Transcript Part I: Introduction - Central South University

Part I: Introduction
Our goal:
get context,
overview, “feel” of
networking
r more depth, detail
later in course
r approach:
m descriptive
m use Internet as
example
r
Assignment: read
chapter 1 in text
Overview:
r
r
r
r
r
r
r
r
r
what’s the Internet
what’s a protocol?
network edge
network core
access net, physical media
performance: loss, delay
protocol layers, service models
backbones, NAPs, ISPs
history
1: Introduction
1
What’s the Internet: “nuts and bolts” view
r
millions of connected
computing devices: hosts,
end-systems
m
m
pc’s workstations, servers
PDA’s phones, toasters
router
server
r
regional ISP
communication links
m
mobile
local ISP
running network apps
r
workstation
fiber, copper, radio,
satellite
routers: forward packets
(chunks) of data thru
network
company
network
1: Introduction
2
“Cool” internet appliances
IP picture frame
http://www.ceiva.com/
World’s smallest web server
http://www-ccs.cs.umass.edu/~shri/iPic.html
Web-enabled toaster+weather forecaster
http://dancing-man.com/robin/toasty/
1: Introduction
3
What’s the Internet: “nuts and bolts” view
r
protocols: control sending,
receiving of msgs
m
r
Internet: “network of
server
workstation
mobile
local ISP
networks”
m
m
r
e.g., TCP, IP, HTTP, FTP, PPP
router
loosely hierarchical
public Internet versus
private intranet
regional ISP
Internet standards
m
m
RFC: Request for comments
IETF: Internet Engineering
Task Force
company
network
1: Introduction
4
What’s the Internet: a service view
r
communication
infrastructure enables
distributed applications:
m
r
communication services
provided:
m
m
r
WWW, email, games, ecommerce, database.,
voting, file (MP3) sharing
connectionless
connection-oriented
cyberspace [Gibson]:
“a consensual hallucination experienced daily by
billions of operators, in every nation, ...."
1: Introduction
5
What’s a protocol?
human protocols:
r “what’s the time?”
r “I have a question”
r introductions
… specific msgs sent
… specific actions taken
when msgs received,
or other events
network protocols:
r machines rather than
humans
r 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: Introduction
6
What’s a protocol?
a human protocol and a computer network protocol:
Hi
TCP connection
req.
Hi
TCP connection
reply.
Got the
time?
Get http://gaia.cs.umass.edu/index.htm
2:00
<file>
time
Q: Other human protocol?
1: Introduction
7
A closer look at network structure:
r network edge:
applications and
hosts
r network core:
m
m
routers
network of
networks
r access networks,
physical media:
communication links
1: Introduction
8
The network edge:
r end systems (hosts):
m
m
m
run application programs
e.g., WWW, email
at “edge of network”
r client/server model
m
m
client host requests, receives
service from server
e.g., WWW client (browser)/
server; email client/server
r peer-peer model:
m
m
host interaction symmetric
e.g.: Gnutella, KaZaA
1: Introduction
9
Network edge: connection-oriented service
Goal: data transfer
between end sys.
r handshaking: setup
(prepare for) data
transfer ahead of time
m
m
r
Hello, hello back human
protocol
set up “state” in two
communicating hosts
TCP - Transmission
Control Protocol
m
Internet’s connectionoriented service
TCP service [RFC 793]
r
reliable, in-order bytestream data transfer
m
r
flow control:
m
r
loss: acknowledgements
and retransmissions
sender won’t overwhelm
receiver
congestion control:
m
senders “slow down sending
rate” when network
congested
1: Introduction
10
Network edge: connectionless service
Goal: data transfer
between end systems
m
r
same as before!
UDP - User Datagram
Protocol [RFC 768]:
Internet’s
connectionless service
m unreliable data
transfer
m no flow control
m no congestion control
App’s using TCP:
r
HTTP (WWW), FTP
(file transfer), Telnet
(remote login), SMTP
(email)
App’s using UDP:
r
streaming media,
teleconferencing,
Internet telephony
1: Introduction
11
The Network Core
mesh of interconnected
routers
r the fundamental
question: how is data
transferred through net?
