Transcript network

Chapter 4
Networking and
the Internet
Chapter 4: Networking and the
Internet
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4.1
4.2
4.3
4.4
4.5
Network Fundamentals
The Internet
The World Wide Web
Network Protocols
Security
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Network classifications
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Networks--Isolated computers can be
connected to work together via networking.
Classifications
Local area network (LAN) --on a single
building or a group of buildings. Such as
university campus, a manufacture plant, or
the like.
Wide area network (WAN)—one LANs can be
connected to other LANs over any distance
through telephone lines or radio waves.
Such as city.
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Network classifications
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Closed, or proprietary--held by an
individual corporation like Novell
networks.
Open--networks have the ownership in
the public domain like the Internet
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Network classifications
Characteristics of Network
 Topology—The geometric arrangement.
 Protocols:The rules and encoding
specifications for sending data.
 Media---Devices are connected by
twisted-pair wire, coaxial cables, or fiber
optics, or radio waves.
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Network topologies
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Ring
Bus
Star
Irregular
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Figure 4.1 Network topologies
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Figure 4.1 Network topologies (cont’d)
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Connecting networks
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Networked computers can be connected in a
hierarchical fashion as an internet.
DARPA (Defense Advanced Research
Projects Agency) initiated the Internet in
1973.
Interconnection of networks are achieved
through routers or proprietary
gateways(earlier terms for routers).
Bridge: connects two compatible networks
Router: connects two incompatible networks
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Resulting “network” is called an internet
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Figure 4.2 The distinction
between a bridge and a router
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Inter-process communication
Clients: a client makes requests to
servers.
 Servers: a server performs the service
and sends replies back to the client (s).
Ex:A machine with high-capacity disk
drive contains all the records of other
machine
(servers, the others—clients)
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Figure 4.3 The client/
server model
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Inter-process communication
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Inside the same machine, or among the
machines over the networks.
Client-server
 One server, many clients
 Server must execute continuously
 Client initiates communication
Peer-to-peer
 Two processes communicating as equals
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Figure 4.4 The client/server model compared
to the peer-to-peer-model
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Distributed systems
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Systems with parts that run on different
computers
Multiple independent computers
communicating over a network to accomplish
a common task
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Infrastructure usually provided by standardized
toolkits
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Example: Enterprise Java Beans from Sun Microsystems
Example: .NET framework from Microsoft
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1.
Which of the following is not a way of classifying networks?
A. WAN versus LAN
C. Router versus bridge
B. Closed versus open
D. Star versus bus
ANSWER:
2 Which of the following is not a means of performing interprocess communication
over a network?
A. Client/server
B. ICANN C. Peer-to-peer
ANSWER:
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The Internet
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The Internet: one internet spanning the
world
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Started by DARPA in 1973
Today involves millions of machines
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Internet Architecture
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Domain = network or internet controlled by
one organization
Gateway = router connecting a domain to the
cloud
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cloud = the rest of the internet
Domains must be registered by their owners
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Internet Corporation for Assigned Names &
Numbers (ICANN) serves as registrar
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Figure 4.5 A typical approach to connecting to
the Internet
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Strategies for connecting to the
Internet
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Large organization: buy a direct
connection
Small organization or individual: link
domain to the domain of an ISP
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ISP = Internet Service Provider
Individual: temporarily link computer
into ISP’s domain
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Internet Addressing: IP
Addresses
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IP address = 32 bit identifier for a machine
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Network identifier = part assigned by ICANN
Host address = part assigned by domain owner
Dotted decimal notation = standard for
displaying IP addresses
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Example: 192.207.177.133
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Internet addressing: host names
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Host name = mnemonic name
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Example: mymachine.aw.com
Domain name = part assigned by a registrar
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Example: aw.com
Top level domain = classification of domain owner
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By usage – Example: .com = commercial
By country – Example: .au = Australia
Subdomains and individual machine names
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Assigned by domain owner
Domain owner must run a name server
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Connecting networks
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InterNIC(Internet Network Information Center)
regulates the 32-bit address of domains and
thus each machine= network identifier (x-bit)
+ host address (32–x -bit).
The network identifier of the mnemonic
domain name“nthu.edu.tw” is “140.114”
determined globally,
while “nyx.cc”is “63.1”assigned locally by the
Computer Center of NTHU.⇒
The host machine “nyx.cc.nthu.edu.tw”has an
address “140.114.63.1”.
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Internet applications
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Electronic main (e-mail)
File Transfer Protocol (FTP)
Remote login: telnet, etc.
World Wide Web
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Electronic mail
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Mail server: set up by domain owner
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Mail sent from domain members goes
through mail server
Mail sent to domain members is collected
by mail server
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If the network identifier of a domain in the Internet is 115.48, how many unique
IP addresses are available for identifying machines within the domain?
A. 4096
B. 16,384
C. 32,768
D. 65,536
. Which of the following is not an application of the Internet?
A. FTP
B. Email
C. Telnet
D. RING
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World Wide Web
Atop the Internet, the WWW allows the propagation of
multimedia documents.
--The hypermedia documents consists of hypertexts:
texts, audiovisual contents, links.
