What is OSI Model?
OSI model. Reference framework for the definition of interconnection architectures for communication systems. It is a functional guideline for communication tasks and therefore does not specify a communication standard for such tasks. However, many standards and protocols comply with the guidelines of the OSI Model.
Summary
1. Background
2 main components
3 The layers of the OSI model
3.1 The IEEE 802.11 standard
4 Operation of the network layer in the OSI model
5 Operation of IP within the OSI model
6 Processing of TCP / IP packets in the OSI model
7 Main reference
During the 1960s and '70s, many networking technologies were created. Each one based on a specific Hardware design. These systems were built in one piece; what we could call a monolithic architecture. This means that designers had to deal with all the elements involved in the process.
We can assume that these elements form a transmission chain that has several parts: the physical connection devices, the software and hardware protocols used in communication, the application programs that carried out the communication, and the human-machine interface that allow the human use the network.
This model, which considers the chain as a monolithic whole, is impractical, since the smallest change may involve altering all its elements. The original Internet design of the American Department of Defense provided a four-layer scheme. Although it dates from the 70s, it is more or less the one that is still used: Physical or Network Access Layer ("Network Access Layer").
Responsible for sending information about the hardware system used in each case. A different protocol is used depending on the type of physical network. The network layer also called the Internet layer ("Internet Layer"). It is responsible for sending the data through the different physical networks that can connect a source machine to the destination machine of the information.
Transmission protocols such as IP are closely associated with this layer. Transport layer ("Host-to-Host Layer"). Controls the establishment and end of the connection; data flow control; retransmission of lost data, and other details of transmission between two systems. The most important protocols at this level are TCP and UDP (mutually exclusive). Application layer ("Application layer").
Comprised of protocols that directly serve user programs; Browser, E-mail, FTP, TELNET, etc. Responding to the general theory prevailing in the world of computing, of designing modular hardware and layered software, in 1978 the ISO organization (International Standards Organization www.iso.ch) proposed a communications model for networks that they named "The reference model of Open Systems Interconnection", generally known as the OSI model.
Its philosophy is based on decomposing the functionality of the transmission chain into various modules, whose interface with the adjacent ones is standardized. This design philosophy has a double advantage: changing a module does not necessarily affect the entire chain. In addition, there may be certain interoperability between various products and hardware/software manufacturers, since the limits and interfaces are perfectly defined. This means, for example, that two different communication software can use the same physical means of communication.
A network model called a Basic Reference Model or Server-layer.
A series of specific protocols.
The network model, although inspired by the Internet model, has no more similarities to that. It is based on a seven-layer model, whereas the primitive Internet was based on 4. Currently, all the developments are based on this 7-level model, which are the following:
Application
Presentation
Session
Transport
Network
Data Link
Physical
Each level performs a specific function and is separated from the adjacent ones by known interfaces, with no other aspect of the total communication involved. Note that this model, to which absolutely all books dealing with networks refer, is only a conceptual abstraction, to which physical reality is (more or less) adapted. However, the consequences of applying this point of view are very useful. The underlying concept is the same that allows us to put the address and return information in a letter; franking it and depositing it in the mailbox of the postal service without worrying about anything else.
The letter follows a series of processes within the postal service without everyone having to worry about those that have preceded or will happen to them. Finally, the letter is delivered to the recipient in their mailbox, who only has to read it. Generally, the devices used in networks limit their operation to one or more of these levels. For example, a hub ("Hub") that amplifies and retransmits the signal through all its ports, is operating exclusively at layer 1, while that a switch ("Switch") operates on layers 1 and 2; a router ("Router") operates on layers 1, 2 and 3. Finally, a user workstation generally handles layers 5, 6 and 7.
Regarding the software, it should be noted that each layer uses a specific protocol to communicate with the adjacent layers and that it adds some additional information ("Protocol Header") to the packet header.
Layers of the OSI Model
The schematic description of the various layers that make up this model is as follows:
1. Physical layer : It is in charge of transmitting the bits of information over the line or medium used for transmission. It deals with the physical properties and electrical characteristics of the various components; with the transmission speed, if it is uni or bidirectional (simplex, duplex or full-duplex), as well as mechanical aspects of connections and terminals, including the interpretation of electrical signals. As a summary of the tasks of this layer, we can say that it is responsible for transforming a binary information packet ("Frame") into a succession of pulses appropriate to the physical medium used in the transmission.