m circuit switching:
dedicated circuit per
call: telephone net
m packet-switching: data
sent thru net in
discrete “chunks”
r
1: Introduction
12
Network Core: Circuit Switching
End-end resources
reserved for “call”
link bandwidth, switch
capacity
r dedicated resources:
no sharing
r circuit-like
(guaranteed)
performance
r call setup required
r
1: Introduction
13
Network Core: Circuit Switching
network resources
(e.g., bandwidth)
divided into “pieces”
pieces allocated to calls
r resource piece idle if
not used by owning call
r
r
dividing link bandwidth
into “pieces”
m frequency division
m time division
(no sharing)
r
dividing link bandwidth
into “pieces”
m frequency division
m time division
1: Introduction
14
Circuit Switching: TDMA and TDMA
Example:
FDMA
4 users
frequency
time
TDMA
frequency
time
1: Introduction
15
Network Core: Packet Switching
each end-end data stream
divided into packets
r user A, B packets share
network resources
r each packet uses full link
bandwidth
r resources used as needed,
Bandwidth division into “pieces”
Dedicated allocation
Resource reservation
resource contention:
r aggregate resource
demand can exceed
amount available
r congestion: packets
queue, wait for link use
r store and forward:
packets move one hop
at a time
m transmit over link
m wait turn at next
link
1: Introduction
16
Network Core: Packet Switching
10 Mbs
Ethernet
A
B
statistical multiplexing
C
1.5 Mbs
queue of packets
waiting for output
link
D
45 Mbs
E
Packet-switching versus circuit switching: human
restaurant analogy
r other human analogies?
1: Introduction
17
Network Core: Packet Switching
Packet-switching:
store and forward behavior
break message into
smaller chunks:
“packets”
r Store-and-forward:
switch waits until chunk
has completely arrived,
then forwards/routes
r Q: what if message was
sent as single unit?
r
1: Introduction
18
Packet switching versus circuit switching
Packet switching allows more users to use network!
1 Mbit link
r each user:
r
m
m
r
circuit-switching:
m
r
100Kbps when “active”
active 10% of time
10 users
N users
1 Mbps link
packet switching:
m
with 35 users,
probability > 10 active
less than .0004
1: Introduction
19
Packet switching versus circuit switching
Is packet switching a “slam dunk winner?”
Great for bursty data
m resource sharing
m no call setup
r Excessive congestion: packet delay and loss
m protocols needed for reliable data transfer,
congestion control
r Q: How to provide circuit-like behavior?
m bandwidth guarantees needed for audio/video
apps
m still an unsolved problem (chapter 6)
r
1: Introduction
20
Packet-switched networks: routing
r
Goal: move packets among routers from source to
destination
m
r
datagram network:
m
m
m
r
we’ll study several path selection algorithms (chapter 4)
destination address determines next hop
routes may change during session
analogy: driving, asking directions
virtual circuit network:
m
m
m
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
1: Introduction
21
Access networks and physical media
Q: How to connection end
systems to edge router?
residential access nets
r institutional access
networks (school,
company)
r mobile access networks
r
Keep in mind:
bandwidth (bits per
second) of access
network?
r shared or dedicated?
r
1: Introduction
22
Residential access: point to point access
Dialup via modem
m up to 56Kbps direct access to
router (conceptually)
r ISDN: integrated services
digital network: 128Kbps alldigital connect to router
r ADSL: asymmetric digital
subscriber line
m up to 1 Mbps home-to-router
m up to 8 Mbps router-to-home
m ADSL deployment: happening
r
1: Introduction
23
Residential access: cable modems
HFC: hybrid fiber coax
m asymmetric: up to 10Mbps upstream, 1 Mbps
downstream
r network of cable and fiber attaches homes to
ISP router
m shared access to router among home
m issues: congestion, dimensioning
r deployment: available via cable companies, e.g.,
MediaOne
r
1: Introduction
24
Residential access: cable modems
Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
1: Introduction
25
Institutional access: local area networks
company/univ local area
network (LAN) connects
end system to edge router
r Ethernet:
m shared or dedicated
cable connects end
system and router
m 10 Mbs, 100Mbps,
Gigabit Ethernet
r deployment: institutions,
home LANs happening now
r LANs: chapter 5
r
1: Introduction
26
Wireless access networks
shared wireless access
network connects end
system to router
