Computer Networks--The ALOHA System
Total Page:16
File Type:pdf, Size:1020Kb
Load more
Recommended publications
-
Evolution of Switching Techniques Frequency Division Multiplexing
Evolution of Switching Techniques 1. Dedicate Channel. Separate wire frequency division multiplexing (FDM) time division multiplexing (TDM) Multiplexor (MUX) Demultiplexor (Concentrator) DEMUX individual lines shared individual lines high speed line Frequency Frequency Channel 1 available bandwidth 2 1 2 3 4 1 2 3 4 1 2 3 4 3 4 FDM Time TDM Time chow CS522 F2001—Multiplexing and Switching—10/17/2001—Page 1 Frequency Division Multiplexing (FDM) chow CS522 F2001—Multiplexing and Switching—10/17/2001—Page 2 Wavelength Division Multiplexing chow CS522 F2001—Multiplexing and Switching—10/17/2001—Page 3 Impact of WDM z Many big organizations are starting projects to design WDM system or DWDN (Dense Wave Division Mutiplexing Network). We may see products appear in next three years.In Fujitsu and CCL/Taiwan, 128 different wavelengthes on the same strand of fiber was reported working in the lab. z We may have optical routers between end systems that can take one wavelenght signal, covert to different wavelenght, send it out on different links. Some are designing traditional routers that covert optical signal to electronical signal, and use time slot interchange based on high speed memory to do the switching, the convert the electronic signal back to optical signal. z With this type of optical networks, we will have a virtual circuit network, where each connection is assigned some wave length. Each connection can have 2.4 gbps tremedous bandwidth. z With inital 128 different wavelength, we can have about 10 end users. If each pair of end users needs to communicate simultaneously, it will use 10*10=100 different wavelength. -
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 -
The Internet Development Process Stockholm October 2010
The Internet development Process Stockholm October 2010 Pål Spilling What I would talk about? • The main Norwegian contributions • Competitions between alternatives • Did Norway benefit from its participation? • Some observations and reflections • Conclusion A historical timeline 1981/82 TCP/IP accepted standard for US 1993 Web browser Mosaic Defence became available 1980 TCP/IP fully 2000 developed 1975 Start of the Internet Project; 1974 Preliminary specificaons of TCP 1977 First 3 – network Demonstration Mid 1973 ARPANET covers US, Hawaii, FFI Kjeller, and UCL London 1950 1955 ‐1960, End 1968 Ideas of resource Start of the ARPANET sharing networks project Norway and UK on ARPANET 1973 London o SATNET o Kjeller Norwegian Contributions • SATNET development – Simulations – Performance measurements • Internet performance measurements • Packet speech experiments over the Internet • Improved PRNET protocol architecture Competitions between alternatives • X.25 (ITU) • ISO standards (committee work) • DECNET (proprietary) • IBM (proprietary) • TCP/IP demonstrated its usefullness i 1977 accepted as a standard for US defence Norwegian benefits • Enabled me to create a small Norwegian internet • Got access to UNIX, with TCP/IP and user services integrated • Gave research scientists early exposure to internet and its services • Early curriculum in computer communications; Oslo University Observations and reflections • Norwegian Arpanet Committee; dissolved itself due to lack of interest • IP address space too small for todays use • TCP split in -
1117 M. Stahl Obsoletes Rfcs: 1062, 1020, 997, 990, 960, 943, M
Network Working Group S. Romano Request for Comments: 1117 M. Stahl Obsoletes RFCs: 1062, 1020, 997, 990, 960, 943, M. Recker 923, 900, 870, 820, 790, 776, 770, 762, SRI-NIC 758, 755, 750, 739, 604, 503, 433, 349 August 1989 Obsoletes IENs: 127, 117, 93 INTERNET NUMBERS Status of this Memo This memo is an official status report on the network numbers and the autonomous system numbers used in the Internet community. Distribution of this memo is unlimited. Introduction This Network Working Group Request for Comments documents the currently assigned network numbers and gateway autonomous systems. This RFC will be updated periodically, and in any case current information can be obtained from Hostmaster at the DDN Network Information Center (NIC). Hostmaster DDN Network Information Center SRI International 333 Ravenswood Avenue Menlo Park, California 94025 Phone: 1-800-235-3155 Network mail: [email protected] Most of the protocols used in the Internet are documented