Transcript 4th Edition: Chapter 1

Comp 365
Computer Networks
Fall 2014
Chapter 1
Introduction
These slides derived from 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
 circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched
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
 millions (>900m) of
PC
connected computing
devices:
 hosts = end systems
 running network apps
server
wireless
laptop
cellular
handheld
 communication links
access
points
wired
links
router


fiber, copper, radio,
satellite
transmission rate =
bandwidth
Mobile network
Global ISP
Home network
Regional ISP
Institutional network
 Packet switches: forward
packets (chunks of data)
 routers and switches
Introduction
1-4
“Cool” internet appliances
Web-enabled toaster +
weather forecaster
IP picture frame
http://www.ceiva.com/
Tweet-a-watt:
monitor energy use
Slingbox: watch,
control cable TV remotely
Internet
refrigerator
Internet phones
Introduction
1-5
What’s the Internet: “nuts and bolts” view
 protocols control sending,
receiving of msgs

networks”


Global ISP
e.g., TCP, IP, HTTP, Skype,
Ethernet
 Internet: “network of

Mobile network
loosely hierarchical
Interconnected ISPs
public Internet versus private
intranet
Home network
Regional ISP
Institutional network
ISP = Internet service provider
Introduction
1-6
What’s the Internet: “nuts and bolts”
view
 Internet standards

RFC: Request for comments
•
•
•
•

the standards documents
Very technical
> 5,000 RFCs
Include TCP, IP, HTTP, SMTP
IETF: Internet Engineering
Task Force
• the body that creates standards
• Other bodies: IEEE 803 LAN/MAN,
etc.
Mobile network
Global ISP
Home network
Regional ISP
Institutional network
ISP = Internet service provider
Introduction
1-7
What’s the Internet: a service view
 communication infrastructure
enables distributed applications:
 Web, VoIP, email, games, ecommerce, file sharing
Introduction
1-8
What’s the Internet: a service view
 communication services provided
to apps:
 reliable data delivery from
source to destination
 “best effort” (unreliable) data
delivery
Introduction
1-9
What’s the Internet: a service view
 Application programming interface
(API):
 Describes how these
distributed apps send
information back and forth
 Like the post office: must put
name, street, city, etc. on an
envelope
 Different internet services
have different APIs.
Introduction
1-10
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
1-11
What’s a protocol?
a human protocol and a computer network protocol:
Hi
TCP connection
request
Hi
TCP connection
response
Got the
time?
Get http://www.awl.com/kurose-ross
2:00
<file>
time
Q: Other human protocols?
Introduction
1-12
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
 end systems, access networks, links
1.3 Network core
 circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched
networks
1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 History
Introduction
1-13
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
Introduction
1-14
The network edge
 end systems (hosts):



run application programs
e.g. Web, email
at “edge of network”
peer-peer
 client/server model


client host requests, receives
service from always-on server
e.g. Web browser/server; email client/server
client/server
 peer-peer model:


minimal (or no) use of dedicated
servers
e.g. Skype, BitTorrent
Introduction
1-15
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
1-16
Dial-up Modem
central
office
home
PC




home
dial-up
modem
telephone
network
Internet
ISP
modem
(e.g., AOL)
Uses existing telephony infrastructure
 Home is connected to central office
Modem converts digital output of PC to analog format
up to 56Kbps direct access to router (often less)
 8 minutes to download 3 minute MP3; days for a movie
Can’t surf and phone at same time: not “always on”
Digital Subscriber Line (DSL)
central office
DSL splitter
modem
voice, data transmitted
at different frequencies over
dedicated line to central office




DSLAM
DSL: digital
subscriber line
telephone
network
DSLAM: digital
subscriber line
access multiplier
ISP
DSL access
multiplexer
uses 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 (typically < 1 <bps)
asymmetric
< 24 Mbps downstream (typically < 10 Mbps)
Local telco is the ISP
Residential access: cable network
cable headend
…
cable splitter
modem
data, TV transmitted at different
frequencies over shared cable
distribution network
CMTS
cable modem
termination system
ISP
 Does not use telephone infrastructure

Instead uses cable TV infrastructure
Introduction
1-19
Residential access: cable network
cable headend
…
cable splitter
modem
data, TV transmitted at different
frequencies over shared cable
distribution network
CMTS
cable modem
termination system
ISP
 HFC: hybrid fiber coax




