Specifications

TCP/IP protocol CP143 H1 / TCP/IP manual
2-6 Rev. 00/07
2.2.1.3 TCP/IP in relation to the ISO-OSI level model
TCP/IP is older than the ISO-OSI level model. For this reason the different layers can not be applied
directly to TCP/IP. The TCP/IP network layers correspond to level 1 and 2 of the ISO-OSI model.
Levels 5 and 6 of the ISO-OSI model are already integrated into the protocols of the TCP/IP
application layer.
Internet Protocol (IP)
The purpose of the internet protocol IP is to transport packets of data from a sender to a receiver via
a number of interlinked networks. It may thus be compared with level 3 of the ISO-OSI level model.
IP data transfer services are not protected and do not require a direct connection. The main IP
services are: the transfer of datagrams via a multitude of interconnected networks, to address the
respective partner correctly, to divide data packets according to the respective network conventions
and to reassemble them, and to transfer information about the sequence of packets and their security
characteristics.
Transmission Control Protocol (TCP)
The transmission control protocol TCP is intended to provide a reliable transport-end-to-end-
connection between two different systems. For this reason TCP may be compared to level 4 of the
ISO-OSI level model and it interfaces directly with the internet protocol IP.
TCP provides the following essential services:
• Orientation towards a connection
• Guaranteed sequences
• Loss detection
• Connection time-out detection
• Multiplexing
• Flow control
• Transparent data transfers
• The secure establishment and termination of connections
User Datagram Protocol (UDP)
This protocol can also be classed with level 4 of the ISO-OSI level model and interfaces directly
with the internet protocol IP. This protocol does not make use of connections or error correction for
network transfers. It also does not expect acknowledgements from the receiver of the data.