Underutilized Links Research Articles

Updating the Theory of Buffer Sizing

Internet routers have packet buffers which reduce packet loss during times of congestion. Sizing the router buffer correctly is important: if a router buffer is too small, it can cause high packet loss and link under-utilization. If a buffer is too large, packets may have to wait an unnecessarily long time in the buffer during congested periods, often up to hundreds of milliseconds. While an operator can reduce the operational size of a router buffer, the maximum size of a router buffer is decided by the router manufacturer, and the operator typically configures the router to use all the available buffers. Without clear guidance about how big a buffer needs to be, manufacturers tend to oversize buffers and operators tend to configure larger buffers than necessary, leading to increased cost and delay.

Green distributed algorithm for energy saving in IP wired networks using sleep scheduling

Energy saving has become a critical issue and a great challenge in the past few decades, and a great effort as well is being made to reduce consumed energy. The Internet forms a major source for energy consumption. Therefore, in this work we propose an algorithm for energy saving in distributed backbone networks, the reduced energy consumption (RedCon) algorithm. In this paper, we introduce a new version for saving energy on the Internet by switching off underutilized links and switching on idle links when the network is overloaded in a distributed manner over the network nodes based on LSA messages and without any knowledge of the traffic matrix. Our algorithm is more accurate and outperforms other algorithms with its time checks and advanced learning algorithm.

Scheduling Inter-Datacenter Video Flows for Cost Efficiency

As video streaming applications are deployed on the cloud, cloud providers are charged by ISPs for inter-datacenter transfers under the dominant percentile-based charging models. In order to minimize the payment costs, existing works aim to keep the traffic on each link under the charging volume. However, these methods cannot fully utilize each link's available bandwidth capacity. As a solution, we propose an economical and deadline-driven video flow scheduling system, called EcoFlow. Considering that different video flows have different transmission deadlines, EcoFlow transmits videos in the order of their deadline tightness and postpones the deliveries of later-deadline videos to later time slots. The flows that are expected to miss their deadlines are divided into subflows to be rerouted to other under-utilized links. We also propose setting each link's initial charging volume to reduce the scheduling latency at the beginning of the charging period and discuss how to deal with issues such as the prediction errors of link available bandwidth and the lack of charging volume's prior knowledge. Furthermore, we designed implementation strategies for using EcoFlow in both centralized and distributed situations. Experimental results demonstrate that EcoFlow achieves lower bandwidth costs and higher video flow transmission rates when compared to existing methods.

Link Congestion Aware Proactive Routing for Dynamic Traffic in Elastic Optical Networks

Fixed alternate routing is a potential routing scheme for routing and spectrum allocation (RSA) in elastic optical networks (EON) which has less complexity and time consumption compared to adaptive routing scheme. However, adaptive routing scheme efficiently reduces the amount of network bandwidth blocking probabilities (BBPs) which uses traffic engineered paths and tunes according to the current network status. In this paper, an algorithm for routing is proposed for dynamic traffic in EON which works iteratively to arrange the pre-computed fixed alternate routes offline to incorporate link loading. During the offline process, the pre-computed routes are arranged with an objective to reduce link congestion and diverts lightpaths to the under-utilized links. The proposed scheme merges the properties of fixed alternate routing and adaptive routing and is utilized for dynamic traffic in EON. It has been shown through simulation results that the proposed scheme efficiently improves the performance of RSA in EON and reduces the amount of BBPs compared to the fixed alternate routing and an existing constrained-lower-indexed-block (CLIB) based adaptive routing algorithm. The proposed LCA greatly reduces congestion over all links during dynamic network operation and lowers congestion spikes over some links which occues in the existing alternate routing scheme in different network scenarios.

Online service provisioning in elastic optical networks with hybrid algorithm for congestion aware routing and spectrum allocation

Abstract Elastic optical networks (EON) has received intensive research attraction due to its agile spectrum management in the underlying optical backbone infrastructure whose channels can be allocated on variable spectrum width. In this paper, a hybrid scheme is proposed for routing and spectrum allocation (RSA) in EON. An optimization formulation is modeled which takes into account the elastic bandwidth characteristics of optical paths as well as maintains a threshold congestion level on all links. The goal of the proposed model is to minimize the cost of using the network links which results in the minimum cost paths between node pairs. The proposed optimization model is solved offline in the initial stage to obtain routing information which is utilized for online traffic in the second stage. The proposed model is integrated with the spectrum allocation subproblem with the continuity and contiguity constraints. The computational time of the optimization model is shown to be in (time unit) seconds for different networks which is an acceptable time to obtain routing information in the initial stage. The proposed RSA scheme helps to efficiently reduce network blocking probabilities in different network scenarios as the optimization model manages to route traffic load to the underutilized links when the quality of service of lightpaths on the overutilized links meet the desired threshold congestion level.