These impulses can be electrical (cable transmission); electromagnetic (Wireless transmission) or luminous (optical transmission).When operating in reception mode, the work is reverse; It is responsible for transforming these pulses into binary data packets that will be delivered to the link-layer (see below). For example, this level defines the measurements of the Ethernet coaxial cable and the BNC connectors used. Another example of standards related to this layer are RS-232 (H2.5.1) for serial communications and X.21
2. Link-layer : This layer can be said to transfer messages to/from the physical layer to the network layer (which we will see below). It specifies how the data is organized when transmitted in a particular medium. P.E. This layer defines how the boxes ("Frames"), addresses and checksums ("Checksum") of the Ethernet packets are.
In addition to local addressing, it deals with the detection and control of errors that occur in the physical layer, control of access to that layer, and data integrity and transmission reliability.
For this, it groups the information to be transmitted in blocks ("Frames") and includes each one a checksum that will allow the receiver to check its integrity. The received datagrams are verified by the receiver. If any datagram has been corrupted, a control message is sent to the sender requesting its forwarding. The PPP protocol [1] is an example of this layer.
Logical Link Control LLC ("Logical Link Control") defines how data is transferred over the physical medium, providing service to the upper layers.
MAC access control ("Medium Access Control"). This sublayer acts as a controller for the underlying hardware (the network adapter). In fact, the network card driver is sometimes called the "MAC driver", and the address The physics contained in the hardware of the card is known as the MAC address ("MAC address" H12.4).
Its main task (which gives it the name -access control-) is to arbitrate the use of the physical means to facilitate that several teams can compete simultaneously for the use of the same means of transport.
The CSMA / CD ("Carrier Sense Multiple Access with Collision Detection") mechanism used in Ethernet (H12.4) is a typical example of this sublayer.
The IEEE 802.11 standard defines the use of the lower two levels of the OSI architecture (physical and data link layers), specifying its performance standards in a WLAN. The protocols of the 802.x branch define the technology of local area networks and metropolitan area networks.
802.11i was ratified on June 24, 2004, to address the issue of security in wireless networks. It is based on the TKIP encryption algorithm, like WPE, but it also supports AES (Advanced Encryption Standard) which is much more secure.
3. Network layer: This layer deals with the transmission of datagrams (packets) and routing each in the appropriate direction ("routing"), a task that can be complicated in large networks like the Internet, but it does not deal with packet errors or losses at all, for example, it defines the Internet address and route structure.
Two types of packets are used at this level: data packets and route update packets. As a consequence, this layer can be considered subdivided into two:
Transport. Responsible for encapsulating the data to be transmitted (user). It uses data packets. In this category is the IP protocol ("Internet Protocol" A3.1).
Switching ("Switching"): This party is in charge of exchanging specific network connectivity information (its activity is rarely perceived by the user).
Routers are devices that work at this level and take advantage of these route update packages. In this category is the ICMP protocol ("Internet Control Message Protocol" A3.7), responsible for generating messages when transmission errors occur and for a special echo mode that can be verified by PING [3].
The most frequently used protocols in this layer are two: X.25 and IP. Webography: OSI: The Network Layer www.cisco.com/warp/public/535/2.html This Cisco Systems page provides an authoritative summary of network layer services and protocols.
4. Transport layer: This layer is concerned with ensuring the reliability of the service, describes the quality and nature of data delivery. P.E. This layer defines when and how retransmission should be used to ensure your arrival. To do this, it divides the message received from the session layer into pieces (datagrams), numbers them sequentially and delivers them to the network layer for sending.
During the reception, if the network layer uses the IP protocol, the Transport layer is responsible for reordering the received packets out of sequence. It can also work in reverse by multiplexing a transport connection between various data connections, allowing data from various applications to share the same flow to the network layer.
A typical example of a protocol used at this layer is TCP ("Transport Control Protocol" A3.1), which with its IP counterpart at the Network layer, configure the TCP / IP suite used on the Internet, although there are others such as UDP (" Universal Datagram Protocol ") a transport layer also used on the Internet by some application programs.
5. Session Layer : It is an extension of the transport layer that offers control of dialogue and synchronization, although, in reality, few applications make use of it. For example, Internet communications do not use it. Note: Some authors indicate that the session layer is merely a theoretical consideration of the model's authors with absolutely no known practical utility.
