Page 68 - M. Abrahim Thesis

Chapter (3) Networking Media and Data Link Layers Protocols

to send data to another device, it can open a communication pathway to the other device by
using its MAC address. When a source device sends data out on a network, the data carries the
MAC address of its intended destination. As this data propagates along the network medium,
the NIC in each device on the network checks to see if its MAC address 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.

78