in the RFC series of notes. Some of the items listed are undocumented. Further information on protocols can be found in the memo "Official Internet Protocols" [40]. The more prominent and more generally used are documented in the "DDN Protocol Handbook" [17] prepared by the NIC. Other collections of older or obsolete protocols are contained in the "Internet Protocol Transition Workbook" [18], or in the "ARPANET Protocol Transition Handbook" [19]. For further information on ordering the complete 1985 DDN Protocol Handbook, contact the Hostmaster. Also, the Internet Activities Board (IAB) publishes the "IAB Official Protocol Standards" [52], which describes the state of standardization of protocols used in the Internet. -
Circuit-Switched Coherence
Circuit-Switched Coherence ‡Natalie Enright Jerger, ‡Mikko Lipasti, and ?Li-Shiuan Peh ‡Electrical and Computer Engineering Department, University of Wisconsin-Madison ?Department of Electrical Engineering, Princeton University Abstract—Circuit-switched networks can significantly lower contention, overall system performance can degrade by 20% the communication latency between processor cores, when or more. This latency sensitivity coupled with low link uti- compared to packet-switched networks, since once circuits are set up, communication latency approaches pure intercon- lization motivates our exploration of circuit-switched fabrics nect delay. However, if circuits are not frequently reused, the for CMPs. long set up time and poorer interconnect utilization can hurt Our investigations show that traditional circuit-switched overall performance. To combat this problem, we propose a hybrid router design which intermingles packet-switched networks do not perform well, as circuits are not reused suf- flits with circuit-switched flits. Additionally, we co-design a ficiently to amortize circuit setup delay. This observation prediction-based coherence protocol that leverages the exis- motivates a network with a hybrid router design that sup- tence of circuits to optimize pair-wise sharing between cores. The protocol allows pair-wise sharers to communicate di- ports both circuit and packet switching with very fast circuit rectly with each other via circuits and drives up circuit reuse. reconfiguration (setup/teardown). Our preliminary results Circuit-switched coherence provides overall system perfor- show this leading to up to 8% improvement in overall system mance improvements of up to 17% with an average improve- performance over a packet-switched fabric. ment of 10% and reduces network latency by up to 30%. -
Medium Access Control Layer
Telematics Chapter 5: Medium Access Control Sublayer User Server watching with video Beispielbildvideo clip clips Application Layer Application Layer Presentation Layer Presentation Layer Session Layer Session Layer Transport Layer Transport Layer Network Layer Network Layer Network Layer Univ.-Prof. Dr.-Ing. Jochen H. Schiller Data Link Layer Data Link Layer Data Link Layer Computer Systems and Telematics (CST) Physical Layer Physical Layer Physical Layer Institute of Computer Science Freie Universität Berlin http://cst.mi.fu-berlin.de Contents ● Design Issues ● Metropolitan Area Networks ● Network Topologies (MAN) ● The Channel Allocation Problem ● Wide Area Networks (WAN) ● Multiple Access Protocols ● Frame Relay (historical) ● Ethernet ● ATM ● IEEE 802.2 – Logical Link Control ● SDH ● Token Bus (historical) ● Network Infrastructure ● Token Ring (historical) ● Virtual LANs ● Fiber Distributed Data Interface ● Structured Cabling Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.2 Design Issues Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.3 Design Issues ● Two kinds of connections in networks ● Point-to-point connections OSI Reference Model ● Broadcast (Multi-access channel, Application Layer Random access channel) Presentation Layer ● In a network with broadcast Session Layer connections ● Who gets the channel? Transport Layer Network Layer ● Protocols used to determine who gets next access to the channel Data Link Layer ● Medium Access Control (MAC) sublayer Physical Layer Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.4 Network Types for the Local Range ● LLC layer: uniform interface and same frame format to upper layers ● MAC layer: defines medium access .. -
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. -
On-Demand Routing in Multi-Hop Wireless Mobile Ad Hoc Networks
