PowerPoint Presentation
Computer Systems
Introduction to Networks
Dr. Mian M. Hamayun
m.m. .uk
Slide #2 of 51
Lecture Objective
The objective of this lecture is to develop a basic
understanding of Computer Networks (in general)
and the Internet.
Slide #3 of 51
Lecture Outline
What is the Internet?
How does the Internet look like?
What is a Distributed System?
Internet vs. Intranet (& Firewall)
Network Principles
Switching Schemes
Internet Structure: Network of Networks
Summary
Slide #4 of 51
What is the Internet? (Nuts and Bolts)
Millions (billions?) of
connected computing
devices:
hosts = end systems
running network apps
Communication links
fiber, copper, radio, satellite
transmission rate: bandwidth
Packet switches: forward
packets (chunks of data)
routers and switches
smartphone
PC
server
wireless
laptop
wired
links
wireless
links
router
mobile network
global ISP
regional ISP
home
network
institutional
network
Slide #5 of 51
“Fun” Internet Appliances
IP picture frame
http://www.ceiva.com/
Web-enabled toaster +
weather forecaster
Internet phones
Internet
refrigerator
Slingbox: watch,
control cable TV remotely
Tweet-a-watt:
monitor energy use
Slide #6 of 51
What is the Internet? (Nuts and Bolts)
Internet: “network of networks”
Interconnected ISPs
Protocols control sending,
receiving of msgs
e.g., TCP, IP, HTTP, Skype, 802.11
Internet standards
RFC: Request for comments
IETF: Internet Engineering Task
Force
mobile network
global ISP
regional ISP
home
network
institutional
network
Slide #7 of 51
What is the Internet? (A Service View)
Infrastructure that provides
services to applications:
Web, VoIP, email, games, e-
commerce, social nets, …
Provides programming
interface to apps
hooks that allow sending and
receiving app programs to
“connect” to Internet
provides service options, analogous
to postal service
mobile network
global ISP
regional ISP
home
network
institutional
network
Slide #8 of 51
What is the Internet? (Access Network &
Physical Media)
Q: How to connect end systems
to edge router?
residential access nets
institutional access networks
(school, company)
mobile access networks
keep in mind:
bandwidth (bits per second) of
access network?
shared or dedicated?
Slide #9 of 51
What is the Internet? (A Closer Look)
network edge:
hosts: clients and servers
servers, often in data centers
access networks, physical
media: wired, wireless
communication links
network core:
interconnected routers
network of networks
mobile network
global ISP
regional ISP
home
network
institutional
network
Slide #10 of 51
2015
Access Net: Home Network
to/from headend or
central office
cable or DSL modem
router, firewall, NAT
wired Ethernet (100 Mbps)
wireless access
point (54 Mbps)
wireless
devices
often combined
in single box
Slide #11 of 51
2015
Access Net: Enterprise (Ethernet)
typically used in companies, universities, etc
10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates
today, end systems typically connect into Ethernet switch
Ethernet
switch
institutional mail,
web servers
institutional router
institutional link to
ISP (Internet)
Slide #12 of 51
2015
Access Net: Wireless Networks
shared wireless access network connects end system to router
via base station aka “access point”
Wireless LANs:
within building (100 ft)
802.11b/g (WiFi): 11, 54
Mbps transmission rate
to Internet
to Internet
Wide-area wireless access
provided by telco (cellular)
operator, 10’s km
between 1 and 100 Mbps
3G, 4G, 5G (Comparison)
https://www.tomsguide.com/features/5g-vs-4g
Slide #13 of 51
2015
Host: Sends Packets of Data
Host sending function:
takes application message
breaks into smaller chunks,
known as packets, of length L
bits
transmits packet into access
network at transmission rate R
link transmission rate, aka
link capacity, aka link
bandwidth
R: link transmission rate
host
12
two packets,
L bits each
packet
transmission
delay
time needed to
transmit L-bit
packet into link
L (bits)
R (bits/sec)= =
1-13
Slide #14 of 51
2015
The Network Core
mesh of interconnected routers
packet-switching: hosts break
application-layer messages into
packets
forward packets from one router
to the next, across links on path
from source to destination
each packet transmitted at full
link capacity
Slide #15 of 51
The Network Core: Key Functions
routing algorithm
local forwarding table
header value output link
0100
0101
0111
1001
3
2
2
1
1
23
011
1
dest address in arriving
packet’s header
routing: determines
source-destination route
taken by packets
routing algorithms
forwarding: move
packets from router’s
input to appropriate
router output
Slide #16 of 51
/ The Opte Project
Visualization of the Routing Paths of the
Internet.
