Computer Networks and the Internet
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A Comparison of Mechanisms for Improving TCP Performance Over Wireless Links
A Comparison of Mechanisms for Improving TCP Performance over Wireless Links Hari Balakrishnan, Venkata N. Padmanabhan, Srinivasan Seshan and Randy H. Katz1 {hari,padmanab,ss,randy}@cs.berkeley.edu Computer Science Division, Department of EECS, University of California at Berkeley Abstract the estimated round-trip delay and the mean linear deviation from it. The sender identifies the loss of a packet either by Reliable transport protocols such as TCP are tuned to per- the arrival of several duplicate cumulative acknowledg- form well in traditional networks where packet losses occur ments or the absence of an acknowledgment for the packet mostly because of congestion. However, networks with within a timeout interval equal to the sum of the smoothed wireless and other lossy links also suffer from significant round-trip delay and four times its mean deviation. TCP losses due to bit errors and handoffs. TCP responds to all reacts to packet losses by dropping its transmission (conges- losses by invoking congestion control and avoidance algo- tion) window size before retransmitting packets, initiating rithms, resulting in degraded end-to-end performance in congestion control or avoidance mechanisms (e.g., slow wireless and lossy systems. In this paper, we compare sev- start [13]) and backing off its retransmission timer (Karn’s eral schemes designed to improve the performance of TCP Algorithm [16]). These measures result in a reduction in the in such networks. We classify these schemes into three load on the intermediate links, thereby controlling the con- broad categories: end-to-end protocols, where loss recovery gestion in the network. is performed by the sender; link-layer protocols, that pro- vide local reliability; and split-connection protocols, that Unfortunately, when packets are lost in networks for rea- break the end-to-end connection into two parts at the base sons other than congestion, these measures result in an station. -
Lecture 8: Overview of Computer Networking Roadmap
Lecture 8: Overview of Computer Networking Slides adapted from those of Computer Networking: A Top Down Approach, 5th edition. Jim Kurose, Keith Ross, Addison-Wesley, April 2009. Roadmap ! what’s the Internet? ! network edge: hosts, access net ! network core: packet/circuit switching, Internet structure ! performance: loss, delay, throughput ! media distribution: UDP, TCP/IP 1 What’s the Internet: “nuts and bolts” view PC ! millions of connected Mobile network computing devices: server Global ISP hosts = end systems wireless laptop " running network apps cellular handheld Home network ! communication links Regional ISP " fiber, copper, radio, satellite access " points transmission rate = bandwidth Institutional network wired links ! routers: forward packets (chunks of router data) What’s the Internet: “nuts and bolts” view ! protocols control sending, receiving Mobile network of msgs Global ISP " e.g., TCP, IP, HTTP, Skype, Ethernet ! Internet: “network of networks” Home network " loosely hierarchical Regional ISP " public Internet versus private intranet Institutional network ! Internet standards " RFC: Request for comments " IETF: Internet Engineering Task Force 2 A closer look at network structure: ! network edge: applications and hosts ! access networks, physical media: wired, wireless communication links ! network core: " interconnected routers " network of networks The network edge: ! end systems (hosts): " run application programs " e.g. Web, email " at “edge of network” peer-peer ! client/server model " client host requests, receives -
Bit & Baud Rate
What’s The Difference Between Bit Rate And Baud Rate? Apr. 27, 2012 Lou Frenzel | Electronic Design Serial-data speed is usually stated in terms of bit rate. However, another oft- quoted measure of speed is baud rate. Though the two aren’t the same, similarities exist under some circumstances. This tutorial will make the difference clear. Table Of Contents Background Bit Rate Overhead Baud Rate Multilevel Modulation Why Multiple Bits Per Baud? Baud Rate Examples References Background Most data communications over networks occurs via serial-data transmission. Data bits transmit one at a time over some communications channel, such as a cable or a wireless path. Figure 1 typifies the digital-bit pattern from a computer or some other digital circuit. This data signal is often called the baseband signal. The data switches between two voltage levels, such as +3 V for a binary 1 and +0.2 V for a binary 0. Other binary levels are also used. In the non-return-to-zero (NRZ) format (Fig. 1, again), the signal never goes to zero as like that of return- to-zero (RZ) formatted signals. 1. Non-return to zero (NRZ) is the most common binary data format. Data rate is indicated in bits per second (bits/s). Bit Rate The speed of the data is expressed in bits per second (bits/s or bps). The data rate R is a function of the duration of the bit or bit time (TB) (Fig. 1, again): R = 1/TB Rate is also called channel capacity C. If the bit time is 10 ns, the data rate equals: R = 1/10 x 10–9 = 100 million bits/s This is usually expressed as 100 Mbits/s. -
Guidelines on Mobile Device Forensics
