Wednesday, August 21, 2019

Satellite Communication Systems Overview

Satellite Communication Systems Overview SATELLITE COMMUNICATION SYSTEMS OVERVIEW Satellite communication enables two Stations on the earth to communicate through radio broadcast which are located far away from each other. The two stations use satellite as a relay station for their communication. One of the earth station will transmit to the satellite. This is called as Uplink. The satellite Transponder will convert the signal and sends it down to the other earth station. This is called a Downlink. The satellite communication is advantageous over terrestrial communication because of the huge coverage area and high bandwidth capabilities. The disadvantages of satellite communication are large propagation delay, communication cost and gradual increase in use of bandwidth. The basic factors to be considered in satellite communication are; elevation angle is the angle of the earth surface to the center line of the satellite transmission beam. This angle gives considerable effects on satellites coverage area. Ideally, elevation angle should be 0 degrees, so that the tr ansmission beam will reach the horizon visible to the satellite in all directions. However, there is a minimum elevation angle of earth stations because of the environmental factors like objects blocking the transmission, atmospheric attenuation, and earth electrical background noise. Coverage angle is the measure of the portion of the earth surface visible to a satellite taking the minimum elevation angle into account. [1] It is denoted as, R/(R+h) = cos (ÃŽ ² + ÃŽ ¸)/cos (ÃŽ ¸) Here R is earth radius (6370 Km), h is satellite orbit height, Î’ is coverage angle and ? is the minimum elevation angle. There are impairments like free space loss, atmospheric attenuation caused by rain and fog will create considerable effects during transmission. [1] There are different type of satellite services namely, Fixed Satellite Services (FSS) to offers point to point communication. Broadcast Satellite Services (BSS) to provide satellite television and radio. Mobile satellite Services (MSS) will provide telephony. There are number of satellites orbiting in different orbits. [1] The types of satellite orbits are (GEO) geostationary earth orbit, Medium earth orbit (MEO), Low earth orbit (LEO) Molniya and tundra orbit.GEO satellites are in orbit 35,863 km above the earths surface along the equator. Objects in Geostationary orbit revolve around the earth at the same speed so as the earth rotates. This means GEO satellites remain in the same position relative to the surface of earth. This satellite has large coverage area which almost one fourth of the earths surface. It has 24 hour continuous view of the particular regions of the earth, so it is used for broadcasting and multipoint applications. These GEO satellites have difficulty in broadcasting in near polar region.LEO satellites are much closer to the earth than GEO satellites, ranging from 500 to 1,500 km above the surface.LEO satellites dont stay in fixed position relative to the surface, and are only visible for 15 to 20 minutes each pass. So a network of LEO satellites is necessary for LEO satellites to be useful. A LEO satellites proximity to earth compared to a GEO satellite gives it a better signal strength and less time delay, which is better for point to point communication. A LEO satellites smaller area of coverage is less of a waste of bandwidth. Atmospheric drag affects LEO satellites, causing gradual orbital deterioration. A MEO satellite is in orbit somewhere between 8,000 km and 18,000 km above the earths surface.MEO satellites are similar to LEO satellites in functionality.MEO satellites are visible for much longer periods of time than LEO satellites, usually between 2 to 8 hours.MEO satellites have a larger coverage area than LEO satellites. Tundra and Molniya Orbit Satellites are used by Russia for decades. Molniya Orbit is an elliptical orbit. The satellite remains in a nearly fixed position relative to earth for eight hours. A series of three Molniya satellites can act like a GEO satellite. It is useful for operations in near Polar Regions. [1] International Teleco mmunication Union (ITU) has done the frequency allocation and planning for all satellite services. To facilitate efficient frequency planning, the whole world is divided into three regions. [1] They are, Region 1: Europe, Africa, Mongolia Region 2: Greenland, South and North America Region 3: Australia, Asia, South west pacific Frequency band are allocated within these regions to provide various satellite services. Some of the satellite services are Broadcasting Satellite Services, Mobile satellite services, fixed satellite services, Navigational and meteorological satellite services. [1] Different types of satellites use various frequency bands. They are given in the table below, FREQUNCY BAND OPERATING FREQUENCY (GHz) TYPES OF SATELLITE SERVICE USES L-Band 1-2 MSS S- Band 2-4 MSS C-Band 4-8 FSS X-Band 8-12.5 FSS Ku-Band 12.5-18 FSS and BSS K-Band 18-26.5 FSS and BSS Ka-band 26.5- 40 FSS References: (

