AN INTRODUCTION TO THE OSI MODEL

Inglés II: LCC- LSI Práctica de Aprendizaje N° 4: “Phrasal Verbs” y Características del Texto Expositivo
Año 2012
PRE-READING ACTIVITY
Actividad 1: Lee los dos primeros párrafos del texto y elegí entre las opciones para completar los
espacios en blanco.
AN INTRODUCTION TO THE OSI MODEL
By Andrew Beattie, February 10, 2012
Takeaway: Instead of serving as protocol, the OSI model has become a teaching tool that shows
how different tasks within a network should be handled in order to promote error-free data
transmission.
Source: Flickr/jonjohnson
The open system interconnection model, better known as the OSI
model, is a network
universal
that was originally developed as a
for creating networks. But instead of serving
as a model with agreed-upon
that would be used
worldwide, the OSI model has become a teaching tool that shows
how different tasks within a network should be handled in order to
promote error-free data transmission.
1. arrangement- frame- map
2. topology- standard- architecture
3. protocols- devices- policies
These jobs are split into seven
, each of which depends on the function’s “handed-
off” from other layers. As a result, the OSI model also provides a guide for
network problems by tracking them down to a specific layer. Here we’ll take a look at the layers
of the OSI model and what functions they
within a network.
4. levels- stages- layers
5. diagnosing- solving- troubleshooting
6. perform- realize- do
READING ACTIVITIES
Actividad 2: Responde con información de todo el texto.
1) ¿Adónde se ubica la capa física y de qué se encarga principalmente? ¿Cuáles son sus pro y
sus contra?
Inglés II: LCC- LSI Práctica de Aprendizaje N° 4: “Phrasal Verbs” y Características del Texto Expositivo
Año 2012
1. Physical Layer
The physical layer is the actual cable, fibers, cards, switches, and other mechanical and
electrical equipment that make up a network. This is the layer that transforms digital data into
signals that can be sent down a wire to transmit data. These signals are often electrical but, as
in the case of fiber optics, they can also be non-electrical signals such as optics or any other type
of pulse that can be digitally encoded. From a networking perspective, the purpose of the
physical layer is to provide the architecture for data to be sent and received. The physical layer
is probably the easiest layer to troubleshoot but the most difficult to repair or construct, as this
involves getting the hardware infrastructure hooked up and plugged in.
2) ¿Qué funciones cumple la capa de enlace?
2. Data Link Layer
The data link layer is where information is converted into coherent “packets” and frames that
are passed to higher layers. Essentially, the data link layer unpacks raw data coming in from the
physical layer and translates information from the upper layers into raw data to be sent over the
physical layer. The data link layer is also responsible for catching and compensating for any
errors that occur in the physical layer.
3) ¿Cuáles son las principales responsabilidades asignadas a la capa de red?
3. Network Layer
The network layer is where the destination for incoming and outgoing data is set. If the data link
layer is the highway for cars to drive on, the network layer is the GPS system telling drivers how
to get there. Addressing is added to the data by tacking on information around the data packet in
the form of an address header. This layer is also responsible for determining the quickest route
to the destination and the handling of any problems with packet switching or network
congestion. This is the layer where routers work to ensure that data is properly re-addressed
before passing it on to the next leg of the packet’s journey.
Inglés II: LCC- LSI Práctica de Aprendizaje N° 4: “Phrasal Verbs” y Características del Texto Expositivo
Año 2012
4) ¿Cómo garantiza la capa de transporte la calidad y confiabilidad de la comunicación.
4. Transport Layer
The transport layer is responsible for streaming data across the
network. At this level, the data is not thought of in terms of
individual packets but more in terms of a conversation. To
accomplish this, protocols -which are defined as “rules of
communication- are used. The protocols watch the complete
transmission of many packets -checking the conversation for
errors, acknowledging successful transmissions and requesting
retransmission
if
errors
are
detected.
The network layer and the transport layer work together like a
postal system. The network layer addresses the data, much like
a person addresses an envelope. Then, the transport layer acts
as the sender’s local postal branch, sorting and grouping all
similarly addressed data into larger shipments bound for other
local branches, where they will then be delivered.
5) ¿Qué rol desempeña la capa de sesión?
5. Session Layer
The session layer is where connections are made, maintained and ended. This usually refers to
application requests for data over the network. Whereas the transport layer handles the actual
flow of data, the session layer acts as an announcer, making sure that the programs and
applications requesting and sending data know their requests are being filled. In technical terms,
the session layer synchronizes data transmission.
6) ¿De qué tarea/s se encarga la capa de presentación?
6. Presentation Layer
The presentation layer is where received data is converted into a format that the application it is
destined for can understand. The work done at this layer is best understood as a translation job.
Inglés II: LCC- LSI Práctica de Aprendizaje N° 4: “Phrasal Verbs” y Características del Texto Expositivo
Año 2012
For example, data is often encrypted at the presentation layer before being passed to the other
layers for sending. When data is received, it will be decrypted and passed on to the application it
is intended for in the format that is expected.
7) ¿Adónde se ubica la capa de aplicación, de qué función se encarga y de qué se vale para
llevarla a cabo?
7. Application Layer
The application layer coordinates network access for the software running on a particular
computer or device. The protocols at the application layer handle the requests that different
software applications are making to the network. If a Web browser wants to download an image,
an email client wants to check the server and a file-sharing program wants to upload a movie,
the protocols in the application layer will organize and execute these requests.
Putting It All Together
We’ve looked at the OSI model from the bottom layer up. A simplified summary of this process
can be broken into three requirements:
1. The computer has to be hooked up to a network (physical layer), and must have a way to
read data (data link layer). The network must also have a proper address (network layer)
to know how to come and go.
2. The network itself has to have ways of efficiently delivering data to the proper recipients
(transport layer) and letting those recipients know it has been delivered (session layer).
3. The data has to be unpacked and delivered to the application in a format it understands
(presentation layer) and then must fill the requests various software applications make to
the network for the user (application layer).
Sending data works in the opposite direction, starting at the top
OSI layer – the application layer - and moving down through the
model, finally ending when the data is received by the recipient
via the physical layer.
Actividad 3: De acuerdo al orden presentado en el texto (comenzando de abajo a arriba) señalá
cuáles de siguientes funciones/tareas realiza cada capa del modelo OSI.
Inglés II: LCC- LSI Práctica de Aprendizaje N° 4: “Phrasal Verbs” y Características del Texto Expositivo
NÚMERO/CAPA
Año 2012
FUNCIÓN/ TAREA
Señal y transmisión binaria.
Representación de los datos en un formato reconocido por otras capas.
Determinación de ruta e IP (Direccionamiento lógico).
Ejecutar aplicaciones de usuarios.
Sincronización de la transmisión de datos.
Conversión de datos.
Conexión eficiente/fiable (de extremo-a-extremo).
All People Seem To Need Data Processing
Please Do Not Throw Sausage Pizza Away
Actividad 4: Elaborá una breve conclusión extraída de los dos párrafos finales
Conclusion: Lessons From the OSI Model
The OSI model provides a conceptual viewpoint of networks by showing what tasks are handled at
each level. On a practical level, however, the picture becomes much more complicated. Some
devices and protocols fit neatly into a single layer, while others operate in multiple layers and
carry out functions that affect every layer. As mentioned, data security in the form of encryption
can be confined to the presentation layer, but network security affects all seven layers.
Real-world networks are much less defined than the OSI model suggests. That said, the model
provides a conceptual framework that can be used to visualize network interactions, both for
troubleshooting existing networks and for designing better networks in the future.
LET´S FOCUS ON VOCABULARY
Actividad 5: Ingresá a: http://www.wordreference.com/es y
A) consultá en / qué significado tienen en el texto los siguientes verbos:
make up
hooked up
plugged in
drive on
tacking on
check for
broken into
carry on
B) Averiguá la traducción y la explicación que brindan los glosarios, con respecto a los siguientes
términos que aparecen en el texto estudiado. Podes consultar:
Inglés II: LCC- LSI Práctica de Aprendizaje N° 4: “Phrasal Verbs” y Características del Texto Expositivo
Año 2012
http://www.tugurium.com/gti/contenidos.asp
http://www.thefreedictionary.com:
a) frame
b) addressing
c) framework
d) troubleshooting
POST-READING ACTIVITIES
Actividad 6: Escuchá atentamente el video: BRIEF DESCRIPTION OF THE OSI MODEL
http://www.youtube.com/watch?v=N8Njjw0ItOE&feature=related y:
A) Re-ordená las siguientes ideas:

