—— of net of real time aether of —— of industrial aether net experienced tremendous growth in going a few years. Although classical spot bus line still abounds in, but they already passed summit summit period. Agreement of popular net of real time aether expanded aether net standard, can satisfy the requirement of real time function. Now, TSN offerred a new approach for net of real time aether.
Real time and communication
Below the setting of factory automation and drive technology, real time means periodic time to want safe, reliable ground to achieve 10 millisecond the following, lowest comes small second. To satisfy these real time requirements, aether net still must obtain real time function.
Does aether net get much —— more quickly than spot bus line that how?
To satisfy the real time requirement of automation, need makes sure transmission bandwidth is mixed transmission defer. Although these bandwidth normally very small (every parts of an apparatus) of a few byte, should transmit a passageway to must be in every I/O cycle usable, and achieve defer requirement.
But, classical aether net does not offer defer and bandwidth to assure. Contrary, if handle need, aether net can discard at any time frame. What do this mean?
Aether net is so called bridge receives a network. Frame (aether net frame) nod to another from a dot hair: Arrive from end points switching equipment (net bridge) , therefrom may send other net bridge, arrive at another end points finally. This framework has ego to configure ability greatly. Net bridge receives frame completely first before transmit frame. A lot of problems go just about here:
? 7? The 8 frame that if be in,peak value time stores count the frame number that buffer storage of over net bridge can contain, discard new afferent frame.
? 7? 8 because frame is long different, because this its defer time is the function of its length. This meeting brings about defer to fluctuate (shake) .
? 7? The 8 port that should send frame through its as a result of switching equipment may have been taken up completely by other frame, can cause additional delay so. Send frame of large aether net (1522 byte) cost 124μs about below 100 Mbps rate.
If say aether net moves normally good, this kind of view is in going up somehow is evenhanded. But, such doing, normally one word of ” is in the “ that we use is insignificant below condition of words of good real time. Satisfying real time requirement normally merely is insufficient, must satisfy this requirement from beginning to end.
The anybody that lives by chemical plant or refinery can understand this. Industrial newsletter is inequitable also: The most important is, control / closed-loop control application has priority from beginning to end.
Graph 1. The real time in automation corresponds.
Graph 2.ISO 7 models.
It is a real time that show to expand with PROFINET and EtherCAT
Because be in charge of the IEEE that aether net standardizes offerring a solution with respect to this problem, the solution —— that is versed in industry developed him proved its creativity again. All sorts of solutions have his advantage and inferior position, solve different market problem finally.
PROFINET: General and applicable
Pass PROFINET, can offer two kinds complementary model solution. PROFINET RT is solution of automation of a kind of factory, periodic time is the longest for 1 Ms. RT is a foundation with standard aether net directly. The possibility of aether net (for example, service quality (QoS, first step) ) be used at generating real time flow first step. This is helped somewhat, but QoS can not solve resource and delay problem completely. This is restricted namely soft real time reason. As other as what use in the network agreement (for example the clear advantage that the good compatibility of HTTP, SNMP and TCP/IP) is this technology.
Graph 4.PROFINET IRT.
To good real time, PROFINET provides synchronous real time (IRT) is patulous. Here, what bandwidth of partial aether net passes hardware of standard aether net is patulous and special withhold for IRT discharge. This can pass the accurate synchronism of the clock in IRT node to come true. Accordingly, the passage can be prevented in every cycle (gules phase) medium normal flow. Only the IRT frame in gules phase arrives at a network. In addition, network participator is in well and truly beforehand calculative time sends IRT frame, what achieve efficiency in gules phase thereby is the biggest change. IRT frame carries a network, do not have almost jump. A good point that such doing is it the length limitation of OK and gules phase is in in lowermost limit; gules phase, all and other discharge must await. Red is phasic and most can take up 50% of bandwidth of aether net passageway.
Graph 3. Consultative overview.
The place before be like is narrated, frame of full-length aether net (1552 byte) cost 124μs about on circuit. If PROFINET IRT takes up all the bandwidth of 50% , the fastest periodic time is 2×124μs=248μs, rounding off hind is 250μs. Only such, other agreement (coexist with its with changeless form like HTTP) ability.
Optimize as a result of what PROFINET 2.3 can use at IRT, include fast transmit, dynamic frame to enclose with section, because this is OK implementation is low the faster periodic time to 31.25μs.
EtherCAT: Bus line of aether network spot
In the development process of EtherCAT, still have other demand in the begining. EtherCAT is to be based on physical aether net (namely the 1st) spot bus line. Even the 2nd also applies in the light of spot bus line and application of high handling capacity undertook optimizing. EtherCAT does not have classical aether net bridge, cable of frame of use sue for peace, make data is transmitted particularly efficient. Every cycle sends EtherCAT one frame, with common aether net different; is in latter, every equipment that the communication between equipment involves sends alone frame. But, this frame includes all data of equipment of the location that be searched. When EtherCAT frame by equipment transmit when, this data of specific facility is inserted by real time take out from inside this frame in this frame. Carry this kind of kind, can realize cutty cycle time, the smallest under 31.25μs.
