What are the differences between inter-network routing and intra-network routing?

- The individual networks when combined together form the inter-network. 

- Intermediate inter networking devices are used for making connections between them. 

- All these networking elements combine to work as single large unit. 

- The creation of the internetworking has been made possible because of the packet switching technology. 

- The router is the most common and important device used for performing inter-network routing and intranetwork routing.

- Routing across various networks in the inter network is termed as internetwork routing and routing within the same network is termed intranetwork routing. 

In this article we discuss about the differences between internetwork routing and intranetwork routing. 

- Just like inter-network, intranetwork also uses IP (internet protocol) technology for computing services and sharing information. 

- But what makes it different from internetworking is that it is limited to some organization whereas internetwork extends beyond all i.e., it is not limited.

- Or we can put it in other words: Internetwork is spread across organizations and Intranetwork lies within an organization. 

- In some cases, the term intranetwork might mean only the internal website of the organization, but in other cases it might be a larger part of the IT infrastructure of the organization. 

- Sometimes, it may span over a number of LANs (local area networks). 

- The intranetwork is driven by the goal of minimizing the time, effort and cost of the individual’s desktop in order to make it more competitive, cost efficient, timely as well as productive.

- An intranetwork is capable of hosting multiple websites that are private to organizations and may even constitute an important part of the collaboration and communication between the members of the organization. 

- Intranetwork also makes use of various well known protocols such as the FTP, SMTP and HTTP. 

- The intranets are often incorporated with the technologies for lending a modern interface to the systems that host the corporate data. 

- These systems are known as the legacy systems. 

- We can see intranetwork to be a private analog of the internetwork. 

- It means the internetwork has been simply extended to an organization for its private use. 

- Extranetworks are a modified version of the intranetworks.

- Here, the website might be accessed by the non-members i.e., the suppliers, customers or some other approved third parties and so on. 

- Intranetworks are well equipped with a special protocol called the AAA protocol. 

- The 3 As stand for authentication, authorization and accounting. 

- There are a number of organizations who are concerned about the security of their intranetworks. 

- They have deployed a firewall and a network gateway for controlling the access to their services. 

- The intermediate systems when connect together form the internetwork whereas they may bound together a part of the internetwork which might be an intranetwork. 

- The intranetwork routing involves routing between two routers which lie in the same network whereas in internetwork routing, routing is done between routers which reside across different networks. 

- Intranetwork routing is quite easy when compared to the internetwork routing. 

- Protocols used in both the types of routing are different.

- Interior gateway protocol is responsible for routing in the intranetworks whereas the exterior gateway protocol takes the responsibility of routing across the internetwork. 

- Most common example of interior gateway protocol is the OSPF or the open shortest path first protocol. 

- And most common example of exterior gateway protocol is the border gateway protocol or BGP. 

- Also, the routing graphs for both the types are different. 

- In the intranetwork’s graph, all the routers are simply linked to one another in the same network. 

- There is less mess.

- On the other hand, the inter network’s graph is quite tedious. 

- This is so because routers of different networks have to be inter-linked with one another. 

Explain the concept of inter-networking?

- The practice in which one computer network is connected with the other networks is called inter-networking. 

- The networks are connected with the help of gateways. 

- These gateways are used since they offer a common method for routing the data packets across the networks.

- The resulting system in which a number of networks are connected is called the inter-network or more commonly as the internet. 

- The terms “inter” and “networking” combine together to form the term “internet working”.  

- Internet is the best and the most popular example of the inter networking. 

- Internet has formed as a result of many networks connected with the help of numerous technologies. 

- Many types of hardware technologies underlie the internet. 

- The internet protocol suite (IP suite) is the inter networking protocol standard responsible for unifying the diverse networks. 

- This protocol is more commonly known as the TCP/ IP. 

- Two computer local area networks (LANs) connected to one another by means of a router form the smallest internet but not the inter network. 

- Inter networking is not formed by simply connecting two LANs together via a hub or a switch. 

- This is called expansion of the original local area network. 

- Inter networking was started as a means for connecting the disparate networking technologies. 

- Eventually, it gained widespread popularity because of the development needs of connecting many local area networks together through some kind of WAN (wide area network). 

