What is meant by load shedding?

The network is monitored by the network monitoring systems. These systems need to be robust and must be capable of inevitably coping with the situations in which the overload occurs. The network gets overloaded because of the nodes generating large volumes of data at high rates. Overload might also occur because of the burstiness of the traffic in its normal course of operation. For reducing the load of the network, load shedding techniques are applied. 

- Load shedding techniques have to be followed if the network is under a lot of stress. 

- This has to be done while monitoring the network for avoiding the packet loss that otherwise might be uncontrollable. 

- Load shedding involves sampling the incoming traffic. 

- CoMo or continuous monitoring has been developed to serve this purpose. 

- It uses such a load shedding scheme which can infer the query’s cost using the relation between the set of features of the traffic and the actual resource usage without having any knowledge of the plug-ins. 

- Here, traffic feature can be defined as a counter describing the incoming traffic’s particular property. 

The property might be any of the following:

Ø  Number of packets

Ø  Number of bytes

Ø  Flows

Ø  Unique IP destination address and so on.

- The CoMo consists of a prediction and the load shedding sub-system for intercepting the packets prior to sending them to the plug-in from the filter.

- A traffic query is implemented by this plug-in. 

- The system completes the process in 4 phases. 

- In the first phase, it forms a batch of packets for each 100ms of the traffic. - It then processes each of these batches for extracting a predefined traffic features’ set that is quite large. 

- From these, the most relevant sets are selected by the feature selection sub-system based up on the present stats of the CPU usage of the query. 

- The selected subset is then supplied as input for the “multiple linear regression subsystem”. 

- This is done for the prediction of the CPU cycles that the query requires for processing the whole batch. 

- If the prediction is greater than the capacity of the system, the batch is pre-processed by the load shedding subsystem for discarding the packet’s portion. 

- The batch is discarded through packet or flow sampling. 

Load shedding is now being seen as an effective method for curbing the overload situations even in the real time systems. 

- It involves shedding excess of the load in such a way that the stability of the system is not disturbed and also the system buffers do not experience any overflows. 

- The idea for applying the technique of load shedding in the field of networking has been adopted from the concept of the electric power management.

- Here, the electric current is intentionally disconnected on particular lines when the demands for the power supply are higher than what is being supplied.

- CoMo is an open source system and can be quickly implemented and can be used for further deploying other network monitoring applications. 

- The system has been written using C language and uses a feature rich API. 

- The system works by predicting the CPU usage of the system and thus anticipates about the resource requirements bursts that might occur in future. 

- The load shedding scheme used by the CoMo has the capability of automatically identifying the features using which the resource usage can be best modeled for each monitoring application.

- This identification is made according to the previous resource usage measurements. 

- These measurements are then used for determining the system’s overall load and by what percentage the load must be shed. 

Comparison between Virtual Circuit and Datagram subnets

Difference #1:

- In virtual circuits the packets are allowed to contain in them the circuit number rather than storing the full address of the destination. 

- This reduces the requirement for a much larger memory and bandwidth. 

- This also makes it cheaper in cost. 

- On the other hand, the data-grams have to contain the full destination address rather than a single circuit number.

- This causes a significant overhead in the data-gram sub nets. 

- Also, this leads to wastage of the bandwidth. 

- All this implies that the data-gram sub nets are more costly when compared to the virtual circuits. 

Difference #2:

- A set up phase is required for the virtual circuits. 

- For establishing this phase a lot of resources are required along with a lot of time. 

- Data-gram sub net in contrast does not require establishment of set up phase. 

- Hence, there is no requirement of resources.

Difference #3:

- In virtual circuits, for indexing purpose the circuit numbers are used by the router. 

- These numbers are stored in a table and are used for finding out the destination of the packet. 

- This procedure is quite simple when compared with the one used by the data-gram sub nets. 

- The procedure used in data-gram sub nets for determining the destination of the packet is quite complex. 

Difference #4:

- Virtual circuits allow for reserving the resources in advance on the establishment of the resources.

- This has a great advantage which is that the congestion is avoided in the sub net. 

- However, in the data-gram sub nets, it is quite difficult to avoid congestion. 

Difference #5:

- If a crash occurs in a router, then it will lose its memory. 

- Even if it backs up after sometime, all the virtual circuits that pass via it must be aborted. 

- This is not a major problem in the case of the data-gram sub nets. 

- Here, if the router crashes, the only packets that will have to suffer will be the ones that were queued for that router at that instant of time. 