EtherCAT still has time synchronism function. Use as to not quite ideal aether net interface will be behaved on PC of EtherCAT advocate equipment, people gave a large number of effort.
Below EtherCAT, aether net discharge (like Web or TCP/IP discharge) can become fraction in order to bear means cent to transmit; only cannot online on direct coexistence.
POWERLINK uses the complete control that with the basic method; with identical EtherCAT its gain pair of aether networks to counterpoise, transmit IP application to node through bearing means. But this is their only collective place. POWERLINK does not use agreement of frame of sue for peace, however, it is behaved in applying actually likewise outstanding.
Like IRT, SERCOS has obligate bandwidth, but what amid uses is agreement of frame of sue for peace. SERCOS allows other agreement coexistence.
TSN opportunity arrives quickly
IEEE from frequency / video bridge is received (the angle of AVB) agreement studied this topic. When undertaking improvement to the agreement, the industry that still considered to have challenge sex more corresponds in real time. The original title AVB2 of these standards changes from this say TSN(shows time is sensitive model network) . Had these levels, can use version of unified determinism aether net now.
This can simplify actually a lot of problems. For example, well-known industrial network is aimed at 100Mbps entirely almost. However, thousand aether net and net of 10 Mbps aether already made the attention central point of special application nowadays. TSN standard covers all rate. Use TSN, need not begin from the beginning: If not be TSN, all and existing standard must undertake in the light of thousand rate this will bring about redefine —— hardware development cost and market fragment influence cost.
What does TSN have to use? TSN real time
TSN expanded aether net the 2nd, brought into real time to operate an a series of needed mechanisms:
? 7? 8802.1AS/802.1AS-Rev considered the issue of high accuracy synchronism of the clock in the network.
? 7? 8 time feel plastic implement (TAS) option makes aether net can be in hard attemper move below mode. Had this option, can prevent in specific time / the one or more alignment that releases QoS model.
? 7? 8 race to control (thrust deep into the enemy forces is rapid discharge) option makes long frame can be decomposed smaller part, thereby the delay that utmost ground reduces the frame with first faster step. When this option can be used at 100 Mbps exceeding in rate, optimize the bracer of TAS or replace TAS.
? 7? The 8 redundant method; that duplicate and eliminate frame to be able to be used in order to raise the option of dependability at the definition to carry a network if in annulus road.
? 7? The transmit of hardware MAC address that the network that 8 use software define means frame to pass target node no longer arrives destination, carry special MAC address however (the sows MAC) and VLAN ID more combination transmit of this locality management. Decide these frame automatically no longer the road in the network by means, undertake configuration by software however. This kind of combination that sows MAC and VLAN ID more is called shed ID, have identical all TSN frame that sheds ID calls TSN to flow. TSN shedding sends a person only from beginning to end, but can have many addressee.
Graph 5. Aether net frame (among them, shed the part related the label to express) with green with TSN data.
In view of existing natural resources, can organize TSN to flow with special kind now, need to discard no longer frame. Now, net bridge uses its resource at the nondestructive transmit that TSN sheds.
Endeavor to serve discharge (standard aether net, IP, Web) uses odd resource (memory / bandwidth) transmit normally.
What did the 2nd above produce?
Backside of agreement of net of every Internet aether has an organization, it is the standardization that it is promoting respective agreement is mixed gain ground. These organizations formulated TSN strategy each times medium. Result, we see, almost all and existing agreement has TSN, just behave a form each different just. Continue to see our case:
To PROFINET, the approach that leads to TSN is opposite shorter, because people had accumulated substantial time to feel plastic experience at present (had been close to IRT) very much, and support the coexistence of trade agreement and IT agreement from beginning to end. To the user, a lot of things did not go, accordingly, familiar environment is helpful for promoting performance.
EtherCAT and similar SERCOS use those who make TSN obtains above of spot administrative levels capacity. For example, etherCAT automation agreement (EAP) suits to pass TSN very much with inferior expense, link a classical EtherCAT network paragraph.
But, this domain also has new participator.
An organization is beginning to define an agreement of brand-new industrial aether net. Somebody uses OPC UA as applied layer. TSN is regarded as to make this agreement has the medium of real time ability. But, here still has much work to want to do. The OPC UA with transmission new need transmits a layer (namely) of agreement of so called OPC UA PUB/SUB.
Graph 6. Good real time (IRT) , flexible real time (RT) and IT agreement (the defer of TCP/IP) / shake extent.
More more useful? Be not in real time domain such
Today, what we use in industrial automation is net of 100 Mbps aether, thousand aether net is very fast with respect to the line on the meeting. But, higher rate does not mean defer to be able to get ensuring, transmit can get ensuring. Accordingly, to good real time, need special mechanism from beginning to end. Had TSN, they already were standardized.