Datalink layer in the IEEE standard is divided into two sub-layers of
LLC and MAC
Data Link Layer Overview
The Data Link Layer is the second layer in the OSI (Open Systems Interconnection) model and the IEEE 802 model. Its primary responsibility is to provide reliable transit of data across a physical link connecting two directly connected nodes. It ensures that data is transferred accurately between network entities by handling physical addressing, framing, flow control, and error control.
IEEE Standard Layering
The Institute of Electrical and Electronics Engineers (IEEE) has specific standards, particularly the IEEE 802 family, that define how networking operates, especially concerning local area networks (LANs). For the Data Link Layer, the IEEE standard specifies a clear division into two distinct sub-layers:
- Logical Link Control (LLC)
- Media Access Control (MAC)
This division helps manage the different functions required for network communication more effectively.
LLC Sub-layer Details
The Logical Link Control (LLC) sub-layer acts as the interface between the Data Link Layer and the Network Layer (like the Internet Protocol - IP). Its main functions include:
- Providing a consistent interface to the Network Layer, regardless of the underlying MAC sub-layer or physical medium.
- Supporting multiplexing, allowing multiple network layer protocols (like IP, IPX) to share the same network connection.
- Optionally providing error control and flow control services, though these are often handled by higher layers in modern protocols like TCP/IP.
MAC Sub-layer Details
The Media Access Control (MAC) sub-layer is responsible for controlling how devices on the network access the physical medium (like Ethernet cables or Wi-Fi) to transmit data. Its key functions include:
- Defining physical addresses (MAC addresses) for devices, which are unique hardware identifiers.
- Managing access to the shared transmission medium, preventing collisions using specific protocols (e.g., CSMA/CD for Ethernet).
- Framing data received from the LLC sub-layer into frames suitable for transmission over the physical medium, adding MAC addresses and error-checking information (like FCS - Frame Check Sequence).
Therefore, the Data Link layer, as defined by IEEE standards, is structured into these two essential sub-layers: LLC and MAC.
Important Questions from Miscellaneous
A stone is thrown horizontally from the top of a 20 m high building with a speed of 12 m/s. It hits the ground at a distance R from the building. Taking g = 10 m/s2 and neglecting air resistance will give :
A sphere of volume V is made of a material with lower density than water. While on Earth, it floats on water with its volume f1V (f1 < 1) submerged. On the other hand, on a spaceship accelerating with acceleration a < g (g is the acceleration due to gravity on Earth) in outer space, its submerged volume in water is f2V. Then:
A railway wagon (open at the top) of mass M1 is moving with speed v1 along a straight track. As a result of rain, after some time it gets partially filled with water so that the mass of the wagon becomes M2 and speed becomes v2. Taking the rain to be falling vertically and the water stationery inside the wagon, the relation between the two speeds v1 and v2 is :
Consider the following statements:
1. Distance between the longitudes becomes zero on North Pole and South Pole.
2. Distance between the longitudes is maximum on the Equator.
3. Number of longitudes is more than number of latitudes.
Which of the statements given above is/are correct?
One block of 2⋅0 kg mass is placed on top of another block of 3⋅0 kg mass. The coefficient of static friction between the two blocks is 0⋅2. The bottom block is pulled with a horizontal force F such that both the blocks move together without slipping. Taking acceleration due to gravity as 10 m/s2, the maximum value of the frictional force is :