 Server disseminates hypertext (or
hypermedia) documents
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Web site = all hypertext documents controlled by
one organization or individual
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Usually all at same internet address
HTML = language of hypertext documents
Other content can also be disseminated
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Example: images
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World Wide Web implementation
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Web server: provides access to documents on
its machine as requested
Browser: allows user to access web pages
Hypertext Transfer Protocol (HTTP):
communication protocol used by browsers
and web servers
Uniform Resource Locator (URL): unique
address of a document on the web
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Figure 4.6 A typical URL
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Hypertext document format
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Entire document is printable characters
Contains tags to control display
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Display appearance
Links to other documents and content
Dynamic functions
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Figure 4.7 A simple Web page
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Figure 4.7 A simple Web page (cont’d)
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Figure 4.8 An enhanced simple Web
page
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Figure 4.8 An enhanced simple Web
page (cont’d)
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Extensible Markup Language (XML)
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XML: a language for constructing
markup languages similar to HTML
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A descendant of SGML(Standard
Generalized Markup Language)
For math, multimedia, music and Web
pages
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Figure 4.9 The first two bars of
Beethoven’s Fifth Symphony
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Dynamic web pages(i.e. search)
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Client-side(specifies topic of interest)
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Examples: java applets, java script,
Macromedia Flash
Server-side(identifying documents)
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Common Gateway Interface (CGI)
Servlets—allow clients to execute programs
units in servers
PHP(personal home page)
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Network protocols: transmission control
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Token ring: one-way communication
around ring network
Ethernet:
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Uses carrier sense, multiple access with
collision detection (CSMA/CD)
Popular for bus networks
Like a conversation in small group
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Figure 4.10 Communication over a ring
network
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Figure 4.11 Communication over a bus
network
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Figure 4.12 Package-shipping example
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Figure 4.13 The Internet
software layers
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Figure 4.14 Following a message
through the Internet
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Internet software layers
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Application layer:
 Example: browser
Transport layer: TCP/IP, UDP
Network layer: handles routing through the internet
Link layer: handles actual transmission of packets
 Token ring or Ethernet
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Delivery of messages
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The transport layer takes the message from the application
layer, packages them with additional tags (50+bytes including
sequence #, …) into packets of a size compatible with the
beneath network layer, and hands over to the network layer.
The network layer will properly forward these packets to the
very network specified by the application layer.
The same prefix of both addresses ⇔on the same network.
Different ⇒the network layer appending the address of a router
in the current network sends the packets to that router. (maybe,
intermediate routers)
The link layer does the actual transmission between machines
and routers by local addressing system with additional wrapping.
⇒striped off at the message destination.
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TCP/IP Protocol Suite
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It is the network layer to determine the destination of the next
hop (network).
The routing table in the network layer contains the final
destination addresses and intermediate addresses. [NAT: IP
address vs. Link address]
The information in this table routinely exchanges and propagate
through the Internet.
Packets of the same message may travel along different paths.
Once all packets of the message are received (using sequence
#), the target transport layer hands it over to its application
layer. [complete delivery]
The response time of the Internet is rather instant in
milliseconds.
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TCP/IP Protocol Suite
The TCP/IP protocol suite defines a collection of protocols beside TCP and
IP.
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IP(Internet Protocol) defines the network layer service.
--Hop count, TTL (time to live, 64): decrement per hop forwarding,
avoiding circling.
TCP(Transmission Control Protocol) defines a reliable transport service.
--Two ends first build an acknowledged connection and confirms each
subsequent packet delivery in sequence.
UDP(User Datagram Protocol) defines a more efficient but less reliable
transport service.
One end sends the data merely to the destination address regardless of its
reception.
ISO (International Organization for Standardization) develops the OSI
(Open System Interconnection) reference model using 7 layers –
Application, Presentation, Session, Transport, Network, Data Link, &
Physical.
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Figure 4.15 Choosing between TCP
and UDP
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Which layer of the TCP/IP hierarchy actually transmits a message?
A. Application
B. Transport
C. Network
D. Link
Which layer of the TCP/IP hierarchy chops messages into units whose size is
compatible with the Internet?
A. Application
B. Transport
C. Network
D. Link
Which layer of the TCP/IP hierarchy decides the direction in which message
segments are transferred across the Internet?
A. Application
B. Transport
C. Network
D. Link
Which layer of the TCP/IP hierarchy presents incoming messages to the
computer user?
A. Application
B. Transport
C. Network
D. Link 49
Network security
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Connecting to the networks, a machine becomes
accessible to the general public.
Unauthorized access: attack on confidentiality.
Protection on personal information
Vandalism: malicious acts from hackers, computer
viruses, or network worms.
Computer Virus—a program segment that attaches itself to
other programs in computer systems.
Worms—an autonomous program that transfers itself
through a network, taking up residence in machines and
forwarding copies of itself through network.
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Network security
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Privacy of communication
 Public-key encryption
 Public key and private key: (asymmetric)
 A and B each have pairs of public key and private key: PA,
pA, and PB, pB.
--Private keys are held by individuals, while public keys are
known to the party.
 Authenticated receiver: (only B has pB to decrypt the
received data)
 Authenticated sender: (only A has pA to send that encrypted
data)
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Network security
Integrity of machine exposed to internet
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Attacks: viruses and worms
Defense: firewall
Firewall software that filters the traffic entering or
passing through a machine(network layer to reject
traffics from an entire domain or a specific IP)
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The primary purpose of which of the following is not the
enhancement of security?
A. ICANN
key
B. Firewall
C. Encryption
D. Public
Which of the following is not a means of referencing entities on the
Internet?
A. URL
Host address
B. IP address
C. Anonymous FTP
D.
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