Tuesday, August 20, 2019

Draw Model For Network Security Computer Science Essay

Draw Model For Network Security Computer Science Essay SENDER: Sender transfer message to other party through some sort of internet. RECEIVER: Receiver receives message send by sender through some sort of internet. Trusted third party: trusted third party is needed o secure the message transmits from one party to another. Third party distributes secret information to both the parties. Third party actually provides authenticity of message transmission. Opponent: An opponent can be a human or a virus that can harm the transmitted message going through some sort of internet. Secure message: It is a message to which a secret key is applied which is not in readable by opponent. Secret information: Secret information is a key applied to message. Ques2:Why is polyalphabetic substitution superior to monoalphatic substitution. Ans: Polyalphabetic ciphers use multiple substitution alphabetic. A monoalphabetic substitution replaces each letter with another letter according to cipher alphabet. Polyalphabetic substitution is superior than monoalphabetic because polyalphabetic substitutions are apparently more secure than monoalphabetic substitution, because frequency distribution reflects the distribution of the underlying alphabet . Ques3:Why are conventional encryption /decryption method not suitable for bank. Ans: Conventional encryption/decryption method is not suitable for bank because it is less secure. If conventional encryption/decryption is using, then the limitation is that the keys must be shared between participants before decryption can occur. If an asymmetric cipher is used instead, only public keys need to be shared private keys do not need to be share. Symmetric encryption is the oldest and best-known technique. A secret key, which can be a number, a word, or just a string of random letters, is applied to the text of a message to change the content in a particular way. This might be as simple as shifting each letter by a number of places in the alphabet. As long as both sender and recipient know the secret key, they can encrypt and decrypt all messages that use this key. Asymmetric Encryption: The problem with secret keys is exchanging them over the Internet or a large network while preventing them from falling into the wrong hands. Anyone who knows the secret key can decrypt the message. One answer is asymmetric encryption, in which there are two related keysa key pair. A public key is made freely available to anyone who might want to send you a message. A second, private key is kept secret, so that only you know it.Any message that are encrypted by using the public key can only be decrypted by applying the same algorithm, but by using the matching private key. Any message that is encrypted by using the private key can only be decrypted by using the matching public key. This means that you do not have to worry about passing public keys over the Internet . A problem with asymmetric encryption, however, is that it is slower than symmetric encryption. It requires far more processing power to both encrypt and decrypt the content of the message. Ques4:Define types of attack based on what is known to attacker. Ans: The following are the cryptographic attacks usually performed by an attacker: Known plaintext attack:  In a known plaintext attack, an attacker should have both the plaintext and ciphertext of one or more messages. These two items are used to extract the cryptographic key and recover the encrypted text. Ciphertext only attack:  In this attack, an attacker obtains encrypted messages that have been encrypted using the same encryption algorithm. For example, the original version of WEP used RC4, and if sniffed long enough, the repetitions would allow a hacker to extract the WEP key. Such types of attacks do not require the attacker to have the plaintext because the statistical analysis of the sniffed log is enough. Man-in-the-middle attack:  In this form of attack, an attacker places himself in the middle of the communications flow between two parties. Once an attacker enters the communications flow, he is able to perform a  ciphertext only attack, exchange bogus keys, etc. Replay attack:  In this type of attack, an attacker tries to repeat or delay a cryptographic transmission. A replay attack can be prevented using session tokens. Chosen plaintext attack:  In a chosen plaintext attack, an attacker somehow picks up the information to be encrypted and takes a copy of it with the encrypted data. This is used to find patterns in the cryptographic output that might uncover a vulnerability or reveal a cryptographic key. Chosen ciphertext attack:  In this type of attack, an attacker can choose the ciphertext to be decrypted and can then analyze the plaintext output of the event. The early versions of RSA used in SSL were actually vulnerable to this attack. 1:Cipher text only attack Given cipher encrypted with same key C1=Ek (p1) ,C2=Ek(p2) Attackers find key. 2:Known plain text attack Plain text is corresponding to the cipher text. Eg: P1,C1=Ek(P1) P2,C2=Ek(P2) 3:Chosen plain text attack Plain text can be chosen that gets encrypted. 4:Adaptive chosen plain text attack Can modify the plain text choice depending on results of previous encryption. 5 :Chosen cipher text attack Can choose different cipher texts to be decrypted. Ques6:Encrypt the following plaintext by playfair substitution wearediscoveredsaveyourself Ans:Playfair is a multi-letter encryption which treats diagrams in the plaintext as a single units and translates these units into ciphertext diagrams. The Playfair algo is based on use of 5*5 matrix of letters constructed using a key. Choosen key is WONDERS W O N D E R S. A B C F G H I/J K L M P Q T U V X Y Z The matrix is constructed by filling in the letters of the keyword WONDERS from left to right and top to bottom and then filling in the remainder of the matrix with the remaining letters in alphabetic order. The letters I and J count as one letter. Rules will be : 1:Repeating plaintext letters that are in same pair are separated with a filler letter . 2: Two plaintext letters that fall in the same of matrix are each replaced by the letter to the right circularly . 3:Two plaintext letters that fall in the same column are each replaced by the letter beneath to it. 4:Otherwise ,each plaintext letter in a pair is replaced by the letter that lies in its own row and the column occupied by the plaintext letter. Given string is WEAREDISCOVEREDSAVE YOURSELF Playfair substitution is OWBSWEHGABEBCGKNASXDZWFCOULgtttttttttfygjhvhghjqqQQCh