6. Presentation Layer : This layer deals with the semantic aspects of communication (it describes the syntax of the data to be transmitted), establishing the necessary arrangements so that machines that use different internal representations to communicate can communicate. the data.PE describes how floating-point numbers can be transferred between computers using different mathematical formats.
This layer is a good candidate for implementing crypto applications. In theory, this layer "presents" the data to the application layer, taking the received data and transforming it into formats such as text, images, and sound. As we will see below, this layer may actually be absent, since few applications make use of it. her. Note: Something similar to the previous one occurs with this layer.
In theory, the client and server should negotiate the format to be used, and this function, and the corresponding formatting of the data, would be the object of this layer. However, this, which made some sense in the 1970s, when much of the networking work was related to inputting and outputting data to large computers using "dumb" terminals of various kinds (which used control codes slightly different) doesn't make much sense anymore.
Currently, the landscape has changed; there is only one option for the data format, despite which the OSI protocol continues to negotiate an encoding scheme (the only one available). On the Internet, the only service that uses this layer is TELNET, which is precisely a service for accessing servers from remote terminals. In this case, the presentation layer is in charge of configuring the terminal to connect to a server with particular characteristics.
7. Application Layer :This layer describes how application programs (browsers, mail clients, remote terminals, file transfers, etc.) do their job. For example, this layer implements the operation with system files. On the one hand, they interact with the presentation layer; on the other, they represent the interface with the user, delivering the information and receiving the commands that direct communication. Examples of protocols used by programs at this layer are HTTP, SMTP, POP, IMAP, Modbus Communication Protocol, etc.
The network layer provides its services to the transport layer, being a complex layer that provides connectivity and selection of the best route for communication between machines that may be located in geographically different networks.
It is responsible for the switching and routing functions of the information (logical addressing), providing the necessary procedures for the exchange of data between the source and the destination, for which it is necessary to know the topology of the network (how nodes are interconnected), in order to determine the most suitable route.
Divide the transport layer messages (segments) into more complex units, called packets, to which it assigns the logical addresses of the computers that are communicating.
Know the network topology and handle the case in which the source machine and the destination machine are in different networks. Route information through the network based on packet addresses, determining switching and routing methods through intermediate devices (routers).
Send packets from node to node using a virtual circuit or datagrams. Assemble the packages on the destination computer. This layer is where routers, devices in charge of routing or directing data packets from source to destination, work through the best possible route between them.
IP packets:
Version. It's 4. Allow updates.
IHL. The length of the header in 32-bit words. The maximum value is 15, or 60 bytes.
Type of service. Determines whether data delivery and speed are reliable. Not used.
Total length. Up to a maximum of 65,535 bytes. Identification. To determine which datagram a fragment belongs to.
DF (Don't Fragment). The target cannot mount the datagram again.
MF (More Fragments). Not established in the last fragment.
Displacement of the fragment. To which part of the datagram this fragment belongs. The size of the elementary fragment is 8 bytes. Time of life. Each jump is decreased.
Protocol. Transport protocol on which the datagram should be based. Options include strict routing (full route specified), loose routing (only a few routers specified in the route), and route recording.
The technical operation in which data is transmitted over the network can be divided into two discrete, systematic steps. At each step, certain actions are performed that cannot be performed in another step. Each step includes its own rules and procedures, or protocol. The protocol steps must be carried out in an appropriate order and that it is the same in each of the computers on the network. On the source computer, these steps have to be carried out from top to bottom.
On the destination computer, these steps have to be carried out from the bottom up. The origin team. The protocols on the source computer:
1. They are divided into smaller sections, called packages.
2. Information about the IP address is added to the packets so that the destination computer can determine if the data belongs to it. 3. Prepare the data to transmit it through the NIC and send it through the network cable.
The destination computer: The protocols on the destination computer consist of the same series of steps, but in reverse.
1. Take the data packets from the cable and put them into the computer through the NIC.
2. Extract from the data packets all the transmitted information eliminating the information added by the originating equipment.
3. Copy the packet data into a buffer to rearrange it and send it to the application. The source and destination teams need to perform each step in the same way so that the data has the same structure when received as to when it was sent.
