Unspecified Bit Research Articles

A Review on Bandwidth Utilization for Bursty Traffic in Asynchronous Transfer Mode Networks

ATM (Asynchronous Transfer Mode) network is connection-oriented high speed multiservice network. Now a days ATM networks are used as backbone networks in Telecom industry. ATM network supports different service classes, include ABR (Available Bit Rate), rt-VBR (real time Variable Bit Rate), nrt-VBR (non real time Variable Bit Rate), CBR (Constant Bit Rate), UBR (Unspecified Bit Rate), and GBR (Guaranteed Bit Rate)to handle multiple services like data, voice, video and so on. But burtsy traffic handled by ABR, rt-VBR, nrt-VBR, GBR service classes, but all have their own limitations. This paper presents an overview of different Traffic shaping, Congestion Control mechanisms to handle bursty traffic in ATM networks.

Minimizing peak current in combinational circuit test

In the VLSI era where millions of transistors are packed in a single chip, the demand for proper power management is of a paramount importance. The problem of low power test is taking center stage for both combinational and sequential circuits in recent years due to its impact on overall yield. This paper proposes a technique that targets the reduction of peak current during combinational circuit test to realize peak power reduction. Unlike previous methods, this approach utilizes peak current defined by the direction of switching activity to find minimum peak power. The proposed framework consists of two main phases where the test set is first reordered using a combined peak current/peak power cost function followed by an x-refilling technique based on Fiduccia-Mattheyses concept to refill unspecified bit values. Experimental results show that the proposed approach reduces peak current, peak power, and total power by 33%, 32%, and 43% respectively compared to Hamming distance-based ordering with random filling.

Scan Power Reduction for Linear Test Compression Schemes Through Seed Selection

XOR network-based on-chip test compression schemes have been widely employed in large industrial scan designs due to their high compression ratio and efficient decompression mechanism. Nevertheless, such a scheme necessitates high unspecified bit ratios in the original test cubes, resulting in quite significant difficulties in preprocessing test cubes for scan power reduction. The linear mapping from the original cubes to the compressed seeds typically provides extra degrees of flexibility as multiple seeds may reconstruct the test cube. Due to the highly divergent power impact of distinct seeds though, appreciable power reductions in the decompressed test data can be attained through the pinpointing of the power-optimal seeds during the compression phase. This work explores the aforementioned flexibility in the seed space, and outlines a mathematical and algorithmic framework for a power-aware linear test compression scheme. The proposed technique incurs no hardware overhead over the traditional linear compression scheme; it can be easily embedded furthermore into the industrial test compaction/compression flow. Experimental results confirm that the proposed technique delivers significant scan power reduction with negligible impact on the compression ratio.

Framework for dynamic optical virtual private networks (VPNs): architecture and analysis

The authors explore the problem of dynamic virtual private networks (VPNs) over wavelength division multiplexing (WDM) networks to facilitate the guarantee of diverse quality of service (QoS) requirements of different traffic streams, especially those with very stringent delay jitter requirements and with bursty characteristics. Each VPN consists of different traffic streams with various quality sensitivities. The proposed QoS model provides three types of QoS services for various VPNs: static, optical burst switching (OBS) and alternative VPNs. All the three types provide transmission in the optical core networks without any O/E/O conversion. The static type has a set of dedicated or shared lightpaths which have been pre-allocated and the traffic from this VPN has a constant bit rate (CBR). The OBS type need to setup the lightpath using so-called optical burst switching while a traffic stream with variable bit rate (VBR) request, is occurring. The alternative type has to set up a lightpath based on two-way reservation protocols such as tell-and-wait (TAW) for the traffic with unspecified bit rate (UBR) or available bit rate (ABR). The proposed model is suitable for carrying the multimedia applications which have various sensitivities to delay and jitter. By employing dynamic VPNs directly over the WDM layer, one can eliminate the often complex QoS related functions in the upper protocol layers, and thus increase the overall communication efficiency. Furthermore, this could be the first step towards providing fine grained service over optical wide area networks. In addition, basic performance analysis and preliminary results are presented, based on simulation, and the network designer is provided with a quantitative assessment of proportion for different traffic types with different QoS service requirements.

