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Data unit at Data Link Layer is called

  • Q. Data unit at Data Link Layer is called
  • filter_dramaExplanation
    Answer is : B

    The correct answer is Frame

    • The Data-link layer takes the packets from the Network Layer and encapsulates them into frames. If the frame size becomes too large, then the packet may be divided into small-sized frames to make efficient flow control and error control.
    • Frames are a data-link layer data unit that is transmitted between network points. It contains complete addressing, necessary protocol, and control information. Before transmission of the frame, the data link layer protocol encapsulates the frame with a trailer and header.​
    • Assume a single link from A to B.
    • Assume service provided by the physical layer is that it will deliver bits to B in the order in which they are sent.
    • So Following are the tasks the data link layer have to do:
      • Error checking - all circuits have errors occasionally.
      • Flow regulation - Line has a finite data rate, and machines have a finite rate at which they can process incoming. Regulate flow so that slow receivers are not swamped by fast senders. 
    • The packet is a generic term for a piece of data that a higher layer wants to send.
    • The data link layer sends frames - small fixed (or max) length pieces of data. Frame length specific to hardware. The frame is packet encoded for transmission on this link.
    • As a packet travels across the Internet from A to B, it may go along multiple types of links (phone, fiber, wireless), each with different frame sizes and formats. The packet may be encoded in a different way for each link it travels on.  

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Similar Questions

  • 1.

    Which of the following statements are true?

    Statement 1: Data refer to unorganized facts that can be processed to generate meaningful result or information. 

    Statement 2: Data can be structured or unstructured.

  • filter_dramaExplanation
    Answer is : A

    The correct answer is option 1.

    Concept:

    Statement 1: Data refer to unorganized facts that can be processed to generate meaningful result or information. 

    True, Data is referred to as "raw facts." That data has not been processed. Data becomes information as it is processed. It refers to disorganized data that may be analyzed to provide useful information or results.

    Statement 2: Data can be structured or unstructured.

    True, Unstructured data is a collection of many different forms of data saved in their native formats, whereas structured data is very particular and stored in a predefined manner. Structured data benefits from schema-on-write, whereas unstructured data benefits from schema-on-read.

    Hence the correct answer is Both statements are true.

  • 2.

    Which of the query in SQL is an example of self-join?

    I. SELECT a.column_name FROM table1 a, table1 b WHERE a.x = b.x;

    II. SELECT b.column_name FROM table1 a, table2 b WHERE a.y = b.y;
  • filter_dramaExplanation
    Answer is : A
    • A self-join is a join in which a table is joined with itself (which is also called Unary relationships), especially when the table has a FOREIGN KEY which references its own PRIMARY KEY
    • To join a table itself means that each row of the table is combined with itself and with every other row of the table
    • In query 1, only one relation is used, that is, table1 and hence it is a self-join but in query II, two different relations are used, that is, table1 and table2 and hence it cannot be an example of self-join
  • 3.

    Which of the following statement is correct?

    S1: Data cube enables data to be modeled and viewed in multiple dimensions.

    S2: Data cubes can never be sparse.

  • filter_dramaExplanation
    Answer is : A

    S1: Data cube enables data to be modeled and viewed in multiple dimensions.

    This statement is correct. When data is combined into multi-dimensional matrices, then these are known as data cubes. Data cube enables data to be modeled and viewed in multiple dimensions. Data cubes are also known as materialized views or multi- dimensional databases.

    S2: Data cubes can never be sparse.

    Given statement is incorrect. A data cube is created form subset of attributes. Data cubes could be sparse sometimes because not every cell in each dimension have a corresponding data in the database.

  • 4.

    Consider the following statements of RDBMS. Which of the following are correct?

    I. Every relation in 3NF is also in BCNF

    II. Every relation in BCNF is also in 3NF

  • filter_dramaExplanation
    Answer is : D

    The correct answer is option 4.

    Concept:

    Boyce-Codd Normal Form should satisfy the following two conditions:

    • It should be in the Third Normal Form.
    • And, for any dependency A → B, A should be a super key.

    Relationship between 1NF, 2NF, 3NF and BCNF:

    I. Every relation in 3NF is also in BCNF

    False, Every relation in BCNF is also in 3NF. A relation schema that is in the third normal form then that table may or may not be in BCNF. Here 3NF is a subset of BCNF hence the given statement is False.

    II. Every relation in BCNF is also in 3NF

    True, Every relation in BCNF is also in 3NF. Here BCNF is a superset of 3NF hence the given statement is True.

    Hence the correct answer is Only II is correct.

  • 5. (<ALL) comparison operator means:
  • filter_dramaExplanation
    Answer is : B

    The ALL operator returns true if all of the subquery values meet the condition

    Syntax

    SELECT column_name(s)
    FROM table_name
    WHERE column_name operator ALL
    (SELECT column_name FROM table_name WHERE condition);

    The operator we can use must be a standard comparison operator (=, <>, !=, >, >=, <, or <=).

    Therefore the Option 2 will be correct i.e, Less than the minimum value in the subquery

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