This information enables features such as data encryption, error checking and packet
sequencing and reassembling

Each packet travels through the layers of the protocol stack

When computer 2 receives the packet, the packet travels up the protocol stack

At each level the protocols remove the control information, make sure that the message
came through without errors, decrypts the information and reassembles the packet into the
original message

Before sending the message, computer 1 breaks it into packets

Let´s look at what happens when computer 1 sends a message to computer 2 over the
network

When the message arrives at the physical layer it is converted into electrical bits and sent
across the transmission media to computer 2

At each layer the protocols add control information to the header of the packet
B) Trabaja con la Ficha: Características del Texto Expositivo e identificá cuáles de las
mencionadas están presentes en este texto:
¿Cuáles elementos de los nombrados se referencian con “It” y cuáles con “they”
Inglés II: LCC- LSI Práctica de Aprendizaje N° 4: “Phrasal Verbs” y Características del Texto Expositivo
Año 2012
Con respecto al vocabulario, ¿identificas tecnicismos y/o neologismos en la clasificación que
hiciste?
¿Podes encontrar: a) paráfrasis (volver a repetir la información usando otras palabras), b)
definiciones, c) ilustraciones, o d) ejemplificación?
¿Qué tiempo verbal predomina? Brinda ejemplos para justificar tu afirmación.
Teniendo en cuenta la clasificación de los textos expositivos, ¿cuál de ellas crees que se adapta
al texto: “BRIEF DESCRIPTION OF THE OSI MODEL”?
C) Observa los esquemas textuales y elegí el que se adapta el texto: “AN INTRODUCTION TO
THE OSI MODEL”
DESCRIPCION
SECUENCIA
aspecto
TEMA
a
1er paso/ etapa/
momento
aspecto
2do paso/etapa/
momento
aspecto
3er paso/etapa/
momento
CAUSA-EFECTO
COMPARACION
similitudes y diferencias
PROBLEMA-SOLUCION
Atributo
A
Característica
Aspecto/ rasgo
B
.......
THE OSI MODEL BY PROFESSOR MESSER
http://www.youtube.com/watch?v=lSK1d8fZyEw&feature=player_detailpage
HOW TCI/IP WORKS http://www.youtube.com/watch?v=HOaIqQAeaik&feature=related
HOW THE INTERNET WORKS IN 5 MINUTES
http://www.youtube.com/watch?v=7_LPdttKXPc&feature=related