Control Systems & PLC's

Communication Test

Protocol testing

Protocol testing

Generally, only the simplest protocols are used alone. Most protocols, especially in the context of communications or networking, are layered together into protocol stacks where the various tasks listed above are divided among different protocols in the stack.Whereas the protocol stack denotes a specific combination of protocols that work together, a reference model is a software architecture that lists each layer and the services each should offer. The classic seven-layer reference model is the OSI model, which is used for conceptualizing protocol stacks and peer entities. This reference model also provides an opportunity to teach more general software engineering concepts like hiding, modularity, and delegation of tasks. This model has endured in spite of the demise of many of its protocols (and protocol stacks) originally sanctioned by the ISO.

In the field of telecommunications, a communications protocol is the set of standard rules for data representation, signaling, authentication and error detection required to send information over a communications channel.protocol testing An example of a simple communications protocol adapted to voice communication is the case of a radio dispatcher talking to mobile stations. Communication protocols for digital computer network communication have features intended to ensure reliable interchange of data over an imperfect communication channel. Communication protocol is basically following certain rules so that the system works properly
The TCP/IP protocol suite establishes the technical foundation of the Internet. (UDP/IP is part of the the family). Development of the TCP/IP was started by DOD projects and now, most protocols in the suite are developed by the industry non-for-profit organization named Internet Engineering Task Force (IETF) under the Internet Architecture Board (IAB), an organization initially sponsored by the US government and now an open and autonomous organization. The IAB provides the coordination for the R&D underlying the TCP/IP protocols and guides the evolution of the Internet. The TCP/IP protocols are well documented by the Request For Comments (RFC), which are drafted, discussed, circulated and approved by the IETF committees. All documents are open and free and could be found online in the IETF site listed in the reference.

In computing, a protocol is a set of rules which is used by computers to communicate with each other across a network. A protocol is a convention or standard that controls or enables the connection, communication, and data transfer between computing endpoints. In its simplest form, a protocol can be defined as the rules governing the syntax, semantics, and synchronization of communication. Protocols may be implemented by hardware, software, or a combination of the two. At the lowest level, a protocol defines the behavior of a hardware connection. A protocol is a formal description of message formats and the rules for exchanging those messages.

 

Software Testing

It is the process used to help identify the correctness, completeness, security, and quality of developed computer . Testing is a process of technical investigation, performed on behalf of stakeholders, that is intended to reveal quality-related information about the product with respect to the context in which it is intended to operate. This includes, but is not limited to, the process of executing a program  with the intent of finding errors. Quality is not an absolute; it is value to some person. With that in mind, testing can never completely establish the correctness of arbitrary computer software; testing furnishes a criticism or comparison that compares the state and behaviour of the product against a specification. An important point is that software testing should be distinguished from the separate discipline of Software Quality Assurance (SQA), which encompasses all business process areas, not just testing.

Discovering the design defects in software, is equally difficult, for the same reason of complexity. Because software and any digital systems are not continuous, testing boundary values are not sufficient to guarantee correctness. All the possible values need to be tested and verified, but complete testing is infeasible. Exhaustively testing a simple program to add only two integer inputs of 32-bits (yielding 2^64 distinct test cases) would take hundreds of years, even if tests were performed at a rate of thousands per second. Obviously, for a realistic software module, the complexity can be far beyond the example mentioned here. If inputs from the real world are involved, the problem will get worse, because timing and unpredictable environmental effects and human interactions are all possible input parameters under consideration.

Good testing provides measures for all relevant factors. The importance of any particular factor varies from application to application. Any system where human lives are at stake must place extreme emphasis on  reliability and integrity. In the typical business system usability and maintainability are the key factors, while for a one-time scientific program neither may be significant. Our testing, to be fully effective, must be geared to measuring each relevant factor and thus forcing quality to become tangible and visible.

Tests with the purpose of validating the product works are named clean tests, or positive tests. The drawbacks are that it can only validate that the software works for the specified test cases. A finite number of tests can not validate that the software works for all situations. On the contrary, only one failed test is sufficient enough to show that the software does not work. Dirty tests, or negative tests, refers to the tests aiming at breaking the software, or showing that it does not work. A piece of software must have sufficient exception handling capabilities to survive a significant level of dirty tests.

A testable design is a design that can be easily validated, falsified and maintained. Because testing is a rigorous effort and requires significant time and cost, design for testability is also an important design rule for software development.

Software reliability has important relations Software testing with many aspects of software, including the structure, and the amount of testing it has been subjected to. Based on an operational profile (an estimate of the relative frequency of use of various inputs to the program, testing can serve as a statistical sampling method to gain failure data for reliability estimation.