What the Internet Actually Looks Like?
Slide #17 of 51
2003
Slide #18 of 51
2009
Slide #19 of 51
2015
Slide #20 of 51
Slide #21 of 51
Korea Telecom
(Zoomed) More at: http://time.com/3952373/internet-opte-project/
Slide #22 of 51
Distributed Systems
“A distributed system is one in which
hardware or software components located
at networked computers communicate and
coordinate their actions only by passing
messages”
–Coulouris et al. (2005)
Slide #23 of 51
What does this allow for?
On a network of computers concurrency is
the norm.
There is no single global notion of the
correct time.
Each component in a network may fail
independently.
Slide #24 of 51
A Typical Portion of the Internet
Slide #25 of 51
The Internet – A Distributed Systems
The Internet is a huge distributed system
that enables users all over the world to
make use of its services.
Slide #26 of 51
A Typical Intranet
Instructor’s Guide for Coulouris, Dollimore and Kindberg
Distributed Systems: Concepts and Design Edn. 4
© 2005
Slide #27 of 51
The Intranet
An intranet is a part of the Internet that is
separately administered and uses a firewall
to enforce its own local security policies.
Users in an intranet share data by means of
file services.
Slide #28 of 51
What is a Firewall?
A firewall is a network security system that monitors and
controls incoming and outgoing network traffic based on
predetermined security rules.
A firewall typically establishes a barrier between a trusted
internal network and untrusted external network, such as the
Internet
Firewalls are generally categorized as network-based or
host-based
Types include Network layer or packet filters and Application-
layer firewalls
More details:
https://www.cisco.com/c/en/us/products/security/firewalls/w
hat-is-a-firewall.html
https://www.cisco.com/c/en/us/products/security/firewalls/what-is-a-firewall.html
https://www.cisco.com/c/en/us/products/security/firewalls/what-is-a-firewall.html
Slide #29 of 51
What is a Firewall?
Intranet
Slide #30 of 51
Example Applications – Cloud Computing
Slide #31 of 51
Slide #32 of 51
Network Principles
Slide #33 of 51
Networking is all about
sending messages
over a carrier
Slide #34 of 51
Key Terms
Latency = any kind of delay that happens in data
communication over a network
Bandwidth = transmission capacity of a computer
network or telecommunication system
Speed = rate at which something is able to move
http://www.speedtest.net
http://www.speedtest.net/
Slide #35 of 51
Packet Transmission
Logical unit of information transmitted via network
Otherwise known as a message
Message = data item of arbitrary length
Message subdivided into packets before transmission
Sequence of 01100010 01101001 01101110 01100001
01110010 01111001 00100000 01100100 01100001
01110100 01100001 of restricted length
Plus addressing information
Slide #36 of 51
Switching Schemes
Network consists of a set of nodes, connected by
circuits
To transmit information between two nodes, a switching
scheme is required
Broadcast – no switching, everything transmitted to everyone
Circuit Switching – plain old telephone system. Connected by
switch at the exchange
Packet Switching – store-and-forward network. Computer at each
switching node. Like postal system
Slide #37 of 51
Circuit Switching
End-to-End resources allocated
to, reserved for “call” between
source & destination:
In diagram, each link has four
circuits.
call gets 2nd circuit in top link and 1st
circuit in right link.
dedicated resources: no sharing
circuit-like (guaranteed) performance
circuit segment idle if not used by call
(no sharing)
Commonly used in traditional
telephone networks
Slide #38 of 51
Packet Switching
packet switching allows more users to use network!
