Cell Loss Priority Research Articles

Policing mechanism and cell loss priority control on voice cells in ATM networks using fuzzy logic

The authors present a fuzzy logic-based implementation of the policing mechanism (PM) and cell loss priority control (CLPC) functions on voice cells in asynchronous transfer mode (ATM) networks. Specifically, a redesigned model of fuzzy leaky bucket (FLB) is presented which serves as an alternative PM on the voice sources in an ATM network. As a continuation of the implementation of the FLB in the ATM network, three models of ATM switches with different algorithms are constructed, to perform CLPC on the voice cells, as well as to enhance the network throughput. Simulation results show that FLB is a better PM than the conventional leaky bucket (LB) in terms of cell loss probability and throughput while the mean transfer delay remains unchanged. It is also shown that the model of ATM switch with fuzzy token generator is the most balanced CLPC scheme as compared with the other two models.

A fuzzy logic based approach to multipriority control in ATM networks

The priority control function in ATM networks allows users to generate traffic flows with different priorities by using the Cell Loss Priority (CLP) bit. The implementation of this function, however, represents a hard task as the network has to guarantee the Quality of Service (QoS) of the higher priority traffic regardless of the presence of low-priority traffic and, at the same time, to reach an efficient use of network resources. The conventional schemes proposed so far suffer from some limitations either in performance (threshold mechanisms) or in feasible implementation (push-out scheme). We propose a queue management strategy based on fuzzy logic, which combines high performance, guaranteeing the QoS requirements and increasing the throughput, with a low implementation cost. In the paper, we assess the fuzzy mechanism by considering several traffic scenarios ranging from bursty traffic to MPEG video traffic. The presented results show that our mechanism is robust and outperforms conventional mechanisms.

Performance Analysis of the UPC/NPC Algorithm for Guaranteed QoS in ATM Networks

It is well known that if usage parameter control/network parameter control (UPC/NPC) functions are used together with a cell loss priority control scheme in ATM networks, the measurement phasing problem can occur. This makes it difficult for a network provider to define and commit the cell loss ratio as a QoS parameter. To solve the problem, we propose a new UPC/NPC algorithm. By using the proposed UPC/NPC algorithm, we can define the cell loss ratios for CLP = 0 and CLP = 0+1 cell streams without the measurement phasing problem under any conditions. We analyzed the performance of the proposed UPC/NPC algorithm. Using a discrete time model for the UPC/NPC architecture with a discrete-time semi-Markov process (DSMP) input model, we obtained the cell discarding probabilities of CLP = 0 and CLP = 0+1 cells streams and showed that more CLP = 0 cells are accepted compared to what was proposed in ITU-T.

Performance of cell loss priority management schemes in shared buffers with poisson arrivals

AbstractThe performances of two important cell loss priority mechanisms (CLPM) in shared buffers with N servers, Partial Buffer Sharing (N‐PBS) and Push‐Out Buffer (JV‐POB), are compared. Each arriving flow i is guided to a shared queue of size K where it is served by the corresponding i‐th server. Further, these flows are Poissonean, independent of each other and consist of a uniformly distributed mix of high (H) and low (L) priorities. Subject to the required cell loss ratios for both priorities, clr*L and clr*H, we determine the maximum allowable traffic intensity λmaxfor each incoming traffic flow as a function of the global priority mix in the buffer of size K. For an arbitrary CLPM, the maximum allowable load is achieved in the symmetrical traffic situation where all N links carry the same load. Only when N> 1, the N‐POB scheme is found to be superior in performance to N‐PBS over the whole priority mix range and for realistic cell loss ratio requirements. Moreover, the difference in performance between N‐POB and N‐PBS increases with increasing N, but decreases with increasing K. Finally, a methodology based on buffer size scaling has enabled the computation of the performance of the N‐POB.