Difference #6:

- The virtual circuits can vanish as a result of the loss or fault on the current communication line.

- In data-gram sub nets, it is comparatively easy to compensate for the fault or loss on the communication line. 

Difference #7:

- In virtual circuits there is one more cause for the traffic congestion. 

- This cause in the use of the fixed routes for the transmission of the data packets throughout the network. 

- This also leads to the problem of unbalanced traffic. 

- In data gram sub nets the routers are given the responsibility of balancing the traffic over the entire traffic.

- This has been made possible because it is allowed to change the routers halfway between the connections. 

Difference #8:

- Virtual circuits are one way of implementing the connection-oriented services. 

- For various types of data gram sub nets, a number of protocols are defined by the internet protocol. 

- Internet protocol provides the data-gram service at the internet layer. 

- In contrast with the virtual circuits, data gram sub nets are connection-less service. 

- It is the best effort message delivery service but at the same time is very unreliable. 

- There are a number of high level protocols such as TCP that are dependent up on the data gram service of the internet protocol.

- This calls for additional functionality. 

- The data gram service of IP is even used by the UDP. 

- The fragments of a data gram might be referred to as the data packets. 

- The IP and UDP both provide unreliable services and this is why both of them are termed as data grams. 

- The fragments of TCP are referred to as TCP fragments to distinguish it from data-grams. 

What is meant by Ovonic Unified Memory?

There is much requirement in the IT industry for a high – speed memory plus that is non–volatile too. A solution to this is provided by the ovonic unified memory. 

- Ovonic Unified Memory is an approach to such a memory. Further, it offers reduced bit rate and cost. 

- There are some other characteristic features of this memory:

1. High endurance
2. Low power consumption
3. Non – volatile RAM
4. Readily scaled.
5. Merged memory/ logic simplified

- Since the ovonic unified memory is readily scaled it is not required to scale the barriers of flash and DRAM memories.

- This represents a new semiconductor technology – a creation of the Energy Conversion Devices, inc. however later it was licensed to the ovonyx inc.

- This technology makes use of a structural phase change that is reversible i.e., from a crystalline phase to the amorphous phase. 

- The material used here is the thin–film chalcogenide alloy. 

- This all constitutes the data storage mechanism of ovonic unified memory (OUM). 

- Each memory cell consists of an active medium in a small volume that acts as the programmable resistor. 

- This resistor switches between the low and high resistance in the dynamic range of greater than 40x. 

- The phase change technology is currently being used in the PD, CD RW, DVD RW and DVD RAM. 

- The basic advantage offered by OUM is in the terms of performance and cost when compared to its conventional counterparts namely the flash and the DRAM memories. 

- OUM has got compatibility with the merged memory/log. 

- A conventional CMOS process is used in the OUM technology along with some additional layers in order to form the memory elements. 

- The OUM products have been commercialized under various licensing agreements. 

- The alloy used in OUM consists of Se and Te elements.

- They exhibit the property of electronic threshold switching phenomenon because of which the OUM memory cells can be programmed at quite low voltages irrespective of which state they are in i.e., whether conductive or resistive. 

- The measurement of the resistance of cell is used to read the information stored. 

- The programming of the OUM devices is done electrically by the alteration of its structure of the alloy. 

- These OUM devices show metallic behavior are independent of the temperature.

- The OUM devices are known for their excellent data retention property in the case of high density array applications. 

- Also, the OUM cells have more than normal life cycle i.e., they can tolerate up to 10¹³ write and erase cycles without any failure. 

- These devices possess quite a large dynamic range.

- This allows them to be programmed for enabling the multi–state data storage at intermediate resistance values.

- For multi–stage data storage, every cell needs to support multiple–bit storage. 

- The technology behind the ovonic unified memory is the device modeling. 

- Here, simple analytical methods show the trends in the properties and size of the material for structures that are spherically equivalent. 

- Other numerical models are inclusive of the mesh evaluation plus the device geometry.

- The behavior of the OUM devices can be predicted using the numerical simulation. 

- The behavior of the OUM material depends up on its bulk properties which have a characteristic that they can be quantified. 

- There are 3 considerations of this model:

1. Phase–change: It includes heat of fusion, crystal growth and nucleation.
2. Electrical: It includes current density, electric field and percolation conduction.
3. Thermal: It includes percolation conduction and the heat equations.

Apart from the cost, another advantage of OUM is its near – idle memory qualities such as:

1. Static
2. Random accessible
3. Non – destructive read

What is meant by Software Process Improvement?

