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Communication Networks

http://www.bbc.co.uk/news/technology-11325452

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Definition

A computer network is a system of autonomous computing elements that are able to exchange data through a communications interconnection.

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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

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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

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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

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Benefits of Redundancy

• Higher reliability - no single point of failure

• Possibility of high-speed computing

• Better peak-loading properties

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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

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Social/Psychological Benefits

• Reduced cost of communication

• Few economic, political, or timing limitations

• Critical mass (synergy) effect

• The one-mind effect

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The Technical Progression• Increasing component density• Decreasing costs for equivalent capability• Increasing network capacity and diversity• Software has made technology accessible

– Office support packages– Web support packages– Publishing (text and graphics) packages– Mathematical analysis packages

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Moore’s Law

• The number of transistors per square inch on integrated circuits will double every 18 – 24 months.

• Moore predicted this in 1965, it has held since then, and is expected to hold for at least another decade.

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Moore’s Law Progress

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Moore’s Law, Continued

INTEL CurveMoore’s Law mapped onto Intel products.

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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

Have we reached the 2010 prediction?

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Prediction: Transistors: 7 billionClock: 10 GHz

Actual: Transistors: 2.3 billionClock: 3.3 GHz

(multiple threads)

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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.

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Network Computing Speeds

• SETI@HOME example (August 26, 2002)

Total 2004 24 Hours

Users 3934617 1908

Results received 593672971 982212

Total PC CPU time 1104655 years 1346 years

Floating Point Ops 1.90 e+21 3.83e+18

Average computing speed as system:

44.34 TeraFLOPs/sec!

How are these rates possible?

• Problem division

• Communications of data

• Multiple processors

• Communications of results

Ans: PARALLEL COMPUTING

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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.

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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 fengd@saic.com 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.

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Growth of Internet Hosts*

*Source: Internet Software Consortium [http://www.isc.org/index.pl?/ops/ds/host-count-history.php]

Internet Hosts

0.0

100.0

200.0

300.0

400.0

500.0

600.0

1975 1980 1985 1990 1995 2000 2005 2010

Year

Hosts (millions)

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Log-Growth of HostsLog-Growth

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

1975 1980 1985 1990 1995 2000 2005 2010

Year

Log of Hosts

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Current Growth Rate

One decade every eight years!

(About one billion hosts by 2015)

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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

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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

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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.

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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)

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2002 Prediction for Year 2010

• 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

Measured: Number of Websites

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Netcraft report

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Comment

• It seems like lots of growth is ahead

• Why is it below predictions?

• What about telco capacity?

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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)– routing– Edge-switching

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World “Broadband” Forecast

http://www.instat.com/press.asp?ID=277&sku=IN020132IA

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“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.

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“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.

• Fiber to the home [TelCo and cable in our area]

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Comment

• Telco technology exists for very high data rates - no present limitation

• But what about labor supply?

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Predicted Labor Growth

(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

Industry Job Description 1998 Jobs 2008 Jobs Annualized GrowthComputer and data processing services(1) 1599.3 3471.6 8.1

Computer and office equipment(1) 379 369 -0.3

Telephone & telegraph communications(1) 1042 1285 2.1

Computer engineers(2) 299 622 10.8

Computer support specialists(2) 429 869 10.2

Systems analysis(2) 617 1194 9.4

Database administrators(2) 87 155 7.7

Desktop publishing specialists(2) 26 44 7.3

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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)

Apparent Limitations

• Semiconductors

• Software

• Manpower

• Political

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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

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Networks and the OSI Model

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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

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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

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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)

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Star Network

• All traffic goes through central hub (bottleneck?)

• Point-to-Point connection

• Asynchronous Transfer Mode (ATM) to edge switches is a typical application

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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

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Tree Network

• Used for ATM networks (connection-oriented)

• Multiway branches are typical

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Mesh Network

• Network core - reliability of redundant pathways

• WAN networks - high interconnectivity

• Point-to-point with store-and-forward nodes

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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

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Satellite Network

• WAN model

• Used with widely separated physical locations

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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)

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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

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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

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Connection-Oriented Networks

• Services (three types)• Connect (sets up channel)

• Data (streaming mode exchange)

• Disconnect (dissolves connection)

• Methods (each service)• Request (indicates desire for service)

• Indication (conveys information about request)

• Response (signals outcome of request)

• Confirm (presents outcome)

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Connectionless Network Frames• destination address

each frame can take separate path

• sequence numberframes can arrive out of order due to path delays

• sender (source) addressfor 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

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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)

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Peer Layers

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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

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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

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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)

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Protocol

• Formally defined procedure for communication

• Set of rules governing:– format of data to be exchanged by peers– meaning of data– sequence of interactions

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The Physical Layer

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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

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The Data Link Layer

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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

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The Network Layer

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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

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The Transport Layer

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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)

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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

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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)

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The Session Layer

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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

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The Presentation Layer

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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

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The Application Layer

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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

SMTP

SNMP

Telnet

DNS

HTTP