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Module 1: Qualification Planning & Design Process

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Interface Standards and Design process

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here we will look at those standards existing for a communication system especiallythe communication architectures for engineering systems.(Refer Slide Time: 01:30)
As I discussed in the last class the standards basically will ensure that an interface willenable the connection of two components. So, the basically we need to ensure that thereis proper communication between two components. So, we can use the standards toensure this communication. And whenever we have a communication between twocomponents we need to ensure that the each component is require to meet given standardand the interface is designed to meet the same standard. So, we need to have thecomponent meeting some standards and the interface also meeting some specifiedstandard in order to accept these components to be part of the communication network.And as I mentioned in the last class there are many benefits for having standards forinterfacing when you say particular standard or we standardize the a interfaces we getmany benefits some of them we saw in the last class basically the interchangeability ofcomponents.(Refer Slide Time: 02:22)
So, when we have these standard components and standard interface it is possible for usto interchange components with performance or cost characteristics.We can look at the components which are having a different performances or differentcost and then try to replace these parts in order to get better design or in order to have alow cost design or a high quality design. So, unless you have this standard we will not beable to choose the components with a various options like the performance or cost. So,that is the first benefit of having a standard. For example, when we have a common
standard for different components then a manufacturer is able to replace one hard disk ora ram or a processor for another one for increase the performance or reducing the cost.So, this interchangeability is an important feature for a many of the systems. So, otherone is interoperability where the ability to operate with a wider variety of externalsystems. So, here also if a system has to interact with the external systems and we needto have wider options otherwise you will be limited with one or two options and then thatmay not be a cost effective way or a reliable way to do the system design. So, if you havethe a standard it is possible to have a interoperability of a components with the system.For example, if you have a parallel port and a serial port in a computer then it is possiblefor us to connect any serial printer or a parallel port printer with the computer or youhave a USB interface then it is possible for us to have a various components attach to thecomputer, so that kind of flexibilities offered by having this kind of standards forsystems.The third one is the portability that is the ability to run a on various systems. So, if youhave a system and it is to run on different environments or different situations then if youhave the standard followed then it is possible to port the system to another one.Examples are basically the software systems were actually can actually port into anyparticular operating system if you develop software and it can be operated on differentplatforms then it provides you a portability of the system to have actually operate undervarious situations, various under various situations in on various systems also.And as you know it actually reduces the cost of the system basically because the cost canbe reduced if you can chose a component which actually better than the existing one or ithas actually a cost benefit then it is possible to chose that component because theinterfaces are same. So, if you have the same interface and the same standard interface itis possible to reduce change the component to reduce the cost and then actually you canreduce the risk also by providing alternative options in the system even if one fails whichis possible for us to replace with another one.So, that way we can reduce the risk also and all these actually leads to an increased lifecycle of a component. So, even we have portability and reduce cost and risk all theselead to an increased life cycle of the system. So, as you can see a following a standard or
having some standards for interfaces actually helps the system designer to have a bettersystem with the low cost as well as a low risk and with a better life cycle.(Refer Slide Time: 05:54)
So, let us see what are the standards or how the standards are classified into undervarious categories. As you can see here there are formal standards, then de jure standardsand de facto standards. So, these are actually coming from different origins. So, formalstandards are the one which actually formally accepted by agencies or standardaccredited agent bodies the negotiated and promulgated by accredited standard bodieslike ISO, ANSI, IEEE, EIA etcetera.
