Manual VIPA System 300V Chapter 6 Deployment CPU 31x with TCP/IP
HB130E - CPU - Rev. 11/50 6-5
The internet protocol covers the network layer (Layer 3) of the ISO/OSI
layer model.
The purpose of IP is to send data packages from on PC to another passing
several other PCs. These data packages are referred to as datagrams.
The IP doesn't guarantee the correct sequence of the datagrams nor the
delivery at the receiver.
For the unambiguous identification between sender and receiver 32Bit
addresses (IP addresses) are used that are normally written as four octets
(exactly 8Bit), e.g. 172.16.192.11.
These internet addresses are defined and assigned worldwide from the
DDN network (Defense Department Network), thus every user may
communicate with all other TCP/IP users.
One part of the address specifies the network, the rest serves the
identification of the participants inside the network. The boarder between
the network and the host portion is variable and depends on the size of the
network.
To save IP addresses, so called gateways are used that have one official
IP address and cover the network. Then the network can use any IP
address.
The TCP (Transmission Control Protocol) bases directly on the IP and thus
covers the transport layer (layer 4) of the OSI layer model. TCP is a
connection orientated end-to-end protocol and serves the logic connection
between two partners.
TCP guarantees the correct sequence and reliability of the data transfer.
Therefore you need a relative large protocol overhead that slows down the
transfer speed.
Every datagram gets a header of at least 20 octets. This header also
contains a sequence number identifying the series. This has the
consequence that the single datagrams may reach the destination on
different ways through the network.
The UDP (User Datagram Protocol) is a connection free transport protocol.
It has been defined in the RFC768 (Request for Comment). Compared to
TCP, it has much fewer characteristics.
The addressing happens via port numbers.
UDP is a fast unsafe protocol for it doesn't care about missing data
packages nor about their sequence.
IP
TCP
UDP
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