Transcript Computer Networks

Client-Server and P2P (Peer-to-Peer) System
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Computer Network Architectures
◦ Types
 Centralised Systems
 Distributed Systems
◦ Communication networks components
◦ Examples of Network architectures
CSY1017-Computer Communications
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Platform as used in a computer context can refer to:
◦ (1) Hardware Platform: The type of processor and/or other hardware
on which a given operating system or application program runs,
 Examples:
 Hardware: mainframe, workstation, desktop, handheld or
embedded
 Processor: such as x86, SPARC, PowerPC or Alpha
◦ (2) the type of Operating System on a computer
 Microsoft Windows systems
 Unix-like systems e.g., Linux, Solaris, FreeBSD
◦ (3) the combination of the type of hardware and the type of operating
system running on it.
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The design and framework
of a network, including
the characteristics of
hardware, software, and
transmission
components and how
they interact to ensure
reliable transfer of
information.
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Example: Internet The
network of networks
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Computer Systems
Centralized Systems
Client-Server
Flat
Hierarchical
Distributed Systems
Peer to Peer
Pure
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Hybrid
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1960s: InteractiveTime-sharing
system
1950s: Non Interactive Batch
Processing
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A group of computers performing a
set of interrelated tasks by exchanging
data automatically in a coordinated
manner.
◦ Consists of multiple software
components on multiple
computers, but run as a single
system.
The computers in a distributed system
can be
◦ physically close together and
connected by a local network, or
◦ they can be geographically distant
and connected by a wide area
network
Mainframe
WAN connection
LAN connection
WAN: Wide Area Network
LAN: Local Area Network
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A common way of
organizing software to run
on distributed systems is to
separate functions into two
parts: clients and servers.
A client is a program that
uses services that other
programs provide.
Servers are programs that
provide the services
Typically, multiple clients
use a single server
Client
Server
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The three tier
client/server systems
uses:
A client that interacts
with the user
An application server
that contains the
business logic of the
application
A resource manager that
stores data
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Client
Client
HTT P interaction
Database server
Web server
SQL query
Account serv ice
p rov isio n
SQL
Custo mer
acco unt
database
Client
Client
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Thin-client model
◦ In a thin-client model, all of the application processing and
data management is carried out on the server.
◦ The client is simply responsible for running the presentation
software.
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Fat-client model
◦ In this model, the server is only responsible for data
management.
◦ The software on the client implements the application logic
and the interactions with the system user.
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Simple definition
◦ A network architecture
without any central coordination
Complex definition
◦ Each node is a client and
a server at the same time
◦ Each node provides
content/resources
◦ Direct exchange between
peers
◦ peers can join or leave at
any time
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Contrast with mp3.com
Server
Machine A
1. Who has
‘XX’ songs?
2. B, C,
and F do
3. Please send ‘XX’
song
Napster.com
4. Here it is
Machine B
Machine C
Machine D
Machine F
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– Devices
• These are used to
communicate with one
another
– Medium
• This is how the devices are
connected together
– Messages
• Information that travels
over the medium
– Rules (Protocols)
• Governs how messages
flow across network
On each floor, hosts
connect to a workgroup
switch via wire or wireless
transmission
A core switch connects
the workgroup switches
to each other
© 2009 Pearson Education, Inc. Publishing as Prentice Hall
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Residential access
◦ Cable, Fiber, DSL
ISP
Backbone ISP
ISP
 The Internet has a
Campus access, e.g.,
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Wired / Wireless
tiered architecture
consisting of local,
regional, backbone
networks
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Wireless Architectures: Cellular network
MSC
 connects cells to wide area net
 manages call setup
cell
 covers geographical
region
 base station (BS)
analogous to 802.11 AP
 mobile users attach
to network through BS
 air-interface: physical
and link layer protocol
between mobile and BS
Mobile
Switching
Center
Public telephone
network, and
Internet
Mobile
Switching
Center
Wide area
network
Courtesy: slides from Kurose and Ross:
Wireless and Mobile Networks
617
Wireless Architectures: personal
area network
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less than 10 m diameter
replacement for cables (mouse,
keyboard, headphones)
ad hoc: no infrastructure
master/slaves:
◦ slaves request permission to send
(to master)
◦ master grants requests
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802.15: evolved from Bluetooth
specification
◦ 2.4-2.5 GHz radio band
◦ up to 721 kbps
P
S
P
radius of
coverage
M
S
P
S
P
M Master device
S Slave device
P Parked device (inactive)
6: Wireless and Mobile Networks
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Wireless Architectures: WiMAX
point-to-point
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like 802.11 & cellular:
base station model
◦ transmissions to/from base
station by hosts with
omnidirectional antenna
◦ base station-to-base station
backhaul with point-to-point
antenna
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point-to-multipoint
unlike 802.11:
◦ range ~ 6 miles (“city rather
than coffee shop”)
◦ ~14 Mbps
6: Wireless and Mobile Networks
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Three important characteristics of network
infrastructures
What is a protocol ?
◦ Example?
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What is an application?
◦ Example?
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