Transcript File

Computer Networks
and the Internet
1-1
Overview
1. Physical Media
2. Switching: Circuit vs. Packet
3. Internet:Edge, Core
4. Network Performance Measures: Delay, Loss, Throughput
5. Protocol Layers
6. Network Security
7. History
Note: This class lecture is based on Chapter 1 of the textbook
(Kurose and Ross) and the slides provided by the authors.
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What is a Network?
q
Network: Enables data transfer among nodes
q Generally heterogeneous nodes
q More than 2 nodes
q E.g., Your home or office network
Server
Server
q
Communication: Two nodes.
q Link level electrical issues.
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Key Concepts
Server
Server
q
q
q
q
q
q
q
End Systems: Systems that are sinks or sources of data, e.g.,
Desktops, Laptops, Servers, Printers, Cell Phones, etc.
Intermediate Systems: Systems that forward/switch data from
one link to another, e.g., routers, switches
Hosts: End Systems
Gateways: Routers
Servers: End Systems that provide service, e.g., print server,
storage server, Mail server, etc.
Clients: End systems that request service
Links: Connect the systems.
Characterized by transmission rate, propagation delay
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Transmission Media
Guided:
q Twisted Pair
q Coaxial cable
q Optical fiber
q Unguided:
q Microwave
q Satellite
q Wireless
q
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Twisted Pair (TP)
Twists decrease the cross-talk
q Neighboring pairs have different twist length
q Most of telephone and network wiring in homes and
offices is TP.
q
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Shielded and Unshielded TP
q
q
Shielded Twisted Pair (STP)
q Metal braid or sheathing that reduces interference
q More expensive
q Harder to handle (thick, heavy)
q Used in token rings
Unshielded Twisted Pair (UTP)
q Ordinary telephone wire
q Cheap, Flexible
 Easiest to install
q No shielding
 Suffers from external interference
q Used in Telephone and Ethernet
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UTP Categories
q
q
q
q
Cat 3
q Up to 16MHz
q Voice grade found in most offices
q Twist length of 7.5 cm to 10 cm
Cat 4
q Up to 20 MHz. Not used much in practice.
Cat 5
q Up to 100MHz
q Used in 10 Mbps and 100 Mbps Ethernet
q Twist length 0.6 cm to 0.85 cm
Cat 5E (Enhanced), Cat 6, Cat 7, …
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Coaxial Cable
Higher bandwidth than UTP. Up to 500 MHz.
q Used in cable TV
q
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Optical Fiber
q
q
q
q
q
A cylindrical mirror is formed by the cladding
The light wave propagate by continuous reflection in the fiber
Not affected by external interference  low bit error rate
Fiber is used in all long-haul or high-speed communication
Infrared light is used in communication
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Multiplexing
q
q
How multiple users can share a link?
Time Division Multiplexing (TDM)
Frequency
1 2 3 4 5 6 7 8
q
Frequency Division Multiplexing (FDM)
1
2
3
4
5
6
7
8
Frequency
q
Time
Time
Other multiplexing methods will be covered as needed.
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Types of Networks
q
Point to point vs Broadcast
Point-to-Point
q
Bus
Circuit switched vs packet switched
Star
q Circuit:
Bits repeated at every switch along the
circuit path
q Packet: Packets are forwarded
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Circuit vs. Packet Switching
Circuit Switching
Call setup
Required
Overhead during call Minimal
State
Stateful
Resource Reservation Easy
Quality of Service
Easy
Sharing
By overbooking
q
Packet Switching
Optional
Per packet overhead
No state
Difficult
Difficult
Easy
Myth: Circuits require dedicated resources
 No sharing
True only for constant bit rate (CBR) circuits
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Types of Networks (Cont)
q
q
q
Enterprise vs Telecom Networks
Ethernet is the most common interface in Enterprise
Frame relay and ATM are common in Telecom Networks
Local Area Networks (LAN) 0-2 km, Single Ownership
Metropolitan Area Networks (MAN) 2-50 km,
Wide Area Networks (WAN) 50+ km
q Originally LAN/MAN/WAN technologies were different
q Now they are all same
Telecom Networks:
q Access: Between subscriber and the service provider
q Metro: Covering a city
q Core: Between cities
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Homework 1A
q
1.
2.
3.
Which networking media will you use for the
following applications and why?
Very large file transfer at home
High-speed multiple channel video transmission at
office
News reading while traveling in a car
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What is Internet?
Net 1
Net 3
Net 2
q
q
q
Internet = Network connecting networks
Approximately 600 million hosts on Internet in July 2008.
ISP: Internet Service Provider.
q Provide access to Internet.
q Telecommunications (Telephone) Companies, AT&T,
Verizon, Comcast, ...
q Coffee Shops (Wi-Fi)
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Structure of the Internet
Enterprise
Networks
Access
Networks
Core
Networks
Enterprise/Home Networks: Stub Networks.