Available Online at www.ijcsmc.com International Journal of Computer Science and Mobile Computing A Monthly Journal of Computer Science and Information Technology ISSN 2320–088X IJCSMC, Vol. 2, Issue. 7, July 2013, pg.317 – 321 RESEARCH ARTICLE ON-DEMAND ROUTING IN MULTI-HOP WIRELESS MOBILE AD HOC NETWORKS P. Umamaheswari 1, K. Ranjith singh 2 1Periyar University, TamilNadu, India 2Professor of PGP College, TamilNadu, India 1 [email protected]; 2 [email protected] Abstract— An ad hoc network is a collection of wireless mobile nodes dynamically forming a temporary network without the use of any preexisting network infrastructure or centralized administration. Routing protocols used in ad hoc networks must automatically adjust to environments that can vary between the extremes of high mobility with low bandwidth, and low mobility with high bandwidth. This thesis argues that such protocols must operate in an on-demand fashion and that they must carefully limit the number of nodes required to react to a given topology change in the network. I have embodied these two principles in a routing protocol called Dynamic Source Routing (DSR). As a result of its unique design, the protocol adapts quickly to routing changes when node movement is frequent, yet requires little or no overhead during periods in which nodes move less frequently. By presenting a detailed analysis of DSR’s behavior in a variety of situations, this thesis generalizes the lessons learned from DSR so that they can be applied to the many other new routing protocols that have adopted the basic DSR framework. The thesis proves the practicality of the DSR protocol through performance results collected from a full-scale 8 node tested, and it demonstrates several methodologies for experimenting with protocols and applications in an ad hoc network environment, including the emulation of ad hoc networks. -
Application Note: 2-Cell Test Environment
Application Note 2-cell Test Environment MD8475A Signalling Tester 1. Background to LTE Rollout Mobile phones appearing in the late 1980s soon experienced rapid evolution of functions from 1990 to 2000 and also spread worldwide as key communications infrastructure. The mobile phone is not limited to just two-way communications between two people but also supports sending and receiving of Short Message Services (SMS), web browsing using the Internet, application and video download, etc., and has become a popular and key cultural tool supporting a fuller lifestyle for many people. Figure 1. Evolution on UE According to one research company, total mobile phone (terminal) shipments at the end of 2010 were valued at $38 billion split between 45% for 2G phones and 49% for 3G. Table 1. Mobile Terminal Shipments Mobile Terminal Shipments ($38 billion total) LTE 1.3% WiMAX 4.0% W-CDMA 40.0% CDMA 9.3% GSM 45.4% 1 MD8475A-E-F-1 The purpose of the shift from 2G to 3G systems was to make more efficient use of frequency bandwidths and was closely related to the explosive growth of the Internet. While still maintaining the easy portability of a mobile phone, users were able to access the information they needed easily at any time and place using the Internet. Similarly to growth of 3G technology, the requirements of LTE systems, which is are positioned in the market as 3.9G to maintain competitiveness with coming 4G systems, are being examined. Connectivity with IP-based core networks must be maintained to support multimedia applications and ubiquitous networks using the packet domain. -
Looking Back
Looking Back Martha E. (Hinds) Crosby Department of Information and Computer Sciences, University of Hawaii [email protected] Abstract: In this chapter, I am reminiscing on some of my experiences from my 53 years of living with computers. I am currently a professor and chair in the department of Information and Computer Sciences at the University of Hawaii. Over the years, I have only experienced computing environments in three locations (Colorado, Washington, D.C. and Hawaii) but they have all been memorable. The computers that I describe are a part of computing history but are rarely documented. Keywords: Computer science, geophysical parameters, mapping program, mathematics. I was not aware of computing before I went to college. I majored in mathematics and I had a professor who believed that computers would be the wave of the future so he gave some short courses on machine language and numerical analysis techniques. Little did I realize that this would make me a qualified applicant for a computing career. I graduated with a Bachelor of Science degree from Colorado State University (CSU) in 1959. At that time, calculators were mechanical and very large and heavy and no one would consider owning one. Also, very few commercial digital computers could be found in the United States and the ones that existed usually occupied a room and were primarily for calculations. I planned to teach mathematics in high school after graduation from CSU. However, I finished my classes a quarter early so teaching positions would be at least a half year away. I was offered positions at Martin Marietta in Denver, Colorado and the National Bureau of Standards (NBS) Central Radio Propagation Laboratories (CRPL) in Boulder, Colorado. -
