This document provides an overview of computer networks. It defines a network as consisting of two or more connected computers that can share resources and information. Networks allow sharing of hardware, software, files and administration. There are different types of networks classified by transmission medium (wired vs wireless), size (LAN, WAN, MAN), management (peer-to-peer, client/server), and topology. Common transmission media are twisted pair cables, coaxial cables, and fiber optic cables. Local area networks connect computers within a building while wide area networks connect locations further apart like across cities. Protocols like TCP/IP and domains names are used to transmit data packets across interconnected networks.

1. 1
Networks and
Telecommunications

2. 2

3. 3
What is a Network?
A network consists of 2 or more computers
connected together, and they can communicate and
share resources (information)

4. 4
Why Networking?
• Sharing information
- Do you prefer these?
- Or this?

5. After
• Sharing hardware or software
Before
E.g. print document

6. 6
• Centralize administration and support
- E.g. Internet-based, so everyone can access the same
administrative or support application from their PCs

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How many kinds of Networks?
• We can classify networks in different ways
• Based on transmission media: Wired (twisted-
pair cables, coaxial cables, fiber-optic cables)
and Wireless
• Based on network size: LAN and WAN (and
MAN)
• Based on management method: Peer-to-peer
and Client/Server
• Based on topology (connectivity): Bus, Star,
Ring …

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Two main categories:
– Guided ― wires, cables
• Twisted-Pair cables
• Coaxial cables
• Fiber-optic cables
– Unguided ― wireless transmission, e.g. radio,
microwave, infrared, sound
Transmission Media

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Coaxial Cables
Twisted-Pair Cables
Fiber-Optic Cables
They are cheap and easy to install
and use. However these cables easily
pick up noise signals
They are highly resistant
to signal interference

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Type of connection
Bandwidth,
bits per second
(bps)
Speed
Twisted-Pair Cables
2 000 0000-
100 000 000 low
Coaxial Cables
200 000 000-
500 000 000 high
Fiber optic cable >1000 000 0000 absolute

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Advantages and Disadvantages
 Noise resistance ― external light is blocked by outer
jacket
 Less signal attenuation ― a signal can run for miles
without regeneration
 Higher bandwidth ― currently, limits on data rates come
from the signal generation/reception technology, not the
fiber itself
 Cost ― Optical fibers are expensive
 Installation/maintenance ― any crack in the core will
degrade the signal, and all connections must be perfectly
aligned
Fiber-Optic Cables

12. • Local Area Network – LAN
• Wide Area Network – WAN
• Metropolitan Area Network - MAN
(on the territorial grounds)

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LAN and WAN
• Local Area Network (LAN)
• Small network, short distance
• A room, a floor, a building
• Limited by no of computers and distance covered
• Usually one kind of technology throughout the LAN
• Serve a department within an organization
• Examples:
• Network inside the Student Computer Room
• Network inside your company

14. Mbit / s.
Coaxial cable, Twisted pair,
Fiber optic cable
LAN
high data rate ≈ 100 Mbit / s

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• Wide Area Network (WAN)
• A network that uses long-range telecommunication links
to connect 2 or more LANs/computers housed in different
places far apart.
• Towns, states, countries
• Example:
• Internet
WAN
Student
Computer
Centre
Your
company
Kazakhstan

17. The Internet is the global system of
interconnected computer networks that
use the Internet protocol suite (TCP/IP) to
link billions of devices worldwide. It is a
network of networks that consists of
millions of private, public, academic,
business, and government networks of
local to global scope.

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Example of WAN: Broadband Cable Network
• Cable TV services have been extensively developed in most
modern cities
• Cable TV companies try to make use of their coaxial cable
installed to deliver broadband data services
• Many cable network wiring has been replaced with hybrid
fiber-coax (HFC) ― i.e. use of fiber-optic cable to connect to
the subscribers’ buildings, and then the coaxial cable to
connect to each household

19. The connection is shared by a
number of subscribers, hence
may raise performance and
security problems
Cable company
Coaxial
Cable
TV
PC
Cable
Drop

20. 20
• Cable is an asymmetrical technology
• Downstream: max 36 Mbps
• Upstream: max 10 Mbps
• Need a special cable modem
Ethernet
link to PC
Coaxial link
from cable TV
socket

21. (MAN)
Metropolitan Area Network, a data network designed for a town or city. MANs are larger than
LANs, but smaller than WANs. MANs are usually characterized by very high-speed connections
using fiber optical cable or other digital media.