About Software Process Improvement

- SPI or Software Process Improvement is a program that has been developed to provide guidance for the integrated long – range plan for the initiation and management of the SPI program. 

- SPI is based up on a model called the IDEAL model which has the following 5 major stages:

1. Initiating
2. Diagnosing
3. Establishing
4. Acting
5. Leveraging

- These 5 major steps form a continuous loop. 

- However, the time taken for the completion of one cycle varies from one organization to other. 

- Depending on the available resources an organization must be able to decide whether or not it would be able to commit to software process improvement. 

- SPI requires many activities to be carried out in parallel to each other. 

- Some part of the organization may take care of the activities in one phase while others take care of the other phase activities.

- Practically, the boundaries of the various stages in a software process improvement are not clearly defined. 

- The infrastructure also plays a great role in the success of the SPI. 

- The value added to SPI by infrastructure just cannot be underestimated. 

- It provides a great help in understanding its roles.

About Initiating Phase

- As the name indicates this is the starting point of the process. 

- This stage involves setting up of the improvement infrastructure. 

- Then the infrastructure’s roles and responsibilities are defined. 

- The resources are checked for availability and assigned.

- Finally, an SPI plan that will guide this initiating phase as well as the other higher stages. 

- It is during this stage that the goals of the software process improvement are defined and established based up on the organization’s business needs. 

- During the establishing phase these goals are further refined and specified.

- Two components are typically established namely:

Ø  A software engineering process group or SEPG

Ø  A management steering group or MSG 

About Diagnosing Phase

- In this stage, the organization as per the SPI plan starts. 

- This stage serves as foundation for the stages that will follow. 

- The plan is initiated keeping in view the vision of the organization along with its business strategy, past lessons, current business issues and long term goals. 

- Appraisal activities are carried out so that a baseline of the current state of the organization. 

- The results of these activities are reconciled with the existing efforts so as to be included in the main plan.

About Establishing Phase

 

- In this stage the issues to be addressed by the improvement activities are assigned priorities.

- Also, the strategies for obtaining a solution are also pursued. 

- The draft of the plan is completed as per the organization’s vision, plan, goals and issues. 

- From general goals, measurable goals are developed and put in to the final SPI plan. 

- Metrics essential to the process are also defined.

About Acting Phase

 

- Solutions addressing the improvement issues discovered in the previous stages are created and deployed in and out of the organization. 

- Other plans are developed for the evaluation of the improved processes.

About Leveraging Phase

 

- This stage is led by the objective of making the next pass through the process more effective. 

- By this time the organization has developed solutions and metrics concerning performance and achievement of the goals. 

- All this data obtained is stored in a process database that will later serve as source information for the next pass. 

- Also, this information would be used for the revaluation of the strategies and methods involved in the SPI program.

- Software process improvement activities work with two components namely, the tactical component and the strategic component. 

- The former is driven by the latter that is based up on the needs of the organization. 

Transition Phase - One of the phase of Rational Unified Process

There are 4 phases which together constitute the rational unified process namely:

1. Inception phase
2. Elaboration phase
3. Construction phase
4. Transition phase

The above mentioned phases are responsible for the representation of the rational unified process at the highest level in the way which is similar to waterfall model representation but the difference is that the key for the rational unified process lies in the development iterations which form an integral part of all the phases of the rational unified process. 

Also, each of the four phases of the rational unified process are characterized by two things namely the objective and the milestone. The objective drives the whole phase from the beginning to the end and the milestone concludes the end of it. 

The phase is said to be complete with successful result if and only if it passes the milestone since this only marks the conclusion of the phase. All of the phases of the rational unified process are visualized in the form of a chart called the RUP hump chart which is drawn over the course of the whole process. 

In this article we shall discuss exclusively about the fourth phase of the rational unified process i.e., the transition phase. 

Objective of Transition Phase

- The primary objective with which the transition phase is driven is “to transit the software system or application” from the phase of development in to the actual phase of production. 

- This also extends the availability of the software system or application to the end user in such a form that it is understandable by the end user. 

- This phase involves the below mentioned activities:

1. Training the end users
2. Training the maintainers as well.
3. Carrying out beta testing on the software system or application for validating it against the expectations of the end users.
4. Checking the software product against the quality level that was set in the inception phase.

- When all the objectives are said to be accomplished, the software system or application is said to reach the ‘product release milestone’ and the development cycle is said to be concluded.