Empirical Investigation of TCP Incast Congestion in Wireless Cloud Computing Networks

The promising services offered by cloud computing environments have led to huge amount of data that need to be processed and stored. Wireless cloud networks rely on Transmission Control Protocol/Internet Protocol (TCP/IP) for reliable transfer of data traffic between the cloud end-users and servers and vise-versa. Even though TCP has been successful for several applications, it, however, does not perform well in wireless cloud environments. The many-to-one communication pattern used in such environments with such huge amount of data resulted in TCP incast problem. Transmission Control Protocol incast problem happens in cluster based storage workloads where a lot of end-users communicate simultaneously to a server in the cloud through a bottleneck router, creating buffers overflows which lead to high packet loss. This paper presents an empirical study on TCP incast in current wireless cloud networks and how it is caused. It evaluates TCP-Vegas and TCP-Sack to examine their behaviors and suitability for short-lived connections in terms of queue occupancy level, packet drops, throughput, link utilization and bandwidth unfairness between the TCP connections. It was found that both protocols suffer from high packet loss and link underutilization with comparable throughput.

Impact of SDN on Optical Router Bypass

Internet traffic is growing rapidly, driven by new applications such as the Internet of things (IoT). To overcome router scaling limitations, router bypass has been introduced. Traditional bypass is based on provisioning fixed-size bypass channels, which was shown to underutilize link capacity. In software defined networking (SDN), router bypass can be requested as a service by the application layer. This study explores the opportunity to bypass routers efficiently without the link underutilization of the traditional bypass.We combine SDN and dynamic layer provisioning to implement dynamic router bypassing and show how this leads to improved efficiency. A simulation built to compare the traditional bypass with the SDN-based bypass showed that SDN-based bypassing enhanced efficiency by 33%. When bypass traffic is increased, we show that the output capacity of a node increases up to 56%, limited by optical capacity rather than router capacity.

Saving energy and improving performance in SDN using rate adaptation technique

Energy efficiency in wired networks has received considerable attention over the past few years for its heavy economic impact. Energy consumption in such network is becoming a challenging issue. Among all these wired networks Software Defined Networking (SDN) is considered as an intelligent network in which use of programmability provides the best solution for network operation. The logical separation of data plane and control plane enhances its network functionality. Despite of all these mechanisms, energy consumption is also an alarming issue in SDN. Various researchers propose many approaches in order to utilize the energy in its best way. Herein we consider the normal scenario of a data center network, and propose a new energy efficient routing algorithms to improve the performance in SDN, called SERAT. In this work, we focus on discrete of data rate of the link in order to minimize energy consumption in the network. In wired network the underutilized links are even operated in high data rate, increasing energy consumption. In order to reduce energy consumption of the network the links must be operated as per their utilization factor. We have used an output buffer queue with two levels of threshold values in order to monitor the performance of the network. Simulation result shows that the proposed technique leads to major amount of energy savings without mush affecting the throughput.

Effect of AQM-Based RLC Buffer Management on the eNB Scheduling Algorithm in LTE Network

With the advancement of the Long-Term Evolution (LTE) network and smart-phones, most of today’s internet content is delivered via cellular links. Due to the nature of wireless signal propagation, the capacity of the last hop link can vary within a short period of time. Unfortunately, Transmission Control Protocol (TCP) does not perform well in such scenarios, potentially leading to poor Quality of Service (QoS) (e.g., end-to-end throughput and delay) for the end user. In this work, we have studied the effect of Active Queue Management (AQM) based congestion control and intra LTE handover on the performance of different Medium Access Control (MAC) schedulers with TCP traffic by ns3 simulation. A proper AQM design in the Radio Link Control (RLC) buffer of eNB in the LTE network leads to the avoidance of forced drops and link under-utilization along with robustness to a variety of network traffic-loads. We first demonstrate that the original Random Early Detection (RED) linear dropping function cannot cope well with different traffic-load scenarios. Then, we establish a heuristic approach in which different non-linear functions are proposed with one parameter free to define. In our simulations, we demonstrate that the performance of different schedulers can be enhanced via proper dropping function.

