Download ppt

Introduction
Computer Networks: Introduction
1
Network Definitions and Classification
• Preliminary definitions and network
terminology
• Sample application paradigms
• Classifying networks by transmission
technology
• Classifying networks by size (or scale)
• Classifying networks by topology
Computer Networks: Introduction
2
Preliminary Definitions
computer network :: [Tanenbaum] a collection of
“autonomous” computers interconnected by a
single technology.
[LG&W] communications network ::a set of equipment and
facilities that provide a service.
[PD] {low level definition} A network can consist of two or
more computers directly connected by some physical
medium such as coaxial cable or an optical fiber.
Wireless connectivity needs to be included in this
definition.
Computer Networks: Introduction
3
Network Building Blocks
• Nodes and Hosts: computers, routers,
switches
• Links: coaxial cable, optical fiber, wireless
communication
– point-to-point
– multiple access
(a)
(b)
P&D slide
Computer Networks: Introduction
4
Preliminary Definitions
In a distributed system the collection of
independent computers appears to its
users as a single coherent system.
Namely, the distinctions lie in the
transparency in assigning tasks to
computers.
Computer Networks: Introduction
5
Switched Networks
Figure 1.3
P&D slide
Computer Networks: Introduction
6
internet
Figure 1.4 Interconnection of networks
P&D slide
Computer Networks: Introduction
7
Network
P&D recursive definition::
i. two or more nodes connected by a
link.
or
ii. two or more networks connected by a
node {an internet}.
Computer Networks: Introduction
8
W1
T
X
Z
W2
W
Y
Host
L
Host
M
W3
AP
Host
A
2
4
1
Host
B
5
nodes
16
14
11
Host
C
Host
J
17
12
15
6
13
10
Host
D
W4
3
Host
H
7
9
Host
E
8
Host
G
Host
F
Computer Networks: Introduction
9
Sample Application Paradigms
Computer Networks: Introduction
10
Client-Server Applications
Figure 1.1 A network with two clients and one
server.
Tanenbaum slide
Computer Networks: Introduction
11
Client-Server Model
Figure 1-2. The client-server model involves
requests and replies.
Tanenbaum slide
Computer Networks: Introduction
12
Peer-to-Peer Applications
Figure 1.3 In a peer-to-peer system there are no
fixed clients and servers.
Tanenbaum slide
Computer Networks: Introduction
13
Mobile Network Users
Figure 1-5. Combinations of wireless
networks and mobile computing.
Tanenbaum slide
Computer Networks: Introduction
14
Classifying Networks by
Transmission Technology
broadcast :: a single communications channel shared
by all machines (addresses) on the network.
Broadcast can be either a logical or a physical concept
(e.g. Media Access Control (MAC) sublayer ) .
multicast :: communications to a specified group.
This requires a group address (e.g. – multimedia
multicast).
point-to-point :: connections are made via links between
pairs of nodes.
Computer Networks: Introduction
15
Network Classification by Size
Figure 1-6. Classification of interconnected processors by
scale.
Tanenbaum slide
Computer Networks: Introduction
16
Network Classification by Size
• LANs {Local Area Networks}
– Wired LANs: typically physically broadcast at
the MAC layer (e.g., Ethernet, Token Ring)
– Wireless LANs
• MANs {Metropolitan Area Networks}
– campus networks connecting LANs logically or
physically.
– often have a backbone (e.g., FDDI and ATM)
Computer Networks: Introduction
17
Wired LANs
transceivers
  
Ethernet bus
Copyright ©2000 The McGraw Hill
Companies
 

Ethernet hub
Leon-Garcia & Widjaja: Communication
Networks
Figure 1.17
Tanenbaum slide
Computer Networks: Introduction
18
Wireless LANs
Figure 1-35. (a) Wireless networking with a base
station. (b) Ad hoc networking.
Tanenbaum slide
Computer Networks: Introduction
19
Metropolitan Area Networks
Figure 1-8. A metropolitan area network based on cable
TV.
Tanenbaum slide
Computer Networks: Introduction
20
MAN
1*
a
2
b
4
3
A
c
Metropolitan network A
consists of access
subnetworks a, b, c, d.
d
Hierarchical Network Topology
A
a
b
g
Copyright ©2000 The McGraw Hill
Companies
Leon-Garcia & Widjaja:
Communication Networks
Computer Networks: Introduction
National network
consists of regional
subnetworks a, b, g.
Metropolitan network
A is part of regional
subnetwork a.
Figure 1.8
21
Network Classification by Size
• WANs {Wide Area Networks}
–
–
–
–
also referred to as “point-to-point” networks.
ARPANET  Internet
usually hierarchical with a backbone.
Enterprise Networks, Autonomous Systems
(ASs)
– VPNs (Virtual Private Networks).
Computer Networks: Introduction
22
AMES
UTAH
McCLELLAN
BOULDER
GWC
CASE
RADC
ILL
CARN
LINC
USC
AMES
MIT
MITRE
UCSB
STAN
SCD
ETAC
UCLA
RAND
TINKER
BBN
HARV
NBS
ARPAnet circa 1972
a point-to-point network
Copyright ©2000 The McGraw Hill
Companies
Leon-Garcia & Widjaja:
Communication Networks
Computer Networks: Introduction
Figure 1.16
23
Wide Area Networks
(WANs)
Figure 1-10.A stream of packets from sender to
receiver.
Tanenbaum slide
Computer Networks: Introduction
24
net 3
G
net 1
G
G = gateway
G
net 2
Copyright ©2000
The McGraw Hill Companies
G
net 5
G
net 4
G
internet - a network of networks
Leon-Garcia & Widjaja:
Communication Networks
Computer Networks: Introduction
Figure 1.18
25
Network Classification by Topology
Bus
flow of data
Bidirectional flow
assumes baseband cable
Repeater
Computer Networks: Introduction
26
Network Classification by Topology
Ring
Repeater
Repeater
Note - a ring implies unidirectional flow
Computer Networks: Introduction
27
Network Classification by Topology
Tree
Headend
Computer Networks: Introduction
28
Network Classification by Topology
Star
hub, switch
or repeater
Computer Networks: Introduction
29
Network Classification by Topology
Star
W1
W2
AP
W3
W4
Wireless Infrastructure
Computer Networks: Introduction
30