Evaluation of congestion control protocols for ABR traffic over ATM networks

Congestion control is very important for effective and stable operation of ATM (Asynchronous Transfer Mode) networks. Owing to the bursty and unpredictable characteristic of data network traffic, its congestion control is particularly a challenge for network researchers and designers. The ATM Forum has recently adopted rate‐based congestion control for ABR (Available Bit‐Rate) traffic which is the service class defined for data network applications. However, there is a number of congestion control schemes prevalent. ATM Forum has decided not to specify switch behaviour for ABR traffic; this has further introduced additional ambiguity. Consequently, an evaluation and comparison of the existing protocols would provide valuable guidance for network designers and engineers; it would also give insight for researchers to explore the essence of different congestion control schemes. In the first part of this paper, we investigate the effectiveness of ABR congestion control in the presence of bursty source traffic and the relationship between the burst time scale and the ABR control time scale. Two ABR congestion control schemes, the ABR Explicit Forward Congestion Indication (EFCI) and ABR Congestion Indication (CI) schemes, are compared with Unspecified Bit Rate (UBR) transport which makes no effort to control congestion. Traffic sources of various burst lengths of 100, 1000, 10000, and an equal mix of 100 and 10000 ATM cells are used in simulations. It is found that ABR congestion control schemes effectively control low frequency, medium to long‐term traffic load transients. This is further supported by the result of integrating TCP over ATM congestion control schemes included in the paper. ABR control schemes do not control high frequency, short‐term load transients well, but ABR control is not necessary in such cases since short‐term transients do not require a large amount of buffering. In the second part of this paper, we evaluate and compare six rate‐based congestion control protocols including Scheme I: EFCI, Scheme II: EFCI with separate RM queues, Scheme III: CI, Scheme IV: CI with separate RM queues, Scheme V: the CAPC2 ER (Explicit Rate), and Scheme VI: the EFCI with utilization‐based congestion indication. Each scheme is simulated and compared in the LAN, WAN, and GFC (General Fairness Configuration) environments specified by the ATM Forum. Effects of varying VC (Virtual Circuits) number and changing endsystem–switch distance has been investigated. Their fairness is also compared using the GFC configuration. We have found that ER control scheme performs significantly better than the other five binary control schemes by its faster response to congestion, smoother regulation of bit‐rates, lower queueing delay, shorter buffer queue length, and fairness. Among the other five schemes, the CI scheme performs better than the EFCI scheme. Providing separate RM queues has significantly improved the EFCI scheme in the WAN environment, but has little effect on the CI scheme. Link utilization‐based congestion detection has suffered from either low utilization or an excess cell loss which is unacceptable in most data applications. Copyright © 2000 John Wiley & Sons, Ltd.     

Performance analysis and interoperability issue of consolidation algorithms in point‐to‐multipoint ABR services

In this paper we propose a performance analysis of the consolidation algorithms in point‐to‐multipoint ABR services in ATM network. We also present a new efficient consolidation algorithm, which overcomes some drawbacks of the previous works. The performance of the previous works and our proposed consolidation algorithms are analysed mathematically. General equations for calculating the response time and allowed cell rate of the source are derived. The derived equations show relatively good agreement with simulation results and can be applied for using in various network topologies. In addition, the interoperability issue in multicast available bit rate (ABR) is investigated. It is found that the branch points implemented with different consolidation algorithms can work interoperably. It is concluded from the simulation results that the performance of the point‐to‐multipoint ABR services is dominated by the most upper stream branch point (the nearest one to the source), therefore, in order to avoid the consolidation noise and get a faster response in the network, the most upper stream branch point has to be implemented with a high accuracy consolidation algorithm while the lower stream branch point(s) should be implemented with a fast response consolidation algorithm with a less degree of complexity. Copyright © 2002 John Wiley & Sons, Ltd.     

On network bandwidth sharing for transporting rate‐adaptive packet video using feedback

While existing research shows that feedback‐based congestion control mechanisms are capable of providing better video quality and higher link utilization for rate‐adaptive packet video, there has been relatively little study on how to share network bandwidth among competing rate‐adaptive video connections, when feedback control is used in a fully distributed network. This paper addresses this issue by presenting a framework of network bandwidth sharing for transporting rate‐adaptive packet video using feedback. We show how a weight‐based bandwidth sharing policy can be used to allocate network bandwidth among competing video connections and design a feedback control algorithm using an Available Bit Rate (ABR)‐like flow control mechanism. A novel video source rate adaptation algorithm is also introduced to decouple a video source's actual transmission rate from the rate used for distributed protocol convergence. Our feedback control algorithm provides guaranteed convergence and smooth source rate adaptation to our weight‐based bandwidth sharing policy under any network configuration and any set of link distances. Finally, we show the on‐line minimum rate renegotiation and weight adjustment options in our feedback control algorithm, which offer further flexibility in network bandwidth sharing for video connections. Copyright © 2000 John Wiley & Sons, Ltd.     

