=OSI Model and Transmission Path=
 A.OSI 7-Layer Model
 B.Signals and Network Media
 C.Data Link Layer
 D.Bridges and Repeaters
 E.ARP and ARP tables
 F.Topologies and Access Methods
  Related Items
 A-1 What is the OSI model?
 A-2 OSI 7-Layer Model and the role of each layer
 A-3 Function modules and Header Additions
 A-4 Concepts of Data transmission
 A-5 Names and IP Addresses
 A-6 Comparison with TCP/IP
 A-7 Evaluation points of network equipment
 

 A-6 Comparison of TCP/IP Layer Model and OSI 7-Layer Model
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Although the OSI 7-layer model has been shown so far, actually the TCP/IP layer model is implemented in equipment.
The main differences between the OSI 7-layer model and TCP/IP layer model are as follows.


1. The session layer (layer 5), presentation layer (layer 6) and application layer (layer 7) of the OSI 7-layer model are not implemented and are included in applications.

Figure A-6-1 Difference of implementation between (a) the OSI 7-layer model and (b) the TCP/IP layer model


Details are shown in the item of TCP/UDP. In the current TCP/IP, applications (both servers and clients) using networks have to manage session, encryption and so on.




2. The name of function module and data unit in each layer is different.

This name difference can be a trigger which causes a confusion, so we must be careful.

Figure A-6-2 shows the function modules and data units in the OSI 7-layer model, and
figure A-6-3 shows the function modules and data units in the TCP/IP layer model.

Figure A-6-2 The function modules and data units in the OSI 7-layer model

Figure A-6-3 The function modules and data units in the TCP/IP layer model


As shown in the following figure, the names of layers other than the transport layer are different. The names of data units are also different as well as the function modules.

The important reminder is that the data unit "packet" is used as a data unit of different function module. The unit data "packet" can be a trigger which causes a confusion because it is often used.
When reading drawing, literature, specification, documentation and manual of network, we have to be careful about which they are based on (the OSI 7-layer model or TCP/IP).
The following is the mapping table for models.


Table A-6-1 Differences of function modules and data units between the OSI 7-layer model and TCP/IP layer model
Layer OSI 7-Layer Model TCP/IP Model
Function module Data unit Function module TCP data unit UDP data unit
5 Session Layer Data Application Layer Stream Message
4 Transport Layer Segment Transport Layer Segment Packet
3 Network Layer Packet Internet Layer Datagram Datagram
2 Data Link Layer Frame Network Access Layer Frame Frame