Page 69 - Handout Computer Network.

matches the physical destination address carried by the data frame. If there is no match, the
NIC discards the data frame. If there is a match, the NIC verifies the destination address in the
frame header to determine whether the packet is properly addressed. When the data passes
its destination station, the NIC for that station makes a copy, takes the data out of the
envelope, and gives the data to the computer to be processed by upper-layer protocols such
as IP and TCP.

https://www.youtube.com/watch?v=HLziLmaYsO0&t=85s

3.7.2 Ethernet Frame Structure

At the MAC sublayer, the frame structure is nearly identical for all speeds of Ethernet

(10/100/1,000/10,000 Mbps). Half-duplex Gigabit Ethernet 1000BASE-T and the “W” versions
of 10-Gb Ethernet have certain timing issues that require minor differences in how the
interframe spacing is handled by the MAC sublayer, but these are otherwise the same as the
other speeds.

However, at the physical layer, almost all versions of Ethernet are substantially different from
one another, and each speed has its own set of architecture design rules.

https://www.youtube.com/watch?v=JsYqqDqmQaE

3.7.3 Ethernet Operation

When multiple stations (nodes) must access physical media and other networking
devices, various media access control strategies are used. This section briefly reviews the
access control strategies and focuses on Ethernet access control method—CSMA/CD. It should
be noted that although CSMA/CD has immense historical importance and practical importance
in original Ethernet, it is diminishing somewhat in implementation for two reasons:
• When four-pair UTP is used, separate wire pairs for transmission (Tx) and reception
(Rx) exist making, copper UTP potentially free from collisions and capable of
fullduplex operation, depending on whether it is deployed in a shared (hub) or
switched environment.

• Similar logic applies to optical fiber links, where separate optical paths.

—a transmission fiber and an reception fiber.

—are used. One new form of Ethernet.

—1000BASE-TX, Gigabit Ethernet over copper.

—uses all four wire pairs simultaneously in both directions, resulting in a
permanent. collision.
In older forms of Ethernet, such a permanent collision, preclude the system from
working. Yet in 1000BASE-TX, sophisticated circuitry can accommodate this
permanent collision, resulting from an attempt to get as much data as possible
over UTP.

69