Networks: Introduction1 Course Objectives 1.To introduce the student to the major concepts involved...
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Networks: Introduction 1
Course Objectives
1. To introduce the student to the major concepts involved in wide-area networks (WANs) and local area networks (LANs).
2. To develop an understanding of modern network architectures from a design and performance perspective.
3. To expose students to some of the current technologies.
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Networks: Introduction 2
Course Objectives
4. To provide an opportunity to do network programming using TCP/IP.
5. To clarify network terminology.
6. To facilitate an understanding of the current literature.
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Networks: Introduction 3
Definitions
computer network :: an interconnected collection of “autonomous” computers.[LG&W] communications network ::a set of equipment
and facilities that provide a service.
distributed system :: the existence of multiple autonomous computers is transparent.
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Networks: Introduction 4
t0t1
Network
Figure 1.6Leon-Garcia & Widjaja: Communication
NetworksCopyright ©2000 The McGraw Hill
Companies
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Networks: Introduction 5
12
1
11
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4
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2
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14
5
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15
3
HostB
HostC
HostL
HostD
HostE
HostG
HostJ
HostA
HostH
HostF
HostK
HostM
16
17
W
T X
Y
Z
nodes
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Networks: Introduction 6
Classifying Networks by Transmission Technology
broadcast :: a single communications channel shared by all machines (addresses) on the network. Broadcast can be both a logical and a physical concept (e.g. Media Access Control (MAC) layer).
multicast :: communications to a specified group. This requires a group address. (example – multimedia multicast).
point-to-point :: connections made via links between pairs of nodes.
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Networks: Introduction 7
Network Classification by Size
• LANs {Local Area Networks}– Typically physically broadcast at the MAC
layer (e.g., Ethernet, Token Ring).
• MANs {Metropolitan Area Networks}– campus networks connecting LANs logically or
physically.– often have a backbone (e.g., FDDI, DQDB, and
ATM)
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Networks: Introduction 8
(a) (b)
transceivers
Figure 1.17Leon-Garcia & Widjaja: Communication Networks
Copyright ©2000 The McGraw Hill Companies
LANs
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Networks: Introduction 9
Metropolitan network A consists of access subnetworks a, b, c, d.
National network consists of regional subnetworks .
Metropolitan network A is part of regional subnetwork .
A
A
Metropolitan
1*
a
c
b
d
(a)
(b)
2
34
Figure 1.8Copyright ©2000 The McGraw Hill Companies
Leon-Garcia & Widjaja: Communication Networks
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Networks: Introduction 10
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– VPN (Virtual Private Networks).
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Networks: Introduction 11
UCLA RAND TINKER
USC
NBS
UCSB
HARV
SCD
BBN
STAN
AMES
AMES McCLELLAN UTAH BOULDER GWC CASE
CARN
MITRE
ETAC
MIT
ILL
LINC
RADC
Figure 1.16
ARPAnet circa 1972
point-to-point network
Leon-Garcia & Widjaja: Communication Networks
Copyright ©2000 The McGraw Hill Companies
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12 Networks: Introduction
G
G
G
G
G
net 1
net 2
net 3
net 4
net 5
G = gateway
G
Figure 1.18Leon-Garcia & Widjaja: Communication Networks
Copyright ©2000 The McGraw Hill Companies
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Networks: Introduction 13
Network Classification by Topology
flow of data
Repeater
Bus
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Networks: Introduction 14
Network Classification by Topology
Repeater
Repeater
Ring
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Networks: Introduction 15
Network Classification by Topology
Headend
Tree
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Networks: Introduction 16
Network Classification by Topology
Star
hub, switch
or repeater
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Networks: Introduction 17
Performance Metrics(General Definitions)
• Utilization:: the percentage of time a device is busy servicing a “customer”.
• Throughput:: the number of jobs processed by the “system” per unit time.
• Response time:: the time required to receive a response to a request (round-trip time).
• Delay:: the time to traverse from one end to the other in a system.
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Networks: Introduction 18
Network Performance
• channel utilization – the average fraction of time a channel is busy [e.g. Util = 0.8]– when overhead is taken into account (i.e.,
excluded from useful bits, channel utilization is often referred to as channel efficiency
• throughput – bits/sec. successfully transmitted [e.g. Tput = 10 Mbps]
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Networks: Introduction 19
Network Performance
end-to-end packet delay :: the time to deliver a packet from source to destination.
{most often we are interested in the packet delay within the communications subnet}
This delay is the sum of the delays on eachsubnet link traversed by the packet. Each link
delay consists of four components [Bertsekas and Gallager]:
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Networks: Introduction 20
Packet Delay
1. The processing delay [PROC] between the time the packet is correctly received at the head node of the link and the time the packet is assigned to an outgoing link queue for transmission.
2. The queueing delay [QD] between the time the packet is assigned to a queue for transmission and the time it starts being transmitted. During this time, the packet waits while other packets in the transmission queue are transmitted.
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Networks: Introduction 21
Packet Delay
3. The transmission delay [TRANS] between the times that the first and last bits of the packet are transmitted.
4. The propagation delay [PROP] between the time the last bit is transmitted at the head node of the link and the time the last bit is received at the tail node. This is proportional to the physical distance between transmitter and receiver.
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Networks: Introduction 22
End-to-End Packet Delay
end-to-end packet delay = sum of ALL link packet delays.Be Careful !! end-to-end can be defined
either from Host-to-Host or only within the subnetwork.
Link packet delay = PROC + QD + TRANS
+ PROP.