Privately owned  Not owned by ISP.
q Access Network: Enterprise to ISP
q Core Network: ISP's network
q
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Types of ISPs
Tier 1
…
Tier 2
Tier 3
…
Tier 1
Tier 3
…
Tier 2
Tier 3
…
Tier 3
Tier 2
Tier 3
…
Tier 3
Tier 1: Global or National, e.g., AT&T, Verizon, …
q Tier 2: Regional
q Tier 3: Local
q
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Network Edge: Enterprise Networks
1.
2.
Ethernet
Wi-Fi
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Ethernet
Uses UTP (Unshielded Twisted Pair)
q 10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps
q Originally bus, now point-to-point (Star) topology
q
Switch
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Wi-Fi
IEEE 802.11
q Uses 2.4 GHz and 5.8 GHz
q
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Access Networks
1.
2.
3.
4.
5.
6.
Dial Up
DSL
Cable
Fiber-To-The-Home
Wi-Fi
WiMAX
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Dial Up
Central
Office
Home PC
ISP’s
Network
Telephone
Network
Modem
Modems
Modem (Modulator/Demodulator) convert electrical
bits to sound waveforms for transmission over
telephone network
q Telephone network designed to carry 4 kHz voice
q Up to 56 kbps
q Does not need much help from the phone company
q
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DSL
q
q
Digital Subscriber Line (DSL)
Can transmit very high data rates on phone wire using special
equipment at the phone company allowing higher frequency
signals
High-Speed
Network
Home PC
q
q
DSL
Modem
DSLAM
ISP’s
Network
Phone
Company
DSL Access Multiplexer (DSLAM)
100 kbps - 100 Mbps
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Cable
Cable companies have a very-high speed
medium (for video transmission)
q Phone wire = 4kHz for voice
Video Cable = 500 MHz for video
One TV Channel = 6 MHz
q 30 Mbps down/1 Mbps up
q Fiber in the main line + Coax in tributaries
 Hybrid Fiber Coax (HFC)
q
Cable
Modem
Home 1 Home 2 Home 3 Home 4
Cable
Company Fiber
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Fiber-To-The-Home (FTTH)
Services
Internet/Ethernet
Optical
Distribution
Network
Leased Line T1/E1
Optical
Frame/Cell Relay
Line
Telephone Terminal
ONU
Interactive Video
Splitter
q
q
q
100+ Mbps per home. Multiple services.
No electronic components in the distribution system
 Passive  Reliable
Passive Optical Network (PON)
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Wireless Access Networks
Wi-Fi hot spots
q Cellular access
q WiMAX
q
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WiMAX
Point to Multipoint
<50km
Point to Point
Telco Core
Base Stations (BSs)
Uplink (UL)
Downlink (DL)
(Rural Areas)
<120km/sec
(Mobile Users)
Subscriber Station (SSs) <70Mbps
(Congested Areas)
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Protocol Layers
q
Problem: Philosophers in different countries speak different
languages. The Telex system works only with English.
I believe there is a God!
Philosopher
Translator
Secretary
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ISO/OSI Reference Model
3
2
1
Application
Presentation
Session
Transport
Network
Datalink
Physical
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File transfer, Email, Remote Login
ASCII Text, Sound
Establish/manage connection
End-to-end communication: TCP
Routing, Addressing: IP
Two party communication: Ethernet
How to transmit signal: Coding
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Service and Protocol Data Units
Application 1
Application 2
Application 1
Application 2
SDU
Transport
PDU
Network
Access
Transport
Network
Access
Service Access Points (SAPs)
q Service Data Units (SDUs)
q Protocol Data Units (PDUs)
q
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Service Data Unit (SDU)
Application
PSDU
Presentation
SSDU
Session
TSDU
Transport
NSDU
Network
DSDU
Datalink
PhSDU
Physical
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Protocol Data Unit (PDU)
Application
Presentation
Session
Transport
Network
Datalink
Physical
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APDU, Message
PPDU
SPDU
TPDU
NPDU, Packet
DPDU, Frame
PhPDU, Frame
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Application
Presentation
Session
Transport
Network
Datalink
Physical
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Service Primitives
q
Indication = Interrupt
Higher Layer
1
Higher Layer
4
3
Lower Layer
1. Request
2. Indication
2
Lower Layer
3. Response
4. Confirm
Unconfirmed service: No confirmation or response
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TCP/IP Reference Model
TCP = Transport Control Protocol
q IP = Internet Protocol (Routing)
q
TCP/IP Ref Model
Application
Transport
TCP/IP Protocols
FTP
Telnet HTTP
TCP
UDP
Internetwork
IP
Host to
Network
Ether Point-to- Packet
net
Point Radio
Physical
Coax Fiber Wireless
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OSI vs TCP/IP
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OSI vs TCP Reference Models
OSI introduced concept of services, interface,
protocols. These were force-fitted to TCP later
 It is not easy to replace protocols in TCP.
q In OSI, reference model was done before protocols.
In TCP, protocols were done before the model
q OSI: Standardize first, build later
TCP: Build first, standardize later
q OSI took too long to standardize.