Energy-aware traffic engineering in hybrid SDN/IP backbone networks

Software Defined Networking (SDN) can effectively improve the performance of traffic engineering and has promising application foreground in backbone networks. Therefore, new energy saving schemes must take SDN into account, which is extremely important considering the rapidly increasing energy consumption from Telecom and ISP networks. At the same time, the introduction of SDN in a current network must be incremental in most cases, for both technical and economic reasons. During this period, operators have to manage hybrid networks, where SDN and traditional protocols coexist. In this paper, we study the energy efficient traffic engineering problem in hybrid SDN/IP networks. We first formulate the mathematic optimization model considering SDN/IP hybrid routing mode. As the problem is NP-hard, we propose the fast heuristic algorithm named HEATE (Hybrid Energy-Aware Traffic Engineering). In our proposed HEATE algorithm, the IP routers perform the shortest path routing using the distribute OSPF link weight optimization. The SDNs perform the multi-path routing with traffic flow splitting by the global SDN controller. The HEATE algorithm finds the optimal setting of OSPF link weight and splitting ratio of SDNs. Thus traffic flow is aggregated onto partial links and the underutilized links can be turned off to save energy. By computer simulation results, we show that our algorithm has a significant improvement in energy efficiency in hybrid SDN/IP networks.

Emergence of core-peripheries in networks.

A number of important transport networks, such as the airline and trade networks of the world, exhibit a characteristic core–periphery structure, wherein a few nodes are highly interconnected and the rest of the network frays into a tree. Mechanisms underlying the emergence of core–peripheries, however, remain elusive. Here, we demonstrate that a simple pruning process based on removal of underutilized links and redistribution of loads can lead to the emergence of core–peripheries. Links are assumed beneficial if they either carry a sufficiently large load or are essential for global connectivity. This incentivized redistribution process is controlled by a single parameter, which balances connectivity and profit. The obtained networks exhibit a highly resilient and connected core with a frayed periphery. The balanced network shows a higher resilience than the world airline network or the world trade network, revealing a pathway towards robust structural features through pruning.

RISO: Enforce Noninterfered Performance With Relaxed Network-on-Chip Isolation in Many-Core Cloud Processors

Workload consolidation is widely used in modern cloud processors to reduce total cost of ownership. Performance isolation has to be enforced between consolidated workloads to achieve controllable quality of service. Networks-on-chip (NoCs), as a major shared resource, often incur traffic interference and violate performance isolation criteria. Previous work resorts to strict isolation strategy that partitions NoC into independent regions to isolate core-to-core communication traffic. However, strict isolation either results in low consolidation density or degrades network performance, and more importantly, cannot be applied to memory access traffic. To address these weaknesses, we propose a novel performance isolation strategy in NoC, called relaxed isolation (RISO). It permits underutilized routers and links to be shared by multiple applications, and, at the same time, it keeps the aggregated traffic in check to enforce performance isolation. Experimental results show that RISO could effectively improve consolidation density and network performance in synergy.

Reducing Energy Consumption in Wired OpenFlow-Based Networks

Due to the proliferation of mobile devices such as smart phones and tablet computers, and increase in the speed of network devices to forward data, the Internet traffic has increased manyfold compare to a decade ago. Energy consumed by network devices handling the network traffic has increased manyfold also. Researchers are not only focusing on battery oriented network such as wireless sensor and ad hoc networks on saving battery power to extend network life but are also focusing on wired network to save energy consumed by network devices. Energy consumed by wired network can be reduced by putting underutilized network devices or links to sleep. If a network device has a few links such as a backbone network device, it is better to consider underutilized device to put to sleep, but if a network device has many links such as in data centers network devices and campus networks devices, it is better to consider underutilized links to put to sleep. In this paper, we consider putting underutilized links to sleep. Off course, if all links of a network device are put to sleep, the device itself will be put to sleep. Furthermore, in this paper we consider OpenFlow-based network as it is software defined network and flexible to control network devices. Besides, OpenFlow is being standardized by big enterprises such as NEC, Google, Cisco, Microsoft etc. We evaluated our approach by simulation and compare it with node based approach to see its effectiveness.