Q2ABR: QoE‐aware adaptive video bit rate solution

In this paper, we propose a new adaptive bit rate (ABR) streaming method. This method is based on estimating and monitoring users' video streaming experience, their quality of experience (QoE). This ensures a good user QoE and optimises bandwidth utilisation by monitoring video buffer fill rate to ensure minimal data traffic. First, we achieve a QoE evaluation model based on network bandwidth, video segment representation, and dropped video frame rate parameters. Second, following our QoE evaluation model, we formulate an ABR method using the reinforcement learning (RL) paradigm to select video representations and using a breakpoint detection mechanism to monitor end‐user QoE variation. The proposed ABR method is called “QoE‐aware adaptive bit rate (Q2ABR)” and is composed of three individual modules, one for QoE estimation using machine learning methods, one for QoE variation monitoring using the breakpoint detection mechanism, and one for video representation selection using reinforcement learning. The design objective of Q2ABR is to ensure the overall QoE of these users while maintaining a minimum variation in the standard deviation of the users' QoE values. Third, the performance of the Q2ABR method is evaluated and compared with several existing ABR approaches in the literature using real traces that we collect on different transport scenarios (such as bus and train, among others). Since this method considers the user's perception of video quality as a regulator for optimising the overall video distribution network, good results are ensured in terms of the user's experience and buffer fill rate.     

A near‐Nyquist rate transmission: A new minimum‐bandwidth direct‐sequence code division multiple access scheme

Bandlimited direct‐sequence code division multiple access (DS‐CDMA) attracts much attention for its compact spectrum and the ability to suppress inter‐symbol interference. Among the various bandlimited DS‐CDMA systems available, minimum‐bandwidth DS‐CDMA (MB‐DS‐CDMA) is the only realizable Nyquist rate transmission system. But, MB‐DS‐CDMA only applies to certain kinds of spreading codes. Accordingly, this study proposes a modified DS‐CDMA structure which extends the application of MB‐DS‐CDMA to all common spreading codes at the expense of a negligible reduction in the transmission rate. Additionally, the bit error rate of the proposed schemes adopting either single‐user or multi‐user detection receiver is analyzed and compared with that of the commonly‐used raised‐cosine‐pulsed DS‐CDMA over multipath fading channels. The numerical results show that given a sufficiently large number of users, the bit error rate performance of modified MB‐DS‐CDMA is comparable to that of the raised‐cosine‐pulsed DS‐CDMA scheme; meanwhile, the realizable modified MB‐DS‐CDMA approaches the ultimate transmission rate.     

Channel capacity and bit error rate optimization of the ultra‐wide bandwidth transmitted‐reference receiver

The channel capacity and the bit error rate of ultra‐wide bandwidth transmitted‐reference systems are optimized with respect to time delay between the reference and the adjacent data pulses. Approximate and theoretical expressions for the signal‐to‐interference‐plus‐noise ratio are derived. Numerical results show that optimizing the receiver can provide a significant capacity improvement of up to 2.2 bits/s/GHz and a bit error rate performance gain of up to 2 dB in effective signal‐to‐noise ratio. Copyright © 2011 John Wiley & Sons, Ltd.     

Bandwidth‐satisfied routing in multi‐rate MANETs by cross‐layer approach

Previous quality‐of‐service (QoS) routing protocols in mobile ad hoc networks (MANETs) determined bandwidth‐satisfied routes for QoS applications. Since the multi‐rate enhancements have been implemented in MANETs, QoS routing protocols should be adapted to exploit them fully. However, existing works suffer from one bandwidth‐violation problem, named the hidden route problem (HRP), which may arise when a new flow is permitted and only the bandwidth consumption of the hosts in the neighborhood of the route is computed. Without considering the bandwidth consumption to ongoing flows is the reason the problem is introduced. This work proposes a routing protocol that can avoid HRP for data rate selection and bandwidth‐satisfied route determination with an efficient cross‐layer design based on the integration of PHY and MAC layers into the network layer. To use bandwidth efficiently, we aim to select the combination of data rates and a route with minimal bandwidth consumption to the network, instead of the strategy adopted in the most previous works by selecting the combination with the shortest total transmission time. Using bandwidth efficiently can increase the number of flows supported by a network. Copyright 2010 John Wiley & Sons, Ltd.     