Adaptive Congestion Control for ATM UBR Service using Neural Networks

Abstract This paper presents an adaptive congestion control scheme using neural networks for the Unspecified Bit Rate (iJBR) service class in ATM networks. The UBR service supports a general delivering mode for those data with less delay and cell loss, and offers the best effort service. Based on the EPD (Early Packet Discazd) technique that basically employs a threshold to define the current traffic status and classifies the cells into two classes, the first cell and the non-fast cell, the proposed method provides an adaptive threshold leazned from the neural networks in advance. The adaptive threshold will become lazger for accommodating both kinds of cells if the traffic is light and become smaller for only accepting the non-fast cell if the traffic is heavy. Simulation results show that this scheme can significantly improve the TCP (Transmission Control Protocol) traffic over the UBR service.

On the performance analysis of ABR in ATM LANs with Stochastic Petri Nets

In this paper we use Generalized Stochastic Petri Nets (GSPNs) and Stochastic Well-formed Nets (SWNs) for the performance analysis of Asynchronous Transfer Mode (ATM) Local Area Networks (LANs) that adopt the Available Bit Rate (ABR) service category in its Relative Rate Marking (RRM) version. We also consider a peculiar version of RRM ABR called Stop & Go ABR; this is a simplified ABR algorithm designed for the provision of best-effort services in low-cost ATM LANs, according to which sources can transmit only at two different cell rates, the Peak Cell Rate (PCR) and Minimum Cell Rate (MCR). Results obtained from the solution of GSPN models of simple ATM LAN setups comprising RRM or Stop & Go ABR users, as well as Unspecified Bit Rate (UBR) users, are first validated through detailed simulations, and then used to show that Stop & Go ABR is capable of providing good performance and fairness in a number of different LAN configurations. We also develop SWN models of homogeneous ABR LANs, that efficiently and automatically exploit system symmetries allowing the investigation of larger LAN configurations.

A study of a new selective cell discard scheme with two threshold control on ATM networks

AbstractWhen UBR (Unspecified Bit Rate) service is used on an ATM network, cells are discarded in congestion and imperfect packets are generated that consume network resources in a wasteful manner. As a remedy, the EPD (Early Packet Discard) control is proposed, in which the cells are discarded on a packet basis in congestion by providing a threshold to the input buffer. However, with EDP control, there is a possibility that the EOP (End Of Packet) cell in AAL5 may be discarded. Thus, two successive packets become invalid. For this reason, the TT‐EPD (Two Threshold‐EPD) that prevents discarding of the EOP cell has been proposed. This scheme sets two threshold values (TH1 and TH2) and the fixed TH1 works similarly to EPD control. TH2 carries out dynamic control and secures the input region for the EOP cell in the buffer. In this scheme, the amount of buffer between TH1 and TH2 decreases and there is an increase in the number of acceptance failures in which the cells composing a packet initially accepted are discarded by TH2. In this paper, a method that keeps the amount of buffer between TH1 and TH2 constant to reduce the acceptance missing packets is proposed. The effectiveness of the proposed scheme is demonstrated by simulation. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(8): 50– 57, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10039

Application performance and service differentiation for best effort traffic in ATM networks

Best effort services continue to be simple and cheap and one of the most widely used networking services. For this class of service the network provides no QoS guarantees and applications compete with each other to gain the network resources they need. In this environment, the Packet Dropping Policy (PDP) is the most important and influential mechanism. PDPs can improve the application performance and the network utilization, achieve fairness among the competing connections, isolate traffic, and even provide service predictability and traffic differentiation. Although there are many Selective Packet Dropping mechanisms for the ATM Unspecified Bit Rate (UBR) service category, there is no single and best policy yet. All of them have advantages and disadvantages and finding a good policy for all scenarios is not easy. In this article we present a flexible PDP called Preemptive Partial Packet Discard (pPPD) that provides better application performance and network utilization than current alternatives. In addition, we demonstrate the flexibility of pPPD proposing four pPPD variants including pPPD-DS, meant to enhance the best effort service and provide relative traffic differentiation. pPPD-DS is proposed as a mechanism to implement the Behaviour Classes recently approved by the ATM Forum in the Differentiated UBR traffic management specifications for the support of the IETF Differentiated Model over ATM networks.