(Refer Slide Time: 06:13)
So, these are the formal standards formally accepted by the community that is acommunication standard or a hardware interface standard there are standards approvedby the agencies like ISO and ANSI and IEEE. If you follow this standard then we canalways ensure that all the manufacturers or all the system providers if follow thesestandards or what we can ensure that what are may be our system design the interfaceneed to follow the standards. So, it always ensure the interchangeability andinteroperability and other features. So, these are the formal standards already accepted bythe agencies.The other one is a de jure standards these are mandated by legal authorities. So, these arelegally bonds everyone has to follow this standards the formal standards are not legallybonds, but if you follow that one there are lot of benefits. But in the case of a de jurestandards these are a legally bond and we need to a everyone has to follow these ruleespecially when it comes to safety and other aspects these de jure or legal rules or thelegal standards need to be followed.So, like IDEF0 is a legal standard for a system development. So, like that there are manystandards legally bond and every designer need to follow this legal standards and the lastcategory is the de facto standards. De facto standard is basically becoming a standardbecause of the popular usage if a large community large a group of people start using thisa particular standard then it becomes a de facto standard. So, they are not legally bond or
they are not formal standard it becomes a standard adopted by the community. And mostof the cases every standard actually start as a de facto standard and then it is gettingformalized as formal standards or de jure standards.Like operating systems and x windows and this kind of standards are de facto standardswhich are not bound by the any legal a restrictions or formal standards. But they arebecome standard by use of particular standards by a group of people or a community ofdesigners. So, these are the three classifications of standards in terms of its origin and interms of its application and the legal validity. Let us go through some of this standardsand then see how they are actually applied or how they are implemented in the realsituations.(Refer Slide Time: 08:59)
See one of the formal standards is known as open system interconnection this is a formalstandard basically a used for a network based communication between end user nodes ina telecommunication network.So, here this is basically for communication networks. So, when you have a many nodesin a communication network. So, this kind of a standard is formally adopted known asthe open system interconnection standards. And this was the work on this standard wasstarted in some sometime in 1977 and there were few de facto standards existing at thattime some of them are proprietary and after lot of negotiations and a discussions. So,
these standards were combined together to make into a formal standard of a standardknown as OSI.So, it was in 1983 ISO and CCITT that is international telephone and telegraphconsultative committee approved a reference model for OSI. So, that the top layer is anot reference model for open system interconnection. And this model contains 7 layersphysical layer, data link, network, transport, session, presentation and application. So,these were the 7 layers identified for the reference model for OSI. And each layer haswhat its own responsibility and its own functions and communication between any twonodes need to follow these layers and then there are standards and functions identifiedfor each layer for making communication between two nodes.(Refer Slide Time: 10:37)
These are actually shows the communication in an OSI reference model. As we can seehere there are host nodes. So, these are the host nodes the between these nodes if want tohave a communication in a system. So, you will be having multiple nodes like this wantto have communication between this node and this node and then these are the 7 layersidentified for the communication node. So, every host nodes should have all these 7layers this three are known as the upper layers and these are known as the lower layers.So, the first 4 are the lower layers and the next 3 are the upper layers.And between these host nodes we will be having intermediate nodes can have a oneintermediate node or more than one intermediate node can be there. And every
intermediate node should have these three layers the first three layers that is the physicaldata link then network layers are there for the intermediate nodes. So, here which isshown that there is only one intermediate node between two host nodes, but that may notbe the case always you can have a multiple intermediate nodes through which thecommunication takes place and the data is transferred from this one host node to theother host node. As we can see here this application presentation session transportnetwork data link and physical are the layers and the physical media is the media throughwhich the communication really takes place. And these responsibility or the functions ofthese nodes basically these layers basically to ensure the communication from thisapplication to this application.So, this application is basically the one which actually starts communication and thisapplication needs to communicate with this application in the other nodes. So, the datacomes from here and passes through the physical media and through the intermediatenode and reaches the application nodes.Other than the physical layer the other layers have the responsibility to make thecommunication between these layers. So, the application has to communicate with apresentation and that has to establish the communication it has to transfer the data and ithas to disconnect the communication similarly presentation has to communicate withsession, session has to communicate with transport, transport has to communicate withnetwork, and network has to communicate with data link, and data link willcommunicate with physical and the physical layer will actually transfer the data to thephysical media and then it will go through the intermediate node and come back to theapplication. So, this is the way in which the communication takes place in the OSIreference model.
(Refer Slide Time: 13:07)
If you look at the functions of this each layers we can identify that the application is thehighest level the seventh layer in this one and the description of this particular layer isbasically to provide communication between the end users application processes and theapplication entity. So, the application entity is the one which actually passes theinformation, so that it provides communication between the end users applicationprocesses and the application entity.So, if the communication need to establish between the application entity and the enduser so that the main job of the application is basically to provide this communication.And the functions of this layer is basically to establish a connection, transfer data andrelease connection. As I mentioned earlier every layer has these three functions as acommon except for the last layer that is the physical every layer has to do the functionsof establish connection, transfer data and release connection.And the next layer presentation basically defines the data syntax for communication. So,the application has to transfer the data establish the connection and transfer data to thepresentation layer and it is a presentation layer which actually defines the syntax for data.So, what kind of syntax to be used for communication is decided by the presentationlayer. Again the functions here are establish connection transfer data and releaseconnection. So, as I mentioned a seven function with these also has to do, but in additionit will actually design about define the data syntax for communication also.
