Latency is increasingly becoming a performance bottleneck for Internet Protocol (IP) networks, but historically networks have been designed with aims of maximizing throughput and utilization. This article offers a broad survey of techniques aimed at tackling latency in the literature up to August 2014, and their merits. A goal of this work is to be able to quantify and compare the merits of the different Internet latency reducing techniques, contrasting their gains in delay reduction versus the pain required to implement and deploy them. We found that classifying techniques according to the sources of delay they alleviate provided the best insight into the following issues: 1) the structural arrangement of a network, such as placement of servers and suboptimal routes, can contribute significantly to latency; 2) each interaction between communicating endpoints adds a Round Trip Time (RTT) to latency, especially significant for short flows; 3) in addition to base propagation delay, several sources of delay accumulate along transmission paths, today intermittently dominated by queuing delays; 4) it takes time to sense and use available capacity, with overuse inflicting latency on other flows sharing the capacity; and 5) within end systems delay sources include operating system buffering, head-of-line blocking, and hardware interaction. No single source of delay dominates in all cases, and many of these sources are spasmodic and highly variable. Solutions addressing these sources often both reduce the overall latency and make it more predictable.

Pricing has become one of the main challenges of the networking community and is receiving a great deal of interest in the literature. In this paper, we analyze the so-called Paris Metro Pricing scheme which separates the network into different and independent subnetworks, each behaving equivalently, except that they charge their customers at different rates. In our model, each subnetwork is represented by a single bottleneck queue, and the "customers" (data packets) choose their subnetwork taking into account not only the prices, but also the expected delay, which is supposed to have an economic impact. We obtain some necessary and sufficient conditions for the stability of the system; we analyze the problem of maximizing the network revenue and compare it with the case of a single network, and present several extensions of the model. Numerical results illustrating some key aspects of the system are provided throughout the paper.

Abstract-Active Queue Management (AQM) design has again come into the spotlight of network operators, vendors and OS developers. This reflects the growing concern and sensitivity about the end-to-end latency perceived by today's Internet users. CoDel and PIE are two AQM mechanisms that have recently been presented and discussed in the IRTF and the IETF as solutions for keeping latency low. To the best of our knowledge, they have so far only been evaluated or compared against each other using default parameter settings, which naturally presents a rather limited view of their operational range. We set thus to perform a broader experimental evaluation using real-world implementations in a wired testbed. We have in addition compared them with a decadeold variant of RED called Adaptive RED, which shares with CoDel and PIE the goal of "knob-free" operation. Surprisingly, in several instances results were favorable towards Adaptive RED.

Abstract-In recent years, the notion of a service offering a degraded performance with respect to the besteffort service traditionally found in IP networks has gained acceptance among network researchers. Such a less-thanbest-effort (LBE) service may be considered as another way of providing a differentiated quality of service, following A. Odlyzko's "damaged goods for the Internet" approach. In this paper we are interested in evaluating, from a pricing perspective, the implications of the two scheduling models commonly proposed for building a LBE service-namely, Priority Queueing and Generalized Processor Sharing (GPS). In particular, we focus on the network operator's issue of maximizing her revenue. We wish to study, for each scheduler, how to set prices and, especially, the impact that a given queueing model may have on revenues when users are mostly sensitive to delay. Drawing on previous work by Mandjes (2003), we present analytical expressions of the revenue earned by the network operator, when a GPS scheduler is used. A comparison of optimal revenues shows that: (a) Priority Queueing is more efficient, in economic terms, than both a GPS scheduler and a simple FIFO queue, that is, a network with no service differentiation; (b) revenues are lower with a GPS scheduler than with a FIFO queue. These results may have implications both on the practical implementation of LBE services and on the Paris Metro Pricing proposal by Odlyzko (1999).

It is widely recognized that the Internet transport layer has become ossified, where further evolution has become hard or even impossible. This is a direct consequence of the ubiquitous deployment of middleboxes that hamper the deployment of new transports, aggravated further by the limited flexibility of the application programming interface (API) typically presented to applications. To tackle this problem, a wide range of solutions have been proposed in the literature, each aiming to address a particular aspect. Yet, no single proposal has emerged that is able to enable evolution of the transport layer. In this paper, after an overview of the main issues and reasons for transportlayer ossification, we survey proposed solutions and discuss their potential and limitations. The survey is divided into five parts, each covering a set of point solutions for a different facet of the problem space: 1) designing middlebox-proof transports; 2) signaling for facilitating middlebox traversal; 3) enhancing the API between the applications and the transport layer; 4) discovering and exploiting end-to-end capabilities; and 5) enabling user-space protocol stacks. Based on this analysis, we then identify further development needs toward an overall solution. We argue that the development of a comprehensive transport layer framework, able to facilitate the integration and cooperation of specialized solutions in an application-independent and flexible way, is a necessary step toward making the Internet transport architecture truly evolvable. To this end, we identify the requirements for such a framework and provide insights for its development.