Thursday, April 15, 2021

HOW DO COMPUTERS UNDERSTAND BINARY LOGIC

 

HOW DO COMPUTER UNDERSTAND THE BINARY LOGIC?



 

As we have shown in the previous post LANGUAGE THAT COMPUTER AS WELL AS HUMAN UNDERSTAND I am going to dig deep of that topic in this post.  I will try to explain how computer understand the binary logic.  So lets begin.  I am going to write about binary logic, that most of the computer manufacturers and developers use.

                

Binary logic deals with variables that take on two discrete values and with operations that assume logical meaning.  The two values the variables take may be called by different names (e.g. true and false, yes and no, etc.), but for our purpose it is convenient to think in terms of bits and assign the values of 1 and 0. 

 

Binary logic is used to describe, in a mathematical way, the manipulation and processing of binary information.  It is particularly suited for the analysis and design of digital systems.  For example, the digital logical circuits of many circuits that perform binary arithmetic are circuits whose behavior is most conveniently expressed by means of binary variables and logical operations.  The binary logic to be introduced in this section is equivalent to an algebra called Boolean algebra.

 

Binary logic consists of binary variables and logical operations.  The variables are designated by letters of the alphabet such as A, B, C, x, y, z, etc., with each variable having two and only two distinct  values : 0 and 1.  There are basic logic operations: AND, OR and NOT.

 

·        AND: This operation is represented by a dot or by the absence of an operator.  For example, x.y = z or xy=z is read “x AND y is equal to z”.  The logical operation  AND interpreted  to mean and z = 1 if and only if x = 1 and y = 1 otherwise z = 0. (Remember that x, y and z are binary variables and can be equal to either 1 or 0 nothing else).

·        OR : This operation is shown by addition symbol.  For example,  x + y = z is read “ x OR  y is equal to z”      meaning that z = 1 if x=1 or y=1 or both x=1 or if both x=1 and y = 1.  If both x = 0 , then y = 0 then z = 0.

·        NOT : This operation is presented by  a prime (sometimes by a bar).  For example , x’ = z (or x not equal to z meaning that x is what z is not) .  In other words, if x = 1, and z = 0 .  But if x=0 then z = 1.

 

Binary logic resembles binary arithmetic and the operations “AND” and “OR” have some similarities to multiplication and additions, respectively.  In fact, the symbols used for AND and OR are the same as those used for multiplication and addition.  However, binary logic should not be confused with binary arithmetic.  One should realize that an arithmetic variable designates a number that may consist of many digits.  A logic variable is either a one or zero.  For example, in binary arithmetic we have 1 + 1 = 1 (read “one plus one equal to 2” while in binary logic we have 1 + 1 = 1 (read “ one or one equal to one”

 

For each combination of the values of x and y there is a value of z specified by the definition of the logical operation.  These definations may be listed in compact form using truth tables.  A truth table is a table of all possible combination of the variables showing the relations between the balues that the variables may take and the result of the operation.  For example, the truth tables for he operations AND and OR with variables x and y are obtained by listing all possible values that the variable may have when combined in pairs.  The result of the operation for each combination is when listed in a separate row.  The truth tables for “AND” , “OR” and “NOT” are as under.

 

                                    AND                        

X

y

x.y

0

0

0

0

1

0

1

0

0

1

1

1

 

                                     OR

 

X

y

x +  y

0

0

0

0

1

1

1

0

1

1

1

1

 

 

                                  

 

                      NOT

X

x’

0

1

0

1

1

0

1

0

 

Thursday, April 8, 2021

RULES OF LOGIC ---> INTERNET PROTOCOL

 RULES OF LOGIC---->INTERNET PROTOCOL



FRIENDS, TODAY I AM GOING TO DISCUSS SOMETHING ABOUT IP ADDRESSING.  IP IS A LOGICAL ADDRESS FULLFORM INTERNET PROTOCOL.  IT PROVIDES LOGICAL ADDRESS TO NETWORKING DEVICES.  

THESE ADDRESSES ARE USED TO DEFINE SOURCE AND DESTINATION OF DATA PACKETS


IP HAS TWO VERSIONS

1. IP VERSION 4

2. IP VERSION 6


IP VERSION 4


IT IS 32 BIT ADDRESS WRITTEN IN DECIMAL NUMBER  FORMAT  192.168.1.1

THE NUMBERS IN THE DIGITS LIKE 192.68.1.1 HERE EVERY NUMBER BEFORE THE DOT IS AN OCTET. HERE IT IS SHOWN THAT EACH DIGIT IS PRECEDED BY DOT IS AN NUMBER BELONGING TO AN OCTET LIKE FIRST OCTET, SECOND OCTET , THIRD OCTET AND FOURTH OCTET.


