What are the advantages and disadvantages of datagram approach?

- Today’s packet switching networks make use of a basic transfer unit commonly known as the datagram. 

- In such packet switched networks, the order of the data packets arrival, time of arrival and delivery comes with no guarantee. 

- The first packet switching network to use the datagrams was CYCLADES. 

- Datagrams are known by different names at different levels of the OSI model. 

- For example, at layer 1 we call it Chip, at layer 2 it is called Frame or cell, data packet at layer 3 and data segment at layer 4. 

- The major characteristic of a datagram is that it is independent i.e., it does not rely on any other thing for the information required for exchange.

- The duration of a connection between any two points is not fixed such as in telephone conversations. 

- Virtual circuits are just the opposite of the datagrams. 

- Thus, a datagram can be called as a self containing entity. 

- It consists of information sufficient for routing it from the source to the destination without depending up on the exchanges made earlier. 

- Often, a comparison is drawn between the mail delivery service and the datagram service. 

- The user’s work is to just provide the address of the destination. 

- But he/she is not guaranteed the delivery of the datagram and if the datagram is successfully delivered, no confirmation is sent to the user. 

- The data gram are routed to some destination without help of a predetermined path. 

- The order in which the data has to be sent or received is given no consideration. 

- It is because of this that the datagrams belonging to a single group might travel over different routes before they reach their common destination. 

Advantages of Datagram Approach

1. Datagrams can contain the full destination address rather than using some number.
2. There is no set up phase required for the datagram circuits. This means that no resources are consumed.
3. If it happens during a transmission that one router goes down, the datagrams that will suffer will include only those routers which would have been queued up in that specific router. The other datagrams will not suffer.
4. If any fault or loss occurs on a communication line, the datagrams circuits are capable of compensating for it.
5. Datagrams play an important role in the balancing of the traffic in the subnet. This is so because halfway the router can be changed.

Disadvantages of Datagram Approach

1. Since the datagrams consist of the full destination address, they generate more overhead and thus lead to wastage of the bandwidth. This in turn makes using datagram approach quite costly.
2. A complicated procedure has to be followed for datagram circuits for determining the destination of the packet.
3. In a subnet using the datagram approach, it is very difficult to keep congestion problems at bay.
4. The any-to-any communication is one of the key disadvantages of the datagram subnets. This means that if a system can communicate with any device, any of the devices can communicate with this system. This can lead to various security issues.
5. Datagram subnets are prone to losing or re - sequencing the data packets during the transition. This puts a great burden on the end systems for monitoring, recovering, and reordering the packets as they were originally.
6. Datagram subnets have less capability of dealing with congestion control as well as flow control. This happens because the direction of the incoming traffic is not specified. In the virtual circuit subnets, the flow of the packets is directed only along the virtual circuits thus making it comparatively easy for controlling it.
7. The unpredictable nature of the flow of the traffic makes it difficult to design the datagram networks. 

What is a choke packet?

- The networks often experience problems with congestion and flow of the traffic. 

- While implementing flow control a special type of packet is used throughout the network. 

- This packet is known as the choke packet. 

- The congestion in the network is detected by the router when it measures the percentage of the buffers that are actually being used. 

- It also measures the utilization of the lines and average length of the queues. 

- When the congestion is detected, the router transmits choke packets throughout the network. 

- These choke packets are meant for the data sources that are spread across the network and which have an association with the problem of congestion. 

- These data sources in turn respond by cutting down on the amount of the data that they are transmitting. 

- A choke packet has been found to be very useful in the maintenance tasks of the network. 

- It also helps in maintaining the quality to some extent. 

- In both of these tasks, it is used for informing the specific transmitters or the nodes that the traffic they are sending is resulting in congestion in the network. 

- Thus, the transmitters or the nodes are forced to decrease the rate at which they are generating traffic. 

- The main purpose of the choke packets is controlling the congestion and maintaining flow control throughout the network. 

- The router directly addresses the source node, thus causing it to cut down its data transmission rate. 

- This is acknowledged by the source node by making reductions by some percentage in the transmission rates. 

- An example of the choke packet commonly used by the most of the routers is the source quench packet by ICMP (internet control message protocol).  

- The technique of using the choke packets for congestion control and recovery of the network involves the use of the routers. 

- The whole network is continuously monitored over by the routers for any abnormal activity.

- Factors such as the space in the buffers, queue lengths and the line utilization are checked by the routers. 

