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Lecture 4
Internet Basics
Namecheap Guidelines
Last update 20.08.2012

2. Internet Basics
ABOUT INTERNET
The Internet is a worldwide, publicly accessible network of interconnected computer networks that transmit data
by packet switching using the standard Internet Protocol (IP). It is a "network of networks" that consists of millions
of smaller domestic, academic, business, and government networks, which together carry various information and
services, such as electronic mail, online chat, file transfer, and the interlinked web pages and other documents of
the world wide web.
Fiber optic network infrastructure Internet network hierarchy
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3. Internet Basics
GLOBAL STRUCTURE OF THE NETWORK
Internet packet routing is accomplished among various tiers of Internet Service Providers
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4. Internet Basics
LOGICAL STRUCTURE OF THE NETWORK
Internet
Main
Server Main
Switch
Router
Workgroup
switch
Hub
Bridge
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5. Internet Basics
NETWORKING HARDWARE
HUB is a device for connecting multiple Ethernet devices together and making them act as a single network
segment. It has multiple input/output (I/O) ports, in which a signal introduced at the input of any port appears at the
output of every port except the original incoming.
BRIDGE is a network device used to allow two or more communication networks, or two or more network
segments creating an aggregate network. E.g. bridging your network connection is a handy method for sharing
your internet connection between two (or more) computers or networks.
SWITCH or switching hub is a networking device that connects network segments. It receives a message from any
device connected to it and then transmits the message only to the device for which the message was meant. This
makes the switch a more intelligent device than a hub.
ROUTER is a device that forwards data packets between computer networks, creating an overlay internetwork. A
router is connected to two or more data lines from different networks. When a data packet comes in on one of the
lines, the router reads the address information in the packet to determine its ultimate destination. Then, using
information in its routing table or routing policy, it directs the packet to the next network on its journey. Routers
perform the "traffic directing" functions on the Internet.
GATEWAY is an internetworking system capable of joining together two networks that use different base protocols.
A network gateway can be implemented completely in software, completely in hardware, or as a combination of
both. So gateway is a network point that acts as an entrance to another network.
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6. Internet Basics
CONNECTING TO THE INTERNET
To connect to the Internet, you need
-Computing device
-Connection device
-Internet Service Provider (ISP)
ISP is an organization that provides access to the Internet and can be either community-owned and non-profit,
or privately owned and for-profit
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7. Internet Basics
BANDWIDTH
BANDWIDTH in computer networking refers to the data rate supported by a
network connection or interface. One most commonly expresses bandwidth in
terms of bits per second (bps).
Bandwidth Access technologies Bandwidth Access technologies
56 kbit/s Modem / Dialup 155 Mbit/s OC3/STM-1
1.5 Mbit/s ADSL Lite 600 Mbit/s Wireless 802.11n
1.544 Mbit/s T1/DS1 622 Mbit/s OC12/STM-4
10 Mbit/s Ethernet 1 Gbit/s Gigabit Ethernet
11 Mbit/s Wireless 802.11b 2.5 Gbit/s OC48/STM-16
44.736 Mbit/s T3/DS3 9.6 Gbit/s OC192/STM-64
54 Mbit/s Wireless 802.11g 10 Gbit/s 10 Gigabit Ethernet
100 Mbit/s Fast Ethernet 100 Gbit/s 100 Gigabit Ethernet
One kilobit per second (Kbps) equals 1000 bits per second (bps).
(Note: Kbps is sometimes also written as “kbps” - both carry the same meaning.)
One megabit per second (Mbps) equals 1000 Kbps or one million bps.
One gigabit per second (Gbps) equals 1000 Mbps or one million Kbps or one billion bps.
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8. Internet Basics
THE WORLD WIDE WEB
The World Wide Web (abbreviated as WWW or W3 commonly known as the Web), is a
system of interlinked hypertext documents accessed via the Internet. With a web
browser, one can view web pages that may contain text, images, videos, and other
multimedia, and navigate between them via hyperlinks.
Web and the Internet are technically two different terms:
The Internet connects multiple computers and forms a network on which a computer can communicate with
another computer.
The Web is a way of accessing and sharing information over the Internet by using Web browsers.
WEB COMPONENTS
Web browser is a SW program that enables you to view and interact with various resources on the Web.
Web page is a document on the Web. It is a formatted text document that a Web browser can display.
Web site is one or more Web pages that reside on a single server.
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9. Internet Basics
HYPERTEXT TRANSFER PROTOCOL
The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed,
collaborative, hypermedia information systems.
HTTP functions as a request-response protocol in the client-server computing model. A web
browser, for example, may be the client and an application running on a computer hosting a
web site may be the server. The client submits an HTTP request message to the server.
The server, which provides resources such as HTML files and other content, or performs other functions on
behalf of the client, returns a response message to the client.