Flow‐level performance analysis of a multi‐rate system supporting stream and elastic services

We consider a multi‐rate system where stream and elastic flows receive service. Both the stream and the elastic classes are associated with peak rate limitation. In contrast to the constant bit rate stream flows, the elastic flows tolerate bandwidth compression while in service. Because of the occasional bandwidth compression, the holding time of elastic flows depends on their perceived throughput. Although this model is Markovian under quite non‐restrictive assumptions, the model's state space grows exponentially with the number of traffic classes. The model is not quasi‐reversible, and therefore, it cannot be evaluated by efficient recursive formulae. We propose a method whereby the original state space is mapped to a two‐dimensional one, independently of the number of the stream and the elastic traffic classes. The special structure of the two‐dimensional model allows us to develop an efficient method that approximates the average throughputs of elastic flows. The state space reduction together with the proposed approximation provides a powerful tool for the performance analysis of this model as it allows the approximation of the average throughputs of elastic flows reasonably accurately in large models as well. Copyright © 2012 John Wiley & Sons, Ltd.     

Mechanism for shaping the emitted traffic at ATM terminal‐points

A mechanism for controlling the emitted traffic to asynchronous transfer mode (ATM) network, system design and implementation architectures are introduced. Specifically, the effective rate of a stream, defined under certain multiplexing conditions and quality‐of‐service specifications, is enforced to desired values by controlling the cell emission rate of the generated bursts. The traffic shaping mechanism is closely associated to an ATM transmitter, which is mainly responsible for ATM cell assembly and header error control. The mechanism has been designed to support data communication services. The whole system has been implemented as a VLSI circuit. Copyright © 2002 John Wiley & Sons, Ltd.     

Switching rate and receiver performance of binary modulations with the selection‐and‐stay combining over independent and correlated Nakagami‐m fading channels

The dual‐branch selection‐and‐stay combining (SSTC) is analyzed for diversity reception on independent and correlated Nakagami‐m fading channels, where the conventional selection combining (SC) is employed only at the switching instance, and the receiver uses the selected branch till its signal‐to‐noise ratio (SNR) estimation is lower than a preset threshold. In this combining scheme, the receiver only needs to continuously estimate the SNR of the single selected branch. For the performance analysis of SSTC, the switching rate and the average bit error rates (BERs) of different binary coherent and non‐coherent modulations are evaluated. Numerical results based on the analysis and simulations are illustrated. According to the analysis and numerical results, the SSTC outperforms the existing switch‐and‐stay combining in the senses of the average BER and switching rate. Copyright © 2011 John Wiley & Sons, Ltd.     

Bit error rate for rectangular QAM with arbitrary constellation mapping in Nakagami‐m channels

We present closed‐form expressions for the bit error rate (BER) of rectangular quadrature amplitude modulation (QAM) in Nakagami‐m fading channels. The presented formulas, which are valid for arbitrary bits‐to‐symbols mapping, thus may be used when non‐Gray mapping is employed, are particularly useful in the low signal‐to‐noise ratio (SNR) range and/or for small values of the parameter m. The advantage of the proposed expressions over the known bounding techniques is illustrated through numerical simulations. Copyright © 2006 John Wiley & Sons, Ltd.     

Improved Delay‐Locked Loop in a UWB Impulse Radio Time‐Hopping Spread‐Spectrum System

As ultra‐wideband impulse radio (UWB‐IR) uses short‐duration impulse signals of nanoseconds, even a small number of timing errors can cause a detrimental effect on system performance. A delay‐locked loop (DLL) is proposed to synchronize and reduce timing errors. The design of the DLL is vital for UWB systems. In this paper, an improved DLL is introduced to a UWB‐IR time‐hopping spread‐spectrum system. Instead of using only two central correlator branches as in a conventional DLL, the proposed system uses two additional correlator branches with different delay parameters and different weight parameters. The performance of the proposed schemes with the optimal parameters is compared with that of traditional schemes through simulation: the proposed four‐branch DLLs achieves less tracking jitter or a longer mean time to lose lock (MTLL) than the conventional two‐branch DLLs if proper parameters are chosen.     

