Academic Journal of Science and Technology 
ISSN: 2771-3032 | Vol. 6, No. 2, 2023 

 

65 

Analysis	of	Communication	Performance	Based	on	
Typical	Weakly	Hard	Real‐time	WorIdFIP	Fieldbus	
Xuying Gao*, Geng Liang, Wei Pei, Xiangyu Feng 

North China Electric Power University, Beijing 100000, China 
* Corresponding author 

 

Abstract: This paper analyzes the fieldbus system of industrial network from the perspective of the typical weak hard real-
time -- hard real-time. Based on the WorldFIP protocol, the periodic and aperiodic management modes of WorldFIP bus are 
discussed, and the utilization formulas of different aperiodic communication modes are given. Finally, the bandwidth utilization 
of centralized control bus protocol WofldFIP's aperiodic task scheduling is analyzed, and the performance is compared under 
different aperiodic arrival rates. 

Keywords: WorIdFIP, Communication performance, Aperiodic task. 
 

1. Introduction 
Embroidery is a famous intangible cultural heritage in 

China. Embroidery contains abundant materials. Interesting 
patterns are directly related to the development of the times, 
economic changes and people's living standards. Although 
embroidery art is a very old art, it is a symbol of a nation and 
an inexhaustible source of Chinese people's creation under the 
whole social background. For fashion designers, it is 
necessary to fully tap the characteristics of traditional 
embroidery art, and then innovate in the continuous design 
process. By giving full play to the artistic value of embroidery, 
it can help the inheritance and development of art, and make 
the development of contemporary fashion art have vigorous 
vitality. 

With the popularity of the network, the application of 
network-based control systems in industry is also increasing. 
However, due to the uncertainty caused by the instability of 
network hardware and the uncontrollable load, it is difficult 
to support hard real-time applications, that is, it is difficult to 
analyze the response time of tasks from the perspective of 
hard real-time. In order to meet the timing constraints of tasks 
in industrial control systems, fieldbus, a special real-time 
communication network with deterministic and finite queuing 
delay, is usually used. 

Fieldbus is a bidirectional serial multi-node digital 
communication system, which is used in the production field 
and realizes the bidirectional serial multi-node digital 
communication between the microcomputer measurement 
and control equipment. It is also called the underlying 
industrial control network of open, digital and multi-point 
communication. It transforms the scattered measurement and 
control devices into network nodes, and connects them into a 
networked control system that can communicate with each 
other, communicate information and complete control tasks 
together by using fieldbus as a link. The field bus ADAPTS 
the control system to the direction of decentralization, 
networking and intelligence, and promotes the current 
automation instruments, distributed control systems and 
programmable controllers and other products to face a major 
change in the architecture and function structure, resulting in 
another renewal of industrial automation products. Therefore, 
the field bus has become a worldwide focus of control 

technology research, is regarded as a cross-century new 
technology of control. 

WorldFIP is one of the most popular bus. The concept of 
WorldFIP was first proposed by the working group led by 
Professor J. P. Thomesse in France, and it became the French 
national standard in 1991. In 1996, it became the European 
standard EN50170V3. In 1999, it became the field bus 
international standard IEC61158. WorldFIP uses different bus 
rates in different application fields: 31.25kbps for process 
control, 1Mbps for manufacturing, and 12.5Mbps for drive 
control; In the application system, dual bus structure can be 
used, one of which is used as a redundant backup to increase 
the security of the system operation. It has a good application 
in process automation, manufacturing, power system 
automation, transportation information integration and other 
fields. 

This paper mainly studies the task scheduling process of 
WofldFIP, and uses random method to analyze the effective 
utilization and performance analysis of WofldFIP under 
different aperiodic information loads and different number of 
aperiodic nodes to be sent. 