- “Catenet” was the original term that was used for the inter network. 

- Inter network includes many types of other networks such as the PAN or personal area network. 

- Gateways were the network elements that were originally used for connecting various networks in predecessor of the internet called the ARPANET. 

- Today, these connecting devices are more commonly known as the internet routers. 

- There is a type of interconnection between the various networks at the link layer of the networking model. 

- This layer is particularly known as the hardware centric layer and it lies below the TCP/ IP logical interfaces level. 

Two devices are mainly used in establishing this interconnection:

Ø  Network switches and

Ø  Network bridges

- Even now this cannot be called as inter networking rather, the system is just a single and large sub-network. 

- Further, for traversing these devices no inter networking protocol is required. 

- However, it is possible to convert a single network in to an inter network. 

- This can be done by making various segments out of the network and also making logical divisions of the segment traffic using the routers. 

- The internet protocol suite has been particularly designed for providing a packet service. 

- This packet service offered by the IPS is quite unreliable. 

- The elements that maintain a network state and are intermediate in the network are avoided by the architecture. 

- The focus of the architecture is more on the end points of the active communication session.

- For a reliable transfer of the data, a proper transport layer protocol must be used by the applications. 

- One such protocol is the TCP (transmission control protocol) and it is capable of providing a reliable stream for communication. 

- Sometimes a simpler protocol such as the UDP (user datagram protocol) might be used by the applications. 

- The applications using this protocol carry out only those tasks for which reliable data delivery is not required or for which realtime is required. 

Examples of such tasks include voice chat or watching a video online etc. Inter networking uses two architectural models namely:

1. OSI or the open system interconnection model: This model comes with 7 layer architecture that covers the hardware and the software interface.
2. TCP/ IP model: The architecture of this model is somewhat loosely defined when compared with the OSI model. 

Explain the single and two level directory structures

About Directory Structure

- Directory structure is referred to the way that the operating system follows for displaying the files and file system to the user in the field of computing. 

- A hierarchical tree structure is used for displaying the files in a typical way. 

- The special kind of string the file name uses or the unique identification of a particular file that is stored in the computer’s file system. 

- Before the 32 bit operating systems actually came in to the scenario; short names of about 6 to 14 characters in size were used for the file names. 

- However, the modern operating systems give permission for file names of longer length i.e., of 250 character and that too per path name element. 

- The drive:\ is the root directory in the operating systems such as the OS/2, windows and DOS for example, “C:\”. 

- The “\” is the directory separator but the forward slash “/” is also internally recognized by the operating system.

- A drive letter is use for naming the drives either physically or virtually. 

- This also implies there does not exist a root directory that is formal. 

- Rather, we have root directories in each drive that are independent of each other. 

- However, one virtual drive letter can be formed by combining in to one. 

- This is done by keeping a RAID setting of 0 for the hard drive. 

- The file system hierarchy standard is used by the operating systems such as the UNIX and other UNIX like systems. 

- This is the most common form for the directory structures used by the UNIX operating systems. 

- It is under the root directory “/” that all the files and the directories are stored even if they are actually present on a number of different physical devices.

About Single – level Directory

- This is the simplest of the directory structures. 

- All files are stored in the same directory itself because it is quite easy to understand as well as support. 

- The first computer of the world i.e., the CDC 6600 also operated on just one directory and it could be used by a number of users at the same time. 

- There are significant limitations of the single-level directory. 

- These limitations come in to play when there are more than one users using the system or when the system has to deal with a large number of files. 

- All the files have to be assigned unique names since they are all stored under the same directory. 

- No two files can have the same file name. 

- It may become difficult to keep the names of the files in mind if they are large in number.

About Two–level Directory

- The limitations of the single level directory structure can be overcome by creating an individual directory for every user. 

- This is the most standard solution for the problems of the single level directories. 

- In this two-level directory structure, a UFD or user file directory is made for every user. 

- The structure of all the user file directories is almost the same, but the difference is that only the files of the individual user are stored in one.

- When a user tries to log in or when he starts a task, the system searches for the MFD or master file directory. 

- The name of the user or his/ her account number is used for indexing the MFDs in the operating system. 