EACH OCTET IS AN NUMBER IN BINARY FORM WRITTEN IN 2^8=256 BINARY FORM HERE THE DIGIT SHOWS THAT A VARIABLE IS IN THE BY POWER OF 2, HERE I WANT TO SAY THAT AS COMPUTER UNDERSTANDS BINARY DIGIT IN WHICH THE VARIABLES ARE 0 AND 1.  AS THE COMPUTER UNDERSTANDS BINARY DIGIT SO IT HAS ONLY 2 VALUES.


HENCE THE POWER IS WRITTEN IN 2. SO THE TOTAL NUMBER IN AN OCTET IS 256, HENCE THE VARIABLE IS IN (0-255) VALUES. AS OCTET HAS FOUR DIVISION SO THE VALUES AS THE NUMBER OF DIGITS IS 2^32.


 HERE I WANT TO ADD THAT THE VALUES IN AN OCTET IS 256 AS IT HAS 8 DIGITS IN A NUMBER AND THERE ARE FOUR OCTETS SO IT IS 2^32 = 429,49,67,296 VALUES OF DIFFERENT IP DIGITS.


NOW LETS GET BACK TO WORK


IP VERSION 4 ADDRESSES  ARE CLASSIFIED IN 5 CLASSES

CLASS A  0.0.0.0 ------127.255.255.255

0.0.0.0 IS RESERVED.  IT IS NOT USED IN FIRST OCTET.

127.0.0.0 – 127.255.255.255 

IS RESERVED FOR AS LOOPBACK ADDRESS.  IT IS USED TO TEST FOR WORKING OF THE LAN CARD.

  SO ACTUAL RANGE OF THE FIRST OCTET IS AS UNDER.

1.0.0.0 -----126.255.255.255



CLASS B  128.0.0.0 191.255.255.255

CLASS C  192.0.0.0 223.255.255.255

CLASS D  224.0.0.0 239.255.255.255

CLASS E  240.0.0.0 255.255.255.255 


CLASS A

CLASS B                  UNICAST + BROADCAST.  CONFIGURE IN PC

CLASS C


CLASS D           MULTICAST


CLASS E             RESERVED FOR SCIENTIFIC PURPOSE.

INTERNET PROTOCOL VERSION 4  IS OFF TWO TYPES

A) PRIVATE IP ADDRESS

B) PUBLIC   IP ADDRESS


A) PRIVATE IP ADDRESS


THIS ADDRESSES ARE USED LIN PRIVATE NETWORK, SUCH AS LAN.  WE CANNOT ACCESS INTERNET WITH THIS IP ADDRESSES.  WE DO NOT NEED TO PAY TO ANY ONE TO USE THIS ADDRESSES

CLASS A  10.0.0.0 10.255.255.255

CLASS B  172.16.0.0 172.31.255.255

CLASS C  192.168.0.0 192.168.255.255


B) PUBLIC IP ADDRESS


THIS ADDRESES ARE USED IN PUBLIC NETWORK SUCH AS WAN AND INTERNET.  WE NEED TO PAY TO SERVICE PROVIDER TO USE THIS IP ADDRESS


Wednesday, March 17, 2021

TOPOLOGIES OF COMMUNICATING MACHINES


TYPES OF NETWORK TOPOLOGY

NETWORK TOPOLOGY IS THE SCHEMATIC DESCRIPTION OF NETWORK ARRANGEMENT, CONNECTING VARIOUS NODES (SENDER AND RECEIVER) THROUGH LINES OF CONNECTION.

 

BUS TOPOLOGY


BUS TOPOLOGY IS A NETWORK TYPE IN WHICH EVERY COMPUTER AND NETWORK DEVICE IS CONNECTED TO A SINGLE CABLE.  WHEN IT HAS EXACTLY TWO END POINTS, THEN IT IS CALLED LINEAR BUS TOPOLOGY.