NIST Special Publication 800-101 Revision 1 Guidelines on Mobile Device Forensics Rick Ayers Sam Brothers Wayne Jansen http://dx.doi.org/10.6028/NIST.SP.800-101r1 NIST Special Publication 800-101 Revision 1 Guidelines on Mobile Device Forensics Rick Ayers Software and Systems Division Information Technology Laboratory Sam Brothers U.S. Customs and Border Protection Department of Homeland Security Springfield, VA Wayne Jansen Booz-Allen-Hamilton McLean, VA http://dx.doi.org/10.6028/NIST.SP. 800-101r1 May 2014 U.S. Department of Commerce Penny Pritzker, Secretary National Institute of Standards and Technology Patrick D. Gallagher, Under Secretary of Commerce for Standards and Technology and Director Authority This publication has been developed by NIST in accordance with its statutory responsibilities under the Federal Information Security Management Act of 2002 (FISMA), 44 U.S.C. § 3541 et seq., Public Law (P.L.) 107-347. NIST is responsible for developing information security standards and guidelines, including minimum requirements for Federal information systems, but such standards and guidelines shall not apply to national security systems without the express approval of appropriate Federal officials exercising policy authority over such systems. This guideline is consistent with the requirements of the Office of Management and Budget (OMB) Circular A-130, Section 8b(3), Securing Agency Information Systems, as analyzed in Circular A- 130, Appendix IV: Analysis of Key Sections. Supplemental information is provided in Circular A- 130, Appendix III, Security of Federal Automated Information Resources. Nothing in this publication should be taken to contradict the standards and guidelines made mandatory and binding on Federal agencies by the Secretary of Commerce under statutory authority. -
Research on the System Structure of IPV9 Based on TCP/IP/M
International Journal of Advanced Network, Monitoring and Controls Volume 04, No.03, 2019 Research on the System Structure of IPV9 Based on TCP/IP/M Wang Jianguo Xie Jianping 1. State and Provincial Joint Engineering Lab. of 1. Chinese Decimal Network Working Group Advanced Network, Monitoring and Control Shanghai, China 2. Xi'an, China Shanghai Decimal System Network Information 2. School of Computer Science and Engineering Technology Ltd. Xi'an Technological University e-mail: [email protected] Xi'an, China e-mail: [email protected] Wang Zhongsheng Zhong Wei 1. School of Computer Science and Engineering 1. Chinese Decimal Network Working Group Xi'an Technological University Shanghai, China Xi'an, China 2. Shanghai Decimal System Network Information 2. State and Provincial Joint Engineering Lab. of Technology Ltd. Advanced Network, Monitoring and Control e-mail: [email protected] Xi'an, China e-mail: [email protected] Abstract—Network system structure is the basis of network theory, which requires the establishment of a link before data communication. The design of network model can change the transmission and the withdrawal of the link after the network structure from the root, solve the deficiency of the transmission is completed. It solves the problem of original network system, and meet the new demand of the high-quality real-time media communication caused by the future network. TCP/IP as the core network technology is integration of three networks (communication network, successful, it has shortcomings but is a reasonable existence, broadcasting network and Internet) from the underlying will continue to play a role. Considering the compatibility with structure of the network, realizes the long-distance and the original network, the new network model needs to be large-traffic data transmission of the future network, and lays compatible with the existing TCP/IP four-layer model, at the a solid foundation for the digital currency and virtual same time; it can provide a better technical system to currency of the Internet. -
F. Circuit Switching
CSE 3461: Introduction to Computer Networking and Internet Technologies Circuit Switching Presentation F Study: 10.1, 10.2, 8 .1, 8.2 (without SONET/SDH), 8.4 10-02-2012 A Closer Look At Network Structure: • network edge: applications and hosts • network core: —routers —network of networks • access networks, physical media: communication links d. xuan 2 1 The Network Core • mesh of interconnected routers • the fundamental question: how is data transferred through net? —circuit switching: dedicated circuit per call: telephone net —packet-switching: data sent thru net in discrete “chunks” d. xuan 3 Network Layer Functions • transport packet from sending to receiving hosts application transport • network layer protocols in network data link network physical every host, router network data link network data link physical data link three important functions: physical physical network data link • path determination: route physical network data link taken by packets from source physical to dest. Routing algorithms network network data link • switching: move packets from data link physical physical router’s input to appropriate network data link application router output physical transport network data link • call setup: some network physical architectures require router call setup along path before data flows d. xuan 4 2 Network Core: Circuit Switching End-end resources reserved for “call” • link bandwidth, switch capacity • dedicated resources: no sharing • circuit-like (guaranteed) performance • call setup required d. xuan 5 Circuit Switching • Dedicated communication path between two stations • Three phases — Establish (set up connection) — Data Transfer — Disconnect • Must have switching capacity and channel capacity to establish connection • Must have intelligence to work out routing • Inefficient — Channel capacity dedicated for duration of connection — If no data, capacity wasted • Set up (connection) takes time • Once connected, transfer is transparent • Developed for voice traffic (phone) g. -
