DE10147429A1 - System for planning data traffic in communications systems, such as real time Ethernet - Google Patents

Abstract

The system uses planning method of data traffic in real time Ethernet with several participants, or subscribers. At least tolerance section of each reception time point of a data telegram is generated. Data telegrams, received outside such a tolerance section, are stored and processed later. The planning of transmit and reception time points is carried out by software initiated by exact relations of the network. The actual reception time point of real time telegram is monitored by a unit at reception switch.

Description

The invention relates to a system and method for Planning of data traffic in communication systems, esp special realtime ethernet.

Under a synchronous, clocked communication system with Equidistance properties are understood as a system of little at least two participants who are on a data network for the purpose of mutual exchange of data or the mutual Transmission of data are interconnected. Doing it the data exchange follows cyclically in equidistant communication cycles by the communication used by the system be set clock. An equidistant determinist Cyclic data exchange in communication systems ba based on a common clock or time base for everyone at the Communication involved components. The clock or time base sis is made of an excellent component (beat racket) transferred to the other components. With isochronous realti me-Ethernet uses a syn chronization master by sending synchronization steps legrams specified. Participants are, for example, central Automation devices, programming, project planning or HMI devices, peripheral devices such as B. I / O Assemblies, drives, actuators, sensors, memory programming bare controls (PLC) or other control units, compu ter, or machines that exchange electronic data with other ma Exchange machines, especially data from other machines to process. Participants also become network nodes or kno called ten. The following reg Understand all types of control or control units, but also, for example, switches and / or switch controllers. As Data networks are, for example, bus systems such. B. fieldbus, Profibus, Ethernet, Industrial Ethernet, FireWire or also  PC internal bus systems (PCI), etc., but especially also isochronous realtime ethernet used.

Data networks enable communication between several Participants through networking, i.e. connecting the individual participants. Communication means that Transfer of data between participants. The too carrying data are sent as data telegrams, d. H. the data is packed into several packages and in this form via the data network to the corresponding emp catcher sent. One therefore speaks of data packets. The term transfer of data becomes synonymous with transmission of data telegrams or data pairs mentioned above keten used.

In distributed automation systems, for example in Be rich drive technology, certain data need to be certain Times arrive at the designated participants and processed by the recipients. One speaks of real-time critical data or data traffic, as a not timely arrival of the data at the destination too un leads to the desired results for the participant, in contrast to the not real-time critical, for example inter- or intra net-based data communication. According to IEC 61491, EN61491 SERCOS interface - Brief technical description (http: / / www.sercos.de/deutsch/index_deutsch.htm) he can consequent real-time critical data traffic of the type mentioned can be guaranteed in distributed automation systems.

In the German patent application DE 100 58 524.8 a Sys system and a method for transmitting data over bare data networks, in particular the Ethernet, discloses that a mixed operation of real-time critical and non-real time critical, especially internet or intranet based data Communication allowed.  

Automation components (e.g. controls, drives,...) today generally have an interface to egg a cyclically clocked communication system. An expiry level automation component (fast cycle) (e.g. storage control, torque control of a drive) is synchronized to the communication cycle. This will the communication clock is fixed. Other, low-performing Algorithms (slow cycle) (e.g. temperature controls) of the Au tomato components can also only use this Communication clock with other components (e.g. binary scarf for fans, pumps,. , .) communicate, although a langsa more cycle would be sufficient. By using only one Communication clock for the transmission of all information the system places high demands on the bandwidth of the Transmission link.

For process control and monitoring in automated -based manufacturing and especially for digital drives techniques are very fast and reliable communication systems with predictable response times required.

With parallel bus systems, such as SMP, ISA, PCI or VME, is a very quick and easy communication buildable between different assemblies. These well-known Bus systems are used in particular in Rech and PCs.

The basic requirement for cyclical real-time data traffic in Ethernet networks (IRT communication) is time-dependent sending and receiving of Ethernet telegrams. For each IRT Ethernet switch, send and receive lists are required, which are processed cyclically, in each isochronous cycle. Processing is linked to the cycle time within an isochronous cycle. An Ethernet telegram sent to switch 1 at time t ₁ must be received at switch 2 taking into account the network runtime Δt at time t ₂ = t ₁ + Δt. The following applies:

• - the cycle time in both Ethernet switches (Switch 1 and 2) must be in sync
• - The network runtime from switch 1 to switch 2 must be known his
• - The outgoing and return lines must be of exactly the same length

Since the above requirements cannot be met exactly in real networks, an Ethernet telegram, which is sent at time t ₁ , is received within a tolerance band around t ₂ .

The synchronous cycle time is a jittery para meter, which is due to the quartz tolerances and synchronisa effects of the PHY building block.

The network runtimes or the symmetry of the lines is gone against an error size that turns out to be constant during operation Represents factor.

The planning of the transmission and reception times is carried out by a Planning software carried out. The software starts from exact conditions of the network as listed above are made. It is to achieve a high data throughput however, it is necessary to close the Ethernet telegrams tightly send. Due to the network uncertainties, the pla software, however, longer network downtimes take into account than would be necessary under exact conditions. A less compact data transmission and therefore a perfor Loss of chance on the network is the result.

Now an exact time-controlled data transmission is carried out Ethernet networks performed, so this problem ge must be solved.

Via a unit on the receive switch, the actual The reception time of the real-time telegram is monitored. there is entered via an upper and lower receive threshold Tolerance range in which the telegram is received that must. The threshold values give the time relative to the planned the time of reception.  

If a telegram is received outside the tolerance range the telegram is stored in a diagnostic memory records and the planning software through a reading option made accessible to this diagnostic memory. With help of the actual reception time stored there, the Planned time of receipt or transmission of the feeder Switches are moved so that the time of reception in next cycle lies within the tolerance range.

An upper threshold is necessary in order to receive prematurely Detect telegrams and use the planning software correct.

A lower threshold is necessary to reduce the jittery ten max. Synchronization error of the cycle time term. This error cannot and must be corrected always be included in the planning. A lower threshold of that the planned time of reception is therefore not permitted sig. Telegrams that are received too late, i.e. after the planned time of reception are also in the diagnosis se memory recorded and along with the actual Planning software reception time provided.

An optimization of the planning of the IRT data traffic is then reached when all IRT telegrams within a tolerance range received in the upper and lower threshold are close together and the max. Clock jitter taken into account is.

This procedure enables planning to be optimized in operation. When planning the first time, planning software only relies on network parameters that it receives via the Ethernet network itself or via an external supply. Inaccuracies such as:

• Clock jitter between two adjacent switches,
• - unequal cable lengths and thus run times,

cannot be scheduled at the beginning, however they are not known.  

Hardware support to optimize IRT planning that can take place during the operation of the network. Thereby is a better data throughput and thus a higher Per formance of the network reached. In addition, there is a new one Network shutdown not necessary.

Establishment of an IRT Ethernet network

It is also of particular advantage that the open bartend procedures in automation systems, in particular in and in packaging machines, presses, plastic injection molding machines, textile machines, printing machines, machine tools, Robotor, handling systems, woodworking machines, glass processing machines, ceramic processing machines as well Hoists can be used or used.

Preferred embodiments of the invention are described below dung explained with reference to the drawings. It demonstrate:

Fig. 1 reception time data telegram,

Fig. 2 Planning real-time data traffic before and after optimization.

Claims (2)

1. Method for planning the data traffic in communication systems with at least two participants, in particular real time Ethernet, characterized in that at least one tolerance range is generated depending on the respectively planned time of reception of a data telegram, data telegrams received outside such a tolerance range being used, saved and edited at a later date. 2. System for performing a method according to claim 1.