 

FEATURE OF BUS TOPOLOGY

1.       IT TRANSMITS DATA ONLY IN ONE DIRECTION

2.       EVERY DEVICE IS CONNECTED TO A SINGLE CABLE.

 

ADVANTAGES OF BUS TOPOLOGY

1.       IT IS COST EFFECTIVE CABLE REQUIRED IS LEAST COMPARED TO OTHER NETWORK TOPOLOGY.

2.       USED IN SMALL NETWORKS

3.       IT IS EASY TO UNDERSTAND

4.       EASY TO EXPAND JOINING TWO CABLES TOGETHER.

 

DISADVANTAGES OF BUS TOPOLOGY

1.       CABLE FAILS THEN WHOLE NETWORK FAILS.

2.       IF A NETWORK TRAFFIC IS HEAVY OR NODES ARE MORE THE PERFORMANCE OF THE NETWORK DECREASES.

3.       CABLE HAS LIMITED LENGTH

4.       IT IS SLOWER THAN RING TOPOLOGY.

 

 

RING TOPOLOGY


IT IS CALLED RING TOPOLOGY BECAUSE IT FORMS A RING AS EACH COMPUTER IS CONNECTED TO ANOTHER COMPUTER, WITH THE LAST ONE CONNECTED TO THE FIRST.  EXACTLY TWO NEIGHBOR FOR EACH DEVICE.

 

FEATURE OF RING TOPOLOGY

1.       A NUMBER OF REPEATERS ARE USED FOR RING TOPOLOGY WITH LARGE NUMBER OF NODES, BECAUSE OF SOMEONE WANTS TO SEND SOME DATA TO THE LAST NODE IN THE RING TOPOLOGY WITH 100 NODES THEN THE DATA WILL PASS THROUGH 99 NODES T EACH THE 100TH NODE.  HENCE TO PREVENT DATA LOSS REPEATERS ARE USED IN THE NETWORK.

2.       THE TRANSMISSION IS UNIDIRECTIONAL BUT IT CAN BE MADE BIDIRECTIONAL BY HAVING TWO CONNECTORS BETWEEN EACH NETWORK NODE.  IT IS CALLED DUAL RING TOPOLOGY.

3.       IN DUAL RING TOPOLOGY, TWO RING NETWORKS ARE FORMED AND DATA FLOW IS OPPOSITE DIRECTION IN THEM.  ALSO IF ONE RING FAILS THE SECOND RING ACTS AS BACKUP TO KEEP THE NETWORK UP.

4.       DATA IS TRANSFERRED IN SEQUENTIAL MANNER I.E. BIT BY BIT.  DATA TRANSMITTED HAS TO PASS THROUGH EACH NODE OF THE NETWORK TILL THE DESTINATION NODE.

 

ADVANTAGES OF RING TOPOLOGY

 

1.       TRANSMITTING NETWORK IS NOT AFFECTED BY HIGH TRAFFIC OR BY ADDING MORE NODES AS THE ONLY NODES HAVE TOKEN CAN TRANSMIT DATA.

2.       CHEAP TO INSTALL AND EXPAND

 

DISADVANTAGES OF RING TOPOLOGY

 

1.       TROUBLESHOOTING IS DIFFICULT IN RING TOPOLOGY.

2.       ADDING OR DELETING THE COMPUTERS DISTURB THE NETWORKING ACTIVITIES.

3.       FAILURE OF ONE COMPUTER DISTURBS THE WHILE NETWORK.

 

 

STAR TOPOLOGY


IN THIS TYPE OF TOPOLOGY ALL THE COMPUTERS ARE CONNECTED TO A SINGLE HUB THROUGH A CABLE. THIS HUB IS THE CENTRAL NODE AND ALL OTHER NODES ARE CONNECTED TO A CENTRAL NODE.

 

FEATURES OF STAR TOPOLOGY

 

1.       EVERY NODE HAS ITS OWN DEDICATED CONNECTION TO THE HUB.

2.       HUB ACTS AS A REPEATER FOR DATA FLOW.

3.       CAN BE USED WITH TWISTED PAIR, OPTICAL FIBER OR COAXIAL CABLE.

 

ADVANTAGES OF STAR TOPOLOGY

 

1.       FAST PERFORMANCE WITH FEW NODES AND  LOW NETWORK TRAFFIC.

2.       HUB CAN BE UPGRADED EASILY.

3.       EASY TO TROUBLESHOOT.

4.       EASY TO SETUP AND MODIFY.

5.       ONLY THAT NODE IS AFFECTED WHICH HAS FAILED, REST OF THE NODES CAN WORK SMOOTHLY.

 

DISADVANTAGES OF STAR TOPOLOGY

 

1.       COST OF INSTALLATION IS HIGH

2.       EXPENSIVE TO USE

3.       IF THE HUB FAILS THEN WHOLE NETWORK IS STOPPED BECAUSE ALL THE NODES UPON THE HUB.

4.       PERFORMANCE IS BASED ON THE HUB I.E. IT DEPENDS ON ITS CAPACITY.

 

 

MESH TOPOLOGY


 

IT IS POINT TO POINT CONNECTION TO OTHER NODES OR DEVICES.  ALL THE NETWORK NODES ARE CONNECTED TO EACH OTHER.  MESH HAS  (n(n-1))/2 PHYSICAL CHANNELS TO LINK N DEVICES.  THERE ARE TWO TECHNIQUES TO TRANSMIT DATA OVER THE MESH TOPOLOGY.