Software testing is not mature. It still remains an art, because we still cannot make it a science. We are still using the same testing techniques invented 20-30 years ago, some of which are crafted methods or heuristics rather than good engineering methods. Software testing can be costly, but not testing software is even more expensive, especially in places that human lives are at stake. Solving the software-testing problem is no easier than solving the Turing halting problem. We can never be sure that a piece of software is correct. We can never be sure that the specifications are correct. No verification system can verify every correct program. We can never be certain that a verification system is correct either.

Conclusions

• Software testing is an art. Most of the testing methods and practices are not very different from 20 years ago. It is nowhere near maturity, although there are many tools and techniques available to use. Good testing also requires a tester's creativity, experience and intuition, together with proper techniques.
• Testing is more than just debugging. Testing is not only used to locate defects and correct them. It is also used in validation, verification process, and reliability measurement.
• Testing is expensive. Automation is a good way to cut down cost and time. Testing efficiency and effectiveness is the criteria for coverage-based testing techniques.
• Complete testing is infeasible. Complexity is the root of the problem. At some point, software testing has to be stopped and product has to be shipped. The stopping time can be decided by the trade-off of time and budget. Or if the reliability estimate of the software product meets requirement.
• Testing may not be the most effective method to improve software quality. Alternative methods, such as inspection, and clean-room engineering, may be even better.

 

Network testing

Users and network administrators often have different views of their networks. Often, users who share printers and some servers form a workgroup, which usually means they are in the same geographic location and are on the same LAN. A community of interest has less of a connection of being in a local area, and should be thought of as a set of arbitrarily located users who share a set of servers, and possibly also communicate via peer-to-peer technologies. technologies.

Network administrators see networks from both physical and logical perspectives. The physical perspective involves geographic locations, physical cabling, and the network elements (e.g., routers, bridges and application layer gateways that interconnect the physical media. Logical networks, called, in the TCP/IP architecture, subnets, map onto one or more physical media. For example, a common practice in a campus of buildings is to make a set of LAN cables in each building appear to be a common subnet, using virtual LAN (VLAN) technology.
Both users and administrators will be aware, to varying extents, of the trust and scope characteristics of a network. Network testing Again using TCP/IP architectural terminology, an intranet is a community of interest under private administration usually by an enterprise, and is only accessible by authorized users (e.g. employees).[5] Intranets do not have to be connected to the Internet, but generally have a limited connection. An extranet is an extension of an intranet that allows secure communications to users outside of the intranet (e.g. business partners, customers).[5]

L2 - L2 protocol testing

L2 - Layer 2

This is also referred to as the OSI (Open Systems Interconnection) Data Link Layer. It provides the means for synchronizing the bit stream flowing to and from the physical layer and for the detection of errors due to transmission problems e.g. noise and interference. An example of a Data Link protocol would be Ethernet operating on a LAN (Local Area Network).

L3 - Layer 3
This is also referred to as the OSI (Open Systems Interconnection) Network Layer. It provides the paths for the transfer of data between systems and across networks. The paths between systems may include switched services and interconnections of multiple subnetworks on route. An example of a protocol operating at the network layer would be IP (Internet Protocol).

 

 

 

About the Author

Is there any utility to test the communication functioning (other than printing) of a printer's parallel port?

. . . If it won't print, nor communicate its online/offline status back to the computer (bi-directional parallel port), despite the cable itself and the parallel port on the computer both being verified as good with a different printer.

Still fighting the battle I see. Sorry it's still an issue.

I did some Google'ing for any possible testers that might still be out there, but didn't find any, nor have I ever heard of a computer software utility to test that. Would be a neat idea, but unfortunately the parallel interface has become a thing of the past and doubt that anybody really supports it anymore due to costs.

I should still have some hardware testers (that had lights & switches for diagnosis and configuration) around here somewhere that I used to use to test both the parallel & serial interfaces of both computers and printers when they were most popular 15 to 27 years ago. But I have no idea where they are presently and don't know where you'd find any anymore. Mine actually came from a couple of printer manufacturers that my company was authorized for.

As a basic test & evaluation of the interface, you can use a good volt meter to measure the signal outputs of each pin to see what's going on. Parallel interfaces use 0-5vdc signal outputs. They are either "high" at 5vdc or "low" at 0vdc. You can see the standard standby signals, but to see the actual handshaking that occurs with each byte of data sent down would require the kind of hardware I have and know what you're looking at. I do vaguely remember something about a few printer interfaces that didn't play well with computers and had to have something unique done to make them work, but I don't remember now offhand.

Here are some web links to help you out.

http://www.lammertbies.nl/comm/cable/parallel.html

http://www.connectworld.net/ieee1284.html

http://pinouts.ru/ParallelPorts/Centronics_pinout.shtml

http://www.interfacebus.com/Design_Connector_Parallel_PC_Port.html

http://allenk.home.infionline.net/techref/ieee1284.html

Best of luck.

Google Nexus S Near Field Communication (NFC) Demonstration