TCP/IP was already in wide use by the time.
q OSI became too complex.
q TCP/IP is not general. Ad hoc.
q
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PDUs in TCP/IP Architecture
User Data
Sub-network Header
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Application
Byte Stream
TCP
Segment
TCP Header
User Data
IP Header TCP Header
User Data
IP
Datagram
IP Header TCP Header
User Data
Subnetwork
Packet
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TCP/IP Applications
MIME
BGP
FTP
urrr
SMTP
TELNET
SNMP
TCP
UDP
ICMP
IGMP
OSPF
RSVP
IP
= Border Gateway Protocol
= �Tra.nsl'u Prot0<0I
HTrP = Hypertext Transfer Protocol
ICl\lP = Internet Control .\Iossa� Protocol
IC.\1P = Internet Croup .\bna�ment Protocol
IP
= Intereet Protocol
"101£ = Multi·Purpose Internet Mail Extension
BCP
FTP
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OSPF' = Open Sborteot Path F'ir.,t
RSVP = R.sourtt ReSu\'atlon Protocol
SMTP
Simple Mail Transfer Protocol
S1'".\IP = Simple '.'iet>1ork Managemmt Protocol
TCP
= Transmission Control Protocol
UDP = u- Datagnom Protocol
=
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Network Security
Security Components
q Types of Malware
q Types of Attacks
q Buffer Overflows
q Distributed DoS Attacks
q
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Security Components
Confidentiality: Need access control, Cryptography,
Existence of data
q Integrity: No change, content, source, prevention
mechanisms, detection mechanisms
q Availability: Denial of service attacks,
q Confidentiality, Integrity and Availability (CIA)
q
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Types of Malware
q
q
q
q
q
q
q
q
Viruses: Code that attaches itself to programs, disks, or
memory to propagate itself.
Worms: Installs copies of itself on other machines on a
network, e.g., by finding user names and passwords
Trojan horses: Pretend to be a utility. Convince users to install
on PC.
Spyware: Collect personal information
Hoax: Use emotion to propagate, e.g., child's last wish.
Trap Door: Undocumented entry point for debugging purposes
Logic Bomb: Instructions that trigger on some event in the
future
Zombie: Malicious instructions that can be triggered remotely.
The attacks seem to come from other victims.
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Types of Attacks
Denial of Service (DoS): Flooding with
traffic/requests
q Buffer Overflows: Error in system programs. Allows
hacker to insert his code in to a program.
q Malware
q Brute Force: Try all passwords.
q Port Scanning:
 Disable unnecessary services and close ports
q Network Mapping
q
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Buffer Overflows
Return address are saved on the top of stack.
q Parameters are then saved on the stack.
q Writing data on stack causes stack overflow.
q Return the program control to a code segment written
by the hacker.
q
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Distributed DoS Attacks
q
q
q
q
Tribe Flood Network (TFN) clients are installed on
compromised hosts.
All clients start a simultaneous DoS attack on a victim on a
trigger from the attacker.
Trinoo attack works similarly. Use UDP packets. Trinoo client
report to Trinoo master when the system comes up.
Stacheldraht uses handlers on compromised hosts to receive
encrypted commands from the attacker.
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History of Internet
1961: Kleinrock developed queueing
theory. Showed effectiveness of
packet-switching
q 1964: Baran’s report on packet-switching
in military nets
q 1967: ARPAnet conceived by Advanced Research
Projects Agency
q 1969: First ARPAnet node operational
First Request for Comment (RFC)
www.ietf.org
q
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Internet Generations
q
Internet 1.0 (1969 – 1989)
q
q
q
q
q
Single ownership  Trust
complete knowledge
Algorithmic optimality  RIP
Users
Users
Hosts
Hosts
IMPs
Internet 2.0(1989–2009) Commerce
Users
q Multiple ownership of infrastructure
 Distrust, Security
Hosts
q No knowledge of internal topology
and resources
A
B
q Policy based routing  BGP
Internet 3.0(2009–2029) Commerce
Users/Data A
q Users, Content, Host ownership
Hosts
q Requirements, Service Negotiation
A
Infras.
q Mobility of users and distributed data
A
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IMPs
Users
Hosts
C
D
B
B
C
C
D
D
B
C
D
©2011 Raj Jain
History of Internet (Cont)
q Early
1990s: HTML, HTTP: Berners-Lee
q 1994: Mosaic, later Netscape
q
2007:
q ~500 million hosts
q Voice, Video over IP
q P2P applications: BitTorrent (file sharing) Skype
(VoIP), PPLive (video)
q Video applications: YouTube, gaming
q Wireless, Mobility
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Key Concepts
Internet Protocol (IP): Protocol
q Address: All systems have an IP address, for example,
125.36.47.23
q Name: All systems have a human readable name, e.g.,
scorpio.cec.wustl.edu, ibm.com.
q Technically called DNS (domain name systems)
name. Details will be introduced later.
q IETF: Internet Engineering Task Force. Make
standards for Internet. IETF.org
q RFC: Request for comments. Documents that describe
Internet protocols.
q
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Homework 1C
Find the IP address of your computer
2. Find the IP address of www.google.com (different
from google.com)
3. Measure delay from your computer to
www.google.com
For all cases submit the screen snapshot showing the
command used and the output. (Use Alt-Print-screen
to capture a window to clipboard and then paste to
word)
1.
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