Chapter 9 (Ethernet)

The Ethernet is known as a most frequently used technology nowadays. It functions on the two layers of OSI model the Data Link Layer and Physical Layer. In the data link layer only the lower portion of the data link layer are covered by the Ethernet which Is called Media Access Control Sub layer, it is mainly concerned on the physical components, that is useful for communication and also it had been considered as IEEE 802.3 standard.  The remaining half of the data link layer is called Logical Link Control that which creates a connection with the upper layers and set as IEEE 802.2 standard.

 As Ethernet evolve from its foundation to the point in time, the first version of Ethernet was known as CSMA/CD or Carrier Sense Multiple Access with Collision Detection, it manage and fix the problems encountered whenever plenty of devices communicate and shared physical medium, it detect and handle collisions and manage the communications. The question is, how it is done by the CSMA/CD? There is what we called as process first is called Carrier Sense in which the source devices will listen to the collision on the line before transmitting the message. Second is the Multi-Access it is where the first device sends signal to the second devices, but the signal didn’t reach to the second device and there’s a possibility that the second devices may sends signal too, without reaching each other and the message will eventually destroyed and corrupted. Next process is Collision Detection where the devices can detect an increase of amplitude signal. Jam Signal and random back off is the last process of CSMA/CD, it happens when the collision is detected, the jamming signal is being send to inform other devices that there is a collision happening. After the collision subside the devices that cause collision will not again send message at the same time, so there is what we called as random back off.

MAC address helps in determining the source and destination address within a network, it is 48-bit binary value expressed as 12 hexadecimal digits. It is sometimes called as Burn-in-address since it was encoded to the ROM chip permanently. It is also used to determine whether the message should pass to the upper layers for processing. The MAC address represented depending on the hardware and software manufacturer and it may look like this 00:05:9A:3C:78:00, or 0005.9A3C.7800, which is assigned to workstations. The mapping of IP address to MAC addresses is done through ARP or Address Resolution Protocol. ARP has two basic functions: resolving IPv4 to MAC addresses and maintaining a cache of mappings.