Szilveszter Nádas

Providing Congestion Control in the Iub Transport Network for HSDPA

The introduction of High Speed Downlink Packet Access (HSDPA) presents new challenges to be solved in the UMTS Terrestrial Radio Access Network. Bandwidth reservation for HSDPA is not efficient and TCP cannot efficiently resolve a congestion situation because lower layer retransmissions hide the congestion situations from TCP. An HSDPA Flow Control algorithm was introduced by 3GPP to control congestion. This HSDPA Flow Control algorithm was originally intended to control radio scheduler queues in Node B. In this paper we propose an algorithm that also provides congestion control in the transport network. The performance analysis concentrates on transport network limited scenarios and shows that the algorithm can achieve high end-user perceived throughput, while maintaining low delay and loss in the transport network. The analysis also shows the advantages of the newly introduced congestion detection functionality.

HSUPA Transport Network Congestion Control

The introduction of high speed uplink packet access (HSUPA) greatly improves achievable uplink bitrate but it presents new challenges to be solved in the radio access network. In the transport network, bandwidth reservation for HSUPA is not efficient and TCP cannot efficiently resolve congestion because of lower layer retransmissions. This paper proposes an HSUPA transport network flow control algorithm that handles congestion situations efficiently and supports quality of service differentiation. In the radio network controller (RNC), transport network congestion is detected. Relying on the standardized control frame the RNC notifies the Node B about transport network congestion. In case of transport network congestion the Node B part of the HSUPA flow control instructs the air interface scheduler to reduce the bitrate of the flow to eliminate congestion. The performance analysis concentrates on transport network limited scenarios. It is shown that TCP cannot provide efficient congestion control. The proposed algorithm can achieve high end-user perceived throughput, while maintaining low delay, loss and good fairness in the transport network.

Connection admission control in UMTS radio access networks

On transport links of UMTS Terrestrial Radio Access Networks, but especially on those connecting base stations and radio network controllers (i.e. on the Iub interface), resource allocation is complex, because packet delay and loss requirements are strict and the amount of transmission resources is relatively low. In this paper a novel connection admission control (CAC) algorithm is provided, which is applicable on the Iub interface with both ATM/AAL2 and IP transport options. The CAC algorithm is validated by mathematical analysis and computer simulation.

Fairness-optimal initial shaping rate for HSDPA transport network congestion control

In the HSDPA (high-speed downlink packet access) Iub transport network (TN) which connects the radio network controller with base stations (node Bs), congestion control is needed. Because of the TN¿s often narrow resources, fairness of resource sharing is an important issue. Basic Additive Increase multiplicative decrease (AIMD) congestion control guarantees convergence to fairness in the long run; all flows converge to an equal share of resources in steady state, where no flows join or leave. However, incoming flows decrease the level of fairness, that is why transient fairness should be taken into account as well. This paper proposes a method which provides fairness-optimal initial rate for incoming HSDPA flows. The proposed method improves average fairness. The method can be applied in a rate based congestion control where flows share the same bottleneck. The paper also gives a general solution for fairness-optimal initial rate in case of second-order fairness measures.

Connection Admission Control in the UTRAN Transport Network

In this paper we propose a Connection Admission Control (CAC) algorithm to provide Quality of Service (QoS) in UMTS Terrestrial Radio Access Networks (UTRAN). In UTRAN, the main QoS requirement is to ensure low packet delays. The CAC algorithm works with priority scheduling, which is used for QoS differentiation. We give a detailed investigation on the performance implications of applying priority scheduler. We provide novel closed-form formulae which are fast, simple and accurate enough for practical implementation of the CAC. A comprehensive performance evaluation study with illustrative numerical examples is also presented. The results are validated by simulations.

