Most widely used technology in networking is Ethernet. As we say in the early lesson that Ethernet work both in the data link layer(Layer 2) and the physical layer (Layer 1). there are different Ethernet standards that support different band of data.
- 10 Mb/s
- 100 Mb/s
- 1000 Mb/s (1 Gb/s)
- 10,000 Mb/s (10 Gb/s)
- 40,000 Mb/s (40 Gb/s)
- 100,000 Mb/s (100 Gb/s)
Ethernet standards define both the Layer 2 protocols and the Layer 1 technologies. For the Layer 2 protocols, as with all 802 IEEE standards, Ethernet relies on the two separate sublayers of the data link layer to operate, the Logical Link Control (LLC) and the MAC sublayers. We also explain MAC and LLC in earlier lessons.
As we know that data link has two sublayers. Upper sub-layer is LLC. So LLC communicate with the upper layers of the OSI model. The LLC get the network protocol data, which is usually an IPv4 packet. LLC adds control information to help deliver the packet to the destination. The LLC is used to communicate with the upper layers of the application and transition the packet to the lower layers for delivery.
LLC is implemented in software, and its implementation is independent of the hardware. The driver software of computer NIC and be considered as LLC. The driver is a software program and instruction that interacts directly with the computer NIC and other hardware. Driver software enables communication between the network device, computer, operating system as well as with other network computers and network devices.
MAC is the lower sublayer of the data link layer. It is implemented by computer hardware, typically in the NIC. The specifics are listed in the IEEE 802.3 standards. Figure 4.2 lists common IEEE Ethernet standards.It shows how the data link layer is divided into the LLC and MAC sublayers. The LLC communicates with the network layer while the MAC sublayer allows various network access technologies. For instance, the MAC sublayer communicates with Ethernet LAN technology to send and receive frames over copper or fiber-optic cable. The MAC sublayer also communicates with wireless technologies such as Wi-Fi and Bluetooth to send and receive frames wirelessly.
As we know that Media Access Control (MAC) layer is between the Logical Link Control (LLC) sublayer and physical layers, The MAC sublayer has following key tasks:
- Data encapsulation
- Media access control
The data encapsulation process includes frame assembly from transmission node and disassembly on receiving node. In forming the frame, the MAC layer adds a header and trailer to the network layer PDU.
Data encapsulation provides three key functions:
- Data Framing-The framing process provides a sequence of one or more characters that are used to recognize a group of bits that make up a frame. These sequences bits provide synchronization between the transmitting and receiving nodes.
- Addressing -The data link layer is the lowest layer in the OSI model that is concerned with addressing. Data Link Layer receive Layer 3 PDU. The encapsulation process in data link layer provides data link layer address. labeling information with a particular destination location. Every device on a network has a unique number, generally called a physical address or MAC address, that is used by the data link layer protocol to ensure that data intended for a specific machine get to it properly.
- Error detection –The data link each frame contains a trailer that used to detect any errors in transmissions.
Media Access Control
The MAC sublayer second responsibility is control access to the media. This sublayer is responsible for the placement of frames on the media and the removal of frames from the media. The MAC sublayer communicates directly with the physical layer.