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1DT057
Distributed Information Systems
Introduction
Chapter 1
Introduction
1-1
CHAPTER 1: OVERVIEW OF THE
INTERNET
Introduction
Our goal:
Overview:
 get context, overview,  what’s the Internet?
“feel” of networking
 what’s a protocol?
 more depth, detail
 network edge
later in course
 network core
 approach:
 Internet/ISP structure
 descriptive
 protocol layers, service models

use Internet as
example
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CHAPTER 1: ROADMAP
Introduction
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Internet structure and ISPs
1.5 Protocol layers, service models
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WHAT’S THE INTERNET?

hosts, end-systems
router
server
workstation
mobile
Introduction

millions of connected
computing devices:
local ISP
PCs workstations, servers
 PDAs, mobile phones
running network apps


communication links

routers
regional ISP
company
network
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WHAT’S THE INTERNET?

protocols control sending,
receiving of msgs

e.g., TCP, IP, HTTP, FTP,
PPP
server
workstation
mobile
Introduction

router
local ISP
Internet: “network of
networks”


regional ISP
loosely hierarchical
public Internet versus private
intranet
company
network
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WHAT’S THE INTERNET: A SERVICE
VIEW
Why do we need
a network ?
Introduction
 Q:
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WHAT’S THE INTERNET: A SERVICE
VIEW


Web, email, games, ecommerce, database., voting,
file (MP3) sharing
Introduction
communication
infrastructure enables
distributed applications:
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WHAT’S A PROTOCOL: FORMAL DEF
… specific msgs sent
… specific actions taken
when msgs received,
or other events
network protocols:
 machines rather than
humans
 all communication
activity in Internet
governed by protocols
Introduction
human protocols:
 “what’s the time?”
 “I have a question”
 introductions
protocols define format,
order of msgs sent and
received among network
entities, and actions
taken on msg
transmission, receipt 1-8
WHAT’S A PROTOCOL?
a human protocol and a computer network protocol:
Introduction
Hi
TCP connection
req
Hi
TCP connection
response
Got the
time?
Get http://www.awl.com/kurose-ross
2:00
<file>
time
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“COOL” INTERNET APPLIANCES
Introduction
Internet Weather Info
FordSync + Microsoft's Automotive ?
Web-enabled toaster+weather forecaster
WiFi Internet Picture Frame
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CHAPTER 1: ROADMAP
Introduction
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Internet structure and ISPs
1.5 Protocol layers, service models
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A CLOSER LOOK AT NETWORK
STRUCTURE:

routers
 network of networks


Introduction

network edge:
applications and hosts
network core:
access networks, physical
media: communication
links
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THE NETWORK EDGE:

end systems (hosts):



client/server model



client host requests, receives
service from always-on server
e.g. Web browser/server; FTP
client/server
Introduction

run application programs
e.g. Web, email
at “edge of network”
peer-peer model:


minimal (or no) use of
dedicated servers
e.g. Skype, BitTorrent, eMule
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THE NETWORK EDGE:
 Q:
client/server model



client host requests, receives
service from always-on server
e.g. Web browser/server; FTP
client/server
Introduction

Which is better ?
peer-peer model:


minimal (or no) use of dedicated
servers
e.g. Skype, BitTorrent, eMule
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CHAPTER 1: ROADMAP
Introduction
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Internet structure and ISPs
1.5 Protocol layers, service models
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THE NETWORK CORE
mesh of interconnected
routers
 the fundamental question:
how is data transferred
through net?

Introduction
circuit switching:
dedicated circuit per call:
telephone net
 packet-switching: data
sent thru net in discrete
“chunks”

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NETWORK CORE: CIRCUIT
SWITCHING
Introduction
End-end resources
reserved for “call”
 link bandwidth,
switch capacity
 dedicated resources:
no sharing
 circuit-like
(guaranteed)
performance
 call setup required
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NETWORK CORE: CIRCUIT
SWITCHING
 dividing link bandwidth
into “pieces”
 frequency division
 time division
Introduction
network resources (e.g.,
bandwidth) divided into
“pieces”
 pieces allocated to calls
 resource piece idle if not
used by owning call (no
sharing)
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CIRCUIT SWITCHING: FDMA AND
TDMA
Example:
FDMA
4 users
Introduction
frequency
time
TDMA
frequency
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time
NUMERICAL EXAMPLE

All links are 1.536 Mbps
 Each link uses TDM with 24 slots/sec
 500 msec to establish end-to-end circuit

