CSC4220/6220 Computer
Networks
Dr. WenZhan Song
Professor, Computer Science
Sensorweb Research Laboratory
-1-
Georgia State University
About Me
Homepage: http://sensorweb.cs.gsu.edu/~song/
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2010 – present, Georgia State University
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Teaching evaluation: 4.8 (CSC 4220)
2005-2010, Washington State University - Vancouver
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Teaching evaluation:
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Average: 4.5/5
Research experience:
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Sensorweb for environment monitoring, smart environments and smart grid
6M+ research funding support from NSF, NASA, USGS, Boeing, including
NSF CAREER award
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http://sensorweb.cs.gsu.edu/news.html
a dream: http://www.youtube.com/watch?v=WF-RKzqNtz0 (3:49)
Research has been featured in MIT technology review, National Geographic,
Network World, etc
2001-2005, Illinois Institute of Technology
2004 Summer, Lucent Technologies
1999-2001, Alcatel Shanghai Bell
Sensorweb Research Laboratory
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Georgia State University
Several Notes
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Course website:
http://sensorweb.cs.gsu.edu/~song/csc4220/
Announcement through emails
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Confirm email: have you received an email from me?
Is it okay to add your email to it?
Announcement and update will be sent through mailing list.
You may also ask questions through mailing list.
Homework submission needs a printed hard-copy, no
hand-written!
Programming projects
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Count Java/C preferences in class – either one is fine
Sensorweb Research Laboratory
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Georgia State University
What to expect
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Significant exposure to computer networking
concepts and fundamental design principles.
Coverage of Internet protocol stacks.
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Details of network control algorithms.
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running example: TCP/IP
e.g. routing, congestion control, flow control, ...
Able to design network protocols and systems.
Sensorweb Research Laboratory
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Georgia State University
What not to expect
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End-user training.
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Trade school stuff.
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e.g. OSI, Appletalk, ...
Massively Parallel Processing
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e.g. How to get Novel NetWare certified, how to setup a Cisco
router, how to administrate network system
Detailed discussion of non-TCP/IP protocols.
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e.g. How to use FTP, NetWare, WWW or HTML, …
e.g. large numbers of interconnected, identical processors
programmed to solve problems in parallel
Telecommunication networks and standards
Sensorweb Research Laboratory
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Georgia State University
Course roadmap
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Introduction
Application Layer: WWW, FTP, email, DNS, multimedia
Transport Layer: reliable end-end data transfer principles, UDP,
TCP
Network Layer: routing, congestion control, QoS
Data Link Layer: framing, error control, flow control
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Medium Access Control (MAC) Layer:
channel allocation
multiple-access,
Physical Layer: wired, wireless, satellite
Other Topics: network security, social issues, hot topics,
research directions
Sensorweb Research Laboratory
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Georgia State University
Human Conversation vs
Computer Communication
Hi
TCP connection
req
Hi
TCP connection
response
Got the
time?
Get http://www.google.com/contact.html
2:00
<file>
time
human conversation vs computer communication
Sensorweb Research Laboratory
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Georgia State University
Communication is challenging
The two-army problem
Sensorweb Research Laboratory
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Georgia State University
Introduction
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Physical overview of Internet
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Physical architecture
Network Edge - Internet access technologies
Network Core – Switching technologies
Software overview of Internet
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Roadmap
Software architecture
The OSI and TCP/IP Reference Models
Internet history
Network standardization body
Sensorweb Research Laboratory
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Georgia State University
Physical overview of Internet
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millions of connected
computing devices: hosts
= end systems
running network apps
communication links
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router
server
Residential access
workstation
mobile
Network
Core
fiber, copper, radio, satellite
transmission rate =
bandwidth
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routers: forward packets
(chunks of data)
Company
network
Sensorweb Research Laboratory
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Georgia State University
Physical overview of Internet
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protocols control sending,
receiving of msgs
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e.g., TCP, IP, HTTP, FTP, PPP
Internet: “network of
server
Residential access
workstation
mobile
networks”
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router
loosely hierarchical
public Internet versus private
intranet
Network
Core
Internet standards
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Called RFC (Request for
comments), developed by IETF
(Internet Engineering Task
Force)
Sensorweb Research Laboratory
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Company
network
Georgia State University
Metric Units