Monday, August 19, 2019

Personal Statement :: College Admissions Essays

Since the beginning of my academic endeavors, I have long cherished a dream to be a member of the social science research community, which gives our society progressive insights into human ecology. I began my undergraduate studies at Ramapo College of New Jersey with a passion for ecological justice and with the intention of majoring in environmental studies. Ramapo College’s progressive liberal arts foundation provided me with ample room to explore the multifarious array of social science courses. As I took more social science courses, however, my understanding of human social groups underwent a metamorphosis. As a result, I decided to pursue a degree in Social Science, with minors in the two fields I felt most passionately interested in, Women’s Studies and African American Studies.   Ã‚  Ã‚  Ã‚  Ã‚  Two courses that were critical in my intellectual development were the Sociology of Social Movements and the Dynamics of Domestic Violence. In the Sociology of Social Movements, I designed a research project, â€Å"Women, War, and Resistance†. In this piece I examined crucial issues surrounding wars on a global level, such as rape as a weapon of war, sexual trafficking, and various grassroots war-resistance groups formed by women on a local level. In addition, after taking the course on Dynamics of Domestic Violence, I had the opportunity of doing field work at a domestic violence shelter. For this independent study, I met with a professor of the women’s studies department on a weekly basis to discuss my experiences and to receive assistance in my research project: â€Å"The Effects of Domestic Violence on Adolescents.† My motivation to research, discover, and stimulate social change is rooted in my childhood experiences. As a young child I grew up in a household filled with domestic violence, which ultimately ended with the suicide of my father. I subsequently came to know a variation of the typical American nuclear family: a single parent household. As I began to study family dynamics further, I was able to see my life experiences in a broader context. In hindsight, I now realize the impact and weight my own mother had on my personal development. It was through her strength, determination, and optimism that I was able to find the spark within myself to set goals and dreams for my future. She encouraged me never to accept anything at face value, including the way our society attempts to define my womanhood. As a result of this, I now question American culture’s classification of a ‘successful’ family and the factors that determine a ‘stable’ family.

Sunday, August 18, 2019

Fields of Battle: The Wars for North America :: Essays Papers

Fields of Battle: The Wars for North America John Keegan, the author of Fields of Battle: The Wars for North America (334 pgs), is a very distinguished military historian. Keegan attended Oxford University, in England, his place of birth. He was Delmas Distinguished Professor of History at Vassar in fall 1997. He was a Fellow of Princeton University in 1984 and Lecturer in Military History at Cambridge, 1986-87. From 1960-1986 he was Senior Lecturer in Military History at the Royal Military Academy, Sandhurst. Since 1986 he has been Defense Editor of The Daily Telegraph. He was awarded the OBE in the Gulf War honors list, 1991. He is a Fellow of the Royal Historical Society, a Fellow of the Royal Society of Literature, and a Doctor of Laws of the University of New Brunswick. He is a Visitor of Hugh Sexey's Hospital, Bruton, and is a Trustee of the National Heritage Memorial and Heritage Lottery Funds. He was the BBC Reith Lecturer for 1998, and has lectured at countless other places around the world. John Keegan is also the aut hor of many other military-history books like The Face of Battle, The Second World War, Who’s Who in Military History, and A History of Warfare, to name a few. Despite being English, Keegan professes his love for America, but interestingly, not for Americans. Keegan says that he has visited America more than fifty times, whether for business or pleasure, but never even hints at having the desire to make the good ole’ U.S.A. his place of residence. Nonetheless, he certainly has a great knowledge of North America and its history of warfare. Fields of Battle: The Wars for North America is sort of a semi-autobiography of John Keegan’s life. At the beginning, end, and countless parts throughout the book, Keegan makes references to trips to America, his childhood conceptions of America, places he has lectured, famous people he met (Bill Clinton included), and old battlefields he has visited. The rest of the book contains very detailed accounts of the major battles fought on North American soil. This begins with the settling of North America by the British and French and their battle for dominance. Next, Keegan covers The Revolutionary War (or The War of Independence, as it is called in England). Then we are informed about the Civil War, wars against the native Indians, and finally about the invention of the airplane and its importance and effect on warfare in more recent years.