 

THEY ARE

1.       ROUTING

2.       FLOODING

 

MESH TOPOLOGY ROUTING

 

IN ROUTING, THE NODES HAVE A ROUTING LOGIC, AS PER THE NETWORK REQUIREMENTS.  THE ROUTING LOGIC TO DIRECT THE DATA TO REACH THE DESTINATION USING THE SHORTEST DISTANCE.  OR ROUTING LOGIC WHICH HAS INFORMATION ABOUT THE BROKEN LINKS, AND IT AVOIDS THOSE LINKS., AND IT AVOIDS THOSE NODES.

WE CAN HAVE ROUTING LOGIC, TO RECONFIGURE THE FAILED NODES.

 

MESH TOPOLOGY FLOODING

 

IN FLOODING, THE SAME DATA IS TRANSMITTED TO ALL NETWORK NODES, HENCE NO ROUTING LOGIC IS REQUIRED.   THE NETWORK IS ROBUST AND IT IS VERY UNLIKELY TO LOOSE THE DATA. BUT IT LEADS UNWANTED LOAD OVER THE NETWORK.

 

TYPES OF MESH TOPOLOGY

 

PARTIAL MESH TOPOLOGY

IN THIS TOPOLOGY SOME OF HE SYSTEMS ARE CONNECTED IN SOME FASHION AS ESH TOPOLOGY BUT SOME DEVICES ARE ONLY ONNECTED TO TWO OR THREE DEVICES.

 

FULL MESH TOPOLOGY

EACH AND EVERY NODES ARE CONNECTED TO EACH OTHER.

 

FEATURES OF MESH TOPOLOGY

 

1.       FULLY CONNECTED

2.       ROBUST

3.       NOT FLEXIBLE

 

 

ADVANTAGES OF MESH TOPOLOGY

 

1.       EACH CONNECTION CAN CARRY ITS OWN DATA LOAD.

2.       IT IS ROBUST

3.       FAULT IS DIAGNOSED EASILY

4.       PROVIDES SECURITY AND PRIVACY

 

DISADVANTAGES OF MESH TOPOLOGY

 

1.       INSTALLATION AND CONFIGURATION IS DIFFICULT

2.       CABLING COST IS MORE

3.       BULK WIRING IS REQUIRE

 

TREE TOPOLOGY


 

IT HAS ROOT NODE AND ALL OTHER NODES ARE CONNECTED TO IT FORMING HIERARCHY  IT IS ALSO CALLED HIERARCHICAL TOPOLOGY.  IT SHOULD AT LEAST THREE LEVELS TO THE HIERARCHY.

 

FEATURES OF TREE TOPOLOGY

 

1.       IDEAL IF WORKSTATION ARE ARRANGED IN GROUP

2.       USED IN WIDE AREA NETWORK.

 

 

ADVANTAGES OF TREE TOPOLOGY

 

1.       EXTENSION OF BUS AND STAR TOPOLOGY

2.       EXPANSION OF NODES IS POSSIBLE AND EASY

3.       EASILY MANAGED AND MAINTAINED

4.       ERROR DETECTION IS EASILY DONE

 

DISADVANTAGES OF TREE TOPOLOGY

 

1.       HEAVILY CABLED

2.       COSTLY

3.       IF MORE NODES ADDED MAINTENANCE IS DIFFICULT

4.       CONTROL HUB FAILS NETWORK FAILS

 

 


Saturday, March 6, 2021

MONITORS IN SUMMARY

 

MONITORS

MONITOR IS A PRIMARY OUTPUT DEVICE.  IT DISPLAYS ALL CURRENT PROCESS APPLICATION AND DATA I.E. RUNNING INSIDE A COMPUTER SYSTEM.  A STANDARD MONITOR USES AN ANALOG , VGA INTERFACE WHICH PLUGS INTO TP15 PIN VGA CONNECTOR TO THE MOTHERBOARD.