Processing of TCP / IP packets in the OSI model:
The TCP / IP protocol within the OSI Model
Protocols like TCP / IP determine how computers communicate with each other over networks like the Internet. These protocols work together and are placed on top of each other in what is commonly known as the protocol stack. Each protocol stack is designed to carry out a special purpose on the sending and receiving computers.
The TCP stack combines the application, presentation, and session stacks into one also called the application stack. In this process, the characteristics of the packaging that takes place to transmit data are given: The TCP application stack formats the data that is being sent so that the lower stack, the transport stack, can send it. The TCP application stack performs the equivalent operations performed by the top three OSI stacks: applications, presentation, and session.
The next stack is the transport stack, which is responsible for the data transfer, and ensures that the data sent and received is, in fact, the same, in other words, that no errors have occurred during the sending of the data. TCP splits the data it gets from the application stack into segments. Add a header that contains information that will be used when the data is received to ensure that it has not been altered en-route and that the segments can be correctly merged back into their original form.
The third stack prepares the data for delivery by entering it into IP datagrams and determining the exact Internet address for it. The IP protocol works on the Internet stack, also called the network stack. Place an IP container with a header on each segment. The IP header includes information such as the IP address of the sending and receiving computers, the length of the datagram and the order of its sequence. The sequential order is added because the datagram could possibly exceed the size allowed for network packets and thus would need to be divided into smaller packets. Including the sequential order would allow them to be re-combined appropriately.
Although there are other models, most network manufacturers today relate their products to the OSI model, especially when they want to teach users how to use their products. Manufacturers consider it to be the best tool available to teach how to send and receive data over a network.
The OSI reference model allows users to see the network functions that occur at each layer. It is an understandable model for users. In addition, the work defined and explained the IP in both its version 4 and its new version, IP version 6. Understanding that the need to create the new version lies in the exhaustion of the addresses of the previous IP. The OSI model was explained and emphasis was made on layer 3, because the Internet protocol, that is, the IP protocol, works or operates in this layer. In this layer, communications are established and the path that the data will take is established. On the net.
Summary
1. Background
2 main components
3 The layers of the OSI model
3.1 The IEEE 802.11 standard
4 Operation of the network layer in the OSI model
5 Operation of IP within the OSI model
6 Processing of TCP / IP packets in the OSI model
7 Main reference
Background:
During the 1960s and '70s, many networking technologies were created. Each one based on a specific Hardware design. These systems were built in one piece; what we could call a monolithic architecture. This means that designers had to deal with all the elements involved in the process.
We can assume that these elements form a transmission chain that has several parts: the physical connection devices, the software and hardware protocols used in communication, the application programs that carried out the communication, and the human-machine interface that allow the human use the network.
This model, which considers the chain as a monolithic whole, is impractical, since the smallest change may involve altering all its elements. The original Internet design of the American Department of Defense provided a four-layer scheme. Although it dates from the 70s, it is more or less the one that is still used: Physical or Network Access Layer ("Network Access Layer").
Responsible for sending information about the hardware system used in each case. A different protocol is used depending on the type of physical network. The network layer also called the Internet layer ("Internet Layer"). It is responsible for sending the data through the different physical networks that can connect a source machine to the destination machine of the information.
Transmission protocols such as IP are closely associated with this layer. Transport layer ("Host-to-Host Layer"). Controls the establishment and end of the connection; data flow control; retransmission of lost data, and other details of transmission between two systems. The most important protocols at this level are TCP and UDP (mutually exclusive). Application layer ("Application layer").
Comprised of protocols that directly serve user programs; Browser, E-mail, FTP, TELNET, etc. Responding to the general theory prevailing in the world of computing, of designing modular hardware and layered software, in 1978 the ISO organization (International Standards Organization www.iso.ch) proposed a communications model for networks that they named "The reference model of Open Systems Interconnection", generally known as the OSI model.
Its philosophy is based on decomposing the functionality of the transmission chain into various modules, whose interface with the adjacent ones is standardized. This design philosophy has a double advantage: changing a module does not necessarily affect the entire chain. In addition, there may be certain interoperability between various products and hardware/software manufacturers, since the limits and interfaces are perfectly defined. This means, for example, that two different communication software can use the same physical means of communication.
Main components
The OSI model has two main components:A network model called a Basic Reference Model or Server-layer.
A series of specific protocols.
