Chapter 1 Introduction
Computer
Networking: A Top
Down Approach
6th edition
Jim Kurose, Keith Ross Addison- Wesley March 2012
Introduction 1-1
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
Introduction 1-2
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
Introduction 1-3
What’s the Internet: “nuts and bolts” view
PC server
wireless laptop
smartphone
hosts = end systems
running network apps
mobile network
home network
institutional network
global ISP
regional ISP
millions of connected computing devices:
communication links
wireless links
wired links
fiber, copper, radio, satellite
transmission rate: bandwidth
router
Packet switches: forward packets (chunks of data)
routers and switches
Introduction 1-4
“Fun” internet appliances
Web-enabled toaster +
IP picture frame http://www.ceiva.com/
weather forecaster
Tweet-a-watt: monitor energy use
Internet refrigerator
Internet phones
Slingbox: watch,
control cable TV remotely
Introduction 1-5
What’s the Internet: “nuts and bolts” view
Internet: “network of networks” Interconnected ISPs
protocols control sending, receiving of msgs
mobile network
global ISP
e.g., TCP, IP, HTTP, Skype, 802.11 home
Internet standards
RFC: Request for comments
IETF: Internet Engineering Task Force
network
regional ISP
institutional network
Introduction 1-6
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
home network
institutional network
global ISP
regional ISP
Introduction 1-7
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
Introduction 1-8
What’s a protocol?
a human protocol and a computer network protocol:
Hi
Hi
Got the time?
2:00
TCP connection request
TCP connection response
Get http://www.awl.com/kurose-ross
Q: other human protocols?
time
Introduction 1-9
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
Introduction 1-10
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
home network
institutional network
global ISP
regional ISP
Introduction 1-11
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?
Introduction 1-12
Access net: digital subscriber line (DSL)
central office
DSLAM
DSL access multiplexer
telephone network
DSL splitte modem
r
voice, data transmitted at different frequencies over dedicated line to central office
ISP
use existing telephone line to central office DSLAM data over DSL phone line goes to Internet
voice over DSL phone line goes to telephone net
< 2.5 Mbps upstream transmission rate (typically < 1 Mbps)
< 24 Mbps downstream transmission rate (typically < 10 Mbps)
Introduction 1-13
Access net: cable network
cable headend
...
cable splitter
modem
O VVVVVV N IIIIIIDDT DDDDDDAAR EEEEEETTO OOOOOOAAL
123456789 Channels
C
frequency division multiplexing: different channels transmitted in different frequency bands
Introduction 1-14
Access net: cable network
cable splitter
modem
data, TV transmitted at different frequencies over shared cable
distribution network
cable headend
...
CMTS
cable modem termination system
ISP
HFC: hybrid fiber coax
asymmetric: up to 30Mbps downstream transmission rate, 2
Mbps upstream transmission rate
network of cable, fiber attaches homes to ISP router
homes share access network to cable headend
unlike DSL, which has dedicated access to central office Introduction 1-15
Access net: home network
wireless devices
often combined in single box
to/from headend or central office
cable or DSL modem
router, firewall, NAT wired Ethernet (100 Mbps)
wireless access point (54 Mbps)
Introduction 1-16
Enterprise access networks (Ethernet)
institutional link to ISP (Internet)
institutional router
Ethernet institutional mail, switch web servers
typically used in companies, universities, etc
10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates
today, end systems typically connect into Ethernet switch
Introduction 1-17
Wireless access 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
wide-area wireless access
provided by telco (cellular) operator, 10’s km
between 1 and 10 Mbps 3G, 4G: LTE
to Internet
Introduction 1-18
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
two packets, L bits each
21
R: link transmission rate host
packet transmission delay
= time needed to transmit L-bit
packet into link
=
L (bits)
R (bits/sec)
1-19
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
Introduction 1-20
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
Introduction 1-21
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)
11Mbps, 54 Mbps
wide-area (e.g., cellular) 3G cellular: ~ few Mbps
satellite
Kbps to 45Mbps channel (or
multiple smaller channels)
270 msec end-end delay
geosynchronous versus low altitude
Introduction 1-22
Fiber Options:
FTTN / FTTLA (fiber-to- the-neighborhood)
FTTC / FTTK (fiber-to-the- curb)
FTTB (fiber-to-the-building) FTTH (fiber-to-the-home)
Info and graphic from Wikipedia.org
Introduction 1-23
Chapter 1: roadmap
1.1 what is the Internet? 1.2 network edge
end systems, access networks, links 1.3 network core
packetswitching, circuitswitching,networkstructure 1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 networks under attack: security
1.7 history
Introduction 1-24
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
Introduction 1-25
Packet-switching: store-and-forward
L bits
per packet
source
321
destination
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)
one-hop numerical example:
L = 7.5 Mbits
R = 1.5 Mbps
one-hop transmission delay = 5 sec
more on delay shortly ...
