Number Of Simultaneous Send/Receive Calls - Siemens SIMATIC NET S7-400 Manual

Characteristic
Maximum data length for AG_LSEND and
AG_LRECV program blocks
Maximum data length for
AG_SSEND and AG_SRECV program blocks
LAN interface max. data field length generat-
ed by CP per protocol data unit
Restrictions for UDP
● Transfer is not acknowledged.
The transmission of UDP frames is unconfirmed, in other words the loss of messages is
not detected or displayed by the send blocks (AG_SEND or AG_LSEND).
● No receipt of UDP broadcast
To avoid overload due to high broadcast load, the CP does not allow reception of UDP
broadcasts.
As an alternative, use the multicast function over a UDP connection. This allows you to
register the CP as a node in a multicast group.
● UDP frame buffering
Length of the frame buffer with buffering enabled:
2 KB
Note:
Following a buffer overflow, newly arriving frames are discarded.
2.3.2

Number of simultaneous SEND/RECEIVE calls

The number of SEND/RECEIVE calls that can be used at the same time is limited both by
the CPU and by the CP.
If the maximum number of simultaneous SEND/RECEIVE calls is exceeded, the value
8302H (no receive resources) is indicated in the STATUS of the surplus SEND functions.
This can, for example, happen when too many SEND/RECEIVE calls are sent at the same
time in OB1.
CP 443-1 RNA
Manual, 03/2019, C79000-G8976-C299-04
Explanation / values
AG_LSEND and AG_LRECV allow the transfer of user data with the fol-
lowing lengths:
1. ISO-on-TCP, TCP, ISO transport: 1 to 8192 bytes
2. UDP: 1 to 2048 bytes
AG_SSEND and AG_SRECV allow the transfer of user data with the
following lengths:
1. ISO-on-TCP, TCP, ISO transport: 1 to 1452 bytes
2. UDP: 1 to 1452 bytes
sending
•
ISO transport, ISOonTCP, TCP:
– 400 bytes / TPDU with AG_SEND / AG_LSEND
– 1452 bytes / TPDU with AG_SSEND
receiving
•
– ISO transport: 512 bytes / TPDU
– ISO-on-TCP: 1452 bytes / TPDU
– TCP: 1452 bytes / TPDU
Performance data
2.3 SEND/RECEIVE interface
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