A traffic scheduling framework in broadband wireless access systems

In this paper, we present a traffic scheduling framework for allocating the upstream channel bandwidth in broadband wireless access systems, where both voice and data applications are supported. Our traffic scheduling framework is aimed at supporting diverse QoS requirements and obtaining high utilization of the upstream bandwidth. It prioritizes traffic streams according to different classes of service, and provides fair access of bandwidth to the users. The presented framework consists of three algorithms: a calibration algorithm for the jittered constant bit rate (CBR) traffic, a scheduling algorithm for the jittered CBR traffic, and a scheduling algorithm for the unspecified bit rate traffic. The proposed algorithms are feasible when either the asynchronous transfer mode or multi-protocol label switching protocol is deployed at the network edge. Simulation results are presented to demonstrate the effectiveness of our algorithms in achieving high bandwidth utilization and the good traffic performance in terms of both cell loss ratio and mean queuing delay.

TCP Explicit Congestion Notification over ATM-UBR: A Simulation Study

The enhancement of Transmission Control Protocol’s (TCP’s) congestion control mechanisms using Explicit Congestion Notification (ECN) over Asynchronous Transfer Mode (ATM) networks is overviewed. TCP’s congestion control is enhanced so that congestion is indicated by not only packet losses as is currently the case but an agent implemented at the ATM network’s edge as well. The novel idea uses EFCI (Explicit Forward Congestion Indication) bits (available in every ATM cell header) to generalize the ECN response to the UBR (Unspecified Bit Rate) service, notify congestion, and adjust the credit-based window size of the TCP. The authors’ simulation experiments show that TCP ECN achieves significantly lower cell loss, packet retransmissions, and buffer utilization, and exhibits better throughput than (non-ECN) TCP Reno.

Buffer management and scheduling schemes for TCP/IP over ATM‐GFR

AbstractToday ATM technology is facing challenges from integrated service IP, IP switching, gigabit IP router and gigabit ethernet. Although ATM is approved by ITU‐T as the standard technology in B‐ISDN, its survivability is still in question. Since ATM‐UBR (unspecified bit rate) provides no service guarantee and ATM‐ABR (available bit rate) is still unattainable for most users, many existing users have little or no incentives to migrate to ATM technology. The guaranteed frame rate (GFR) service is introduced to deal with this dilemma. The GFR can guarantee the minimum cell rate (MCR) with fair access to excess bandwidth. This paper studies various schemes to support the GFR. We have studied different discarding and scheduling schemes, and compared their throughput and fairness when TCP/IP traffic is carried. Through simulations, it is shown that only per‐VC queueing with weighted round robin (WRR) can guarantee minimum cell rate. Among all the schemes that have been explored, we recommend dynamic threshold–early packet discard (DT–EPD) integrated with MCR+ (a WRR variant) to support the GFR service. Copyright © 2001 John Wiley & Sons, Ltd.

Buffer management and rate guarantees for TCP over satellite‐ATM networks

AbstractFuture broadband satellite networks will support a variety of service types. Many such systems are being design with ATM or ATM‐like technology. A majority of Internet applications use TCP for data transfer. As a result, these systems must efficiently transport TCP traffic and provide service guarantees to such traffic. Several mechanisms have been presented in recent literature to improve TCP performance. Most of these can be categorized as either TCP enhancements or network‐based buffer management techniques. Providing minimum rate guarantees to TCP traffic has also been suggested as a way to improve its performance in the presence of higher priority traffic sharing the link. However, the relative performance of the TCP enhancements versus the buffer management schemes has not been analyzed for long latency networks. In this paper, we address three issues. First, we present a performance analysis of TCP over satellite‐ATM links using a best effort service—the ATM unspecified bit rate (UBR) service. This analysis shows that the relative impacts of buffer management, TCP policies and rate guarantees on TCP performance, depend heavily on the latency of the network. Second, we show through simulations that the buffer size required in the network for high TCP performance is proportional to the delay‐bandwidth product of the network. Third, we propose a buffer management scheme called differential fair buffer allocation (DFBA) and show how it is used to implement a service that provides minimum rate guarantees to TCP traffic. An example of such a service is the ATM guaranteed frame rate (GFR) service, which is being standardized by the ATM Forum and the ITU. Copyright © 2001 John Wiley & Sons, Ltd.

