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Industrial Ethernet S7-300/400 CPs -- Product information -- System description (protocols)
Which technical data applies for the SIMATIC Modbus/TCP blocks and for which CPUs and CPs is it released.
How many devices can you connect to an S7-300/S7-400 using the Modbus/TCP protocol?
When compiling a CFC chart, why is the error message "Time stamp conflict" displayed in connection with the Modbus/TCP FBs for S7-400 CPUs?
How many licenses are required for the Modbus/TCP block in the S7-300/S7-400?
Which IO controllers and IO devices support the following functions in STEP 7 (TIA Portal): IRT, prioritized startup, MRP, MRPD, PROFIenergy, Shared device, MSI/MSO, I device, Isochronous mode, System redundancy and Option handling?
How are the communication resources assigned in the S7-300?
How do you load the 3D, CAx and ePLAN data for the SIMATIC products?
What are the differences between OPEN MODBUS / TCP Redundant V1 and OPEN MODBUS / TCP Redundant V2?
What should you watch out for when you enable the "SNMP" function in the configuration of the security module?
Which security modules support the dynamic DNS function (DDNS)?
What should you watch out for when enabling and using the security functions of CP343-1 Advanced and CP443-1 Advanced?
What should you watch out for when upgrading from previous modules to the successor module CP443-1 or CP443-1 Advanced?
How do you verify the authenticity of the Siemens modules CP343-1 and CP443-1?
What should you watch out for when operating a port of CP343-1, 6GK7343-1CX10-0XE0 and 6GK7343-1EX30-0XE0 with firmware V2.1 or higher, with 10 Mbit/s half duplex?
Which IO controllers and IO devices support the following functions in STEP 7 V5.5: IRT, prioritized startup, MRP, MRPD, PROFIenergy, Shared device, I device, sochronous mode, System redundancy and Option handling?
Where do you procure the firmware extension for the CP 343-1 ERPC for database connection?
Which SIMATIC S7-300/S7-400 modules support the NTP time-of-day message and how do you activate this kind of time synchronization?
Which modules can you use when implementing software redundancy?
Which types of connection/protocols do the S7-300/400 CPUs and the CPs support by default?
Which PROFINET nodes support automatic commissioning (device replacement without interchangeable medium) in the case of topological configuration and device replacement without topological configuration?
Which PROFINET nodes support the extended PN diagnostics and what do you have to configure?
Using C-PLUG with network components and SIMATIC CPs
What properties have the communication services and protocols that can be used in the Industrial Ethernet network?
Behavior of the communication processors during data transfer via TCP connections without RFC 1006
What should you watch out for with the ICMP Redirect (Internet control message protocol) function regarding the IP address of the router used for Industrial Ethernet CPs?
What should you pay attention to with the autonegotiation function for negotiating the LAN mode in Industrial Ethernet CPs?
What is the connection between subnet masks and IP addresses with regard to subnetting and supernetting (Classless Inter Domain Routing CIDR)?
Which modules support the S7 routing function?
In the case of open TCP/IP communication via Industrial Ethernet using T blocks with IE CPs and CPUs, why are different amounts of messages sent when the maximum length of 1452 bytes of user data is transferred?
What properties, advantages and special features does the ISO protocol offer?
What properties, advantages and special features does the UDP protocol offer?
What properties, advantages and special features does the ISO-on-TCP protocol offer?
What properties, advantages and special features does the S7 protocol offer?
What properties, advantages and special features does the TCP protocol offer?
What are the requirements for disabling the PROFINET CBA interface for CP443-1EX40?
"Time Wait" with TCP connection setup
What are the different data block lengths for the various protocols of Send/Receive communication?
What is RFC1006 and what do I need this service for?
Meaning and function of the "Keep Alive" in TCP connections
What should you pay attention to with the autonegotiation function for negotiating the LAN mode in Industrial Ethernet CPs?
Part number:

This entry describes what you should pay attention to with regard to the autonegation and autosensing functions in Industrial Ethernet CPs.
The communication processors always try to use the most powerful and fastest contol mode. To understand the following explanaitions, it is necessary to explain some terms about the possible states of the LAN controller when negotiating the LAN operation mode.
Term Explanation
PHY Physical level converter that is put in front of the LAN-controler. The PHY passes the telegrams which are on the LAN to the LAN-controler.
Autoswitching This is a special operation mode of the PHY of the respective module. The PHY is in 10 MBit/sec Half-Duplex mode and is waiting for a corresponding link. In this stat no 100 MBit/sec link will be identified.
Autosensing Autosensing is the automatic identification of the transfer rate (10/100 MBit/sec).
Autonegotiation This is the automatic identification/negotiaton of the transfer rate (10/100 MBit/sec) and of the operation mode (Full-Duplex/Half-Duplex).
Table 1: Term explanation

Autonegotiation and Autosensing are supported by all Industrial Ethernet communication processors that support the operation modes 10MBit/sec and 100MBit/sec. The mechanism is used for the automatical identification of the most effective operation mode between two partner devices. Partner devices are (usually) a communication processor or a network component.

The following operation modes can be negotiated:
Baud rate Operation mode

10 Megabit

10 Megabit Full-Duplex
100 Megabit Half-Duplex
100 Megabit Full-Duplex
Table 2: Summary of the possible baudrates and operation modes.

Meaning of the operation modes

  • Full-Duplex means that a bidirectional data exchange is possible. On the transmission network each of both users can send independently from each other.
  • In Half-Duplex operation a bidirectional data exchange is possible as well. On the transmission network, however, always only one data transport in one direction at one time between two components is possible. A data transfer between two components can not take place at the same time, it must be done by turns.

