An application‐ and management‐based approach to ATM scheduling

Two frame‐based ATM scheduling strategies, Delayed Frame Queueing (DFQ) and Virtual Frame Queueing (VFQ), are described for real‐time network applications. Both strategies guarantee explicit upper bounds on delay and jitter on a per virtual connection (VC) basis without relying on per‐VC queueing. They also resolve the disadvantages often associated with other frame‐based schedulers. The DFQ scheduler employs Resource Management cells to enable work‐conserving forwarding at intermediate nodes while retaining the option for non‐work‐conserving forwarding at terminal nodes. This allows delay bounds to be uncoupled from jitter bounds. The VFQ scheduler requires no such overhead cell transmissions, but is more limited in its ability to uncouple these two types of bounds. ATM network simulation results indicate that both proposed disciplines offer favorable multiplexing performance in comparison to a well documented high performance service discipline. Finally, we contrast our proposal against the significant difficulties that alternative scheduling strategies based on bandwidth guarantees will face with regard to network management and network synthesis issues. This revised version was published online in June 2006 with corrections to the Cover Date.     

Congestion control for multimedia services

The problem of congestion control in high-speed networks for multimedia traffic, such as voice and video, is considered. It is shown that the performance requirements of high-speed networks involve delay, delay-jitter, and packet loss. A framing congestion control strategy based on a packet admission policy at the edges of the network and on a service discipline called stop-and-go queuing at the switching nodes is described. This strategy provides bounded end-to-end delay and a small and controllable delay-jitter. The strategy is applicable to packet switching networks in general, including fixed cell length asynchronous transfer mode (ATM), as well as networks with variable-size packets     

Real-time multimedia scheduling policies for end-to-end delayjitter and loss guarantees across ATM satellite systems

We propose a simple first-in first-out (FIFO)-based service protocol which is appropriate for a multimedia ATM satellite system. The main area of interest is to provide real-time traffic with upper bounds on the end-to-end delay, jitter, and loss experienced at various service queues within a satellite network. Various service protocols, each based on a common underlying strategy, are developed in light of the requirements and limitations imposed at each of the satellite's subsystems. These subsystems include the uplink (UL) earth station (ES) service queue, on-board processing (OBP) queues, and the downlink (DL) ES service queue feeding into a wireline ATM network or directly to an end-user application. Numerous network simulation results demonstrate the tractability, efficiency, and versatility of the underlying service discipline. Key features of our strategy are its algorithmic and architectural simplicity, its non-ad-hoc scheduling approach, and its unified treatment of all real-time streams at all service queues. In addition, the delay and jitter bounds are uncoupled. In this way, end-to-end jitter can be tightly controlled even if medium access requires long indeterminate waiting durations     

Toward a broadband congestion control strategy

The congestion control problem in asynchronous transfer mode (ATM) based broadband networks is defined. In general, a suitable set of congestion controls will include features for admission control, buffer and queue management, traffic enforcement, and reactive control. The leading alternatives for each of these congestion control features are summarized. An approach for choosing the best of these alternatives is presented, and a reasonable set of such alternatives that captures the increased utilization due to statistical multiplexing is suggested. It uses separate and static bandwidth pools for each service category; a statistical multiplexing gain determined for each bandwidth pool that supports a variable-bit-rate (VBR) service category; traffic enforcement on a virtual circuit basis using a leaky bucket algorithm with parameters set to accommodate anticipated levels of cell transfer delay variation; and multilevel loss priorities as well as a reactive control for appropriate VBR service categories based on multithreshold traffic enforcement and explicity congestion notification     

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     

Analysis of interdeparture processes for bursty traffic in ATMnetworks

Admission control in asynchronous transfer mode (ATM) networks is considered. An ATM switch is modeled as a discrete-time single-server queue at which the following three different kinds of arrival processes are allowed to join together: arrivals of cells with a general interarrival time distribution; Bernoulli arrivals of cells in batches; and interrupted Poisson processes. An exact analysis is given to derive the waiting-time distributions and interdeparture-time distributions for arriving cells subject to admission control in ATM networks. The model is extended to approximately obtain the end-to-end delay distributions for the designated traffic stream. Such an analysis is important for voice or coded video because they require a playout mechanism at the destination. Since the analysis is approximate, the simulation results needed to assess its accuracy are provided. Numerical examples show how the traffic characteristics of the designated traffic stream are affected by the total traffic load at the switching node, the number of other bursty traffic sources, and the degree of burstiness of the traffic source itself     