LTE-Advanced
Table of Contents INTRODUCTION........................................................................................................ 5 EXPLODING DEMAND ............................................................................................... 8 Smartphones and Tablets ......................................................................................... 8 Application Innovation .............................................................................................. 9 Internet of Things .................................................................................................. 10 Video Streaming .................................................................................................... 10 Cloud Computing ................................................................................................... 11 5G Data Drivers ..................................................................................................... 11 Global Mobile Adoption ........................................................................................... 11 THE PATH TO 5G ..................................................................................................... 15 Expanding Use Cases ............................................................................................. 15 1G to 5G Evolution ................................................................................................. 17 5G Concepts and Architectures ................................................................................ 20 Information-Centric -
RTM-100 Troposcatter Modem Improved Range, Stability and Throughput for Troposcatter Communications
RTM-100 Troposcatter Modem Improved range, stability and throughput for troposcatter communications The Raytheon RTM-100 troposcatter modem sets new milestones in troposcatter communications featuring 100 MB throughput. Benefits Superior Performance The use of turbo-coding An industry first, the waveform forward error correction The RTM-100 comes as n Operation up to 100 Mbps of Raytheon’s RTM-100 (FEC) and state-of-the-art a compact 2U rack with troposcatter modem offers digital processing ensures an n Unique waveform for multipath standard 70 MHz inputs/ strong resiliency to multipath, unprecedented throughput cancellation and optimized outputs. algorithms for fading immunity which negatively affects up to 100 Mbps. The modem n Quad diversity with soft decision troposcatter communications. integrates a non-linear digital algorithm Combined with an optimized pre-distortion capability. time-interleaving process and n Highly spectrum-efficient FEC The Gigabit Ethernet (GbE) signal channel diversity, the processing data port and the ability RTM- 100 delivers superior n Dual transmission path with to command and control transmission performance. independent digital pre- the operation over Simple The sophisticated algorithms, distortion Network Management including Doppler n Ethernet data and control Protocol (SNMP) simplify the compensation and maximum interface (SNMP and Web integration of the device into ratio combining between the graphical user interface) a net-centric Internet protocol four diversity inputs, ensure n Compact 2U 19-inch -
On the Goodput of TCP Newreno in Mobile Networks
On the Goodput of TCP NewReno in Mobile Networks Sushant Sharma Donald Gillies Wu-chun Feng Virginia Tech, Blacksburg, VA, USA Qualcomm, San Diego, USA Virginia Tech, Blacksburg, VA, USA Abstract—Next-generation wireless networks such as LTE and WiMax can achieve throughputs of several Mbps with TCP. These higher throughputs, however, can easily be destroyed by frequent handoffs, which occur in urban environments due to shadowing. A primary reason for the throughput drop during handoffs is the out of order arrival of packets at the receiver. As a result, in this paper, we model the precise effect of packet-reordering on the goodput of TCP NewReno. Specifically, we develop a TCP NewReno model that captures the goodput of TCP as a function of round-trip time, average time duration between packet-reorder events, average number of packets reordered during every reorder event, and the congestion window threshold of TCP NewReno. We also developed an emulator that runs on a router to implement packet reordering events from time to time. We validate our NewReno model by comparing the goodput results obtained by transferring data between two hosts connected via the emulator to the goodput results that our model predicts. I. MOTIVATION Next-generation wireless technologies such as WiMax and LTE (long term evolution) offer very high data rates (on Fig. 1. Handoff description. the order of several Mbps) to mobile users. As a result, mobile users will come to expect better peak performance a rare event in the wired Internet [12], [13], [14], [15], and from the networks than from current mobile networks. -
Webrtc Based Network Performance Measurements Miranda Mcclellan