metric prefixes for data rate
Note:
data rates – kbps (103), Mbps(106), Gbps(109) … bits per second
data sizes – KB (210), MB(220), GB(230), … bytes
ms(msec): millisecond µs: microsecond ns: nanosecond
Sensorweb Research Laboratory
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Georgia State University
Introduction
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Physical overview of Internet
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Physical architecture
Network Edge - Internet access technologies
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Residential access
Company access
Network Core – Switching technologies
Software overview of Internet
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Roadmap
Software architecture
The OSI and TCP/IP Reference Models
Internet history
Network standardization body
Sensorweb Research Laboratory
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Georgia State University
Residential Internet Access
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Phone Company
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Cable TV Company
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Dialup
ADSL
HFC
Wireless Company
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WiMax
Sensorweb Research Laboratory
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Georgia State University
Residential access
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Phone Company
Dialup via modem
 up to 56Kbps direct access to
router (often less)
 Can’t surf and phone at same
time: can’t be “always on”
ADSL: asymmetric digital subscriber line
 up to 1 Mbps upstream (today typically < 256 kbps)
 up to 8 Mbps downstream (today typically < 1 Mbps)
Sensorweb Research Laboratory
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Georgia State University
Dialup
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Local loops
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Trunks
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Analog twisted pairs going to houses and businesses
Digital fiber optics connecting the switching offices
Toll Office (Switching offices)
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Where calls are moved from one trunk to another
Sensorweb Research Laboratory
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Georgia State University
ADSL: asymmetric digital subscriber line
Design goal:
(1) Work over exist 3 UTP twisted pair local
loops.
(2) Not affect customers’ existing telephone
and fax machine
(3) Much faster than 56kbps
(4) Always on – monthly charge
Sensorweb Research Laboratory
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Georgia State University
ADSL
A typical ADSL equipment configuration.
Sensorweb Research Laboratory
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Georgia State University
ADSL
256 Channel over 1.1MHz:
0 (POTS), 1-5(unused), 6-255(data channels)
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ANSI T1.413 and ITU G.992.1: up to 8 Mbps downstream and 1
Mbps upstream.
Standard service: 512 kbps downstream and 64 kbps upstream
Premium service: 1 Mbps downstream and 256 kbps upstream
Sensorweb Research Laboratory
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Georgia State University
Residential access
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Cable TV Company
HFC: hybrid fiber coax
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asymmetric: up to 27Mbps downstream, 9 Mbps
upstream
network of cable and fiber attaches homes to ISP
router
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homes in same community share bandwidth
deployment: available via cable TV companies
Sensorweb Research Laboratory
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Georgia State University
Community Antenna Television
An early cable television system.
Sensorweb Research Laboratory
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Georgia State University
HFC
Internet over TV Cable
Sensorweb Research Laboratory
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Georgia State University
Compare to ADSL
Internet over ADSL
Sensorweb Research Laboratory
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Georgia State University
Cable vs ADSL
Cable
ADSL
Physical
Coax
Twisted pair
Medium access
Shared
Independent
Security
Okay
Better
ISP choices
Usually not
Flexible
Data rate
Depends on # of
1Mbps down
shared users,
256kbps up
Up to 27Mbps/9Mbps
Sensorweb Research Laboratory
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Georgia State University
Spectrum Allocation
Frequency allocation in a typical cable TV system
used for Internet access
Sensorweb Research Laboratory
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Georgia State University
Signal Splitter
Sensorweb Research Laboratory
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Georgia State University
Cable Modems
Typical details of the upstream and downstream
channels in North America.
Upstream: QPSK, slotted Aloha with binary exponential backoff
Downstream: QAM–64/QAM-256, time division multiplexing
Sensorweb Research Laboratory
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Georgia State University
Residential access
Wireless Company
400~700kbps
Up to 2Mbps
- according to Verizon
Wireless Local Loop
Example: IEEE 802.16 WiMax – Verizon Wireless
Sensorweb Research Laboratory
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Georgia State University
Other ways for residential access?
Electricity company
 PLC (Power Line Communication)
 BPL (Broadband over Power Line)
http://en.wikipedia.org/wiki/Power_line_communication
How about other utility companies: Gas,
Water, …… 
Sensorweb Research Laboratory
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Georgia State University
Introduction
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Physical overview of Internet
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Physical architecture
Network Edge - Internet access technologies
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Residential access
Company access
Network Core – Switching technologies
Software overview of Internet
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Roadmap
Software architecture
The OSI and TCP/IP Reference Models
Internet history
Network standardization body
Sensorweb Research Laboratory