R bps
R bps
Introduction 1-26
Packet Switching: queueing delay, loss
A
B
R = 100 Mb/s
C
R = 1.5 Mb/s queue of packets
waiting for output link
D
E
queuing and 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
Introduction 1-27
Two key network-core functions
routing: determines source- destination route taken by packets
routing algorithms
forwarding: move packets from router’s input to appropriate router output
routing algorithm
local forwarding table
header value
output link
0100 0101 0111 1001
3 2 2 1
3
dest address in arriving packet’s header
1 2
Network Layer 4-28
Alternative core: circuit switching
end-end resources allocated to, reserved for “call” between source & dest:
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
Introduction 1-29
Circuit switching: FDM versus TDM
FDM frequency
TDM frequency
Example:
4 users
time
time
Introduction 1-30
Packet switching versus circuit switching
packet switching allows more users to use network!
example:
1 Mb/s link
each user:
• 100 kb/s when “active” • active 10% of time
circuit-switching: 10 users
packet switching:
with 35 users, probability > 10 active at same time is less than .0004 *
N
users
* Check out the online interactive exercises for more examples
Introduction 1-31
1 Mbps link
Q: how did we get value 0.0004? Q: what happens if > 35 users ?
Packet switching versus circuit switching
is packet switching a “slam dunk winner?”
great for bursty data
resource sharing
simpler, no call setup
excessive congestion possible: packet delay and loss
protocols needed for reliable data transfer, congestion
control
Q: How to provide circuit-like behavior?
bandwidth guarantees needed for audio/video apps still an unsolved problem (chapter 7)
Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?
Introduction 1-32
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
Internet structure: network of networks
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 net
access net
access net
Internet structure: network of networks
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 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 access net
net
Internet structure: network of networks
Option: connect each access ISP to a global transit ISP? Customer and provider ISPs have economic agreement.
access net
access net
access net
access net
access net
access net
access net
access net
access net
access net
global ISP
access net
access net
access net
access net
access net
access net
Internet structure: network of networks
But if one global ISP is viable business, there will be competitors ….
access net
ISP A
access net
access net
access net
access net
access net
access net
access net
access net
access net
ISP B
access net
access net
ISP C
access net
access access net
net
access net
Internet structure: network of networks
But if one global ISP is viable business, there will be competitors …. which must be interconnected
access net
access net
Internet exchange point
access net
access net
access net
access net
access net
access net
ISP A
access net
IXP
access net
IXP
ISP B
peering link
access access net
net
access net
access net
ISP C
access net
access net
Internet structure: network of networks
… and regional networks may arise to connect access nets to ISPS
access net
ISP A
access net
access net
access net
access net
access net
access net
access net
access net
IXP
access net
IXP
access net
access net
ISP C
ISP B
regional net
access access net
net
access net
access net
Internet structure: network of networks
… and content provider networks (e.g., Google, Microsoft, Akamai ) may run their own network, to bring services, content close to end users
access net
ISP A
access net
access net
access net
access net
access net
access net
access net
access net
IXP
access net
ISP B
Content provider network
IXP
ISP B
regional net
access access net
net
access net
access net
access net
access net
Internet structure: network of networks
Tier 1 ISP Tier 1 ISP
Google
IXP
IXP IXP
Regional ISP Regional ISP
access access access access ISP ISP ISP ISP
access access access access
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
Introduction 1-41
ISP ISP ISP
ISP
Tier-1 ISP: e.g., Sprint
POP: point-of-presence
to/from backbone peering
……
to/from customers
Introduction 1-42
…
… …
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
Introduction 1-43
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
packet being transmitted (delay)
A
B
packets queueing (delay)
free (available) buffers: arriving packets dropped (loss) if no free buffers
Introduction 1-44
Four sources of packet delay
transmission
B
A
propagation
nodal processing
queueing
dnodal = dproc + dqueue + dtrans + dprop
dproc: nodal processing check bit errors
determine output link typically < msec
dqueue: queueing delay
time waiting at output link
for transmission
depends on congestion level of router
Introduction 1-45
Four sources of packet delay
transmission
B
A
propagation
nodal processing
queueing
dprop: propagation delay:
d: length of physical link
s: propagation speed in medium (~2x108 m/sec)
dnodal = dproc + dqueue + dtrans + dprop
dtrans: transmission delay: L: packet length (bits)
R: link bandwidth (bps)
dtrans = L/R
dprop = d/s
* Check out the Java applet for an interactive animation on trans vs. prop delay
dtrans and dprop very different
Introduction 1-46
Caravan analogy
ten-car caravan
100 km
toll toll
100 km booth
time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec
time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr)= 1 hr
A: 62 minutes
cars “propagate” at 100 km/hr
toll booth takes 12 sec to service car (bit transmission time)
car~bit; caravan ~ packet
Q: How long until caravan is lined up before 2nd toll booth?
booth
Introduction 1-47
Caravan analogy (more)
100 km
100 km
ten-car caravan
toll booth
toll booth
suppose cars now “propagate” at 1000 km/hr
and suppose toll booth now takes one min to service a car
Q: Will cars arrive to 2nd booth before all cars serviced at first booth?
A: Yes! after 7 min, 1st car arrives at second booth; three cars still at 1st booth.