r wireless LANs:
r
m
m
r
radio spectrum replaces
wire
e.g., Lucent Wavelan 11
Mbps
wider-area wireless
access
m
CDPD: wireless access to
ISP router via cellular
network
router
base
station
mobile
hosts
1: Introduction
27
Home networks
Typical home network components:
r ADSL or cable modem
r router/firewall
r Ethernet
r wireless access
point
to/from
cable
headend
cable
modem
router/
firewall
Ethernet
(switched)
wireless
laptops
wireless
access
point
1: Introduction
28
Physical Media
physical link:
transmitted data bit
propagates across link
r guided media:
r
m
r
signals propagate in
solid media: copper,
fiber
unguided media:
m
Twisted Pair (TP)
r two insulated copper
wires
m
m
Category 3: traditional
phone wires, 10 Mbps
Ethernet
Category 5 TP:
100Mbps Ethernet
signals propagate
freely, e.g., radio
1: Introduction
29
Physical Media: coax, fiber
Coaxial cable:
r
wire (signal carrier)
within a wire (shield)
m
m
baseband: single channel
on cable
broadband: multiple
channel on cable
bidirectional
r common use in 10Mbs
Ethernet
r
Fiber optic cable:
glass fiber carrying
light pulses
r high-speed operation:
r
m
m
r
100Mbps Ethernet
high-speed point-to-point
transmission (e.g., 5 Gps)
low error rate
1: Introduction
30
Physical media: radio
signal carried in
electromagnetic
spectrum
r no physical “wire”
r bidirectional
r propagation
environment effects:
r
m
m
m
reflection
obstruction by objects
interference
Radio link types:
r
microwave
m
r
LAN (e.g., WaveLAN)
m
r
2Mbps, 11Mbps
wide-area (e.g., cellular)
m
r
e.g. up to 45 Mbps channels
e.g. CDPD, 10’s Kbps
satellite
m
m
m
up to 50Mbps channel (or
multiple smaller channels)
270 Msec end-end delay
geosynchronous versus
LEOS
1: Introduction
31
Delay in packet-switched networks
packets experience delay
on end-to-end path
r four sources of delay
at each hop
r
nodal processing:
m
m
r
queueing
m
m
transmission
A
check bit errors
determine output link
time waiting at output
link for transmission
depends on congestion
level of router
propagation
B
nodal
processing
queueing
1: Introduction
32
Delay in packet-switched networks
Transmission delay:
r R=link bandwidth (bps)
r L=packet length (bits)
r time to send bits into
link = L/R
transmission
A
Propagation delay:
r d = length of physical link
r s = propagation speed in
medium (~2x108 m/sec)
r propagation delay = d/s
Note: s and R are very
different quantities!
propagation
B
nodal
processing
queueing
1: Introduction
33
Queueing delay (revisited)
R=link bandwidth (bps)
r L=packet length (bits)
r a=average packet
arrival rate
r
traffic intensity = La/R
La/R ~ 0: average queueing delay small
r La/R -> 1: delays become large
r La/R > 1: more “work” arriving than can be
serviced, average delay infinite!
r
1: Introduction
34
“Real” Internet delays and routes
traceroute: routers, rt delays on source-dest path
also: pingplotter, various windows programs
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
1: Introduction
35
Protocol “Layers”
Networks are complex!
r many “pieces”:
m hosts
m routers
m links of various
media
m applications
m protocols
m hardware,
software
Question:
Is there any hope of
organizing structure of
network?
Or at least our discussion
of networks?
1: Introduction
36
Organization of air travel
ticket (purchase)
ticket (complain)
baggage (check)
baggage (claim)
gates (load)
gates (unload)
runway takeoff
runway landing
airplane routing
airplane routing
airplane routing
r a series of steps
1: Introduction
37
Organization of air travel: a different view
ticket (purchase)
ticket (complain)
baggage (check)
baggage (claim)
gates (load)
gates (unload)
runway takeoff
runway landing
airplane routing
airplane routing
airplane routing
Layers: each layer implements a service
m via its own internal-layer actions
m relying on services provided by layer below
1: Introduction
38
Layered air travel: services
Counter-to-counter delivery of person+bags
baggage-claim-to-baggage-claim delivery
people transfer: loading gate to arrival gate
runway-to-runway delivery of plane
airplane routing from source to destination
1: Introduction
39
ticket (purchase)
ticket (complain)
baggage (check)
baggage (claim)
gates (load)
gates (unload)
runway takeoff
runway landing
airplane routing
airplane routing
arriving airport
Departing airport
Distributed implementation of layer functionality
intermediate air traffic sites
airplane routing
airplane routing
airplane routing
1: Introduction
40
Why layering?
