what is the purpose of the layer 2 llc sublayer?

The information link layer is split up into logical sublayers, top of the sublayer, referred to as LLC sublayer, that ‘talks’ to the network layer and also the lower sublayer, referred to as MAC sublayer, that ‘talks’ to the physical layer below. This short article presents a short function both sublayers from the data link layer. The Figure below illustrates the dwelling of LLC and MAC Sublayers?

LLC Sublayer Overview and performance

 

Table of Contents

Top of the sublayer from the data link layer is called LLC sublayer. It communicates with upper layers from the OSI model. It will get the network protocol data, which almost always is an IPv4 packet. LLC sublayer also adds control information to assist provide the packet towards the destination. The LLC sublayer ‘talks’ to the upper layers from the application and transition the packet towards the lower layers for delivery.

LLC is implemented in software, and it is implementation is in addition to the hardware. The motive force software laptop or computer NIC and become regarded as LLC. The motive force is really a computer software and instruction that interacts directly using the computer NIC along with other hardware. Driver software also enables the communication between your network device, computer, and operating-system in addition to along with other network computers and network devices.

 

Multiplexing/De-Multiplexing

When I pointed out earlier that LLC ‘talks’ to the uppers i.e network layer. Once the data link layer received a frame in the physical layer, the LLC is searching in the Layer 3 Protocol type and paying the datagram towards the correct Layer 3 protocol. It’s known as the de-multiplexing process.

When Layer 3 transmits a packet, LLC takes it from various Layer 3 protocols like IP, IPX, ARP etc., and forward it to the MAC layer after adding the Layer 3 protocol enter in the LLC header area of the frame multiplexing. This method is known as the multiplexing process.

LLC optionally present reliable frame forwarding.  By the aid of LLC the delivering node numbering each frame during transmission known as sequnce number, in the other hands, the receiving node acknowledged each received frame while using acknowledgement number.

When the frame lost during transmission, the delivering node retransmits lost frames.  The LLC offers flow control optionally by permitting the receivers to manage the sender’s speed through control frames referred to as Receive Delay and Receive Not Delay. LLC offers the following kinds of services.

 

Unacknowledged Connectionless Service

Connectionless services are also referred to as the very best effort service e.g. IP datagram service, without prior connection establishment between source and destination and without acknowledgement. Within the connectionless service, the information is distributed towards the peer directly with no connection establishment. The connectionless services are also hard to rely on because reliability, flow control and error control are supplied in the transport layer. It’s provided flow control optionally.

 

Connectionless Acknowledged Service

In this kind of service, the information is directly sent between Layer2 peers with no prior logical link establishment. However the difference with previous is this fact service mark each frame using its sequence figures and also the peer acknowledges each frame received utilizing an Acknowledgment number field. This particular service mode can be used where data reliability is required.

The information sender can track lost or broken frames and retransmit these frames to complete reliability. The wireless links use connectionless acknowledged service, where the caliber of the hyperlink isn’t good.

 

Connection-Oriented Service

Before delivering data, may well connection is made between peers in this kind of service. Before start bandwith, the service exchanges the control frames referred to as Supervisory Frames to determine may well connection. Actual bandwith starts following the connection establishment phase has ended. There’s two types are utilized in connection-oriented service, the first is without acknowledgement and the other is by using acknowledgement.

 

Connection-oriented service Without Acknowledgment

In this kind of service may well link is made before actual bandwith start but with no idea of frames being numbered and acknowledged through Sequence number and acknowledgement number fields. The instance of the services are HDLC, PPP and LAPB.

 

Connection-oriented service with Acknowledgment

In this kind of service may well link is made before actual bandwith start, however with the idea of frames being numbered and acknowledged through Sequence number and acknowledgement number fields. Reliability and flow control services will also be supplied by the LLC sublayer by using sequence number, acknowledgement number and retransmission of lost frames. Sliding window mechanism provides Flow control.  The majority of the internet use this kind of services since the Internet uses TCP,

 

The part of MAC sublayer

MAC may be the lower sublayer from the data link layer. It’s indexed by the IEEE 802.3 standards. The figure above lists common IEEE Ethernet standards. Additionally, it shows the way the data link layer split into the LLC and MAC sublayer. The LLC sublayer ‘talks’ to the network layer as the MAC sublayer enables various network access technologies.

For example, the MAC sublayer communicates with Ethernet LAN technology to receive and send frames over copper or fibre-optic cable. The MAC sublayer also communicates with wireless technologies for example Wi-Fi and Bluetooth to receive and send frames wirelessly.

As you may know the Media Access Control (MAC) layer is between your LLC sublayer and physical layers, The MAC sublayer has got the following key tasks:

  • Data encapsulation
  • Media access control

 

Data encapsulation

The information encapsulation process includes frame set up in the transmission node and disassembly around the receiving node. To create the frame, the MAC layer adds a header and trailer towards the network layer PDU. Data encapsulation provides three key functions:

  • Data Framing-The framing process supplies a sequence of a number of figures to acknowledge several bits that comprise a frame. These sequences bits provide synchronization between your transmitting and receiving nodes
  • Addressing -The information link layer may be the cheapest within the OSI model worried about addressing. Data Link Layer receive Layer 3 PDU. The encapsulation process within the data link layer provides data link layer address in addition to labelling information having a particular destination location. Every device on the network includes a unique number, generally known as an actual address or MAC address, which is used through the data link layer protocol to make sure that data meant for a particular machine reach it correctly.
  • Error recognition -The information link each frame includes a trailer that accustomed to identify any errors in transmissions.

 

Media Access Control

The Press Access Control sub-layer second responsibility would be to control accessibility media. This sub-layer can also be accountable for the position of frames around the media and removing frames in the media. The MAC sub-layer communicates directly using the physical layer.

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