Window-based HSDPA Transport Network Congestion Control

In the High-Speed Downlink Packet Access (HS-DPA) Iub Transport Network (TN) which connects the Radio Network Controller (RNC) with base stations (Node Bs), congestion control is needed. This paper reviews existing congestion control solutions and describes a novel, non-standardized, cross-layer, window-based HSDPA Transport Network Congestion Control which uses the standardized congestion detection and signalling framework. This solution is based on the idea of extending the Radio Link Control (RLC) protocol with congestion control functionality. This idea originates from the interesting duality between the TCP and the RLC protocols. TCP was originally designed for wired networks, therefore many extensions have been proposed to make TCP to be efficiently used over wireless networks. RLC was originally designed exclusively for handling radio link failures and no RLC extensions have been proposed to make RLC to be efficiently used over congested wired links. This paper proposes such an RLC extension where the RLC transmission window size is used to control the bitrate of the flow. Simulation analysis of this window-based solution is performed and it is shown that the proposed method is a possible solution for and efficient Iub Transport Network congestion control.

Per Packet Value: A Practical Concept for Network Resource Sharing

Governing how network resources are shared among various traffic flows is not a completely solved problem. The ideal system can implement a wide variety of detailed and flexible policies; enforces those policies under all possible offered traffic combinations and scales well with the number of flows. In this paper we introduce a framework that approximates the ideal system well. It consists of flow-aware Packet Value marking at the edges and flow-unaware operation inside the network. We show that inside the network relatively simple scheduling and AQM algorithms operating solely on Packet Value are suitable to implement the policies set at the network edge. We also discuss, how the framework can be used to support resource sharing over radio networks (where the cost of transmission varies) and how it enables load balancing, resource balancing and optimal network-wide load distribution.

HSUPA transport network congestion control

The introduction of High Speed Uplink Packet Access (HSUPA) greatly improves achievable uplink bitrate but it presents new challenges to be solved in the WCDMA radio access network. In the transport network, bandwidth reservation for HSUPA is not efficient and TCP cannot efficiently resolve congestion because of lower layer retransmissions. This paper proposes an HSUPA transport network flow control algorithm that handles congestion situations efficiently and supports Quality of Service differentiation. In the Radio Network Controller (RNC), transport network congestion is detected. Relying on the standardized control frame, the RNC notifies the Node B about transport network congestion. In case of transport network congestion, the Node B part of the HSUPA flow control instructs the air interface scheduler to reduce the bitrate of the flow to eliminate congestion. The performance analysis concentrates on transport network limited scenarios. It is shown that TCP cannot provide efficient congestion control. The proposed algorithm can achieve high end-user perceived throughput, while maintaining low delay, loss, and good fairness in the transport network.

Take your own share of the PIE

In this paper, we propose the PVPIE Active Queue Management (AQM) method that combines the packet scheduling and dropping algorithms of PIE AQM and the packet marking-based resource sharing of the Per Packet Value (PPV) concept. The algorithm calculates dropping probabilities needed for keeping the queueing delay at a predefined level using the PIE algorithm. Then instead of applying this drop probability directly on incoming packets it translates the dropping probability to a Congestion Threshold Value (CTV) filter and drops (or marks) all incoming packets with Packet Value smaller than the threshold. The translation is based on statistics collected about Packet Values of incoming packets. Our evaluation based on simulations shows that PVPIE AQM combines the benefits of PIE and PPV concepts, keeping a target queueing delay and implementing policy-based resource sharing at the same time. The motivation for the proposed algorithm is simplicity and ease of deployment in real networks, since the schedulers of the original PPV approach need to perform drops from the middle of the queue. Such drops may be costly and may not be supported by current hardware.

Towards a Congestion Control-Independent Core-Stateless AQM

In this paper, we propose CSAQM, a novel approach of Active Queue Management (AQM) for network traffic with multiple Congestion Control algorithms. Our goal is similar to that of PI2 AQM that supports both Classic and Scalable TCP in a single queue. In contrast to existing solutions, CSAQM has two key advantages: 1) arbitrary congestion controls (including unresponsive flows) can also be handled and 2) it supports a rich set of resource sharing policies beyond equal sharing. CSAQM is based on the core-stateless Per Packet Value resource sharing concept and extends it with a congestion control-independent AQM. The performance of the proposed CSAQM and its behavior under various network conditions have been analyzed through extensive simulations.