This is the 21st day of my participation in the November Gwen Challenge. Check out the event details: The last Gwen Challenge 2021
13. MAC Layer hardware address (MAC address)
On a LAN, a hardware address is also called a physical address or MAC address
Strictly speaking, the “address” of the 802 standard should be the “name” or identifier of each station.
But since we’re used to calling 48-bit names “addresses,” we’ll stick with that idiom, though it’s not too strict.
RA, the REGISTRATION authority of IEEE, is responsible for assigning the first three bytes (i.e., the highest 24 bits) of the address field to the vendor.
The last three bytes in the address field (i.e., the lower 24 bits) are designated by the vendor as extended identifiers. The adapter must be produced with no duplicate addresses.
An address block can produce 2 to the 24 different addresses. This 48-bit address is called MAC-48, and its common name is EuI-48.
MAC Address is actually the adapter address or adapter identifier EUI-48.
(1) The adapter checks the MAC address
Each time the adapter receives a MAC frame from the network, it first checks the MAC address in the MAC frame with hardware
If the frame is sent to this site, accept it and then do other processing.
Otherwise, the frame is discarded and no further processing is done.
“Frames sent to this site” includes the following three types of frames:
Unicast frames (one-to-one)
Broadcast frames (a pair of plenary frames)
Multicast frames (one-to-many)
14. MAC frame format for Ethernet V2
The frame length is not an integer of bytes
The received frame check sequence FCS is used to detect errors
The length of the data field is between 46 and 1500 bytes
The valid MAC frame length ranges from 64 to 1518 bytes
If an invalid MAC frame is detected, it is simply discarded. Ethernet is not responsible for retransmitting the discarded frame.
15. Minimum interval between frames
The minimum interval between frames is 9.6μs, which is equivalent to 965bit transmission time.
After a station detects that the bus is idle, it has to wait 9.6μs before sending data again. This is done so that the receiving cache of the station that has just received the data frame can be cleaned up and ready to receive the next frame
16. Consider extensions at the physical level
1) The host is connected to the hub using optical fiber and a pair of optical fiber modems
2) Reduce the collision domain
3) Advantages and disadvantages of using hubs to extend LAN
Advantages:
It enables computers belonging to different collision domains to communicate across collision domains and expands the geographical scope of LAN coverage.
Disadvantages:
The collision domain is larger, but the overall throughput is not.
If different collision domains use different data rates, they cannot be connected using hubs.
17. Consider scaling at the data link layer
Extended Lans at the data link layer use Bridges.
The bridge works at the data link layer and forwards frames received according to the destination address of the MAC frame.
The bridge has the function of filtering frames. When the bridge receives a frame, instead of forwarding it to all interfaces, it checks the destination MAC address of the frame and then determines which interface to forward the frame to
The most widely used bridge is the Transparent bridge.
“Transparent” means that the site on the LAN does not know which Bridges the frame will pass over because the Bridges are invisible to the stations.
Transparent bridge is a plug and play device whose standard is IEEE 802.1d.