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Georgia State University
Company access: local area networks
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company/univ local area
network (LAN) connects end
system to edge router
Ethernet:
 shared or dedicated link
connects end system and
router
 10 Mbs, 100Mbps, Gigabit
Ethernet
Sensorweb Research Laboratory
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Georgia State University
Wireless access networks
Shared wireless access network
connects end system to router
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wireless LANs:
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802.11b (WiFi): 11 Mbps
802.11a, 802.11g …
wider-area wireless access
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via base station aka “access point”
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router
base
station
WiMax – talked before
3G ~ 384 kbps
4G ~ 100Mbps – 1Gbps
WAP/GPRS in Europe
wireless ad hoc networking
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mobile
hosts
Talk with each other directly inside
Through a gateway to visit outside
Sensorweb Research Laboratory
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Ad hoc
networking
Georgia State University
Introduction
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Physical overview of Internet
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Physical architecture
Network Edge - Internet access technologies
Network Core – Switching technologies
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circuit switching
packet switching
Software overview of Internet
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Roadmap
Software architecture
The OSI and TCP/IP Reference Models
Internet history
Network standardization body
Sensorweb Research Laboratory
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Georgia State University
The Network Core
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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”
Sensorweb Research Laboratory
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Georgia State University
Network Core: Circuit Switching
End-end resources
reserved for “call”
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link bandwidth, switch
capacity
dedicated resources: no
sharing
circuit-like (guaranteed)
performance
call setup required
Sensorweb Research Laboratory
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Georgia State University
Network Core: Circuit Switching
network resources (e.g.,
bandwidth) divided
into “pieces”
 pieces allocated to
calls
 resource piece idle if
not used by owning
call (no sharing)
Sensorweb Research Laboratory
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dividing link
bandwidth into
“pieces”
 frequency division
 time division
Georgia State University
Circuit Switching: FDM and TDM
Example:
FDM
4 users
frequency
time
TDM
frequency
time
Sensorweb Research Laboratory
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Georgia State University
Numerical example
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How long does it take to send a file of 640,000
bits from host A to host B over a circuitswitched network?
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All links are 1.536 Mbps = 1536 kbps
Each link uses TDM with 24 slots
500 msec to establish end-to-end circuit
Solution:
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Each circuit transmission rate: 1.536Mbps/24 =
64kbps
Time to transmit file: 640,000bits/64kbps = 10 sec
Total: 10.5 sec
Sensorweb Research Laboratory
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Georgia State University
Network Core: Packet Switching
10 Mb/s
Ethernet
A
B
statistical multiplexing
C
1.5 Mb/s
queue of packets
waiting for output
link
D
E
Sequence of A & B packets does not have fixed pattern 
statistical multiplexing.
In TDM each host gets same slot in revolving TDM frame.
Sensorweb Research Laboratory
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Georgia State University
Network Core: Packet Switching
each end-end data stream divided
into packets
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user A, B packets share network
resources
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each packet uses full link
bandwidth
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resources used as needed
Bandwidth division into “pieces”
Dedicated allocation
Resource reservation
Sensorweb Research Laboratory
resource contention:
 aggregate resource
demand can exceed
amount available
 congestion: packets
queue, wait for link use
 store and forward:
packets move one hop
at a time
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Node receives complete
packet before forwarding
Georgia State University
Packet-switching: store-and-forward
L
R
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R
R
Example:
 L = 7.5 Mbits
 R = 1.5 Mbps
 delay = 15 sec
Takes L/R seconds to
transmit (push out)
packet of L bits on to
link of R bps
Entire packet must
arrive at router before it
can be transmitted on
next link: store and
forward
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delay = 3L/R
Sensorweb Research Laboratory
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Georgia State University
Packet switching versus circuit switching
Packet switching allows more users to use network!
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1 Mb/s link
each user:
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circuit-switching:
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100 kb/s when “active”
active 10% of time
N users
10 users
1 Mbps link
packet switching:
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with 35 users, probability of
more than 10 active users is
less than .0004
n10 Pp0.1 (n | 35)  1  n0 Pp0.1 (n | 35)
35
9
probability of exact n of N users active:
Sensorweb Research Laboratory
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Georgia State University
Packet switching versus circuit switching
Is packet switching a “slam dunk winner?”
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Great for bursty data
 resource sharing
 simpler, no call setup
Excessive congestion: packet delay and loss
 protocols needed for reliable data transfer,
congestion control
Q: How to provide circuit-like behavior?
