Lecture1 intro

Introduction 1-1
Chapter 1
Introduction
Computer
Networking: A Top
Down Approach
6th
edition
Jim Kurose, Keith Ross
Addison-Wesley
March 2012
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All material copyright 1996-2012
J.F Kurose and K.W. Ross, All Rights Reserved

Introduction
Chapter 1: introduction
our goal:
 get “feel” and
terminology
 more depth, detail
later in course
 approach:
 use Internet as
example
overview:
 what’s the Internet?
 what’s a protocol?
 network edge; hosts, access net,
physical media
 network core: packet/circuit
switching, Internet structure
 performance: loss, delay, throughput
 security
 protocol layers, service models
 history
1-2

Introduction
Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
 end systems, access networks, links
1.3 network core
 packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 networks under attack: security
1.7 history
1-3

Introduction
What’s the Internet:“nuts and bolts” view
millions 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
wired
links
wireless
links
router
mobile network
global ISP
regional ISP
home
network
institutional
network
smartphone
PC
server
wireless
laptop
1-4

A day in the life of an application
e.g., Comcast
Google’s networkweb server
DNS server
school network
web page
browser ISP network
wireless
access point
campus
access switch

Introduction
“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
1-6
Tweet-a-watt:
monitor energy use
web-enabled
music/shopping/etc

Introduction
 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 EngineeringTask Force
What’s the Internet: “nuts and bolts” view
mobile network
global ISP
regional ISP
home
network
institutional
network
1-7

What’s 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
Introduction 1-8

Introduction
What’s a protocol?
human protocols:
 “what’s the time?”
 “I have a question”
 introductions
… 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
protocols define format, order
of msgs sent and received
among network entities,
and actions taken on msg
transmission, receipt
1-9

Introduction
a human protocol and a computer network protocol:
Q: other human protocols?
Hi
Hi
Got the
time?
2:00
TCP connection
response
Get http://www.awl.com/kurose-ross
<file>
time
TCP connection
request
What’s a protocol?
1-10

Introduction
Chapter 1: roadmap
1.2 network edge
1.3 network core
1.7 history
1-11

Introduction
A closer look at network structure:
 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
1-12

Introduction
Access networks and 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?
1-13

Introduction
Physical media
 bit: propagates between
transmitter/receiver pairs
 physical link: what lies
between transmitter &
receiver
 guided media:
 signals propagate in solid
media: copper, fiber, coax
 unguided media:
 signals propagate freely,
e.g., radio
twisted pair (TP)
 two insulated copper
wires
 Category 5: 100 Mbps, 1
Gpbs Ethernet
 Category 6: 10Gbps
1-14

Introduction
Physical media: coax, fiber
coaxial cable:
 two concentric copper
conductors
 bidirectional
 broadband:
 multiple channels on cable
 HFC
fiber optic cable:
 glass fiber carrying light
pulses, each pulse a bit
 high-speed operation:
 high-speed point-to-point
transmission (e.g., 10’s-100’s
Gpbs transmission rate)
 low error rate:
 repeaters spaced far apart
 immune to electromagnetic
noise
1-15

Introduction
Physical media: radio
 signal carried in
electromagnetic spectrum
 no physical “wire”
 bidirectional
 propagation environment
effects:
 reflection
 obstruction by objects
 interference
radio link types:
 terrestrial microwave
 e.g. up to 45 Mbps channels
 LAN (e.g., WiFi)
 802.11n/ac 1.2 Gbps
 wide-area (e.g., cellular)
 3G cellular: ~ few Mbps
 LTE: 100s of Mbps downstream
 satellite
 Kbps to 45Mbps channel (or
multiple smaller channels)
 270 msec end-end delay
 geosynchronous versus low
altitude
1-16

Introduction
Chapter 1: roadmap
1.2 network edge
1.3 network core
1.7 history
1-17

Introduction
 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
The network core
1-18

Network Layer 4-19
Two key network-core functions
forwarding: move packets from
router’s input to appropriate
router output
routing: determines source-
destination route taken by
packets
 routing algorithms
routing algorithm
local forwarding table
header value output link
0100
0101
0111
1001
3
2
2
1
1
23
0111
dest address in arriving
packet’s header

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 stepwise approach to describe current Internet
structure

Question: given millions of access ISPs, how to connect them
together?
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
netaccess
net
access
net
…
…
……
…
…

Option: connect each access ISP to every other access ISP?
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
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access
net
access
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access
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access
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access
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access
netaccess
net
access
net
…
…
……
…
…
…
…
…
……
connecting each access ISP
to each other directly doesn’t
scale: O(N2
) connections.

