Erica Joy Blog Post!

Ms. B’s Requirements

File Directory

 Directory  is a location for storing files on your computer. Directories are found in a hierarchical file system, such as Linux, MS-DOS, OS/2, and Unix.

A.a Single-level directory

Single level directory is simplest directory structure.In it all files are contained in same directory which make it easy to support and understand.

A single level directory has a significant limitation, however, when the number of files increases or when the system has more than one user. Since all the files are in the same directory, they must have the unique name . if two users call their dataset test, then the unique name rule violated.

A.b Two-level directory

As we have seen, a single level directory often leads to confusion of files names among different users. the solution to this problem is to create a separate directory for each user.

In the two-level directory structure, each user has there own user files directory (UFD). The UFDs has similar structures, but each lists only the files of a single user. system’s master file directory (MFD) is searches whenever a new user id=s logged in. The MFD is indexed by username or account number, and each entry points to the UFD for that user.

A.c Tree-structured directory

Once we have seen a two-level directory as a tree of height 2, the natural generalization is to extend the directory structure to a tree of arbitrary height.
This generalization allows the user to create there own subdirectories and to organize on their files accordingly.

A.d Acyclic graph directory

An acyclic graph is a graph with no cycle and allows to share subdirectories and files. The same file or subdirectories may be in two different directories. It is a natural generalization of the tree-structured directory.

It is used in the situation like when two programmers are working on a joint project and they need to access files. The associated files are stored in a subdirectory, separating them from other projects and files of other programmers, since they are working on a joint project so they want the subdirectories to be into their own directories. The common subdirectories should be shared. So here we use Acyclic directories.

It is the point to note that shared file is not the same as copy file . If any programmer makes some changes in the subdirectory it will reflect in both subdirectories.

A.e General graph directory structure

In general graph directory structure, cycles are allowed within a directory structure where multiple directories can be derived from more than one parent directory.
The main problem with this kind of directory structure is to calculate total size or space that has been taken by the files and directories.

Reference:

geeksforgeeks.Retrieved(2019).fromhttps://www.geeksforgeeks.org/structures-of-directory-in-operating-system/.

File Sharing

File sharing is public or private sharing of data in a network with separate levels of accessibility. Depending on the accessibility permissions, file sharing allows a select number of people to read, view or edit the file based on the level of authority the file sharer has provided. File sharing services typically allocate a certain amount of file storage per user per account.

A.a File transfer protocol programs (FTP):

The most common file transfer system on the internet to date is known as the File Transfer Protocol or FTP. FTP is used to access or edit files among a set number of users with a password. The users can then gain access to the files shared from an FTP server site. Many FTP sites offer public file sharing or allow users to view or download files using a public password.

A.b Peer-to-peer networks:

Peer-to-peer networking involves computer hardware and software to communicate without the need for a central server. This type of file sharing indicates the direction of digital files over a p2p network where the files are located on one’s computer and shared with other members rather than on the main server.

A.c Removable storage media:

This involves anything that can be removable from a device or computer. The user can transfer or insert files from their device onto the removable storage media and then physically hand it to whomever they would like to share the files with. These can include an FTP server for security purposes, asking for a valid login and password from others to allow access.

A.d Online file sharing services:

Online file sharing services include web services that allow users to store or share data on the internet for personal or professional use. One member may upload photos, documents, PDFs, etc. to an online file sharing platform which allows others to download these files using the same platform.

Reference:

panda security.com.Retrieved November 13,2019 2:29 PM>.from https://www.pandasecurity.com/mediacenter/panda-security/secure-file-sharing/

Hybrid Topology

Source:https://ph.images.search.yahoo.com

Hybrid topology-is a type of network topology that uses two or more differing network topologies. These topologies include a mix of bus topology, mesh topology, ring topology, star topology, and tree topology.

Advantages of Hybrid Network Topology

• Very reliable and easy to detect the Faulty system.
• Troubleshooting is easy.
• It includes both wired and wireless network.
• It is an expandable network.

Disadvantages of Hybrid Topology

• Its design is difficult to understand.
• The cost of this network design is high, because of the requirement of a lot of cables, cooling systems, etc.
• MAU ( Multi-station Access Unit) is required.

