This article through analyzes the ethernet the
network correspondence mechanism, had pointed out the ethernet enters
the question and its some solutions which in the industry
correspondence network exists. Subsequently in detail introduced
in a present industry correspondence network applies the quite
widespread industry ethernet (SIMATIC NET).
The field bus appearance, played the huge impetus role regarding
the realization face the equipment automated system, but the field bus
this kind of special-purpose real-time communication network had the
cost high, the speed low and the support application was limited and
so on the flaw, in addition the main line correspondence agreement
multiplicity, enabled the different main line product mutually to
interlock, mutually used with mutually to operate and so on, thus the
field bus industry network further development has received the
enormous limit. Along with the ethernet technology development,
specially the high speed ethernet appearance enabled the ethernet to
be able to overcome own itself flaw, entered the industry domain to
become the industry ethernet, thus caused the people to be allowed to
use the ethernet equipment to replace the expensive industry network
equipment.
1. ethernets main flaws
In speaks the ethernet in front of the main flaw, it is
necessary first to understand the ethernet the correspondence
mechanism. The ethernet is refers follows the IEEE802.3
standard, may network which transmits in the optical cable and the
twisted pair line. It most early appears in 1972, founds by
XeroxPARC. The current ethernet uses the star and the main line
structure, the transmission speed is 10Mb/s, 100 Mb/s, 1,000 Mb/s or
is higher. The ethernet has the detention main reason is the
conflict, its reason was it has used the CSMA/CD technology. In
traditional shared network, because in ethernet therefore the stand,
uses the same physical medium to be connected, this meant when 2
equipment simultaneously send out the signal, can appear the mutual
conflict which the signal sees. In order to solve this problem,
the ethernet stipulated that, in front of a stand visit medium, must
first monitor in the network to have other stands simultaneously to
use this medium. If has must wait for, this time has had the
conflict. In order to reduce the probability which the conflict
occurs, the ethernet often uses 1- continues CSMA, must continues
CSMA, P- continues CSMA the algorithm 2. Because the ethernet is
automatically changes into the goal design by the work, certainly
incompletely conforms to the industry environment and the standard
request, uses in the industry domain the traditional ethernet also to
exist the obvious flaw. But its cost compared to industry
network low, the technical transparency is high, specially it followed
the IEEE802.3 agreement greatly to open gate of the convenience for
various field bus merchant, but, had to cause the ethernet to conform
to in the craft requirement below, but also had to overcome the flaw:
1.1 determinism
Because the ethernet MAC level agreement is CSMA/CD,
this agreement enables in the network to have the conflict, specially
when network load oversized, is more obvious. Regarding an
industry network, if has the massive conflicts, must result in
reissues the data many times, causes between the net to correspond not
the definite big increase. In the industry control network this
kind from to another determinism, inevitably cannot bring the systems
control performance reducing.
1.2 timeliness
In the industry control system, real-time may define as
the system to some event reaction time measurability. In other
words, occurs after an event, the system must make the reflection in
the time scope which may accurately foresee. However, in
industry logarithm according to the transmission timely request is
extremely strict, often the data renewal is completes in dozens of ms.
But similarly because the ethernet exists CSMA/CD mechanism,
when occurs conflicts, must reissue the data, are most may attempt 16
to be next many. The very obvious this kind of solution conflict
mechanism is take pays the time as the price. Moreover one but
appears the line, that feared is the merely several seconds kind of
time, has the possibility to create the entire production to stop even
is the equipment, the personal safety accident.
1.3 reliability
Because the ethernet at the beginning of the design,
certainly is not embarks from the industry network application.
When it applies the industry scene, facing the bad operating
mode, the serious space disturbance and so on, these all inevitably
can cause its reliability to reduce. The industry network must
have a better reliability in the production environment, 可恢复,
as well as maintainability. Namely guaranteed when in a network
system any module breaks down, cannot cause the application procedure,
the operating system, even network system collapse and paralysis.
2. Ethernet industrial application solution mechanism
Three big flaws and industry domain exists which in view
of the ethernet to industry network special request, at present has
used the many kinds of methods to improve the ethernet the performance
and the quality, satisfies the industry domain the request.