 bandwidth guarantees needed for audio/video apps
 still an unsolved problem
Sensorweb Research Laboratory
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Georgia State University
Packet-switched networks: forwarding
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Goal: move packets through routers from source to
destination
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datagram network:
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we’ll study several path selection (i.e. routing) algorithms
destination address in packet determines next hop
routes may change during session
analogy: driving, asking directions
virtual circuit network:
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each packet carries tag (virtual circuit ID), tag determines next hop
fixed path determined at call setup time, remains fixed thru call
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routers maintain per-call state
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Sensorweb Research Laboratory
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Georgia State University
Network Taxonomy
Networks
Packet-switched
networks
Circuit-switched
networks
FDM
Networks
with VCs
TDM
e.g., telephone networks
e.g., ATM networks
Datagram
Networks
e.g., Internet
• Datagram network is not either connection-oriented
or connectionless.
• Internet provides both connection-oriented (TCP) and
connectionless services (UDP) to apps.
Sensorweb Research Laboratory
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Georgia State University
Connection-oriented vs Connectionless
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Key differences:
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Connection-oriented: packets arrives in the order of
sending out (e.g., FIFO), and need connection
setup phase
Connectionless: packets may (or may not) arrive in
different order of sending out, and does not need
connection pre-setup
Example:
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Circuit Switch Network: connection-oriented
Packet Switch Network
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Virtual circuit network: connection-oriented
Datagram network depends on layers and protocols:
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TCP – connection-oriented
UDP, IP - connectionless
Sensorweb Research Laboratory
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Georgia State University
Introduction
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Physical overview of Internet
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Physical architecture
Network Edge - Internet access technologies
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Circuit switching: setup path before communication, have
dedicated resource per call
Packet switching: store and forward, share resource and need
contend for
Software overview of Internet
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Residential access: dialup, ADSL, cable, WiMax
Company access: LAN, WLAN
Network Core – Switching technologies
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Roadmap
Software architecture
The OSI and TCP/IP Reference Models
Internet history
Network standardization body
Sensorweb Research Laboratory
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Georgia State University
Protocol “Layers”
Networks are complex!
 many “pieces”:
 hosts
 routers
 links of various
media
 applications
 protocols
 hardware, software
Sensorweb Research Laboratory
Question:
Is there any hope of
organizing structure of
network?
Or at least our discussion
of networks?
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Georgia State University
Internet protocol stack
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application: supporting network
applications
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transport: host-host data transfer
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IP, routing protocols
link: data transfer between
neighboring network elements,
including encapsulating bits into
frames
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TCP, UDP
network: routing of datagrams from
source to destination
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FTP, SMTP, HTTP, etc
PPP, Ethernet, etc
application
transport
network
link
physical
physical: bits “on the wire”
Sensorweb Research Laboratory
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Georgia State University
Analogy scenario
The philosopher-translator-secretary architecture.
Sensorweb Research Laboratory
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Georgia State University
Services to Protocols Relationship
The relationship between a service and a protocol:
each layer implements a service
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via its own internal-layer actions or protocols
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relying on services provided by layer below
Sensorweb Research Laboratory
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Georgia State University
Why layering?
Dealing with complex systems:
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explicit structure allows identification, relationship of
complex system’s pieces
 layered reference model for discussion
modularization eases maintenance, updating of
system
 change of implementation of layer’s service
transparent to rest of system
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e.g., changing common language of translators does not
affect the communication between the philosopher
layering considered harmful?
Sensorweb Research Laboratory
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Georgia State University
source
message
segment Ht
datagram Hn Ht
frame
Hl Hn Ht
M
M
M
M
application
transport
network
link
physical
Typical network flow
Hl Hn Ht
M
link
physical
Hl Hn Ht
M
switch
destination
M
Ht
M
Hn Ht
Hl Hn Ht
M
M
application
transport
network
link
physical
Sensorweb Research Laboratory
Hn Ht
Hl Hn Ht
M
M
network
link
physical
Hn Ht
Hl Hn Ht
M
M
router
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Georgia State University
General situation of end-end flow
Example information flow supporting virtual communication in layer 5.
Sensorweb Research Laboratory
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Georgia State University
Introduction