Performance of cell loss priority management schemes in a single server queue

The throughput optimality of priority management strategies in a single buffer has been studied for a general aggregate arrival law. The tight upper bounds found are useful to understand optimality in the utilization of specific priority schemes such as push-out buffer (POB) and partial buffer sharing (PBS). This paper further focuses on the maximum allowable load ρmax versus the priority mix α for a PBS and a random push-out buffer (RPOB) of size K for a wide variety of arrival processes. The role of priorities in a special type of bursty arrivals, the compound Poisson process with constant burst length and random priority assignment within the burst is found to be less pronounced than that of ‘pure’ Poisson arrivals. On the other hand, the results for ON–OFF cell arrivals modelled by a MMPP(2), MMPP(3), and higher order Markov modulated processes (MMP) closely follow the behaviour of the maximum allowable load in the RPOB with Poisson arrivals, however, scaled to lower loads. The results indicate that the priority mix distribution within the aggregate arrival flow influences the shape of ρmax(α)-curve more than the aggregate arrival distribution itself. © 1997 John Wiley & Sons, Ltd.

A high-performance priority scheme for ATM switching systems

In this paper, cell loss priority schemes in the ATM switches are studied. Many schemes had been proposed to manage buffer access for priority classes. However, these schemes suffered from poor buffer utilization or prohibitive implementation complexity. Therefore, we propose a simple priority scheme called Separate logic Queues with Complete buffer Sharing (SQCS). In the SQCS scheme, buffers are shared by priority classes and two service strategies, First-Come-First-Service (FCFS) and High-Priority First (HPF), are employed to serve priority classes. The performance of our proposed scheme is evaluated and compared with those of other priority schemes. The results indicate that our proposed scheme has a better performance and low implementation complexity. Hence, the SQCS scheme is an effective priority scheme for the ATM switching system.

Performance management issues in ATM networks: traffic and congestion control

The goal is first to introduce performance monitoring aspects of asynchronous transfer mode (ATM) networks and then to focus on traffic and congestion control schemes. To deal with this performance monitoring management, a framework for defining a generic intelligent and integrated model for network management is described. As an example of the efficiency of this intelligent management architecture, we measure the performance of a new congestion control scheme. This scheme uses the cell loss priority (CLP) bit, the explicit forward congestion indicator and the explicit backward congestion indicator. The intelligent management uses different parameters and builds a complex but efficient control scheme. We show that this new control scheme allows performance to be increased by an order of magnitude.

UPC/NPC algorithm for guaranteed QoS in ATM networks

In Broadband Integrated Services Digital Networks (B-ISDN) based on the Asynchrous Transfer Mode (ATM) technology, the required Quality of Service (QoS) must be guaranteed for connection. Cell loss ratio, which is one of the QoS parameters specified by the user in an ATM traffic contract of connection, may depend on the traffic enforcement mechanism known as the Usage Parameter Control/Network Parameter Control (UPC/NPC) or traffic policing. If two UPC/NPC algorithms are not equivalent with respect to cell discarding/tagging for a given traffic configuration, a common understanding about legality between the user and the network operator does not exist. To cope with this legality problem, the concept of cell conformance has been developed by the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T). However, the Cell Loss Priority (CLP) bit, which ITU-T introduced in the ATM cell header to discriminate between a high priority cell (CLP = 0) and a low priority cell (CLP = 1), may cause the measurement phasing problem in cell conformance testing in ATM networks. This makes it difficult for a network provider to define and commit cell loss ratio as a QoS parameter. In this paper, we investigate measurement phasing problems and difficulties in commitment of the cell loss ratio in ATM networks. We propose a QoS guaranteed UPC/NPC algorithm to commit the cell loss ratio, and show an example of applications of the proposed UPC/NPC algorithm.

