|
The Ethernet architecture is now the most
popular type of LAN architecture. Architecture refers to the overall
structure of a computer or communication system. It determines the
capabilities and limitations of the system. The Ethernet architecture
is based on the IEEE 802.3 standard. The IEEE 802.3 standard specifies
that a network implements the Carrier Sense Multiple Access with Collision
Detection (CSMA/CD) access control method. CSMA/CD uses
baseband transmission over coaxial or twisted-pair cable that is laid
out in a bus topology (a linear or star bus). Standard transfer rates
are 10 Mbps or 100 Mbps, but new standards provide for gigabit
Ethernet, which are capable of attaining speeds up to 1 Gbps over
fiber-optic cable or other high-speed media.
10BASE-T
Currently 10BASE-T is one of the most popular Ethernet
implementations. It uses a star topology. The 10 stands for the
common transmission speed of 10 MBps, the "BASE" stands for
baseband mode, and the "T" stands for twisted pair cabling. The
term Ethernet cable is used to describe the Unshielded Twisted-Pair
(UTP) cabling that is generally used in this
architecture. Shielded Twisted-Pair (STP) also can be used.
10BASE-T and its cousin, 100BASE-X, make networks that are easy to
set up and expand.
- Advantages of 10BASE-T –
Networks based on the 10BASE-T specifications are
relatively inexpensive. Although a hub is required to connect more
than two computers, small hubs are available at a low cost. The
10BASE-T network cards are inexpensive and widely available.
Twisted-pair cabling, especially the UTP most commonly used,
is thin, flexible, and easier to work with than coaxial. It uses
modular RJ-45 plugs and jacks, so it is literally a
"snap" to connect the cable to the NIC or hub.
Another big advantage of 10BASE-T is its ability to be upgraded.
By definition a 10BASE-T network runs at 10 Mbps. However, by using
Category 5 cable or above and 10/100 Mbps dual-speed NICs, an
upgrade to 100 Mbps can be achieved by simply replacing the hubs.
- Disadvantages of 10BASE-T–
The maximum length for a 10BASE-T segment (without repeaters) is
only 100 meters, which is about 328 feet. The UTP used in such a
network is more vulnerable to Electromagnetic
Interference (EMI)
and attenuation than other cable types. Finally, the extra cost of
a hub may not be feasible.
The high-bandwidth demands of many modern applications such as
live video conferencing and streaming audio have created a need
for speed. Many networks require more throughput than is possible
with 10 Mbps Ethernet. This is where 100BASE-X, also called Fast
Ethernet, becomes important.
100BASE-X
100BASE-X comes in several different varieties. It can be
implemented over 4-pair Category 3, 4, or 5 UTP (100BASE-T). It can
also be implemented over 4-pair Category 5 UTP or Shielded Twisted
Pair (STP) (100BASE-TX), or as Ethernet over 2-strand fiber-optic
cable (100BASE-FX).
- Advantages of 100BASE-X – Regardless of the implementation, the big advantage of
100BASE-X is its high-speed performance. At 100 Mbps, transfer rates
are 10 times that of 10BASE2/10BASE5 (both outdated technologies), and
10BASE-T.
Because it uses twisted-pair cabling, 100BASE-X also shares the
same advantages enjoyed by 10BASE-T. These include its low cost,
flexibility, and ease of implementation and expansion.
- Disadvantages
of 100BASE-X – 100BASE-X
shares the disadvantages inherent to twisted-pair cabling of 10BASE-T,
such as susceptibility to Electromagnetic Interference
(EMI) and
attenuation. 100 Mbps NICs and hubs are generally somewhat more
expensive than those designed for 10 Mbps networks, but prices have
dropped as 100BASE-X has gained in popularity. Fiber-optic cable
remains an expensive cabling option, not so much because of the cost
of the cable itself, but because of the training and expertise
required to install it.
1000BASE-T
If 100BASE-X is known as Fast Ethernet, 1000BASE-T must be
considered a speed demon. Its common nickname is Gigabit Ethernet.
Although not yet in widespread implementation in production
networks, this architecture supports data transfer rates of 1 Gbps,
which is remarkably fast. Gigabit Ethernet is, for the most part,
a LAN architecture although its implementation over fiber-optic
cable makes it suitable for Metropolitan Area Networks
(MANs).
- Advantages
of 1000BASE-T – The
greatest advantage of 1000BASE-T is performance. At 1 Gbps, it is 10
times as fast as Fast Ethernet and 100 times as fast as standard
Ethernet. This makes it possible to implement bandwidth-intensive
applications, such as live video, throughout an intranet.
- Disadvantages
of 1000BASE-T – The
main disadvantages associated with 1000BASE-T are those common to all
UTP networks, as detailed in the sections on 10BASE-T and 100BASE-T.
|
|