Developing a cohesive traffic management strategy for ATM networks

The background and some of the rationale for the development of an asynchronous transfer mode (ATM) traffic management framework to support the wide variety of services to be carried over the B-ISDN are discussed. The advantages of statistical, as opposed to deterministic, multiplexing are examined. Given the anticipated B-ISDN service characteristics, two classes of quality of service are defined based on cell delay and cell loss. The key ATM traffic management tools are reviewed. These tools are broadly classified as either preventive, limiting the total amount of traffic admitted to the network in order to virtually eliminate probability of cell-level congestion, or reactive, assisting the network and individual connections to avoid the onset of congestion and minimize its severity when it does occur. A strategy for the initial introduction and the long-term evolution of an ATM traffic management framework is described     

Performance management issues of currently operated ATM enterprisenetworks

The author proposes a solution for the allocation and balancing of resources to maximize available bandwidth shared among corporate users. Currently established broadband virtual private networks (BVPNs) based on asynchronous transfer mode (ATM) technology comprise ATM cross-connects (ATM-CCs) and a lot of intelligent customer premises equipment (CPE). The CPE, an intelligent ATM service switcher or ATM multiplexer, enables the corporate user to connect routers, private branch exchanges (PBXs), or codecs onto the ATM network. One fundamental characteristic of CPE is that it is capable of accumulating asynchronous and synchronous traffic which may belong to different corporate users' sites. A typical example given of a BVPN configuration serving two corporate network users with four user sites each. In general, each user site needs to exchange asynchronous (connectionless) data streams for the inter-local area network (LAN) communication and synchronous (connection-oriented) data streams with constant bit rates for video/voice communication. The configuration and the performance aspects of inter-LAN communications employing a connectionless server (CLS) are discussed. The bandwidth allocation aspects of the BVPN having to convey synchronous and asynchronous traffic in an ATM environment without a CLS are discussed, including the bandwidth allocation algorithm. The important characteristics of the proposed algorithm is also summarised     

Intelligent voice smoother for silence-suppressed voice overInternet

When transporting voice data with silence suppression over the Internet, the problem of jitter introduced from the network often renders the speech unintelligible. It is thus indispensable to offer intramedia synchronization to remove jitter while retaining minimal playout delay (PD). We propose a neural network (NN)-based intravoice synchronization mechanism, called the intelligent voice smoother (IVoS). The IVoS is composed of three components: (1) the smoother buffer; (2) the NN traffic predictor; and (3) the constant bit rate (CBR) enforcer. Newly arriving frames, assumed to follow a generic Markov modulated Bernoulli process (MMBP), are queued in the smoother buffer. The NN traffic predictor employs an online-trained back propagation NN (BPNN) to predict three traffic characteristics of every newly encountered talkspurt period. Based on the predicted characteristics, the CBR enforcer derives an adaptive buffering delay (ABD) by means of a near-optimal simple closed-form formula. It then imposes the delay on the playout of the first frame in the talkspurt period. The CBR enforcer in turn regulates CBR-based departures for the remaining frames of the talkspurt, aiming at assuring minimal mean and variance of distortion of talkspurts (DOT) and mean PD. Simulation results reveal that, compared to three other playout approaches, the IVoS achieves superior playout, yielding negligible DOT and PD, irrespective of traffic variation     

突发大时延下的IP语音缓冲算法

当网络中存在突发大时延时,就会出现极大丢包率或极大端到端时延的情况,从而难以获得好的语音质量。对于这个问题,提出针对突发大时延存在下的自适应语音缓冲算法。算法通过控制语音包在语音缓冲队列中的位置来控制语音包的播放时间,从而可以尽量减小语音裂缝(Gap)的出现。算法将突发大时延存在下的最大丢包率可以扩大到20％,而一般的预测算法只能容忍5-10％的最大丢包率。通过基于听觉模型的客观音质评价(PESQ)仿真计算,以及实际应用表明本文的算法对有突发大时延存在的网络中的语音通信质量有一定的改善作用。     

突发性业务环境下周期性信元流通过ATM复接器的时延抖动

在输入ATM网络的业务源中,周期性信元流是很重要的一种.本文精确地分析了一个有限缓存的ATM复接器,其输入业务源由一路周期性信元流、多路随机性贝努利(Bernoulli)信元流和突发性两状态马尔科夫调制贝努利(MMBP)信元流构成.得出了该路周期性信元流的排队时延分布、时延抖动的自相关函数和功率谱.揭示了突发性业务环境下周期性信元流通过ATM复接器的时延抖动行为.计算机模拟验证了分析结果的正确性.     

