., independent of the motion of the satellites); limiting the functionality of the switches in the sky; and using adequate addressing and routing procedures     

ATM支持中低速话音业务的新方案

时延和效率问题是ＡＴＭ不能很好地支持中、低速话音业务的关键,因此,ＩＴＵ－Ｔ提出了新型ＡＡＬ２规程－组合信元技术。ＡＡＬ２规程的基本思想是用一个ＡＴＭ连接支持多个ＡＡＬ２用户信息流,从而减少时延。ＡＡＬ２由公共部分子层（ＣＰＳ）和业务特定会聚子层（ＳＳＣＳ）组成,其中面向话音应用的ＳＳＣＳ是中、低速话音业务解决方案的核心,文中对其功能、业务、等时同步问题的解决等作了详细介绍。最后,还介绍了有关标准     

Designing a practical ATM LAN

The adaptor cards and driver software for workstations and local asynchronous transfer mode (ATM) switches and switch control software used in an ATM local area network (LAN) system are discussed. It is shown that the ATM hardware and software components together provide services that are essential for ATM to be considered a realistic alternative to current shared-media LANs. These services include: completely transparent support for the TCP/IP protocol suite, an application programming interface for full access to the underlying ATM capabilities, support for AAL5, AAL3/4, and the null AAL, both connection-oriented and connectionless service, dynamic connection establishment or switched virtual circuits, resource reservation of guaranteed bandwidth and quality of service, full-bandwidth multicast and broadcast, virtual path and channel routing among multiple switches, automatic configuration and failure recovery, dynamic address assignment and internetwork address resolution, and network management via the simple network management protocol (SNMP)     

Cells-In-Frames: a system overview

Cells-In-Frames provides an efficient mechanism for integrating both voice and data traffic on an existing campus network that is currently supporting legacy LAN workstations. The solution suggested by this article is to export ATM services within standard LAN frames. Each frame will carry the traffic from one or more ATM cells, but any given LAN frame is associated with only one ATM virtual circuit. The widely different qualities of service required for voice and data traffic is achieved rough the use of AAL1 and AAL5 services. The AAL functions are split appropriately between the workstation and the LAN switch that interfaces to an ATM backbone network. With the use of the Q.2931 signalling protocols defined for ATM, Cells-in-Frames achieves a long-sought-after goal of providing switched networking services to LAN-attached workstations     

MPEG—2在ATM网络的传输

随着ATM技术和编码技术的成熟,ATM上可以传送增强型媒体,这使得视听业务的广泛应用成为可能,主要讨论在ATM网络上恒定比特率（CBR）或可变比特率（VBR）的MPEG-2的传输,这涉及到适配层的选择,MPEG-2帧的封装,ATM业务类型的选择等问题。     

Performance modeling of partial packet discarding using theend-of-packet indicator in AAL type 5

The ATM adaptation layer type 5 (AAL5) is an adaptation layer protocol for the ATM layer of broadband integrated services digital networks (BISDNs), which targets connection-oriented services. Among several features, it is unique in the sense that it includes an end-of-packet (EOP) indicator in the header of the ATM cell (the ATM-layer-user-to-ATM-layer-user (AUU) parameter in the payload type (PT) field). It was suggested that the use of this indicator may be used to provide a means by which buffer occupancy can be reduced by selectively dropping cells from already incomplete packets [Armitage and Adams, 1993]. The objective of this paper is to study the performance of this layer and the effectiveness of the EOP indicator. The performance measures of interest are the probability of packet loss and the mean packet delay. An approximate analytical model is constructed in which the blocking of a tagged source is kept track of in an exact manner. The rest of the sources are modeled approximately. The accuracy of the model is enhanced through an iterative approach. A simulation model is also constructed to assess the accuracy of the approximate model     

The jitter time-stamp approach for clock recovery of real-timevariable bit-rate traffic

When multimedia streams arrive at the receiver, their temporal relationships may be distorted due to jitter. Assuming the media stream is packetized, the jitter is then the packet's arrival time deviation from its expected arrival time. There are various ways to reduce jitter, which include synchronization at the application layer, or synchronization at the asynchronous transfer mode (ATM) adaptation layer (AAL). The new source rate recovery scheme called jitter time-stamp (JTS) provides synchronization at the ATM adaptation layer 2 (AAL2) which is used to carry variable bit-rate traffic such as compressed voice and video. JTS is implemented, and experiments have shown that it is able to recover the source rate     

基于FPGA的ATM层与适配层的设计与实现

文中介绍了ATM网络各层工作原理和FPGA的结构及工作原理．结合ATM网络各层的处理过程，重点阐述了ATM网络各层在FPGA中的硬件结构及实现，提出了一种基于FPGA的ATM层和适配层处理的实现方案．     

ATM网络安全技术

指出了ATM网络存在的安全威胁,讨论了ATM网络的数据加密技术、完整性服务等ATM网络安全技术。在基于将ATM的安全层置于AAL层和ATM层之间的观点上,本论文设计了一个数字签名结构和密钥交换协议,该协议作为呼叫建立过程的一部分,嵌于现存的ATM信今协议中。这些安全技术可透明地加入到B—ISDN的协议参考模型中,无需改变现存的协议标准。