IEC 61158-4-7:2007/COR1:2014
(Corrigendum)Corrigendum - Industrial communication networks - Fieldbus specifications - Part 4-7: Data-link layer protocol specification - Type 7 elements
Corrigendum - Industrial communication networks - Fieldbus specifications - Part 4-7: Data-link layer protocol specification - Type 7 elements
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IEC 61158-4-7
(First edition – 2007)
Industrial communication networks –
Fieldbus specifications –
Part 4-7: Data-link layer protocol specification – Type 7 elements
CO RRI G E NDUM 1
Annex C – Topology of multi-segment DL-subnetwork
Replace the existing text of the annex by the following:
Annex C
(informative)
Topology of multi-segment DL-subnetwork
C.1 Introduction
This annex describes how to specify the topology of a multi-segment DL-subnetwork. The aim
is to propose a data structure, which could be minimal while allowing correct operation of the
bridge retransmission function.
The topology of a DL-subnetwork can first be specified globally, in order to verify a certain
number of properties (topological connectivity, non-meshing, etc.); then on the basis of this
specification the local data base specific to each bridge must be calculated in order to ensure
it operates correctly.
Although this appendix proposes a method to achieve this goal, only the specifications of the
data structures, global or local to each bridge, which define the DL-subnetwork topology, as
well as the properties which it should fulfil, must be taken into account in the standard. The
suggested method shows how to obtain a solution to the problem by taking into account
certain optimization problems.
C.2 Global specification
The topology of a multi-segment DL-subnetwork can be defined by the following elements:
— the set S of its segments: S = {s i ∈[1,n ] }
i
— the set B of its bridges: B = {b k ∈[1,m ] }
k
k
k
— and for each bridge of B, the data of a matrix B of dimension n × n. whose coefficients b
ij
are defined by:
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k
— b = 0 if i = j;
ij
k
— b = ∞ if the bridge b does not allow transfer of messages from segment s to
i
ij k
segment s ;
j
k
+
— b = α with α ∈R *, if the bridge b allows the transfer of messages from segment s
i
ij k
towards segment s with α as load coefficient which allows taking into account of a
j,
different efficiency rate according to the transfers.
k
A load coefficient b can represent the load, as a rate of occupation of the medium, of the
ij
retransmission segment s In reality, either the destination is directly s , or there are several
j. j
paths possible, passing through intermediate segments, to reach s and in this case the
j
choice shall be to pass by the least loaded path.
It is of course possible to take as coefficients the same value (1 for example).
If a bridge allows two-way retransmission with the same load coefficient for the two directions,
its matrix is symmetrical.
k
The matrix B of a bridge also allows knowing all the segments to which it is connected:
k
— either in reception, S = { segments whose corresponding line in the matrix includes at
r
k k
least one non-null finite coefficient}; note n = card (S ),
r r
k
— or in transmission, S = {segments whose corresponding column in the matrix includes at
e
k k
least one non-null finite coefficient}; note n = card (S ).
e e
C.3 Local specification
The information which a bridge must have locally allows it to answer the following question:
k
when I receive a message on a segment sr ∈ S destined for another segment s , must I do
r j
i
k
nothing or must I retransmit on segment se ∈ S ).
e
h
k
To fulfil this purpose, it is enough to allocate to each bridge b a transfer matrix T with
k
k
k
dimensions n × n, whose elements r are defined by:
r
ij
k k
— the line index i ∈ [1, n ] references segments sr connected in reception (∈ S ),
r r
i
— the column index j ∈ [1, n] references the segments s of the DL-subnetwork (∈ S),
j
k
k
— r = 0 if on reception of a message on segment sr ∈ S addressed to segment s , the
r j
ij
i
bridge shall not do anything, either because s cannot be reached via this bridge, or
j
because sr = s (a bridge shall not retransmit a message received from a segment
i j
towards this same segment),
k
k k
— r = se with se ∈ S , if on reception of a message on segment sr ∈ S addressed
, e r
ij h
h i
to segment s , the bridge must retransmit to segment se .
j
h
NOTE Indexes i and h correspond to channel numbers whereas sr is the segment connected in reception to
i
channel i and se is the segment connected in transmission to channel h.
h
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C.4 Properties
The properties which should satisfy the DL-subnetwork are topological connectivity and non-
meshing.
Topological connectivity consists in ensuring that there is always a path from any given
segment of S to any other segment of S.
Non-meshing consists in ensuring that the transmission of a message from a transmitter
located on segment s and addressed to a receiver located on segment s can be routed by
e r
only one path (thus preventing the message from being received more than once).
In fact, it is the definition of the local specification of each bridge and the calculation of its
transfer matrix which ensure this property: by definition, o
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