TCP / IP Introduction to OSI Layer

 TCP / IP Introduction to OSI Layer

By the time we start the step into the science of computer network, the first thing we learn is usually TCP / IP. TCP / IP can be in such language analogy. When humans exchange information, people will speak in a language that can be understood by speakers and listeners. So is the case with the host computer or in a network. Communication and exchange of information in order to be well established, it takes the same language. Although different brands of the network host - different, the host can still communicate with other hosts because it uses the same communication standard, namely TCP / IP. Internet Protocol was first designed in the 1980s. But in the 1990's where the internet is increasingly popular and more and more hosts, ranging bemunculan protocol that can only be used by certain circles, or protocol made by certain manufacturers that are not necessarily compatible with other protocols from other plants as well. So in the end the body the International Standards Organization (ISO) to standardize protocols that are currently known to the protocol of the Open Systems Interconnection or OSI abbreviated. The OSI reference model is widened and the basic concepts of a theory of how the protocol. In the development of TCP / IP is used as a de facto standard.

OSI Layer
When the ISO (International Standard Organization) to standardize the protocol, it creates a standard reference model containing the workings of the protocol. Reference model which was then called the Open Systems Interconnection (OSI). Based on the document recommendation X.200, the OSI standard has 7 layers. Each layer has a different function definitions.

Layer 7: Application Layer
Is the layer where the interaction with the end user interface applications that work using the network functionality, make arrangements of how the application works using the network resources, to then memberika message when an error occurs. Some of the services and protocols that are in this layer as HTTP, FTP, SMTP, etc..

Layer 6: Presentation Layer
This layer works to translate the data format to be transmitted by the application over the network, into a format that can be transmitted by the network. In this layer the data will be encrypted or in-description.

Layer 5: Session Layer
Session layer defines how connections can be made, maintained, or destroyed. In this layer there are protocols Name Recognition, NFS and SMB.

Layer 4: Transport Layer
This layer will split data into packets of data and provide the serial number on the data packets that can be rearranged when it came to the side of the goal. In addition, at this level, will determine the protocol that will be used to transmit the data, eg TCP protocol. This protocol will transmit data packets, as well as to ensure that the packet received successfully (acknowledgment), and retransmit the packets that are lost or damaged on the way.

Layer 3: Network Layer
Network layer will make header for packets that contain IP information, both the sender's IP data and IP destination data. Under certain conditions, this layer will also perform routing through the use of internetworking routers and layer 3 switches.

Layer 2: The data-link layer
Befungsi to determine how the data bits are grouped into a format called a frame. In addition, at this level of error correction, flow control, addressing hardware (such as the Media Access Control address (MAC address)), and determine how the network devices such as hubs, bridges, repeaters, and a layer 2 switch operates. IEEE 802 specification, dividing it into two levels level children, the layer Logical Link Control (LLC) layer and the Media Access Control (MAC).

Layer 1: Physical Layer
Layer Physcal work by defining the network transmission media, signaling method, bit synchronization, network architectures (such as Ethernet or Token Ring), network topology and cabling. In addition, this level also defines how the Network Interface Card (NIC) can interact with cable or radio media.

The process of sending data can pass through each layer analogy like when we send a letter. The letter is the data that will be sent (layer 7 -> 5). Then, according to standard delivery, we put the letter into an envelope (layer - 4). So that we can sent the letter, we need to add the address where the mail is sent, as well as who the sender of the letter was (Layer - 3). Furthermore, the letter we submitted to the expedition, and the expedition we will be sending a letter earlier (layer - 2 & 1).

Packet Header
In the previous review we discuss how a process of data transmitted, now we will try to unload data. What's in sebiah data so that data can be transmitted. analogy when we send data on the Internet is like sending a POS, it can be said that the data is the contents of the letter, then the packet headers is an envelope, stamp, address, and other equipment. Packet header provides some additional information. If we surgical ditrasnmisikan a data packet using ipv4, then the contents of the data packets can be seen as shown below:

IPVer: Storing information used IP version (IPv4 or IPv6).
IHL (IP Header Leght): Information overall length of the data packet header. The minimum length of the IP header is 20 bits, and the maximum length is 24 bits.
TOS: It is a field in the IPv4 header has a length of 8 bits and is used to indicate the type of Quality of Service (QoS) that is used by the datagram in question to be submitted to the internetwork routers. Implementation of this TOS is usually when we do the limitations of HIT in the web proxy service proxy or VOIP.
Bit 16 Total Length: 16 bits The contents of this gives the overall size information packet (fragment) including header and data. Information is displayed in a format bytes
16 Bit Identification, Fragment Offset Flag / Length: At the time of ip packet goes on the internet, this pack will probably pass some routers can not handle the size of the packet, for example, the value of Maximum transmission unit (MTU) that is smaller than its IP datagram size, then The package will be broken or fragmented packets - smaller package would then be reassembled later. These parameters will be used for fragmentation and rearrangement.
TTL: There is the possibility of an IP packet wander aimlessly in the Internet network. Case example of an error routing or routing loops. In order for this package is not circling the Internet forever, the TTL value will be deducted each time a data packet passes through a router. When the TTL value of a packet of data has been exhausted or has a value of 0, then the packet is dropped or discarded.
Protocol: Contains information what protocol is used to transmit data.
16 Bit Header checksum: information is calculated based on the calculation of the value of the IP header content. Used to determine if there is an error at the time of transmission of the data.
32 Bit Source IP Address: 32 bits data packet source IP information.
Bit 32 Destination IP Address: 32 bits IP destination information of data packets.
Options (if any): This parameter includes rarely used, has a variable length, from 0 to a multiple of 32 bits. This parameter can be used to store a value for the security option, Record Route, Time Stamp, etc..
Data: Contains the data that is transmitted.

From the packet header information above, at the end of a data can be sent from one host to another.

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