- This fourth phase of the rational unified process does the fine tuning of the software product.

- It is based on the feedback from the user and the software product is made ready for the release. 

- The transition phase is basically focused on the availability of the software system or application to the end users.

- The transition phase often involves the spanning of the several iterations. 

- The software product is tested in order to prepare it for the release and also minor adjustments are made as per the feedback provided by the end users. 

- When this point in the software development life cycle is reached, it is required that the feedback from the end user should be majorly focused up on the following issues:

1. Fine tuning of the software system or the application.
2. Configuration of the product
3. Installation issues
4. Usability issues

- By this time, almost all the major issues of the product structure should have been worked out in the earlier phases of the software development life cycle. 

- The product release milestone can be defined as a point where it is decided that all the objectives of the project have been met and whether or not another development cycle is required. 

- The basic and majority of the evaluation as well as the refinement of the software system or application is done based up on the feedback from the user.

- This can be considered to be a kind of fine tuning exercise for the software system since the system has already met the requirements of the users as it is driven by the use cases. 

- At the end, a final evaluation is done and accordingly the project is released to the public or is considered for another development cycle. 

Construction Phase - One of the phase of Rational Unified Process

There are 4 phases which together constitute the rational unified process namely:

1. Inception phase
2. Elaboration phase
3. Construction phase
4. Transition phase

For representing the process at a high level, it is necessary that all of the above mentioned four phases should work together just as it is done for the water fall styled model. But here the key difference is that the primary key to the process is nothing but the development iterations that are involved in each of the development phase. Each of the above mentioned phases is driven by the objective and ended by milestone. The RUP hump chart gives the visualization for all the above 4 phases. 

Here we shall talk about the third phase i.e., the construction phase. 

About Construction Phase of Rational Unified Process

- The construction phase is driven by the primary objective for building the software system or application. 

- The primary focus of the construction phase is taken up by the components development as well as the development of the other features of the software system or application. 

- A bulk of coding is carried out in this phase only. 

- For developing a large project, it is required that several construction iterations are carried out in order to make an effort for dividing the use cases in to the segments that are manageable and that can be used in the production of the demonstrable prototypes. 

- The software version that is released in this phase is its first external release.

- The elaboration phase is concluded with the initial operational capability milestone. 

- The major thing with which the construction phase is concerned is moving the executable architecture that was created in the elaboration phase to the operational system. 

- Therefore, a beta version of the software system or application is ready to be evaluated by the project team. 

- In the elaboration phase the software product resides on the architectural baseline.

- Here, it is moved to a system that is so complete enough that it can make transition to the end users’ community. 

- The architectural baseline is grown enough to become the completed operational system via the refining of the designing in to the code. 

- This phase acquires the largest part of the whole rational unified process. 

- The remaining part of the software system or application is built on the foundation that was laid earlier in the elaboration phase. 

- Short and time boxed iterations help towards the implementation of the features of the system where an executable release of the system or application is released at the end of each iteration. 

- In this phase, writing the full test use cases becomes customary where each one marks the beginning of a new iteration. 

- The elaboration phase makes use of certain UML (unified modelling language) diagrams which are mentioned below:

1. Activity
2. Sequence
3. Collaboration
4. State i.e., transition and
5.  Interaction overview diagrams

- The purpose of the rational unified process is to provide the industry tested practices for the development, implementation and delivery of the software system or application. 

- It also provides a comprehensive frame work for the effective project management. 

- This process is actually one of the many other processes which are contained within the rational process library of the IBM RMC (rational method composer). - This makes it easy to make selection and deploy the only components that you need for your process. 

- The rational unified process is adopted for 1000s of the projects nowadays worldwide. 

- It lessens the burden of inventing a new thing again and again rather it focuses on re-usability. 

Elaboration Phase - One of the phase of Rational Unified Process

The life cycle for a project under the context of the rational unified process is known to consist of the following four phases:

1. Inception phase

2. Elaboration phase

3. Construction phase

4. Transition phase

Here we shall discuss about the second phase of the unified process i.e., the elaboration phase. In Rational Unified Process, the four phases represent the process at a high level although the iterations that are carried out in every phase of development are the key to the process. 

Each phase here is provided with an objective and a milestone. It is necessary to have a milestone for each so that it could be decided that when and where a particular phase is ending and the next one is starting. All the above phases as well as the process disciplines are visualized in to what is called an “RUP hump chart”. 