Introduction 1-48
Queueing delay (revisited)
R: link bandwidth (bps)
L: packet length (bits)
a: average packet arrival rate
La/R ~ 0: avg. queueing delay small
La/R -> 1: avg. queueing delay large
La/R > 1: more “work” arriving
traffic intensity = La/R
than can be serviced, average delay infinite!
* Check out the Java applet for an interactive animation on queuing and loss
La/R -> 1
La/R ~ 0
Introduction 1-49
average queueing delay
“Real” Internet delays and routes what do “real” Internet delay & loss look like?
traceroute program: provides delay measurement from source to router along end- end Internet path towards destination. For all i:
sends three packets that will reach router i on path towards destination
router i will return packets to sender
sender times interval between transmission and reply.
3 probes 3 probes
3 probes
Introduction 1-50
“Real” Internet delays, routes traceroute: gaia.cs.umass.edu to www.eurecom.fr
3 delay measurements from
gaia.cs.umass.edu to cs-gw.cs.umass.edu
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms
2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms
3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms
4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms
5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms
6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms
7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms
8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms
9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms
10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms
11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms
12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms
13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms
14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms
15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms
17 * * *
18 * * *
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms * Do some traceroutes from exotic countries at www.traceroute.org
trans-oceanic link
* means no response (probe lost, router not replying)
Introduction 1-51
Packet loss
queue (aka buffer) preceding link in buffer has finite capacity
packet arriving to full queue dropped (aka lost)
lost packet may be retransmitted by previous node,
by source end system, or not at all
A
B
buffer (waiting area)
packet being transmitted
* Check out the Java applet for an interactive animation on queuing and loss
Introduction 1-52
packet arriving to full buffer is lost
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
link capacity
link capacity
server sends bits
pipe that can carry
pipe that can carry
file of F bits
R bits/sec
s fluid at rate
R bits/sec
c fluid at rate
(fluid) into pipe
to send to client
Rs bits/sec)
Rc bits/sec)
Introduction 1-53
Throughput (more)
Rs < Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
Rs > Rc What is average end-end throughput?
Rc bits/sec
bottleneck link
link on end-end path that constrains end-end throughput
Rs bits/sec
Introduction 1-54
Throughput: Internet scenario
per-connection end-
end throughput: Rs min(Rc,Rs,R/10) Rs
Rs
R
Rc
in practice: Rc or Rs is often bottleneck
Rc
Rc
10 connections (fairly) share backbone bottleneck link R bits/sec
Introduction 1-55
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
Introduction 1-56
Protocol “layers” Networks are complex,
with many “pieces”:
hosts
routers
links of various
media
applications
protocols
hardware, software
Question:
is there any hope of organizing structure of
network?
…. or at least our discussion of networks?
Introduction 1-57
Organization of air travel
ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing
ticket (complain) baggage (claim) gates (unload) runway landing airplane routing
a series of steps
airplane routing
Introduction 1-58
Layering of airline functionality
ticket (purchase) ticket (complain) ticket
baggage (check) baggage (claim baggage
gates (load) gates (unload) gate
runway (takeoff) runway (land) takeoff/landing
airplane routing airplane routing airplane routing airplane routing airplane routing
departure intermediate air-traffic arrival airport control centers airport
layers: each layer implements a service
via its own internal-layer actions
relying on services provided by layer below
Introduction 1-59
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?
Introduction 1-60
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
Introduction 1-61
ISO/OSI reference model
presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions
session: synchronization, checkpointing, recovery of data exchange
Internet stack “missing” these layers!
these services, if needed, must be implemented in application
needed?
application
presentation
session
transport
network
link
physical
Introduction 1-62
source
Encapsulation
application
transport
network
link
physical
message segment
M
Ht
M
datagram frame
Hn
Ht
M
Hl
Hn
Ht
M
link
physical
switch
destination
network
Hn
Ht
M
application
transport
network
link
physical
link
Hl
Ht
M
M
Hn
M
physical
Ht
Hn
Ht
M
router
Hl
Hn
Ht
M
Hn
Ht
M
Introduction 1-63
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
Introduction 1-64
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!
Introduction 1-65
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
Introduction 1-66
Bad guys: attack server, network infrastructure
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
target
Introduction 1-67
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
C
src:B
dest:A
payload
B
wireshark software used for end-of-chapter labs is a (free) packet-sniffer
Introduction 1-68
Bad guys can use fake addresses
IP spoofing: send packet with false source address
A
C
src:B
dest:A
payload
B
… lots more on security (throughout, Chapter 8)
Introduction 1-69
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
Introduction 1-70
Internet history
1961-1972: Early packet-switching principles
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
Introduction 1-71
Internet history
1972-1980: Internetworking, new and proprietary nets
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
Introduction 1-72
Internet history
1980-1990: new protocols, a proliferation of networks
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
Introduction 1-73
Internet history
1990, 2000’s: commercialization, the Web, new apps
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 the Web
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
Introduction 1-74
Internet history
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)
Introduction 1-75
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!
Introduction 1-76