access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
netaccess
net
access
net
…
…
……
…
…
Option: connect each access ISP to a global transit ISP? Customer
and provider ISPs have economic agreement.
global
ISP

access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
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access
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access
net
access
netaccess
net
access
net
…
…
……
…
…
But if one global ISP is viable business, there will be competitors
….
ISP B
ISP A
ISP C

access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
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access
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access
net
access
netaccess
net
access
net
…
…
……
…
…
But if one global ISP is viable business, there will be competitors
…. which must be interconnected
ISP B
ISP A
ISP C
IXP
IXP
peering link
Internet exchange point

access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
netaccess
net
access
net
…
…
……
…
…
… and regional networks may arise to connect access nets to
ISPS
ISP B
ISP A
ISP C
IXP
IXP
regional net

access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
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access
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access
net
access
netaccess
net
access
net
…
…
……
…
…
… and content provider networks (e.g., Google, Microsoft,
Akamai ) may run their own network, to bring services, content
close to end users
ISP B
ISP A
ISP B
IXP
IXP
regional net
Content provider network

Introduction
 at center: small # of well-connected large networks
 “tier-1” commercial ISPs (e.g., Level 3, Sprint,AT&T, NTT), national &
international coverage
 content provider network (e.g, Google): private network that connects
it data centers to Internet, often bypassing tier-1, regional ISPs 1-28
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

Introduction
Tier-1 ISP: e.g., Sprint
…
to/from customers
peering
to/from backbone
…
…
…
…
POP: point-of-presence
1-29

Introduction
Chapter 1: roadmap
1.2 network edge
1.3 network core
1.7 history
1-30

Introduction
How do loss and delay occur?
packets queue in router buffers
 packet arrival rate to link (temporarily) exceeds output link
capacity
 packets queue, wait for turn
A
B
packet being transmitted (delay)
packets queueing (delay)
free (available) buffers: arriving packets
dropped (loss) if no free buffers
1-31

Introduction
Throughput
 throughput: rate (bits/time unit) at which bits
transferred between sender/receiver
 instantaneous: rate at given point in time
 average: rate over longer period of time
server, with
file of F bits
to send to client
link capacity
Rs bits/sec
link capacity
Rc bits/sec
server sends bits
(fluid) into pipe
pipe that can carry
fluid at rate
Rs bits/sec)
pipe that can carry
fluid at rate
Rc bits/sec)
1-32

Introduction
Throughput (more)
 Rs < Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
 Rs > Rc What is average end-end throughput?
link on end-end path that constrains end-end
throughput
bottleneck link
Rs bits/sec Rc bits/sec
1-33

Introduction
Throughput: Internet scenario
10 connections (fairly) share
backbone bottleneck link R bits/sec
Rs
Rs
Rs
Rc
Rc
Rc
R
 per-connection end-
end throughput:
min(Rc,Rs,R/10)
 in practice: Rc or Rs is
often bottleneck
1-34

Introduction
Chapter 1: roadmap
1.2 network edge
1.3 network core
1.7 history
1-35

Introduction
Organization of air travel
 a series of steps
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
airplane routing
1-36

Introduction
ticket (purchase)
baggage (check)
gates (load)
runway (takeoff)
airplane routing
departure
airport
arrival
airport
intermediate air-traffic
control centers
airplane routing airplane routing
ticket (complain)
baggage (claim
gates (unload)
runway (land)
airplane routing
ticket
baggage
gate
takeoff/landing
airplane routing
Layering of airline functionality
layers: each layer implements a service
 via its own internal-layer actions
 relying on services provided by layer below
1-37

Introduction
Why layering?
dealing with complex systems:
 explicit structure allows identification, relationship
of complex system’s pieces
 layered reference model for discussion
 modularization eases maintenance, updating of
system
 change of implementation of layer’s service transparent
to rest of system
 e.g., change in gate procedure doesn’t affect rest of
system
 layering considered harmful?
1-38

Introduction
Internet protocol stack
 application: supporting network
applications
 FTP, SMTP, HTTP
 transport: process-process data
transfer
 TCP, UDP
 network: routing of datagrams from
source to destination
 IP, routing protocols
 link: data transfer between
neighboring network elements
 Ethernet, 802.111 (WiFi), PPP
 physical: bits “on the wire”
application
transport
network
link
physical
1-39

Introduction
Chapter 1: roadmap
1.2 network edge
1.3 network core
1.7 history
1-40