2. WorldFIP Real-time 
Communication Performance 
Analysis 

2.1. Communication mode of WorldFIP 
periodic information 

Due to the diversity of tasks in industrial processes and the 
importance of real-time task scheduling, WorldFIP clearly 
distinguishes periodic tasks and aperiodical tasks, and gives 
different strategies respectively. WorldFIP adopts a 
centralized media control strategy and manages the realtime 
communication of periodic tasks according to the 
Producer/Distributor/Consumer (PDC) model. At any time, 
only one active node on a network segment plays the role of 
node Arbitrator, which is responsible for task scheduling and 
information communication between various nodes on the 
network, and is called Bus Arbitrator (BA) in WorldFIP. PDC 
(Bus Arbitrator) model is a management model of task 
scheduling, which adopts centralized media control strategy. 
In this model, producers send process variables (tasks), 



 

66 

consumers receive process variables, and arbiters are 
responsible for coordinating the demands of producers on the 
bus among different nodes.  

In PDC model, there is only one producer for each process 
variable, but there can be multiple consumers. Every node 
that provides a process variable must provide the producer 
function to transmit the process variable to the node where its 
consumers are located. When working, the producer is first 
granted the right to use the bus by the arbiter. After that, the 
producer broadcasts the task to the entire network segment, 
and all nodes in the segment are hosted to the task. After 
receiving the task, a node keeps the task only if it is needed 
by a consumer on the node, and the other nodes discard the 
task.  

Usually, the relationship between a producer and a 
consumer is set through configuration. Because periodic tasks 
have the characteristics of time certainty. BA utilizes the 
scheduling ST to manage periodic task communication. 
According to the characteristics of periodic tasks, such as 
interarrival interval, execution time, deadline requirement, 
priority, etc. Using the relevant real-time scheduling 
algorithm, BA establishes the schedule of periodic task 
delivery service in ST. At runtime, BA scans the ST 
continuously and sends the channel usage right to the 
producer according to the periodic tasks in the ST and the 
periodic information transfer service schedule in the ST.  

2.2. WorldFIP aperiodic information 
communication mode  

WorldFIP uses the remaining idle time of periodic 
information scheduling in the scheduling table (that is, the 
aperiodic scheduling time) to transmit aperiodic information. 
WorldFIP adopts query mode for the transmission of 
aperiodic tasks. Aiming at the characteristics of 
nondeterministic arrival time of aperiodic tasks, WorldFIP 
sets aperiodic task identification bit in the data frame of 
periodic task transmission, and implements the real-time 
transmission of aperiodic tasks by using the strategy of 
direction-inquiry-service. It is easy to see from the aperiodic 
task scheduling strategy that aperiodic task service is divided 
into three stages.  

The first phase is aperiodic task indication. When 
processing the periodic buffer transfer service, the BA 
broadcasts the ID_DAT frame, which contains the 
identification number of the variable, let's say X. When the 
producer of variable X receives ID_DAT, it sends out the 
RP_DAT response, which contains the numerical value of 
variable X. If the node where X is located hasaperiodic tasks 
to be sent. Then RP_DAT_R0 position 1. RP_DAT_RQ 
represents aperiodic task demand, and I / 0 represents 
with/without aperiodic tasks, respectively. When the 
RP_DAT_RQ instruction is received, BA stores the 
identification number of variable X in BA's aperiodic queue.  

WorldFIP aperiodic tasks are divided into two levels: 
urgent and normal (including available). And there are two 
aperiodic queues corresponding to the two levels of aperiodic 
tasks. This phase is carried out at the same time when the 
communication process of periodic tasks is completed.  

The second phase is aperiodic task inquiry. In the aperiodic 
task window, the BA sends the identity request frame ID_RQ 
to the producer of variable X. Upon receiving the ID_RQ 
frame, the producer of x sends the identity list RP_RQ to the 
BA, which contains the list of identification numbers of the 
aperiodic tasks to be sent. After receiving the list of 

identification numbers, BA puts it in another list to be sent. 
For a node, no matter how many aperiodic tasks are to be sent, 
only one query is needed, so the communication overhead of 
a query in the second phase is bytes, where len represents the 
number of bits of task frames transmitted on the bus; len 

ID_RQ＋RP_RQ +2trb is the minimum interval to wait for 

the arrival of the next frame after each frame is sent, which 
can be expressed in bytes.  

