Siemens S7-400 - Page 23

Performance data
2.3 SEND/RECEIVE interface
CP 443-1 Advanced
Equipment Manual, 03/2023, C79000-G8976-C256-07
23
Characteristic
Explanation / values
Maximum data length for AG_SEND and
AG_RECV program blocks
AG_SEND and AG_RECV were shipped with predecessors of the CP and
allow the transfer of user data with a length from 1 to 240 bytes. The
version of the CP described here continues to support these blocks.
Maximum data length for AG_LSEND and
AG_LRECV program blocks
AG_LSEND and AG_LRECV allow the transfer of user data with the
following lengths:
1. ISO-on-TCP, TCP, ISO transport: 1 to 8192 bytes
2. UDP: 1 to 2048 bytes
3. E-mail (job header + user data): 1 to 8192 bytes
Maximum data length for
AG_SSEND and AG_SRECV program blocks
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
LAN interface max. data field length generated
by CP per protocol data unit
• 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
* Notes on TCP connections:
• Avoid receive overload
The flow control on TCP connections cannot control permanent overload of the recipient.
You should therefore make sure that the processing capabilities of a receiving CP are not
continuously exceeded by the sender (approximately 150200 messages per second).
• TCP connections for FTP
Of the available TCP connections, a maximum of 20 TCP connections can be configured /
used with the "Use FTP protocol" option; see Characteristic data for FTP / FTPS mode
(Page 27).
Restrictions for UDP
• Transfer is not confirmed
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.