The network model, although inspired by the Internet model, has no more similarities to that. It is based on a seven-layer model, whereas the primitive Internet was based on 4. Currently, all the developments are based on this 7-level model, which are the following:
Application
Presentation
Session
Transport
Network
Data Link
Physical
Each level performs a specific function and is separated from the adjacent ones by known interfaces, with no other aspect of the total communication involved. Note that this model, to which absolutely all books dealing with networks refer, is only a conceptual abstraction, to which physical reality is (more or less) adapted. However, the consequences of applying this point of view are very useful. The underlying concept is the same that allows us to put the address and return information in a letter; franking it and depositing it in the mailbox of the postal service without worrying about anything else.
The letter follows a series of processes within the postal service without everyone having to worry about those that have preceded or will happen to them. Finally, the letter is delivered to the recipient in their mailbox, who only has to read it. Generally, the devices used in networks limit their operation to one or more of these levels. For example, a hub ("Hub") that amplifies and retransmits the signal through all its ports, is operating exclusively at layer 1, while that a switch ("Switch") operates on layers 1 and 2; a router ("Router") operates on layers 1, 2 and 3. Finally, a user workstation generally handles layers 5, 6 and 7.
Regarding the software, it should be noted that each layer uses a specific protocol to communicate with the adjacent layers and that it adds some additional information ("Protocol Header") to the packet header.
The layers of the OSI model:
Layers of the OSI Model
The schematic description of the various layers that make up this model is as follows:
1. Physical layer : It is in charge of transmitting the bits of information over the line or medium used for transmission. It deals with the physical properties and electrical characteristics of the various components; with the transmission speed, if it is uni or bidirectional (simplex, duplex or full-duplex), as well as mechanical aspects of connections and terminals, including the interpretation of electrical signals. As a summary of the tasks of this layer, we can say that it is responsible for transforming a binary information packet ("Frame") into a succession of pulses appropriate to the physical medium used in the transmission.
These impulses can be electrical (cable transmission); electromagnetic (Wireless transmission) or luminous (optical transmission).When operating in reception mode, the work is reverse; It is responsible for transforming these pulses into binary data packets that will be delivered to the link-layer (see below). For example, this level defines the measurements of the Ethernet coaxial cable and the BNC connectors used. Another example of standards related to this layer are RS-232 (H2.5.1) for serial communications and X.21
2. Link-layer : This layer can be said to transfer messages to/from the physical layer to the network layer (which we will see below). It specifies how the data is organized when transmitted in a particular medium. P.E. This layer defines how the boxes ("Frames"), addresses and checksums ("Checksum") of the Ethernet packets are.
In addition to local addressing, it deals with the detection and control of errors that occur in the physical layer, control of access to that layer, and data integrity and transmission reliability.
For this, it groups the information to be transmitted in blocks ("Frames") and includes each one a checksum that will allow the receiver to check its integrity. The received datagrams are verified by the receiver. If any datagram has been corrupted, a control message is sent to the sender requesting its forwarding. The PPP protocol [1] is an example of this layer.
The link-layer can be considered divided into two sublayers:
Logical Link Control LLC ("Logical Link Control") defines how data is transferred over the physical medium, providing service to the upper layers.
MAC access control ("Medium Access Control"). This sublayer acts as a controller for the underlying hardware (the network adapter). In fact, the network card driver is sometimes called the "MAC driver", and the address The physics contained in the hardware of the card is known as the MAC address ("MAC address" H12.4).
Its main task (which gives it the name -access control-) is to arbitrate the use of the physical means to facilitate that several teams can compete simultaneously for the use of the same means of transport.
The CSMA / CD ("Carrier Sense Multiple Access with Collision Detection") mechanism used in Ethernet (H12.4) is a typical example of this sublayer.
The IEEE 802.11 standard:
The IEEE 802.11 standard defines the use of the lower two levels of the OSI architecture (physical and data link layers), specifying its performance standards in a WLAN. The protocols of the 802.x branch define the technology of local area networks and metropolitan area networks.802.11i was ratified on June 24, 2004, to address the issue of security in wireless networks. It is based on the TKIP encryption algorithm, like WPE, but it also supports AES (Advanced Encryption Standard) which is much more secure.
3. Network layer: This layer deals with the transmission of datagrams (packets) and routing each in the appropriate direction ("routing"), a task that can be complicated in large networks like the Internet, but it does not deal with packet errors or losses at all, for example, it defines the Internet address and route structure.