The next layer is session where it provides connection controls for the host. Andbasically the control of the connection between the layers that the host will be providedby the session and establish connection transfer data establish synchronization points,manage activity, release connection, report exceptional conditions are the main functionsof the session layer.So, apart from this establishing connection a transferring data and release connection;these layers has an additional job of establishing the synchronization points with theother layers, and then manage the communication activity and a report exceptionalconditions. So, if there are any exceptional conditions are arising that has to be reportedto the application immediately when whenever that arises. So, the function of this layeris basically apart from establishing connection and transferring data we will look at thesynchronization as well as the exceptional conditions.The next layer is transports here it establishes transparent and reliable end to endtransmission of data between host nodes. So, the transport layer is basically responsiblefor transporting the data it establish a transport and reliable end to end transmission ofdata between host nodes. So, this actually takes care of the transmission of data from onenode to another node. Of course, it has to communicate with the session for the data ifthe data is coming from this layer. So, it will establish a connection with the layers andthen transfer data it will provide error detection and recovery and release connection. So,apart from communication it has got the additional function of error detection andrecovery and that is the function of the transport layer. So, it establish the connection andthen transfer the data to the other nodes. So, the basic transmission is the responsibilityof transport layer.The other layers are the network layer here it determines the establishment of connectionand handles the routing. So, the establishment of connection is the responsibility of anetwork that irrespective of the type of network it has to establish a connection. So,whatever maybe the network architecture it will establish a connection and handles therouting of a data, so to which node it has to how it has to be transmitted what kind ofdata to be used will be decided by the network layer. And here you can see establishconnection, transfer data, perform multiplexing, provide error control and releaseconnection. So, establishing connection and release connection as the basic one, but apartfrom that it has to perform the multiplexing and provide error control. So, these are the
additional functions it has to perform other than establishing connection and transferringdata.The next layer is the data link. Here it establishes a reliable transmission on the physicallayer. So, data link is responsible for transferring the data to the physical layer that is areliable transmission on the physical layer its responsibility of the data link. Here thisestablishes connection, negotiate quality of service, it transfer data, provide flow control,reset connection and release connection. So, these are the functions. So, it has tonegotiate the quality of service is the quality of the service is basically the responsibilityof the data link. So, it will negotiate in terms of rate and the speed and other informationabout basically if you look at the integrity of the data and then try to ensure that theintegrity of the data is not compromised because of various reason and that is theresponsibility of the data link and it provide a flow control also and then reset connectionand release connection. So, these are the functions of data link.The last one is a physical layer. So, it defines how the physical network is accessed inorder to provide with transparent transmission. So, now, the next one is from here thephysical layer it means the data will be going to the physical link, from there, it has todefine how this physical network is accessed in order to provide bit transparenttransmission. So, that is the job of physical. The main functions are determine a presenceof a signaling pulses determine timing of signaling pulses. So, these functions need to beprovided by the physical layer in order to ensure that the physical network is accessedand then a bit transparent transmission is taking place. So, these are the main layers inthe OSI and the functions of different layers.As I told you the every node every transmission node the host node as well as thereceiving node, need to have these a physical layers and then it will be interactingthrough the intermediately node where there will be only a three layers. So, there can bemultiple intermediary nodes, but whatever the number of intermediately nodes the hostnode as well as the receiving nodes should have all these physical layers and theirfunctions are already explained.So, based on the responsibility of the functions of each layer the communication willtake place. So, that is the standard a formal standard for communication between twonodes in the OSI architecture.
(Refer Slide Time: 19:39)
Let us look at another standard which is known as the common request brokerarchitecture this is basically a standard used for software development. So, when youhave different software modules used for a particular system as for interfacing thesystems or a communication between the systems or subsystems, this CORBA isfollowed as a standard. So, this is a standard that would permit programmers to integratesoftware modules resident on the same network by treating each application as an object.So, this actually helps the programmers to integrate different software modules treatingeach application as an object. So, each application will be considered as an object andthen how do we actually integrate this object or these modules is defined in thearchitecture the common request broker architecture of standard.This was developed in association with industries like HP, Hyperdesk, SUN and so on.So, there are many industries participating in the development of this kind of a standardthis CORBA was developed in association with a HP, Hyperdesk and SUN. And ainteresting aspect of a CORBA is that it actually is part of the CORBA that is theinterface definition language or a IDL, it is a formal standard adopted by ISO.So, part of a CORBA is a formal standards and it is a de jure standard in the US. So, inthe US everyone has to follow and this standard because it is as per the legal itsmandatory as per the legal standard a CORBA is to be followed in software developmentand especially for when you develop different modules and want to integrate these
modules. But it is a de facto standard in other parts of the world. So, though it is not themandatory in other parts of the world and it is not a formal standard many of thedevelopers follow this standard in other parts of the world. So, it becomes a de factostandard.So, we can say that it is a combination of all the three type of a standards that is theformal standard and de jure standard and de facto standard. So, part of CORBA the IDLis an ISO standard and CORBA is a de jure standard in the US and in other parts of theworld it is a de facto standard, most of the software developers tried to follow thisCORBA standard when developing the software’s modules.(Refer Slide Time: 22:01)
We will just look at what are the important features of this IDL. As you can see that IDLinterface definition language is a universal notation for software interfaces defining aboundary between the client codes and the software objects that implement both services.So, IDL as you can see it is a formal standard and it is a universal notation for softwareinterfaces defining a boundary between the client code that is the request for services andthe software objects that implement those services. So, it actually provides an universalnotation for the interfaces. Client code the request for services as well as those forimplementing these services they can actually follow this codes the universal notationwhen they develop the software. So, that actually is the interface definition language.