Slide #39 of 51
Packet Switching: Store and Forward
takes L/R seconds to transmit
(push out) L-bit packet into link at R
bps
store and forward: entire packet
must arrive at router before it can
be transmitted on next link
end-end delay = 2L/R (assuming
zero propagation delay)
In general: dend-to-end = NL/R
(with N links and N-1 routers)
one-hop numerical
example:
L = 7.5 Mbits
R = 1.5 Mbps
one-hop transmission
delay = 5 sec
source
R bps
destination
123
L bits
per packet
R bps
Slide #40 of 51
Packet Switching: Queueing Delay / Loss
Queuing and packet loss:
If arrival rate (in bits) to link exceeds transmission
rate of link for a period of time:
packets will queue, wait to be transmitted on link
packets can be dropped (lost) if memory (buffer) fills up
A
B
C
R = 100 Mb/s
R = 1.5 Mb/s
D
Equeue of packets
waiting for output link
Slide #41 of 51
Internet Structure: Network of Networks
End systems connect to Internet via access ISPs
(Internet Service Providers)
Residential, company and university ISPs
Access ISPs in turn must be interconnected.
So that any two hosts can send packets to each other
Resulting network of networks is very complex
Evolution was driven by economics and national policies
Let’s take a step-wise approach to describe current
Internet structure
Slide #42 of 51
Internet Structure: Network of Networks
Question: given millions of access ISPs, how to connect
them together?
access
net
access
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access
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access
netaccess
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…
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Slide #43 of 51
Internet Structure: Network of Networks
Question: given millions of access ISPs, how to connect
them together?
access
net
access
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connecting each access ISP to each
other directly doesn’t scale: O(N2)
connections.
Slide #44 of 51
Internet Structure: Network of Networks
Option: connect each access ISP to a global transit ISP?
Customer and provider ISPs have economic agreement.
access
net
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netaccess
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…
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global
ISP
Slide #45 of 51
Internet Structure: Network of Networks
But if one global ISP is viable business, there will be
competitors …
access
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access
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…
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ISP B
ISP A
ISP C
Slide #46 of 51
Internet Structure: Network of Networks
But if one global ISP is viable business, there will be
competitors … which must be connected
access
net
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ISP B
ISP A
ISP C
IXP
IXP
peering link
Internet exchange point
Slide #47 of 51
Internet Structure: Network of Networks
… and regional networks may arise to connect access nets
to ISPs
access
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ISP B
ISP A
ISP C
IXP
IXP
regional net
Slide #48 of 51
Internet Structure: Network of Networks
… and content provider networks (e.g., Google, Microsoft)
may run their own network, to bring services, content
close to end users
access
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ISP B
ISP A
ISP B
IXP
IXP
regional net
Content provider network
Slide #49 of 51
Internet Structure: Network of Networks
At center: small # of well-connected large networks
“tier-1” commercial ISPs (e.g., Sprint, AT&T, NTT), national &
international coverage
content provider network (e.g, Google): private network that connects
its data centers to Internet, often bypassing tier-1, regional ISPs
access
ISP
access
ISP
access
ISP
access
ISP
access
ISP
access
ISP
access
ISP
access
ISP
Regional ISP Regional ISP
IXP IXP
Tier 1 ISP Tier 1 ISP Google
IXP
Slide #50 of 51
Summary
In this lecture:
What is the Internet and how can we visualize it.
What is a Distributed System and how the Internet is also
considered a distributed system
We have discussed the difference between Internet and
Intranets; We have also looked at the role of Firewalls.
We have discussed the Packet and Circuit Switching
schemes and pros / cons of each.
We concluded this lecture by having a look at the Internet
Structure, which is a very large Network of Networks.
Slide #51 of 51
References / Links
Chapter #1: Computer Networks and the Internet,
Computer Networking: A Top-Down Approach (7th
edition) by Kurose & Ross
What is a Firewall:
https://www.cisco.com/c/en/us/products/security/firewalls/w
hat-is-a-firewall.html
4G vs. 5G Compared:
https://www.tomsguide.com/features/5g-vs-4g
What is an IXP
https://www.cloudflare.com/learning/cdn/glossary/internet-exch
ange-point-ixp/
https://www.cisco.com/c/en/us/products/security/firewalls/what-is-a-firewall.html
https://www.cisco.com/c/en/us/products/security/firewalls/what-is-a-firewall.html
https://www.tomsguide.com/features/5g-vs-4g
https://www.cloudflare.com/learning/cdn/glossary/internet-exchange-point-ixp/
https://www.cloudflare.com/learning/cdn/glossary/internet-exchange-point-ixp/
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