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OSI modelThe third part of the series on computer networks. The OSI model is the established term for the Open Systems Interconnection Basic Reference Model. It is an abstract description of network communication and the protocols used for communication between computers, which is divided into seven layers. In communication, encapsulation is performed - encapsulate on the sender side and unpack on the receiver side. It starts with layer 7, which is encapsulated in layer 6, and so on. This model was created to standardize communication so that hardware and software from different vendors could communicate with each other.
The description of the OSI model was created many years ago, and although it is considered the foundation for network technologies, it has never been precisely implemented. An equivalent of the OSI model is TCP/IP, which can be said to be based on the OSI model but modifies it to be more flexible. According to the OSI model, communication is always possible only with the layer above or below. All layers must be included in the communication, which in many practical tasks brings unnecessary overhead (both time and data). Nevertheless, the OSI model is good for explaining and theoretically describing networks.
| |
Layer EN |
Layer CZ |
Unit |
Layer Function |
Example |
| Layer 7 |
Application |
Aplikační |
Data |
Network processes for the application, user authentication, everything dependent on the application. |
Telnet, FTP |
| Layer 6 |
Presentation |
Prezentační |
Data |
Data representation and encryption. Resolves differences in data representation between the application and network format - encodes data for transmission. |
MIDI, MPEG |
| Layer 5 |
Session |
Relační |
Data |
Connection between applications, session management. Communication of one application with another, sending multiple data in succession. Maintains the entire connection between two computers. |
NetBIOS |
| Layer 4 |
Transport |
Transportní |
Segments |
End-to-end system connection, reliability - ensures complete data transmission, quality of service. Resolves reliable sending of all data from source to destination using segmentation and acknowledgment. |
TCP, UDP |
| Layer 3 |
Network |
Síťová |
Packets |
Logical addressing - routing - determining the packet path, data transmission from point to point, uses IP addresses. Communication between source and destination devices using IP addresses. |
IP, ICMP, ARP, RIP |
| Layer 2 |
Data Link |
Linková |
Frames |
Physical addressing, MAC - media access control and LLC - logical link control, data flow, frame synchronization, 1-hop communication, uses MAC addresses. Error detection, flow and access control to the medium. Communication between two devices in one subnet (or to the gateway) using MAC addresses. Creates frames (header + data + footer). |
Ethernet, FDDI, Token Ring, PPP, SLIP |
| Layer 1 |
Physical |
Fyzická |
Bits |
Physical parameters of the link - media (cables, radio, light), signals, and binary transmission. Resolves physical data transmission (does not assign any meaning to transmitted bits). |
100BaseT, RS-232, 802.11g |
Comparison of OSI vs. TCP/IP
In practical cases, especially when using the TCP/IP protocol, we can use the TCP/IP model. A rough comparison with the ISO OSI model is here.
| TCP/IP |
OSI |
| Application |
Application |
| Presentation |
| Session |
| Transport |
Transport |
| Network |
Network |
| Network Interface Layer |
Data Link |
| Physical |
Related articles:
This series covers the basics of computer networking. Important practical aspects that everyone interested in networking should know are briefly described. It contains some of the most widely read articles on this site. It is used for teaching in schools.
- OSI model [05.03.2007 08:09] ...... reading now
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switchovani bych zaradil do L2
respond to [1]Vojtech: Samozřejmě máte pravdu. Nevím jak jsem mohl napsat takovou hloupost.
Jen bych podotknul, že Síťová vrstva modelu TCP/IP se také někdy nazývá jako Internet layer, tedy Internetová vrstva.
podle toho, co jsem si našel k tomuto tématu na netu, tak je to opačně: protokol TCP/IP vznikl v 60. letech pro potřeby sítě ARPANET, v roce 1979 vzniká ISO/OSI jako standardizace vrstev.
No, sice studuji sítě teprve 4 měsíce, ale řekl bych, že médiem pro rádiový přenos je vzduch a ne rádio. Nebo ne? :-)
[7] mno ... nemas pravdu :) mediem radiosignal ;-) sirici se ne jen vzduchem, ale i vodou ci vakuem pokud me pamet neklame. Jo jo zapelkita fyzika :-)
[8]resp radiosignal neni mediem, ale "nosicem dat" :-) coz nemeni nic na veci, ze je mu jedno v jakem prostredi pokud nestini, se pohybuje. Pro radio kominikaci (WiFi bych se asi vyrazu prenosove medium vyhnul)
Pan co provozuje tuhle stranku je zachrance.