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Entry type: FAQ Entry ID: 26562314, Entry date: 01/09/2019
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Which quantity frameworks hold for a SCALANCE W client module that is configured as L2T client?

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  • Associated product(s)
If you are operating multiple nodes on a SCALANCE W client and would like to transfer PROFINET IO data cyclically, then the sum of the user data of all the nodes must not exceed a value of 2300 bytes per cycle.

Configuration Notes
This entry is valid for the following products:

  • Access Points SCALANCE W700 in Client mode; for iPCF you need the "KEY PLUG W740 iFeatures"
  • Clients SCALANCE W730, SCALANCE W740; for iPCF you need the "KEY PLUG W740 iFeatures"
  • Client SCALANCE W722-1

Multiple MAC nodes (PROFINET IO devices, for example) are connected to the Ethernet interface of a client module. In the configuration of the relevant client module the MAC Mode parameter is given the setting "Layer2 Tunnel". A client module with this setting is designated as an L2T client in the following.

The following quantity frameworks hold for reliable communication:

  • There must not be more than 8 nodes connected after the L2T client.
  • When transferring cyclic PROFINET IO data in iPCF mode, you must make sure that the sum of the user data of all the nodes on the L2T client does not exceed a value of 2300 bytes per cycle. This specification also includes the frame header. A SIMATIC user must therefore also take the header into consideration in the configuration along with the net data.


Here is an example for calculating the amount of user data. This sample calculation is valid for an ET 200SP (PROFINET IO device) with a maximum configuration of 256 bytes input and 256 bytes output divided among 8 I/O slots.

Notes about calculating

  • The Ethernet header consists of the following:

    Destination MAC = 6 bytes

    Source MAC = 6 bytes

    802.1Q = 4 bytes

    Ethernet type = 2 bytes 

  • If you use VLAN, the amount of user data increases by another 4 bytes.
  • If you configure input and output data in one slot, this slot counts as two slots. You have to calculate 1 byte per slot.
    Example: You are using 8 I/O slots with input and output data. You have to specify the number of slots with 8 * 2 * 1 byte = 16 bytes.

Example calculation
Amount of user data =

Ethernet header (16 bytes) +
Number of output bytes (256 bytes) +
Number of slots + header group + PM-E (18 bytes) +
PROFINET status (4 bytes) +
FCS (4 bytes)

= 298 bytes.

The following number of ET 200SP modules can be determined from this result:

Number of ET 200SP modules =

Sum of all the user data at the L2T client (2300 bytes) /
Amount of user data (298 bytes)

= 7.7

Explanation
Since the sum of the user data of all nodes on the L2T client must not exceed a value of 2300 bytes per cycle, in the cycle time you can operate a maximum of 7 ET200S modules with a maximum configuration of 256 bytes input and 256 bytes output divided among 8 I/O slots.



Security information
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https://www.siemens.com/cybersecurity#Ouraspiration.