Transmission Control Protocol | EPFL Graph Search

The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonly referred to as TCP/IP. TCP provides reliable, ordered, and error-checked delivery of a stream of octets (bytes) between applications running on hosts communicating via an IP network. Major internet applications such as the World Wide Web, email, remote administration, and rely on TCP, which is part of the Transport Layer of the TCP/IP suite. SSL/TLS often runs on top of TCP. TCP is connection-oriented, and a connection between client and server is established before data can be sent. The server must be listening (passive open) for connection requests from clients before a connection is established. Three-way handshake (active open), retransmission, and error detection adds to reliability but lengthens latency. Applications that do not requi

Extending R2P2 with Congestion Control and Request-Level Scheduling

Konstantinos Prasopoulos

Distributed low-latency datacenter applications must meet strict service-level objectives in the order of microseconds. R2P2 is a novel datacenter transport protocol designed for such services. This work extends R2P2 with congestion control and request-level scheduling. It provides a configurable upper bound to in-network queuing using the idleness of the ToR-to-host link as the congestion signal. It also reduces the mean and tail RPC latency by minimizing head-of-line blocking in the network through shortest remaining processing time scheduling. The receiver driven scheduling mechanism is general and can support a variety of scheduling policies. The extension improves the performance of R2P2 under network load by at least 23% and up to two orders of magnitude. Finally, it enables R2P2 to perform similarly to a theoretically near-optimal, clean-slate transport protocol design.

2020

Schemes and architectures for wireless ad hoc networks and cooperative communication

Tarik Tabet

The focus of this thesis is on the study of decentralized wireless multi-hop networks. We are particularly interested in establishing bounds on the traffic-carrying capabilities of wireless ad hoc networks and conditions on the scalability of such networks with node mobility. This theoretical investigation brings forward challenges on the design of such networks. This leads to a second part of this thesis that considers the feasibility and the design of physical layer architectures and schemes for decentralized wireless multi-hop networks. In the first part of this thesis, bounds on the capacity of wireless ad hoc networks with two types of non-uniform traffic patterns are established. We focus on the impact of traffic patterns where local communications predominate and show the improvement in terms of per user-capacity over ad hoc networks with unbounded average communication distances. We then study the capacity of hybrid wireless networks, where long-distance relaying is performed by a fixed overlay network of base-stations. We investigate the scaling of capacity versus the number of nodes and the density of base-stations in the area of the network. It is shown that the gain in performance is mainly due to the reduction in the mean number of hops from source to destination. Then, we investigate the impact of mobility on the ad hoc network capacity. We propose a set of necessary and sufficient conditions under which the long-term averaged throughput in an ad hoc network can remain constant as the number of nodes increases. The main idea is to use a connectivity graph that does not represent the actual physical network, but rather the available communication resources. This graph also allows to translate the problem of maximizing the throughput in ad hoc networks to the multi-commodity flow problem and directly apply related results. In contrast to these macroscopic studies, in the second part we focus on a microscopic analysis of ad hoc wireless networks. We are interested in characterizing the performance of decentralized multiple-access and retransmission schemes for multi-hop wireless networks with the goal of drawing conclusions on cross-layer design. We investigate different transmission strategies in order to assess the tradeoff between spatial density of communications and the range of each transmission. We present tools for characterizing the spatial throughput as a function of topological parameters (e.g node population density) and system parameters (propagation, bandwith etc). The results of this work also show that coding and retransmissions provide means of reliable communication coupled with a completely decentralized multiple-access strategy. Finally, an efficient protocol for the delay-limited fading Automatic Retransmission reQuest (ARQ) single relay channel is considered for cooperative communications. The proposed protocol exploits two kinds of diversity: (i) space diversity available through the cooperative (relay) terminal, which retransmits the source's signals, (ii) ARQ diversity obtained by leveraging the retransmission delay to enhance the reliability. The performance characterization is in terms of the achievable diversity, multiplexing gain and delay tradeoff for a high signal-to-noise ratio (SNR) regime. Then, by letting the source's power level vary over the retransmission rounds, we show the benefits of power control on the diversity.

EPFL2007

Cross-Layer Based Analysis of Multi-Hop Wireless Networks

Tarik Tabet

In this work, we revisit classical packet radio networks with a modern treatment of physical-layer (PHY) procedures, medium-access (MAC) and geographic channel-driven routing protocols. Our network model assumes that nodes are randomly distributed on the plane according to a homogeneous spatial Poisson process, using which we provide a novel representation of interference statistics resulting from packet collisions. Using this representation, we develop a cross-layer analysis methodology which allows multi-hop routing protocols to be treated using generic information-theoretic models for the underlying PHY/MAC procedures. These models inherently characterize modern procedures such as channel code rate adaptation, incremental redundancy and packet combining/capture. These models further allow for the assessment of the tradeoff between spatial throughput, measured in bit-meters per signal-space dimension, the range of each transmission and the average transmission delay. A generic formulation based on system parameters, such as system bandwidth, propagation models, etc., is given to analyze this tradeoff in an operational setting which can be used to build system simulators for such networks. Finally, from a purely PHY perspective, the results of this work show that coding and incremental retransmission provide a means for reliable communication coupled with a completely decentralized multiple-access strategy.

2010

Schemes and architectures for wireless ad hoc networks and cooperative communication

Tarik Tabet

EPFL2007