A mathematical theory of de‐integrating long‐time integrated rainfall and its application for predicting 1‐min rain rate statistics

To date, the methods devised for converting long‐term experimental probability distribution (pd), , of the rain rate ρ_T integrated in T min (T > > 1 min) to 1‐min pd, P_R(R), of the instantaneous rain rate R, are based on flawed T‐min data and, as such, are not based on fully reliable first principles. is not only an upward translated version of P_R(R) but also rotated clockwise and distorted. The current methods do not correct these errors. We propose and discuss a mathematical theory, which corrects these errors and thus de‐integrates T‐min experimental pds into the corresponding 1‐min pd, the input required by all rain attenuation prediction methods. The theory is based on simple first principles whose parameters are calibrated by means of a large and reliable rain‐rate data bank recorded in Spino d'Adda, a site held as an experimental laboratory and used for exploratory data analysis. We show that P_R(R) is modelled by four distinct functions in four disjoint ranges, and that this modelling is physically meaningful. We have tested the theory up to integration times of 12 h, with a large experimental data bank of 1‐min rain‐rate time series recorded in Gera Lario, Fucino, Rome, Prague, and Montreal, besides Spino d'Adda. Defined the fraction of rainy time in an average year, P_o (%), we have found that: (a) the modelling is very good up to 6 h; (b) in the range from about P_o to 0.001%, the error values are constant, with average error set at about ? 3% and RMS error less than 8% for T ≤ 120 min, less than about 9% for 120 < T ≤ 360 min. We have also applied the theory to rain‐rate time series provided by meteorological agencies with integration time T = 60 min (blind test) with excellent result. Copyright © 2011 John Wiley & Sons, Ltd.     

Multi‐topology routing based egress selection approach to achieve hybrid intra‐AS and inter‐AS traffic engineering

Hot‐potato routing is a border gateway protocol policy that selects the ‘closest’ egress router in terms of interior gateway protocol cost. This policy imposes inherent interactions between intra‐AS (Autonomous System) and inter‐AS traffic engineering. In light of this observation, we present a hybrid intra‐AS and inter‐AS traffic engineering scheme named egress selection based upon hot potato routing. This scheme involves link weight optimization, which can not only minimize the time that IP (Internet Protocol) packets travel across the network by assigning specified egress router but also balance the load among the internal links of the transit network. Egress selection based upon hot potato routing also incorporates multi‐topology routing technique to address the problem that one set of link weights might not guarantee specified egress routers. Accordingly, we formulate the link weights optimization problem using multi‐topology routing as a mixed integer linear programming model. And we present a new heuristic algorithm to make the problem tractable. Numerical results show that only a few topologies are needed to guarantee specified egress router, and maximum link utilization is also reduced. Copyright © 2014 John Wiley & Sons, Ltd.     

Mobile GPS carrier phase tracking using a novel intelligent dual‐loop receiver

Carrier phase information is necessary for accurate measurements in global positioning system (GPS) applications. This paper presents a novel intelligent GPS carrier tracking loop with variable‐bandwidth characteristics for fast acquisition and better tracking capability in the presence of dynamic environments. Our dual‐loop receiver is composed of a frequency‐locked loop‐assisted phase‐locked loop structure, the fuzzy controllers (FCs), and the ATAN discriminator functions. The soft‐computing FCs provide the time‐varying loop gains to perform accurate and reliable control of the dual‐loop paradigm. Once the phase dynamic errors become large under kinematic conditions, the fuzzy loop gains increase adaptively and achieve rapid acquisition. On the other hand, when the tracking errors approach zero in the steady state, the loop gains decrease and the corresponding dual‐loop receiver returns to a narrowband system. Four types of carrier phase signals, i.e. phase offset, decaying sinusoidal phase jitter, frequency offset, and frequency ramp offset, are considered to emulate realistic mobile circumstances. Simulation results show that our proposed receiver does achieve a superior performance over conventional tracking loops in terms of faster settling time and wider acquisition range while preventing the occurrence of cycle slips. Copyright © 2008 John Wiley & Sons, Ltd.     