Dealing with complex systems:
explicit structure allows identification,
relationship of complex system’s pieces
m layered reference model for discussion
r modularization eases maintenance, updating of
system
m change of implementation of layer’s service
transparent to rest of system
m e.g., change in gate procedure doesn’t affect
rest of system
r layering considered harmful?
r
1: Introduction
41
Internet protocol stack
r
application: supporting network
applications
m
r
transport: host-host data transfer
m
r
ip, routing protocols
link: data transfer between
neighboring network elements
m
r
tcp, udp
network: routing of datagrams from
source to destination
m
r
ftp, smtp, http
application
transport
network
link
physical
ppp, ethernet
physical: bits “on the wire”
1: Introduction
42
Layering: logical communication
Each layer:
r distributed
r “entities”
implement
layer functions
at each node
r entities
perform
actions,
exchange
messages with
peers
application
transport
network
link
physical
application
transport
network
link
physical
network
link
physical
application
transport
network
link
physical
application
transport
network
link
physical
1: Introduction
43
Layering: logical communication
E.g.: transport
r
r
r
r
r
take data from app
add addressing,
reliability check
info to form
“datagram”
send datagram to
peer
wait for peer to
ack receipt
analogy: post
office
data
application
transport
transport
network
link
physical
application
transport
network
link
physical
ack
data
network
link
physical
application
transport
network
link
physical
data
application
transport
transport
network
link
physical
1: Introduction
44
Layering: physical communication
data
application
transport
network
link
physical
application
transport
network
link
physical
network
link
physical
application
transport
network
link
physical
data
application
transport
network
link
physical
1: Introduction
45
Protocol layering and data
Each layer takes data from above
r adds header information to create new data unit
r passes new data unit to layer below
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
M
message
M
segment
M
M
datagram
frame
1: Introduction
46
Internet structure: network of networks
roughly hierarchical
r national/international
backbone providers (NBPs)
r
m
m
r
regional ISPs
m
r
e.g. BBN/GTE, Sprint,
AT&T, IBM, UUNet
interconnect (peer) with
each other privately, or at
public Network Access Point
(NAPs)
connect into NBPs
local ISP, company
m
local
ISP
regional ISP
NBP B
NAP
NAP
NBP A
regional ISP
local
ISP
connect into regional ISPs
1: Introduction
47
National Backbone Provider
e.g. Sprint US backbone network
1: Introduction
48
Internet History
1961-1972: Early packet-switching principles
r
r
r
r
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
r
1972:
m ARPAnet demonstrated
publicly
m NCP (Network Control
Protocol) first hosthost protocol
m first e-mail program
m ARPAnet has 15 nodes
1: Introduction
49
Internet History
1972-1980: Internetworking, new and proprietary nets
r
r
r
r
r
r
1970: ALOHAnet satellite
network in Hawaii
1973: Metcalfe’s PhD thesis
proposes Ethernet
1974: Cerf and Kahn architecture for
interconnecting networks
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:
m minimalism, autonomy no internal changes
required to
interconnect networks
m best effort service
model
m stateless routers
m decentralized control
define today’s Internet
architecture
1: Introduction
50
Internet History
1980-1990: new protocols, a proliferation of networks
r
r
r
r
r
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
r 100,000 hosts
connected to
confederation of
networks
r
1: Introduction
51
Internet History
1990’s: commercialization, the WWW
r
r
r
Early 1990’s: ARPAnet
decommissioned
1991: NSF lifts restrictions
on commercial use of NSFnet
(decommissioned, 1995)
early 1990s: WWW
m hypertext [Bush 1945,
Nelson 1960’s]
m HTML, http: Berners-Lee
m 1994: Mosaic, later
Netscape
m late 1990’s:
commercialization of the
WWW
Late 1990’s:
est. 50 million
computers on
Internet
r est. 100 million+
users
r backbone links
running at 1 Gbps
r
1: Introduction
52
Introduction: Summary
Covered a “ton” of material!
r Internet overview
r what’s a protocol?
r network edge, core, access
network
m packet-switching versus
circuit-switching
r performance: loss, delay
r layering and service
models
r backbones, NAPs, ISPs
r history
You now have:
r context, overview,
“feel” of networking
r more depth, detail
later in course
1: Introduction
53