Jani Lakkakorpi

Comparison of Different Scheduling Algorithms for WiMAX Base Station: Deficit Round-Robin vs. Proportional Fair vs. Weighted Deficit Round-Robin

In this paper, we present a performance comparison of different WiMAX base station (BS) scheduling algorithms: deficit round-robin (DRR) vs. proportional fair (PF) vs. weighted deficit round-robin (WDRR). Our simulations show that when the radio channel conditions are taken into account (in PF and WDRR schedulers), the improvements in throughput can be considerable.

Active Queue Management for Reducing Downlink Delays in WiMAX

In WiMAX networks, the base station (BS) is a likely bottleneck for downlink (DL) TCP connections due to difference in available bandwidth between the fixed network and the wireless link. This may result in buffer overflows or excessive delays at the BS, as these buffers are connection-specific. In order to avoid buffer overflows, different active queue management (AQM) methods may be applied at the BS. This paper presents an analysis of several AQM mechanisms and proves that they are indeed very useful: AQM reduces considerably DL delays at the WiMAX BS without sacrificing TCP goodput.

Adaptive connection admission control for differentiated services access networks

In our earlier work, we have proposed some modifications for the bandwidth broker framework. With our modifications, it is possible to use measurement-based admission control in addition to the more traditional parameter-based admission control. Moreover, we have presented a new flexible admission control scheme that has proven to be very efficient in terms of bottleneck link utilization. Two problems, however, have arisen: the use of scheduling weights in admission control and bursty connection arrivals. In this paper, we present that the former one can be dealt with the use of adaptive scheduling weights, while the latter one can be fought with adaptive reservation limits. The proposed new algorithms are validated through simulations and their performance is compared against the nonadaptive basic scheme.

Comparison of different active queue management mechanisms for 3G radio network controllers

In WCDMA networks, radio network controller (RNC) is a potential bottleneck for TCP connections - due to difference in available bandwidth between the core network (CN) and the radio access network (RAN). This may result in packet data convergence protocol (PDCP) buffer overflows or excessive delays at the RNC, as PDCP buffers are flow-specific. In order to avoid PDCP buffer overflows, different active queue management (AQM) methods may be applied at the RNC. This paper is a comparison of four AQM schemes: three well-known ones and one new-TTLRED

Uplink VoIP Delays in IEEE 802.16e Using Different ertPS Resumption Mechanisms

In this paper, we present different IEEE 802.16e uplink channel access mechanisms that can be used to activate extended real-time polling service (ertPS) voice over IP (VoIP) connections after a silence period. The performance, especially uplink delay, of different resumption mechanisms is compared with each other using simulations. In addition to uplink VoIP delay, we study the uplink resource usage with different mechanisms. In our studies, we have found that using the fast feedback channel or multicast polling are the most promising approaches for efficient ertPS VoIP resumption.

Active Queue Management in EGPRS

Active queue management (AQM) schemes such as random early detection (RED) or explicit congestion notification (ECN) for TCP-based traffic are important components of the general packet radio service (GPRS) system performance because of potential traffic bottlenecks caused by, e.g., limited radio capacity. Poorly implemented or configured AQM may lead to intolerable end-to-end buffer delays in the serving GPRS support node (2G-SGSN) as well as reduced overall throughput when the system load increases. Although the usefulness of AQM in the fixed Internet is well known, the need for adequate AQM in GPRS or enhanced GPRS (EGPRS) has not been much documented. In this paper, we evaluate the performance of various AQM schemes by means of simulations and we show that RED and ECN are among the most efficient for reducing buffer delay and improving overall end-user experience

Backhaul as a Bottleneck in IEEE 802.16e Networks

In this paper, we assume that the bottleneck in IEEE 802.16e networks is not necessarily the air interface but it can sometimes be the backhaul, too, since over provisioning is not always feasible. Our simulations show that applying Differentiated Services and Active Queue Management on the bottleneck links as well as taking the bottleneck link load into account in connection admission control decisions leads into more efficient use of the scarce backhaul capacity.

Simple measurement-based admission control for DiffServ access networks

In order to provide good Quality of Service (QoS) in a Differentiated Services (DiffServ) network, a dynamic admission control scheme is definitely needed as an alternative to overprovisioning. In this paper, we present a simple measurement-based admission control (MBAC) mechanism for DiffServ-based access networks. Instead of using active measurements only or doing purely static bookkeeping with parameter-based admission control (PBAC), the admission control decisions are based on bandwidth reservations and periodically measured & exponentially averaged link loads. If any link load on the path between two endpoints is over the applicable threshold, access is denied. Link loads are periodically sent to Bandwidth Broker (BB) of the routing domain, which makes the admission control decisions. The information needed in calculating the link loads is retrieved from the router statistics. The proposed admission control mechanism is verified through simulations. Our results prove that it is possible to achieve very high bottleneck link utilization levels and still maintain good QoS.

Measurement-Based Connection Admission Control Methods for Real-Time Services in IEEE 802.16e

In this paper, we present two simple-to-implement measurement-based admission control methods for real-time services in IEEE 802.16e networks. The first method simply utilizes the averaged number of free slots as input in admission decisions while the second method is more advanced and it tunes the admission thresholds according to current traffic load. Our simulations show that the proposed methods lead into more efficient use of scarce radio resources – without sacrificing the Quality of Service (QoS) requirements – than using parameter-based, i.e., static, connection admission control.

Flexible admission control for DiffServ access networks

In our earlier work, we have presented a simple measurement-based admission control (MBAC) scheme for modified Bandwidth Broker framework. In that scheme, real time (RT) traffic is basically able to starve non-admission controlled non-real time (NRT) traffic. By concentrating on real time application requirements it may be hard or even impossible to use other objectives in admission decisions; some non-real time applications (e.g., audio streaming) also need a certain minimum bandwidth for proper operation. In order to fix this problem, we present a solution, where the bottleneck link bandwidth is shared dynamically between real time and non-real time traffic. As a second enhancement to our earlier work, we propose the use of coefficients for the requested resources. These coefficients are derived from the price the user is paying for the connection. A requested peak rate is multiplied by the coefficient before comparison to available bandwidth. The proposed scheme is validated through simulations and its performance is compared against other admission control schemes. The simulation results show that it is possible for a network operator to gain more revenue with the proposed scheme.