Draw an Entity relationship diagram (ER) for a university according to the following rules: 1- ­‐ For each student the university needs to keep track of: first name, last name, student id, address, phone no and their major.
2- ­‐ The student id is identical for each student.
3- ­‐ Each course has a number, name and credit. The course number is unique for each course.
4- ­‐ Each department has a name, code and location. The code is unique for each department.
5- ­‐ Each course may has one or more sections where each section is belong to only one course.
6- ­‐ A department offers one or many courses. 7-­‐ Some courses have perquisite courses.
8-­‐ Each student could register in one or more courses.

In your diagram you need to show the following: 1-­‐ The primary key for each entity.
2-­‐ The cardinality and participation between entities.

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?