 

 THERE ARE TWO TYPES OF MONITOR TECHNOLOGY AVAILABLE TO THE MARKET.

HERE ARE THOSE

 

CATHODE RAY TUBE (CRT)

THIS MONITOR IS FADING IN POPULARITY BUT STILL IN WIDESPREAD USE WITH OLDER COMPUTER SYSTEMS. IT IS ANALOG STANDARD MONITOR. A CRT USES A PICTURE TUBE THAT WAS USED IN OLDER TUBE BASED TV SETS.


 

THE NARROW END OF PICTURE TUBE CONTAINS AN ELECTRON GUN.  IT EMITS 3 ELECTRON BEAMS.  ONE EACH FOR RED, GREEEN, BLUE LIGHT.  THE FRONT END OF THE PICTURE TUBE IS COATED WITH PHOSPHOROUS. 

 

WHEN THE ELECTRON HITS PHOSPHOROUS COATING IT STARTS TO GLOW.  JUST BEFORE THE PHOSPHOROUS COATING A METAL PLATE CALLED SHADOW MASK IS USED TO DIVIDE THE IMAGE CREATED BY THE ELECTRON GUN INTO RED, GREEN AND BLUE PIXELS ON STRIPS THAT FORM THE IMAGE. 

 

SHADOW MASK USES ON OF THREE TECHNOLOGIES.  A PHOSPHOUR TRIAD, AN APERTURE GRILL, A SLOTTED MASK.  CRT MONITORS ARE BULKY TAKES MORE DISK SPACE,   CONSUMES MORE POWER AND EMITS MORE HEAT.  CRT MONITOR WAS AVAILABLE FROM 15 INCH TO 19 INCH SIZE.  IT USES VGA CONNECTOR TO ATTACH WITH A CPU

 

LCD AND LED SCREENS

 

THE MOST POPULAR MONITOR IN TODAY MARKET IS LED MONITOR SUPPRESED LCD MONITORS.  BECAUSE IT GIVES BETTER COLOUIR QUALITY, WIDE VIEWING ANGLE AND CONSUMES LESS POWER.  


 

IT USES LIQUID CRYSTAL CELLS TO POLARIZE THE LIGHT.   LCD MONITORS USES FLUOROSCENT LAMP AND LED MONITORS USES LED LAMPS FOR BAKCLIGHTING .  THIS DISPLAY USES AN ARRAY OF TRANSISTORS TO CONTROL EACH CELL.

 

VARIATION ARE THE COLOUR BIT, RESPONSE TIME  AND THE REFRESH RATE.   THIS MONITORS COMES WITH TWO TYPES OF TRANSISTOR TECHNOLOGY 1) PASSIVE MATRIX 2) ACTIVE MATRIX

 

PASSIVE MATRIX

 


A PASSIVE MATRIX DISPLAY DOESNOT HAVE A DEDICATED TRANSISTOR FOR EACH PIXEL OR SUB PIXEL,  BUT INSTEAD A MATRIX OF CONDUCTIVE TRACES.  IN SIMPLIFIED TERMS FOR A SINGLE PIXEL WHEN THE DISPLAY  IS INSTRUCTED TO CHANGE THE CRYSTAL LINE ALIGNMENT FOR A PARTICULAR PIXEL.

 

IT SENDS A SIGNAL ACROSS THE X AND Y COORDINATE TRACES THAT INTERSECT AT THAT PIXEL, THUS TURNING IT ON.  A 1366 X 768 RESOLUTION MONITOR CONTAINS 1366  TRANSISTOR AT THAT HORIZONTAL EDGE AND 768 TRANSISTORS AT THE VERTICAL EDGE.

 

THE VIEWING ANGLE IS A MOST UNCONSIDERABLE ISSUE OF A PASSIVE MATRIX DISPLAY.  THE PICTURE QUALITY IS MUDDY BECAUSE THE CONDUCTIVE TRACES SOMETIMES EFFECTS THE NEIGHBOURING IXELS OF A TARGET PIXEL

 

THE ONE ADVANTAGE OF PASSIVE MATRIX IS IT ONSUMES LESS POWER COMPARING TO ACTIVE MATRIX DISPLAY.

 

DUAL SCAN DISPLAY

 


A DUAL SCAN IS A VARIATION OF THE PASSIVE METRIC DISPLAY.  THE CLASSIC PASSIVE MATRIX SCREEN IS SPLIT IN HALF TO IMPLEMENT A DUAL SCAN DISPLAY.  EACH HALF OF THE DISPLAY IS REFRESHED SEPERATELY LEADING TO INCREASED QUALITY.

