2.2 OSI Model and Data Encapsulation

In the OSI model, which of the following functions are performed at the Application layer? (Select two.) 1. Enabling of communication between network clients and services. 2. Device control for data transmission rates. 3.Integration of network functionality into the host operating system. 4. Communication setup, maintenance, and teardown. 5. Standard setting for sending and receiving signals

1. Enabling of communication between network clients and services 3. Integration of network functionality into the host operating system The Application layer enables network services and integrates network functionality into the host operating system. Applications actually run above the OSI Application layer. (The setup, maintenance, and teardown of communication happens at the Session layer. The Data Link layer controls the rate of data transmission between hosts (flow control). The Physical layer sets standards for sending and receiving electrical signals between devices.)

How is a webpage transmitted from one host to another using an OSI model? It wants to send the page to a computer which is the destination device. First, what happens to the data at the presentation layer? Second, what happens at the sessions layer? Third, transport layer? Fourth, what is passed to the network layer? Fifth, what happens at the data link layer?

1st. The data is compressed and encrypted at the presentation layer 2. Then the session ID is appended at the session layer 3. The data is broken down into blocks called segments and appends a port number to identify which top-layer application needs to receive the data on the destination device. 4. Each segment is passed to the network layer, and it appends the source and destination IP addresses to create a packet. 5. The packet is then passed through the data link layer which adds the source and destination MAC addresses, as well as the CRC. Packet is now called a frame. 6. Frame is sent to the physical device where it is translated into some kind of signal, such as electrical, radio, or light.

The middle layers are called the transport layers, which are made up of which two layers?

4. transport and 3.network

Another common way to group the OSI model is to separate the two middle layers - layers 3 and4- from the top, creating three groups. The top layers are called the application layers, which are made up of which three layers?

7. Application 6. Presentation 5. Session

A Cyclic Redundancy Check, or CRC, is also included in what?

A CRC is included in a frame

Name the 7 layers of the OSI model.

Application, Presentation, Session, Transport, Network, Data Link, Physical

Both the segment and the __________________ are examined and looked at and it is forwarded up the OSI model layer to the appropriate application specified by the ______________.

Both the segment and the PORT NUMBER are examined and looked at and it is forwarded up the OSI model layer to the appropriate application specified by the PORT NUMBER.

The transport layer can identify the upper layer protocol that the data is intended for by using what?

By using a port number, the transport layer can identify the upper layer protocol that the data is intended for.

What is known as a mathematical value that helps the receiving device identify any errors that may have occurred during transmission?

CRC

Connection establishment is associated with which layer?

Connection establishment is controlled through Session layer protocols

What is data at the data link layer referred to as?

Data at this layer is called a frame

What is each data point is the string called?

Each data point in the string is called a bit.

What are 4 protocols associated with the application layer?

HTTP, FTP, TFTP, and SMTP

The rationale for creating the OSI model was to design a standardized network communications model in order to create what?

In order to create consistency with the industry. People had to buy hosts, network interfaces, and network connecting medium all from same vendor otherwise wouldn't work

The data link layer is divided into two sub layers. What is the top sublayer called?

It is called the logical link control sub layer, or LLC.

The frame then becomes a signal, what does the signal represent?

It represents a series of zeros and ones.

What is MAC responsible for?

MAC is responsible for identifying how devices can access the physical medium.

What is the bottom sublayer of the data link layer called?

Media access control sublayer, or MAC.

What type of model is a reference model for how applications communicate over a network without regard to its underlying internal structure and technology?

Open Systems Interconnections (OSI) Model

What are two things that routing protocols specify?

Routing protocols specify how each router identifies destination networks and the path data should take to arrive at that destination network

During TCP/IP communication between two network hosts, information is encapsulated on the sending host and decapsulated on the receiving host using the OSI model. Match the information format on the left with the appropriate layer of the OSI model on the right. Segments ---> Packets ---> Frames ---> Bits --->

Segments = Transport layer Packets = Network layer Frames = data link layer Bits = physical layer Encapsulation is the process of breaking a message into packets, adding controls and other information, and transmitting the message through the transmission media. The following is the five-step data encapsulation/decapsulation process used by the OSI model: Upper layers prepare the data to be sent through the network. The Transport layer breaks the data into pieces called segments, adding sequencing and control information. The Network layer converts the segments into packets, adding logical network and device addresses. The Data Link layer converts packets into frames, adding physical device addressing information. The Physical layer converts the frames into bits for transmission across the transmission media.