Introduction
How long does it take to send a file of 640,000
bits from host A to host B over a circuit-switched
network?
Let’s work it out!
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NETWORK CORE: PACKET
SWITCHING
Introduction
each end-end data stream
divided into packets
 user A, B packets share
network resources
 each packet uses full link
bandwidth
 resources used as needed
Bandwidth division into “pieces”
Dedicated allocation
Resource reservation
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PACKET SWITCHING: STATISTICAL
MULTIPLEXING
10 Mbs
Ethernet
A
C
1.5 Mbs
Introduction
B
statistical multiplexing
queue of packets
waiting for output
link
D
E
Sequence of A & B packets does not have fixed pattern,
shared on demand  statistical multiplexing.
TDM: each host gets same slot in revolving TDM frame.
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CHAPTER 1: ROADMAP
Introduction
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Internet structure and ISPs
1.5 Protocol layers, service models
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INTERNET STRUCTURE: NETWORK
OF NETWORKS
roughly hierarchical
 at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity,
Sprint, AT&T), national/international coverage

treat each other as equals
Tier-1
providers
interconnect
(peer)
privately
Tier 1 ISP
Tier 1 ISP
NAP
Introduction

Tier-1 providers
also interconnect
at public network
access points
(NAPs)
Tier 1 ISP
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INTERNET STRUCTURE: NETWORK
OF NETWORKS

“Tier-2” ISPs: smaller (often regional) ISPs

Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs
Introduction
Tier-2 ISP pays
tier-1 ISP for
connectivity to
rest of Internet
 tier-2 ISP is
customer of
tier-1 provider
Tier-2 ISP
Tier-2 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
NAP
Tier 1 ISP
Tier-2 ISP
Tier-2 ISPs
also peer
privately with
each other,
interconnect
at NAP
Tier-2 ISP
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INTERNET STRUCTURE: NETWORK
OF NETWORKS

“Tier-3” ISPs and local ISPs

last hop (“access”) network (closest to end systems)
Local and tier3 ISPs are
customers of
higher tier
ISPs
connecting
them to rest
of Internet
Tier 3
ISP
Tier-2 ISP
local
ISP
local
ISP
local
ISP
Tier-2 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
local
local
ISP
ISP
Introduction
local
ISP
NAP
Tier 1 ISP
Tier-2 ISP
local
ISP
Tier-2 ISP
local
ISP
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INTERNET STRUCTURE: NETWORK
OF NETWORKS

a packet passes through many networks!
Tier 3
ISP
Tier-2 ISP
local
ISP
local
ISP
local
ISP
Tier-2 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
local
local
ISP
ISP
Introduction
local
ISP
NAP
Tier 1 ISP
Tier-2 ISP
local
ISP
Tier-2 ISP
local
ISP
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CHAPTER 1: ROADMAP
Introduction
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Internet structure and ISPs
1.5 Protocol layers, service models
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INTERNET PROTOCOL STACK

application: supporting network
applications

transport: host-host data transfer


network: routing of datagrams from
source to destination


IP, routing protocols
link: data transfer between
neighboring network elements


TCP, UDP
PPP, Ethernet
application
transport
Introduction

FTP, SMTP, STTP
network
link
physical
physical: bits “on the wire”
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LAYERING: LOGICAL
COMMUNICATION
application
transport
network
link
physical
application
transport
network
link
physical
network
link
physical
application
transport
network
link
physical
Introduction
Each layer:
 distributed
 “entities”
implement
layer functions
at each node
 entities perform
actions,
exchange
messages with
peers
application
transport
network
link
physical
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LAYERING: PHYSICAL
COMMUNICATION
application
transport
network
link
physical
network
link
physical
application
transport
network
link
physical
Introduction
data
application
transport
network
link
physical
data
application
transport
network
link
physical
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PROTOCOL LAYERING AND
DATA
source
M
Ht M
Hn Ht M
Hl Hn Ht M
application
transport
network
link
physical
destination
application
Ht
transport
Hn Ht
network
Hl Hn Ht
link
physical
Introduction
Each layer takes data from above
 adds header information to create new data unit
 passes new data unit to layer below
M
message
M
segment
M
M
datagram
frame
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source
message
segment
M
Ht
M
datagram Hn Ht
M
frame Hl Hn Ht
M
ENCAPSULATION
application
transport
network
link
physical
Introduction
link
physical
switch
destination
M
Ht
M
Hn Ht
Hl Hn Ht
M
M
application
transport
network
link
physical
Hn Ht
Hl Hn Ht
M
M
network
link
physical
Hn Ht
M
router
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ISO 7-LAYER REFERENCE MODEL
application
transport
presentation
network
session
Introduction
application
link
physical
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INTRODUCTION: SUMMARY

packet-switching versus
circuit-switching
You now have a “big
picture”:
 context, overview, “feel”
of networking
Introduction
Internet overview
 what’s a protocol?
 network edge, core, access
network

Internet/ISP structure
 Internet protocol stack

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PRACTICES


1.
2.

% /bin/ping <machine_name>
% /usr/sbin/traceroute <machine_name>
Introduction
Log into a Unix machine (or Windows)
Read the manual of ping and traceroute, and
try them on a machine
Look at the web sites of the routers you see
through traceroute
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