What is Media Access Control and Logical Link Control

[Pakhi]

I have recently started learning about the networking. I have just completed the basics of architecture and topology of the protocols that are used in LAN. Now I am looking for the notes to understand about the Media Access Control(MAC) and Logical Link Control(LLC). I am having some basic information about it, but it is not sufficient for me to understand the concepts. So please tell me what is Media Access Control and Logical Link Control? More information about the MAC and LLC would be helpful.

[Unnat]

The MAC is the mechanism responsible for controlling access of each station in the middle. The MAC can be done in a distributed when all the stations together to determine how and when to access the network. Also be performed centrally using a driver. The centralized system has the following advantages:

1. Priorities can provide rejection and firm capacity.
2. Access logic is simple.
3. Resolves conflicts between stations equal priority.

The main drawbacks are:

1. If the central node fails, the whole network fails.
2. The central node can be a bottleneck.

[Pratap Gad]

The techniques of media access control can be synchronous or asynchronous. The synchronous make the network behave as circuit switching, which is not recommended for LAN and WAN. The asynchronous are more acceptable because the LAN acting unpredictably and is therefore not appropriate to the maintenance of fixed accesses. The asynchronous are subdivided into 3 categories: circular rotation, backup and competition.

• Circular rotation: it rotates the opportunity to transmit to each station, so if it has nothing to transmit, declines the offer and gives way to the next station. The station wants to transmit, only allowed a certain amount of data in each shift. This system is efficient when almost all the stations want to transmit something, so that the transmission time is shared equally. But is inefficient when only a few stations are those that want to transmit as much time is wasted spinning on stations that do not wish to convey.
• Book: This technique is appropriate when the station wants to transmit a long period of time, so reserve time slots to be shared between all stations.
• Competition: In this case, all stations that want to pass on competing to do so (the media access control are distributed among all stations). Techniques are simple to implement and efficient at low load but very inefficient for high loads (when there are many stations that want access and also transmit much data.)

[Taipai]

I would like to discuss about the Logical Link Control. This layer is responsible for transmitting frames between two stations without having to go through any intermediate node. This layer should allow multiple access. This layer should identify all possible access to it, whether as a top coat or other destination stations.

• Services LLC, the LLC must control the exchange of data between two users, and can therefore establish a permanent connection, a connection when required by the exchange of data or a mixture of both (permanent connection is established only when needed).
• Protocol LLC: There are several ways of using this protocol shipments ranging from frame to frame confirmation request to logical connections between two stations sharing frames previous connection request.

[Aldous]

The Media Access Control Media Access Control is a sub-layer, by the standards of computer networks IEEE 802 . x, the lower portion of the link layer of data in the OSI model . It serves as an interface between the software part controls the binding of a node ( Logical Link Control ) and physical layer (hardware). Therefore, it is different depending on the type of physical media used ( Ethernet , Token Ring , WLAN , ...) The role of the MAC sublayer is mainly:

• recognize the start and end frames in the bitstream received from the physical layer ;
• delineate the frames sent by inserting information (such as bit extra) or in between them so that the recipient can determine the beginning and end;
• detect transmission errors, for example using a checksum (checksum) inserted by the sender and verified by the receiver;
• add the MAC addresses of source and destination of each transmitted frame;
• filter received frames by keeping only those which are intended, by checking their MAC address of destination;
• control access to physical media when it is shared.

A MAC address is a sequence of 6 bytes (often represented as hexadecimal 01:23:45:67:89: ab) that uniquely identifies each network interface.