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802

With the IEEE Project 802 reworks the second layer of the OSI model to provide detailed specifications on most popular networks. In particular, to standardize and make them compatible with networks MAN LAN networks, the data link layer, as shown in the figure below, is divided into two sub-layers, called LLC (Logical Link Control) and MAC (Media Access Control).

1. The project
802.1
With the project, the IEEE 802.1 prepare general specifications of the entire project, introducing the idea that networks LAN and MAN , even though they use different transmission techniques, must have a common interface to the network level. Therefore defines the standard for connecting and managing local and metropolitan networks, including, in project 802.1D Spanning Tree Protocol.
The MAC sublayer then interface directly with the physical layer, and depends on the technology used to connect the network. It depends on the particular network architecture, as it communicates with the network card of the workstation and the transceiver and is involved in deciding which computer to use the means of transmission and how to send the information correctly. The MAC layer allows, through the card network to identify each host in a unique way.
The IEEE has decided to describe this tube in special forms, each of which reflects a given topology. The standard MAC sublayer and Layer 1 of the OSI model are in fact defined by the individual projects, in particular dall'802 .3, .4 dall'802, dall'802 .5 and so on.

2. The project
802.2 802.2
The project deals exclusively with the LLC sublayer , making it independent of the LAN technology used, so it includes its own protocol data unit and its interfaces and is in the process of encapsulation of the data.
This sublayer, common to all networks, it acts as an interface to the network layer above and to the MAC sublayer. It specifies how to use SAP, ie points of access to services; LLC adds to the package of control information, such as DSAP (Destination Service Access Point) and SSAP (Source Service Access Point), to allow is delivered to its destination. LLC supports both connectionless service that the connection-oriented protocol used by the highest level. The project 802.2 specifies a number of fields in the frame, which enable multiple higher layer protocols to share a single physical data link. Do not differ from an topology network to another, workstations thus refer to SAP to move the message from the LLC sublayer to the network layer of the OSI model.

3. The Standard IEEE 802.3


The Project refers to the IEEE 802.3 Ethernet already developed in 1975 by Xeros, and more particularly to a standard document, drawn up by Xeros in collaboration with Intel and Digital, which replaced the previous version of Ethernet, with a new one called Ethernet II or DIX, named after the three companies that collaborated in the new implementation. The first publication of the document by the IEEE was in 1983, and contained the physical and electrical specifications for a Ethernet network operating at 10 Mbps over coaxial cable. The project was extended several times n, and Ethernet was standardized for connecting networks with linear bus topology or star-bus, which use different types of cables, which Thicknet, Thinnet or UTP, base-band with variable bitrates, between 10 and 100 Mbps was also established as a means of accessing the transmission medium CSMA / CD.