CHAPTER 4
NETWORKING AND THE INTERNET
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Chapter 4: Networking and the
Internet
Network
The World
Fundamental The Internet
Wide Web
s
Internet Simple Client
Security
Protocols Server
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4.1 Network Fundamentals
• Network Software allows users to exchange information
and share resources
– Content
– Software
– Data storage facilities
• Network software has evolved into a network-wide
operating system
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Network Classifications
Scope
• Personal Area Network (short-range)
• Local Area Network (building/campus)
• Metropolitan Area Network (community)
• Wide Area Network (greater distances)
Ownership
• Closed versus open
Topology (configuration)
• Bus (Ethernet)
• Star (Wireless networks with central Access Point)
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Figure 4.1 Two popular network topologies
(1 of 2)
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Protocols
• Rules by which activities are conducted on a network
– Example: Coordinating the transmission of
messages between computers
• Need to avoid all machines transmitting at the
same time
• Allows vendors to build products that are compatible
with products from other vendors
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Protocols for Transmitting Messages
• CSMA/Collision Detection
– used in Ethernet
– both machines stop and wait for a independent, random
time
• CSMA/Collision Avoidance
– used in WiFi, where not all machines can hear each other
(hidden terminal problem)
– give advantage to the machine that has already been
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waiting 8
Figure 4.2 Communication over a bus
network
Combining Networks
• Repeater: passes all messages across two busses
• Bridge: passes only messages that are destined for
computers on the other bus
• Switch: acts like a bridge, but with connections to
multiple busses
• Router: Connects two incompatible networks
resulting in a network of networks called an
internet
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Methods of Process Communication
• Client-server
– Many clients, one server (executing continuously)
– Clients make requests of other processes
– Server satisfies requests made by clients
• Peer-to-peer (P2P)
– Two processes communicating as equals
– Processes execute on a temporary basis
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Figure 4.6 The client/server model
compared to the peer-to-peer model
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Distributed Systems
• Systems units that execute as processes on different computers
– Cluster computing
• Independent computers work closely together instead of a
single, much larger machine
– Grid computing
• Millions of home PCs (not connected to each other) work
on a complex problem
– Cloud computing
• Provide services, hide the details
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4.2 The Internet
• The Internet is an internet that spans the world
– Original goal was to link a variety of networks into a
connected system unaffected by local disasters
– Today, it is a commercial undertaking that links a
worldwide combination of PANs, LANs, MANs, and
WANs involving millions of computers
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Internet Architecture
• Internet Service Provider (ISP)
– Tier-1 (Internet backbone)
– Tier-2
• Access or Tier-3 ISP: Provides connectivity to the Internet
– Hot spot (wireless)
– Telephone lines
– Cellular
– Cable/Satellite systems
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Internet Addressing
• IP address: pattern of 32 or 128 bits often represented in dotted
decimal notation
• Mnemonic address:
– Domain names (mu.edu)
– Top-Level Domains
• .org, .gov, .com, .mil, .net, .au, .ca, .biz, ….
• Domain name system (DNS)
– Name servers
– DNS lookup
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Internet Corporation for Assigned
Names & Numbers (ICANN)
Allocates blocks of IP addresses to ISPs who then
assign those addresses within their regions.
Oversees the registration of domains and domain
names.
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More Recent Applications
Voice Over IP (VoIP) Internet Multimedia
Streaming
N-unicast
Multicast
On-demand streaming
Content delivery networks (CDNs)
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4.3 World Wide Web
Hypertext combines internet
Embeds hyperlinks to other
technology with concept of documents
linked-documents
Browsers present materials to the user
Webservers provide access to documents
Documents are identified by URLs and transferred using HTTP
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Figure 4.8 A typical URL
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Figure 4.9 A simple webpage
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Extensible Markup Language (XML)
• XML: A language for constructing markup languages
similar to HTML
• A descendant of the Standard Generalized Markup
Language
• Opens door to a World Wide Semantic Web
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Figure 4.11 The first two bars of
Beethoven’s Fifth Symphony
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Client Side Versus Server Side
Client-side activities (browser)
• Javascript
• Java applets
• Macromedia Flash
Server-side activities (webserver)
• Common Gateway Interface (CGI)
• Servlets
• JavaServer Pages (JSP) / Active Server Pages (ASP)
• PHP
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4.4 Internet Protocols
Control how messages are transferred over the
Internet
This software must reside on every computer in the
Internet
Accomplished by a multi-level hierarchy
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Figure 4.12 Package-shipping example
Internet Software Layers
Application: Constructs message with address
Transport: Chops message into packets
Network: Handles routing through the Internet
Link: Handles actual transmission of packets
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TCP/IP Protocol Suite
Transport Layer Network Layer
Transmission Control Protocol (TCP) Internet Protocol (IP)
User Datagram Protocol (UDP) • IPv4
• IPv6
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Figure 4.15 Choosing between TCP
and UDP
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4.5 Simple Client Server Program
• Socket: an abstraction for processes at the application
layer to connect to the network via the transport layer
– Needs to know
• Source Address name (localhost)
• Source Port number(1023…65535)
• Destination Address
• Destination Port number
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4.6 Cybersecurity
• Forms of Attack
– Malware (viruses, worms, Trojan horses, spyware, phishing software)
– Denial of service (DoS)
– Spam (common medium for delivering malware)
• Protection and Cures
– Firewalls
– Spam filters
– Proxy Servers
– Antivirus software
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Cryptography
HTTPS for secure Internet access
Public key: Used to encrypt
Public-key Encryption messages
(asymmetric) Private key: Used to decrypt
messages
Trusted to maintain lists of public
keys
Certificate Authorities Provide Certificates to clients
containing a party’s name and its
public key
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Thank you
Dr AlRAWI musabalrawi@halic www.halic.edu.tr
.edu.tr
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