Carla Panarello

Energy saving and network performance: a trade-off approach

Power consumption of the Information and Communication Technology sector (ICT) has recently become a key challenge. In particular, actions to improve energy-efficiency of Internet Service Providers (ISPs) are becoming imperative. To this purpose, in this paper we focus on reducing the power consumption of access nodes in an ISP network, by controlling the amount of service capacity each network device has to offer to meet the actual traffic demand. More specifically, we propose a Green router (G-router) implementing a congestion control technique named Active Window Management (AWM) coupled with a new capacity scaling algorithm named Energy Aware service Rate Tuner Handling (EARTH). The AWM characteristics allow to detect whether a waste of energy is playing out, whereas EARTH is aimed at invoking power management primitives at the hardware level to precisely control the current capacity of access nodes and consequently their power consumption. We test the benefits of the AWM-EARTH mechanism on a realistic scenario. Results show that the capacity scaling technique can save up to 70% of power consumption, while guaranteeing Quality of Service and traffic demand constraints.

Active Window Management: An Efficient Gateway Mechanism for TCP Traffic Control

Many techniques have been proposed in the last few years to address performance degradations in end-to-end congestion control. Although these techniques require parameter tuning to operate in different congestion scenarios, they miss the challenging target of both minimizing network delay and keeping goodput close to the network capacity. In this paper we propose a new mechanism, called Active Window Management (AWM), which addresses these targets by stabilizing the queue length in the network gateways. AWM acts on the Advertised Window parameter in the TCP segment carrying the acknowledge, but it does not affect the TCP protocol. The proposed technique is implemented in the network access gateways, that is, in the gateways through which both the incoming and outgoing packets related to a given TCP connection are forced to go, whatever the routing strategy used in the network. We show that when the access gateways implementing AWM are the bottleneck in the networks, TCP performance is very close to that of a pseudo constant bit rate protocol providing no loss, while network utilization is close to one.

Measuring and modeling energy consumption to design a green NetFPGA giga-router

One of the most weighty matter in the Internet today is the waste of energy due to the fact that consumption of network nodes is not tuned with the input traffic. For this reason, the implementation of rate adaptation facilities in the routers constitutes a challenging problem to make the network energy efficient. Rate adaptation in the green routers is usually achieved by scaling the processing power according to the data rate the router has to manage; at this purpose the clock frequency driving the router processes can be modified according to the input data rate. In this context this paper, starting from a measurement study of the Reference Router implemented on the NetFPGA platform, defines a model of the consumed power as a function of both the managed input traffic and the available clock frequencies. As demonstrated in the paper, the model can be applied by router designers to choose the main router platform parameters, i.e. the number of clock frequencies and the clock frequency switching time, while respecting a given tradeoff between the percentage of energy saved and the maximum tolerated loss probability due to frequency switch.

Achieving energy savings and QoS in internet access routers

In order to provide high quality communications over a best-effort network, an alternative to complex QoS control procedures is represented by generously over-provisioning the network resources. This approach has guaranteed in the near past reasonably performance for many applications, but it implies a waste of energy that today is unsustainable. This paper proposes an autonomous measurement mechanism, named G-Router, to allow an access node in the Internet to align its power consumption to either the maximum capacity the user traffic requires, or the minimum available capacity in the network path between source and destination. Simulation results show that allowing access network nodes to adapt the switching and transmission resources to the minimum between the above values, the G-Router guarantees the maximum QoS while minimizing the energy consumption.

On the intertwining between capacity scaling and TCP congestion control

Recent works advocate the possibility of improving energy efficiency of network devices by modulating switching and transmission capacity according to traffic load. However, addressing the trade-off between energy saving and Quality of Service (QoS) under these approaches is not a trivial task, specially because most of the traffic in the Internet of today is carried by TCP, and is hence adaptive to the available resources. In this paper we present a preliminary investigation of the possible intertwining between capacity scaling approaches and TCP congestion control, and we show how this interaction can affect performance in terms of both energy saving and QoS.

