3 January 2017

LAN Technologies- Ethernet, Ethernet Media Standards, Token Ring & Fibre Distributed Data Interface (FDDI)


Ethernet, Fast Ethernet and Gigabit Ethernet are the LAN technologies most commonly used today. Ethernet Version 1 was developed by Xerox Corporation during the early 1970s. Later in 1982 Xerox, Intel and DEC (Digital Equipment Corporation) together released Ethernet Version 2. Since then, Ethernet is the most popular LAN technology used in networking.

The network topology on which all the latest Ethernet technologies built is Star Topology.
Advantages of Ethernet are
       Low cost components
       Easy to install
       Easy to troubleshoot

All the devices (Servers, Workstations, Printers, Scanners etc) connected in an Ethernet network share a common transmission medium. Ethernet uses Carrier Sense Multiple Access/Collision Detection (CSMA/CD) for determining when a computer is free to transmit data on to the access medium.

 Using Carrier Sense Multiple Access/Collision Detection (CSMA/CD), all computers monitor the transmission medium and wait until the medium is free before transmitting. If two computers try to transmit at the same time, a collision occurs. The computers then stop, wait for a random time interval, and attempt to transmit again.

Collisions were common in Ethernet network (when used in a shared media) and network infrastructure devices like Ethernet Hubs usually have a small light on their front panel, that blink when collisions happen in your network.

These days, all the business networks are installed and connected using Ethernet Switches instead of Ethernet Hubs. There is no collision when devices are connected using Ethernet Switches.

Original Ethernet operate at a speed of 10 Mbps (Mega bits per second). Ethernet is capable of using a variety of media. Another faster version of Ethernet, which is even faster than Fast Ethernet, is Gigabit Ethernet.

Gigabit Ethernet provides a data transmission speed of 1,000Mbps. Gigabit Ethernet was first designed and developed as a high-speed backbone medium for large LANs. But almost all latest LANs are Gigabit Ethernet capable and Category 5e and Category 6 UTP cable can be used as the Gigabit Ethernet medium.

Ethernet networks typically operate at baseband speeds of either 100Mbps (Fast Ethernet), 1000Mbps (Gigabit Ethernet).

Fast Ethernet (100 Mbps) or Gigabit Ethernet (1000 Mbps) cannot operate on network infrastructure devices like Ethernet Hubs, Ethernet Switches and network cards designed for a 10Mbps Ethernet network. Many latest network infrastructure devices like Ethernet Switches and Ethernet network cards are capable to operate at speed of 10 Mbps or 100 Mbps or 1000 Mbps. (10/100/100).

Even a faster version of Gigabit Ethernet, 10 Gigabit Ethernet is now available. 10 Gigabit Ethernet works well with both fiber optic and copper media.

Ethernet Media Standards

Ethernet, Fast Ethernet and Gigabit Ethernet, are identified by three-part names, which is also known as Media Standard. An example of Media Standard is 10BASE-T. The first part of the Media Standard specifies the transmission speed (10, in this case specifies 10 Mbps).

The second part of the name BASE specifies that the Ethernet signal is a Baseband signal.
The final part of the Ethernet Media Standard specifies the kind of cable used. Here Tspecifies twisted-pair cable.

Token Ring

Token-Ring Lan Technology was developed by IBM in the middle 1980s as a fast and reliable alternative to Ethernet. Token ring technology uses a different concept, known as token passing, for allowing network adapters to transmit data on the media. Token Ring uses a Star Ring topology, a hybrid topology, looking physically like a Star Topology but logically wired as a Ring Topology.

Token-Ring operates in Ring Topology, in a logical ring, where the central device which is used to connect the network devices (Servers, Workstations, Printers, Scanners etc.) hosts an internal ring, where access to the network media for a network device is given only by the possession of a token that is passed from device to device on the ring. 

The central device which is used to connect the network devices is called as a Multistation Access Unit, or MAU. Please click the link to view an image of IBM token ring MAU from Wikipedia webpage.

Token-Ring is more sophisticated than Ethernet., and it includes a number of built-in diagnosis and correction mechanisms that can help troubleshoot network problems and Token-Ring networks does not produce the collisions that can take place in the Ethernet. Network. The main difference of Ethernet and Token ring is that, Ethernet uses Star Topology and Token ring uses logical Ring topology.

When a Token-Ring network starts up, the devices take part in a negotiation to decide who will become the Active Monitor. In Token-Ring network, Active Monitor is a machine with the highest MAC address and all other machines are 'Standby Monitors'. 

The job of the Active Monitor is to make sure that none of the machines are causing problems on the network, and to re-establish the ring after a break or an error has occurred.

A computer that passes the token to the next computer on the logical ring would be called the nearest active upstream neighbor (NAUN). The computer receiving the token is the nearest active downstream neighbor (NADN). Once a computer takes possession of the token and transmits data, it then creates a new token and passes it to its NADN.

Early Token-Ring networks had 4Mbps speed and later 16Mbps and 100Mbps speed Token-Ring networks were also available. Token Ring networks were replaced by Ethernet family technologies due to the advantages of Ethernet technologies.
These days, it is extremely difficult to find a business network operating using Token ring technology.

Fibre Distributed Data Interface (FDDI)

Fiber Distributed Data Interface (FDDI) is an expensive LAN technology that employs a pair of fibre-optic rings. One is primary ring and the second ring is used to replace the primary ring in the case of a network failure. Fiber Distributed Data Interface (FDDI) uses fiber-optic cable and is wired in a ring topology and Fiber Distributed Data Interface (FDDI) uses token passing as its media-access method and can operate at high speeds.

The Fiber Distributed Data Interface (FDDI) provides high-speed network backbones that can be used to connect and extend LANs.

Like token ring, FDDI also has error-detection and correction capabilities. In a normally operating Fiber Distributed Data Interface (FDDI) ring, the token passes by each network device fast. If the token is not seen within the maximum amount of time that it takes to circulate the largest ring, it indicates a network problem.

Fiber-optic cable such as the cable used with Fiber Distributed Data Interface (FDDI) can support very large volumes of data over large distances.

Fiber Distributed Data Interface (FDDI) is an expensive technology to set up because the network devices require a special network card and also fiber-optic cabling is required, which is expensive than twisted-pair cable. Because most Fiber Distributed Data Interface (FDDI) installations use a redundant second ring, more cabling is required.

Thanks for reading...

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