- In case the congestion occurs in the network, the choke packets are sent by the routers to the corresponding parts of the network instructing them to reduce the throughput. 

- The node that is the source of the congestion has to reduce its throughput rate by a certain percentage that depends on the size of the buffer, bandwidth that is available and the extent of the congestion. 

- Sending the choke packets is the way of routers telling the nodes to slow down so that the traffic can be fairly distributed over the nodes. 

- The advantage of using this technique is that it is dynamic in nature. 

- The source node might send as much data as required while the network might inform that it is sending large amounts of traffic.

- The disadvantage is that it is difficult to know by what factor the node should reduce its throughput.

- The amount of the congestion being caused by this node and the capacity of the region in which congestion has occurred is responsible for deciding this. 

- In practical, this information is not instantly available. 

- Another disadvantage is that after the node has received the choke packet, it should be capable of rejecting the other choke packets for some time. 

- This is so because many additional choke packets might be generated during the transmission of the other packets. 

The question is for how long the node is supposed to ignore these packets? 

- This depends up on some dynamic factors such as the delay time. 

- Not all congestion problems are same, they vary over the network depending up on its topology and number of nodes it has. 

Flooding - a kind of static algorithm

An algorithm designed for the distribution of the material to each and every part of the graph is referred to as the flooding algorithm. 

- The algorithm has got its name from the concept that involves inundation caused by a flood. 

- The main application of these algorithms is in graphics and computer networking. 

- These algorithms also come very handy in solving a number of mathematical problems. 

- Examples of such problems that are graph theory problems, maze problems and so on. 

- Flooding algorithm though it sounds complicated is quite a simple one. 

- Here, every incoming packet is sent via every outgoing link. 

- Only the link through which the packet arrived is saved. 

This algorithm has many applications in the following:

1. Systems that require bridging, systems like use net.
2. Peer to peer file sharing.
3. Used as a part of the routing protocols such as the DVMRP, OSPF etc.
4. Used in protocols used for the adhoc wireless networks.

Nowadays the flooding algorithm is available with its many variants. The following are two main steps that each variant follows while working:

1. Each node in the network might act as both receiver and the transmitter.
2. The incoming message is forwarded by the receiving node to each of its neighboring nodes except the one which is the source code.

- This causes the message to be delivered to each and every part of the network that is reachable. 

- Algorithms are required as a precaution for avoiding the wastage of the infinite loops and the duplicate deliveries and for allowing the messages for expiring. 

- All these issues are addressed partially by a variant of the flooding algorithm called the selective flooding.

- The usual flooding algorithm sends the packets to all the routers that lie in the same direction. 

- But the selective flooding algorithm does not send the packet to each router rather it selects only few of them which lie in the right direction approximately. 

Advantages and Disadvantages of Flooding Algorithm

Advantages:

1. If it is possible for delivering the packet, it will be delivered but a number of times.
2. In flooding algorithm every path in the network is naturally utilized and so the shortest path is also used.
3. The implementation of the flooding algorithm is quite simple.

Disadvantages:

1. The cost of the flooding algorithm can be very high because a lot of bandwidth is wasted. Even if there is one destination of the message, it will be sent to all the hosts on the network unnecessarily. If in case there occurs a denial of service attack or a ping flood, the reliability of the whole network will be affected badly.
2. In the computer network, the message might get duplicated. This in turn can increase the load on the bandwidth of the network. This will call for increasing the complexity of the processing for rejecting the duplicates of the messages.
3. The packets that are duplicate might keep on circulating forever, if the following precautions are not taken:

Ø  Using a time to live count or a hop count to be included with every packet. The value of the count has to include the number of the nodes through which the packets have to be passed while on the way to destination.

Ø  Each and every node should be used for keeping track of every packet that passes through it and a packet should be forwarded only once.

Ø  The network topology must be enforced without any loops. 

What are data gram sub-nets?

- A data gram is defined as the basic transfer unit used in the networks that operate with the help of packet switching network. 

- In such networks, the time of the arrival and delivery is not guaranteed. 

- Also, the network services do not guarantee that whether it will be an ordered delivery or not. 

- The first project to use the data grams was the CYCLADES which was again a packet switching network. 

- The hosts in this network were responsible for making a reliable delivery rather than relying on the network for doing so. 

- This they did using the data grams that were themselves so unreliable and by associating the mechanisms of the end to end protocols. 

