Upload
samgishika
View
222
Download
0
Embed Size (px)
Citation preview
8/8/2019 Bbit 213 Lecture 2
1/25
Lecture 2: Introduction to Networks
A network consists of multiple computers connectedusing some type of interface, each having one ormore interface devices such as a Network Interface
Card (NIC) and/or a serial device for PPP networking. Each computer is supported by network software that
provides the server or client functionality.
The hardware used to transmit data across thenetwork is called the media. It may include copper
cable, fiber optic, or wireless transmission. The standard cabling used for the purposes of this
document is 10Base-T category 5 ethernet cable.
8/8/2019 Bbit 213 Lecture 2
2/25
Network Categories
There are two main types of network categorieswhich are:
Server based
Peer-to-peer
In a server based network, there are computersset up to be primary providers of services such asfile service or mail service.
The computers providing the service are calledservers and the computers that request and use
the service are called client computers. In a peer-to-peer network, various computers on
the network can act both as clients and servers.
8/8/2019 Bbit 213 Lecture 2
3/25
8/8/2019 Bbit 213 Lecture 2
4/25
Store-and-Forward Systems
Messages may be stored at intermediate nodes
along the transmission path between sender and
receiver in store-and-forward systems
This helps ensure message delivery withoutobligating the sender to wait until a message is
delivered before transmitting other messages
It also helps ensure message delivery in the case
of link or destination failure while the message is
in transit
Store-and forward algorithms are valuable in time-
staged delivery systems and in networks that
assign priorities to different messages
8/8/2019 Bbit 213 Lecture 2
5/25
Serial and Parallel transmission
The transmission mode refers to the number ofelementary units of information (bits) that can besimultaneously translated by the communications
channel. Parallel connection means simultaneous
transmission ofNbits. These bits are sentsimultaneously overNdifferent channels
Serial connection - the data are sent one bit at a
time over the transmission channel. However,since most processors process data in parallel, thetransmitter needs to transform incoming paralleldata into serial data and the receiver needs to dothe opposite.
8/8/2019 Bbit 213 Lecture 2
6/25
The parallel-serial transformation isperformed using a shift register. The shiftregister, working together with a clock, willshift the register (containing all of the datapresented in parallel) by one position to theleft, and then transmit the most significant bit(the leftmost one) and so on:
Tohelp protectyour privacy, PowerPointprevented thisexternalpicturefrom being automatically downloaded.Todownload and display thispicture, click Optionsin theMessageBar, and then click Enableexternalcontent.
Tohelp protectyour privacy, PowerPointprevented thisexternalpicturefrom being automatically downloaded. Todownload and display thispicture, click Optionsin theMessageBar, and then click Enableexternalcontent.
8/8/2019 Bbit 213 Lecture 2
7/25
Network Topology, Architecture, and
Complexity Network topologyrefers to the physical layout
of a network, the way that nodes attach to the
communication medium Network architecture refers to the way in
which media, hardware, and software areintegrated to form a network
Network complexityis concerned with extentto which network architectures are simple ordiverse in their make
8/8/2019 Bbit 213 Lecture 2
8/25
Network Topologies
Bus All Pcs connect to a common cable/bus. Bothends of the network must be terminated with aterminator.
Star - All devices revolve around a central hub,which is what controls the networkcommunications, and can communicate with otherhubs. Range limits are about 100 meters from thehub.
Ring - Devices are connected from one to anotherin a ring. A data token is used to grant permissionfor each computer to communicate.
Mesh - allow each computer to have a directconnection to each of the other computers.
There are also hybrid networks including a star-bushybrid, star-ring network, and tree networks withconnections between various computers on the
network.
8/8/2019 Bbit 213 Lecture 2
9/25
Reason for multiple topologies
Each topologies has advantages and
disadvantages. Give them.
8/8/2019 Bbit 213 Lecture 2
10/25
Telecom Channels
Channels - the links by which data orvoice are transmitted between sending
and receiving devices in a network twisted wires
coaxial cable
fiber-optic cable
wireless microwave
satellite
8/8/2019 Bbit 213 Lecture 2
11/25
Telecom Channels other Wireless
Cellular
Mobile data networks (2-way)
PCS (personal communication
systems)- to the end user acts like
cellular, but different
Personal data assistants
8/8/2019 Bbit 213 Lecture 2
12/25
Transmission Speeds
Medium Speed Cost
Twisted Wire 300 bps-10 Mbps Low
Microwave 256 Kbps-100 MbpsSatellite 256 Kbps-100 Mbps
Coaxial Cable 56 Kbps-200 Mbps
Fiber-Optic Cable 500 Kbps-10 Gbps High
8/8/2019 Bbit 213 Lecture 2
13/25
Transmission Media These transmission channels are made up of
several segments that allow the data to circulate inthe form of electromagnetic, electrical, light or evenacoustic waves.
In order for data to be exchanged, an encoding
must be chosen for the transmission signals. Thisdepends basically on the physical medium used totransfer the data, the guaranteed data integrity andtransmission speed.
Data transmission is called "simple" if there are
only two machines communicating, or if only asingle piece of data is sent. Otherwise, it isnecessary to install several transmission lines toshare the line among several differentcommunication actors. This sharing is called
multiplexing.
