Chapter 1

Computer Networks
and the Internet

Computer Networking:
A Top Down Approach
Featuring the Internet,
2nd edition.
Jim Kurose, Keith Ross
Addison-Wesley, July
2002.

Introduction 1-1
Chapter 1: Introduction
Our goal: Overview:
‰ get context, ‰ what’s the Internet
overview, “feel” of ‰ what’s a protocol?
networking ‰ network edge
‰ more depth, detail ‰ network core
later in course
‰ access net, physical media
‰ approach:
‰ Internet/ISP structure
 descriptive
‰ performance: loss, delay
 use Internet as
example ‰ protocol layers, service models
‰ history

Introduction 1-2
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Delay & loss in packet-switched networks
1.7 Protocol layers, service models
1.8 History

Introduction 1-3
What’s the Internet: “nuts and bolts” view
‰ millions of connected router
workstation
computing devices: hosts,
end-systems server
mobile
 PCs workstations, servers local ISP
 PDAs phones, toasters
running network apps
‰ communication links regional ISP
 fiber, copper, radio,
satellite
 transmission rate =
bandwidth
‰ routers: forward packets company
(chunks of data) network

Introduction 1-4
“Cool” internet appliances

IP picture frame
http://www.ceiva.com/

Web-enabled toaster+weather forecaster

World’s smallest web server

http://www-ccs.cs.umass.edu/~shri/iPic.html

Introduction 1-5
What’s the Internet: “nuts and bolts” view
‰ protocols control sending, router
workstation
receiving of msgs server
 e.g., TCP, IP, HTTP, FTP, PPP mobile
‰ Internet: “network of local ISP
networks”
 loosely hierarchical
 public Internet versus regional ISP
private intranet
‰ Internet standards
 RFC: Request for comments
 IETF: Internet Engineering
Task Force company
network

Introduction 1-6
What’s the Internet: a service view
‰ communication
infrastructure enables
distributed applications:
 Web, email, games, e-
commerce, database.,
voting, file (MP3) sharing
‰ communication services
provided to apps:
 connectionless
 Connection-oriented
‰ Currently, no gurantees about
performance (Best Effort).

Introduction 1-7
What’s a protocol?
human protocols: network protocols:
‰ “what’s the time?” ‰ machines rather than

‰ “I have a question” humans

‰ introductions ‰ all communication
activity in Internet
… specific msgs sent governed by protocols
… specific actions taken protocols define format,
when msgs received, order of msgs sent and
or other events 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 TCP connection
req
Hi
TCP connection
Got the response
time? Get http://www.awl.com/kurose-ross
2:00
<file>
Time
All activity in the Internet that involves two or more
communicating remote entities is governed by a
protocol. (Routing protocols, Congestion Control
Introduction
protocols, media access protocols, etc.) 1-9
A closer look at network structure:

‰ network edge:
applications and
hosts
‰ network core:
 routers
 network of
networks
‰ access networks,
physical media:
communication links
Introduction 1-10
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Delay & loss in packet-switched networks
1.7 Protocol layers, service models
1.8 History

Introduction 1-11
 The network edge:
‰ end systems (hosts):
 run application programs
 e.g. Web, email
 at “edge of network”
‰ client/server model
 client host requests, receives
service from always-on server
 e.g. Web browser/server;
email client/server
‰ peer-peer model:
 minimal (or no) use of
dedicated servers
 e.g. Gnutella, KaZaA
Introduction 1-12
Network edge: connection-oriented service

Goal: data transfer between TCP service [RFC 793]

end systems
‰ reliable, in-order byte-
handshaking: setup
stream data transfer
‰
(prepare for) data transfer
ahead of time  loss: acknowledgements,
 Exchange control packets time-outs and,
retransmissions
 set up “state” in two
communicating hosts (e.g. ‰ flow control:
Sequence number of next
 sender won’t overwhelm
packet)
receiver (receiver may be
‰ TCP - Transmission Control slower/busier than sender)
Protocol
 Internet’s connection-
‰ congestion control:
oriented service  senders “slow down sending
rate” when network
congested Introduction 1-13
Network edge: connectionless service

