OSI Model

OSI Model - Send messages from one network to another is a very complex process. A little story of the formation of the OSI, in 1977 a subcommittee of the International Organization for Standarddization (ISO) began work to create multiple sets of standards to facilitate network communication. The work was completed in 1984 and known as the OSI reference model - Open Systems Interconnection. The OSI model is the method most widely used to describe the communication network. The following sections cover topics:

The OSI model divides the tasks into 7 layer network.

1. Layer 7: Application Layer

2. Layer 6: Presentation Layer

3. Layer 5: Session Layer

4. Layer 4: Transport Layer

5. Layer 3: Network layer

6. Layer 2: Data link layer

7. Layer 1: Physical Layer

Physical layer is the first layer, but common in the list at the bottom of the last order to emphasize how a message is sent over the network. Here's a brief description of each OSI layer-2 and I try a simple analogy to the concept of our lives.

Layer 7: Application Layer

Layer 7 is the Application layer defines the interface between two software applications that communicate mmerlukan to communicate out of the computer where the application is located. Application Layer-2 explains the rules for the following:

Provision of network services
Quote - advertising network services
Accessing network services
The following example is a protocol that implements the rule-2 Application layer.

Netware's services advertising protocol (SAP)
TCP / IP Network File System (NFS)
TCP / IP Simple Mail Transfer Protocol (SMTP), Telnet; HTTP; FTP; WWW browser
Included in this example is the file; prints; application database; message.
Layer 6: Presentation Layer

Layer 6 is a presentation layer where the main objective is to define data formats such as ASCII text, EBCDIC text, binary, BCD and jpeg. Encryption also is defined in layer 6. Presentation Layer-2 specifies the rules for the following:

Translating Data
Encryption and compression of data
Protocol-2 The following are examples of Presentation layer that implements rules

NetWare Core Protocol (NCP)
AppleTalk Filing Protocol (AFP)
JPEG; ASCII; EBCDIC; TIFF; GIF; PICT; encryption; MPEG; MIDI
Eg mainframe EBCDIC format has, while WIndows have ASCII data format. Task Presentation layer is to translate the different formats it so that it can connect with each other.

Layer 5: Session Layer

Session layer defines how to start, control, and end a conversation (called a session). It is included in the control and management of a variety of bidirectional messages so that the application can be notified when some message is complete. Fifth Session Layer-2 specifies the following rules:

Control of the communication session between the two devices
Making; manage, and remove connections
The following is a protocol implementing the session layer of the OSI model:

Netware's Servise Advertising Protocol (SAP)
TCP / IP remote procedure call (RPC)
SQL; NFS; NetBIOS names; AppleTalk ASP; DECnet SCP
A simple example is the operator telephone analogy. If you want to call a number while you do not know the number, then you can nanya to the operator. This session layer analogy yach kayak Getu telephone operator.

Layer 4: Transport Layer

Layer 4 (Transport Layer) focus on issues related to computer data transmission such as error recovery, segmentation of the block of data from the application into small pieces-2 to be sent, and on the recipient's computer-2 pieces are rearranged.

Layer OSI to this 4-2 specifies the rules for the following:

Hiding the network structure of the layer above it
Notice that the data message has been received
Ensuring reliability, error-free message delivery
The following example is a protocol-2-2 transport layer that implements rules

Netware's Sequence Packet Exchange (SPX) protocol
TCP / IP 's Transmission Control Protocol (TCP)
TCP / IP 's Domain Name System (DNS)
Analogy of the transport layer is like a parcel delivery service providers, eg, Tiki or Fedex. Tiki or Fedex are solely responsible for the arrival of packets to the destination address and the packet in one piece without any defect. As well as ISP, if we type WWW.dotkom.com then the ISP will translate into a destination address.

Layer 3: Network Layer

Network layer of the OSI model defines the packet delivery end-to-end. To complete this work, the network layer defines logical address so that each end point can be identified. This layer also defines how routing works and how routes can be studied so that all packets sent.

Network Layer-2 specifies the rules for the following:

Routing data between many networks
Frakmentasi and reconstruct the data
Identification of a network cable segment
Protocol-2 following rules apply network layer

's Netware Internetwork Packet Exchange (IPX) Protocol
TCP / IP 's Internet Protocol (IP), AppleTalk DDP
The analogy of this layer duty to send a letter or package to a specific city or zip code, not directly sent to the destination address. This layer is very important in complex networks, where the network layer to send data packets to a logical network. The router function at this layer.

Layer 2: Data link layer

The data link layer specifies the following rules:

Coordination bits into two logical groups of an information
Sometimes error detection and correction
Controlling the flow of data
Identification of network devices
Protocol-2 data link layer implements the following:

Ntware's Link Support Layer (LSL)
Asynchronouse Transfer Mode (ATM)
IEEE 802.3/802.2, HDLC, Frame Relay, PPP, FDDI, IEEE 802.5/802.2
The analogy is like a data link sent you a registered letter to the address of the house and is guaranteed up to the receipt signed by the recipient. This layer identifies the real address of a device.

