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Communication Networks 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 1 Definition A computer network is a system of autonomous computing elements that are able to exchange data through a communications interconnection. 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 2 Network Objectives • to provide common access to data and facilities • to provide common access to software • to provide redundant data /computing • to communicate thoughts and data • to unite parties to a transaction or exchange 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 3 Benefits of Common Access • Everyone works with same data & software • Access programming can be replicated, lowering cost and increasing reliability • Uniform backup and recovery management • Offloading of data entry & processing 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 4 Benefits of Network Modularity • • • • • • Simplification of programming Possible parallel computing at high speed Reduced failure liability Locally managed security Scalability - ease of expansion Minimal diagnosis and repair time 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 5 Benefits of Redundancy • Higher reliability - no single point of failure • Possibility of high-speed computing • Better peak-loading properties 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 6 Benefits of Broadcast Capability • Simultaneous data to all users – price changes, engineering changes, etc. – simultaneous command facilitates management • Same data to all users – credit reports – prices, data sheets, etc. • Same software to all users – simultaneous updates 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 7 Social/Psychological Benefits • Reduced cost of communication • Few economic, political, or timing limitations • Critical mass (synergy) effect • The one-mind effect 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 8 The Technical Progression • • • • Increasing component density Decreasing costs for equivalent capability Increasing network capacity and diversity Software has made technology accessible – – – – 5/25/2017 Office support packages Web support packages Publishing (text and graphics) packages Mathematical analysis packages © 2008 Raymond P. Jefferis III Lect 01 - 9 Moore’s Law • The number of transistors per square inch on integrated circuits will double every 18 months. • Moore predicted this in 1965, it has held since then, and is expected to hold for at least another decade. 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 10 Moore’s Law Progress 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 11 Moore’s Law, Continued INTEL Curve Moore’s Law mapped onto Intel products. 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 12 The Moore’s Law Consequence • Atoms/bit in storage – falling by factor of ten per decade* • bit densities of 1012 bits/ cm2 by 2015 (said to equal human brain synapse density) *Zhirnov, V. V. and Herr, J. C., IEEE Computer, Vol. 34 No.1 (January 2001), pp34-43. 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 13 Moore’s Law - Present & Future • Pentium IV (2001) – Speed: 1.5 GHz – Transistors: 42 million – Operating voltage: 1.7 Volts • Future (est. 2010) – Speed: 10 GHz – Transistors: 7 billion – Operating Voltage: <1.0 Volts 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 14 Network Computing Speeds • SETI@HOME example (August 26, 2002) Total Users Results received Total PC CPU time Floating Point Ops 3934617 593672971 1104655 years 1.90 e+21 2004 24 Hours 1908 982212 1346 years 3.83e+18 Average computing speed as system: 44.34 TeraFLOPs/sec! 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 15 Internet Computing Capability* • Effective computing speed: 107 GHz – 1016 OPS estimated* - too conservative! – already exceeded by SETI@HOME! • Effective storage capacity: 104 TB * Clark, David, IEEE Computer, Vol. 34, No. 1 (January 2001), pp18 - 21. 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 16 World Network Data Rates City Traffic [Tb/sec](1) City Traffic [Tb/sec](1) London 18 Washington 4.0 New York 13.2 San Francisco 3.9 Amsterdam 10.9 Toronto 3.5 Frankfurt 10.5 Chicago 2.7 Paris 9.7 Seattle 2.6 Brussels 6.2 Vancouver 2.5 Geneva 5.9 Tokyo 2.4 Stockholm 4.4 Rate of growth(2) 14% (1) E-mail from [email protected] 28NOV99 at 13:48:50 These numbers seem too large but are interesting if real. (2) http://www.telegeography.com/ This number is supported by data and seems firm. 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 17 Growth of Internet * Hosts Internet Hosts 600.0 Hosts (millions) 500.0 400.0 300.0 200.0 100.0 0.0 1975 1980 1985 1990 1995 2000 2005 2010 Year *Source: Internet Software Consortium [http://www.isc.org/index.pl?/ops/ds/host-count-history.php] 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 18 Log-Growth of Hosts Log-Growth 10.00 9.00 8.00 Log of Hosts 7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 1975 1980 1985 1990 1995 2000 2005 2010 Year 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 19 Current Growth Rate One decade every eight years! (About one billion hosts by 2015) 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 20 Host Addressing • Present – IPv4: 32 bits 232 (4 x 109) addresses – not realizable because of reserved blocks – already approaching limit • Future – IPv6: 128 bits 2128 (3 x 1038) addresses – No foreseeable limitation 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 21 Number of Unique Web sites by Year • 1998: 2,636,000* • 1999: 4,662,000* • 2000: 7,128,000* • 2001: 8,443,000* • 2002: 8,712,000 Growth rate: 18% per year * Source: http://www.oclc.org/research/projects/archive/wcp/stats/size.htm 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 22 Web Sites & Pages • • • Web sites(1): 8.71 million (June ‘2002) Web pages(2): 8,058,044,651 Click distance(3): 19 clicks References: 1 http://www.dlib.org/dlib/april03/lavoie/04lavoie.html 2 http://www.google.com [May 2005] 3 Science News, September 25, 1999, p203. 