Goal: data transfer App’s using TCP:

between end systems ‰ HTTP (Web), FTP (file
 same as before! transfer), Telnet
‰ Connection-less: (remote login), SMTP
 No hand shaking. (email)
‰ UDP - User Datagram
Protocol [RFC 768]: App’s using UDP:
Internet’s ‰ streaming media,
connectionless service teleconferencing, DNS,
 unreliable data Internet telephony
transfer
 no flow control
Introduction
 no congestion control
1-14
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Delay & loss in packet-switched networks
1.7 Protocol layers, service models
1.8 History

Introduction 1-15
The Network Core
‰ mesh of interconnected
routers
‰ the fundamental
question: how is data
transferred through net?
 circuit switching:
dedicated circuit per
call: telephone net
 packet-switching: data
sent thru net in
discrete “chunks”

Introduction 1-16
Network Core: Circuit Switching

End-end resources
reserved for “call”
‰ link bandwidth, switch
capacity
‰ dedicated resources:
no sharing
‰ circuit-like
(guaranteed)
performance
‰ call setup required

Introduction 1-17
Network Core: Circuit Switching
network resources ‰ dividing link bandwidth
(e.g., bandwidth) into “pieces”
divided into “pieces”  frequency division
‰ pieces allocated to calls  time division
‰ resource piece idle if
not used by owning call
(no sharing)

Introduction 1-18
Circuit Switching: TDMA and TDMA
Example:
FDMA
4 users

frequency

time
TDMA

frequency

time
Introduction 1-19
Network Core: Packet Switching
each end-end data stream resource contention:
divided into packets ‰ aggregate resource
‰ Different users' packets demand can exceed
share network resources amount available
‰ each packet uses full link ‰ congestion: packets
bandwidth queue, wait for link use
‰ resources used as needed ‰ store and forward:
packets move one hop
at a time
Bandwidth division into “pieces”  transmit over link
Dedicated allocation
 wait turn at next
Resource reservation
link
Introduction 1-20
Packet Switching: Statistical Multiplexing
10 Mbs
A Ethernet statistical multiplexing C

1.5 Mbs
B
queue of packets
waiting for output
link

D E

Sequence of A & B packets does not have fixed

pattern Î statistical multiplexing.
In TDM each host gets same slot in revolving TDM
frame.
Introduction 1-21
Packet switching versus circuit switching
Packet switching allows more users to use network!
‰ 1 Mbit link
‰ each user:
 100 kbps when “active”
 active 10% of time
N users
‰ circuit-switching: 1 Mbps link
 10 users
‰ packet switching:
 with 35 users,
probability > 10 active
less than .0004

Introduction 1-22
Packet switching versus circuit switching
Is packet switching a “slam dunk winner?”

‰ Great for bursty data

 resource sharing
 Simpler, may have no call setup
‰ Excessive congestion: 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 6)

Introduction 1-23
Packet-switching: store-and-forward
L
R R R

‰ Takes L/R seconds to Example:

transmit (push out) ‰ L = 7.5 Mbits
packet of L bits on to ‰ R = 1.5 Mbps
link or R bps
‰ Transmission delay =
‰ Entire packet must 15 sec
arrive at router before
Circuit Switching:
it can be transmitted
on next link: store and ‰ L = 7.5 Mbits