 

ALTHOUGH DUAL SCAN IMPROVES THE QUALTY OF REFRESH RATE BUT IT CANNOT RIVAL THE QUALITY PRODUCED BY ACTIVE MATRIX.

 

ACTIVE MATRIX

 

THIS SCREEN IS MADE OF SEVERAL INDEPENDENT LCD OR LED PIXELS.  A TRANSISTOR AT EACH PIXEL LOCATION, WHEN SWITCHED AMONG VARIOUS LEVELS.  ACTIVATES TWO OPPOSING ELECTRODES THAT ALIGH THE PIXELS CRYSTALS AND ALTER THE PASSAGE OF LIGHT AT THAT LOCATION TWO PRODUCE MILLIONS OF COLOUR SHADES.  THIS TYPE OF DISPLAY IS VERY CRISP AND EASY TO LOOK FROM ANY ANGLE.

 

IT DOESN’T REQUIRE AN SCAN REFRESHING TO MAINTAIN AN IMAGE, BECAUSE REANSISTORS CONDUCT CURRENT ONLY IN ONE DIRECTION AND THE PIXELS ACT LIKE A CAPACITOR BY HOLDING ITS CHARGE UNTIL IT IS REFRESHED

 

HIGHER REFRESH RATES ESULTS IN BETTER VIDEO OR GAING PERFORMANCE NOT FOR STILL IMAGE.   THE MAJOR DISADVANTAGE OF ACTIVE MATRIX SCREEN THAT IT REQUIRES MORE POWER TO OPERATE ALL TRANSISTOR.   EVEN IF THE BACKLIGHT IS TURNED OF THE SCREEN CAN STLL CONSUME POWER AT AN ALARMING RATE. 

 

ANOTHER PROBLEM WITH ACTIVE MATRIX IS LIGHT BLEED.

 

THANKS FOR READING.  I HOPE YOU LIKED IT.

Tuesday, February 16, 2021

NETWORKING DEVICES A GENERAL SUMMARY

 NETWORKING DEVICES USED IN INTERNET CONNECTION: A GENERAL SUMMARY

NETWORK DEVICES, OR NETWORKING HARDWARE, ARE PHYSICAL DEVICES THAT ARE REQUIRED FOR COMMUNICATION AND INTERACTION BETWEEN HARDWARE ON A COMPUTER NETWORK.


LAYER 4 -> FIREWALL

LAYER 3 -> ROUTER

LAYER 2 -> BRIDGE, SWITCH

LAYER 1 ->LAN CARD, REPEATER, HUB, MODEM, ACCESS-POINT.


NETWORK INTERFACE CARD(NIC) A LAN CARD


IT IS A LAYER 1 DEVICE.  IT IS USED TO CONNECT A PC, LAPTOP, WORK STATION AND A SERVER TO A NETWORK.

A LAN CARD IS BUILT INTO A MOTHERBOARD BUT WE CAN PURCHASE ADDITIONAL LAN CARD ATTACH IT IN A PCI OR USB SLOT.  EVERY LAN CARD HAS ITS OWN MAC ADDRESS.


REPEATER





REPEATER IS A LAYER ONE DEVICE. IT WORKS LIKE N AMPLIFIER, BUT REMEMBER APLIFIER WORKS IN ANALOG SIGNAL WHERE REPEATER WORKS IN DIGITAL SIGNAL.  IT IS USED TO FIX THE PROBLEM OF ATTENUATION.


HUB



IT IS ALSO A LAYER1 DEVICE IT WORKS LIKE A REPEATER BUT REMEMBER REPEATER CANNOT BE A HUB.  A HUB CONTAIN 4, 6, 8, 12, 16 PORTS.  HUB REGENERATE AND INCOMMING SIGNAL AND FORWARDS IT BY ALL OFF ITS ACTIVE PORT.  THIS TYPE OF COMMUNICATION IS KNOWN AS BROADCAST.

HUB WORKS IN HALF DUPLEX MODE.  WHEN TWO DEVICES TRIES TO COMMUNICATE WITH EACH OTHER AT A SAME POINT OF TIME.  THEIR DATA GETS COLLIDED.


COLLISION DOMAIN


IN A HALF DUPLEX NETWORK WHEN TWO OR MORE THAN TWO COMPUTERS TRIES TO COMMUNICATE WITH EACH OTHER AT THE SAME POINT OF TIME THEIR DATA PACKETS GET COLLIDED.  IT IS CALLED COLISION DOMAIN.


