Download Communications and Society

Communication Networks
http://www.bbc.co.uk/news/technology-11325452
5/25/2017
© 2010 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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© 2010 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
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© 2010 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
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© 2010 Raymond P. Jefferis III
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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© 2010 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
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© 2010 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
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© 2010 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
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© 2010 Raymond P. Jefferis III
Lect 01 - 8
The Technical Progression
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Increasing component density
Decreasing costs for equivalent capability
Increasing network capacity and diversity
Software has made technology accessible
–
–
–
–
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Office support packages
Web support packages
Publishing (text and graphics) packages
Mathematical analysis packages
© 2010 Raymond P. Jefferis III
Lect 01 - 9
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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© 2010 Raymond P. Jefferis III
Lect 01 - 10
Moore’s Law Progress
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© 2010 Raymond P. Jefferis III
Lect 01 - 11
Moore’s Law, Continued
INTEL Curve
Moore’s Law mapped
onto Intel products.
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© 2010 Raymond P. Jefferis III
Lect 01 - 12
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
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© 2010 Raymond P. Jefferis III
Lect 01 - 13
Have we reached the 2010 prediction?
Prediction:
Transistors:
Clock:
7 billion
10 GHz
Actual:
Transistors:
Clock:
2.3 billion
3.3 GHz
(multiple threads)
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© 2010 Raymond P. Jefferis III
Lect 01 - 14
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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© 2010 Raymond P. Jefferis III
Lect 01 - 15
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!
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© 2010 Raymond P. Jefferis III
Lect 01 - 16
How are these rates possible?
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Problem division
Communications of data
Multiple processors
Communications of results
Ans:
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PARALLEL COMPUTING
© 2010 Raymond P. Jefferis III
Lect 01 - 17
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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© 2010 Raymond P. Jefferis III
Lect 01 - 18
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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© 2010 Raymond P. Jefferis III
Lect 01 - 19
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]
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© 2010 Raymond P. Jefferis III
Lect 01 - 20
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
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© 2010 Raymond P. Jefferis III
Lect 01 - 21
Current Growth Rate
One decade every eight years!
(About one billion hosts by 2015)
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© 2010 Raymond P. Jefferis III
Lect 01 - 22
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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© 2010 Raymond P. Jefferis III
Lect 01 - 23
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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© 2010 Raymond P. Jefferis III
Lect 01 - 24
Web Sites & Pages
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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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© 2010 Raymond P. Jefferis III
Lect 01 - 25
May 2002 Situation
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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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© 2010 Raymond P. Jefferis III
Lect 01 - 26
2002 Prediction for Year 2010
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Computing speed:
Traffic growth:
Internet hosts:
Web sites:
Web pages:
Click distance:
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> 20 GFLOPS
370% (14% per year)
5.3 billion
1.3 billion
58.1 billion
~22
© 2010 Raymond P. Jefferis III
Lect 01 - 27
Measured: Number of Websites
Netcraft report
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© 2010 Raymond P. Jefferis III
Lect 01 - 28
Comment
• It seems like lots of growth is ahead
• Why is it below predictions?
• What about telco capacity?
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© 2010 Raymond P. Jefferis III
Lect 01 - 29
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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© 2010 Raymond P. Jefferis III
Lect 01 - 30
World “Broadband” Forecast
http://www.instat.com/press.asp?ID=277&sku=IN020132IA
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© 2010 Raymond P. Jefferis III
Lect 01 - 31
“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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© 2010 Raymond P. Jefferis III
Lect 01 - 32
“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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© 2010 Raymond P. Jefferis III
Lect 01 - 33
Comment
• Telco technology exists for very high data
rates - no present limitation
• But what about labor supply?
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© 2010 Raymond P. Jefferis III
Lect 01 - 34
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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© 2010 Raymond P. Jefferis III
Lect 01 - 35
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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© 2010 Raymond P. Jefferis III
Lect 01 - 36
Apparent Limitations
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Semiconductors
Software
Manpower
Political
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© 2010 Raymond P. Jefferis III
Lect 01 - 37
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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© 2010 Raymond P. Jefferis III
Lect 01 - 38
Networks and the OSI Model
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© 2010 Raymond P. Jefferis III
Lect 01 - 39
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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© 2010 Raymond P. Jefferis III
Lect 01 - 40
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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© 2010 Raymond P. Jefferis III
Lect 01 - 41
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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© 2010 Raymond P. Jefferis III
Lect 01 - 42
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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© 2010 Raymond P. Jefferis III
Lect 01 - 43
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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© 2010 Raymond P. Jefferis III
Lect 01 - 44
Tree Network
• Used for ATM networks (connection-oriented)
• Multiway branches are typical
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Lect 01 - 45
Mesh Network
• Network core - reliability of redundant pathways
• WAN networks - high interconnectivity
• Point-to-point with store-and-forward nodes
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© 2010 Raymond P. Jefferis III
Lect 01 - 46
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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© 2010 Raymond P. Jefferis III
Lect 01 - 47
Satellite Network
• WAN model
• Used with widely separated physical locations
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© 2010 Raymond P. Jefferis III
Lect 01 - 48
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 - 49
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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© 2010 Raymond P. Jefferis III
Lect 01 - 50
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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© 2010 Raymond P. Jefferis III
Lect 01 - 51
Connection-Oriented Networks
• Services (three types)
• Connect
(sets up channel)
• Data
(streaming mode exchange)
• Disconnect (dissolves connection)
• Methods (each service)
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•
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Request
Indication
Response
Confirm
(indicates desire for service)
(conveys information about request)
(signals outcome of request)
(presents outcome)
© 2010 Raymond P. Jefferis III
Lect 01 - 52
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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© 2010 Raymond P. Jefferis III
Lect 01 - 53
The OSI Reference Model
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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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© 2010 Raymond P. Jefferis III
Lect 01 - 54
Peer Layers
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© 2010 Raymond P. Jefferis III
Lect 01 - 55
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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© 2010 Raymond P. Jefferis III
Lect 01 - 56
The OSI Model Criteria
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–
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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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© 2010 Raymond P. Jefferis III
Lect 01 - 57
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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© 2010 Raymond P. Jefferis III
Lect 01 - 58
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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© 2010 Raymond P. Jefferis III
Lect 01 - 59
The Physical Layer
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Lect 01 - 60
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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© 2010 Raymond P. Jefferis III
Lect 01 - 61
The Data Link Layer
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© 2010 Raymond P. Jefferis III
Lect 01 - 62
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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© 2010 Raymond P. Jefferis III
Lect 01 - 63
The Network Layer
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© 2010 Raymond P. Jefferis III
Lect 01 - 64
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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© 2010 Raymond P. Jefferis III
Lect 01 - 65
The Transport Layer
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Lect 01 - 66
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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© 2010 Raymond P. Jefferis III
Lect 01 - 67
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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© 2010 Raymond P. Jefferis III
Lect 01 - 68
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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© 2010 Raymond P. Jefferis III
Lect 01 - 69
The Session Layer
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Lect 01 - 70
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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© 2010 Raymond P. Jefferis III
Lect 01 - 71
The Presentation Layer
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Lect 01 - 72
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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© 2010 Raymond P. Jefferis III
Lect 01 - 73
The Application Layer
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Lect 01 - 74
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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© 2010 Raymond P. Jefferis III
Lect 01 - 75