Physical overview of Internet
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
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


Physical architecture
Network Edge - Internet access technologies
Network Core – Switching technologies
Software overview of Internet


Roadmap
Software architecture
The OSI and TCP/IP Reference Models
Internet history
Network standardization body
Sensorweb Research Laboratory
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Georgia State University
The design principles of OSI Reference Models
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A layer should be created when a different abstraction
is needed
Each layer should perform a well-defined function
The function of each layer should be chosen with an
eye toward defining internationally standardized
protocols
The layer boundaries should be chosen to minimize
the information flow across the interfaces
The number of layers should be large enough that
functions need not be thrown together in the same
layer out of necessity and small enough that the
architecture does not become unwieldy
Sensorweb Research Laboratory
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Georgia State University
OSI Reference Models
The OSI
reference
model.
Sensorweb Research Laboratory
Concern the syntax and semantics of
information transmitted
Allow users on different machines to
establish sessions
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Georgia State University
TCP/IP Reference Models
The TCP/IP reference model.
Sensorweb Research Laboratory
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Georgia State University
TCP/IP Reference Models
123
Major protocol and application components common to most
commercial TCP/IP software packages and their relationship
Sensorweb Research Laboratory
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Georgia State University
A Critique of the OSI Model and Protocols
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Bad
Bad
Bad
Bad
timing
technology
implementations
politics
Sensorweb Research Laboratory
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Georgia State University
A Critique of the TCP/IP Reference Model
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Service, interface, and protocol not distinguished
Not a general model
Host-to-network “layer” not really a layer
No mention of physical and data link layers
Minor protocols deeply entrenched, hard to
replace
Sensorweb Research Laboratory
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Georgia State University
Hybrid flow in the lecture
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application: supporting network
applications