WHEN A COLLISION OCCURS A JAM SIGNAL IS GENERATED AND ALL OF THE DEVICES INSIDE A NETWORK STOPS FORWARDING DATA.


BROADCAST DOMAIN

WHEN IN A NETWORK, A PC GENERATES A BROADCAST FRAME; ALL OF THE DEVICES INSIDE THT NETWORK GETS A COPY OF THE FRAME.   IT IS CALLED A BROADCAST DOMAIN.


A HUB NETWORK RESIDES INSIDE A SINGLE BROADCAST AND COLLISION DOMAIN.



CSMA – CD(CARIER SENSE MULTIPLE ACCESS COLLISION DETECTION)


IN A MULTI ACCESS NETWORK THE CARRIER SENSE MECHANISM DETECTS IF THE CHANNEL IS FREE OR NOT.  IT CHECKS FOR VOLTAGE LEVEL IN COPPER WIRE AND LIGHT IN FIBRE OPTICS.


THE COLLISION DETECTION MECHANISM DETECTS THE JAM SIGNAL AND STOPS FORWARDING DATA.  THEN A BACK OF ALGORITHM IS CALCULATED AND AGAIN THOSE COLIDDED DEVICES START SENDING THE DATA WITH LITTLE TIME GAP.



SWITCH



IT IS A LAYER 2 DEVICE.  IT WORKS WITH MAC ADDRESS.  IT IS A HARDWARE DEVICE.  IT IS ALSO KNOWN AS MULTIPORT BRIDGE.  A SWITCH CONTAINS  4, 8, 12, 16, 24, 48, 64 PORTS. EACH PORT WORKS AT FULL DUPLEX MODE.  EACH SIGNLE PORT OF A SWITCH IS IN SEPARATE COLLISION DOMAIN.


SWITCH CANNOT BREAK BROADCAST DOMAIN.  A SWITCHED NETWORK RESIDES INSIDE A SINGLE BROADCAST DOMAIN.  SWITCH HAS A PROCESSOR NAMED ASIC (APPLICATION SPECIFIC INTEGRATED CIRCUIT) WHICH LEARNS THE MAC ADDRESS OF ALL CONNECTED DEVICES AND STORES IN A TABLE CALLED CAM (CONTENT ADDRESSABLE MEMORY).


SWITCH IS OFF TWO TYPES (1) MANAGED SWITCH AND (2) UNMANAGED SWITCH.  (1)MANAGED SWITCH – THIS SWITCH CAN BE MANUALLY CONFIGURE (2) UNMANAGED SWITCH - THIS SWITCH CAN NOT BE CONFIGURED MANUALLY.


NOW I WILL SOMETHING ABOUT SWITCHING METHODS.


(1) CUT THROUGH SWITCHING

THIS TYPE OF SWITCH STARTS FORWARDING DATA FRAME IMMEDIATELY AFTER LEARNING DESTINATION MAC ADDRESS OF THAT FRAME.

IT IS A FASTEST SWITCHING METHOD.  THE PROBLEM WITH THE SWITCHING METHOD IS THAT IT CAN FORWARD CORRUPT FRAME AND RUNT FRAME (FRAME SIZE LESS THAN 64 BYTE).


(2)STORE AND FORWARD SWITCHING

THIS SWITCHING METHOD STORES THE ENTIRE FRAME INTO ITS BUFFER MEMORY.  THEN RUNS CRC(CYCLIC REDUNDANCY CHECK) TO VERIFY CORRUPTED DATA IF THE DATA IS GOOD THEN STARTS FORWARDING.

IT IS THE SLOWEST METHOD OF SWITCHING BUT NO CORRUPTED FRAME IS FORWARDING.  IF A BAD FRAME IS FOUND WITH BAD FCS(FRAME CHECK SEQUENCE).  IT WILL DROP THAT FRAME.


(3)FRAGMENT FREE SWITCHING

IT IS AN ADVANCED VERSION OF AS CUT THROUGH SWITCHING.  A SWITCH RUNNING IN FRAGMENT FREE MODE LEARNS THE FIRST 64 BYTE OF A FRAME, THEN STARTS FORWARDING THAT FRAME.  THIS METHOD DOESN’T ALLOW ANY RUNT FRAME TO BE FORWARDED.