- According to Louis Pouzin, there are two sources from which came the inspiration for the data grams namely the Donal Davie’s studies and simplicity of the things. 

- The concept of the data gram sub-net was eventually adopted for the formulation of the protocols such as apple talk, Xerox network systems and of course the internet protocol.

- Data grams are used at the first 4 layers of the OSI model. 

- Each layer has its own name for the data grams as we mention below:

1. Layer 1: chip (CDMA)
2. Layer 2: frames (IEEE 802.3 and IEEE 802.11), cell (ATM)
3. Layer 3: data packet
4. Layer 4: data segment

- A data gram is a data packet that is self-reliant. 

- This means it does not rely on any of the exchanges made earlier since the fixed connection between the two points of communication has no connection such as in a majority of the telephonic conversations. 

- Virtual circuits and data gram sub-nets are two equally opposite things. 

Data gram is defined as an independent and self-contained data entity by the RFC 1594 that carries sufficient information required for routing from one source to another without relying on the transporting network and the earlier exchanges between the two same hosts.

- The services offered by the data gram sub nets can be compared to the mail delivery services. 

- This is so because the user needs to mention only the destination address.

- However, this service does not give any guarantee of whether the data gram will be delivered or not and also does not provide any confirmation upon successful delivery of the packet. 

- These are of course two major disadvantages of the data gram sub nets. 

- In data gram sub nets, the data grams or the data packets are routed along a route that is created at the same time. 

- In data gram sub nets the routes are not predetermined. 

- This again has its disadvantages. 

- Also, the order in which the data grams have to be sent or received is not considered. 

- In some cases, a number of data grams having same destination might travel along various different routes.

- There are two components of every data gram namely the header and the data payload.

- The former consists of all the information that is enough for the routing purpose from source to the destination without being dependent on the exchanges that were made before between the network and the equipment. 

- The source as well the destination address might be included in the header as a kind of a field. 

- The data that is to be transmitted is stored in the latter part of the data gram. 

- In some cases the data payloads might be nested in to the tagged header. 

- This process is commonly known as the encapsulation. 

- There are various types of data grams for which various standards are defined by the internet protocol or IP. 

What are advantages and disadvantages of having international standards for network protocols?

Without rules governing the exchange of data and establishment of connections between networks, there would have a big chaos in the industry. These rules are called line protocols and are very crucial for the inter-networking and communication across the networks. 

The mode and the speed of communication are controlled by what are called the communications software packages. These network protocols are defined by the international standards. However, having international standards for the protocols has got both advantages and disadvantages. 

- A number of standard network protocols for carrying out several functions such as routing, packetizing, and addressing and so on. 

- All these protocols lay out a standard definition of how the routing and addressing has to be done. 

- They also define the specifications for the structure of the packets to be transferred between different hosts. 

- Some commonly used routing protocols are:

Ø  X.25

Ø  IPX/ SPX

Ø  TCP/ IP

Ø  OSI

- The OSI stands for open systems interconnection. 

- Early networking systems had a big problem which was that there was a lack of consistency between the protocols employed by several types of different computers. 

- As a consequence of this problem, the international standards came in to the picture. 

- Thus, international standards were established for the various data transmission protocols. 

- For example, OSI is a set of standard protocols developed by ISO (international standards organization).

- In this model, the functionalities of the network protocols have been divided in to seven layers of the communication rules or protocols. 

- The purpose of this model is to identify the functions being offered by the system. 

- The following three layers appear in the host systems and other units such as processor and control unit etc.:

1. Physical layer
2. Data link layer
3. Network layer

- The leftover layers are found in the host systems only. 

Advantages of having International Standards

Ø  If all the systems are following the same standard, it becomes easy for everyone to connection to everyone else. In other words, the international standards provide easy interconnectivity.

Ø  If any standard is widely used, it gains economies of scale. For example, VLSI chips etc.

Ø  With all the systems using the same standard, the installation and the maintenance of the connections become quite easy.

Ø  Software designed by the developers from all over the world, won’t have any problem in interfacing with the host system and the other software. They will work well with a wide range of operating systems and hardware since both are using the same standard.

Disadvantages of having International Standards

Ø  Poor standards may be formed as a result of the frequent standardization.

Ø Once the standard is adopted internationally, it’ll be difficult to make changes to it. It will be difficult to introduce new and better techniques in to it.

Ø  If a problem occurs, it has to be seen as an international problem.

