Origen
De acuerdo como lo expone el autor Charles E. Spurgeon en su libro "Ethernet: The Definitive Guide" (2000), capitulo 1, sección 1.1, la historia de la Internet podría decirse que comienza en el año 1973:
"On
May 22, 1973, Bob Metcalfe (then at the Xerox Palo
Alto Research Center, PARC, in California) wrote a memo describing the Ethernet
network system he had invented for interconnecting advanced computer
workstations, making it possible to send data to one another and to high-speed
laser printers. Probably the best-known invention at Xerox PARC was the first
personal computer workstation with graphical user interfaces and mouse pointing
device, called the Xerox Alto. The PARC inventions also included the first
laser printers for personal computers, and, with the creation of Ethernet, the
first high-speed LAN technology to link everything together.
This
was a remarkable computing environment for the time, since the early 1970s were
an era in which computing was dominated by large and very expensive mainframe
computers. Few places could afford to buy and support mainframes, and few
people knew how to use them. The inventions at Xerox PARC helped bring about a
revolutionary change in the world of computing.
A
major part of this revolutionary change in the use of computers has been the
use of Ethernet LANs to enable communication among computers. Combined with an
explosive increase in the use of information sharing applications such as the
World Wide Web, this new model of computing has brought an entire new world of
communications technology into existence. These days, sharing information is
most often done over an Ethernet; from the smallest office to the largest
corporation, from the single schoolroom to the largest university campus,
Ethernet is clearly the networking technology of choice."
Con respecto a la evolución y estandarización de las redes,
Spurgeon agrega lo siguiente:
"The original 10 Mbps
Ethernet standard was first published in 1980 by the DEC-Intel-Xerox vendor
consortium. Using the first initial of each company, this became known as the DIX Ethernet standard. This standard, entitled The
Ethernet, A Local Area Network: Data Link Layer and Physical Layer
Specifications, contained the specifications for the operation of
Ethernet as well as the specs for a single media system based on thick coaxial cable. As is true for most standards, the DIX
standard was revised to add some technical changes, corrections, and minor
improvements. The last revision of this standard was DIX V2.0.
When the DIX standard was
published, a new effort led by the Institute
of Electrical and
Electronics Engineers (IEEE) to develop open network standards was also getting
underway.[3]
Consequently, the thick coaxial variety of Ethernet ended up being standardized
twice—first by the DIX consortium and a second time by the IEEE. The IEEE
standard was created under the direction of the IEEE
Local and Metropolitan Networks (LAN/MAN) Standards Committee, which identifies
all the standards it develops with the number 802.
There have been a number of networking standards published in the 802 branch of
the IEEE, including the 802.3[4]
Ethernet and 802.5 Token Ring standards.
[3] The IEEE is the world's largest technical professional society, with
members in 150 countries. The IEEE provides technical publishing, holds
conferences, and develops a range of technical standards, including computer and
communications standards. The standards developed by the IEEE may also become
national and international standards.
The IEEE 802.3 committee took
up the network system described in the original DIX standard and used it as the
basis for an IEEE standard. The IEEE standard was first published in 1985 with
the title IEEE 802.3 Carrier Sense Multiple Access
with Collision Detection (CSMA/CD) Access Method and Physical Layer
Specifications . The IEEE standard does not use
"Ethernet" in the title, even though Xerox
relinquished their trademark on the Ethernet name. That's because open
standards committees are quite sensitive about using commercial names that
might imply endorsement of a particular company. As a result, the IEEE calls
this technology 802.3 CSMA/CD or just 802.3. However,
most people still use the Ethernet name when referring to the network system
described in the 802.3 standard.
The IEEE 802.3 standard is the
official Ethernet standard. From time to time you may
hear of other Ethernet technology "standards" developed by various
groups or vendor consortiums. However, if the technology isn't specified within
the IEEE 802.3 standard, it isn't an official Ethernet technology.
Periodically, the latest IEEE 802.3 standards are presented to the American National Standards
Institute (ANSI), which forwards them on, where they are adopted by the International Organization for Standardization (ISO).
This organization is described in more detail later in this chapter. Adoption
by the ISO means that the IEEE 802.3 Ethernet standard is also a worldwide
standard, and that vendors from around the globe can build equipment that will
work together on Ethernet systems.”
Modelo OSI
El modelo de referencia OSI (
Open System Interconnection) se compone de 7 "capas" ascendentes del hardware al usuario final:
- Capa física
- Capa de enlace de datos
- Capa de red
- Capa de transporte
- Capa de sesión
- Capa de presentación
- Capa de aplicación
Es un modelo de referencia que no se implementó por estas razones:
•Mal momento
•Mala tecnología
•Mala implementación
•Malas políticas
A continuación se muestra un gráfico del modelo de referencia OSI:
Tanenbaum, 4 ed. 2003
Modelo TCP /IP
Modelo de descripción de protocolos de red desarrollado en los años 70, implantado en la red ARPANET la primera red de área amplia o WAN, desarrollada por encargo de DARPA, una agencia del Departamento de Defensa de los Estados Unidos, y predecesora de la actual red Internet
Tanenbaum, 4 ed. 2003
Crítica al modelo TCP /IP
• El servicio, la interface y el protocolo no están diferenciados
• No es un modelo general
• La capa de cliente a red (host to network) no es en realidad una capa.
• No se mencionan las capas fìsica y de enlace de datos.
•Los protocolos menores son dìficiles de reemplazar.
Equipos Básicos de Comunicación
Topologías de Redes
Fuente: http://www.glogster.com/rodri17/topologia-de-redes/g-6kuo1qi4591ngs7f82vrba0
Fuentes: Wikipedia
Charles E. Spurgeon en su libro "Ethernet: The Definitive Guide" (2000).
O'Reilly.