DELAY JITTER OF A PERIODIC CELL STREAM THROUGH AN ATM MULTIPLEXER IN A BURSTY TRAFFIC ENVIRONMENT

The periodic cell stream is a very important member among the input traffic sources in ATM networks. In this paper, a finite-buffered ATM multiplexer with traffic sources composed of a periodic cell stream, multiple i.i.d Bernoulli cell streams and bursty two-state Markov Modulated Bernoulli Process (MMBP) cell streams is exactly analyzed. The probability mass function of queuing delay, the autocorrelation and power spectrum of delay jitter for this periodic cell stream are derived. The analysis is used to expose the behavior of delay jitter for a periodic cell stream through an ATM multiplexer in a bursty traffic environment. The simulation results indicate that the analytical results are accurate.     

Optimal queueing discipline for real-time traffic at ATM switchingnodes

Queueing disciplines at asynchronous transfer mode (ATM) switching nodes handling various kinds of real-time traffic are investigated. ATM can support various new services including voice, data, and video. However, the characteristics of superposed traffic carried by ATM are not known, and a control effective for a versatile arrival process is required. The optimal discipline which minimizes the number of cells being delayed beyond the specified maximum allowable time, and thus being discarded is derived, without assumptions on the arrival process of cells and buffer management schemes. Also discussed is implementation of the optimal discipline and a method of satisfying cell loss probability requirements of individual classes     

Applying ATM to mobile infrastructure networks

In response to the explosive increase in the number of mobile subscribers and the ever stronger demand for mobile multimedia services, the authors propose introducing the ATM technique for next-generation mobile network infrastructures in order to handle a high volume of traffic and develop multimedia communications. First, this article clarifies mobile-specific requirements for and advantages of applying ATM to mobile infrastructure networks. However, it is risky for network operators en bloc to replace the conventional STM-based infrastructure by ATM. Therefore, this article shows a smooth evolution path for the mobile network infrastructure to convert from conventional STM to ATM as mobile multimedia services mature. Even in future mobile networks, the main traffic may still be voice communications, whose bit rate is too low for efficient use of the radio frequency band. Applying ATM to such very-low-bit-rate mobile voice streams is inefficient due to the delay in filling out the payload of an ATM cell; this “packetization delay” degrades the quality of service. This problem can be solved by using a layered cell structure for the mobile ATM network. This cell structure enables the efficient transfer of voice signals ranging from very-low-bit-rate signals to high-speed multimedia signals with little delay. Standardization of this cell structure is progressing in ITU-T and the ATM Forum. Transmission efficiency is estimated by simulation     

An adaptive reservation scheme for VBR voice traffic in wireless ATM networks

A reservation scheme, named dynamic hybrid partitioning, is proposed for the Medium Access Control (MAC) protocol of wireless ATM (WATM) networks operating in Time Division Duplex (TDD) mode. The goal is to improve the performance of the real-time Variable Bit Rate (VBR) voice traffic in networks with mixed voice/data traffic. In most proposed MAC protocols for WATM networks, the reservation phase treats all traffic equally, whether delay-sensitive or not. Hence, delay-sensitive VBR traffic sources have to compete for reservation each time they wake up from idle mode. This causes large and variable channel access delays, and increases the delay and delay variation (jitter) experienced by ATM cells of VBR traffic. In the proposed scheme, the reservation phase of the MAC protocol is dynamically divided into a contention-free partition for delay-sensitive idle VBR traffic, and a contention partition for other traffic. Adaptive algorithms dynamically adjust the partition sizes to minimize the channel bandwidth overhead. Simulation results show that the delay performance of delay-sensitive VBR traffic is improved while minimizing the overhead.     