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 23 May 2002 Situation • • • • PC clock speed > 2.53 GHz Internet hosts (1) : 147 million Web pages (2): 2,469,940,685 Unique Web site 8,443,000 (1) http://www.isc.org/ds/WWW-200101/index.html (2) www.google.com, August 2002 (may contain double listings) 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 24 Extrapolation to Year 2010 • • • • • • PC Computing speed: > 20 GFLOPS Traffic growth: 370% (14% per year) Internet hosts: 5.3 billion Web sites: 1.3 billion Web pages: 58.1 billion Click distance: ~22 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 25 Comment • It seems like lots of growth is ahead • But what about telco capacity? 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 26 Telco Technology • Present – SONET (OC192 - fiber) backbone - ~10 Gb/s – Circuit-switch or router to edges – Copper “last mile” • Near Future – WDM backbone - ~160 Gb/s (27 Tb/s possible) – l routing – Edge-switching 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 27 Telco Technology • http://www.instat.com/catalog/downloads/whitepaper_terabit-net.asp • http://www.instat.com/catalog/downloads/whitepaper_bbubiquity.asp 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 28 World “Broadband” Forecast http://www.instat.com/press.asp?ID=277&sku=IN020132IA 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 29 “Broadband” Worldwide • More than 46 million people across the world will have fast internet access by the end of the year, says a report. • If this happens, it will mean a jump of 16 million subscribers in a year and the number is set to continue rising, say technology analysts In-Stat. 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 30 “Broadband” Home Connectivity • American cable modem subscribers continue to outnumber DSL subscribers by a wide margin. • At the beginning of 2002, there were 7.12 million US cable modem subscribers and only 4.6 million DSL subscribers • Other ways of getting broadband, such as via satellite or wireless make up just 5% of the market. 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 31 Comment • Telco technology exists for very high data rates - no present limitation • But what about labor supply? 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 32 Predicted Labor Growth Industry Job Description Computer and data processing services(1) Computer and office equipment(1) Telephone & telegraph communications(1) Computer engineers(2) Computer support specialists(2) Systems analysis(2) Database administrators(2) Desktop publishing specialists(2) 1998 Jobs 2008 Jobs Annualized Growth 1599.3 379 1042 299 429 617 87 26 3471.6 369 1285 622 869 1194 155 44 8.1 -0.3 2.1 10.8 10.2 9.4 7.7 7.3 (1) http://stats.bls/gov/opub/mlr/1999/11/art4full.pdf (2) http://stats.bls.gov/news.release/ecopro.t06.htm Note: Jobs are stated in thousands 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 33 Observations! • More Internet hosts predicted than people on earth to manage them! • 10 Web pages for every person on earth! • Who will do all this work? • Jobs expected to grow at only 8-11% /yr(1) • Something must change! What will it be? When will it happen? (1) http://stats.bls.gov (US Bureau of Labor Statistics) 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 34 Permanent Assignment! • Keep up with current events in telecommunications and network (Internet) developments • Watch for signs of slowdown • Identify the bottlenecks • Identify developing technologies • Submit semester summary report 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 35 Networks and the OSI Model 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 36 Types of Networks • Point-to-point – direct (mesh) connection – store-and-forward nodes • Broadcast – all users share single channel (conflict arbitration required) – messages must contain user address – users must filter messages 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 37 Network Classification by Area • System Level – length 0.2 to 200 cm – parallel bus (for speed) or serial link (for circuit voltage isolation) • Local Area Networks (LAN) – length < 1 km, serial data with established protocols – users must conform to standards or connect through “bridge” device • Municipal Area Network (MAN) – length between 1 and 10 km • Wide Area Networks (WAN) – length >10 km, serial data with established protocols – typically interconnected subnets 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 38 Common Topologies • • • • • • Star (single node connects all) Ring (each node connects to two others) Tree (each node connects to disjoint subtrees) Mesh (nodes are arbitrarily interconnected) Bus (all nodes connect to common data highway) Satellite (mesh of connected subnets) 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 39 Star Network • All traffic goes through central hub (bottleneck?) • Point-to-Point connection • Asynchronous Transfer Mode (ATM) to edge switches is a typical application 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 40 Ring Network • Token passing or dual “counter-rotating” Fiber Distributed Data Interconnect (FDDI) rings are typical • Two access paths available to any node • Broadcast type - all users hear messages 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 41 Tree Network • Used for ATM networks (connection-oriented) • Multiway branches are typical 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 42 Mesh Network • Network core - reliability of redundant pathways • WAN networks - high interconnectivity • Point-to-point with store-and-forward nodes 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 43 Bus Network • Traffic saturation can be problematic • Used for Local Area Network (LAN) communications • Carrier Sense Multiple Access (CSMA) arbitration • Broadcast type - all users hear and filter messages 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 44 Satellite Network • WAN model • Used with widely separated physical locations 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 45 Network Standards • Specify and facilitate computer interface • Functions separated into layers • Open System Interconnection (OSI) model – adopted by International Standards Organization (ISO) – has seven layers (we will discuss five of these) 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 46 Network Switching Models • Circuit switched – communication channel is opened – data is sent on dedicated channel – channel is closed • Packet switched – data broken into frames – frames routed to their destination addresses – no open channel; no guarantee of delivery 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 47 Service Models • Connection-oriented – circuit switched, like phone calls – data transmitted in streaming mode – used by ATM and frame relay networks • Connectionless – packet switched, like telegrams or letters – propagation by store-and-forward nodes – used by Ethernet, token ring, and FDDI 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 48 Connection-Oriented Networks • Services (three types) • Connect (sets up channel) • Data (streaming mode exchange) • Disconnect (dissolves connection) • Methods (each service) • • • • 5/25/2017 Request Indication Response Confirm (indicates desire for service) (conveys information about request) (signals outcome of request) (presents outcome) © 2008 Raymond P. Jefferis III Lect 01 - 49 Connectionless Network Frames • destination address each frame can take separate path • sequence number frames can arrive out of order due to path delays • sender (source) address for return of undeliverable frames • Check sum (error control bits) channel cannot be characterized, no open channel • QoS tag bits (if 802.1Q supported) recent development for VLANs 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 50 The OSI Reference Model • • • • • • • Physical layer (lowest) Data link layer Network layer Transport layer Session Layer (we will omit this layer) Presentation Layer (we will omit this layer) Application Layer (highest) 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 51 Peer Layers 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 52 Peer Layers • Opposite ends of a virtual communication link (peer-to-peer) • Established by means of a protocol – a formally defined procedure, which governs: • the communication format • its sequence • the meaning of its components – TCP/IP is protocol of choice for the Internet 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 53 The OSI Model Criteria – – – – – – – each layer encapsulates a level of abstraction each layer performs a well-defined function layers offer and use services, above & below layer functions amenable to protocol standard layer boundaries chosen to minimize data flow layers optimize complexity tradeoff Note: each layer adds/removes header 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 54 Service • An abstract operator on a datatype • The data are in the message (frame) • A layer offers a set of services – provides to “user” layer above – encapsulated (private) 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 55 Protocol • Formally defined procedure for communication • Set of rules governing: – format of data to be exchanged by peers – meaning of data – sequence of interactions 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 56 The Physical Layer 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 57 The Physical Layer • Included in TCP/IP Data Link Layer • Specifies mechanical, electrical. And procedural aspects of interconnection • Specifies signaling forms, such as modulation techniques, timing, and frequencies to be used 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 58 The Data Link Layer 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 59 The Data Link Layer • • • • • • • TCP/IP Link Layer Function: to transfer data and remove errors Divides data into frames for transmission Recognizes frame boundaries on reception Sends and receives acknowledgment frames Retransmits non-acknowledged frames Ethernet NIC driver included in this layer 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 60 The Network Layer 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 61 The Network Layer • • • • • TCP/IP Internet Layer Internet Protocol (IP) operates in this layer Converts “host” messages to packets Tracks packets to destination through route Performs accounting & statistics (successes, failures, byte counts, etc.) on packets • Packets routed dynamically or by tables 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 62 The Transport Layer 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 63 The Transport Layer • TCP/IP Transport Layer • Conveys data between “host” computer – Session Layers in OSI model – Application Layers in TCP/IP model • Two modes in this layer: – Transmission Control Protocol (TCP) – User Datagram Protocol (UDP) 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 64 Transmission Control Protocol (TCP) • Connection-oriented – like a phone call sequence – Connection established before data exchange • Splits data into smaller units (packets) • Passes packets to Network Layer for transmission • Ensures arrival of all data pieces at destination 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 65 User Datagram Protocol (UDP) • Connectionless – like mailing letter at a Post Office – no guarantee of data arrival – reliability can be added at Application Layer • Simple Network Management Protocol (SNMP) 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 66 The Session Layer 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 67 The Session Layer • Not in TCP/IP • A connection between two Presentation Layer processes (log-in, file transfer, etc.) • User provides destination address, authentication, and data to be transferred • Layer adds transport address, sends data, recovers from broken link, assembles message fragments until complete 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 68 The Presentation Layer 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 69 The Presentation Layer • Not in TCP/IP • Performs translational services for user – text compression – code transformations – file format transformations • Allows computers to use differing codes for numbers and characters 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 70 The Application Layer 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 71 The Application Layer • Highest TCP/IP layer • User program layer – users agree on data and its meaning • Network protocols (assigned port numbers for access by TCP and UDP in Transport Layer) FTP Telnet SMTP DNS SNMP HTTP 5/25/2017 © 2008 Raymond P. Jefferis III Lect 01 - 72