HTTP resources are identified and located on the network by Uniform Resource Identifiers (URIs).
URI is a string of characters used to identify a name or a resource.
URIs can be classified as locators (URLs), as names (URNs), or as both.
A uniform resource name (URN) functions like a person's name, while a
uniform resource locator (URL) resembles that person's street address.
In other words: the URN defines an item's identity, while the URL provides a
method for finding it.
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10. Internet Basics
HYPERTEXT TRANSFER PROTOCOL
Hyperlink (or link) is a reference to data that the reader can directly follow, or that is followed
automatically.
A hyperlink points to a whole document or to a specific element within a document.
http://www.microsoft.com/learning/default.asp
Element Description
http:// Indicates the protocol to be used to access a file
www Indicates that the Web site is on the World Wide Web
microsoft Indicates the name of the Web site
.com Indicates the type of domain
/learning Indicates the path to the document
/default.asp Indicates the name of the document
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11. Internet Basics
NETWORK ARCHITECTURE
The CLIENT/SERVER model is a computing model that acts as a
distributed application which partitions tasks or workloads between the
providers of a resource or service, called servers, and service requesters,
called clients.
Client side
Server side
Web Server Database Server
FTP Server Application Server
Print Server Proxy Server
Mail Server DNS Server
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12. Internet Basics
PROTOCOLS
The standard model for networking protocols and
distributed applications is the International Standard
Organization's Open System Interconnect
(ISO/OSI) model.
ISO/OSI model defines seven network layers
Control is passed from one layer to the next, starting at the application layer in one station, and
proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.
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13. Internet Basics
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14. Internet Basics
PROTOCOLS
Application (Layer 7) This layer supports application and end-user processes. Communication
partners are identified, quality of service is identified, user authentication and privacy are
considered, and any constraints on data syntax are identified. Everything at this layer is
application-specific. This layer provides application services for file transfers, e-mail, and other
network software services.
Presentation (Layer 6) This layer provides independence from differences in data
representation (e.g., encryption) by translating from application to network format, and vice
versa. This layer formats and encrypts data to be sent across a network, providing freedom
from compatibility problems. It is sometimes called the syntax layer.
Session (Layer 5) This layer establishes, manages and terminates connections between
applications. The session layer sets up, coordinates, and terminates conversations, exchanges,
and dialogues between the applications at each end. It deals with session and connection
coordination.
Transport (Layer 4) This layer provides transparent transfer of data between end systems, or
hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete
data transfer.
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15. Internet Basics
PROTOCOLS
Network (Layer 3) This layer provides switching and routing technologies, creating logical
paths, known as virtual circuits, for transmitting data from node to node. Routing and
forwarding are functions of this layer, as well as addressing, internetworking, error handling,
congestion control and packet sequencing.
Data Link (Layer 2) At this layer, data packets are encoded and decoded into bits. It furnishes
transmission protocol knowledge and management and handles errors in the physical layer,
flow control and frame synchronization. The data link layer is divided into two sublayers: The
Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sublayer
controls how a computer on the network gains access to the data and permission to transmit it.
The LLC layer controls frame synchronization, flow control and error checking.
Physical (Layer 1) This layer conveys the bit stream - electrical impulse, light or radio signal --
through the network at the electrical and mechanical level. It provides the hardware means of
sending and receiving data on a carrier, including defining cables, cards and physical aspects.
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16. Internet Basics
PROTOCOLS
So the end-to-end layers reside at the end-user devices only and consist of the Application, Presentation,
Session, and Transport Layers.
And the chained layers, Network, Data Link, and Physical, are the layers concerned with moving information
through a data network.
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17. Internet Basics
PROTOCOLS
The TCP/IP model or internet layering scheme and its relation to some common protocols
1. The link layer contains communication technologies for a local network.
2. The internet layer connects local networks, thus establishing internetworking.
3. The transport layer handles host-to-host communication.
4. The application layer contains all protocols for specific data communications services on a process-to-process level
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18. Internet Basics
NETWORK ADDRESSING
An Internet Protocol address (IP address) is a numerical label assigned to each
device (e.g., computer, printer) participating in a computer network that uses the
Internet Protocol for communication.
Two versions of the Internet Protocol (IP) are in use: IP Version 4 (IPv4) and IP Version 6 (IPv6)
IPv4 IPv6
September 1981 6 June 2012
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19. Internet Basics
NETWORK ADDRESSING
IPv4 uses 32-bit (four-byte) addresses, which limits the address space to
4,294,967,296 (232) addresses.
IPv4 addresses are canonically
IPv4 represented in dot-decimal notation,
which consists of 4 decimal numbers,
each ranging from 0 to 255, separated by
dots, e.g., 172.16.254.1.
