This document discusses computer networks and their basic components. It begins by defining a computer network as a group of interconnected computers that allows sharing of resources and information. It then covers communication models including simplex, half-duplex and full-duplex transmission. The document also categorizes networks by scale, structure, topology and media. Finally, it discusses important network concepts such as internetworking, intranets and the development of the Internet.

4.  Computer Networks
 Communication Model
 Transmission Modes
 Communication Types
 Classification Of Computer Networks
 By Scale
 By Structure
 By Topology
 Network Media
 Internetworking

5.  A computer network is a group of interconnected computers.
 It allows computers to communicate with each other and to
share resources and information.
 First Network : The Advanced Research Projects Agency
(ARPA) funded the design of the "Advanced Research
Projects Agency Network" (ARPANET) for the United States
Department of Defense

7.  Source
 generates data to be transmitted
 Transmitter
 Converts data into transmittable signals
 Transmission System
 Carries data
 Receiver
 Converts received signal into data
 Destination
 Takes incoming data

9.  Simplex
 One direction
 e.g. Television
 Half duplex
 Either direction, but
only one way at a time
 e.g. police radio
 Full duplex
 Both directions at the
same time
 e.g. telephone

10.  Unicasting (one-to-one)
 Multicasting (one-to-many)
 Broadcasting (one-to-all)

11.  By Size or Scale
 LAN
 WAN
 MAN
 CAN
 PAN

12.  Contains printers, servers and computers
 Systems are close to each other
 Contained in one office or building
 Organizations often have several LANS

13.  Two or more LANs connected
 Over a large geographic area
 Typically use public or leased lines
 Phone lines
 Satellite
 The Internet is a WAN

14.  Large network that connects different
organizations
 Shares regional resources
 A network provider sells time

15.  A LAN in one large geographic area
 Resources related to the same organization
 Each department shares the LAN

16.  Very small scale network
 Range is less than 2 meters
 Cell phones, PDAs, MP3 players

17.  By Structure / Functional Relationship
 Client / Server
 Peer to Peer (P2PN)

18.  Nodes and servers share data roles
 Nodes are called clients
 Servers are used to control access
 Database software
 Access to data controlled by server
 Server is the most important computer

19.  All nodes are equal
 Nodes access resources on other nodes
 Each node controls its own resources
 Most modern OS allow P2PN
 Distributed computing is a form
 Kazaa

20.  By Topology / Physical Connectivity
 BUS
 STAR
 RING
 MESH
 TREE

21.  Logical layout of wires and equipment
 Choice affects
Network performance
Network size
Network collision detection

22.  Also called linear bus
 One wire connects all nodes
 Terminator ends the wires
 Advantages
 Easy to setup
 Small amount of wire
 Disadvantages
 Slow
 Easy to crash

23.  All nodes connect to a hub
 Packets sent to hub
 Hub sends packet to destination
 Advantages
 Easy to setup
 One cable can not crash network
 Disadvantages
 One hub crashing downs entire network
 Uses lots of cable
 Most common topology

24.  Nodes connected in a circle
 Tokens used to transmit data
 Nodes must wait for token to send
 Advantages
 Time to send data is known
 No data collisions
 Disadvantages
 Slow
 Lots of cable

25.  All computers connected together
 Internet is a mesh network
 Advantage
 Data will always be delivered
 Disadvantages
 Lots of cable
 Hard to setup

26.  Hierarchal Model
 Advantages
 Scaleable
 Easy Implementation
 Easy Troubleshooting

27.  Links that connect nodes
 Choice impacts
 Speed
 Security
 Size

28.  Most common LAN cable
 Called Cat5 or 100BaseT
 Four pairs of copper cable twisted
 May be shielded from interference
 Speeds range from
1 Mbps to 1,000 Mbps

29.  Similar to cable TV wire
 One wire runs through cable
 Shielded from interference
 Speeds up to 10 Mbps
 Nearly obsolete

30.  Data is transmitted with light pulses
 Glass strand instead of cable
 Immune to interference
 Very secure
 Hard to work with
 Speeds up to
100 Gbps

31.  Data transmitted through the air
 LANs use radio waves
 WANs use microwave signals
 Easy to setup
 Difficult to secure

32.  An internetwork is the connection of two or
more distinct computer networks or network
segments via a common routing technology.
 Any interconnection among or between public,
private, commercial, industrial, or governmental
networks may also be defined as an
internetwork.

33.  An extranet is a network or internetwork that is
limited in scope to a single organization or entity
but which also has limited connections to the
networks of one or more other usually, but not
necessarily, trusted organizations or entities
 by definition, an extranet cannot consist of a
single LAN; it must have at least one connection
with an external network.

34.  An intranet is a set of networks, using the Internet
Protocol and IP-based tools such as web browsers
and file transfer applications, that is under the
control of a single administrative entity.
 Most commonly, an intranet is the internal
network of an organization

35.  The Internet consists of a worldwide interconnection of
governmental, academic, public, and private networks
based upon the networking technologies of the Internet
Protocol Suite.
 It is the successor of the Advanced Research Projects
Agency Network (ARPANET) developed by DARPA of
the U.S. Department of Defense.
 The Internet is also the communications backbone
underlying the World Wide Web (WWW).