forward ‰ R = 1.5 Mbps

‰ delay = 3L/R ‰ Transmission delay = 5

sec
Introduction 1-24
Packet Switching: Message Segmenting

Now break up the message

into 5000 packets
‰ Each packet 1,500 bits
‰ 1 msec to transmit packet on
one link
‰ pipelining: each link works in
parallel
‰ Delay reduced from 15 sec
to 5.002 sec (as good as
circuit switched)
‰ What did we achieve over
circuit switching?
‰ Drawbacks (of packet vs.
Message)
Introduction 1-25
Packet-switched networks: forwarding
‰ Goal: move packets through routers from source to
destination
 we’ll study several path selection (i.e. routing)algorithms
(chapter 4)
‰ datagram network:
 destination address in packet determines next hop
 routes may change during session
 analogy: driving, asking directions
‰ virtual circuit network:
 each packet carries tag (virtual circuit ID), tag
determines next hop
 fixed path determined at call setup time, remains fixed
thru call
 routers maintain per-call state
Introduction 1-26
Virtual Circuit Networks
‰ VC consists of:
 A path
 VC numbers (one for each
link)
 VC number translation
tables A VC network
‰ “State” is maintained
‰ Why different
numbers?
 Length of label reduced
 Easier to manage
(number can be
generated independently) Table in PS1
Introduction 1-27
Datagram Networks
‰ Like postal service
‰ Routing based on destination address
‰ No path set-up, no label
‰ Every router looks at destination address
(or part of it), and the routing table
‰ No connection state – each packet is
treated completely independently

Introduction 1-28
Network Taxonomy
Telecommunication
networks

Circuit-switched Packet-switched
networks networks

Networks Datagram
FDM TDM
with VCs Networks

• Datagram network is not either connection-oriented

or connectionless.
• Internet provides both connection-oriented (TCP) and
connectionless services (UDP) to apps.
Introduction 1-29
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Delay & loss in packet-switched networks
1.7 Protocol layers, service models
1.8 History

Introduction 1-30
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 1-31
Residential access: point to point access

‰ Dialup via modem

 up to 56Kbps direct access to
router (often less)
 Can’t surf and phone at same
time: can’t be “always on”
‰ ADSL: asymmetric digital subscriber line
 up to 1 Mbps upstream (today typically < 256 kbps)
 up to 8 Mbps downstream (today typically < 1 Mbps)
 FDM: 50 kHz - 1 MHz for downstream
4 kHz - 50 kHz for upstream
0 kHz - 4 kHz for ordinary telephone
Introduction 1-32
Residential access: cable modems

‰ HFC: hybrid fiber coax

 asymmetric: up to 10Mbps upstream, 1 Mbps
downstream
‰ network of cable and fiber attaches homes to
ISP router
 shared access to router among home
 issues: congestion, dimensioning
‰ deployment: available via cable companies

Introduction 1-33
Company access: local area networks
‰ company/univ local area
network (LAN) connects
end system to edge router
‰ Ethernet:
 shared or dedicated link
connects end system
and router
 10 Mbs, 100Mbps,
Gigabit Ethernet
‰ deployment: institutions,
home LANs happening now
‰ LANs: chapter 5
Introduction 1-34
Wireless access networks
‰ shared wireless access
network connects end system
to router router
 via base station aka “access
point” base
‰ wireless LANs: station
 802.11b (WiFi): 11 Mbps
‰ wider-area wireless access
 provided by telco operator
3G ~ 384 kbps
mobile


• Will it happen??
hosts
 WAP/GPRS in Europe

Introduction 1-35
Physical Media
Twisted Pair (TP)
‰ Bit: propagates between ‰ two insulated copper
transmitter/rcvr pairs wires
‰ physical link: what lies  Category 3: traditional
between transmitter & phone wires, 10 Mbps
receiver Ethernet
Category 5 TP: 100Mbps
‰ guided media: 

Ethernet
 signals propagate in solid
media: copper, fiber, coax
‰ unguided media:
 signals propagate freely,
e.g., radio

Introduction 1-36
Physical Media: coax, fiber

Coaxial cable: Fiber optic cable:

‰ glass fiber carrying light
‰ two concentric copper
pulses, each pulse a bit
conductors
‰ high-speed operation:
‰ bidirectional
 high-speed point-to-point
‰ baseband: transmission (e.g., 2.5 Gps)
 single channel on cable ‰ low error rate: repeaters
 legacy Ethernet spaced far apart ; immune
‰ broadband: to electromagnetic noise
 multiple channel on cable
 HFC