Layer 1: Physical Layer

Physical Layer of the OSI model is related to the characteristics of the transmission media. Example-2 specification of connectors, pins, use of pins, electrical currents, encoding, and light modulation. Usually in completing all the details from the Physical layer involves many specifications. This layer-2 specifies the following rules:

The physical structure of a network eg forms and rules pin connector on the RJ-45 connector. 802.3 Ethernet standard defines the use of the cable to pin 1,2,3 and 6 are used in Cat 5 cable with RJ-45 connector for Ethernet connection.
Rules in the use of mechanical and electrical transmission medium
Ethernet protocols such as IBM Token Ring; AppleTalk
Fiber Distributed Data Interface (FDDI) EIA / TIA-232; V.35, EIA/TIA-449, RJ-45, Ethernet, 802.3, 802.5, B8ZS
 Synchronization signals electrically-2 over a network
 Encoding data in electronic
To enable you to remember the OSI model is to use the following sentence:

I (Application)

Got (Presentation)

Milk (Session)

Eggs (Transport)

Drinking (Network)

In (Data)

Plastics (Physical)

Weleh why even dech not connect ... dah pake aja boso kromo ngingetnye let's easy:

All People Seems To Need Data Processing, which mappingnya like this:

All (Application)

People (Presentation)

Seems (Session)

To (Transport)

Need (Network)

Data (Data link)

Processing (Physical)

Protocol Implementation

Keep in mind that the OSI model is a theory about how to view the communication in the network. Each layer specifies the standards to be followed when mengimplementsikan a network. However, keep in mind that the OSI layers tuhas not do real tasks, OSI is the model. The following discussion summarizes the advantages and disadvantages of the use of the OSI model to describe the communication network.

Advantages and disadvantages of the OSI model

You must fully understand the OSI model because it is so widely used when talking about communication. However, keep in mind that this is just a theoretical model that defines the standards for programmers and system administrators network, so it is not the actual physical layer models.

Using the OSI model konseps discussion networks have several advantages:

Provide the same language and references between fellow professionals network
Divide tasks into network-2-2 logical layer for ease of understanding
Provides flexibility-2 special features level-2 different
Ease of troubleshooting
Encouraging interoperability standards between networks and devices
Provide modularity in the feature-2 network (developers can change the feature-2 without changing the overall approach), so you can play dirty between modules Getu lho
However, you need to know a few limitations:

OSI Layer-2 is theoretical and does not perform the actual function-2
In the implementation of industry rarely have a relationship layer-to-layer
2 different protocols in the stack perform two different functions that help receive and send data messages overall
The implementation of a specific protocol can not represent every layer OSI (or can be spread across multiple layers)
In practice, the task-2 computer network communication protocol implemented by way of implementation. No matter what protocol it's ... it's like a standard protocol nich imdustri vendor-specific software tools used in the process of communication in its duty-2 network communication. The following describes some of the concepts are important to know about the real-2 protocol.

Most vendors and industry standard implementations using a layer-2 approach. A set of standard-2 is meant to be used simultaneously is called a protocol suite or protocol stack.

Protocol-2 in a suite-2 has the following traits:

Each protocol implementing one or more network communication tasks
Protocol-2-2 can carry out tasks in several different OSI layers
Some of the protocol in a similar suite can perform the same task
Some protocol suite allows a choice of special protocol suite to perform a specific task or to enable certain features.
Protocol-2 should work together, send and receive-2 protocol data to others.
Protocol-2 can also be divided into one of three categories according to the functions they do-2. The division between protocol often fall in three different divisions.

Services
Transportation Data
Physical connection

Protocol-2 at the level of transport (ie transport and network layer) to establish communication sessions between computers; ensure that the data is transmitted reliably, and deliver inter-network routing.

Protocol-2 at the level of physical form relationships with the bottom layer of the OSI model (Data link and Physical layer). Protocol-2 is handling information; perform error-checking, and send resend requests - (retransmit request).

Note:

Some protocols are on more than one level protocol, so the protocol-2 may not fit exactly with the model-2 network. This is because the protocol is intended to fulfill a specific task in communication, which is not always associated with some form of model.

Communication between network devices

-2 network devices can communicate between each other because of that-2 devices are running the same protocol stack, even if they use different operating systems. Data is sent from one device to walk down to the underlying protocol stack through a transmission medium, and then up to the protocol stack on the opposite side of the communication device.

Both devices communicate with each other must use the same protocol stack. A data message sent from one device to another device goes through the following process:

Message data is broken into packets-2
Each protocol in the stack adds control information into packets, re-enable features such as encryption and the second error check. Each package usually has the following components: Header, Data and Trailer.
At the physical layer, the packets are converted into electrical proper format for transmission.
Protocol at each layer-2 device related to the opponent (on the receiver) will remove the header and trailer are added when shipping. Package-2 are then reassembled as the original data.
Note:

Header and trailer information is added at each OSI layer-2 is intended to be read by the recipient's computer. Missal, the information is added to the transport layer on the sending computer will be interpreted by the transport layer is also on the recipient's computer. Hence OSI layer communication interaction is often described as the communication between peer layers.

Header - Header package contains the following information:

Home address of the computer sending
Destination address of the message sent
Information to synchronize the clock
Data - Each packet contains data that is:

Real data of the application, as part of the file sent
Size of 48 bytes of data can be nearby for up to 4 kilobytes
Trailer - Trailer package may include:

Error-checking information
Other information that helps control the data transmission
Encapsulation Process

Process is split into packets of a message-2, additional controls and other information, and then transmits the message through the medium of transmission. You have to understand fully the process of sending this message.

There are 5 different steps in the process of data encapsulation:

Layer the top of the set of data to be sent over the network
Transport layer breaks the data into pieces called segments-2, adding sequence information and control information.
Convert the segment into the network layer-2 packet, adding logical network and adding devices address.
Data link layer converts packets into frame-2-2, adding a physical address information of the device.
Convert physical layer-2 frame into bit-2 to be transmitted through the transmission medium.

Use the following summary:

Upper layer - Data
Transport Layer - Segment
Network Layer - a package that contains the logical address
Data link layer - frame containing the physical address
Physical Layer - bits