DoD layer model
The DoD Internet Architecture Model is a layered architecture for network protocols .
In this model, the individual tasks involved in data transmission are divided into layers that build on each other (see also the TCP / IP reference model ). For each layer there is a series of protocols (see Internet protocol family ) that solve the tasks of the respective layer in different ways. The model was developed by DARPA for the United States Department of Defense (DoD) in the late 1960s and initially consisted of four layers. It was about a purely military application in connection with the development of the ARPANET , which should be protected from failures by a decentralized structure.
| No. | layer | Examples |
|---|---|---|
| 4th | Process | Telnet , SMTP , FTP |
| 3 | Host-to-host | TCP , UDP |
| 2 | Internet | IP , IPX |
| 1 | Network Access | Ethernet , Token Ring , V.24 |
layers
Network access layer
In the network access layer, the problem of data transfer between computers and processes is solved on the physical level. It is important here which transmission medium ( copper cable , radio network , etc.), which line code ( RZ code , NRZ code , AMI code , etc.) and which access protocol (e.g. Ethernet , V.24 ) is used. An address is used to specify which computer or process is to receive the data packet.
Internet layer
The task of the protocols of the Internet layer is to provide network-wide addressing independently, e.g. B. to enable the transmission medium. A network address is assigned to each computer or network card. Unlike the address of the network access layer, this address is assigned according to logical criteria and thus enables large networks to be managed. It can be compared to telephone numbers that have an area code and thus prevent a switching system from having to know all the telephone numbers in the world. This makes it possible to send data packets over several networks. The most common protocol of this layer is the Internet Protocol .
Host-to-host layer
The task of the protocols of the host-to-host layer is to enable the transport of data between two processes on the different computers (end-to-end connection). This is necessary because it is not enough to transport the data to the target computer; it must also be specified which of the programs running there that are waiting for data from the network should receive the respective packet. There are different approaches to transferring information:
- In the case of connectionless transmission, there is no control built into this layer to ensure that the packet actually arrives. The control must take place in the process layer. This is comparable to sending a letter in the real world.
- In the case of a confirmed, connectionless transmission , a confirmation message is provided to report the receipt of the packet to the sender. It is equivalent to sending a registered letter with acknowledgment of receipt.
- In the case of connection-oriented transmission , a logical connection is established and maintained before the transmission. Even if no data is transmitted, control information is exchanged between the computers. This procedure enables control of the packet sequence and data flow control .
The two protocols TCP and UDP are available for this on the Internet . TCP is a connection-oriented protocol. It enables reliable transmission of the data. However, this also means a large amount of additional information that is transmitted in addition to the actual message. UDP, on the other hand, is a connectionless protocol. With this protocol, the network load is kept lower due to the lower administrative overhead, and a higher data throughput can be achieved. On the other hand, UDP does not automatically recognize the loss of packets, and there is a risk that the messages sent will arrive in a different order than they were sent.
Process layer
The protocols of the process layer define the structure of the actual message. The actual user data is stored here according to the selected protocol. The best known are used to transfer e-mails ( SMTP ), websites ( HTTP ) or files ( FTP ). For each piece of information that has to be transmitted, its exact position in the message and its precise structure are specified here.
Package structure
Each level of the layer model adds information as a packet header when the data is sent , which is evaluated at the same level by the recipient. You can imagine it to be like a large envelope with a slightly smaller envelope in it and in this in turn a very small envelope, which ultimately only contains the sheet with the actual information. The information that is required in the respective shift is on each envelope:
|
The OSI layer model
A few years after the DoD model, the OSI model was developed by the International Organization for Standardization (ISO). The structure is similar to the DoD model, but distributed over seven instead of just four layers. Although the DoD model had proven its worth in practice, the major computer companies considered using the OSI model for their own transmission protocols. Since 1988 even the US government has supported the new model. This is how the OSI model ultimately prevailed. Nevertheless, the DoD model is still often used to describe communication processes on the Internet. For this it is necessary to summarize some layers of the OSI model:
| Layers OSI model | Layers DOD model | ||
|---|---|---|---|
| 7th | application
(Application) |
4th | application
(Process) |
| 6th | presentation
(Presentation) |
||
| 5 | meeting
(Session) |
||
| 4th | transport
(Transport) |
3 | transport
(Host-to-host) |
| 3 | Mediation / package
(Network) |
2 | Internet
(Internet) |
| 2 | Fuse
(Data link) |
1 | Network access
(Network Access) |
| 1 | Data transfer
(Physical) |
||
Individual evidence
- ↑ a b Vinton G. Cerf , Edward Cain: The DoD Internet Architecture Model (PDF; 866 kB) Pennsylvania State University . 1983. Retrieved July 6, 2013.
