Transcript Computer Communications

Communication Networks
Raymond P. Jefferis III
4/13/2016
© 2006 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.
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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
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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
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Lect 01 - 4
Benefits of Network Modularity
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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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Lect 01 - 5
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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Lect 01 - 8
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.
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Lect 01 - 9
Moore’s Law Progress
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Lect 01 - 10
Moore’s Law - Present/Predicted
• Pentium IV (2003)
– Speed:
3.2 GHz
– Transistors:
42 million
– Operating voltage: 1.7
• Future (est. 2005)
– Speed:
10 GHz
– Transistors:
400 million
– Operating Voltage: 1.0
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Lect 01 - 11
2005 - Actual
• 2005 actual
Intel Itanium-2
Speed: 1.6 GHz (64 bits)
Transistors: 1.72 Billion
Operating Voltage: Variable
http://dewww.epfl.ch/~ionescu/Nanoelectronics_1_0506.pdf
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Lect 01 - 12
Multicore Computers
While Intel touts breaking the one billion transistor
mark as a major milestone, Gordon Haff of Illuminata
said that there is "nothing magical" about the
number. "They are following Moore's Law, and in
order to get the most out of that law, Intel is obliged
to go the multicore route,"
ftp://download.intel.com/technology/computing/archinn
ov/platform2015/download/Platform_2015.pdf
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Lect 01 - 13
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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Lect 01 - 14
Network Computing Speeds
• SETI@HOME example (December 23, 2003)
Total
Users
Results received
Total PC CPU time
Floating Point Ops
JAN-2004/24 Hours
5322367
487
1731114441
773043
2193381years 554 years
6.335531e+21 3.014868e+18
Average computing speed as system:
34.89TeraFLOPs/sec !
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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.
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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.
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Growth of Internet Hosts
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109.5 million in January 2001 (0)
318 million in January 2005
66.6 million in January 2000 (1)
233 million in January 2004
43.2 million in January 1999(2)
172 million in January 2003
29.7 million in January 1998(2)
147 million in January 2002
16.2 million in January 1997 (2)
9.5 million in January 1996 (3)
4.9 million in 1995 (3)
2.2 million in 1994 (3)
http://www.isc.org/ds/host-count-history.html
1.3 million in 1993 (3)
(0)Ref:http://www.isc.org/ds/WWW-200101/index.html
(1)Ref:http://www.mids.org/ Map avail: http://www.mids.org/mapsale/world/index.html
(2)Ref: http://www.isc.org/ds/WWW-9907/report.html
(3)Ref: http://www.mit.edu:8001/people/mkgray/net/internet-growth-summary.html
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Growth of Internet
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Hosts - Graph
Hosts (Millions)
Internet Host Growth
200
180
160
140
120
100
80
60
40
20
0
1992
172
147
109.6
66.6
1.3 2.2
1994
4.9
9.5
1996
16.2
29.7
1998
43.2
2000
2002
2004
Year
*Source: Internet Software Consortium [http://www.isc.org/ds/host-count-history.html]
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Lect 01 - 19
Host Addressing
• Present
– IPv4: 32 bits
232 (4 x 109) addresses
– not realizable because of reserved blocks
– already approaching limit
• Future
– IPv6: 128 bits
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2128 (3 x 1038) addresses
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Lect 01 - 20
Number of Unique Web sites by Year
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1998: 2,636,000*
1999: 4,662,000*
2000: 7,128,000*
2001: 8,443,000#
2002: 8,712,000#
* Source: http://www.oclc.org/oclc/press/20001016a.htm
# Source: http://wcp.oclc.org/stats/size.html
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June 1999 - Web Sites & Pages
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Web sites(1):
Growth rate(1):
Web pages(2):
Click distance(2):
4.88 million (June ‘99)
was ~75%/year
800 million
19 clicks
References:
(1) http://www.oclc.org/oclc/research/projects/webstats/
(2) Science News, September 25, 1999, p203.
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Lect 01 - 22
January 2001 Situation
• PC clock speed
• Internet hosts (1) :
• Web pages (2):
> 1.5 GHz
109.6 million
1,346,966,00
(1) http://www.isc.org/ds/WWW-200101/index.html
(2) www.google.com, March 30, 2001 (may contain double listings)
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January 2003 Situation
• PC clock speed > 3.2 GHz
• Internet hosts (1) : 172 million
• Web pages (2):
3,307,998,701
(1) http://www.isc.org/ds/host-count-history.html
(2) www.google.com, December 25, 2003 (may contain double listings)
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January 2005 Situation
• PC clock speed
• Internet hosts:
• Web pages:
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>
3.5 GHz
200 million
8,058,044,651
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Lect 01 - 25
Extrapolation to Year 2010
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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
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Lect 01 - 26
Comment
• It seems like lots of growth is ahead
• But 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)
– l routing
– Edge-switching
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Lect 01 - 28
Comment
• Telco technology exists for very high data
rates - no present limitaiton
• But what about labor supply?
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Lect 01 - 29
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
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Lect 01 - 30
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)
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Lect 01 - 31
Permanent Assignment!
• Keep up with current events in
telecommunications and network (Internet)
developments
• Watch for signs of slowdown
• Identify the bottlenecks
• Identify developing technologies that can
overcome the bottlenecks.
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Lect 01 - 32
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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Lect 01 - 33
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
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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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Lect 01 - 35
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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Lect 01 - 37
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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Lect 01 - 40
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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Lect 01 - 42
Network Switching Models
• Circuit switched
– communication channel is opened
– data is sent
– 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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Lect 01 - 43
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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Lect 01 - 44
Connection-Oriented Networks
• Services (three types)
• Connect
(sets up channel)
• Data
(streaming mode exchange)
• Disconnect (dissolves connection)
• Methods (each service)
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Request
Indication
Response
Confirm
(indicates desire for service)
(conveys information about request)
(signals outcome of request)
(presents outcome)
© 2006 Raymond P. Jefferis III
Lect 01 - 45
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
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Lect 01 - 46
The OSI Reference Model
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Physical layer (lowest)
Data link layer
Network layer
Transport layer
Session Layer
Presentation Layer
Application Layer (highest)
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Lect 01 - 47
Peer Layers
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Lect 01 - 48
Peer Layers
• Opposite ends of a virtual communication
link
• 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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Lect 01 - 49
The OSI Model Criteria
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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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Lect 01 - 50
Service
• An abstract operator on a datatype
• 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
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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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Lect 01 - 57
The Network Layer
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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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Lect 01 - 58
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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Lect 01 - 60
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
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Telnet (virtual terminal emulation)
File Transfer Protocol (FTP)
Simple Mail Transfer Protocol (SMTP)
Simple Network Management Protocol (SNMP)
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Lect 01 - 62
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
Telnet
SMTP
DNS
SNMP
HTTP
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