Ø The manufacturers and companies will be bound to follow the same international standards and so they won’t be able to develop something better of their own.

Ø  Large multinational companies won’t be able to pool everyone in to using their proprietary protocols and therefore no huge profits.

TCP/ IP protocol was developed to make communication easy between the dissimilar systems. A number of hardware and software vendors support this protocol ranging from mainframes to microcomputers. A number of corporations, universities and govt. agencies are making use of this protocol. 

What are advantages and disadvantages of artificial neural networks?

The artificial neural networks, since they can simulate the biological nervous system are used in many real life applications which are also their one of the biggest advantages. 

They have made it easy for carrying out complex processes such as:

Ø  Function approximation

Ø  Regression analysis

Ø  Time series prediction

Ø  Fitness approximation

Ø  Modeling

- With the artificial neuron networks, the classification based on sequence and pattern recognition along with other difficult things such as the sequential decision making and the novelty detection is possible. 

- A number of operations falling under the data processing category such as clustering, filtering, compression and blind source separation etc. are also carried out with the help of artificial neural networks. 

- Artificial neural networks can be considered as the backbone of the robotics engineering field. 

- They are used in computer numerical control and in directing the manipulators.

- It offers advantages in the following fields of:

1. System control (this including process control, vehicle control and natural resources management),
2. System identification,
3. Game – playing,
4. Quantum chemistry
5. Decision making (in games such as poker, chess, backgammon and so on.)
6. Pattern recognition (including face identification, radar systems, object recognition and so on.)
7. Sequence recognition (in handwritten text recognition, speech, gesture etc.)
8. Medical diagnosis
9. Financial applications i.e., in automated trading systems
10. Data mining
11. Visualization
12. E – mail spam filtering

- Today several types of cancers can be diagnosed using the artificial neural networks. 

- HLND is an ANN based hybrid system for detection of lung cancer. 

- The diagnosis carried out with this is more accurate plus the speed of radiology is more. 

- These diagnoses are then used for making some models based up on information of the patient. 

- Its following theoretical properties are nothing but an advantage to the industry:

1. Computational power: It provides a universal function approximator i.e., the multilayer perceptron or MLP.
2. Capacity: This property indicates about the ability of ANN to model almost any given function. It has a relation with both the notion of complexity and information contained in a network.
3. Convergence: This property is dependent on a number of factors such as:

Ø  Number of existing local minima which in turn depends up on model and the cost function.

Ø  Optimization method used

Ø  Impracticality of few methods for a large amount of parameters.

4. Generalization and statistics: Over training is quite a prominent problem in the applications where it is required to create a system that is capable of generalizing in unseen examples. This in turn leads to problem of the over specified or the convoluted systems along with the network exceeding the limit of the parameters. There are two solutions offered by ANN for this problem:

-   Croos – validation and

-   Regularization

Disadvantages of Artificial Neural Networks

1. It requires a lot of diverse training for making the artificial neural networks ready for the real world operations which is a drawback more prominent in the robotics industry.

2. Many storage and processing resources are required for implementing large software neural networks using ANNs.

3. The human has the ability to process the signals via a graph of neurons. A similar simulation of even a very small problem can call for excessive HD and RAM requirements.

4. Time and money cost for building ANNs is very large. 

5. Furthermore, simulation of the signal transmission through all the connections and associated neurons is required.     

What is Keyword driven testing? What are base requirements for keyword driven testing?

Table driven testing, action word testing or key word driven testing, whatever you may call it, it is one and the same thing – a software testing methodology that has been especially designed for automated testing.

However, the approach followed by this testing methodology is quite different and involves dividing the test creation process in to 2 distinct phases namely:

1. Planning phase and the
2. Implementation phase

What is Keyword Driven Testing?

- It has been specially designed for automated testing.

- It does not mean that it cannot be employed for carrying out manual testing. - It can be very well used for manual testing as well. 

- The biggest advantage provided by the automated tests is of re-usability and so all this has eased up the maintenance of the tests that were developed at an abstraction level that was too high. 

- To say in simple words, one or more atomic test steps together form a key word.

- The first phase i.e., the planning phase involves the preparation of the testing tools and test resources. 

- The second phase i.e., the implementation phase depends up on the frame work or tool and thus differs accordingly. 

- Often a frame work is implemented by the automation engineers which has key words like enter and check. 

- This makes it easy for the test designers who do not have any knowledge of programming, to design the test cases based on such key words, that have already been defined by the engineers in planning phase that has already been implemented. 

