ch1_introduction.pdf
TRANSCRIPT
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CmpE 206 Copyright 2013 by Fatoohi, All Rights Reserved 1
San Jose State University
College of Engineering
Computer Network Design (CmpE 206)
by
Rod Fatoohi, Ph.D.
Note: These course notes are provided exclusively for the
students convenience to follow the presentations. They cannot
be reproduced without a written permission from the author.
Some of these materials are from the following textbooks:
Computer Networks, 5th ed., 2011, Tanenbaum & Wetherall,
Prentice-Hall.
Data and Computer Communications, 9th ed., 2011, Stallings,
Prentice-Hall.
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Overview
Protocol Hierarchies
Reference Models
Network Classifications
Internet Architecture
Standards
Units
Chapter 1
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Computer Network: collection of
interconnected computer systems w/ software
protocol structure that enables communication.
Protocol: agreement between communicating
parties on how communication is to be done.
It contains rules governing communication.
Introduction
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Overview
Protocol Hierarchies
Reference Models
Network Classifications
Internet Architecture
Standards
Units
Chapter 1
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Protocol Hierarchies (Layering):
Networks are in general organized as series of
layers, each one built upon one below it.
Each layer provides services to higher layers.
Service is set of primitives (operations) that
layer provides to layer above it (what the
layer does).
Between adjacent layers there is interface.
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Interface specifies which primitive
operations & services lower layer offers to
upper layer
how above layer access that layer?
Peers are entities (active elements) in same
layer of different machines.
Network Architecture: set of layers &
protocols.
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Communication:
Conceptually, peers assume that they are
communicating horizontally.
Actually, each layer passes data & control
information to layer below it (vertically), until
lowest layer is reached.
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Service vs Protocol:
Protocol: set of rules governing format &
meaning of messages within layer.
Service defines operations that layer
provides to layer above it.
Service is like abstract data type or object
it defines operations but not implementation
Protocol relates to implementation of
service
its not visible to user.
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Service vs Protocol
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Advantages of Layering:
Divide & Conquer
Modularity
Well-defined interfaces (Ex. API).
Disadvantages of Layering:
Performance.
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Overview
Protocol Hierarchies
Reference Models
Network Classifications
Internet Architecture
Standards
Units
Chapter 1
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OSI Reference Model:
Developed by International Standards
Organization (ISO).
Called ISO OSI (Open Systems
Interconnection) Reference Model.
Open System: specifications are publicly
available.
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OSI Reference Model:
The Physical Layer is concerned w/
transmission of raw bits over physical link.
The Data Link Layer provides reliable
transfer of frames across physical link.
The Network Layer is responsible for
establishing, maintaining & transmission
connections across networks.
The Transport Layer provides reliable
transparent transfer of data w/ error
recovery & flow control.
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OSI Reference Model (cont)
The Session Layer is responsible for
establishing, managing & termination of
sessions between applications.
The Presentation Layer performs useful
transformations on data to provide
standardized application interface &
common communications services.
The Application Layer provides services
to users.
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The Link Layer (Network Access Layer)
not well defined.
mainly concerned w/ exchange of data between
end system and network & between two end
systems attached to same network.
includes device driver in OS & corresponding
Network Interface Card (NIC).
The Network Layer (Internet Layer)
handles movement of packets around
network.
The TCP/IP Reference Model (Internet
Reference Model):
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TCP/IP Reference Model (cont)
The Transport Layer (Host-to-Host
Layer) provides flow of data between two
end systems.
The Application Layer (Process Layer)
handles details of various user applications.
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IEEE 802 Reference Model :
Physical Layer:
encoding/decoding of signals.
preamble generation/removal (synchronization)
bit transmission/reception.
transmission Medium.
Medium Access Control Sublayer:
assembling transmitting data into frames on
transmission w/ address & error-detection.
disassembling frames on reception & performing
address recognition & error detection.
governing access to LAN transmission medium
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IEEE 802 vs OSI
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IEEE 802 Reference Model (Cont.)
Logical Link Control
providing one or more Service Access Points
(SAPs).