Multimedia Satellite Networks and TCP/IP Traffic Transport

To meet an increasing demand for multimedia services and electronic connectivity across the world, satellite networks will play an indispensable role in the deployment of global networks. A number of satellite communication systems have been proposed using geosynchronous (GEO) satellites, medium earth orbit (MEO) and low earth orbit (LEO) constellations operating in the Ka-band and above. At these frequencies, satellite networks are able to provide broadband services requiring wider bandwidth than the current services at C or Ku-band. Most of the next-generation broadband satellite systems will use ATM or "ATM-like" switching with onboard processing to provide full two-way services to and from earth stations. The new services gaining momentum include mobile services, private intranets, and high-data-rate internet access carried over integrated satellite-fiber networks. Several performance issues need to be addressed before a transport layer protocol like TCP can satisfactorily work over satellite ATM for large delay-bandwidth networks. The authors review the proposed satellite systems and discuss challenges such as traffic management and QoS requirements for broadband satellite ATM networks. The performance results of TCP enhancements for Unspecified Bit Rate over ATM (ATM-UBR+) for large bandwidth-delay environments with various end system policies and drop policies for several buffer sizes are presented.

Improving goodputs of IP packets under ATM UBR traffic with port-based queueing schemes

ATM networks are widely adopted as backbone networks. TCP/IP are the most popular protocols today and it is quite possible that packets are forwarded by ATM networks. In ATM networks, UBR (unspecified bit rate) service and ABR (available bit rate) service are common in transmitting IP packets. Because TCP has its own flow control mechanism, the flow control of ABR service could become redundant. Moreover, it could interfere with the TCP flow control. In this paper, we will focus on buffer management schemes of ATM switches with UBR service. Researchers have proposed several buffer management schemes for UBR service. However, all schemes do not consider the influence of output rates. In addition, most researchers assume that each port has its own buffers. A basic scheme called dedicated buffers per port is compared with four proposed schemes. The paper considers the situation that switch buffers are shared among all output ports and proposes a scheme called shared buffers among all ports. Then, two schemes, dedicated buffers with early packet discarding (EPD) and shared buffers with EPD, are proposed. The EPD scheme is modified. Instead of using a threshold for each flow, only one threshold is applied to buffers of each output port. The fifth proposed scheme is called shared buffers with EPD + differential buffer allocation (DBA), which also considers the effects of various output rates. Results show that goodputs are increased apparently by applying the DBA scheme. Results also show that for goodputs, when packets pass two or more switches, packet discarding schemes are far more important than whether we adopt schemes of shared buffers or schemes of dedicated buffers. Hence, we can simply adopt schemes of dedicated buffers, which are easy to implement, and incorporate a packet-discarding scheme in most cases.

Bandwidth management for AAL2 traffic

Bandwidth management in AAL2 networks is investigated mainly from the traffic performance point of view. AAL2 is a new asynchronous transfer mode (ATM) adaptation layer. Since it is designed to carry low-bit-rate voice signals efficiently, it should be used in the ATM backbone for mobile networks, especially in the IMT-2000 network (International Mobile Telecommunication in the Year 2000 network). Three alternatives for bandwidth management, which differ in the way the ATM layer service is used and how admission of AAL2 connections to a virtual channel (VC) is judged, are shown and their performances are evaluated theoretically. The best performance is obtained by the alternative of using unspecified bit rate VCs and judging admission of AAL2 connections to a virtual path. The advantage of using a variable bit rate is found to be limited. The effectiveness of introducing AAL2 switching nodes is also shown.