Two types of packets are used at this level: data packets and route update packets. As a consequence, this layer can be considered subdivided into two:
Transport. Responsible for encapsulating the data to be transmitted (user). It uses data packets. In this category is the IP protocol ("Internet Protocol" A3.1).
Switching ("Switching"): This party is in charge of exchanging specific network connectivity information (its activity is rarely perceived by the user).
Routers are devices that work at this level and take advantage of these route update packages. In this category is the ICMP protocol ("Internet Control Message Protocol" A3.7), responsible for generating messages when transmission errors occur and for a special echo mode that can be verified by PING [3].
The most frequently used protocols in this layer are two: X.25 and IP. Webography: OSI: The Network Layer www.cisco.com/warp/public/535/2.html This Cisco Systems page provides an authoritative summary of network layer services and protocols.
4. Transport layer: This layer is concerned with ensuring the reliability of the service, describes the quality and nature of data delivery. P.E. This layer defines when and how retransmission should be used to ensure your arrival. To do this, it divides the message received from the session layer into pieces (datagrams), numbers them sequentially and delivers them to the network layer for sending.
During the reception, if the network layer uses the IP protocol, the Transport layer is responsible for reordering the received packets out of sequence. It can also work in reverse by multiplexing a transport connection between various data connections, allowing data from various applications to share the same flow to the network layer.
A typical example of a protocol used at this layer is TCP ("Transport Control Protocol" A3.1), which with its IP counterpart at the Network layer, configure the TCP / IP suite used on the Internet, although there are others such as UDP (" Universal Datagram Protocol ") a transport layer also used on the Internet by some application programs.
5. Session Layer : It is an extension of the transport layer that offers control of dialogue and synchronization, although, in reality, few applications make use of it. For example, Internet communications do not use it. Note: Some authors indicate that the session layer is merely a theoretical consideration of the model's authors with absolutely no known practical utility.
6. Presentation Layer : This layer deals with the semantic aspects of communication (it describes the syntax of the data to be transmitted), establishing the necessary arrangements so that machines that use different internal representations to communicate can communicate. the data.PE describes how floating-point numbers can be transferred between computers using different mathematical formats.
This layer is a good candidate for implementing crypto applications. In theory, this layer "presents" the data to the application layer, taking the received data and transforming it into formats such as text, images, and sound. As we will see below, this layer may actually be absent, since few applications make use of it. her. Note: Something similar to the previous one occurs with this layer.
In theory, the client and server should negotiate the format to be used, and this function, and the corresponding formatting of the data, would be the object of this layer. However, this, which made some sense in the 1970s, when much of the networking work was related to inputting and outputting data to large computers using "dumb" terminals of various kinds (which used control codes slightly different) doesn't make much sense anymore.
Currently, the landscape has changed; there is only one option for the data format, despite which the OSI protocol continues to negotiate an encoding scheme (the only one available). On the Internet, the only service that uses this layer is TELNET, which is precisely a service for accessing servers from remote terminals. In this case, the presentation layer is in charge of configuring the terminal to connect to a server with particular characteristics.
7. Application Layer :This layer describes how application programs (browsers, mail clients, remote terminals, file transfers, etc.) do their job. For example, this layer implements the operation with system files. On the one hand, they interact with the presentation layer; on the other, they represent the interface with the user, delivering the information and receiving the commands that direct communication. Examples of protocols used by programs at this layer are HTTP, SMTP, POP, IMAP, Modbus Communication Protocol, etc.
Operation of the network layer in the OSI model:
The network layer provides its services to the transport layer, being a complex layer that provides connectivity and selection of the best route for communication between machines that may be located in geographically different networks.It is responsible for the switching and routing functions of the information (logical addressing), providing the necessary procedures for the exchange of data between the source and the destination, for which it is necessary to know the topology of the network (how nodes are interconnected), in order to determine the most suitable route.
Its main functions are:
Divide the transport layer messages (segments) into more complex units, called packets, to which it assigns the logical addresses of the computers that are communicating.
Know the network topology and handle the case in which the source machine and the destination machine are in different networks. Route information through the network based on packet addresses, determining switching and routing methods through intermediate devices (routers).
Send packets from node to node using a virtual circuit or datagrams. Assemble the packages on the destination computer. This layer is where routers, devices in charge of routing or directing data packets from source to destination, work through the best possible route between them.