Introduction
Network security
 field of network security:
 how bad guys can attack computer networks
 how we can defend networks against attacks
 how to design architectures that are immune to
attacks
 Internet not originally designed with (much)
security in mind
 original vision: “a group of mutually trusting users
attached to a transparent network” 
 Internet protocol designers playing “catch-up”
 security considerations in all layers!
1-41

Introduction
Bad guys: put malware into hosts via Internet
 malware can get in host from:
 virus: self-replicating infection by receiving/executing
object (e.g., e-mail attachment)
 worm: self-replicating infection by passively receiving
object that gets itself executed
 spyware malware can record keystrokes, web
sites visited, upload info to collection site
 infected host can be enrolled in botnet, used for
spam. DDoS attacks
1-42

Introduction
target
Denial of Service (DoS): attackers make resources
(server, bandwidth) unavailable to legitimate traffic
by overwhelming resource with bogus traffic
1. select target
2. break into hosts around
the network (see botnet)
3. send packets to target from
compromised hosts
Bad guys: attack server, network infrastructure
1-43

Introduction
Bad guys can sniff packets
packet “sniffing”:
 broadcast media (shared ethernet, wireless)
 promiscuous network interface reads/records all packets
(e.g., including passwords!) passing by
A
B
C
src:B dest:A payload
 wireshark software used for end-of-chapter labs is a
(free) packet-sniffer
1-44

Introduction
Bad guys can use fake addresses
IP spoofing: send packet with false source address
A
B
C
src:B dest:A payload
1-45
… lots more on security (throughout, Chapter 8)

Introduction
Chapter 1: roadmap
1.2 network edge
1.3 network core
1.7 history
1-46

Introduction
Internet history
 1961: Kleinrock -
queueing theory shows
effectiveness of packet-
switching
 1964: Baran - packet-
switching in military nets
 1967: ARPAnet
conceived by Advanced
Research Projects
Agency
 1969: first ARPAnet node
operational
 1972:
 ARPAnet public demo
 NCP (Network Control
Protocol) first host-host
protocol
 first e-mail program
 ARPAnet has 15 nodes
1961-1972: Early packet-switching principles
1-47

Introduction
 1970: ALOHAnet satellite
network in Hawaii
 1974: Cerf and Kahn -
architecture for interconnecting
networks
 1976: Ethernet at Xerox PARC
 late70’s: proprietary
architectures: DECnet, SNA,
XNA
 late 70’s: switching fixed length
packets (ATM precursor)
 1979: ARPAnet has 200 nodes
Cerf and Kahn’s
internetworking principles:
 minimalism, autonomy - no
internal changes required to
interconnect networks
 best effort service model
 stateless routers
 decentralized control
define today’s Internet
architecture
1972-1980: Internetworking, new and proprietary nets
Internet history
1-48

Introduction
 1983: deployment of
TCP/IP
 1982: smtp e-mail
protocol defined
 1983: DNS defined for
name-to-IP-address
translation
 1985: ftp protocol defined
 1988: TCP congestion
control
 new national networks:
Csnet, BITnet, NSFnet,
Minitel
 100,000 hosts connected
to confederation of
networks
1980-1990: new protocols, a proliferation of networks
Internet history
1-49

Introduction
early 1990’s: ARPAnet
decommissioned
1991: NSF lifts restrictions on
commercial use of NSFnet
(decommissioned, 1995)
early 1990s: Web
 hypertext [Bush 1945, Nelson
1960’s]
 HTML, HTTP: Berners-Lee
 1994: Mosaic, later Netscape
 late 1990’s: commercialization
of theWeb
late 1990’s – 2000’s:
 more killer apps: instant
messaging, P2P file sharing
 network security to
forefront
 est. 50 million host, 100
million+ users
 backbone links running at
Gbps
1990, 2000’s: commercialization, the Web, new apps
Internet history
1-50

Introduction
2005-present
 ~750 million hosts
 Smartphones and tablets
 Aggressive deployment of broadband access
 Increasing ubiquity of high-speed wireless access
 Emergence of online social networks:
 Facebook: soon one billion users
 Service providers (Google, Microsoft) create their own
networks
 Bypass Internet, providing “instantaneous” access to
search, emai, etc.
 E-commerce, universities, enterprises running their
services in “cloud” (eg,Amazon EC2)
Internet history
1-51

Introduction
Introduction: summary
covered a “ton” of material!
 Internet overview
 what’s a protocol?
 network edge, core, access
network
 packet-switching versus
circuit-switching
 Internet structure
 performance: loss, delay,
throughput
 layering, service models
 security
 history
you now have:
 context, overview, “feel”
of networking
 more depth, detail to
follow!
1-52

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