Split-TCP based acceleration gateway over packet lossy networks

The conservative Additive Increase Multiplicative Decrease mechanism of traditional TCP causes the link under-utilization in the Wide Area Networks (WANs) due to the WANs' intrinsic nature of high latency and high packet loss. To alleviate the problem, we present the design and implantation of STAG, an Acceleration Gateway with Split-TCP in the paper. STAG is built on embedded network equipment and acts as a transparent proxy. In STAG, a new improved congestion control method named Rapid TCP is adopted, which determines whether or not to decrease the congestion window based on the packet loss trend. In particular, in the fast recovery phase, it chooses different window adjustment strategies based on the current size of congestion window to achieve higher utilization. The performance validation of STAG is done on both our emulation testbed and the real wide area network. The results show that STAG with Rapid TCP effectively adapts to the high loss network environment and significantly speeds up the applications without loss of fairness.

Dynamic Distributed Flow Scheduling with Load Balancing for Data Center Networks

Current Flow Scheduling techniques in Data Center Networks(DCN) results in overloaded or underutilized links. Static flow scheduling techniques such as ECMP and VLB use hashing techniques for scheduling the flows. In case of hash collision a path gets selected number of times resulting overloading of that path and underutilization of other paths. Dynamic flow scheduling techniques like global first fit employ centralized scheduler and always selects first fittest candidate path for scheduling. Thus in addition to single-point-of-failure the overall link uti- lization also remains a problem as the flows are not scheduled on the best available candidate path. This paper presents firstly a Dynamic Distributed Flow Scheduling(DDFS) mechanism that will lead to fair link utilization in globally used fat-tree topology of DCN. Secondly, it presents a mechanism to restrict the flow scheduling de- cisions to the lower layers thus avoiding saturation of core switches. The entire DCN is simulated using Colored Petri Nets (CPN). The load measured at the aggregate switches for various flow patterns in DCN reveals that the load factors at the aggregate switches vary by at most 0.11 which signifies the fair utilization of links.

Energy efficient online routing of flows with additive constraints

A number of studies report that ICT sectors are responsible for up to 10% of the worldwide power consumption and that a substantial share of such amount is due to the Internet infrastructure. To accommodate the traffic in the peak hours, Internet Service Providers (ISP) have overprovisioned their networks, with the result that most of the links and devices are under-utilized most of the time. Thus, under-utilized links and devices may be put in a sleep state in order to save power and that might be achieved by properly routing traffic flows. In this paper, we address the design of a joint admission control and routing scheme aiming at maximizing the number of admitted flow requests while minimizing the number of nodes and links that need to stay active. We assume an online routing paradigm, where flow requests are processed one-by-one, with no knowledge of future flow requests. Each flow request has requirements in terms of bandwidth and m additive measures (e.g., delay, jitter). We develop a new routing algorithm, E2-MCRA, which searches for a feasible path for a given flow request that requires the least number of nodes and links to be turned on. The basic concepts of E2-MCRA are look-ahead, the depth-first search approach and a path length definition as a function of the available bandwidth, the additive QoS constraints and the current status (on/off) of the nodes and links along the path. Finally, we present the results of the simulation studies we conducted to evaluate the performance of the proposed algorithm.

Proposed Low-Power High-Speed Microring Resonator-Based Switching Technique for Dynamically Reconfigurable Optical Interconnects

The dynamic bandwidth re-allocation (DBR) technique balances traffic by re-allocating bandwidth from under-utilized links to over-utilized links in a network. In this letter, we propose a nonblocking, fast, low-power, and integratable optical switch that enables DBR. The basic building blocks of the proposed switch are silicon-on-insulator-based microring resonators. Analytical and numerical studies show that the active switch design gives similar performance in throughput and latency, while reducing cost (number of lasers) and area significantly when compared to implementation of DBR with only passive components. There is a slight increase in power (~0.4% for worst-case traffic pattern) using the active switch implementation.