Revenue maximization in ATM networks using the CLP capability and buffer priority management

The cell loss priority (CLP) bit in the header of the ATM cell may be used either by the network to tag noncompliant cells, or by the application to declare two levels of quality-of-service (QoS) within the same virtual circuit (VC). We study the possibility of the use of this bit by the application alone. An application can offer two types of traffic streams to the network, namely, a precious traffic stream (with stringent QoS requirements, e.g., cell loss ratio (CLR) <10/sup -9/ and identified by the CLP bit=0) and a less precious stream (CLP=1 and less stringent QoS requirements, e.g., CLR <10/sup -4/). We study the performance of an ATM multiplexer with two traffic classes with different QoS requirements. The buffer priority schemes adopted are partial buffer sharing (PBS) and PBS+push-out (PO). We first obtain the engineering trade-off curves, between CLP=0 and CLP=1 traffic. To identify an operating point, we formulate a revenue optimization problem in which the constraints are the engineering trade-off curve and a simple model of the variation of CLP=1 demand with its price.

A traffic control method for service quality assurance in an ATM network

The authors describe an ATM traffic control method to avoid both long-term and short-term congestion. Call admission control and policing based on user-specified traffic parameters have mainly been studied as ways to avoid long-term congestion. However, these control methods are not practical since it is difficult for users to specify accurate values of traffic parameters that include the effects of cell collision controllers and multiplexers in the customer premises network. In order to solve the problem, they propose an intelligent call admission control method. This method consists of a function to determine user's traffic parameters by monitoring the cell traffic flow of each service and a function to statistically predict long-term congestion by using Gaussian and Poisson distributions. They show that congestion can be predicted by deriving the peak, average, and variation. They also describe how to derive traffic parameters and determine their values. To avoid short-term congestion, we propose reactive control, which drops cells with lower cell loss priority when congestion occurs, and we show the buffer construction and buffer control algorithm used to achieve this. Computer simulations prove that their control strategy is effective for cell toss sensitive services such as VBR (variable bit rate) video service. >

A novel congestion control strategy in ATM networks

In order to guarantee a committed Quality of Service (QoS) to the users of a Broadband Integrated Services Digital Network (B-ISDN), preventive congestion control becomes critical, and is implemented through Call Acceptance Control (CAC), Usage Parameter Control (UPC), and Space Priority functions. Currently, Asynchronous Transfer Mode (ATM) cells are equipped with a 1-bit Cell Loss Priority (CLP) field, which can be used for service-oriented and/or UPC marking. This creates a conflict, since these two marking approaches may have contradicting objectives, and are designed to operate independently. Moreover, by admitting excessive cells as marked traffic, this group is allowed to grow uncontrollably, thereby jeopardizing the QoS committed to other (low priority) marked cells. This paper presents a solution to these problems based on a new 4-class priority strategy that unifies the two marking approaches, by utilizing a 2-bit CLP field. This is implemented by expanding the CLP field with the adjacent 1-bit RES field in the ATM cell header. A new variant of the “marking Leaky Bucket” UPC mechanism, called the Forgiving Leaky Bucket (FLB) will then be positioned at the Network-Node-Interface (NNI) of interworking ATM-based Broadband ISDN subnetworks. The FLB additionally has the power of un-marking ( forgiving) previously marked ATM cells, whenever the network conditions are appropriate. As a result, the end-to-end survival probability of a cell is improved significantly. Furthermore, “forgiving” corrects access-point bias, a phenomenon observed in interworked ATM subnetworks of different congestion conditions. Through simulations it is shown that this new priority strategy provides a significant improvement over the traditional marking Leaky Bucket UPC mechanism.

Internetting LAN's and MAN's to B-ISDN's for connectionless traffic support

One of the challenges in the interconnection of LANs and MANs to asynchronous transfer mode (ATM) networks is the support of connectionless traffic in the ATM network. A commonly proposed strategy consists of maintaining a thin, low bandwidth virtual path (VP) between each pair of gateways and requesting more bandwidth whenever a burst comes in from the LAN or MAN. Unfortunately, this strategy places a heavy burden on the ATM control processors; furthermore, it is overly conservative in the use of bandwidth. An alternative solution is proposed: on the-fly tranmission of bursts without prior bandwidth reservation. The key conditions for this scheme to work are the use of the cell loss priority (CLP) bit in the ATM cell header and the knowledge of available bandwidth on the path through bandwidth advertising. An on-the-fly strategy for connectionless traffic is described and is compared with a bandwidth renegotiation strategy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>