References:

Penna Sparrow .(2019).ianswer4u.com.Retrieve.<November,8,2019,1:49PM>.from.https://www.ianswer4u.com/2012/05/hybrid-topology-advantages-and.html

Tree Topology

Soource: https://www.google.com.ph/search?q=Tree+topology+gif

A tree topology is a special type of structure in which many connected elements are arranged like the branches of a tree. For example, tree topologies are frequently used to organize the computers in a corporate network, or the information in a database.

In a tree topology, there can be only one connection between any two connected nodes. Because any two nodes can have only one mutual connection, tree topologies form a natural parent and child hierarchy.

Advantages of tree topology:

• Scalable as leaf nodes can accommodate more nodes in the hierarchical chain.
• A point to point wiring to the central hub at each intermediate node of a tree topology represents a node in the bus topology
• Other hierarchical networks are not affected if one of them gets damaged
• Easier maintenance and fault finding

Disadvantages of tree topology:

• Huge cabling is needed
• A lot of maintenance is needed
• backbone forms the point of failure.

References:

Gaspard Abel.(2019).fossbytes.com.Retrieve.<November 8,2019,1:36PM>.from.https://fossbytes.com/tree-topology-advantage-disadvantage/

Ring Topology

Source: https://www.google.com/search?q=ring+topology&source

A Ring network is a network topology in which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node – a ring. Data travels from node to node, with each node along the way handling every packet.

Advantages

• Very orderly network where every device has access to the token and the opportunity to transmit
• Performs better than a bus topology under heavy network load
• Does not require a central node to manage the connectivity between the computers
• Due to the point to point line configuration of devices with a device on either side (each device is connected to its immediate neighbor), it is quite easy to install and reconfigure since adding or removing a device requires moving just two connections.
• Point to point line configuration makes it easy to identify and isolate faults.
• Reconfiguration for line faults of bidirectional rings can be very fast, as switching happens at a high level, and thus the traffic does not require individual rerouting.

Disadvantages

• One malfunctioning workstation can create problems for the entire network. This can be solved by using a dual ring or a switch that closes off the break.
• Moving, adding and changing the devices can affect the network
• Communication delay is directly proportional to number of nodes in the network
• Bandwidth is shared on all links between devices
• More difficult to configure than a Star: node adjunction = Ring shutdown and reconfiguration

References:

techopedia.com.(2019).techopedia.com.Retrive.<November 7,2019,2:09PM>.from. https://www.techopedia.com/definition/17262/ring-topology

fossbytes.com.(2019).fossbytes.com. .Retrive.<November 7,2019,2:09PM>.from. https://fossbytes.com/what-is-ring-topology-advantages-and-disadvantages-of-ring-topology/

Mesh Topology

Source:https://www.google.com/search?q=mesh+topology+gif

 Mesh Topology – all the computers are inter-connected to each other in a network. Each computer not only sends its own signals but also relays data from other computers. This type of topology is very expensive as Its very difficult to establish the connections of the mesh topology. In a Mesh topology every node has a point-to-point connection to the other node. The connections in the mesh topology can be wired or wireless.

Advantages of Mesh topology

1) Data can be transmitted from different devices simultaneously. This topology can withstand high traffic.
2) Even if one of the components fails there is always an alternative present. So data transfer doesn’t get affected.

3) Expansion and modification in topology can be done without disrupting other nodes.

Disadvantages of Mesh topology

1) There are high chances of redundancy in many of the network connections.
2) Overall cost of this network is way too high as compared to other network topologies.
3) Set-up and maintenance of this topology is very difficult. Even administration of the network is tough.

References:

ianswer4u.com.(2019).ianswer4u.com.Retrieve.<November 6,2019,3:50PM>.from.https://www.c/2011/05/mesh-topology-advantages-and.html

GoDaddy.(2019).computernetworktopology.com.Retrieve.<November 6,2019,3:50PM>.from.https://computernetworktopology.com/what-is-mesh-topology-advantages-disadvantages/

Star Topology

Source:https://www.google.com/search?q=star+topology+gif

A network structure comprising a central node to which all other devices attached directly and through which all other devices intercommunicate. As illustrated in Figure S-9, the central node is in the form of a hub, switch, or router with multiple ports to which devices connect, usually through unshielded twisted pair (UTP) or shielded twisted pair (STP). In the public switched telephone network (PSTN), each carrier serving area (CSA) is a star, with local loops radiating from the central office (CO). Star configurations include 100Base-T and 1000Base-T local area networks (LANs). See also 100Base-T, 1000Base-T, CO, CSA, hub, node, PSTN, router, STP, switch, Token Ring, topology, and UTP.