Under introduces several kind of solutions mechanisms:
2.1 exchanges technologies
In order to improve an ethernet load heavier time the
network jam question, may use the ethernet switchboard (switch).
It uses the local area network which will share to carry on the
effective conflict territory division technology. Between each
conflict territory with the switchboard connection, reduces the
conflict question and the wrong transmission which the CSMA/CD
mechanism brings. This may avoid the occurrence as far as
possible which conflicts, enhances the system indeed qualitatively,
but this method cost is higher, has the certain time delay in the
assignment and the cushion process.
2.2 high speed ethernets
We knew works as in the network the load to be bigger,
indignantly has the conflict rate to be also bigger. Some
materials demonstrated when a network negative ?is lower than 36%,
basically cannot have the conflict, when the load is below 10%, 10M
ethernet conflict probability for every five years. 100M
ethernet conflict probability for every 15 years. But after
surpasses 36% to have the conflict along with the load increase to be
indignant rate is by the geometric series speed increase.
Obviously enhances the ethernet the correspondence speed, may
effectively reduce the network the load. Lucky was the present
ethernet already appears the correspondence speed to reach 100M/S, the
1G/S high speed ethernet, in added on the careful comprehensive design
and carries on the control to in the system network point quantity and
the traffic flow, definitely was allowed to use the ethernet to take
the industry network.
2.3 IEEE1588 to time mechanism
IEEE1588 has defined in the survey and the control
network, with the network exchange, local calculates with the
assignment object related precise synchronized clock agreement (PTP).
This agreement certainly is not an antiforeign, but specially
suits to based on the ethernet technology, the precision may reach a
microsecond scope. Its period of revolution seal comes the
synchronized local time the mechanism. Even if in network
correspondence time when the synchronization control signal has the
certain undulation, it achieved the precision still might answer the
purpose. This causes it especially to be suitable for based on
the ethernet system.
Through uses this kind of technology, the ethernet TCP/IP
agreement does not need the big modification to be allowed to move in
the high accuracy network control system. The precision it
achieved which in the region main line has gone far beyond the
existing each kind of system. In addition, uses in enterprise's
various levels based on the ethernet TCP/IP agreement network
technology has the huge superiority.
At least includes a master clock and many subordinates clock
including IEEE1588 to the time machine-made simple system. If
simultaneously has many latent master clocks, then moves the master
clock will act according to optimized the master clock algorithm
decision. All clocks unceasingly and master clock comparison
clock attribute, if the new clock joins the system or the extant
master clock and the network separates, then other clocks can redecide
the master clock. If many PTP subsystem needs to interconnect,
then must realize by the boundary clock. Boundary clock some
port can take is subordinated the port and the subsystem unites, and
provides the clock standard for the overall system. Therefore
this subsystem master clock is the overall system rightful owner
clock. The boundary clock other ports can take the host port,
transmits through boundary clock these ports the synchronizing
information the subsystem. The boundary clock port antithetical
couplet system said is the ordinary clock.
IEEE1588 defines the precise network synchronous protocol has
realized in the network highly synchronization, causes when the
assignment control work does not need to carry on the special
synchronous communication again, thus has achieved the correspondence
time pattern and the application program time pattern separated
effect. As a result of the high accuracy synchronized work,
causes the ethernet technology inherent data transmission time
undulation to reduce to may accept, does not affect the control
precision the scope. A IEEE1588 big merit is its standard
extremely has the representation, and is open style. As a result
of its openness, the supplier which now already had many control
systems applies this standard their product. Moreover the
different equipment producers all follow the similar standard, like
this between their product also may guarantee the very good
synchronism.
3. typical industries ethernets
Along with the ethernet technology high speed
development and its 80% market share and the field bus obvious flaw,
urges the labor to control the domain each big merchant to research
and develop in abundance suits the oneself labor to control the
product also the compatible strong industry ethernet. Applies
one of most widespread industry ethernets is SIMATIC which the Germany
siemens researches and develops the NET industry ethernet. It
has provided open, is suitable under the industry environment each
kind of control rank different communications system, these
communications systems based on the country and the international
standard, conform to the ISO/OSI network reference model.
SIMATIC the NET industry ethernet main system structure is by
the network hardware, the network part, the topology, the general
processor and SIMATIC NET software and so on partially composes.
