Uses of Computer Networks

1
Introduction
2
Uses of Computer Networks

• Business Applications
• Home Applications
• Mobile Users
• Social Issues

3
Business Applications of Networks

• Resource sharing
• Client-server model

Server
Network
Client
User
4

• Client-server model involves requests and replies

Client machine
Server machine
Request
Network
Reply
Client process
Server process
5
Home Network Applications

• Access to remote information
• Person-to-person communication
• Interactive entertainment
• Electronic commerce

6
Network Hardware

• Local Area Networks
• Metropolitan Area Networks
• Wide Area Networks
• Wireless Networks

7
Types of transmission technology

• Broadcast links a single communication channel
  shared
• by all machines in the network
• - broadcasting
• Point-to-point links network consists of many
  links
• between individual machines
• - unicasting

8
Classification of networks by scale
Distance between machines
Machines located in the same
Example
1 m Square meter
Personal area network 10 m
Room 100 m
Building 1 km
Campus 10 km City
Metropolitan area
network 100 km Country 1000
km Continent 10000 km Planet The
Internet
Local area network
Wide area network
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Local Area Networks (LANs)
Computer
Cable

• Restricted in size up to a few kilometres
• Broadcast networks bus and ring
• Transmission speeds from 1 Mbit/s to 1000 Mbit/s
• Channel allocation centralized or decentralized
• IEEE 802.3 network (Ethernet) is the most
  popular LAN

10
Metropolitan Area Networks (MANs)

• Covers a city
• Cable TV network, LAN backbone

junction box
Antenna
Head end
Internet
11
Wide Area Networks (WANs)
router
host
subnet

• Subnet a collection of routers and
  communication lines
• (also has to do with network addressing)
• Router has a routing and switching function

12
Stream of packets from sender to receiver
router
Sending host
subnet
B
A
Receiving host
C
D
packets
Switching decision forward to D not to B
13
Enterprise Network
LAN Local Area Network MAN Metropolitan Area
Network , WAN Wide Area Network
MAN
WAN
LAN
14
Wireless Networks

• Categories of wireless networks
• System interconnection
• Wireless LANs
• Wireless WANs

15
Examples of wireless networks
To fixed network
Base station
printer
mouse
keyboard
Wireless LAN (WLAN)

• Bluetooth configuration
• connects components of
• computer (short range radio)

- connects computers
16
Network Software

• Protocol Hierarchies
• Design Issues for the Layers
• Connection-Oriented and Connectionless Services
• Service Primitives

17
Protocol Hierarchies
Host 2
Host 1
Layer 5 protocol
Layer 5
Layer 5
Layer 4/5 interface
Layer 4 protocol
Layer 4
Layer 4
Layer 3/4 interface
Layer 3 protocol
Layer 3
Layer 3
Layer 2/3 interface
Layer 2 protocol
Layer 2
Layer 2
Layer 2/3 interface
Layer 1 protocol
Layer 1
Layer 1
Physical medium
18
Definitions

• Network architecture a set of layers and
  protocols
• Protocol an agreement between communicating
  parties on
• how the communication is to proceed
• Protocol stack a list of protocols used by a
  certain system

19
The philosopher-translator-secretary architecture
20
Example information flow supporting virtual
communication in layer 5
Layer 5 protocol
M
M
Layer 4 protocol
M
H4
M
H4
Layer 3 protocol
M2
H4
H3
M1
H4
H3
M2
H4
H3
M1
H4
H3
Layer 2 protocol
M1
H4
H3
H2
T2
M1
H4
H3
H2
T2
M1
H4
H3
H2
T2
Source machine
Destination machine
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Design Issues for the Layers

• Addressing to specify a specific destination
• Error Control to deal with bit errors,
  sequencing
• Flow control to prevent a fast sender from
  swamping a slow receiver
• Multiplexing underlying layer may use the same
• connection for separate conversations
• Routing with multiple paths the proper path
  must
• be chosen

22
Connection-Oriented and Connectionless Services

• Connection-oriented modeled after the telephone
  system
• - pick up the phone
• - dial
• - talk
• - hang up
• Connectionless modeled after the postal system
• - each packet contains address information
• - packets are delivered independent of other
  packets

23
Service Primitives

• The service is specified by primitives they
  tell the service
• to perform some action based on action taken
  by peer entity

• Five service primitives for implementing a
  simple
• connection-oriented service

24

• Packets sent in a simple client-server
  interaction on a
• connection-oriented network

25
Reference Models

• The OSI Reference Model
• The TCP/IP Reference Model
• A Comparison of OSI and TCP/IP
• A Critique of the OSI Model and Protocols
• A Critique of the TCP/IP Reference Model

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Application data
Application process A
Application process B
The OSI Reference Model
Data

AH
A-data
7
Application
Application
Presentation
Presentation
6
PH
P-data
Session
SH
S-data
5
Session
TPDU
Transport
TH
T-data
Transport
4
Packet
Network
NH
N-data
3
Network
Frame
Data link
LH
L-data
F
F
2
Data link
1
Physical
Physical
Bits
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OSI-model, layer functions

• Physical layer concerned with transmitting raw
  bits over
• a communication channel
• Data Link Layer provides error-free
  transmission over a link
• framing, flow control, error detection and
  correction
• Network Layer controls the operation of the
  subnet how the
• packets are routed, congestion control,
  interconnection of
• different types of networks
• Transport Layer error-free transport of
  segments from source
• to destination (end-to-end)

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• Session Layer allows users to establish
  sessions
• dialog control, synchronization
• Presentation Layer syntax and semantics of the
  transmitted
• information, encoding, encryption
• Application Layer needed for the application
  (http, ftp )

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The TCP/IP Reference Model
OSI
TCP/IP
Application
Application
Not present in the model
Presentation
Session
Transport
Transport
Network
Network
Data Link
Host to network
Physical
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TCP/IP Protocol Suite
7. Application Layer 4. Transport Layer 3.
Network Layer Host to network
FTP Telnet SMTP
TFTP
HTTP
SNMP
Private
TCP
UDP
IP
ARP RARP
SNAP
DHCP
LLC
LAN
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Example Networks

• The Internet
• Connection-Oriented Networks ATM
• Ethernet

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The Internet

• What is it? A vast collection of networks that
  use certain
• common protocols and provide certain common
  services

33
Asynchronous Transfer Mode (ATM)

• Connection-oriented packet-switching network
• Used mostly in WANs
• Data transmitted in cells
• Uses virtual circuits

bytes 5 48
Header User data
34
Ethernet

• Corporate LANs are Ethernet-based

Core switch
1 Gbit/s
1 Gbit/s
Edge switch
35
Network Standardization

• ITU International Telecommunication Union
• Main sectors
• Radiocommunications
• Telecommunications Standardization
• Development
• Classes of Members
• National governments
• Sector members
• Associate members
• Regulatory agencies

36
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.