Advantages of Star Topology

 1.) As compared to Bus topology it gives far much better performance, signals don’t necessarily get transmitted to all the workstations. A sent signal reaches the intended destination after passing through no more than 3-4 devices and 2-3 links. Performance of the network is dependent on the capacity of central hub.

2.) Easy to connect new nodes or devices. In star topology new nodes can be added easily without affecting rest of the network. Similarly components can also be removed easily.

3.) Centralized management. It helps in monitoring the network.

4.)  Failure of one node or link doesn’t affect the rest of network. At the same time its easy to detect the failure and troubleshoot it.

Disadvantages of Star Topology

1.) Too much dependency on central device has its own drawbacks. If it fails whole network goes down.

2.) Too much dependency on central device has its own drawbacks. If it fails whole network goes down.

3.)  Performance and as well number of nodes which can be added in such topology is depended on capacity of central device.

References:

Sparrow,Penna.(2019).ianswer4u.com.Retrieve.<November 6,2019,3:29PM>.from.https://www.ianswer4u.com/2011/05/star-topology-advantages-and.html

yourdictionary.com.(2019).yourdictionary.com.Retrieve.<November.6,2019,3:29PM>.from.https://www.yourdictionary.com/star-topology

Bus Topology

A bus topology is a topology for a Local Area Network (LAN) in which all the nodes are connected to a single cable. The cable to which the nodes connect is called a “backbone”. If the backbone is broken, the entire segment fails. Bus topologies are relatively easy to install and don’t require much cabling compared to the alternatives.

Advantages (benefits) of Linear Bus Topology

1)  It is easy to set-up and extend bus network.
2)  Cable length required for this topology is the least compared to other networks.
3)  Bus topology costs very less.
4) Linear Bus network is mostly used in small networks. Good for LAN.

Disadvantages (Drawbacks) of Linear Bus Topology

1)  There is a limit on central cable length and number of nodes that can be connected.
2)  Dependency on central cable in this topology has its disadvantages.If the main cable (i.e. bus ) encounters   some problem, whole network breaks down.
3)  Proper termination is required to dump signals. Use of terminators is must.
4)  It is difficult to detect and troubleshoot fault at individual station.
5)  Maintenance costs can get higher with time.
6)  Efficiency of Bus network reduces, as the number of devices connected to it increases.
7)  It is not suitable for networks with heavy traffic. 
8)  Security is very low because all the computers receive the sent signal from the source.

References:

ianswer4u.com.(2019). ianswer4u.com .Retrieve.<November 6,2019,2:57PM>.from.https://www./2011/05/bus-topology-advantages-and.html

techopedia.com.(2019).techopedia.com.Retrieve.<November 6,2019,2;57PM>.from.https://www.techopedia.com/definition/17045/bus-topology

Point to Point Topology

Point to Point topology is the simplest topology that connects two nodes directly together with a common link. The entire bandwidth of the common link is reserved for transmission between those two nodes. The point-to-point connections use an actual length of wire or cable to connect the two ends, but other options, such as satellite links, or microwaves are also possible.

When you change TV channels by remote, you are establishing a point-to-pointconnection between the remote control and the TV’s control system.

The transfer of data in a point-to-point topology can be in multiple ways across the network: in a simplex, in full duplex, or half duplex.

References:

conceptdraw.com.(2019).conceptdraw.<November 6,2019,2:27 Pm>.from.https://www.conceptdraw.com/How-To-Guide/point-to-point-network-topology.

wiki.p2pfoundation.(2019).wiki.p2foundation.<November 6,2019,2:27 Pm>.fromhttps://wiki.p2pfoundation.net/Network_Topology.

Priority

In case of priority scheduling the priority is not always set as the inverse of the CPU burst time, rather it can be internally or externally set, but yes the scheduling is done on the basis of priority of the process where the process which is most urgent is processed first, followed by the ones with lesser priority in order.

Processes with same priority are executed in FCFS manner.

The priority of process, when internally defined, can be decided based on memory requirements, time limits ,number of open files, ratio of I/O burst to CPU burst etc.

Whereas, external priorities are set based on criteria outside the operating system, like the importance of the process, funds paid for the computer resource use, makrte factor etc.

Reference:

https://www.studytonight.com/operating-system/priority-scheduling.(2019).Wikipedia.Retrieved(2019).