3.1 SIMATIC NET industry ethernet basic type and network
hardware
SIMATIC the NET industry ethernet has 2 kind of types,
respectively is the 10Mbit/s industry ethernet and the 100Mbit/s
industry ethernet. It uses the belt transmission technology,
uses the CSMA/CD medium access method based on IEEE802.3 the unit
level and the control level transmission network. In Simens
industry ethernet, usual use physics transmits the medium is the
shielded twisted pair (TP), industry shielded twisted pair (ITP) as
well as optical fiber. TP connects commonly used to the
end-to-end connection. A data terminal equipment (DTE) the
direct company receives the network connection part port, but this
equipment is responsible the signal to carry on enlarges and
retransmits. In SIMATIC in the NET industry ethernet, these
network connection parts have OLM (optical link template) ELM
(electrical connection template) OSM (optics switchboard template) and
ESM (electrical switchboard template). DTE and between
connection part through TP or ITP electric cable connection.
3.2 SIMATIC NET industry ethernet network part
SIMATIC NET industry ethernet network part including
industry ethernet link template OLM, ELM and industry ethernet
switchboard OSM/ESM and ELS as well as industry ethernet link module
OMC. OLM (light link module) has 3 ITP connection and two BFOC
connection. The ITP connection may connect three terminal
devices and the webpage, the BFOC connection may connect two paths of
rays equipment (for example OLM and so on), the speed is 10Mbit/s.
ELM (electrical link module) has 3 ITP connection and a AUI
connection. May connect through the AUI connection the network
equipment on LAN, the speed is 10Mbit/s. On ordinary OSM, the
electrical connection (TP/ITP) all is 10/,100 Mbit/s auto-adapted also
the line foreword auto-adapted. The optical fiber connection is
100 Mbit/s the entire duplex BFOC connection, is suitable to the
multi- molds optical fiber connection. Between two OSM most
long-distance range is 3km. Are most in the identical webpage
may connect 50 OSM, then the expansion distance is 150km.
Simultaneously it also has the address study, the address
deletes, the establishment transmission baud rate (10 or 100 Mbit/s)
and the auto-adapted function, simplified the network configuration
and strengthened the network expansion ability. In addition,
according to the IEEE802.1Q standard, OSM/ESM also supports VLAN
(virtual local area network), it provides the data packet the VLAN
priority label. It for from lowers the data assignment to is
high (0-7) the priority rank, regarding does not have the destination
address the data packet to regard as the low priority the data frame.
3.3 SIMATIC NET industry ethernet topology
3.3.1 main lines topology
In OLM or in the ELM main line topology, the DTE
equipment may through the ITP electric cable and the connection
connection on OLM or ELM. Each OLM or ELM have three ITP
connection. Between OLM may carry on the connection through the
optical cable, are most may cascade 11. But may standard
electric cable carry on the connection between ELM through ITP the XP,
are most may cascade 13. ESM may through the TP/ITP electric
cable connected composition always network. Any port all may do
for the cascade port use. Between two ESM distance cannot
surpass 100m, the entire network are most may connect 50 ESM.
3.3.2 annular topology
OLM may be connected through the optical cable the main
line network head and tail, thus constitutes moves in a circle the
network. In the entire network are most may cascade 11 OLM,
compared the redundant ring net with the main line network to increase
the data exchange reliability. But OSM/ESM also can constitute
the ring net topology, they have the network redundancy management
function. They may establish in the network through the DIP
switch any OSM/ESM to do for the redundancy management. Thus may
compose the redundancy the ring net, on OSM/ESM 7, 8 achievement ring
nets optical cable level continually connection. Does monitors 7
for redundancy management OSM, 8 conditions, once will examine the
network severance, rewill construct the entire network, will cut the
network the backup on the channel, guaranteed the data exchange will
not be able to sever. The network heavy construction time is
smaller than 0.3S.
