The two most prominent LAN technologies in use today are Ethernet (supports bandwidths of up to 100 Gbps equivalent to 100,000 Mbps) and WLAN.

Ethernet operates in the data link layer and the physical layer. Ethernet sublayers are related to the frame fields. The Ethernet MAC address is used and a MAC address table is built up in a switch. On the switch ports there is forwarding methods and port settings available on Layer 2. Also switch speeds come into the methods.

Logic to physical to logic
IEEE 802.2 to IEEE 802.3 (fast ethernet, over fibre over, copper over 10gbt fibre) to IEEE 802.2

The frame size is 64 bytes to a maximum of 1518 bytes, excluding the preamble. Runt list than 64bytes are discarded/dropped by receiving stations. They are invalid. Bigger than 1500 are called jumbo frames. A reason for bad frames could be collision or unwanted signals.

Ethernet Switching

  1. All frames must be at least 64 bytes long. Additional bits called a "pad" are used to increase the size of small frames to the minimum size.
  2. The FCS field uses a CRC to detect errors in a frame.
  3. The EtherType field identifies the upper layer protocol that is encapsulated in the Ethernet Frame.
  4. The first few bytes of the preamble inform the receiver of a new frame.
  5. The LLC sublayer is responsible for controlling the network interface card through software drivers
  6. The LLC works with upper layers to support higher level protocols.
  7.  A function of the MAC sublayer is checks for bit errors, supports (with either avoidance or detection of collisions) Ethernet technologies, and controls access to the media

Switch It

The fundamentals are learning and forwarding, then filtering frames using the MAC address table. These tables are stored in the switch. The frame can be sent to the default gateway if the IP address is for a remote network.

So to recap the switch forwards a frame based on the source MAC address, the destination MAC address, and information in the switch MAC table.

A the following are possible when the switch forwards the frame.

The switch adds the source MAC address which is currently not in the MAC address table, Frame is a broadcast frame and will be forwarded to all ports, Frame is a unicast frame and will be sent to either a specific port only or will be flooded to all ports, but could be dropped at the switch.

A function or operation performed by the logic layer control LLC sublayer is that it communicates with upper protocol layers.

Two functions or operations performed by the media access control MAC sublayer are that it is responsible for Media Access Control and it adds a header and trailer to form an OSU layer PDU.

Switch Speeds and Forwarding Methods

  1. The two methods for switching data between ports on a switch are cut-through switching and store-and-forward switching.
  2. Cut-through switching is implemented using either fast-forward switching or fragment-free switching.
  3. Switches use two memory buffering techniques: Port-based memory buffering and shared memory buffering.
  4. Autonegotiation is a technology that automatically negotiates the speed and duplex between two connected devices.

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