Adding Enhanced Services to the Internet: Lessons from History
Adding Enhanced Services to the Internet: Lessons from History kc claffy and David D. Clark [email protected] and [email protected] September 7, 2015 Contents 1 Introduction 3 2 Related technical concepts 4 2.1 What does “enhanced services” mean? . 4 2.2 Using enhanced services to mitigate congestion . 5 2.3 Quality of Service (QoS) vs. Quality of Experience (QoE) . 6 2.4 Limiting the use of enhanced services via regulation . 7 3 Early history of enhanced services: technology and operations (1980s) 7 3.1 Early 1980s: Initial specification of Type-of-Service in the Internet Protocol suite . 7 3.2 Mid 1980s: Reactive use of service differentation to mitigate NSFNET congestion . 10 3.3 Late 1980s: TCP protocol algorithmic support for dampening congestion . 10 4 Formalizing support for enhanced services across ISPs (1990s) 11 4.1 Proposed short-term solution: formalize use of IP Precedence field . 11 4.2 Proposed long-term solution: standardizing support for enhanced services . 12 4.3 Standardization of enhanced service in the IETF . 13 4.4 Revealing moments: the greater obstacle is economics not technology . 15 5 Non-technical barriers to enhanced services on the Internet (2000s) 15 5.1Early2000s:afuneralwakeforQoS............................ 15 5.2 Mid 2000s: Working with industry to gain insight . 16 5.3 Late 2000s: QoS becomes a public policy issue . 17 6 Evolving interconnection structure and implications for enhanced services (2010s) 20 6.1 Expansion of network interconnection scale and scope . 20 6.2 Emergence of private IP-based platforms to support enhanced services . 22 6.3 Advancing our empirical understanding of performance impairments . -
Features of the Internet History the Norwegian Contribution to the Development PAAL SPILLING and YNGVAR LUNDH
Features of the Internet history The Norwegian contribution to the development PAAL SPILLING AND YNGVAR LUNDH This article provides a short historical and personal view on the development of packet-switching, computer communications and Internet technology, from its inception around 1969 until the full- fledged Internet became operational in 1983. In the early 1990s, the internet backbone at that time, the National Science Foundation network – NSFNET, was opened up for commercial purposes. At that time there were already several operators providing commercial services outside the internet. This presentation is based on the authors’ participation during parts of the development and on literature Paal Spilling is studies. This provides a setting in which the Norwegian participation and contribution may be better professor at the understood. Department of informatics, Univ. of Oslo and University 1 Introduction Defense (DOD). It is uncertain when DoD really Graduate Center The concept of computer networking started in the standardized on the entire protocol suite built around at Kjeller early 1960s at the Massachusetts Institute of Technol- TCP/IP, since for several years they also followed the ogy (MIT) with the vision of an “On-line community ISO standards track. of people”. Computers should facilitate communica- tions between people and be a support for human The development of the Internet, as we know it today, decision processes. In 1961 an MIT PhD thesis by went through three phases. The first one was the Leonard Kleinrock introduced some of the earliest research and development phase, sponsored and theoretical results on queuing networks. Around the supervised by ARPA. Research groups that actively same time a series of Rand Corporation papers, contributed to the development process and many mainly authored by Paul Baran, sketched a hypotheti- who explored its potential for resource sharing were cal system for communication while under attack that permitted to connect to and use the network.