Pride in Things Fall Apart, by Chinua Achebe :: essays research papers

In the novel Things Fall Apart, by Chinua Achebe, the main character, Okonkwo, has a lot of pride. There is a well-known aphorism, ?Pride goes before a fall.? Through Okonkwo?s hard work, he became a great man, with a sense of pride and haughtiness. He then suffered a loss of pride, which ultimately led to his down fall and even his suicide. So, through Okonkwo?s actions, Achebe suggests that excessive pride can lead to down fall. For my first point, I am going to start with a joke: ?One day there was an airplane flying Bill Clinton, Bill Gates, Bill (a kid), and Billy Gram. Something went wrong with the plane, and so it had to be abandoned. The pilot strapped on a parachute and said to the passengers, ?There are only four parachutes, and I am taking one.? Bill Clinton grabbed the second and said, ?I am the most important man, and my country needs me, so I am taking one, too.? Then, Bill Gates grabbed the third one and said, ?I am the smartest man in the world, and my people need me.? After Bill Gates left, Bill (the kid) was just looking at the last parachute, when Billy Gram said, ?I am old and you are young, and you have your whole life ahead of you, so take the last parachute.? After a little while, Bill looked up at Billy Gram and said, ?I was not thinking about that, it is just that the smartest man took my back pack.? As you saw from the joke and the book, both Okonkwo and Bill Gates were full of prejud ice pride. Both thought they were great men, and saw others as inferior compared to them. But their pride led to their destruction. Second, Okonkwo?s pride was greatly bruised while attending a great warrior?s funeral, named Ezeudu. It was when ?Darkness was around the corner? (page 124), when Okonkwo?s life took a sharp turn down hill. ?Guns fired the last salute and the cannon rent the sky. And then from the center of the delirious fury came a cry of agony and shouts of horror. It was as if a spell had been cast. All was silent. In the center of the crowd a boy lay in a pool of blood. It was the dead man?s sixteen-year-old son, who with his brothers and half-brothers had been dancing the traditional farewell to their father.