- Each of those entries points to the UFD belonging to that user. 

- When a reference is made to some file, the system only searches for the user file directory for example, when a file has to be deleted or created. 

What is the difference between a passive star and an active repeater in fiber optic network?

There are two important components of a fiber optic network namely passive star coupler and active repeaters. 

Passive Star in Fiber Optic Network

- Passive star couplers are single mode fiber optic couplers with reflective properties.  

- These couplers are used for optical local area networking at very high speeds. 

- These couplers are made from very simple components such as mirrors and 3 db couplers. 

- Besides this, these star couplers save a lot of optical fiber when compared to its trans-missive counterpart. 

- They are free of any multi-paths so as to avoid any interference. 

- A fiber optic network may consist of any number of passive star couplers and each of them is capable of connecting a number of users. 

- The input and output from every passive star coupler is given to the output and input of an active coupler. 

- The round trip transmission tile is stored by the active star coupler. 

- When it receives a signal from a passive star coupler, it stops the output to that coupler for the duration of the signal.

- It also inhibits the incoming data from all the other passive star couplers for the round trip transmission delay plus signal duration. 

- The purpose of a star coupler is to take one input signal and then splitting it in to a number of output signals. 

- In telecommunications industry and fiber optics communication, this coupler is used in network applications being a passive optical device. 

- If an input signal is introduced to one of the input ports, it is distributed to all of the output ports of the coupler. 

- As per the construction of the passive star coupler, the number of ports it will have is given by the power of 2. 

- For example, in a two port coupler or in a directional coupler or splitter, there are 2 input ports and 2 output ports.

- In a four port coupler, there are 4 i/p ports and 4 o/p ports and so on. 

- The digital equipment corporation also sold a device by the name of star coupler which was used for interconnecting the links and computers through coaxial cable instead of using optical fibers. 

Active Repeater in Fiber Optic Network 

- Active repeater is an important telecommunications device used for re transmitting the signal it receives to a higher level and with higher basically to the other side of an obstacle so that long distances can be covered. 

- Repeater is an electro-mechanical device that helps in regenerating the telegraphy signals. 

- It may be defined as an analog device for amplifying the input signal, reshaping it, re-timing it for re-transmission. 

- A re-generator is a repeater that can perform the re-timing operation. 

- Repeaters just tend to amplify the physical signal without interpreting the data transmitted by the signal. 

- The 1^st layer i.e., the physical layer is where the repeaters operate. 

- Repeaters are employed for boosting the signals in optical fiber lines as well as in twisted pair and coaxial cables. 

- When a signal travels through a channel, it gets attenuated with the distance and time because of the energy loss (dielectric losses, conductor resistance etc.). 

- When light travels in optical fibers, it scattered and absorbed and hence is attenuated. 

- Therefore, in long fiber lines, repeaters are installed at proper intervals for regenerating and strengthening the signal. 

Repeater in optical communication performs the following functions:

Ø  Takes the input signal

Ø  Converts it in to electrical signal

Ø  Regenerates it.

Ø  Converts it in to optical signal

Ø  Re-transmits it

- These repeaters are usually employed in submarine as well as transcontinental communication cables as the loss is unacceptable in these cases.  

What are the various Desk Scheduling methods?

About Disk Scheduling

The I/O system has got the following layers:

1. User processes: The functions of this layer including making I/O calls, formatting the I/O and spooling.
2. Device independent software: Functions are naming, blocking, protection, allocating and buffering.
3. Device drivers: Functions include setting up the device registers and checking their status.
4. Interrupt handlers: These perform the function of waking up the I/O drivers up on the completion of the I/O.
5. Hardware: Performing the I/O operations.

- Disk drives can be pictured as large 1 – D array consisting of logical blocks that are smallest unit of transfer.  

- These blocks are mapped in to the disk sectors in a sequential manner. 

- Mapping is done in the same manner. 

- The responsibility of using the hardware efficiently is the duty of the operating system for the disk drives for increasing the speed of access and bandwidth of the disk. 

Algorithms for Scheduling Disk Requests

There are several algorithms existing for the scheduling of the disk requests:

Ø  SSTF: 

- In this method the request having the minimum seek time is selected from the present head position. 