3.4 ring nets redundancies
In the Simens industry ethernet, on each OSM/ESM
(eliminates OSM TP22 and ESM TP40) all has the standby-sync
connection. Uses for OSM/ESM, through DIP switch establishment
spare (standby) master station and spare from station. With ITP
the XP standard electric cable, connects the spare connection, then
should be allowed to use for the redundancy to OSM/ESM to connect
other ring net. Spare master station and from station through
ITP XP9/9 standard electric cable connection. When the spare
master station channel appears the breakdown, spare from station
connection channel work; When the spare master station channel
restores normally, the spare master station can inform spare from the
station, spare from will stand the knock off. But the entire
network heavy construction time is smaller than 0.3m.
3.5 SIMATIC NET industry ethernet correspondence processor
Commonly used SIMATIC the NET industry ethernet
correspondence processor (CP), including uses the processor CP243-1
series which stands in S7PLC, the CP343-1 series, the CP443-1 series
as well as uses on PC the net card, and provides ITP, ethernet
connection and so on the RJ45 and AUI. They by 10/,100 Mbit/s
speed PLC or PC connection to industry ethernet. The CP series
template is S7 series PLC carries on the correspondence when the
composition industry ethernet uses, may be very convenient through the
CP series template user carries on S7 series PLC through the ethernet
the connection, and supports uses STEP7-Micro/WIN32 software
Carries on the long-distance configuration through the ethernet
to S7 series PLC, the programming and the diagnosis At the same
time, through CP, in the S7 series between each PLC may carry on the
ethernet connection, and also may carry on the correspondence with on
PC OPC Server.
3.6 SIMATIC NET industry ethernet software
SIMATIC NET industry ethernet software including SIMATIC
NET V6.2 and OPC (OLE for Process Control), SIMATIC NET software
enhanced a unified Windows session of surface, simultaneously also
integrated and renewed more functions, it has specially provided APC
(Advanced PC Configuration) the high-level PC disposition tool,
through the APC configuration, PC was allowed to take the overall
system control system a stand carried on the correspondence with other
PLC station, simultaneously has provided OPC Server as well as the
data processing function. OLE (object linking and inserts type)
itself is based on Microsoft a COM technology application, but the OPC
connection is based on the OLE open unified software connection.
OPC does not depend upon a Yu merchant, nearly therefore the
labor controls softly, hardware control business all integrated the
OPC connection, therefore between each different hardware merchant
equipment correspondence may carry on through the unified OPC
connection, thus avoided the different equipment merchant creating the
data exchange difficult problem as a result of the correspondence
agreement difference. SIMATIC NET OPC is the server/customer end
structure, the customer end visits the server the procedure connection
to have the automated connection and the user from the definition
connection, only has from the definition connection may use for to
visit the breakdown to report to the police and to trigger the event
news. The SIMATIC NET OPC structure is the graduation pattern,
namely OPC server --- OPC group --- OPC item, OPC data accessing based
on this structure.
4. Industry ethernet prospect and forecast
The industry ethernet by its unique low cost, the high
actual effect, high extended and the high intelligent charm, is
attracting the more and more many manufacturing industries merchant.
On the one hand so multitudinous merchant development and
development industry ethernet technology, if does not perform to unify
a minute standard, looks like the field bus the situation to be same,
standard multitudinous, the compatibility is bad, subsequently affects
the industry ethernet development. Is precisely so, the
international society already started to begin to formulate an
industry ethernet standard. Convenes in 2004.5 Beijing the
international industry ethernet series standard draft work team
(IEC/SC65C/WGs) in the third conference, we already could see had the
young line of industry ethernet international standard to at the
beginning of, this series sign brigadier general to 2005.8 finalized a
manuscript, after passes through 2006.2 and 2006.122 opinions
solicits, in 2007 second half year official issue. Enables this
series standard to become the IEC standard from the IS standard 6.
On the other hand, the ethernet and the communication progresses
by leaps and bounds also urges the industry ethernet technology
further to develop. Now the industry ethernet technology already
started to the real-time industry ethernet and the wireless industry
ethernet direction develops. Specially Austrian shell Calais
(B&R) already developed has in the true significance the real-time
ethernet (Ethernent Powerlink), but near future, also will appear face
the future industry network new generation of industry ethernet
module. Because the ethernet has "a net" the fine reputation,
namely it may continuously extend to the enterprise scene device
control level, can substitute the present along with the industry
ethernet technology development based on the field bus industry
network, will become in the industry network the mainstream
technology. |