Fiber from cable head end to neighborhood level junctions
Coaxial cable to house
Special cable modems used through ethernet port
asymmetric: up to 30Mbps downstream, 2 Mbps upstream
Introduction
1-20
Residential access: cable networks
 network of cable and fiber attaches homes to ISP router




homes share access to router
Every packet sent by head end travels to every link to every
home
unlike DSL, which has dedicated access to central office
Need shared distributed multiple-access protocol to
coordinate upstream transmissions and avoid collisions
Introduction
1-21
Residential access: cable networks
Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
Introduction
1-22
Cable Network Architecture: Overview
Typically 500 to 5,000 homes
cable headend
cable distribution
network (simplified)
home
Introduction
1-23
Cable Network Architecture: Overview
server(s)
cable headend
cable distribution
network
home
Introduction
1-24
Cable Network Architecture: Overview
cable headend
cable distribution
network (simplified)
home
Introduction
1-25
Access net: home network
wireless
devices
to/from headend or
central office
often combined
in single box
cable or DSL modem
wireless access
point (54 Mbps)
router, firewall, NAT
wired Ethernet (100 Mbps)
Introduction
1-26
Cable Network Architecture: Overview
FDM (more shortly):
Frequency-division multiplexing
different channels transmitted
in different frequency bands
cable headend
…
cable splitter
modem
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Channels
Introduction
1-27
Fiber to the HomeFTTH
Verizon PON
(passive optical
network)
Internet
OLT
OLT: optical
line terminator
central office (CO)
ONT
optical
fibers
ONT
optical
fiber
optical
splitter
Splitter replicates every
packet on every line
ONT
 Optical links from central office to the home
 Two competing optical technologies:


ONT: optical
network terminator
Passive Optical network (PON)
Active Optical Network (PAN) (like ethernet: see chap 5)
 Much higher Internet rates; fiber also carries television and
phone services (10-20Mbps download; 2-10 up)
Ethernet Internet access
Typically use
twisted-pair
copper wire
institutional link to
ISP (Internet)
institutional router
Ethernet
switch
institutional mail,
web servers
 Typically used in companies, universities, etc
 10 Mbs, 100Mbps, 1Gbps, 10Gbps, 100Gbps Ethernet
 Today, end systems typically connect into Ethernet
switch
Wireless access networks (chap 6)
 shared wireless access
network connects end system
to router

via base station aka “access
point”
 wireless LANs:
 802.11b/g (WiFi): 11 or 54 Mbps
 within building (100 ft)
router
base
station
mobile
hosts
Introduction
1-30
Wireless access networks (chap 6)
 wider-area wireless access
 provided by telco operator
 1-10Mbps over cellular system
(EVDO, HSDPA)
 3G (third generation) wireless:
packet-switched wide-area
wireless.
4G (various technologies):
100Mbps up to 1Gbps
 LTE
router
base
station

mobile
hosts
Introduction
1-31
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
*Network Address Translator
wireless
laptops
wireless
access
point
Introduction
1-32
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
packet
transmission
delay
=
two packets,
L bits each
2 1
R: link transmission rate
host
time needed to
transmit L-bit
packet into link
=
L (bits)
R (bits/sec)
1-33
Physical Media
 Bit: propagates between
transmitter/rcvr pairs
 physical link: what lies
between transmitter &
receiver
 Physical propagation is by
electromagnetic waves or
optical pulses
 Can use various types of
physical medium in one
network
 guided media:
 signals propagate in
solid media: copper,
fiber, coax
 unguided media:
 signals propagate
freely, e.g.,
Introduction
1-34
Physical Media costs
 Labor cost: (installing physical medium) orders of
magnitude higher than medium itself.
 Medium cost: varies by medium.

Several types often installed in case needed in future.
Introduction
1-35
Physical Media
Twisted Pair (TP)
 Least expensive physical
medium
 Also used for phone lines
(shielded)
 two insulated twisted copper wires
 Internet access over
Category 3: traditional phone wires,
telephone wires use
10 Mbps Ethernet
twisted pair
Category 5 UTP:
1Gbps Ethernet up to 100 meters
 UTP: unshielded twisted
Category 6 UTP: 10Gbps
pair; often used in LANs
Rates depend on thickness of the
wire and distance between
transmitter and receiver
Introduction
1-36
Physical Media: coax
Coaxial cable:
 two concentric copper
conductors

Coax is concentric, twisted pair is parallel
two conductors: the central
wire and the tubular shield
 bidirectional
 baseband:
 single channel on cable
 legacy Ethernet
 broadband:
 multiple channels on cable
 HFC
RG-59 flexible coaxial cable composed of:
A: outer plastic sheath
B: woven copper shield
C: inner dielectric insulator
D: copper-plated core
(image from wikipedia:
http://en.wikipedia.org/wiki/Coaxial_cable)
Introduction
1-37
Physical Media: fiber
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 Gps)
 low error rate: repeaters spaced far
apart ; immune to electromagnetic
noise
 Used in Internet backbone, longdistance telephone networks, overseas
links.
 Expensive.
Introduction
1-38
Physical media: radio
 signal carried in
electromagnetic
spectrum
 no physical “wire”,
penetrate walls
 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
 Geostationary versus low
altitude
Introduction
1-39