Finally, the aperiodic task service phase. The BA processes 
the aperiodic task requests stored in the to-be-sent list. When 
processing aperiodic task requests, BA adopts the same 
mechanism as periodic task requests, that is, an aperiodic task 
transaction is completed through ID_DAT and RP_DAT. 
len

ID_RQ＋RP_RQ
+2trThe corresponding overhead to complete each 

aperiodic task scheduling is: FIG. 1 shows the complete 
process diagram of an aperiodic information transaction. 

 

 
Figure 1. WorldFIP aperiodic information service process 

 

2.3. WorldFIP aperiodic communication model  
WorldFIP is mainly used in process control, and its typical 

process control communication rate is 31.25kbps. Let denote 
the WorldFIP communication rate, rate is 31.25kbps. 
Suppose that a WorldFIP network segment has N nodes and 
each node has aperiodic information to be sent, its periodic 
information set is: ∏={Mp

i =(Cp
i ,Tp

i ,Dp
i )|1≤i≤np} , where 

denotes the ith periodic information, and, respectively 
denotes the calculation time, period and deadline of periodic 
information, and denotes the number of periodic informatio 

The ST of periodic information is generally constructed by 
the Least Common Multiple/Highest Common Factor 
(LCM/HCF) method. Here, it is assumed that both buses use 
LCM/HCF to construct ST:T=LCM(Mp

i ),i=1,...,np.Therefore, 
the macro period of ST can be obtained.  

It is assumed that the arrival rate1 of aperiodicity 
information in the WorldFIP network segment is λ1 and λ2 
(frame/s or frame/s), both of which are served unrestrictively. 
Then, in macro period T, the average total number of 
aperiodic messages sent by N nodes in WorldFIP is Tλ1 and 
Tλ2, respectively. The bus utilization is defined as the ratio of 
the effective data transmitted by the bus to the total data 
transmitted in a certain period of time. 

2.4. WorldFIP aperiodic communication 
analysis  

For WorldFIP applied to process control, the transmission 
time required for a node to send an aperiodic message is: 

 

T1=[lenID_RQ＋RP_RQ+2tr+lenID_DAT＋RP_DAT+2tr]∙β
-1     (1) 

 



 

67 

Where ID_RQ is the identity request frame sent by BA to 
the producer of variable X. RP_RQ is that the producer of 
variable X sends the identity list frame to BA,ID_DAT and 
RP_DAT are the data that BA instructs to send and the 
producer sends, respectively. In the WorldFIP protocol, 
frames ID_RQ and RP_RQ have the same type as ID_DAT 
and are 64bit, andRP_DAT is (48+8*n), where n denotes the 
number of valid data bytes. So Equation (1) can be written as 
follows. 

 

T1=[len3×ID_DAT＋RP_DAT+4tr]∙β
-1

=(240+8n+4tr)∙β
-1  (2) 

 
Case1 Tλ1≥N  
 
If the information is distributed as evenly as possible in 

each node, then at this time, N nodes have aperiodic 
information to be sent, and the total amount of aperiodic 
information to be sent is Tλ1. For a single section of aperiodic 
information to be sent, no matter how many aperiodic 
information there are, its query only needs to be completed 
once, so the total time required to complete the 
communication of aperiodic information is:  

T1
total=[N×lenID_RQ＋RP_RQ+Tλ1lenID_DAT＋RP_DAT+(Tλ1+N)×2tr]∙β

-1 

=[(128+2tr)N+(112+8n+2tr)Tλ1]∙β-1 
Then, the utilization rate η1 under Case1 can be obtained as 

follows: 
 

η1=（8nTλ1）∙[(128+2tr)∙N+(112+8n+2tr)Tλ1]-1   (3) 
 

Considering the system stability requirements, that is, 
the total communication time of periodic and aperiodic 
information in a macro period must be less than T, the 
aperiodic information arrival rate1 λ of WorldFIP must meet 
the following equation: 

[(128+2tr)∙N+(112+8n+2tr)Tλ1]∙β-1+∑ Mp
inp

i=1 ≤T  
The necessary conditions for λ1 can be obtained as follows.  