WebRTC Based Network Performance Measurements by Miranda McClellan Submitted to the Department of Electrical Engineering and Computer Science in partial fulfillment of the requirements for the degree of Masters of Engineering in Computer Science and Engineering at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 2019 c Massachusetts Institute of Technology 2019. All rights reserved. Author.............................................................. Department of Electrical Engineering and Computer Science May 24, 2019 Certified by. Steven Bauer Research Scientist Thesis Supervisor Accepted by . Katrina LaCurts Chair, Master of Engineering Thesis Committee 2 WebRTC Based Network Performance Measurements by Miranda McClellan Submitted to the Department of Electrical Engineering and Computer Science on May 24, 2019, in partial fulfillment of the requirements for the degree of Masters of Engineering in Computer Science and Engineering Abstract As internet connections achieve gigabit speeds, local area networks (LANs) be- come the main bottleneck for users connection. Currently, network performance tests focus on end-to-end performance over wide-area networks and provide no platform- independent way to tests LANs in isolation. To fill this gap, I developed a suite of network performance tests that run in a web application. The network tests support LAN performance measurement using WebRTC peer-to-peer technology and statis- tically evaluate performance according to the Model-Based Metrics framework. Our network testing application is browser based for easy adoption across platforms and can empower users to understand their in-home networks. Our tests hope to give a more accurate view of LAN performance that can influence regulatory policy of internet providers and consumer decisions. Thesis Supervisor: Steven Bauer Title: Research Scientist 3 4 Acknowledgments I am grateful to the Internet Policy Research Initiative for providing support and context for my technical research within a larger ecosystem of technology policy and advancements. -
Circuit-Switching
Welcome to CSC358! Introduction to Computer Networks Amir H. Chinaei, Winter 2016 Today Course Outline . What this course is about Logistics . Course organization, information sheet . Assignments, grading scheme, etc. Introduction to . Principles of computer networks Introduction 1-2 What is this course about? Theory vs practice . CSC358 : Theory . CSC309 and CSC458 : Practice Need to have solid math background . in particular, probability theory Overview . principles of computer networks, layered architecture . connectionless and connection-oriented transports . reliable data transfer, congestion control . routing algorithms, multi-access protocols, . delay models, addressing, and some special topics Introduction 1-3 Overview: internet protocol stack application: supporting network applications . FTP, SMTP, HTTP application transport: process-process data transfer transport . TCP, UDP network network: routing of datagrams from source to destination link . IP, routing protocols link: data transfer between physical neighboring network elements . Ethernet, 802.111 (WiFi), PPP physical: bits “on the wire” Introduction 1-4 Logistics (1/3) Prerequisite knowledge . Probability theory is a must . Mathematical modeling . Data structures & algorithms Course components . Lectures: concepts . Tutorials: problem solving . Assignments: mastering your knowledge . Readings: preparing you for above . Optional assignments: things in practice, bonus Introduction 1-5 Logistics (2/3) Text book . Computer Networking A Top-Down Approach Featuring the Internet 5th Edition, J. F. Kurose and K. W. Ross Lecture slides . Many slides are (adapted) from the above source . © All material copyright . All rights reserved for the authors Introduction 1-6 Logistics (3/3) For important information on . Lecture and tutorial time/location . Contact information of course staff (instructor and TAs) . Office hour and location . Assignments specification and solution . -
From Packet Switching to the Cloud
Professor Nigel Linge FROM PACKET SWITCHING TO THE CLOUD Telecommunication engineers have always drawn a picture of a cloud to represent a network. Today, however, the cloud has taken on a new meaning, where IT becomes a utility, accessed and used in exactly the same on-demand way as we connect to the National Grid for electricity. Yet, only 50 years ago, this vision of universal access to an all- encompassing and powerful network would have been seen as nothing more than fanciful science fiction. he first electronic, digital, network - a figure that represented a concept of packet switching in which stored-program computer 230% increase on the previous year. data is assembled into a short se- was built in 1948 and This clear and growing demand for quence of data bits (a packet) which heralded the dawning of data services resulted in the GPO com- includes an address to tell the network a new age. missioning in July 1970 an experi- where the data is to be sent, error de- T mental, manual call-set-up, data net- tection to allow the receiver to confirm DATA COMMUNICATIONS 1 work that used modems operating at that the contents of the packet are cor- These early computers were large, 48,000bit/s (48kbit/s). rect and a source address to facilitate cumbersome and expensive machines However, computer communica- a reply. and inevitably a need arose for a com- tions is different to voice communi- Since each packet is self-contained, munication system that would allow cations not only in its form but also any number of them can be transmit- shared remote access to them.