- This method is a modification of the SJF (shortest job first) scheduling and therefore contains some possibility of process starvation.

Ø  SCAN: 

- From one end of the disk, the disk arm starts and continues in the direction of the other end, serving to the requests till the opposite end. 

- At this end the head is reversed and the process continues. 

- This is sometimes called as the elevator algorithm.

Ø  C – SCAN: 

- A better algorithm then the previous one. 

- This one offers a more uniform waiting time than the previous one. 

- The movement of the head is from one end to another while it services the requests encountered along the way. 

- However, the difference is that when it comes to the other it straightaway goes to the beginning without heeding to any of the requests in the way and then again starts. 

- The cylinders are treated as the circular list wrapped around last and the first cylinder.

Ø  C – Look: 

- This is a modified version of the C – SCAN. 

- Here the arm or the head travels only up to the last request rather than going till the far end. 

- Then immediately the direction is reversed and the process continues.

- For disk scheduling it is important that the method be selected as per the requirements only. 

- The first one is the most commonly used and appeals to the needs naturally. 

- For a system where often there is a heavy load on the disk, the SCAN and C- SCAN methods can help. 

- The number as well as the kind of requests affects the performance in a number of ways.

- On the other hand, the file – allocation method influences the requests for the disk services. 

- These algorithms have to be written as an individual module of the OS so that if required it can be replaced with a different one easily. 

- As a default algorithm, the LOOK or the SSTF is the most reasonable choice. 

Ways to attach to a disk

There are two ways of attaching the disk:

Ø  Network attached: This attachment is made via a network. This is called the network attached storage. All such connected storage devices together form the storage area network.

Ø  Host attached: This attachment is made via the I/O port.

All these disk scheduling methods are for the optimization of the secondary storage access and for making the whole system efficient. 

Explain the concept of Spooling and Buffering?

Concept of Spooling

- In the field of computer science, the ‘simultaneous peripheral operations on – line’ has been shortened down to the acronym ‘spool’. 

- A SPOOL software such as that of the IBM’s ‘SPOOL system’ was used by the computer systems in the time period from late 1950 to early 1960. 

- From one medium to another, files could be copied using this software. For example:

1. From tape to punch card
2. From punch card to tape
3. From tape to printer
4. From one card to another card

- IBM released less expensive software called the IBM 1401 that from some time brought down the application of the spool software.

- The print spooling is the most common application of this concept.

- The documents to be printed are formatted and stored at an area of the disk and retrieved when the print command is given.

- The printer prints out these documents at its defined rate. 

- Typically, at a time only one document can be printed by a printer and for doing so it takes a few minutes or seconds depending up on how fast it is. 

- Spooling speeds up this process, but how? 

- With a spool software many documents can be written to the print queue by the multiple processes without having to wait. 

- As soon as the process wrote its document in the spooling device, it was free to carry out the other tasks. 

- At the same time another process would handle the printing of the document. 

- If there was no spooling, the processor would not be able to continue until and unless the pending process is finished. 

- This would lead to long waits during processing and thus making the paradigm inefficient.

Concept of Buffering

- The physical memory storage has a region where it temporarily stores the data when it is being sent to another location.

- Typically whenever data is taken from some input device such as a keyboard or a mouse, it is stored in the buffer before sending it to the processor or output device. 

- Buffers can be implemented either through some virtual data buffer or in a fixed memory location.

- In majority of the cases, implementation of buffers is done with software that point to some location in the physical memory and use faster RAM. 

- The data access from buffers is quite fast when compared to that of the hard disk drives. 

- Buffers are used wherever a difference occurs between the rate of receiving data and rate of processing it.

- It also occurs if the two data rates are variable such as in online video streaming, printer spooler and so on. 

- The timing in a buffer is adjusted with the implementation of a FIFO algorithm or we can say a queue in the memory. 

- This would allow at the same time to write the data at the one end and read it from another end and both being done at different rates.

- Buffers are used along with I/O to hardware like in transmitting and receiving data in a network, disk drives, playing some song on the speakers etc.

- Buffers used in telecommunication are called the telecommunication buffers and make use of a storage medium or buffer routine.