36.  Federal Networking Council definition of
Internet highlights three important concepts
that are basis for understanding the Internet:
 Packet switching
 TCP/IP communications protocol
 Client/server computing

37.  A method of slicing digital messages into packets,
sending the packets along different communication paths
as they become available, and then reassembling the
packets once they arrive at their destination
 Uses routers: special purpose computers that interconnect
the computer networks that make up the Internet and
route packets to their ultimate destination
 Routers use computer programs called routing algorithms
to ensure packets take the best available path toward their
destination

39.  Protocol: a set of rules for formatting, ordering,
compressing and error-checking messages
 TCP: Establishes the connections among sending and
receiving Web computers, handles thee assembly of
packets at the point of transmission, and their reassembly
at the receiving end
 IP: Provides the Internet’s addressing scheme
 TCP/IP is divided into 4 separate layers:
 Network Interface Layer
 Internet Layer
 Transport Layer
 Application Layer

41.  Internet address (also called IP address): a 32-
bit number expressed as a series of four
separate numbers marked off by periods, such
as 201.61.186.227
 IPv4 the current version of IP. Can handle up
to 4 billion addresses
 IPv6 (next generation of IP) will use 128-bit
addresses and be able to handle up 1
quadrillion addresses

42. Figure 3.6, Page 129

43.  Domain name: IP address expressed in natural
language
 Domain name system (DNS): allows numeric
IP addresses to be expressed in natural
language
 Example: cnet.com = 216.200.247.134
 Uniform resource locator (URL): addresses
used by Web browsers to identify location of
content on the Web

45.  Circuit switching was the switching technique
used in communication networks because it is
simple enough to carry analog signals.
 Eg. Phone system
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46.  Circuit switching provides traffic isolation
and traffic engineering, but at the expense of
using bandwidth inefficiently and signaling
overhead. It is often said that these two
drawbacks make circuits
witching highly inflexible, especially in a
highly dynamic environment such as the
Internet..
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47.  Packet switching is the basis for the
InternetProtocol (IP) In packet switching,
information flows are broken into variable-size
packets (or fixed-size cells as in the case of
ATM).These packets are sent, one by one, to the
nearest router, which will look up the destination
address, and then forward them to the
corresponding next hop. This process is repeated
until the packet reaches its destination. The
routing of the information is thus done locally,
hop-by-hop. Routing decisions are independent
of other decisions in the past and in other routers;
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48.  Model of computing in which very
powerful personal computers (clients) are
connected in a network with one or more
server computers that perform common
functions for the clients, such as storing
files, software applications, etc.

50.  Peer-to-peer computing an outgrowth of client/server
computing model
 Allows client computers to share resources without
intervention of a central server
 Most often used for sharing music and other file over the
Internet, in violation of copyright laws
 However, some new legitimate uses such as Groove
Workspace, a P2P platform developed by Groove
Networks

51.  A network interface card (NIC) is a circuit board
or card that is installed in a computer so that it
can be connected to a network.
 A network interface card provides the computer
with a dedicated, full-time connection to a
network. Personal computers and workstations
on a local area network (LAN) typically contain
a network interface card specifically designed for
the LAN transmission technology
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52.  Definition: Traditional modems used on
dialup networks convert data between the
analog form used on telephone lines and the
digital form used on computers. Standard dial-
up network modems transmit data at a
maximum rate of 56,000 bits per second (56
Kbps). However, inherent limitations of the
public telephone network limit modem data
rates to 33.6 Kbps or lower in practice.
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53.  Routers and modems are two of the most
common computer peripherals, yet many people
don't know the function of each one. While the
two devices may look similar, they each serve a
difference purpose. Fortunately, the functions of
the two devices are pretty easy to understand.
 A router is a small box that allows multiple
computers to join the same network (see below).
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54. Routers Modem
 A modem is a device that
provides access to the
Internet (see below).
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55.  A common connection point for devices in a
network. Hubs are commonly used to connect
segments of a LAN. A hub contains multiple
ports. When a packet arrives at one port, it is
copied to the other ports so that all segments
of the LAN can see all packets.
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57.  In networks, a device that filters and forwards
packets between LAN segments. Switches
operate at the data link layer (layer 2) and
sometimes the network layer (layer 3) of the
OSI Reference Model and therefore support
any packet protocol. LANs that use switches
to join segments are called switched LANs or,
in the case of Ethernet networks, switched
Ethernet LANs.
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59.  A device that forwards data packets along
networks. A router is connected to at least two
networks, commonly two LANs or WANs or a
LAN and its ISP.s network. Routers are located
at gateways, the places where two or more
networks connect. Routers use headers and
forwarding tables to determine the best path for
forwarding the packets, and they use protocols
such as ICMP to communicate with each other
and configure the best route between any two
hosts.
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60.  Definition: A network 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.
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61.  A device that connects two local-area
networks (LANs), or two segments of the
same LAN that use the same protocol, such as
Ethernet or Token-Ring.
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