Operation of IP within the OSI model:
The IP protocol is the fundamental foundation of the Internet. It makes it possible to send data from source to destination. The transport level splits the data stream into datagrams. During its transmission, a datagram can be divided into fragments that are mounted again at the destinationIP packets:
Version. It's 4. Allow updates.
IHL. The length of the header in 32-bit words. The maximum value is 15, or 60 bytes.
Type of service. Determines whether data delivery and speed are reliable. Not used.
Total length. Up to a maximum of 65,535 bytes. Identification. To determine which datagram a fragment belongs to.
DF (Don't Fragment). The target cannot mount the datagram again.
MF (More Fragments). Not established in the last fragment.
Displacement of the fragment. To which part of the datagram this fragment belongs. The size of the elementary fragment is 8 bytes. Time of life. Each jump is decreased.
Protocol. Transport protocol on which the datagram should be based. Options include strict routing (full route specified), loose routing (only a few routers specified in the route), and route recording.
The technical operation in which data is transmitted over the network can be divided into two discrete, systematic steps. At each step, certain actions are performed that cannot be performed in another step. Each step includes its own rules and procedures, or protocol. The protocol steps must be carried out in an appropriate order and that it is the same in each of the computers on the network. On the source computer, these steps have to be carried out from top to bottom.
On the destination computer, these steps have to be carried out from the bottom up. The origin team. The protocols on the source computer:
1. They are divided into smaller sections, called packages.
2. Information about the IP address is added to the packets so that the destination computer can determine if the data belongs to it. 3. Prepare the data to transmit it through the NIC and send it through the network cable.
The destination computer: The protocols on the destination computer consist of the same series of steps, but in reverse.
1. Take the data packets from the cable and put them into the computer through the NIC.
2. Extract from the data packets all the transmitted information eliminating the information added by the originating equipment.
3. Copy the packet data into a buffer to rearrange it and send it to the application. The source and destination teams need to perform each step in the same way so that the data has the same structure when received as to when it was sent.
Processing of TCP / IP packets in the OSI model:
The TCP / IP protocol within the OSI Model
Protocols like TCP / IP determine how computers communicate with each other over networks like the Internet. These protocols work together and are placed on top of each other in what is commonly known as the protocol stack. Each protocol stack is designed to carry out a special purpose on the sending and receiving computers.
The TCP stack combines the application, presentation, and session stacks into one also called the application stack. In this process, the characteristics of the packaging that takes place to transmit data are given: The TCP application stack formats the data that is being sent so that the lower stack, the transport stack, can send it. The TCP application stack performs the equivalent operations performed by the top three OSI stacks: applications, presentation, and session.
The next stack is the transport stack, which is responsible for the data transfer, and ensures that the data sent and received is, in fact, the same, in other words, that no errors have occurred during the sending of the data. TCP splits the data it gets from the application stack into segments. Add a header that contains information that will be used when the data is received to ensure that it has not been altered en-route and that the segments can be correctly merged back into their original form.
The third stack prepares the data for delivery by entering it into IP datagrams and determining the exact Internet address for it. The IP protocol works on the Internet stack, also called the network stack. Place an IP container with a header on each segment. The IP header includes information such as the IP address of the sending and receiving computers, the length of the datagram and the order of its sequence. The sequential order is added because the datagram could possibly exceed the size allowed for network packets and thus would need to be divided into smaller packets. Including the sequential order would allow them to be re-combined appropriately.
Main reference:
One of the most pressing needs of a communication system is the establishment of standards, without them only equipment from the same manufacturer and using the same technology could communicate with each other. The connection between electronic equipment has been gradually standardized, the OSI Model is the main reference for network communications.Although there are other models, most network manufacturers today relate their products to the OSI model, especially when they want to teach users how to use their products. Manufacturers consider it to be the best tool available to teach how to send and receive data over a network.
The OSI reference model allows users to see the network functions that occur at each layer. It is an understandable model for users. In addition, the work defined and explained the IP in both its version 4 and its new version, IP version 6. Understanding that the need to create the new version lies in the exhaustion of the addresses of the previous IP. The OSI model was explained and emphasis was made on layer 3, because the Internet protocol, that is, the IP protocol, works or operates in this layer. In this layer, communications are established and the path that the data will take is established. On the net.
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