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Overview
Protocol Hierarchies
Reference Models
Network Classifications
Internet Architecture
Standards
Units
Chapter 1
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Network Classifications
(based on geographical scope)
Personal Area Networks
Local Area Networks
Metropolitan Area networks
Wide Area Networks
Internet
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Network Classifications (2)
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Personal Area Network (PAN):
Within range of a person
used to connect computer w/ its peripherals
Cover short distance (few meters) w/ low speed
May use master-slave paradigm
Ex: Bluetooth, RFID.
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Personal Area Network Example
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Local Area Network (LAN):
within building: home, office, factory,
owned & operated by single organization
used to connect PCs & other devices
used to share resources & exchange information
Early wired LANs were broadcast shared medium; currently mostly switching
Wired LANs run at speeds of 100 Mbps to 10 Gbps w/ low latency & very low error rate
Ex: Ethernet & WiFi.
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Local Area Network Examples
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Metropolitan Area Network (MAN):
Within a city or a metropolitan area
Larger than LAN but smaller than WAN
Evolved w/ technologies used
Early example: Distributed Queue Dual Bus (IEEE 802.6) obsolete
Currently: Cable TV, WiMAX (IEEE 802.16)
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Metropolitan Area Network Example
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Wide Area Network (WAN):
cover large geographical area (country).
relay mainly on circuits provided by common
carrier (leased).
have many interconnected switching elements.
traditionally provide modest data rates to
customers, higher rates to business
traditionally have long delay & relatively high
error rates to customers
more scalable
Ex: Frame Relay (1.5 Mb/s), ATM (155 Mb/s
& 622 Mb/s).
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Wide Area Network Example
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Internet
internet (internetworking): collection of interconnected networks using common protocol suite.
Internet collection of ISP (Internet Service Provider) networks to connect companies, universities, government offices, and private individuals & uses TCP/IP protocol suite.
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Overview
Protocol Hierarchies
Reference Models
Network Classifications
Internet Architecture
Standards
Units
Chapter 1
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Internet Architecture
Tiered hierarchy of Internet Service Providers (ISPs)
At the top tier-1 ISPs, Internet backbone operators
operate large networks w/ fast routers (forwarding
packets at high rates) & high-speed links ( 622 Mbps)
directly connected to each other at private peering points
& Network Access Points (NAPs) network of switches
& routers that exchange large quantities of traffic
Connected to & provide services to tier-2 ISPs
small number ( dozen): AT&T, Sprint, Level 3 Comm,
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Internet Architecture (2)
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Internet Architecture (3)
Next, tier-2 ISPs, regional providers
Connected to & costumers to a few tier-1 ISPs
Might be directly connected to other tier-2 ISPs
Next, lower-tier ISPs & access ISPs
Connected to & costumers to higher-tier ISPs
Service providers to users & content providers
ISPs are connected to each others at Points of Presence (POPs) collection of routers at which routers of other ISPs can connect
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Rules for Data Transfer
Simplex Communication
Data travel in one direction only.
Half-duplex Communication:
Data can travel in either direction but not simultaneously
Full-duplex Communication:
Data can travel in both directions at once.
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Types of Networks
Circuit-Switched:
has three phases: connection establishment, data
transfer & connection termination.
Channel capacity must be available & reserved
between end systems during connection.
All packets follow the same path
Data transferred at fixed rate w/o delay except
propagation delay.
In heavy traffic, some calls are blocked.
Unused bandwidth during connection is wasted.
charging based on time & distance
Ex: Telephone network, PBX. CmpE 206 Copyright 2013 by Fatoohi, All Rights Reserved 41
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Types of Networks (2)
Packet-Switched: Data are transferred in blocks called packets.
Larger messages are divided into many packets.
Packets can follow different paths.
Re-assembly at destination might be needed
Channel efficiency is high since it can be dynamically shared by packets.
Data rate conversion is possible.
In heavy traffic, packets are accepted but more delay
Better fault tolerant (w.r.t switches crash).
charging based on volume of traffic.
Ex: LANs. CmpE 206 Copyright 2013 by Fatoohi, All Rights Reserved 42
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Circuit Switching vs Packet Switching
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Circuit Switching vs Packet Switching (2)
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Circuit Switching vs Packet Switching (3)
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Types of Network Services:
Connection-oriented Service:
has three phases: connection establishment,
data transfer & connection termination.
modeled after telephone system.
usually sending host sends stream of data
Communication doesnt have to be continuous.
data ordering preserved
provides information in case of failure.
uses some resources
Ex: TCP
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Connectionless Service:
modeled after postal system.