FIREWALL


IT IS LAYER 4 DEVICE.  IT WORKS WITH ALL TYPES OF NETWORK ADDRESES (MAC, IP, PORT NUMBER).  IT IS A SECURITY APPLIANCE.   IT IS USED TO SECURE OUR NETWORK FROM UNATHOURIZED ACCESS, SUCH AS HACKING, NETWORK ATTACKS, VIRUSES AND WORMS.


FIREWALL IS OF TWO TYPES

1> SOFTWARE FIREWALL

2> HARDWARE FIREWALL


LET US SEE SOFTWARE FIREWALL

 IT IS A SOFTWARE BASE PROGRAM WHICH PROTECTS OUR PCS, LAPTROPS , SERVERS EG:- ANTIVIRUS FIREWALL, WINDOWS FIREWALL, COMODO FIREWALL, WINDOWS DEFENDER.


LET US SEE HARDWARE FIREWALL

IT IS A HARDWARE COMPONENT WHICH WORKS WITH SOFTWARE COMPONENT. IT CONTAINS VARIOUS SECURITY PROTOCOLS WHICH HELPS TO PROTECT A WHOLE NETWORK.

FOR EXAMPLE ->CISCO ASA, PIX, A5BIG IP, CHECK POINT, TALO ALTO


MODES OF FIREWALL


1.INTRUSION DETECTION SYSTEM

IT IS A PASSIVE PROTECTION WHICH DOESNOT BLOCK ANY MALICIOUS NETWORK ACTIVITY.  IT  HELPS TO MONITOR AND DETECT THOSE ACTIVITIES.


2.INTRUSION PREVENTION SYSTEM

IT IS A AN ACTIVE PROTECTION WHICH BLOCKS ANY MALICIOUS NETWORK ACTIVITY.



MODEM

MODEM MEANS MODULATION AND DEMODULATION.  THIS DEVICE CONVERTS ANALOG SIGNAL INTO DIGITAL SIGNAL AND VICE VERSA.IT IS USED WITH BROADBAND CONNECTION PROVIDED BY PLAIN OLD TELEPHONE SYSTEM (POTS) AND TELCO NETWORK. FOR EXAMPLE BSNL LANDLINE


MODEM IS OFF TWO TYPES:-

1> ADSL 2 WHICH PROVIDES WIRED NETWORK.

2> ADSL 2+ WHICH PROVIDED BOTH WIRED AND WIRELESS NETWORK.


ADSL – ASSYNCHRONOUS DIALUP SUBSCRIBER LINK


ACCESS POINT

IT IS A LAYER 1 DEVICE.  IT IS USED TO CREATE A WIRELESS LAN.  IT USES WIFI TECHNOLOGY .  IT NEVER MAKES COLLISION BUT WORKS INSIDE A SAME BROADCAST DOMAIN.  DATA ACCESS MECHANISM CSMA\CA  (CARRIER SENSE MULTI ACCESS WITH COLLISION AVOIDANCE).


THE COLLISION IS AVOIDED BY EXCHANGING CTS AND RTS MESSAGE.  ACCESS POINT WITH LAYER 3 ENGINE CAN FORWARD I TRAFFIC FROM ONE NETOWK TO ANOTHER THEN IT IS CALLED A WIFI ROUTER.


THE WIFI STANARDS COMES UNDER IEEE (INSTITUTE OF ELECRICAL AND ELECTRONICS ENGINEERS) 802 PROJECT.  WIFI COMES UNDER 802.11 STAMDARD.  IT HAS 5 SUB STANDARD.802.11 A,  802.11B, 802.11G, 80211N, 802.11AC.


ROUTER



IT ISS A LAYER 3 DEVICE.  IT IS USED TO CONNECT MULTIPLE NETWORKS.  IT WORKS WITH IP ADDRESS.  A ROUTER FORWARDS DATA PACKETS FROM ONE NETWORK TO ANOTHER ACCORDING TO THE DESTINATION IP OF THE DATA PACKET.


IF A DESTINATION IP NETWORKIS UNKNOWN TO THE ROUTER IT WILL DROP THAT PACKET.  TO LEARN ABOUT THIS NETWORK INFORMATION VARIOUS ROUTING PROTOCOLS ARE IMPLEMENTED IN A ROUTER.


ROUTER STORES THE UNKNOWN NETWORK INFOMRATION IN A TABLE KNOWN AS ROUTING INFORMATION BASE(RIB) OR ROUTING TABLE.  ROUTER WORKS AT FULL DUPLEX MODE.  IT NEVER BROADCAST .  EACH SINGLE PORT OF A ROUTER IS IN SEPERATEDE BROADCAST DOMAIN AND COLLISION DOMAIN.


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