Lec 1: Internet Overview
ECE5650
Overview
1-1
Intenet
 Physical Connectivity
Topology
 Access network and physical media

 Layered Internet Protocol Stack
 History
Overview
1-2
What’s the Internet: “nuts and bolts” view
 millions of connected
computing devices: hosts
= end systems
 running network apps
 communication links



router
server
workstation
mobile
local ISP
fiber, copper, radio,
satellite
transmission rate =
regional ISP
bandwidth
routers: forward packets
(chunks of data)
company
network
Overview
1-3
What’s the Internet: a service view

Distributed applications:


Web, email, games, e-commerce,
file sharing
Network protocols: used by
applications to control sending,
receiving of msgs:


TCP, IP, HTTP, FTP, PPP
Internet standards
• RFC: Request for comments
• IETF: Internet Engineering Task
Force

Communication services
provided to apps:


Connectionless unreliable
connection-oriented reliable
Overview
1-4
A closer look at network structure:
 network edge:
applications and
hosts
 network core:
routers
 network of
networks

 access networks,
physical media:
communication links
Overview
1-5
The network edge:
 end systems (hosts):



run application programs
e.g. Web, email
at “edge of network”
 Programs in end-systems use the
serivce of the Internet to send msgs
to each other
 client/server model
• client host requests, receives service from
always-on server; e.g. web, email

peer-peer model:
• minimal (or no) use of dedicated servers
• e.g. Gnutella, KaZaA, Skype, BitTorrent
Overview
1-6
The Network Core
 Physical connectivity of
local area networks

mesh of interconnected
routers
 Logical connectivity: how
is data transferred
through net?
Overview
1-7
Internet structure: network of networks
 roughly hierarchical
 at center: “tier-1” ISPs or Internet backbone networks
(e.g., MCI, Sprint, AT&T, Cable and Wireless),
national/international coverage, connect to large tier-2 ISPs and
to all tier-1 ISPs and many customer networks.
Tier-1
providers
interconnect
(peer)
privately
Tier 1 ISP
Tier 1 ISP
NAP
Tier-1 providers
also interconnect
at public Network
Access Points
(NAPs).
Tier 1 ISP
Overview
1-8
Commercial Internet ISP
Connectivity
 Roughly hierarchical


Divided into tiers
Tier-1 ISPs are also called
backbone providers, e.g.,
AT&T, Sprint, UUNet,
Level 3, Qwest, Cable &
Wireless
 An ISP runs (private)
Points of Presence (PoP)
where its customers and
other ISPs connect to it


E.g., MCI has 4,500 PoP
called private peering
 ISPs also connect at
(public) Network Access
Point (NAP)

called public peering
Overview
1-9
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
NAPs (Network Access Points) are complex high-speed switching networks often
concentrated at a single building. Operated by 3rd party telecom or Internet backbone ISP-1.
 PoPs (Points of Presence) are private group of routers within each ISP and used to connect it
(peer it) with other up/down/equal ISPs and is the new trend in connectivity.
Tier-2 ISPs also
peer privately with
each other,
Tier-2 ISP
Tier-2 ISP pays
Tier-2 ISP
interconnect at
tier-1 ISP for
public NAPs or
connectivity to
private POPs.

rest of Internet,
tier-2 ISP is
customer of
tier-1 provider
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
NAP
Tier 1 ISP
Tier-2 ISP
Tier-2 ISP
Overview
1-10
Internet structure: network of networks
 “Tier-3” ISPs and local ISPs
 last hop (“access”) network (closest to end systems)
local
ISP
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
NAP
Tier 1 ISP
Tier-2 ISP
local
ISP
Tier-2 ISP
local
ISP
Overview
1-11
Internet structure: network of networks
 a packet passes through many networks!
local
ISP
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
NAP
Tier 1 ISP
Tier-2 ISP
local
ISP
Tier-2 ISP
local
ISP
Overview
1-12
Tier-1 ISP: e.g., Sprint
Introduction
1-13
ATT Global Backbone IP Network
From http://www.business.att.com
Overview
1-14
MichNet: Statewide Backbone
 Nation’s longest-
running regional
network
 An 2.5 Gigabit
(OC48c) backbone,
with 24 backbone
nodes
 Two diverse 2.5
gigabit (2x OC48) to
chicago
 www.merit.edu/mn
Overview
1-15
Overview
1-16
Intenet
 Physical Connectivity
Structure
 Access network and physical media