Size of network Size of rest Number Addresses Start
Class End address
number bit field bit field of networks per network address
Class A 8 24 128 (27) 16,777,216 (224) 0.0.0.0 127.255.255.255
Class B 16 16 16,384 (214) 65,536 (216) 128.0.0.0 191.255.255.255
Class C 24 8 2,097,152 (221) 256 (28) 192.0.0.0 223.255.255.255
Class D (multicast) not defined not defined not defined not defined 224.0.0.0 239.255.255.255
Class E (reserved) not defined not defined not defined not defined 240.0.0.0 255.255.255.255
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20. Internet Basics
NETWORK ADDRESSING
IPv6 uses 128-bit addresses, allowing for 2128, or approximately 3.4×1038
addresses.
IPv6 addresses, as commonly displayed
IPv6 to users, consist of eight groups of four
hexadecimal digits separated by colons,
for example:
2001:0db8:85a3:0042:0000:8a2e:0370:7334
An IPv6 address may be abbreviated by using one or more of the following rules:
1. Remove leading zeroes from one or more groups of hexadecimal digits; this is normally done to all
groups that have leading zeroes. (For example, convert the group 0042 to 42.)
2. Combine consecutive sections of one or more zeroes, using a double colon (::) to denote the omitted
sections. The double colon may only be used once in any given address, as the address would be
indeterminate if it was used multiple times. (For example, 2001:db8::1:2 is valid, but 2001:db8::1::2 is not
permitted.)
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21. Internet Basics
NETWORK ADDRESSING
There are two methods to assigning IP addresses to computers:
DYNAMIC and STATIC.
Static IP addresses are used primarily for servers so that they don't appear to
"move" while non-servers are usually assigned dynamic IP addresses. Most
dynamic IP address users are users of internet service providers (ISPs) since
not all the users of an ISP are online at one time and the ISPs can "get away" with not having enough IP
addresses for each user.
Static IP addresses are manually assigned to a computer by an administrator.
Dynamic IP addresses are most frequently assigned on LANs and broadband networks by Dynamic Host
Configuration Protocol (DHCP) servers.
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22. Internet Basics
NETWORK PORTS
A NETWORK PORT is a number that identifies one
side of a connection between two computers.
Computers use port numbers to determine to which
process a message should be delivered.
As network addresses are like street address, port
numbers are like suite or room numbers.
PORT RANGES
0 - 1023 – Defaults for popular network services
1024 - 49151 – IANA reserved
49152 - 65535 – Dynamic or private ports
Port Description Port Description
20/21 File Transfer Protocol (FTP) 110 Post Office Protocol (POP3)
22 Secure Shell (SSH) 115 Simple File Transfer Protocol (SFTP)
23 Telnet remote login service 143 Internet Message Access Protocol (IMAP)
25 Simple Mail Transfer Protocol (SMTP) 443 HTTP Secure (HTTPS)
53 Domain Name System (DNS) service 993 IMAP over SSL (IMAPS)
80 Hypertext Transfer Protocol (HTTP) 995 POP3 over SSL (POP3S)
Any program may use any port, though some port numbers have a standard use and some programs may
be limited in which ports they can use for security reasons.
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23. Internet Basics
HTTP SESSION
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24. Internet Basics
HTTP STATUS CODES
The first digit of the status code specifies one of five classes of response:
1xx INFORMATIONAL
2xx SUCCESS
3xx REDIRECTION
4xx CLIENT ERROR
5xx SERVER ERROR
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25. Internet Basics
HTTP STATUS CODES
1xx INFORMATIONAL
100 CONTINUE
Client should continue with request
101 SWITCHING PROTOCOLS
Server is switching protocols
102 PROCESSING
Server has received and is processing the request
122 REQUEST-URI TOO LONG
URI is longer than a maximum of 2083 characters
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26. Internet Basics
HTTP STATUS CODES
2xx SUCCESS
200 OK
Standard response for successful HTTP requests
201 CREATED
Request has been fulfilled; new resource created
202 Accepted
Request accepted, processing pending
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27. Internet Basics
HTTP STATUS CODES
3xx REDIRECTION
301 MOVED PERMANENTLY
This and all future requests directed to the given URI
302 FOUND
Response to request found via alternative URI
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28. Internet Basics
HTTP STATUS CODES
4xx CLIENT ERROR
400 BAD REQUEST
Request cannot be fulfilled due to bad syntax
403 FORBIDDEN
Server refuses to respond to request
404 NOT FOUND
Requested resource could not be found
408 REQUEST TIMEOUT
Server timed out waiting for the request
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29. Internet Basics
HTTP STATUS CODES
5xx SERVER ERROR
500 INTERNAL SERVER ERROR
Generic error message
502 BAD GATEWAY
Server received an invalid response from upstream server
503 SERVICE UNAVAILABLE
Server is currently unavailable
504 GATEWAY TIMEOUT
Gateway did not receive response from upstream server
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30. Internet Basics
WELCOME TO OUR TEAM
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