Introduction 1-37
Physical media: radio
‰ signal carried in Radio link types:
electromagnetic ‰ terrestrial microwave
spectrum  e.g. up to 45 Mbps channels
‰ no physical “wire” ‰ LAN (e.g., WaveLAN)
‰ bidirectional  2Mbps, 11Mbps
‰ propagation ‰ wide-area (e.g., cellular)
environment effects:  e.g. 3G: hundreds of kbps
 reflection ‰ satellite
 obstruction by objects  up to 50Mbps channel
 interference  270 msec end-end delay
 geosynchronous versus low-
altitude

Introduction 1-38
Physical Media

Introduction 1-39
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Delay & loss in packet-switched networks
1.7 Protocol layers, service models
1.8 History

Introduction 1-40
Internet structure: network of networks

‰ roughly hierarchical
‰ at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity,
Sprint, AT&T, Tata Indicom, Reliance, VSNL),
national/international coverage
 treat each other as equals
Tier-1 providers
also interconnect
Tier-1
providers
Tier 1 ISP at public network
NAP access points
interconnect (NAPs)
(peer)
privately
Tier 1 ISP Tier 1 ISP

Introduction 1-41
Tier-1 ISP: e.g., Sprint
Sprint US backbone network

Introduction 1-42
 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

Tier-2 ISPs
Tier-2 ISP pays Tier-2 ISP also peer
Tier-2 ISP privately with
tier-1 ISP for
connectivity to Tier 1 ISP each other,
rest of Internet NAP interconnect
‰ tier-2 ISP is
at NAP
customer of
tier-1 provider Tier 1 ISP Tier 1 ISP Tier-2 ISP

Tier-2 ISP Tier-2 ISP

Introduction 1-43
Example of Tier 2 carrier in India – Satyam
 Internet structure: network of networks

‰ “Tier-3” ISPs and local ISPs

 last hop (“access”) network (closest to end systems)

local
ISP Tier 3 local
local local
ISP ISP
ISP ISP
Local and tier- Tier-2 ISP Tier-2 ISP
3 ISPs are
customers of Tier 1 ISP
higher tier NAP
ISPs
connecting
them to rest Tier 1 ISP
of Internet
Tier 1 ISP Tier-2 ISP
local
Tier-2 ISP Tier-2 ISP
ISP
local local local
ISP ISP ISP Introduction 1-44
Internet structure: network of networks

‰ a packet passes through many networks!

local
ISP Tier 3 local
local local
ISP ISP
ISP ISP
Tier-2 ISP Tier-2 ISP

Tier 1 ISP
NAP

Tier 1 ISP Tier 1 ISP Tier-2 ISP

local
Tier-2 ISP Tier-2 ISP
ISP
local local local
ISP ISP ISP Introduction 1-45
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Delay & loss in packet-switched networks
1.7 Protocol layers, service models
1.8 History

Introduction 1-46
 How do loss and delay occur?
packets queue in router buffers
‰ When packet arrival rate to link exceeds output link
capacity
‰ packets queue, wait for turn
packet being transmitted (delay)

B
packets queueing (delay)
free (available) buffers: arriving packets
dropped (loss) if no free buffers
Introduction 1-47
Four sources of packet delay
‰ 1. nodal processing: ‰ 2. queuing
 check bit errors  time waiting at output
 determine output link link for transmission
 depends on congestion
level of router

transmission
A propagation

B
nodal
processing queueing

Introduction 1-48
Delay in packet-switched networks
3. Transmission delay: 4. Propagation delay:
‰ R=link bandwidth (bps) ‰ d = length of physical link