transport: host-host data transfer


IP, routing protocols
link: data transfer between
neighboring network elements,
including encapsulating bits into
frames


TCP, UDP
network: routing of datagrams from
source to destination


FTP, SMTP, HTTP, DNS
MAC (Multiple Access Control) sublayer
application
transport
network
link
physical
physical: bits “on the wire”
Sensorweb Research Laboratory
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Georgia State University
Introduction

Physical overview of Internet






Physical architecture
Network Edge - Internet access technologies
Network Core – Switching technologies
Software overview of Internet


Roadmap
Software architecture
The OSI and TCP/IP Reference Models
Internet history
Network standardization body
Sensorweb Research Laboratory
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Georgia State University
Internet History
1961-1972: Early packet-switching principles
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1961: Kleinrock - queueing theory shows effectiveness of packetswitching
1964: Baran - packet-switching in military nets
1967: ARPAnet conceived by Advanced Research Projects Agency
1969: first ARPAnet node operational
(a) Structure of the
telephone
system.
(b) Baran’s proposed
distributed
switching
system.
Sensorweb Research Laboratory
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Georgia State University
Internet History
1961-1972: Early packet-switching principles

1972:
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ARPAnet demonstrated publicly
NCP (Network Control Protocol) first host-host protocol
first e-mail program
ARPAnet has 15+ nodes
Growth of the ARPANET
(a) December 1969.
(b) July 1970.
(c) March 1971.
(d) April 1972.
(e) September 1972.
Sensorweb Research Laboratory
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Georgia State University
Internet History
1972-1980: Internetworking, new and proprietary nets
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1970: ALOHAnet satellite
network in Hawaii
1973: Metcalfe’s PhD thesis
proposes Ethernet
1974: Cerf and Kahn architecture for interconnecting
networks
late70’s: proprietary
architectures: DECnet, SNA,
XNA
late 70’s: switching fixed length
packets (ATM precursor)
1979: ARPAnet has 200 nodes
Sensorweb Research Laboratory
Cerf and Kahn’s internetworking
principles:

minimalism, autonomy - no
internal changes required to
interconnect networks

best effort service model

stateless routers

decentralized control
define today’s Internet architecture
-66-
Georgia State University
Internet History
1990, 2000’s: commercialization, the Web, new apps
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

Early 1990’s: ARPAnet
decommissioned
1991: NSF lifts restrictions on
commercial use of NSFnet
(decommissioned, 1995)
early 1990s: Web
 hypertext [Bush 1945, Nelson
1960’s]
 HTML, HTTP: Berners-Lee
 1994: Mosaic, later Netscape
 late 1990’s: commercialization
Late 1990’s – 2000’s:
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more killer apps: instant
messaging, P2P file sharing
network security to forefront
est. 50 million host, 100
million+ users
backbone links running at
Gbps
of the Web
Sensorweb Research Laboratory
-67-
Georgia State University
Internet Usage

Traditional applications (1970 – 1990)
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E-mail
News
Remote login
File transfer
Today in addition

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WWW: news, shopping, gaming, maps, trading, etc
Multimedia: Internet video, audio, radio
P2P file sharing
Blogs
Messenger
……
Sensorweb Research Laboratory
-68-
Georgia State University
Introduction

Physical overview of Internet


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

Physical architecture
Network Edge - Internet access technologies
Network Core – Switching technologies
Software overview of Internet


Roadmap
Software architecture
The OSI and TCP/IP Reference Models
Internet history
Network standardization body
Sensorweb Research Laboratory
-69-
Georgia State University
Network Standardization

Telecommunications World
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ITU (International Telecommunication Union), called
CCITT during 1956-1993
International Standards World
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ISO (International Standards Organization)

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U.S: ANSI (American National Standards Institute)
Other countries …
IEEE (Institute of Electrical and Electronics Engineers)
Internet Standards World

Internet Society
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IAB (Internet Activities Board)
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IRTF (Internet Research Task Force): long-term research
IETF (Internet Engineering Task Force): short-term engineering
issues – RFC documents
Sensorweb Research Laboratory
-70-
Georgia State University
IEEE 802 Standards
The 802 working groups. The important ones are marked with *. The ones
marked with  are hibernating. The one marked with † gave up.
Sensorweb Research Laboratory
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Georgia State University
Summary
Covered a “ton” of material!

Physical overview of Internet






to follow!
Software overview of Internet


Physical architecture
Network Edge - Internet access
technologies
Network Core – Switching
technologies
You now have:
 context, overview,
“feel” of networking
 more depth, detail
Software architecture
The OSI and TCP/IP Reference
Models
Internet history
Names and terms in network
society
Sensorweb Research Laboratory
-72-
Georgia State University
Suggestion



Read Chapter 1
Preview Chapter 2 (Application Layer)
Install WireShark and read its manual:
http://www.wireshark.org/download.html

Wireshark is a free and open-source packet analyzer. It is
used for network troubleshooting, analysis, software and
communications protocol development, and education.
Originally named Ethereal, in May 2006 the project was
renamed Wireshark due to trademark issues.
Sensorweb Research Laboratory
-73-
Georgia State University