Saturday, August 17, 2019

Playgroups support and offer valuable opportunities Essay

Playgroups support and offer valuable opportunities for parents to meet and share their experiences and for children to play and socialise. They are coordinated by qualified community workers who give parenting tips and advice and provide information about other community services for families. Expert guest speakers are invited to talk about topics related to parenting or childhood development. Parents are encouraged to become involved in planning and running playgroup activities. Playgroups provide a range of learning experiences to stimulate children’s intellectual growth. They learn about interactions with other children and can develop their communication skills. The community workers can help parents with behaviour-management techniques, provide information for parents about topics such as child development, health, hygiene and child safety. They can also help with developing social networks for parents, and identify developmental problems and refer families to relevant services. BENEFITS FOR FAMILIES Supported playgroups bring a number of benefits to the communities in which they operate and to the people who take part. These benefits areThis is a service that lends toys, games, puzzles and educational aids to families. The items from the toy libraries must be returned at a certain time. At some toy libraries, children are allowed to attend the library to play with the toys there. Leisure library – this provides play materials for adults, especially for disabled adults and families from disadvantaged backgrounds, who have not known the joy of play. Teenagers can also benefit form these libraries, as there is challenging activities that could positively counteract effects of boredom, such as drugs and alcohol abuse. The libraries for children, the toys/resources that are lent, can help children to develop physically, mentally, socially and emotionally. They can learn through play by imitating, exploring, creating, solving problems and sharing with others, (brothers/sisters). Toy libraries promote ACTIVE LEARNING. The libraries also help low-income families who are not able to provide their children with adequate learning opportunities. The parents may not be able to send their child to any form of pre-school centres. Specialist toys and equipment, which can be very expensive to buy, can be available for children who have special needs. Many toys which can be bought at home, end up lying about the house, with the toy library, 1 toy is exchanged for another. Other benefits for having a toy library is that it can help parents learn about and are empowered to provide suitable stimulation for their child. Some may say that parents don’t want to get involved, but the fact is that the parent doesn’t know what to do or how to do it. The toy library could help the children and parents to play together, to share the activities, this would help to strengthen the family unit. Children who are ‘at risk’ can receive preventive stimulation, the toys at the library may be graded, this can help the child make steady progress on their development. The child’s self confidence may increase with each toy, when they master the activity. Therapists report that children receiving therapy and also belong to a toy library, generally improve faster with their development and social well-being. There can be additional services that can be offered by toy libraries, these are names of childminders, schools in the area. Leaflets giving information about organisations, nutrition and different workshops, that are available in the local area. Homestart This is a charity organisation, in which parent volunteers help families and children through rough patches in their lives. Volunteers help all types of parents, mums struggling with post-natal depression, young couples who don’t have any idea of what to do during their babies early years, professional women having difficulty coping with the switch from the structured work environment, to home life and late parenthood. The volunteers provide non-judgement support to allow the people to build on their own strengths. Homestart volunteers set out to end the isolation that parents with young children experience. It offers friendship, practical help and support. They are trained how to talk, encourage, when necessary to guide mums and dads. The parent volunteers create an atmosphere in which families can cope with the pressures they are facing, this can then reduce the potential, for family breakdown. The volunteers can also help families get their act together sufficiently so they no longer need the supervision of statutory social services. E. g. in 2003/4, 822 children whose families were supported by Homestart were removed form the child protection register. The volunteers work alongside parents, not telling them how to bring up their children, but may offer advice if asked. Sure start children’s centres These centres are in the most disadvantaged areas. The services they provide are:- Good quality early learning, combined with full day care provision for children, this could be effective for both child and parents. The child would make friends, learn and develop their skills and their developmental stage. The parents may be able to go out and find work. There are effective links with Jobcentre Plus for training or employment. Their would be support and services to parents and children who may need different services. I. e. special needs. The workers there, give information and advice to parents on a range of subjects, I. e.  childcare, looking after babies and young children, education services for 3 and 4 year olds. They have drop in sessions and other activities for children and parents, this can help parents socialise with other parents, make friends, look at other children and see other children playing, parents playing with their children and learning them to do the same. It can stop parents form being isolated in their home, getting them out and active, letting them discover new activities, learning about themselves and others around them, discovering new hobbies.

Friday, August 16, 2019

Misconception of African Americans Essay

Since the beginning of time African Americans have been viewed negatively. We have always been viewed as a threat to society and frowned upon by many races. There are many cliches displayed in the media of what African Americans are supposed to act like. These conclusions cause almost immediate negative feelings from other races and sometimes by our own race. African American females in television shows and movies are often shown as the loud â€Å"ghetto† acting, angry black girl who is always â€Å"telling someone off†. Actor Tyler Perry has been criticized for illustrating African American females as â€Å"big momma†, another negative portrayal of black women. Other times shapely video vixens cause other black females to be portrayed as â€Å"jump-offs† or gold diggers. African American males have even greater judgments to overcome. They are viewed as a menace to society. They are illustrated as wild, angry, dangerous â€Å"gang bangers†. Black men are viewed as absentee fathers or abusive husbands. Although, in some cases, African American males do possess some of these characteristics, there are just as many black men that are positive role models. These ignorant judgments are called stereotypes. A stereotype is defined as â€Å"a widely held but fixed and oversimplified image or idea of a particular type of person or thing†. Stereotypes, in my own words, are judgments blindly made by people who use ignorance as an excuse to be biased against those who are different from them. There are many different types of stereotyping. Racial stereotyping, sexist stereotyping, stereotypes about cultures, and sexual orientation stereotypes are all judgments that can affect one’s life in many ways. Stereotypes are, sadly, made by everyone. Racial stereotyping, however, is the most common type of stereotyping, and can sometimes be dangerous. The Trayvon Martin story, for example, is a situation where stereotyping turned tragic. Trayvon Martin was a young African American boy who was walking from the store with nothing but Skittles and a drink in his pockets. Because of his race, and the stereotype of what black Males are capable of, he was targeted, and tragically killed. There have been many similar cases of dangerous stereotyping. People’s fear of what the media shows we are suited to do, has gotten out of control. Too many of us are dying because of this fear. While many stereotypes do seem to be believable, people like Barack Obama, Michelle Obama, my grandparents, and my mom allow me to realize that not all stereotypes are true.