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Consider a slotted aloha system, where the time slot equals the fixed duration of each packet. assume that there are 4 stations a,b,c,d sharing the medium. (a) stations a,b,c,d receive one packet each from higher layers at times 1.3, 1.5, 2.6,5.7 respectively. show which transmissions take place when, according to the slottedaloha protocol; describe all transmissions until all four packets have been successful.when needed, each station has access to the following sequence of random number, provided by a random number generator and drawn uniformly between 0 and 1: (1) station a draws numbers: 0.31, 0.27, 0.78, 0.9, 0.9, 0.11, 0. (2) station b draws numbers: 0.45, 0.28, 0.11, 0.83, 0.37, 0.22, 0. (3)station c draws numbers: 0.1, 0.2, 0.3, 0.4, 0. (4) station d draws numbers: 0.36, 0.77, 0.9, 0.1, 0.1, 0.1, 0.1, 0. (b) in slotted aloha, a station transmits in each time slot with a given probability. what probabilities would you assign to each of the four stations so as to: (i) maximize the efficiency of the protocol? (ii) maximize fairness among the four stations? (c) will the efficiency increase or decrease if we modify slotted aloha as follows: (i) get rid of slots and allow stations to transmit immediately? (ii) implement carrier sensing? (iii) implement collision detection? (iv) implement collision avoidance?

Discuss the ways in which electronic information associated with payments is addressed in terms of security. include encryption, secure sockets layers, and secure electronic transactions in your discussion. are there any other ways that consumers and businesses can keep their payment information secure in an electronic commerce environment? do you feel that your information is safe when conducting electronic business? why or why not?

[java] create an application called registrar that has the following classes: a. a student class that minimally stores the following data fields for a student: - name - student id number - number of credits - total grade points earned and this class should also be provides the following methods: - a constructor that initializes the name and id fields - a method that returns the student name field - a method that returns the student id field - methods to set and retrieve the total number of credits - methods to set and retrieve the total number of grade points earned. - a method that returns the gpa (grade points divided by credits) b. an instructor class that minimally stores the following data fields for an instructor: - name - faculty id number - department the following methods should be provided: - a constructor that initializes the name and id fields - methods to set and retrieve the instructor’s department. c. a course class that minimally stores the following data for a course: - name of the course- course registration code- maximum number of 35 students- instructor- number of students- students registered in the course (an array)the following methods should also be provided: - a constructor that initializes the name, registration code, and maximum number of students- methods to set and retrieve the instructor- a method to search for a student in the course; the search should be based on an id number.- a method to add a student to the course. if the course is hill, then an exception with an appropriate message should be raised (try creating your own exception class for this). also, be sure that the student is not already registered in the course. the list of students should be in the order that they registered.- a method to remove a student from the course. if the student is not found, then an exception with an appropriate message should be raised (use the same exception class mentioned a method that will allow course objects to be output to a file using object serialization- a method that will allow course objects to be read in from a file created with object serializationyou will note that the student and instructor classes described above have some commonality. create aperson class that captures this commonality and uses it as a base class for student and instructor. this class should be responsible for the name and id fields and also provide atostring method that returns a string of the form name, id. this will be the inheritedtostring method for the student and instructor classes.1. draw a uml diagram for diss application.2. implement the previous classes in java. write a main program that can serve as a test class that tests all of the methods created and demonstrates that they are working