‰ L=packet length (bits) ‰ s = propagation speed in

‰ time to send bits into medium (~2x108 m/sec)

link = L/R ‰ propagation delay = d/s

Note: s and R are very

different quantities!
transmission
A propagation

B
nodal
processing queueing
Introduction 1-49
 Caravan analogy
100 km 100 km
ten-car toll toll
caravan booth booth
‰ Cars “propagate” at ‰ Time to “push” entire
100 km/hr caravan through toll
‰ Toll booth takes 12 sec to booth onto highway =
service a car 12*10 = 120 sec
(transmission time) ‰ Time for last car to
‰ car~bit; caravan ~ packet propagate from 1st to
2nd toll both:
‰ Q: How long until caravan
100km/(100km/hr)= 1 hr
is lined up before 2nd toll
booth? ‰ A: 62 minutes
Introduction 1-50
Caravan analogy (more)
100 km 100 km
ten-car toll toll
caravan booth booth
‰ Yes! After 7 min, 1st car
‰ Cars now “propagate” at at 2nd booth and 3 cars
1000 km/hr still at 1st booth.
‰ Toll booth now takes 1 ‰ 1st bit of packet can
min to service a car arrive at 2nd router
‰ Q: Will cars arrive to before packet is fully
2nd booth before all transmitted at 1st router!
cars serviced at 1st  See Ethernet applet at AWL
booth? Web site

Introduction 1-51
Nodal delay

‰ dproc = processing delay

 typically a few microsecs or less
‰ dqueue = queuing delay
 depends on congestion
‰ dtrans = transmission delay
 = L/R, significant for low-speed links
‰ dprop = propagation delay
 a few microsecs to hundreds of msecs

Introduction 1-52
Queueing delay (revisited)

‰ R=link bandwidth (bps)

‰ L=packet length (bits)
‰ a=average packet
arrival rate

traffic intensity = La/R

‰ La/R ~ 0: average queueing delay small

‰ La/R -> 1: delays become large
‰ La/R > 1: more “work” arriving than can be
serviced, average delay infinite!
Introduction 1-53
“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 1-54
“Real” Internet delays and routes
traceroute: gaia.cs.umass.edu to www.eurecom.fr
Three 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 trans-oceanic
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 link
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 * * * * means no response (probe lost, router not replying)
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms

Introduction 1-55
Packet loss
‰ queue (aka buffer) preceding link in buffer
has finite capacity
‰ when packet arrives to full queue, packet is
dropped (aka lost)
‰ lost packet may be retransmitted by
previous node, by source end system, or not
retransmitted at all

Introduction 1-56
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Delay & loss in packet-switched networks
1.7 Protocol layers, service models
1.8 History

Introduction 1-57
Protocol “Layers”
Networks are complex!
‰ many “pieces”:

 hosts Question:
 routers Is there any hope of
 links of various organizing structure of
media network?
 applications
 protocols Or at least our discussion
 hardware, of networks?
software

Introduction 1-58
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
‰ layering considered harmful?

Introduction 1-59
Internet protocol stack
‰ application: supporting network
applications application
 FTP, SMTP, STTP
‰ transport: host-host data transfer transport
 TCP, UDP
‰ network: routing of datagrams from network
source to destination
 IP, routing protocols link
‰ link: data transfer between
neighboring network elements physical
 PPP, Ethernet
‰ physical: bits “on the wire”
Introduction 1-60
Layering: logical communication
Each layer: application
transport
‰ distributed network
‰ “entities”
link
physical
implement network
layer functions application link
at each node transport physical
network
‰ entities link
perform physical
application application
actions, transport transport
exchange network network
link link
messages with physical physical
peers

Introduction 1-61
Layering: logical communication
data
E.g.: transport application
transport
transport
‰ take data from app network
‰ add addressing, link
reliability check physical
info to form ack network
“datagram” application link
‰ send datagram to transport data physical
network
peer
link
wait for peer to data
‰ physical
ack receipt application application
transport transport
transport
‰ analogy: post network network
office link link
physical physical

Introduction 1-62
Layering: physical communication
data
application
transport
network
link
physical
network
application link
transport physical
network
link
physical data
application application
transport transport
network network
link link
physical physical