22. Internet Connections
There are various technologies available that you can use
to connect a home computer to the Internet
– A phone modem converts computer data into an
analog audio signal for transfer over a telephone
line, and then a modem at the destination converts it
back again into data
– A digital subscriber line (DSL) uses regular
copper phone lines to transfer digital data to and
from the phone company’s central office
– A cable modem uses the same line that your cable
TV signals come in on to transfer the data back and
forth

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Peer-to-Peer Networks
• Peer-to-peer network is also called workgroup
• No hierarchy among computers  all are equal
• No administrator responsible for the network
Peer-to-peer

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• Advantages of peer-to-peer networks:
• Low cost
• Simple to configure
• User has full accessibility of the computer
• Disadvantages of peer-to-peer networks:
• May have duplication in resources
• Difficult to uphold security policy
• Difficult to handle uneven loading
• Where peer-to-peer network is appropriate:
• 10 or less users
• No specialized services required
• Security is not an issue
• Only limited growth in the future

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Clients and Servers
• Network Clients (Workstation)
• Computers that request network resources or services
• Network Servers
• Computers that manage and provide network resources
and services to clients
• Usually have more processing power, memory and
hard disk space than clients
• Run Network Operating System that can manage not
only data, but also users, groups, security, and
applications on the network
• Servers often have a more stringent requirement on its
performance and reliability

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• Advantages of client/server networks
• Facilitate resource sharing – centrally administrate and
control
• Facilitate system backup and improve fault tolerance
• Enhance security – only administrator can have access
to Server
• Support more users – difficult to achieve with peer-to-
peer networks
• Disadvantages of client/server networks
• High cost for Servers
• Need expert to configure the network

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Topology ― 3 basic types
• How so many computers are connected together?
Bus Topology Ring Topology
Star Topology
Hub

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• Bus Topology
• Simple and low-cost
• A single cable called a trunk (backbone, segment)
• Only one computer can send messages at a time
• Passive topology - computer only listen for, not
regenerate data
• Star Topology
• Each computer has a cable connected to a single point
• More cabling, hence higher cost
• All signals transmission through the hub
• Depending on the intelligence of hub, two or more
computers may send message at the same time

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How to construct a network
with Bus / Star Topology?
Star Topology
Bus Topology
BNC T-Connector
Coaxial
cable
Network Card

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• Ring Topology
• Every computer serves as
a repeater to boost signals
• Typical way to send data:
• Token passing
• only the computer who
gets the token can send
data
• Disadvantages
• Difficult to add computers
• More expensive
• If one computer fails, whole network fails
T
T
T
data
T
data
T
data
T data T data
T data
T Ack
T Ack
T Ack
T
Ack T

31. Packet Switching
• To improve the efficiency of transferring information over
a shared communication line, messages are divided into
fixed-sized, numbered packets
• Network devices called routers are used to direct
packets between networks

32. Internet, Packets and Routing
At the sender, data is broken into packets
and sent to the nearest node (router)
At each router, it sends the packet to
another router that is closer to the final
destination
At the receiver, packets are reassembled
to get the original data
A simple analogy: mailing system

33. Mailing System
A B
Admin Admin

34. OSI (Open Systems Interconnection) model
• The International
Organization for
Standardization (ISO)
established the Open
Systems
Interconnection (OSI)
Reference Model
• Each layer deals with a
particular aspect of
network communication

35. • Layer 7: Application - This is the layer that actually
interacts with the operating system or application
whenever the user chooses to transfer files, read
messages or perform other network-related activities.
• Layer 6: Presentation - Layer 6 takes the data provided
by the Application layer and converts it into a standard
format that the other layers can understand.
• Layer 5: Session - Layer 5 establishes, maintains and
ends communication with the receiving device.
Application Set
OSI

36. Transport Set
• Layer 4: Transport - This layer maintains flow control of data and
provides for error checking and recovery of data between the devices.
Flow control means that the Transport layer looks to see if data is coming
from more than one application and integrates each application's data into
a single stream for the physical network.
• Layer 3: Network - The way that the data will be sent to the recipient
device is determined in this layer. Logical protocols, routing and
addressing are handled here.
• Layer 2: Data - In this layer, the appropriate physical protocol is assigned
to the data. Also, the type of network and the packet sequencing is
defined.
• Layer 1: Physical - This is the level of the actual hardware. It defines the
physical characteristics of the network such as connections, voltage levels
and timing.
OSI

37. Network Protocols
• Network protocols are layered such that each
one relies on the protocols that underlie it
• Sometimes referred to as a protocol stack

38. TCP/IP
• TCP stands for Transmission Control
Protocol
TCP software breaks messages into packets, hands
them off to the IP software for delivery, and then
orders and reassembles the packets at their
destination
• IP stands for Internet Protocol
IP software deals with the routing of packets
through the maze of interconnected networks to
their final destination

39. TCP/IP and Domain Names
Basic task of IP – moving packets as quickly
as possible from one router to another
Yet, it doesn’t check whether packets are
delivered successfully, thus need TCP
TCP (Transmission Control Protocol) –
disassemble/reassemble packets, error
checking, ACK packets