 Layered Internet Protocol Stack
 History
Overview
1-17
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?
Overview
1-18
Residential access: point to point access
 Dialup via modem
Uses existing telephony infrastructure; Home is
connected to central office
 up to 56Kbps direct access to router (often less)
 Can’t surf and phone at same time: can’t be
“always on”central

office
home
PC
home
dial-up
modem
telephone
network
Internet
ISP
modem
(e.g., AOL)
Overview
1-19
 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
Existing phone line:
0-4KHz phone; 4-50KHz
upstream data; 50KHz-1MHz
downstream data
home
phone
Internet
DSLAM
telephone
network
splitter
DSL
modem
home
PC
central
office
Overview
1-20
Residential access: cable modems
 HFC: hybrid fiber coax
asymmetric: up to 30Mbps downstream, 2
Mbps upstream
 network of cable and fiber attaches homes to
ISP router
 homes share access to router so
communication activity is visible to each
other.
 deployment: available via cable TV companies

Overview
1-21
Residential access: cable modems
Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
Overview
1-22
Cable Network Architecture: Overview
Typically 500 to 5,000 homes
cable headend
cable distribution
network (simplified)
home
Overview
1-23
Cable Network Architecture: Overview
cable headend
cable distribution
network (simplified)
home
Overview
1-24
Cable Network Architecture: Overview
server(s)
cable headend
cable distribution
network
home
Overview
1-25
Cable Network Architecture: Overview
FDM:
V
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Channels
cable headend
cable distribution
network
home
Overview
1-26
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
 LANs: chapter 5
Overview
1-27
Wireless access networks
 shared
wireless access network
connects end system to router

via base station aka “access point”
 wireless LANs:


802.11a/b/g (WiFi): 11 Mbps ~54Mbps
802.11n: 100~200Mbps (theoretically
up to 300Mbps)
 wider-area wireless access



provided by telco operator
3G ~ 384 kbps
• Will it happen??
WAP/GPRS in Europe
 WiMAX


router
base
station
mobile
hosts
~100Mbps
~10 miles
Overview
1-28
Home networks
Typical home network components:
 DSL or cable modem
 router/firewall/NAT
 Ethernet
 wireless access
point
to/from
cable
headend
cable
modem
router/
firewall
Ethernet
wireless
laptops
wireless
access
point
Introduction
1-29
Physical Media
 Bit: propagates between
transmitter/rcvr pairs
 physical link: what lies
between transmitter &
receiver
 guided media:

signals propagate in solid
media: copper, fiber, coax
Twisted Pair (TP)
 two insulated copper
wires


Category 3: traditional
phone wires, 10 Mbps
Ethernet
Category 5:
100Mbps Ethernet
 unguided media:
 signals propagate freely,
e.g., radio
Introduction
1-30
Physical Media: coax, fiber
Coaxial cable:
Fiber optic cable:
conductors
 bidirectional
 baseband:
pulses, each pulse a bit
 high-speed operation:
 two concentric copper


single channel on cable
legacy Ethernet
 broadband:
 multiple channels on
cable
 HFC
 glass fiber carrying light

high-speed point-to-point
transmission (e.g., 10’s100’s Gps)
 low error rate: repeaters
spaced far apart ; immune
to electromagnetic noise
Introduction
1-31
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: ~ 1 Mbps
 satellite
 Kbps to 45Mbps channel (or
multiple smaller channels)
 270 msec end-end delay
 geosynchronous versus low
altitude
Introduction
1-32
Intenet
 Physical Connectivity
Topology
 Access network and physical media

 Layered Internet Protocol Stack
 History
Overview
1-33
What’s a protocol?
human protocols:
 “what’s the time?”
 “I have a question”
 introductions
network protocols:
 machines rather than
humans
 all communication
activity in Internet
governed by protocols
A protocol is a set of rules that govens how
two or more communicating parties are
to interact. It defines:
- msg format
- order of msgs sent & received
- actions taken on msg transmission &
receipt
Overview
1-34
Protocol “Layers”
Networks are complex!
 many “pieces”:
 hosts
 routers
 links of various
media
 applications
 protocols
 hardware, software
 Layered Protocol
 Modular approach to
network functionality