A Model-Assisted Cross-Layer Design of an Energy-Efficient Mobile Video Cloud

In the last decade, one of the main goals in wireless telecommunications has been to reduce energy consumption of mobile devices. However, making a network device green can cause performance deterioration. The target of this paper is to propose a cross-layer approach for the design of a mobile video cloud for the uplink transmission towards the Internet. The proposed approach is adaptive in both the video sources and the wireless transmitter. A source Rate Controller is applied to compensate transmission bandwidth reduction due to the energy saving policies. Energy saving in wireless transmission on the mobile cloud cellular channel is achieved by introducing an energy-efficient ARQ protocol. This protocol can apply different transmission laws, in order to exploit the correlation of the cellular channel behavior. An analytical model of the system is defined to compare the transmission laws, and provide some design guidelines to choose one of them and design its parameters.

Applying Active Window Management for Jitter Control and Loss Avoidance in Video Streaming over TCP Connections

Improving video streaming performance is a main target today for the development of services and related business opportunities in the Internet. For this reason the definition of an efficient video transport paradigm is yet a challenging task. The most common protocol for data transmission in the Internet is TCP but it has been widely believed not suitable for multimedia streaming because of bandwidth instability and retransmissions. However, the dominance of TCP makes desirable the possibility to use it without any modifications. The main idea of this paper is to improve the performance of video streaming by using TCP, by combining it with Active Window Management (AWM), an algorithm to be implemented by video content Providers in their Internet access router. Through an extensive analysis the paper demonstrates that thanks to AWM, packet losses are avoided while per-packet delivery delay is maintained almost constant, strongly decreasing transmission jitter; consequently the required video playout buffer can be substantially reduced with respect to the classical approaches.

EE-ARQ: a Green ARQ-Based Algorithm for the Transmission of Video Streams on Noise Wireless Channels

The challenge in the next future is to increase the energy efficiency of telecommunications networks, and specifically wireless devices that present the highest energy consumption coefficient per bit transmitted among all the networking devices. However, making a network device green can cause performance deterioration. The target of this paper is to propose a new algorithm for the transmission of multiplexed rate-controlled multimedia streams over wireless channels. The algorithm is an energy-efficient variant of ARQ to exploit the correlation of the wireless channel behavior. In addition, in order to compensate transmission bandwidth reduction due to the energy saving policies, a cross-layer approach is applied introducing a source Rate Controller working to modify the video quality according to the state of the transmission buffer. An analytical model of the whole system is presented in order to evaluate performance and provide some guidelines to design the configuration parameters of the proposed algorithm.

A Module for Packet Hijacking in NetFPGA Platform

The reference router implementation on the Net FPGA platform has been changed in order to hijack the incoming packets according to rules specified by the user through Net FPGA registers. This means that we are able to change any field of any incoming packets, of course, depending on whether we are changing TCP or IP header fields, we need to recompute the TCP or IP checksum and store them back into the packets. It might be useful to change information of the IP or TCP header or the data itself. For example, we could crypto the data, change the URL address in order to point to the desired web site or for URL filtering, change the priority information of a bunch of data, and much more. Our implementation works at user data path level and modifies packet fields if certain conditions defined by the user through Net FPGA registers are satisfied. The project has been implemented as a fully open-source project and serves as an exemplar project on how to build and distribute Net FPGA applications. All the code (Verilog, system software, graphical user interface, verification scripts, make files, and support tools) can be freely downloaded from the Net FPGA.org website.

Active window management: performance assessment through an extensive comparison with XCP

The most efficient approaches defined so far to address performance degradations in end-to-end congestion control exploit the flow control mechanism to improve end-to-end performance. The most authoritative solution in this context seems to be the eXplicit Control Protocol (XCP) which achieves high performance but requires changes in both network routers and hosts which make it difficult to deploy. To this aim we have developed a new mechanism, called Active Window Management (AWM), which is able to maintain the queue length in network routers almost constant providing no loss, while maximizing network utilization. The idea at the basis of AWM is to allow network routers to manipulate the Advertised Window field in TCP ACKs. In this way no modifications to the TCP protocol are required. The target of this paper is to propose an extensive numerical analysis of AWM to compare it with the XCP protocol, chosen as reference case.