40. High-Level Protocols
• Other protocols build on the foundation
established by the TCP/IP protocol suite
– Simple Mail Transfer Protocol (SMTP)
– File Transfer Protocol (FTP)
– Telnet
– Hyper Text Transfer Protocol (http)

41. Firewalls
• Firewall A machine and its software that serve
as a special gateway to a network, protecting it
from inappropriate access
– Filters the network traffic that comes in, checking
the validity of the messages as much as possible
and perhaps denying some messages altogether
– Enforces an organization’s access control policy

42. Firewalls

43. Network Addresses
Hostname - a unique identification that specifies
a particular computer on the Internet
For example
matisse.csc.villanova.edu
condor.develocorp.com
Network software translates a hostname into its
corresponding IP address
For example
205.39.145.18
Every host on the Internet has a unique IP address,
made up of four numbers. E.g.. 192.56.215.131,
each number is between 0 and 255

44. Network Addresses
• An IP address can be split into
– network address, which specifies a specific
network
– host number, which specifies a particular machine
in that network
Figure
An IP address is
stored in four
bytes

45. Domain Name System
• A hostname consists of the computer name
followed by the domain name
• csc.villanova.edu is the domain name
– A domain name is separated into two or more
sections that specify the organization, and possibly
a subset of an organization, of which the computer
is a part
– Two organizations can have a computer named the
same thing because the domain name makes it
clear which one is being referred to

46. The numbers in an IP address is hard to
remember, while names are easier
Domain Name System – a mapping
between the human-readable name (domain
name) of a host and its IP address
A domain name consists of two or more
parts, e.g. do.ektu.kz
The rightmost label conveys the top-level
domain, e.g. kz

47. Each label to the left specifies a
subdomain, in our example, subdomain is
ektu, and sub-subdomain is do.
A top-level domain contains of multiple
subdomains, each subdomain can contain
multiple sub-subdomain, so on.
Mapping between a domain name and an
IP address is stored on DNS server.

48. Domain Name System
• The very last section of the domain is called its
top-level domain (TLD) name

49. Domain Name System
• Organizations based in countries other than
the United States use a top-level domain that
corresponds to their two-letter country codes

50. Domain Name System
• The domain name system (DNS) is chiefly
used to translate hostnames into numeric IP
addresses
– DNS is an example of a distributed database
– If that server can resolve the hostname, it does so
– If not, that server asks another domain name server

51. 1 What is a computer network?
A Two or more computers connected together to exchange data and programs
B) A connection between keyboard and monitor
C) A group of computers that share the same power supply
D) A computer that is used by many different human users
E) A computer that can run many programs from its hard disk
2 Which unit network engineers describe network speeds?
A) bits per second
B) bits per minute
C) bytes per hour
D) LAN
E) Gigabytes
3 Which of the following devices is used for connecting to the network?
A) Graphic card
B) Sound card
C) CPU
D) Hard disk
E) Network card

52. 4 What of the following devices connects computers to one network?
A) CPU
B) Switch
C) Sound card
D) USB cable
E) Scanner
5 How is called World global network?
A) Intranet
B) Localhost
C) USB connection
D) Internet
E) Wi-Fi network
6 How is the set of rules called to make communications between the devices in
a network?
A) Bandwidth
B) Switch
C) Broadcast
D) Protocol
E) Package
52

53. 7 Which LAN topology connects all the workstations to a central point, using a hub
or switch?
A) All to all
B) Bus
C) Hierarchical
D) Ring
E) Star
8 What protocol is used for transferring web pages from server?
A) FTP
B) Telnet
C) HTTP
C) Gopher
E) Usenet
9 Which of extension below do web pages have?
A) .html
B) .java
C) .cpp
D) .doc
E) .xls
53

54. 10 The WWW is also called?
A) Multimedia
B) World Wide Learn
C) Virus
D) World Wide Web
E) Games
11 The World Wide Web allows text, pictures, sound and movies to be
displayed on the Internet user's screen, via a software called …
A) Multimedia
B) Utilities
C) Web Browsers
D) The Internet
E) Games
12 When WWW is began?
A) 1983
B) 1981
C) 1984
D) 1986
E) 1980
54

55. 13 The Internet was created for the U.S Department of Defense for military
communications purposes in …
A) 1966
B) 1967
C) 1968
D) 1969
E) 1970
14 Translates domain names to their IP addresses and vise versa.
A) FTP Server
B) Mail Server
C) Web Site
D) Domain Name Server
E) Web Browsers
15 How is the bandwidth described?
A) Bits per second
B) Bytes per second
C) Meter
D) Cost per meter
E) Byte
55

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57. A Visualization of Internet