Traffic Asymmetry Research Articles

Performance evaluation of a novel scheme for QoS provision in UTRA TDD

Satisfying Quality of Service (QoS) requirements, is one of the main goals of UMTS (Universal Mobile Telecommunications System), which represents a major 3G wireless technology. The Internet services have a significant impact on the radio frequency network over which resources are particularly scarce. To guarantee different QoS requirements for diverse traffic types, while at the same time maintaining fair and high utilization of wireless resources, an efficient resource management, specifically the slot allocation and resource reservation during admission and handoffs, is essential for UMTS systems. In this paper, we propose a novel scheme for slot allocation and resource reservation for handoff using the concepts of traffic asymmetry, signal to interference ratio, and cell differentiation. The study of the effects of this scheme on the quality of service provision is accomplished through a modeling of the main QoS parameters and a simulation that gives an evaluation of the system behavior.

Optical storage area networks

Storage area networks (SANs) are a promising technology to efficiently manage the ever-increasing amount of business data. Extending SANs over large distances becomes essential to facilitate data protection and sharing storage resources over large geographic distances. A WDM metropolitan ring network is examined as a suitable extension for SANs where it is shown that sectioning the ring can help deal with traffic asymmetry and hot node (SAN node on ring) scenarios. Several network architectures are studied: One of the architectures accommodates a single SAN and its mirror connected through a sectioning link. Another architecture accommodates two pairs of SANs and their mirrors with sectioning links connecting each pair. Issues investigated include impact of the number of co-existing IP (non SAN) nodes; traffic models: Poisson and self-similar; slotted regime: fixed-size (FS), variable-size (VS) and supersize (SS) slot schemes; MAC protocol design; handling traffic asymmetry and performance measures.

Dynamic resource allocation for CDMA‐TDD indoor wireless systems

AbstractFuture wireless communication systems are expected to provide a broad range of multimedia services that have a significant traffic asymmetry between uplink and downlink. The code division multiple access‐time division duplex (CDMA‐TDD) system is a promising solution to cope with the problem of traffic asymmetry. However, the TDD system is subject to inter‐cell interference compared to frequency division duplex (FDD) system. Since both uplink and downlink share the same frequency in TDD, uplink and downlink may interfere each other especially when neighboring cells require different rates of traffic load. Thus, the resource allocation among cells is an important issue in TDD. In this paper, the resource allocation in the CDMA‐TDD is formulated as a mixed integer programming (MIP) problem. A dynamic resource allocation algorithm (DRAA) is provided that effectively solves the traffic asymmetry problem. The MIP problem is also solved by a well‐known branch and bound procedure. Both the crossed slot and non‐crossed slot allocation are examined and compared to the DRAA. Computational result shows that proposed DRAA gives a good performance as the traffic asymmetry increases between the uplink and downlink. Copyright © 2003 John Wiley & Sons, Ltd.

Call admission control for CDMA mobile communications systems supporting multimedia services

The call admission control (CAC) belongs to the category of resource management. Since the radio spectrum is very scarce resource, CAC is one of the most important engineering issues for mobile communications. In this paper, we propose a CAC scheme for direct sequence code-division multiple-access cellular systems supporting mobile multimedia communications services. There are multiple call classes in multimedia services and the required signal-to-interference ratio (SIR) varies with call classes. Call admission decision in the proposed scheme is based on SIR measurement. We take account of the traffic asymmetry between uplink and downlink, which is the most important characteristic of multimedia traffic. In addition, the proposed scheme guarantees the priority of handoff call requests over new call requests. We evaluate the performance of the proposed scheme using Markov analysis. The performance measures which we focus on are the system throughput and the blocking probabilities of handoff calls and new calls. The outage probability of a call in progress is also calculated, which is the probability that the measured bit energy-to-noise density ratio of the call is smaller than the required value for maintaining adequate transmission quality. We present some numerical examples with practically meaningful parameter values and, as a result, show that the proposed CAC scheme can operate well in the mobile multimedia systems such as the International Mobile Telecommunications-2000 (IMT-2000) systems.

Influence of the IP Traffic Asymmetry on the Cost of the Optical Network Layer

The main traffic to be carried by a backbone network in the future (or even now) will be (is) IP traffic, which is unidirectional and asymmetric in nature. Today, most backbone networks are still designed for bidirectional, symmetrical services like SDH/SONET. In the future, the transmission links in the optical layer will probably still be symmetric (same amount of capacity installed in both directions of the optical link), and operators will probably continue to lease bidirectional capacity to their customers. However, the traffic that will be conveyed over those bidirectional transmission links will be mainly unidirectional and asymmetric. This paper studies the influence of the asymmetric nature of IP traffic on the underlying optical layer. In case the optical layer contains bidirectional symmetric capacity (as is almost always the case nowadays), it shows how cost(in)efficient this optical capacity is used for IP traffic patterns with varying asymmetry. The comparison is also made with a unidirectional optical layer, in which the capacity (line-systems) installed in the network is asymmetric (more capacity can be present in one direction of an optical link than in the other direction), or in which the capacity that is leased by operators is asymmetric (e.g., an ISP can choose to lease two wavelengths from city A to city B and five wavelengths in the other direction, from city B to city A).

