Ethernet standard, like those associated with conducted media,

was the first commercially available local area network system and remain,
without a doubt, the most popular local area network system today. The wired
version of Ethernet is  based primarily
on the star-wired bus topology and uses the CSMA/CD medium access protocol.
Because Ethernet is so popular and has been around the longest, it has evolved
into a number of different forms. To avoid mass mayhem, the IEEE created a set
of individual standards specifically for Ethernet  or CSMA/CD local area networks, all under the
category of 802.3.let’s examine the different 802.3 protocol in alittle more
detail. For your reference, the 802.3 standars to be discussed are summarized
in table 1.1

Table 1.1

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original 802.3 standard include 10Base5, 10Base2, 1Base5, and 10BaseT. The 10Base5
standard was one of the first Ethernet standards approved. The term “Base” is
an abbreviation for baseband signals using a Manchester encoding. Recall the
baseband signals are digital signals. Because there is no multiplexing of digital
signals on any baseband LAN’s there is onlt one channel of information on the
network. The 10 of 10Base5 represent a 10-Mbps transmission speed, and the 5
represents 500-meter maximum cable segment length.(Note that these standard,
like those associated with conducted media, are based on the Metric system;
where applicable, the English equivalent will be provided.)


Cheapernet) was designed to  allow for a
less-expensive network by using less-expensive components . The 10Base2 network
can transmit 10-Mbps digital signals over coaxial cable, but  only for a maximum of 200 meters (the value 2
in 10Base2).



1Base5 was a system designed for twisted pair writing,
but with only a 1-Mbps data transfer rare for 500 meter. Perhaps the most
popular Ethernet system ( and the most popular local area network system
overall) is 10BaseT.A 10BaseT system transmit 10-Mbps baseband (digital)
signals over twisted pair maximum of 100 meters per segment length.


Since each mode on a
10 Base-T network has its own cable connecting it to a central hub,it is far
less likely that any node can cause the entire network to fail. The hub also
has a “partitioning” function built into it which allows it to detect a problem
on any of its ports.If a problem is found,the node is disconenected from the
rest of the network. This isolates thr problem until the node can be
troubleshot and repaired.Because of the partitioning function built in to the
hubs and the star-wired topology, it is generally easy to troubleshoot a
10BaseT a worst-case scenario,one can be trounleshoot by simple
disconnecting nodes from the hub one at a time until the network recovers. Usually,the
hub will give an indication as to which node is causing  a problem,allowing the technician to
troubleshoot that node as opposed to speding many hours finding where the
problem is.

Token-Ring Lan Technology was developed by IBM in the middle
1980s a fast  and reliable alternative to
Eternet.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, Workstation, Printers, Scanners and etc.) hosts an internal ring,where acess to the network
media for a network device is given only by the possession of a token that is
passed from device to device in the ring. The central device which is used to
connect the network device is called as a Multistation Acess Unit,or MAU.
Token-ring is more sophisticated than Ethernet , and it includes a number of
built-in diagnosis and correction mechanism that can help troubleshoot shoot
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 Monithor 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 ti
its NADN.Early Token-Ring network has 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 .

Token Ring networks are deterministic in nature. In English,
this means that the nodes may only transmit at certain, well defined times. This
eliminates incidents of two or more nodes transmitting at the same time and
corrupting each other,s transmission (collisions).  The elimination of collisions results in a network
where data almost always gets to its destination on the first attempt, greatly
reducing retransmissions which waste bandwidth at the same wire speed.