Transcript Lecture1R

ITEC350 Networks I
Lecture 1
Hwajung Lee
What is Computer Networks?
A collection of autonomous computers
interconnected by a single technology
 Interconnected via:
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Copper wire
Fiber optics
Microwaves
Infrared
Communication satellites, etc.
Why Computer Networks?
Business Applications
 [Goal1] Resource Sharing
• To connect isolated computer and information
to be able to extract and correlate information
about the entire company.
• To make all programs, equipment (ex: printers,
scanners, and CD burners), and especially data
available to anyone on the network without
regard to the physical location of the resource
an the user.
 [Goal 2] Communication Medium
• Electronic mail (e-mail)
• Shared resources (ex: shared hard driver)
• Videoconferencing, a shared virtual blackboard
 [Goal 3] Electronic Commerce (e-commerce)
• To do business electronically with other
companies. (ex: order the parts of a product
from a variety of suppliers)
• To do business with consumers over the
Internet.
Home Applications
 [Goal 1] Access to remote information
• Newspapers, Digital library
 [Goal 2] Person-to-person communication
• Email, Instant messaging, Chat room,
Worldwide newsgroups
• Peer-to-peer communication (ex: Napster)
• Internet phone, Internet video phone, Internet
radio, Telelearning
Home Applications (cont.)
 [Goal 3] Interactive entertainment
• Video on demand, Interactive live television
show, Multiperson real-time simulation games –
possibly with worldwide shared virtual reality.
 [Goal 4] Electronic commerce
• Home shopping, Electric flea markets, On-line
auctions
 Mobile Network Users
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[Goal] To have a portable office
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Cellular phone, PDA, Military use, Wireless
sensor networks, Mobile-commerce,
Wearable wireless computers
Combinations of wireless networks and mobile computing.
Network Types Based on Roles
 Terminal Connection
Network Types Based on Roles
 Client-server
Network Types Based on Roles
Peer-to-peer
 Computers act as both client and server on
the network
 There is no reliance on a centralized server
to provide access to data and other
resources
 Compared to a centralized client-server
model, peer-to-peer is decentralized,
meaning any host can communicate with any
other host
Network Topologies
RING
STAR
MESH
HYBRIDS
OF THESE
BUS
Comparison of Basic Topologies
Topology
Bus
Star
Ring
Advantages
Physical
Broadcast
Inherent
Security,
Limited Delay
Reliability,
Limited Delay
Disadvantages
Poor
Security –
Poor Reliability
All
stations see the data
at once
Inefficient –
collisions when two
or more stations
send at once.
Poor Security
(central controller – All stations
is single point of
see the data
failure)
as is travels
around the
ring
Classification of interconnected
processors by scale.
Personal Area Network (PAN)
 A person’s body or desk area
Local Area Networks (1)
Local Area Network (LAN)
 Limited geographical distance: home,
office, building, campus, industrial part
 Customer premises operation
• User firm chooses technology
• User firm needs to manage on ongoing basis
 Low cost per bit transmitted
• Companies can afford high speed
• 100 Mbps to the desktop is typical
Local Area Networks (2)
Two broadcast networks
(a) Bus (b) Ring
Local Area Networks (3)
 Ethernet
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Most popular LAN
Architecture of the original Ethernet.
Metropolitan Area Networks
Metropolitan Area Network (MAN)
 Single urban area (city and its suburbs)
 Faster than long-distance WANs
 Still slower than LANs
Metropolitan Area Networks
A metropolitan area network based on cable TV.
Wide Area Network (WAN)
WAN
 To link sites
• Long distances
 Requires the use of carriers to provide service
• Limited and complex choices but carrier manages
 High cost per bit transmitted
• Companies cannot afford high speeds
• Usually low speed (56 kbps to a few megabits per
second)
Wide Area Networks (1)
Relation between hosts on LANs and the subnet.
Wide Area Networks (2)
A stream of packets from sender to receiver.
Wireless Networks
 Categories of wireless networks:
 System interconnection
 Wireless LANs
• Speed: Upto about 50Mbps
• Distance: Tens of meters
 Wireless WANs (ex: cellular system)
• Speed: below 1Mbps
• Distance: Kilometers
Wireless Networks (2)
(a) Bluetooth configuration (b) Wireless LAN
 Wireless LANs
(a) Wireless networking with a base station.
(b) Ad hoc networking.
 Standard for Wireless LANs
IEEE 802.11 network.
Network Software
 Protocol Hierarchies
 Design Issues for the Layers
 Connection-Oriented and
Connectionless Services
 Service Primitives
 The Relationship of Services to
Protocols
Network Software
Protocol Hierarchies
 Layers, protocols, and interfaces.
Protocol Hierarchies
The philosopher-translator-secretary
architecture.
Connection-Oriented and
Connectionless Services (1)
The software used to maintain each
protocol is often called a protocol stack
Transport layer protocols can be:
 Connectionless, or stateless, which sends each
packet without regard to whether any other
packet was received by the destination
computer (implementation: packet switching,
UDP)
Connection-Oriented and
Connectionless Services (2)
 Connection oriented, or stateful, which
maintains information about which packets
have been correctly received by the
destination computer (implm.:circuitswitching, TCP)
Connection-Oriented and
Connectionless Services
 Six different types of service.
Why
Standard or Reference Model?
Consumer
 Easy to select a product which is
compatible with other equipments.
Supplier
 Minimize risk when it develops new
technologies.
Reference Models
 The OSI Reference Model
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ISO (International Organization for
Standardization)
OSI (Open Systems Interconnection) Model
 The TCP/IP Reference Model
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TCP (Transmission Control Protocol)
IP (Internet Protocol)
 A Critique of the OSI Model and Protocols
 A Critique of the TCP/IP Reference Model
OSI Reference Model
OSI Reference Model
The TCP/IP reference model
Conceptual Models of Networking
(1)
Acronyms
 POP (Post Office Protocol)
 FTP (File Transfer Protocol)
 UDP (User Datagram Protocol)
 TCP (Transmission Control Protocol)
 SMTP (Simple Mail Transport Protocol)
 HTTP (Hypertext Transport Protocol)
 DNS (Domain Name Service)
 ICMP (Internet Control Message Protocol)
 PPP (Point-to-Point Protocol)
 SATNET (Satellite Networks)
 IRC (Internet Relay Chat)
A Critique of the OSI Model and
Protocols
 Why OSI did not take over the world
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Bad timing
Bad implementations
Bad politics
Bad Timing
 The apocalypse of the two elephants.
A Critique of the TCP/IP
Reference Model
 Problems:
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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
Networking Technologies
Ethernet
 Most widely used technology
 Three variation of Ethernet based on
transmission speed, or bandwidth
Token-ring
 Uses a token to identify which computer on
the network has the right to transmit data
 Not as fast as Ethernet, and may be more
expensive
Networking Technologies
Network Standardization
 Who’s Who in the Telecommunications World
 Who’s Who in the International Standards
World
 Who’s Who in the Internet Standards World
ITU
(International Telecommunication Union)
 Main sectors
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Radiocommunications
Telecommunications Standardization
Development
 Classes of Members
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National governments
Sector members
Associate members
Regulatory agencies
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.
Metric Units
The principal metric prefixes.