Throughput–complexity trade-off for ABR traffic in an ATM satellite network under cell loss constraints

This work refers to an ATM satellite system, supporting different QoS classes via the standard ATM traffic categories, i.e. Constant Bit Rate (CBR), Variable Bit Rate (VBR), Available Bit Rate (ABR) and Unspecified Bit Rate (UBR). The focus of this work is on ABR (i.e. closed loop control) and the central issue is to find trade-offs between a high ABR throughput and processing burden/buffer space required on board satellite, under the constraint that no buffer overflow occurs. ABR fairness issues are not central to this work and hence are not considered. The focus of the paper is to evaluate how adaptive prediction of higher priority CBR/VBR traffic can enhance ABR traffic performance, with respect to a simpler worst case based approach. Results show that a significant improvement of performance can be obtained even with rather straightforward prediction algorithms.

Providing rate guarantees for internet application traffic across ATM networks

The TCP/IP protocol suite is the standard requirement for all applications that need to communicate over the Internet. As TCP/IP applications are unable to specify the QoS parameters needed for most asynchronous transfer mode (ATM) services, they tend to use the unspecified bit rate (UBR) service category when running across ATM networks. The UBR service utilizes any bandwidth that is left unused by the rest of the ATM services. This has led the ATM forum's traffic management group to define a new service category called guaranteed frame rate (GFR). GFR is intended to provide minimum cell rate guarantees and fair access to excess bandwidth left over from higher-priority services. This article first presents a tutorial overview of GFR and then presents a survey of the research work that has been carried out toward the design and implementation of associated ATM switch mechanisms.

Performance of TCP in IP/ATM internetworks

The Asynchronous Transfer Mode (ATM) level flow control schemes and their impact on Transmission Control Protocol (TCP) over ATM have been extensively studied (Fang et al., A simulation study of TCP performance in ATM networks, in: Proceedings of IEEE GLOBECOM'94, San Francisco, 28 November–2 December 1994, pp. 1217–1223; S. Kalyanaraman et al., Performance of TCP/IP over ABR, in: Proceedings of Globecom'96, London, November 1996; H. Li et al., A simulation study of TCP performance in ATM networks with ABR and UBR services, in: INFOCOM'96, March 1996). In this paper, we extend the work of Yin and Jagannath (End-to-end traffic management in IP/ATM internetworks, ATM Forum Contribution 96-1406, October 1996) on TCP over available bit rate (ABR) and unspecified bit rate (UBR) services in an IP/ATM internetworking environment, and provide a more comprehensive study on this important issue. We compare TCP performance in terms of goodput and fairness and discuss the performance tradeoff among different types of services. We also investigate the ATM edge congestion with different traffic scenarios in various networks configurations and system setups. In particular, a simple and effective scheme to prevent ATM edge buffer overflow is proposed in this paper. Simulation results are provided to show that our scheme can reduce the ATM edge congestion, and therefore provide significant improvement of TCP goodput.

ABR Flow Control for Multipoint Connections

Multipoint capabilities are essential for ATM networks to efficiently support many applications, including IP multicasting and overlay applications. The current signaling and routing specifications for ATM define point-to-multipoint capabilities. Multipoint-to-point connection support is also being discussed by the signaling and PNNI groups, and will be defined in the near future for the unspecified bit rate (UBR) service. We examine point-to-multipoint and multipoint-to-point flow control for the available bit rate (ABR) service, as discussed in the traffic management working group.

Link-sharing method for ABR/UBR services in ATM networks

This paper presents an efficient link-sharing method for available bit rate and unspecified bit rate services in ATM networks. The method comprises an algorithm that performs cell multiplexing and scheduling such that the outgoing link is fairly shared by multiple traffic flows. The proposed algorithm adopts a dynamic priority assignment to each ATM cell, and schedules those cells having the same priority level into repeating cycles in a round-robin fashion. The algorithm also guarantees each ABR connection a specified minimum cell rate and a satisfied cell loss rate. The performance is evaluated through simulations and is also compared with another fixed method called weighted round robin. Finally, a corresponding hardware design that uses a two-stage leaky bucket circuit is presented.