Introduction 1-63
Layering: physical communication
data
application
transport
network
link
physical
network
application link
transport physical
network
link link
Switching
physical physical
Hub

application data
application
transport transport
network network
link link
physical physical
Introduction 1-64
 Protocol layering and data
Each layer takes data from above
‰ adds header information to create new data unit

‰ passes new data unit to layer below

source destination
M application application M message

Ht M transport transport Ht M segment

Hn Ht M network network Hn Ht M datagram
Hl Hn Ht M link link Hl Hn Ht M frame
physical physical

Introduction 1-65
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 ISPs and Internet backbones
1.6 Delay & loss in packet-switched networks
1.7 Internet structure and ISPs
1.8 History

Introduction 1-66
Internet History
1961-1972: Early packet-switching principles
‰ 1961: Kleinrock - queueing ‰ 1972:
theory shows  ARPAnet demonstrated
effectiveness of packet- publicly
switching
 NCP (Network Control
‰ 1964: Baran - packet- Protocol) first host-
switching in military nets host protocol
‰ 1967: ARPAnet conceived  first e-mail program
by Advanced Research
 ARPAnet has 15 nodes
Projects Agency
‰ 1969: first ARPAnet node
operational

Introduction 1-67
 Internet History
1972-1980: Internetworking, new and proprietary nets
‰ 1970: ALOHAnet satellite Cerf and Kahn’s
network in Hawaii internetworking principles:
‰ 1973: Metcalfe’s PhD thesis  minimalism, autonomy -
proposes Ethernet no internal changes
‰ 1974: Cerf and Kahn - required to
architecture for interconnect networks
interconnecting networks  best effort service
‰ late70’s: proprietary model
architectures: DECnet, SNA,  stateless routers
XNA
 decentralized control
‰ late 70’s: switching fixed
define today’s Internet
length packets (ATM
architecture
precursor)
‰ 1979: ARPAnet has 200 nodes
Introduction 1-68
Internet History
1980-1990: new protocols, a proliferation of networks

‰ 1983: deployment of ‰ new national networks:

TCP/IP Csnet, BITnet,
‰ 1982: SMTP e-mail NSFnet, Minitel
protocol defined ‰ 100,000 hosts
‰ 1983: DNS defined for connected to
name-to-IP-address confederation of
translation networks
‰ 1985: FTP protocol
defined
‰ 1988: TCP congestion
control
Introduction 1-69
Internet History
1990, 2000’s: commercialization, the Web, new apps
‰ Early 1990’s: ARPAnet Late 1990’s – 2000’s:
decommissioned
‰ more killer apps: instant
1991: NSF lifts restrictions on
‰
messaging, peer2peer
commercial use of NSFnet
(decommissioned, 1995)
file sharing (e.g.,
Napster)
‰ early 1990s: Web
 hypertext [Bush 1945, Nelson
‰ network security to
1960’s] forefront
 HTML, HTTP: Berners-Lee
‰ est. 50 million host, 100
 1994: Mosaic, later Netscape
million+ users
 late 1990’s: ‰ backbone links running
commercialization of the Web at Gbps

Introduction 1-70
Introduction: Summary
Covered a “ton” of material!
You now have:
‰ Internet overview
‰ context, overview,
‰ what’s a protocol?
“feel” of networking
‰ network edge, core, access
‰ more depth, detail to
network follow!
 packet-switching versus
circuit-switching
 Virtual circuit vs
datagram
‰ Internet/ISP structure
‰ performance: loss, delay
‰ layering and service
models
‰ history Introduction 1-71
Fun Examples
‰ Communications with Mars (Spirit)

60000000 bits, data 7356416 one image size

12000 bits per second 8.156146 images

5000 seconds, transm delay

300000000 meters/sec, speed of light

3.2E+11 meters, distance to mars

1066.666667 seconds, propagation delay

101.11 minutes

Introduction 1-72