λ1≤
[t-∑ Mp

inp

i=1 ]×β-(128+2tr)∙N

（112+8n+2tr）T
 

Case2 Tλ1＜N 

In this case, there are only N nodes with aperiodic 
information to be sent from N1 nodes, and N with no 
aperiodic information to be sent (N2 = N1+N2). The T 位 
aperiodic1 information to be sent is distributed over N1 nodes, 
that is, Tλ1= N1. Then the total time to complete the 
transmission under Case2 is:  

 

T1
total=[N1×lenID_RQ＋RP_RQ+Tλ1lenID_DAT＋RP_DAT+(Tλ1+N1)×2tr]∙β

-1 

=[(128+2tr)N1+(112+8n+2tr)Tλ1]∙β-1 
=(240+8n+4tr)Tλ1]∙β-1             (5) 

 
Similarly, the aperiodic information arrival rate λ1 must 

satisfy the following equation:  
 

λ1≤[(T-∑ Mp
inp

i=1 )×β][(240+8n+4tr)T]-1      (6) 
 

At this time, the bus utilization η1′: 
 

η1'=
8nTλ1

T1
total =

8nTλ1

(240+8n+4tr)Tλ1
=

8n

240+8n+4tr
        (7) 

 

Without loss of generality, the effective data transmission 
byte n can take the value of 10 for the above various, N is the 
maximum number of nodes in a single network segment of 
the bus 32, generally tr is 10-70bit, and it is 30bit when 
discussed in this paper. 

From the simulation results in FIG. 2, for the same arrival 
rate, assuming that aperiodic information is uniformly 
distributed in each node and there are not many nodes to send 
aperiodic information (that is, when Tλ1≤32, the number of 
nodes to send is equal to the number of aperiodic information 
arriving), For T (500× 10-3 s) given by HCF/LCM method 
from periodic information, it can be seen from Figure 2 that 
the effective utilization rate of WorldFIP is about 0.20, and 
the number of nodes to be sent is equal to that of non-periodic 
information. With the increase1 of the amount of aperiodic 
information Tλ =2 Tλ > 32 (the number of nodes to send 
WorldFIP aperiodic information is N), the growth of 
WorldFIP utilization rate is not large. When the system load 
is concentrated to nodes to send with probability P, that is, the 
number of nodes originally sending aperiodic information is 
reduced to P times (that is, N →PN, N '→PN'), for WorldFIP, 
Figure 2 shows that its utilization rate has been improved to a 
certain extent. It can be seen that the aperiodic information 
sending method of query mode is suitable for the control 
system with light load and concentration.  

 

 
Figure 2. Relationship between utilization rate and arrival 

rate of WorldFIP (n = 10, tr = 30) 
 

Obviously, the value of tr and n also directly affect the 
utilization of the bus. The curves of Figure 3 and Figure 4 
show the influence of the two on the utilization at a certain 
arrival rate respectively.  

 

 
Figure 3. Relationship between utilization of WorldFIP 

and tr (λ1 =λ2 = 40, n = 10) 



 

68 

 
Figure 4. Relationship between utilization rate of 

WorldFIP and n (λ1 =λ2 = 40, tr = 30) 

3. Conclusion 
WorldFIP is a field bus widely used in the field of industrial 

control. The communication of aperiodic information is a 
complex process. The query method and round robin method 
are suitable for different loads of aperiodic information and 
their distribution in each node. This paper analyzes the 
communication process of aperiodic information, gives the 
utilization formula of WorldFIP, compares the utilization of 
WorldFIP under different loads, and analyzes the influence of 
aperiodic information distribution, which provides engineers 
and technicians with ideas in system design and bus selection. 
For the study of bus protocol, improving the existing protocol, 
The task scheduling algorithm is designed to improve the bus 
cooperation. The real-time performance of the bus is 
improved. A protocol analysis method is established, which 
can provide ideas for the design and development of bus 
protocols. 

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