Manual VIPA CPU 21x Chapter 4 Deployment of the CPU 21x-2BT10 with TCP/IP
HB103E - Rev. 05/45 4-9
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.
The TCP transport service works stream orientated. This means that data
packages assembled by the user not necessarily have to receive the
partner in the same packaging. Depending on the data amount, packages
may though come in in the correct sequence but differently packed. This
causes that the recipient may not recognize the package borders anymore.
For example you may send 2x 10Byte packages but the counter station
receives them as 20Byte package. But for most of the applications the
correct packaging is important.
Due to this you need another protocol above TCP. This purpose is defined
in the protocol RFC1006. The protocol definition describes the function of
an ISO transport interface (ISO 8072) basing upon the transport interface
TCP (RFC793).
The basic protocol of RFC1006 is nearly identical to TP0 (Transport
Protocol, Class 0) in ISO 8073.
For RFC1006 is run as protocol for TCP, the decoding takes place in the
data section of the TCP package.
• In contrast to TCP here the receipt of one telegram is confirmed.
• Instead of ports TSAPs are used for the addressing besides of the IP
address. The TSAP length may be 1 ... 16Byte. The entry may happen
in ASCII or Hex format. Foreign and local TSAPs may only be identical
at 1 connection.
• Independently of the used protocol the VIPA handling blocks AG_SEND
(FC5) and AG_RECEIVE (FC6) are necessary for data transfer.
• Contrary to TCP different telegram lengths can be received using
RFC1006.
UDP
ISO-on-TCP
RFC1006
Properties
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