What keeps data streams separated so that information requested by one client isn't sent to another client.?

Session IDs

Which are two specific protocols that are used at the transport layer?

TCP and UDP

What does TCP take advantage of to ensure that data sent from upper layers is received at the receiving device?

TCP takes advantage of sequencing, error correction, and flow control to ensure that data sent from the upper layers is received at the receiving device

Physical network device identification and data transmission between hosts are part of which layer?

The Data Link Layer controls device identification on networks, as well as how messages travel through the network (the logical topology)

The ____________ within the packet are examined and removed, and the packet is forwarded to the transport layer as a ___________.

The IP ADDRESSES within the packet are examined and removed, and the packet is forwarded to the transport layer as a SEGMENT.

In the OSI model, routing messages between networks is the primary function of which layer?

The Network layer is responsible for routing messages between networks.

The fourth benefit: What does the OSI model aid in specifically?

The OSI model aids in troubleshooting

The sixth benefit: What does the OSI model provide in networking features, and what does it allow developers to do?

The OSI model provides modularity in networking features, and the OSI model allows developers to change features without changing the entire approach.

Coordinating rules for sending and receiving electrical signals is the basic purpose of which OSI layer?

The OSI physical layer sets standards for sending and receiving electrical signals between devices

Data segmentation and reassembly, end-to-end flow control, and reliable message delivery are functions performed by which layer?

The OSI transport layer is responsible for breaking upper-layer data into segments and allowing reliable communication through end-to-end flow control, error detection, and error correction.

In the OSI model, data encryption and data format specifications are the following functions performed at which layer?

The Presentation layer encrypts data, changes and converts character sets, and compresses data formats (such as .jpg, .wmv, and .wav)

The ___________ is used, the ___________ is removed, and the data is presented in its original form to the application that needs to interpret it; in this case, a browser.

The SESSION ID is used, the ENCRYPTION is removed, and the data is presented in its original form to the application that needs to interpret it; in this case, a browser

The application system provides an interface between which two things?

The application layer provides an interface between an application running on the system and the rest of the network. -it doesn't refer to the application itself

What is one very important thing that happens at the network layer?

The assignment of IP addresses is the one very important thing that happens at the network layer. *this is why the IP address is often referred to as a network layer address or a layer three address

One way to group the OSI model layer is to separate the bottom two layers from the top five layers. This is done because the bottom layers (1. Physical 2. Data link) are related to something, what is it?

The bottom layers are related to network architecture also known as the physical hardware.

What do the bottom layers dictate when it comes to devices and data?

The bottom layers dictate how devices are connected and how data is transmitted

Which layer is responsible for interfacing between the physical transmission media - the physical devices - and the network layer?

The data link layer is responsible for interfacing between the physical transmission media and the network layer

The network interface prepares this signal and sends it out on the transmission medium. The destination device receives this series of __________ and interprets them as a __________.

The destination devices receives this series of BITS and interprets them as a FRAME.

There are 6 OSI Model benefits. The first benefit is that the OSI model provides what for network professionals?

The first benefit of the OSI model is that it provides a common language and reference point for network professionals.

The OSI model provides seven different layers of communications. The host on the _______ is the sender. The host on the ________ is the receiver.

The host on the left is the sender and the host on the right is the receiver.

When a message is sent from the sender on the left, where does the message go through before being transmitted across the network?

The message goes through all the layers of the OSI model before being transmitted across the network. This mode allows standardized communications between these layers on different devices on a network.

Which layer is responsible for moving data between systems throughout the internetwork and is where routing happens?

The network layer is responsible for moving data between systems throughout the internetwork and is where routing happens.

Which layer deals with syntax, encryption, and compression?

The presentation layer, also known as the formatting layer, deals with syntax, encryption. and compression.

The sequence number helps the receiving device reassemble the segment blocks in the right order. What does the sequence number identifying segments help to allow?

The sequence number helps identify any segments that got lost in transit, allowing a device to request transmission of a lost segment.

What does the session layer use to identify unique sessions?

The session layer uses a session ID to identify unique sessions.

What happens when a segment is passed off the to network layer?

The source and IP addresses are added to the segment and the data then becomes a packet

Which layer is responsible for integrating network services with the operating system?

The top and 7th layer known as the application layer

What are the top five layers known as?

The top five layers are the networking protocols, such as TCP/IP. *These layers aren't really concerned with hardware as much as the software and the applications on the computer.

