What Is A Role Of The Logical Link Control Sublayer?

what is a role of the logical link control sublayer?

Question: What is a role of the logical link control sublayer?

1: To provide data link layer addressing.

2: To provide access to various Layer 1 network technologies.

3: To define the media access processes performed by network hardware.

4: To mark frames to identify the network layer protocol being carried.

Final Answer: [4] To mark frames to identify the network layer protocol being carried.

What Is Logical Control Sublayer?

What is a role of the logical link control sublayer? However, before we dive into that, let’s find out the logical link control layer. 

The Logical Link Control (LLC) sublayer controls the flow control, data link layer’s synchronization, and error-checking capabilities and offers data link logic. Unlike the MAC sublayer, this layer can manage direct link signals, but it can also provide connectionless service. 

Class I LLC is for connectionless activities, but Class II LLC may handle connectionless and connection-oriented operations. Accordingly, each LLC sublayer frame sent is acknowledged in a connection-based communication.

The LLC sublayer on the receiving device keeps track of the LLC blocks it obtains, also known as protocol data units (PDUs). If a chassis is lost through the transfer of data, it can request the output terminal to restart the transmission from the beginning, starting with the PDU that never turned up.

The LLC sublayer resides much above the MAC sublayer and serves as a bridge between the higher layers and the MAC sublayer protocols. IEEE 802.2 defines the LLC sublayer itself. 

The LLC sublayer is primarily concerned with managing mac addresses in message frames. This layer also handles sequencing, link addressing, and the definition of service access points.

Role Of Logical Control Sublayer

What is a role of the logical link control sublayer? If you want to know the answer, you must understand the OSI model first, which has seven levels, and it uses all of them to communicate over a network. The logical link control sublayer lies at the top of the data link layer. 

There are two sublayers in the data link LLC. The logical connection layer is one, and the Media access control layer is the other. It’s used to provide the many ways to get to the medium access layer.

In return, the LLC protocol gets services from the other. Therefore, what is a role of the logical link control sublayer? Let’s take a look:

  • One station delivers data in the form of frames to the other workstations without waiting for approval from the target address.
  • It does not create a connection between the two stations and does not terminate it after the conversation is over.
  • If data is lost during data transfer, the frames will not be recovered.
  • It’s ideal for media communication since it only allows for the shortest possible delay between stations.
  • The logical link control services have a meager error rate.
  • Before the broadcast, no link is created between the two stations.
  • These services are mainly used to establish a point-to-point connection.
  • Before commencing communication between the two workstations, the LLC network supplies the connection-oriented services.


The 802. standards specify all the functions of a logical link control layer. We all know that the logical link control sublayer’s primary function is to deliver services at the network layer. The network layer is supported by the logical link control, which offers service access points. 

If you are clear about what is a role of the logical link control sublayer, let us resume the discussion with the precise functions of an LLC sublayer.

1: Multiplexing/De-Multiplexing

What is a role of the logical link control sublayer? 

As we previously said, LLC connects with the top layers, i.e., the network layer. When the data link layer receives a frame from the physical layer, the LLC examines the Layer 3 Protocol type before transferring the datagram to the appropriate Layer 3 protocol. The technique is known as de-multiplexing. 

When Layer 3 delivers a packet, LLC extracts it from various Layer 3 protocols such as IP, IPX, ARP, and so on. It also forwards it to the MAC layer after specifying the Layer 3 protocol type in the LLC header section of the multiplexed frame. 

On the other hand, the receiving node uses the acknowledgment number to acknowledge each received frame.

2: Unacknowledged Connectionless Service

Without previous connection establishment between source and destination and without acknowledgement, a connectionless service is sometimes known as a best-effort service, such as an IP datagram service. 

LLC offers dependable frame forwarding as an alternative. The transmitting node uses LLC to number each frame during transmission, referred to as the sequence number. Then, without establishing a connection, data is transferred directly to the peer in the connectionless service. 

The connectionless service is likewise unreliable because dependability, flow management, and error control are supplied at the transport layer. That posits flow control as the only viable option.

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3: Connectionless Acknowledged Service

In this sort of service, data is transferred immediately between Layer 2 peers without the need for a logical link to be established beforehand. However, unlike the previous service, this one assigns a sequence number to each frame.

Thus, the peer acknowledges each frame received with an acknowledgment number field. When someone requires data dependability, they employ this service.

The data transmitter can track missing or broken frames and retransmit them to ensure dependability. In addition, when the link quality is poor, the wireless connections employ connectionless acknowledged service.

4: Connection-Oriented Service

What is a role of the logical link control sublayer? Well, logical links also offer a connection-related service to its connected networks. A logical link is created between peers before transferring data in this form of service. 

The service exchanges control frames known as Supervisory Frames before beginning data transfer to establish a logical connection. 

After the connection formation step is completed, the actual data transfer begins. In connection-oriented services, there are two types: one with acknowledgment and another without acknowledgement.


What is a role of the logical link control sublayer? We have already explained it. However, if you have some other questions, take a look below:

1: What Are Two Services Performed By The Data Link Layer Of The OSI Model?

Ans: The data link layer is the second phase of the seven-staged OSI Model. It accepts the Layer 3 packets and encloses them into frames. On the other hand,  the data link layer also performs error detection services and offers media access control.

2: What Is Logical Link Control Layer?

Ans: Logical Link Control Layer offers logic for the data link in a way like it controls the data synchronization, flow control, multiplexing, and even error-checking functions. It is divided into two sublayers, the medium access control, and the LLC sublayer.

3: What Is The Purpose Of The MAC Sublayer?

Ans: The primary purpose of the MAC sublayer is to act as a bridge between layer 1 and LLC Ethernet sublayer. It imitates a duplex logical communication channel in a multipoint network. On the other hand, this channel provides broadcast, unicast, or multicast communication services.

The Bottom Line

In this article, we have tried our best to answer the ‘What is a role of the logical link control sublayer?’ question. We have described its roles and responsibilities and shed light on its primary functions. If you are still unsatisfied with these answers and are stuck on something else, let us know in the comment section below.

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