- Such designed test cases are executed via a driver. 

- The purpose of this driver is to read the key word and execute the corresponding code.

- There are other testing methodologies which put everything right in to the implementation phase instead of performing the test designing and engineering separately.

- In such a case, the test automation is only confined to the test design.

- There are some keywords that are created using the tools which had the necessary code already written for them such as edit and check. 

- This helps in cutting down the extra number of engineers in the process of test automation. 

- This makes the implementation of the keyword a part of the tool. 

Advantages of Key word Driven Testing

There are some advantages of key word driven testing as stated below:

1. Concise test cases.
2. Test cases are readable only by the stake holders.
3. Easily modifiable test cases.
4. Easy reuse of the existing keywords by the new test cases.
5. Keywords can be re used simultaneously across multiple test cases.
6. Independent of programming languages as well as specific tool.
7. Labor gets divided.
8. Less requirement of tool and programming skills.
9. Lower domain skills required for keyword implementation.
10. Layer abstraction.

Disadvantages of Keyword Driven Testing

1.   A longer time is required for marketing when compared to manual testing.

2.   Initially, high learning curve.

Base Requirements of Key word driven Testing

1. Full separation of test development and test automation processes: The separation of these two processes is very much required for test automation since both of them have very different skill requirements. The fundamental idea behind this is that the testers should not be programmers. Testers should have the ability of defining test cases which can be implemented without having to bother about the underlying technology.
2. The scope of the test cases must be clear and differentiated: The test cases must not deviate from their scope.
3. Right level of abstraction must be used for writing the tests: Tests must be written at levels such as lower user interface, higher business level etc. 

What are the advantages and drawbacks of QTP?

Though the quick test professional is quite useful like every other object in this world, it has got its advantages and drawbacks. The same thing is going to be discussed here in this article. 

Advantages of Quick Test Professional

1. The quick test professional has got such simplicity that it can be understood easily by even a non programmer and can begin with the testing by adding the test cases.

2. The quick test professional provides support for record and playback of the scripts. Plus it comes with the ability to edit the scripts just after the recording is complete. Different recording modes or options are available with the quick test professional:

    a)   Normal or context sensitive recording mode

    b)   Analog recording mode and

    c)   Low level recording mode

3. Quick test professional (QTP) possesses an excellent object identification mechanism.

4. Quick test professional comes with an extended support for the following add ins:

    a)   SAP

    b)   Oracle

    c)   Java

    d)   .NET

    e)   Siebel

    f)    Main frame or terminal emulators

    g)   Web services

    h)   Web forms and so on.

5. With quick test professional the existing tests and test scripts can be enhanced even if the AUT or application under test in not there with the help of an active screen.

6. Almost all of the popular test automation frame works (such as key word driven, data driven, modular testing approach, hybrid and so on) are supported by the quick test professional.

7. An IDE or integrated development environment is inbuilt in to the quick test professional which is quite easy to use and has got a simple interface. 

8.The scripting language “VBScript” which is used by the quick test professional is just like English and can be learned easily. There are plenty of sources via which one can learn VBScript.

9. In many of the test automation suites it is found difficult to implant the MOM i.e., the Microsoft object model but in quick test professional it is an easy task to do.

10.To make quick test professional further better it can be embellished with other test management tools such as the HP QC or quality center, functional testing tools such as winrunner and test management tools such as test director and so on. Once the tests have been mapped to the automation scripts, they can be executed directly from the HP quality center. Also, winrunner test execution can be kicked off by the quick test professional.

11.With quick test professional several types of suites can be maintained namely:

    a)   Sanity

    b)   Smoke

    c)   Regression and so on.

12. Like most of the test automation suites it provides support for xml.

13. Excel or data base files can be used easily in quick test professional with a variety of methods to use them.

14. Data and the test iterations can be easily maintained.

15. Test reports provided by the quick test professional are complete with all details required for analysis.

Drawbacks of Quick Test Professional

1. Proves to be costlier than any other test automation suite in terms of license and maintenance.

2. It does not support multiple threads and instances execution.

3. It will be surprising to know that the quick test professional has got no high speed rather it has got much slower speed than most of the open source tools such as selenium.

4. Support is provided from HP QC only on the renewal of the license.

5. Add- ins (such as SAP, oracle, java, .net, Seibel, peoplesoft and so on) have to be purchased separately.