Technology and Media access control method for Ethernet networks

Certification: Cisco CCIE Routing and Switching - Cisco Certified Internetwork Expert Routing and Switching

In this era there are lots of advances mainly in terms of internet technology, for example there is technology and media access control methods that are used for Ethernet networks. These are considered to be important only when one is able to understand well what they actually mean.

Media Access Control Method

It is commonly referred to as MAC which is simply one of the sub layers of the OSI model that is made up of seven layers to be more precise it is layer number two and acts as interface that allows computers to transmit signals between a control link that is logic and the physical layer of a network. In other words it allows flow of the network therefore detecting and preventing their collision.

Another importance of MAC method is that it allows several channels to communicate within networks that are of multiple accesses hence incorporating a shared medium; because of this there is also the emulation of duplex communication that is considered to be full hence enabling  the following communication services; single cast, multicast or broadcast communication. Its hardware is known as Media access controller and there are four main media access controls used in networking:

• Carrier sense multiple access with collision detection used in Ethernet networking which is also the area of interest in this case.
• CSMA/CA that is used for apple talk networking
• Demand priority in 100 Base VG networking
• Token ring, token passing and fiber distributed data networking

Ethernet networks

Ethernet is simply a local area networking that was first developed by the Digital Equipment Corporation whose latest MAC serial number is IEEE 802.3u and for most applications it is considered to be reasonably fast and flexible when it comes to its usage and it is also inexpensive. There are several types of Ethernet networks namely;

• 10 Base-FL technology
• 10 Base-2  technology that is thin
• 10 Base-5 technology which is thick
• 10 Base-T technologies which is the most common type of Ethernet network.

Functions of MAC method in Ethernet networks

This is according to 802.3-2002 under section 4.1.4 some of the functions are listed below

• To receive and transmit normal frames which is its main function
• To append and also confirm the frame sequence
• To bring about inter frame gap enforcement
• To discard any frames that appear to be malformed
• Can either append or remove the start frame delimiter and padding incase of any problem
• Half duplex compatibility and retransmission of back offs and any MAC addresses.

As earlier seen the technology and MAC method that mostly deals with Ethernet network is referred to as carrier sense multiple access with collision detection abbreviated as CSMA/CD.

CSMA/CD:

This can be simply defined as a media access control method that is mostly used in Ethernet network which is one of the local area networking systems. It has a scheme that is usually highly carrier sensing whereby there is a data station that detects other signals and in the process there is transmission of a frame and when it detects a collision it immediately stops transmitting the frame and later on tries to resend the frame.

Each MAC contains a unique serial number that is known as MAC address that uniquely identifies a specific network in this case Ethernet network from other available networks. The most common Ethernet network physical address is the IEEE 802 with 48bits. The advantage of having an address is to allow easy delivery of data packets within the sub network.

Procedure of the CSMA/CD:

There are several steps undertaken when it comes to CSMA/CD in other words how it works since it is an automatic process:

• Transmission of the frame. If it appears to be ready then it goes to the next point.
• Detection of whether the medium is idle.

If this not the situation it waits till it is ready to start transmission

• It then starts the transmission
• It then detects whether any collision occurred during transmission if so, it proceeds to the collision detection procedure
• Lastly, there is the resetting of retransmission counters and then the end frame transmission.

Collision detection procedure

The process is quite simple, first of all there is a continued transmission using a jam signal. Jam signal usually carries a 32-bit binary pattern which is commonly sent by the data station to inform others not to transmit because of occurrence of a collision. Next it increments the retransmission counter and continues to attempt he transmission till the maximum number of attempts is reached after which it aborts. When this is done there is the calculation of random back off period basing on the number of collisions after which the last stage is to go back to the first stage of the procedure of how CSMA/CD operates.

Applications:

It is mostly common in the following:

• Shared media Ethernet variants for that matter 10BASE5 and 10BASE2
• In the twisted pair Ethernet repeater hub
• Modern Ethernet network built mostly with switches and full duplex connections
• IEEE standard 802.3

Benefits of Technology and MAC methods for Ethernet networks

One of the benefits is that it improves the performance of the Ethernet networks, the ability to detect any collision allows for easy and faster fixing of the problem and as a result allows smooth flow of the network since it takes a very short time before transmission can go ahead as required. Another benefit is that there is no need to buy and install this program because it is automatic and also when it comes to it performing its functions there is no need to alert its user.

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