Using TCP flow-aggregation to enhance data experience of cellular wireless users

All over the world Global System for Mobile Communication (GSM) cellular mobile networks have been upgraded to support the "always-on" general packet radio service (GPRS). Despite the apparent availability of levels of bandwidth not dissimilar to that provided by conventional fixed-wire telephone modems, the user experience using GPRS is still considerably poor. In this paper, we examine the performance of protocols such as transmission control protocol (TCP) over GPRS, and show how certain network characteristics interact badly with TCP to yield problems such as: link underutilization for short-lived flows, excess queueing for long-lived flows, acknowledgment bunching, poor loss recovery, and gross unfairness between competing flows. We present the design and implementation of a transparent TCP proxy that mitigates many of these problems without requiring any changes to the TCP implementations in either mobile or fixed-wire end systems. The proxy is interposed in the cellular provider's network, and splits TCP connections transparently into two halves-the wired and wireless sides. Connections destined for the same mobile host are treated as an aggregate due to their statistical dependence. We demonstrate packet scheduling and flow control algorithms that use information shared between the connections to maximize performance of the wireless link, while interworking with unmodified TCP peers. We also demonstrate how fairness between flows and response to loss is improved, and that queueing and, hence, network latency is reduced. We discuss how TCP enhancing proxies could be transparently deployed, and conclude that installing such a proxy into GPRS network would be of significant benefit to users.

Optimizing Web delivery over wireless links: design, implementation, and experiences

World over wide-area wireless Global System for Mobile Communication (GSM) networks have been upgraded to support the general packet radio service (GPRS). GPRS brings always-on wireless data connectivity at bandwidths comparable to that of conventional fixed-line telephone modems. Unfortunately many users have found the reality to be rather different, experiencing very disappointing performance when, for example, browsing the Web over GPRS. In This work, we show what causes the web and its underlying transport protocol TCP to underperform in a GPRS wide-area wireless environment. We examine why certain GPRS network characteristics interact badly with TCP to yield problems such as: link underutilization for short-lived flows, excess queueing for long-lived flows, ACK compression, poor loss recovery, and gross unfairness between competing flows. We also show that many Web browsers tend to be overly aggressive, and by opening too many simultaneous TCP connections can aggravate matters. We present the design and implementation of a web optimizing system called GPRSWeb that mitigates many of the GPRS link-related performance problems with a simple software update to a mobile device. The update is a link-aware middleware (a local proxy) that sits in the mobile device, and communicates with a server proxy located at the other end of the wireless link, close to the wired-wireless border. The dual-proxy architecture collectively implements a number of key enhancements-an aggressive caching scheme that employs content-based hash keying to improve hit rates for dynamic content, a preemptive push of Web page support resources to mobile clients, resource adaptation to suit client capabilities, delta encoded data transfer of modified pages, DNS lookup migration, and a UDP-based reliable transport protocol that is specifically optimized for use over GPRS. We show that these enhancements results in significant improvement in web performance over GPRS links.

A RED function design targeting link utilization and stable queue size behavior

In this article we introduce a derivation method for the Random Early Detection (RED) drop function, drawing on heuristics and control theory. This way the negative effects experienced by deploying the original linear RED drop probability function are improved so that link under-utilization and heavy oscillations are avoided and the function is applicable to a wide load range. As it is impossible to include all of these requirements in one approach, we show two separate approaches and combine them at the end. The first approach aims at avoiding link under-utilization and is achieved heuristically. Therefore we provide a few examples from simulations to illustrate that the original linear RED drop function fails to avoid under-utilization and is not applicable to a wide load range. We use these examples to define conditions a proper drop function has to meet in order for under-utilization to be avoided. Bearing these conditions in mind, we propose a heuristic approach, where even a class of non-linear drop functions originates, with, apart from the usual RED parameters, one parameter free to define. Simple simulations show that such a non-linearity in the drop function should be preferred concerning the metric of under-utilization. According to the second approach the drop function is derived analytically based on the condition to achieve system stability, i.e. to avoid heavy oscillations. Here, we use a mathematical model for the TCP window queue size behavior of a router operating with TCP and apply control theory for the derivation process. The term stability refers to the oscillation amplitude of the steady state queue size, whereas heavy oscillations indicate an unstable state. The analytically derived function is polynomial and can be approximated by using the findings of the first approach. The derived function thus avoids both under-utilization and heavy oscillations. The applicability to an arbitrary load range is included automatically in the derivation process. The impacts of parameter variations are investigated. Simulative comparisons of the derived function with ARED and with GRED (parameter variation included) with both FTP and Web traffic clearly attest to the advantage of the derivation process and to an improvement in RED performance, especially in metrics, such as link utilization, forced drops and queue size variation.