Purpose of this method
This is aimed to get the highest possible baudrate with the best possible operation mode - that is a baudrate of 100 MBit of the control mode fullduplex.

Two different kinds of approach have to be distinguished for negotiating the LAN operating mode. Since August 2001, the mechanism has been changed to guarantee an automatic coupling to almost all partner stations. In the following, the different versions V1 and V2 are described. Which modules or firmware versions belong to which group is described below.

Autonegotiation is a 100 MBit/sek attribute, which is not available for modules with only one AUI interface, or an ITP interface with 10MBit/sec or a fix preselection in the hardware configuration.

Description of the negotiation procedure V1:
After starting the module the communication processor executes the autonegotiation. If it is supported by the partner, the highest possible operating mode will be negotiated. The active communication processor will recommend 100MBit/sec full-duplex, and if required it will switch to the supported operating mode of the parter unit.

If it does not receive an answer because the partner does not support autonegotiation, the mode will switch to "Autoswitching". This would be the same as 10 MBit/sec half-duplex. It is the default control mode of the communication processor.

All units which only support 10MBit/sec half-duplex will not answer to the autonegotiation pulse. A communication is after this is still possible because the partner station has been set to the default.

If no partner was available after the start-up, the default setting is still active. If a partner responds later, a 10MBit/sec link will be created at first. After this the communication processor initiates another autonegotiation activity, because the partner might support more than 10MBit/sec.
Both partners can now agree on a 100MBit/sec full-duplex, it both support it.
If the communication processor receives no answer to a autonegotiation, it will remain on the 10 MBit/sec half-duplex.

If a partner just supports 100MBit/sec full-duplex, but also autonegotiation, two cases have to be distinguished. Such a unit is for excample the OMC (optical media converter):

  • Are both partners connected while starting-up, the first autonegotiation attempt will lead to a negotiation of the communication processor with 100 MBit/sec full-duplex. During the autonegotiation, a 100MBit/sec link will be identified and afterwards the control mode full-duplex.
  • If the 100 MBit/sec component is connected later, the communication processor is already in the autoswitching mode. This is the result of the first unsuccessful autonegotiation, and now a 10 MBit/sec link is absolutely necessary. Since the partner station (OMC) does not support 10 MBit/sec, a connection can never be established.

    Moduls which support the autonegotiation V1:
    Module Moduletype Firmwareversion
    6GK7 343-1EX10-0XE0 CP 343-1 to version V1.0.3
    6GK7 443-1EX10-0XE0 CP 443-1 to version V1.1.0
    6GK7 443-1EX11-0XE0 CP 443-1 to version V1.1.0
    6GK7 343-1GX00-0XE0 CP 343-1 IT to version V1.0.1
    6GK7 443-1GX10-0XE0 CP 443-1 IT to version V1.1.0
    6GK7 443-1GX11-0XE0 CP 443-1 IT to version V1.1.0
     Table 3: Modules which support Autonegotiation V1

    Description of the negotiation procedure V2:

    The following changes have been implemented because of the OMC properties:
    The communication processor switches cyclycally between autoswitching and autonegotiation (after start up and disappearance of a link). This way, a corresponding component can be coupled under any circumstances. Therefore, all cases described above can be controlled.

    While switching, the FAST-LED will blink slowly.
    The communication processor finally changes into the status AUI (corresponding to 10 MBit/sec half-duplex) if it receives telgrams via the AUI cable (activitiy control). Autoswitching is started at the same time to identify a possible 10 MBit link of an interim placed twisted pair-cable.
    If such a link was identified, autonegotiation will be started again to negotiate the highest possible operational mode between both partners.

    Modules which support autonegotiation version V2:
    All the current Industrial Ethernet CPs, except for those listed in Table 03, support autonegotiation version V2.

    If the operating mode "100 MBit/sec full-duplex" has been negotiated or set with project planning, a sporadical loss of telegrams might occur. This affects only high demand cases where the CP itself needs to process the larger part of telegram communication.
    This effect will be amplified if the CP has a lot of partner stations which are able to send and receive asynchronously.

    The circumstance described apply to the following Industrial Ehternet Communication processors:
    Modules Moduletype Firmwareversion
    6GK7 443-1EX10-0XE0 CP 443-1  to version V1.1.0
    6GK7 443-1EX11-0XE0 CP 443-1 to version V1.1.0
    6GK7 443-1GX10-0XE0 CP 443-1 IT to version V1.1.0
    6GK7 443-1GX11-0XE0 CP 443-1 IT to version V1.1.0
    Table 4: Modules with restrictions in full-duplex operation

    The effect appears in temporary "dropouts" on a corresponding connection. Due to the telegram loss the partner station is waiting on an acknowledge on transmission level. This will not happen. After about one second the partner station repeats the last telegram sent and the communication continues. Because of this behaviour the performance decreases. Neither the connection will be closed nor will the telegram be lost, since the superposed transport layer will provide for a repeat of the telegrams.

    The communication partners (CP and network components) have to be set fixed to an operating mode unequal to "100 Mbit/sec full duplex", that means no autonegotiation. It is important here that both partners are set fixed, because otherwise different operating modes might occur in the two communication partners.
    This behavior does not occur in the following firmware versions of the communication processors listed in Table 04 and in the current Industrial Ethernet CPs. Then in none of the operating modes will messages be lost.

    Network, network protocol, data loss

 Entry ID:15048972   Date:2008-03-17 
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