But apart from IDL and there are 4 additional categories of objects that comprise ORBwhich is the object request broker, and then CORBA facilities, CORBA services andCORBA domains. So, these are the 4 categories additional categories of objects that isneeded in a in the CORBA language, CORBA standards. So, IDL forms the a basis forthe interface and the other categories of objects like ORB and facilities services anddomains become additional objects. ORB the object request broker is the interfacebetween the client and server. So, whenever there is a client and server and you want tohave an interface then ORB is the interface object request broker is the interface in thiscase.(Refer Slide Time: 23:34)
Now, how this is implemented in the system is shown over here. As you can see theevery application will be having these interfaces. So, application is the one whichactually tries to connect to the next node. So, this application will be having their clientand server and then object request broker is either intermediate or the one which actuallyconnects between the client and server as shown here. So, there is communicationbetween client and server and this is actually controlled or the standard for thiscommunication is the object request broker.So, this actually shows the CORBA overlaid on an OSI 7 layer model. So, these are the 7layer model. So, this layer application layer will be having the CORBA standard or theobject request broker in the application module. Basically the standard for
communication between the client and the server, so that is the object request brokerwhich actually interfaces client and server. So, this is how the ORB is implemented inthe OSI standard. So, that was about the standards used in the system design. So, we sawa few formal standards based on ISO and other predicted bodies and then we saw someof the one standard like this is a CORBA which is used for the software.The first one that OSI was for a communication networks and CORBA is used mainly forthe software modules. So, one is formal standard and CORBA is actually partly formalstandard and then it is a de jure standard in the US and the de facto standard in the otherparts of the world. Those are some of the standards being used for developing theinterfaces. We discussed about the interfaces different kinds of interfaces and then adifferent standard for interfaces. So, let us look at what is the process of designing aninterface or a how interface is designed by the design engineers or what are the stagesthrough which they go in order to develop the interface.(Refer Slide Time: 25:18)
So, the first stage is basically to define the interface requirements as you know when wedo a system design we try to develop the system requirements in the same way interfacedesign process also can be considered as a developing as a process where we try toidentify the requirements. Basically we identify the items to be transported. So, what arethe items to be transported what kind of data needs to be transported between the systemsor the subsystems that need to be identified this is an example.
So, one example may be the emergency communications from the elevator to thebuilding or emergency response team. So, this could be an item to be transported. So,when we look at the design we identify the items to be transported. For example, theelevator case study you can see the emergency communication could be one item to betransported from one system to other system or one subsystem to another subsystem. So,like this we can identify for every interface we can identify what are the items to betransported. So, that is the first stage in the interface development, identify all the itemsto be transported.The next one is define the operational concept. So, what kind of a system or what kind ofa an interface can be designed for this particular data that is the operational concept.
Wecan have various concepts for operation then we will identify which one is the best oneand accordingly we define a particular operational concept for that particular interface.And then bound the problem with an external diagram, so we look at that particular partalone the interface alone and then bound the problem with an external diagram. So, whatare the other systems will be which will be interacting with this interface and what kindof a interaction are needed between these interfaces that will be identified in the externaldiagram.So, once you identify the data to be transferred and then you have operational conceptthen we go for the external system diagram for the particular interface. And then definethe objectives hierarchy, so here again you will be having many objectives this one is weneed to transfer the data, then we will be having the transferring the data at a particularrate, then you will be having the cost objectives. So, we will write down all theobjectives for the interface and then a hierarchy of these objectives we need to find outwhich one is more important whether the transmission rate is more important or thequantity of data to be transfer is more important or the cost of operation is moreimportant or the cost of the whole system is more important. So, accordingly we developan objectives hierarchy.Like availability of interface fidelity of the communicated message operational costdeployment cost. So, these are some of the objectives. So, then we will give a value forthese objectives as we discussed in the previous lectures about objectives hierarchy wewill identify the hierarchy of these objectives based on the requirement of the particular
system. So, the system designer will be knowing what is more important in this case andaccordingly he will prepare an objectives hierarchy.And then once you have this identified then we will write down the actual requirementsof the design process. So, we start with the items to be transported, then we have anoperational concept, then we will have the external diagram, then the objectiveshierarchy once you complete all this, then we will be having all the requirementsidentified and then write the requirement as we discussed in the originating requirementsdocument similar way we can write down the requirement for the interface also. Theinterface system requirement will be separately identified.(Refer Slide Time: 28:51)
And then select high level interface architecture for the interface. So, you need to havethe architecture for the interface. So, we will select very high level interface architecturefor the interface or what kind of architecture can be implemented based on therequirements identified. So, here we can actually identify several candidate architectures.Basically if you want to have an emergency communication we can think of a telephoneconnection, you can think of a dedicated communication system