Input queued switches for variable length packets: analysis for Poisson and self-similar traffic

We consider nonblocking, variable length packet switches where packet lengths and interarrival times have continuous distributions as is applicable in IP networks. A general throughput-delay model for Poisson and self-similar packet arrivals of eponential lengths to a single stage M× N switch with infinite and finite buffers is obtained. Analytical results are compared against simulation results on traces statistically similar to Bellcore traces. Tradeoffs between fixed packet length virtual output queued (VOQ) switches and variable length FIFO-combined input/output queued (CIOQ) switches with speedup and parallelism (multiple switching planes) are also studied. Analysis shows that a parallelism of four achieves 99.9% throughput. We also analyze the effect of traffic asymmetries and hotspots.

Call admission control for mobile multimedia communications with traffic asymmetry between uplink and downlink

The call admission control (CAC) for mobile communications is one of the most important engineering issues since it belongs to the category of resource management and the radio spectrum is a very scarce resource. In future mobile cellular systems, the CAC scheme should be efficient for multimedia services as well as for voice services. This paper proposes an advanced CAC scheme for mobile multimedia communications. A characteristic of the proposed scheme is that it takes account of the traffic (load) asymmetry between uplink and downlink in mobile multimedia environments, we evaluate the performance of the proposed scheme using Markov analysis. The performance measures on which we focus are the utilization of resources and the blocking probabilities of handoff calls and new calls. We present some numerical examples with practically meaningful parameter values. As a result, we show that the proposed CAC scheme can be a good choice for mobile multimedia systems such as the International Mobile Telecommunications-2000 systems.

Comparison of time slot allocation strategies for CDMA/TDD systems

The traffic (load) asymmetry between uplink and downlink is a remarkable traffic characteristic in cellular mobile multimedia communications. The code division multiple access system with time division duplex mode (CDMA/TDD system), adopting unbalanced slot allocation between uplink and downlink, is a good solution for this traffic asymmetry. However, the level of traffic asymmetry may be significantly different from cell to cell. In this paper, we investigate a slot allocation strategy (DA strategy), by which each cell has its own slot allocation according to the level of traffic asymmetry. We compute the system capacity with DA strategy and find out the optimal slot allocation for the system. We also compare the maximum capacity to that with another strategy (SA strategy), by which all cells have the same slot allocation. As a result, this paper shows that the system with DA strategy outperforms the system with SA strategy in the aspect of capacity.

Performance comparison criteria for ATM switch models

Performance of ATM networks will depend on switch performance and architecture. In this paper a set of 11 questions is presented in order to be able to study performance. It is necessary to clearly identify the main characteristics of switch architecture and traffic which are considered so as to be able to derive relevant comparisons. The questions concern the level of study, the placement of the memory, the monopath or multipath architecture, the uniformity of input stream, the destination hypotheses, the routing rules inside the switch, the eventual resequencing, etc. In case of cell level study and output buffers, the answers to the six main questions lead to a tree including 14 realistic switch and traffic types. A survey of the modelling method for these cases is then presented. In order to illustrate the methodology, few results are given in some of the realistic cases and some general conclusions appear to be pertinent: importance of traffic asymmetry, best performance for multipath switches, use of path reservations inside the switch.

Time slot allocation in CDMA/TDD systems for mobile multimedia services

An important issue in wireless multimedia communications is to cope with the traffic asymmetry between uplink and downlink. The asymmetrical slot allocation in the code division multiple-access systems with time-division duplex mode (CDMA/TDD systems) can be a good solution for this problem. However, the level of traffic asymmetry can be significantly different from cell to cell. In this letter, we calculate the utilization of a CDMA/TDD system for the multicell model. In addition, we suggest an optimal slot allocation that maximizes the frequency utilization.

Channel sense spread spectrum with overload detection against FFDI: a delay/throughput comparison

The delay/throughput performance of the one-persistent channel sense spread spectrum with overload detection protocol is compared with that of FDDI using simulation. Throughput and delay are given against offered load with the degree of traffic asymmetry as a parameter, these results demonstrating the robustness of the spread spectrum protocol.