A distributed MAC scheme supporting voice services in mobile ad hoc networks

Future mobile ad hoc networks are expected to support voice traffic. The requirement for small delay and jitter of voice traffic poses a significant challenge for medium access control (MAC) in such networks. User mobility presents unique difficulties in this context due to the associated dynamic path attenuation. In this paper, a MAC scheme for mobile ad hoc networks supporting voice traffic is proposed. With the aid of a low‐power probe prior to DATA transmissions, resource reservation is achieved in a distributed manner, thus leading to small packet transmission delay and jitter. The proposed scheme can automatically adapt to dynamic path attenuation in a mobile environment. Statistical multiplexing of on/off voice traffic can also be achieved by partial resource reservation for off voice flows. Simulation results demonstrate the effectiveness of the proposed scheme. Copyright © 2009 John Wiley & Sons, Ltd.     

Jitter calculus in ATM networks: multiple nodes

We provide simple techniques for estimating the end-to-end jitter incurred by a periodic traffic in an asynchronous transfer mode (ATM) network. Our analysis is based on the careful examination of light and heavy traffic behavior of jitter incurred to a tagged renewal stream in a single node. Our results indicate that, in the heavy traffic as the number of nodes increases, the jitter distribution approaches to a limiting distribution which only depends on the behavior of the background traffic. We provide the functional equation satisfying this limit which bounds the moments of the jitter for arbitrary level of traffic. A simple approximation method based on the heavy and light traffic analysis of the jitter process is also provided and the results is supported by extensive simulation     

Expedited forwarding end‐to‐end delay and jitter in DiffServ

The scheduling disciplines and active buffer management represent the main components employed in the differentiated services (DiffServ) data plane, which provide qualitative per‐hop behaviors corresponding to the QoS required by supported traffic classes. In the first part of this paper, we compute the per‐hop delay bound that should be guaranteed by the different multiservice scheduling disciplines, so that the end‐to‐end (e2e) delay required by expedited forwarding (EF) traffic can be guaranteed. Consequently, we derive the e2e delay bound of EF traffic served by priority queuing–weighted fair queuing (PQ–WFQ) at every hop along its routing path. Although real‐time flows are principally offered EF service class, some simulations on DiffServ‐enabled network show that these flows suffer from delay jitter and they are negatively impacted by lower priority traffic. In the second part of this paper, we clarify the passive impact of delay jitter on EF traffic, where EF flows are represented by renewal periodic ON–OFF flows, and the background (BG) flows are characterized by the Poisson process. We analyze through different scenarios the jitter effects of these BG flows on EF flow patterns when they are served by a single class scheduling discipline, such as first‐input first‐output, and a multiclass or multiservice scheduling discipline, such as static priority service discipline. As a result, we have found out that the EF per‐hop behaviors (PHBs) configuration according to RFCs 2598 and 3246 (IETF RFC 2598, June 1999; RFC 3246, IETF, March 2002) cannot stand alone in guaranteeing the delay jitter required by EF flows. Therefore, playout buffers must be added to DiffServ‐enabled networks for handling delay jitter problem that suffers from EF flows. Copyright © 2008 John Wiley & Sons, Ltd.     

Voice over ATM: an evaluation of network architecture alternatives

This article describes eight application scenarios in which there is a business case for voice over ATM. It then evaluates alternative network architectures for implementing the required network functionality. The article incorporates much of the ongoing work of the ATM Forum and the ITU, but does not restrict itself to standards and implementation agreements. In addition, it evaluates nonstandardized alternatives for ATM transport of voice traffic. There are two main areas: N×64 kb/s structured data transfer, also known as composite cell transport-a network operator may aggregate individual voice calls into N×64 kb/s blocks for transport to an intermediate point in the network. At that point the individual calls need to be remapped into new M×64 kb/s blocks for the next stage of their transport. Architectural alternatives and advantages of remapping are investigated. Interworking of signalling is of two types: network interworking, in which the end users are connected to non-ATM networks and an ATM network is used for backbone transport; and service interworking, in which an ATM user is connected to a non-ATM user. Functionality and architectural alternatives for network and service interworking are evaluated     

Bandwidth-dependent scheduling algorithm to limit cell delayvariation for CBR traffic in ATM networks

A multiplexing control scheme is proposed for limiting the cell delay variation (CDV) caused by multiplexing of constant bit rate (CBR) traffic in asynchronous transfer mode (ATM) networks. The control scheme is based on a bandwidth-dependent scheduling algorithm. The limitation of the CDV is proved