- This routine compensates for the two different rates while receiving and sending data. 

- Buffers are also used in making interconnections between digital circuits working at different rates, for making timing corrections, delaying transmission time and so on. 

What are characteristics of autonomic system?

Autonomic systems bring both challenges as well as opportunities for the future networking. The increasing numbers of users have had a negative impact on the complexity of the networks; it has also increased by multiple folds. Autonomic systems provide a solution for this problem. 

Characteristics of Autonomic System

1. High intelligence: These systems have more intelligence incorporated in to them which lets them tackle this increasing complexity easily.
2. Business Goal: They are driven by the business goal that the quality of experience of the user must be high. Even with the changing environment, there goals remain the same. But there are changes that take place in the low – level configurations. For example, when a user switches over to a low bandwidth network, the bit rate of the video has to be reduced in order to satisfy the goals of the business.
3. Complex operations: All the operations carried out in an autonomic system are complex in nature even for the simplest of the services. For example, authentication, video encoding, billing, routing, shaping, QoS prioritizing, admission control.
4. High level objectives: The human operator just has to specify the high – level objectives and it is left to the system whether it chooses to optimize one or more of the goals. In order to achieve this, the system has to translate these objectives in to low – level configurations.
5. Adaptability: The system has the ability to adapt itself to the current environment.
6. Policy continuum: There are a number of perspectives to this as mentioned below:

Ø  Business view: Includes guidelines, processes and goals.

Ø  System view: The service should be independent of the technology as well as the device that is being used.

Ø  Network view: It should be specific to technology but independent of the device.

Ø  Device view: Both technology and device specific.

Ø  Instance view: Operation should be specific to an instance.

7. Elements: The elements of the network are assumed to be heterogeneous by the autonomic communication systems whereas in plain autonomic computing the elements are taken to be as the homogeneous.
8. Distributed: These systems work up on a distributed environment.
9. Complexity: The complexity in autonomic systems is more because of the complex autonomic loop that includes the following operations:

Ø  Interaction between the context  and the business goals

Ø  The MAPE (monitor, analyze, plan and execute) loop.

10. Reliability: In autonomic systems, the network has the authority to decide for itself focusing on high level objectives. Autonomic systems rely heavily up on artificial intelligence. However, there are issues associated with artificial intelligence like it becomes difficult to intervene in between when the things go wrong.It is quite difficult to know whether the system is doing the things it is supposed to do or not.

11. Scalability: This is another major characteristic of autonomic systems. It is required to keep track of the large amounts of knowledge and information. Autonomic systems have three tools to take care of this:

Ø Distributed ontologies

Ø Distributed large – scale reasoning

Ø Exchanging only the useful information

ØDistributing information among the different components of the autonomic network.

But in these cases, detection of the conflicts is a difficult task. For handling the various interactions taking place the various autonomic components efficient protocols are required. 

Currently two approaches have been suggested for developing the autonomic networking systems namely:

1. Evolutionary Approach: Incorporating the autonomic behavior in to the pre – existing infrastructure. This approach will consist of updates in increments till a fully autonomic system is developed. This approach is more likely to be adopted even though it requires a lot of patchwork.

2.  Clean slate approach: This approach is focused up on re – designing of the internet.

Introduction to Routers

A computer networking device which forwards data packets across a network toward their destinations, through a process of routing is known as Router. In companies and large corporations, a central computer system acts as a router to connect all of the company's computers to one network. This allows group participation and collaboration on large projects or just to connect all of the company's resources at one central location. It also aids in reliable communication between employees working on different floors in the building or in different countries.

1. Router is required to connect multiple networks, like your LAN to the Internet.
2. Routers store large tables of networks and addresses, then using algorithms to determine the shortest routes to individual addresses within those networks.
3. Routers not only facilitate intra-network communications, but also play a role in overall network performance.
4. Routers help in delivering the information faster.
5. Routers also protect LAN from Internet.
6. Router blocks any packet that has a destination address outside of the LAN. If the destination address is valid, the router could check the Packet for an error. If there is an error, the router could discard the Packet and send a message to the originating address.
7. Routers have address translation and filtering capabilities.