8/8/2019 Bbit 213 Lecture 2
14/25
COPPERWIRES
Conventional computers use copper wires as theprimary medium to connect computers becausethey are inexpensive and easy to install.
To minimize interference, networks use one oftwo basic wiring types:- twisted pair or coaxialcable
The simple twists change the electrical propertiesof the wire and make it suitable for use in a
network.- they limit electromagnetic energy thewire emits, the twists prevent electric currentfrom radiating energy that interferes with otherwires and others from interfering with its own.
8/8/2019 Bbit 213 Lecture 2
15/25
The jacketprotects the cable from the externalenvironment. It is usually made of rubber (or
sometimes Polyvinyl Chloride (PVC) or Teflon). The shield (metal envelope) surrounding the cables
protects the data transmitted on the medium frominterference (also called noise) that could corrupt thedata.
The insulator surrounding the central core is made ofa dielectric material that prevents any contact with theshield that could cause electrical interactions (shortcircuit).
The core, which actually transports the data, generally
consists of a single copper strand or of several braidedstrands.
8/8/2019 Bbit 213 Lecture 2
16/25
GLASS FIBERS Computers use flexible glass fibers called optical
fibers to transmit data
A transmitter at the end of one fiber uses LED orlaser to send pulses of light through the fiber
Advantages over copper wires:- They are not susceptible to electrical signal
interference
Carry pulses of light much farther that copper
Light can encode more information thanelectrical signals hence optical fiber can carrymore data.
Data from more than one source can betransmitted at a go.
8/8/2019 Bbit 213 Lecture 2
17/25
Disadvantages
Expensive and technically difficult to install andmaintain
If the fiber breaks internally, it is difficult to locatethe problem.
Radio Phones use electromagnetic waves to transmit
computer data.
A network that uses electromagnetic radio waves
is said to operate at a radio frequency andtransmissions are referred to as RF transmissions.
Each participating computer attaches an antennawhich can both transmit and receive RF signals.
8/8/2019 Bbit 213 Lecture 2
18/25
Satelites
A communications satellite (sometimesabbreviated to COMSAT) is an artificial satellitestationed in space for the purpose oftelecommunications.
Radio transmissions do not bend around the surfaceof the earth, RF is combined with satellites to give asolution to this.
The satellite contains a transponder which consists ofa radio receiver and transmitter.
The transponder accepts radio signals, amplify andtransmit the signal back at a different angle
A single satellite contains multiple transponders (sixto twelve) each using a different frequency making itpossible for multiple communications to proceedsimultaneously.
8/8/2019 Bbit 213 Lecture 2
19/25
Communication satellites can be grouped intotwo:- Geosynchronous and geostationary
Geosynchronous (GEO) is placed in an orbitthat is synchronized with the earth rotation.
The laws of physics are use to determine theexact distance 35 785 KM also called Highearth orbit
Thee is a limited amount of space available inthe orbit because they have to be separatedby some distance between them
The minimum separation distance dependson power of the transmitters generally 4 to 8degrees the entire equator can hold 45 to90
8/8/2019 Bbit 213 Lecture 2
20/25
Low earth Orbits (LEO)
They do not stay at a single location but travelaround the earth faster than the earth.
A single LEO can complete an entire orbit in 1.5
hrs. Having a satellite that does not appear stationary
causes problems
Can only be used during the time the orbitspass between two ground stations
Maximal utilization requires complex controlsystems that continuously move the groundstations
How are they therefore used?
8/8/2019 Bbit 213 Lecture 2
21/25
Microwave Electromagnetic waves beyond the radio and
television frequencies can be used totransport information.
Although they are a few frequencies higher
than radio frequencies they behave differently They can be aimed at a single direction.
They also carry more data at lower frequencytransmissions
Microwaves cannot penetrate metalstructures and work best under a clear pathbetween the transmitter and receiver
8/8/2019 Bbit 213 Lecture 2
22/25
Infrared
Infrared light lies between the visibleand microwave portions of the
electromagnetic spectrum.
It is limited in distance The transmitter must be pointed to
receiver and does not require an
antenna
8/8/2019 Bbit 213 Lecture 2
23/25
Data Communication
Frameworks Two major data communication
frameworks have been developed to
help ensure that networks meetbusiness and communicationrequirements:
Open Systems Interconnection (OSI)
reference model developed by theInternational Standards Organization (ISO)
Transmission Control Protocol/InternetProtocol (TCP/IP) suite
8/8/2019 Bbit 213 Lecture 2
24/25
Models of the Internet
OSI/ISO Reference Model TCP/IPReference Model
Open Systems Interconnection
(International Standards Office)
Application
PresentationSessionTransportNetworkData LinkPhysical
Model Layers
Application
TransportInternetHost-to-network
Transmission Control
Protocol/
Internet Protocol
8/8/2019 Bbit 213 Lecture 2
25/25
Summary
Data Communications Supports Applications
The Operating System manages the
resources of the computer.
There must however, be a system that
provides a bridge between applications and
the devices so they can communicatethis is
called a Transaction Control Process (TCP)