Examples:
• Taking an airplane trip
• Mailing service
Overview
1-35
Internet protocol stack
 application: supporting network
applications

FTP, SMTP, HTTP
 transport: process-process data
transfer

TCP, UDP
 network: host-host data transfer
 IP
 link: data transfer between
neighboring network elements

application
transport
network
link
physical
PPP, Ethernet
 physical: bits “on the wire”
Overview
1-36
source
message
segment Ht
datagram Hn Ht
frame
Hl Hn Ht
M
M
M
M
Encapsulation
application
transport
network
link
physical
Hl Hn Ht
M
link
physical
Hl Hn Ht
M
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
Hl Hn Ht
M
M
router
Overview
1-37
Characteristics of Layering
 Layering positives:
Each layer relies on services from layer below
and exports services to layer above
 Interface defines interaction
 Hides implementation - layers can change
without disturbing other layers (black box)

 Layering negatives: duplicate functionality and
inter-dependency.
Overview
1-38
Internet History
1961-1972: Early packet-switching principles
 1961: Kleinrock - queueing
theory shows
effectiveness of packetswitching
 1964: Baran - packetswitching in military nets
 1967: ARPAnet conceived
by Advanced Research
Projects Agency
 1969: first ARPAnet node
operational
 1972:




ARPAnet demonstrated
publicly
NCP (Network Control
Protocol) first hosthost protocol
first e-mail program
ARPAnet has 15 nodes
Overview
1-39
Initial ARPANET
 1965-1968
 ARPANET plan,
implemented by BBN
(Bolt, Beranek,
Newman): packet switch
to build IMP
 1969
 ARPANET
commissioned: 4 nodes,
50kbps
Overview
1-40
Initial Expansion of the ARPANET
Dec. 1969
July 1970
Apr. 1972
Mar. 1971
Sept. 1972
Overview
RFC 527: ARPAWOCKY; RFC 602: The Stockings Were Hung by the Chimney with
Care
1-41
Internet History
1972-1980: Internetworking, new and proprietary nets
 1970: ALOHAnet satellite
network in Hawaii
 1973: Metcalfe’s PhD thesis
proposes Ethernet
 1974: Cerf and Kahn – archi.
for interconnecting networks


Initially, named NCP
Later, split to TCP/IP
 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
2005 ACM Turing Award
“A protocol for packet network
interconnection”, IEEE Trans. on
Communications Technology,
vol.22(5), 627-641
Overview
1-42
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-IPaddress translation
1985: FTP protocol
defined
1988: TCP congestion
control
 new national networks:
Csnet, BITnet,
NSFnet, Minitel
 100,000 hosts
connected to
confederation of
networks
Overview
1-43
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)
Late 1990’s – 2000’s:
 more killer apps: instant
messaging, peer2peer file
sharing (e.g., BitTorrent,
YouTube)
 1992, 1 million hosts
 network security to
 early 1990s: Web
forefront
 hypertext [Bush 1945, Nelson  Today:
1960’s]
 400 million users, 150
countries
 HTML, HTTP: Berners-Lee
 backbone links running at 10
 1994: Mosaic, later Netscape
Gbps
 late 1990’s:
commercialization of the Web
Overview
1-44
Growth of the Internet
Number of Hosts on the
Internet:
Aug. 1981
213
Oct. 1984
1,024
Dec. 1987
28,174
Oct. 1990
313,000
Jul. 1993
1,776,000
Jul. 1996 19,540,000
Jul. 1999 56,218,000
Jul. 2004 285,139,000
Jan. 2005 317,646,000
Jul. 2005 353,284,000 About 2B users out of 6.8B people,
from 16M in 1995, 350M in 2000,1B in 2005
Overview
1-45
Summary
 Physical Connectivity
Topology
 Access network and physical media

 Layered Internet Protocols
 History
Overview
1-46