Each message carries identification for routing.
Messages may get lost.
no reordering.
requires less initial overhead
can run faster
uses less resources
Ex: UDP
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Overview
Protocol Hierarchies
Reference Models
Network Classifications
Internet Architecture
Standards
Units
Chapter 1
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allow different devices to communicate
increase market share for standard products
2 categories: de facto from the fact & de jure
by law
Standard organizations for networking:
Telecommunications
International standards
Internet standards
Standards
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International Telecommunications Union (ITU)
Standardize international telecommunications
UN specialized agency
State Dept. represents USA
many countries represented by Post, Telegraph &
Telephone (PTT) admin
Over 700 sector & associate members
3 main sectors:
Telecommunications standardization sector (ITU-T)
Radio-communications sector (ITU-R)
Development sector (ITU-D)
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ITU-T
Formally known as International Telegraph & Telephone Consultative Committee (CCITT)
makes recommendations about telephone, telegraph & data communication
has 10 study groups
Over 3000 recommendations produced which become standards:
DSL
H.264 (MPEG-4 AVC)
X.509 public key certificates
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International Standards
ISO (International Standards Organization)
voluntary organization whose members are national standard organizations of 157 countries.
over 200 technical committees on many subjects.
Over 17000 standards issued
member of ITU-T
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International Standards (2)
ISO Standard Process:
1. Idea is assigned to technical committee
2. Committee assigns working group to study it & generates Committee Draft (CD)
3. CD is circulated for comments for 6 months
4. If idea is good & approved, Draft International Standard (DIS) generated for comments for 5 months.
5. If DIS approved*, Final DIS (FDIS) generated for approval within 2 months
6. If approved*, International Standard (IS) is generated.
*Approval for requires 2/3 majority
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International Standards (3)
ANSI (American National Standards Institute)
private, nonprofit organization
member of ISO
its standards are frequently adopted by ISO
NIST (National Institute of Standards &
Technology)
US government agency.
Issues standards for US government.
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International Standards (4)
IEEE (Institute of Electrical & Electronics
Engineers)
professional organization which develops
standards in EE & Computing.
IEEE 802 is key standard for LAN.
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IEEE 802 Standards
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IEEE 802 Standards (2)
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Internet Standards
IAB
In 1979, ARPA formed Internet Control &
Configuration Board (ICCB) to coordinate
design of protocols & architecture of internet.
In 1983, ICCB was renamed Internet Activities
Board (IAB), then Internet Architecture Board.
Each of its ten members headed a task force.
met several times a year.
Volunteers did most of work.
Communication was done by a series of
technical reports called Request for Comments.
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Internet Standards (2)
Request For Comments (RFCs)
numbered in chronological order of creation.
as short as one page & as long as 200 pages.
edited but not refereed.
cover a broad concept or details.
7359 issued (as of August 2014)
publicly available from several sites:
http://www.rfc-editor.org/rfc.html
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Internet Standards (3)
IAB (2)
In 1989, IAB was reorganized into 2 groups: Internet
Research Task Force (IRTF) for long-term research &
Internet Engineering Task Force (IETF) for short-
term engineering issues.
Each group has a steering group: IRSG, IESG.
IETF was divided into over 70 working groups:
routing & addressing, security, network management,
user information, new applications,
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Internet Standards (4)
Internet Society
professional society was formed in 1992 to
promote the Internet
W3C (World Wide Web Consortium)
Develops protocols & guidelines for the Web
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Internet Standards (5)
Internet Standard Process:
An idea must be explained in an RFC &
generates sufficient interest to become
proposed standard.
There must be a working implementation in 2
independent sites to become draft standard for
at least 4 months.
If idea is sound & software works, IAB can
declare the RFC as Internet standard.
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Overview
Protocol Hierarchies
Reference Models
Network Classifications
Internet Architecture
Standards
Units
Chapter 1
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Data Rate Unit
used for speed of transmission line (ex: 1 kbps)
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Data Rate Unit (2)
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Capacity Unit
used for memory, disk, file & database sizes
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Exp. Explicit Prefix
210 1,024 Kilo (KB)
220 1,048,576 Mega (MB)
230 1,073,741,824 Giga (GB)
240 1,099,511,627,776 Tera (TB)