For example, if you were downloading a 4 MB file, what does the transport layer know and do?

The transport layer knows that a 4 MB file can't be sent all at once so it segments the data

You install a web server and an email server on the same physical server system. Information received from the lower levels needs to be redirected to the appropriate service running on the server. What is this an example of?

This is an example of using port numbers at the transport layer. Each service is associated with a unique port number (80 for HTTP, 25 for SMTP)

What exactly is UDP more concerned with?

UDP is more concerned with moving data through the network, without necessarily ensuring that everything arrives at the destination device.

Which specific protocol is referred to as the "connectionless protocol"?

UDP is referred to as the connectionless protocol

An application functioning at the application layer of the model doesn't need to know how sessions between devices are handled or what physical medium is being used, what does it only need to know?

an application functioning at the application layer of the model only needs to know how to format the information according to its layer specifications and then send it to the next layer.

It then passes that same data to the network layer as a ___________.

as a packet

And the bottom layers are the architecture layers, which are made up of which two layers?

data link and physical

What is each client connection called?

each client connection is called a session

The second OSI benefit is that it divides networking tasks into logical layers for what reason?

for easier comprehension

Multiple clients connected to a web server is an example of which layer?

it is an example of the session layer because each connected client is identified as a session.

Once the destination devices interprets the series of bit as a frame, what does it look at and then removed?

it looks at the MAC addresses and the CRC, and then removes them.

The other objective of the OSI model making network communications modular means what?

means network products wouldn't be proprietary anymore. which means that network equipment could be bought from multiple vendors and would work together

7 layer sender to receiver mneomic

physical - please data link - do network - not transport - throw session - sausage presentation - pizza application - away

The physical layer also includes protocols that identify what three things that can be used on the network?

protocols that identify cables, connectors, and devices that can be used on the network (ex: Use the CAT6 protocol to define type of cables used in network, and RJ-45 protocol to define the connectors to use)

How is a message sent through routing?

routing takes a message sent from a device to another router - maybe through several routers - to the destination device.

The fifth benefit: What kind of standards are promoted between networks and devices by the OSI model

standards of interoperability are promoted between networks and devices.

What does the LLC provide?

the LLC provides interface between the lower layers and the upper layers.

When a packet arrives from the network layer, what is added to the packet?

the MAC address is added to the packet when a packet arrives from the network layer

What does the OSI model divide to make network communications possible?

the OSI Mode divides network communications between two hosts into layers. And the layers break down the communication process into general tasks.

The third benefit of the OSI model benefit is that it allows what at different levels?

the OSI model allows specialization of features at different levels.

Which specific protocol is referred to as a "connected-oriented protocol" ?

the TCP is referred to as the connection-oriented protocol

Which layer is where the MAC address is assigned?

the data link layer

Which layer also defines the logical topology of the network, or how devices access the media?

the data link layer also defines the logical topology of the network, or how devices access the media

Which layer is responsible for creating sessions between communications devices?

the fifth layer known as the session layer

What does the next layer do before forwarding it to the next layer until the information is transmitted to the receiving device?

the layer processes that information according to its specifications before forwarding it to the next layer.

Which layer group handles how messages get from one device to another through the network but isn't really concerned with the physical devices of the network?

the middle layers

Which layer do you work with the physical hardware?

the physical layer

A web site using the HTTP protocol is an example of which layer?

the presentation layer. When data is encrypted, the HTTP protocol doesn't do this. Instead the SSL protocol encrypts the data at the presentation layer.

When the information arrives at the receiver, what is used, but in reverse?

the same 7 layer process is used in reverse. Each layer processes the information according to its specifications and then sends it up to the next layer until it finally reaches the receiving device's application layer.

Many protocols associated with the application layer will extend to which layer?

the session layer

Now with this grouping, which layers handle service protocols such as HTTP, DNS, and other service related protocols?

the top layers handle the service protocols

Which layer is responsible for delivering data on a network?

the transport layer

What does the transport layer assign which helps identify an upper layer service running on a server?

the transport layer assigns port numbers which port numbers help identify an upper layer service running on a server

Into what does the transport layer divide the data into?

the transport layer divides data into smaller blocks called segments and identifies each block with a sequence number

Which layer is also responsible for flow control between two hosts?

the transport layer is responsible for flow control between two hosts *if data is being sent too fast or two slow, the receiving device can send a message telling the sending device to slow don or speed up.

A frame is a network layer packet with what two things added?

with the MAC address of the source and destination devices added