A cause of self‐similarity in TCP traffic

We analyse the statistical properties of aggregated traffic flows generated by TCP, in order to clarify a possible cause of self‐similarity in Internet traffic. Using ns‐2 simulation, we first show that aggregated traffic flows by TCP can be characterized by phase transition phenomena between non‐congested and congested phases in statistical physics. Interestingly, although the traffic exhibits self‐similarity with the Hurst parameter H ≈ 1.0 at the critical point between them, it is close to Poissonian away from the critical point. This result is consistent with results from real WAN traffic measurement. The main contribution of our work is to show that TCP itself contains a mechanism for generating self‐similarity, without assuming self‐similarity or long‐range dependency (LRD) in the application layer (e.g. packet inter‐arrival, connection arrival, and file size distribution). Moreover, we find that the value of the Hurst parameter at the critical point is determined by the simple feedback control called stop‐and‐wait flow control. Namely, it appears even without any packet retransmission events and is independent of the explicit rate increment algorithm such as slow‐start and congestion avoidance. Additionally, we demonstrate that the value of the Hurst parameter at the critical point depends on the constant bit rate algorithm and topology of network. Finally, we indicate that the time series of the round trip time follow the same statistics at the critical state. Copyright © 2005 John Wiley & Sons, Ltd.     

Performance evaluation of TCP under dynamic allocation scheme for down‐link transmission rate in W‐CDMA systems

IMT‐2000 has attracted much attention as the Next Generation Mobile Communication System. IMT‐2000 can provide high‐bit‐rate data communication service, so that a great number of packets conveyed by TCP (transmission control protocol) can be transmitted over a wireless link. W‐CDMA, standardized in 3GPP (which standardizes IMT‐2000), allows dynamically allocating transmission rates to flow over a wireless link in response to a changing FER for each flow, which is thought to be essential for a next generation mobile communication system. Therefore, in this paper, we study the characteristics of the dynamic allocation scheme when TCP flows share a wireless link, and, in particular, we focus on the throughput performance of these TCP flows. First, we use simulations to examine the effectiveness of the dynamically allocating down‐link transmission rate for TCP flows in response to changing the frame error rate (FER). Through the simulation results, we will show how it can improve the total throughput performance of TCP flows. Furthermore, we can obtain an effective way to allocate transmission rates to flows with different FERs in order to achieve high total throughput. Finally, we will deal with a case of multiple flows from a fixed host to a mobile host. In actual networks, this often happens. In this case, we will show that the total throughput of TCP flows degrades less than in the single‐flow case, even when the FER is high. Copyright © 2004 John Wiley & Sons, Ltd.     

Performance analysis of congestion avoidance algorithms with non‐zero MCR guarantee for ABR service in ATM networks

This paper proposes a novel explicit rate allocation algorithm called Fast Rate Allocation Congestion Avoidance (FRACA) algorithm supporting non‐zero minimum cell rate (MCR). The non‐zero MCR guarantee strategy for ABR service in ATM networks focused in this paper is MCR plus equal share (The ATM Forum Traffic Management Specification, version 4.0. April 1996). The main goals for designing the algorithm are the fast convergence according to the max–min fairness criteria, fairness among all sessions, maximum network utilization while the switch queue length is properly controlled. At the same time, it should work well under a wide range of network conditions without the need for adjusting the algorithm parameters. The performance of the proposed algorithm is evaluated and compared with the Generic Weighted Fairness (GWF) ERICA + (J Comput Comm 2000; 149). Simulation results show that the proposed algorithm achieves the design goals in the evaluated scenarios. Copyright © 2004 John Wiley & Sons, Ltd.     

The extended connection‐dependent threshold model for call‐level performance analysis of multi‐rate loss systems under the bandwidth reservation policy

Firstly, we reviewed two extensions of the Erlang multi‐rate loss model, whereby we can assess the call‐level QoS of telecom networks supporting elastic traffic: (i) the extended Erlang multi‐rate loss model, where random arriving calls of certain bandwidth requirements at call setup can tolerate bandwidth compression while in service; and (ii) the connection‐dependent threshold model, where arriving calls may have several contingency bandwidth requirements, whereas in‐service calls cannot tolerate bandwidth compression. Secondly, we proposed a new model, the extended connection‐dependent threshold model. Calls may have alternative bandwidth requirements at call setup and can tolerate bandwidth compression while in service. We proposed a recurrent formula for the efficient calculation of link occupancy distribution and consequently call blocking probabilities, link utilization, and throughput per service class. Furthermore, in the proposed model, we incorporated the bandwidth reservation policy, whereby we can (i) equalize the call blocking probabilities of different service classes, (ii) guarantee specific QoS per service class, and (iii) implement different maximum bandwidth compression/expansion rate per service class so that the network supports both elastic and stream traffic. The accuracy of the new model is verified by simulation. Moreover, the proposed model performs better than the existing models. Finally, we generalize the proposed model by incorporating service classes with either random or quasi‐random arrivals. Copyright © 2011 John Wiley & Sons, Ltd.