About Elaboration Phase in Rational Unified Process

- The primary objective of the elaboration phase is defined as the mitigation of the key risk items whose identification is done by the analyzation of the whole phase from the beginning till the end. 

- It is here in the elaboration phase where the project starts taking the shape. - In elaboration the following 2 basic things take place:

1. The analyzation of the problem domain is done.

2. Basic form is given to architecture. 

- The following are the outcomes of the elaboration phase:

1. A use case is obtained in which both the actors and use cases have been identified. This use – model consists of most of the developed use – case descriptions. It is required that this use – case model should be at least 80 percent complete. 

2. A description concerning the architecture of the software system in a development process. 

3. An architecture that is executable and realizes the use cases which have an architectural significance. 

4. A revised risk list.

5. A revised business case.

6. A plan for the overall development of the project. 

7. Prototypes which give a demonstration on the mitigation of the identification of the technical risks. 

8. An optional preliminary user manual.

- There is a milestone criteria called the life cycle architecture milestone which involves answering the following questions:

1. Stability of the architecture?

2. Stability of the vision of the product?

3. Have the major risk elements been addressed and resolved and has been indicated by the executable demonstration?

4. Has the sufficient detailing has been done for the construction phase plan and is it accurate?

5. Have all the stakeholders agreed for achieving the current vision using the current plan under the current architectural context?

6. Is the expenditure of planned resource vs. actual resource acceptable?

- It is important that the project should pass this milestone and if it doesn’t there are 2 possibilities:

1. It can either be redesigned or

2. It can be cancelled.

- However, when the project leaves this phase, the project is transitioned in to an operation that involves high – risk i.e., to say here the changes are quite detrimental as well difficult to be made. 

- The system architecture serves as the key domain analysis for the elaboration phase. 

- The basic thing here is addressing of the major technical risks threatening the project. 

- Another thing is to have a bare system which provides answers to all of the major technical questions. 

- Once all the questions have been answered by the end, the development team will know whether a working system can be successfully built or not. 

Inception Phase - One of the phase of Rational Unified Process

There are 4 phases which together constitute the rational unified process namely:

1. Inception phase
2. Elaboration phase
3. Construction phase
4. Transition phase

This article is dedicated entirely to the first phase of the unified process i.e., the inception phase. The major development takes place in the iterations of development which are carried out within each phase. All of the above four phases have their unique key objective as well as milestones.

The accomplishment of the objective is denoted by the milestone. An RUP hump chart is used for the visualization of all the four phases of the rational unified disciplines and phases over the time. 

Objective of Inception Phase

- The primary objective of the inception phase provide adequate scope to the software system or application as a basis on which the validation of the budgets and initial costing could be done.

- The inception phase involves the establishment of a business case which is inclusive of the following:

1. Business context
2. Success factors such as the market recognition, expected revenue and so on.
3. Financial forecast

- In order to complement the business case, the following things are generated:

1. A basic use case model
2. Project plan
3. Initial risk assessment
4. Project description which in turn includes the following:

    a)   Key features

    b)   Constraints and

    c)   The core project requirements

- Once the generation of the above mentioned sources is complete, the verification of the project begins against the following criteria:

1. Stake holder concurrence on the following:

  a)   Cost estimates

  b)   Schedule estimates and

  c)   Scope definition

2. Understanding of the requirements as per the evidence obtained by the fidelity of the use cases.
3. Credibility of the following:

  a)   Cost and schedule estimates

  b)   Priorities

  c)   Development process and

  d)   Risks involved

4. The depth and breadth that was developed for any architectural prototype.
5. Establishment of a base line using which the planned expenditures and actual expenditures can be compared.

- If for one or the other reason the project is unable to pass the milestone (commonly termed as the life cycle objective mile stone) then there are only two possibilities after redesigning the program (for meeting the criteria in a better way) as mentioned below:

1. It can be cancelled or
2. It can be repeated

- This phase is involved with launching the project. 

- A proper business case can be developed for the project. 

- It is by the end of the inception that the development team comes to whether to carry on with the project or not. 

- In inception phase, one can see a core idea being developed in to a vision for a product. 

- In this phase may reviews, discussions, etc. are carried out regarding the business case involved in the project. 

- The scope of the project is delimited in the inception phase and also the product feasibility is established. 

- This is perhaps the smallest of all the phases of a project and also according to its ideal nature it should be short. 

- If the duration of the inception phase is too long it indicates that there has been an excessive up – front specification (even though this goes against the spirit of the rational unified process.).