1.3 Exchanging data Flashcards
How data is exchanged between different systems
Layering
Application
Definition: Divides complex tasks of networking into smaller simpler tasks that work in tandem with each other.
Layers:
- Application
- Transport
- Internet
- Link
Application Layer:
The application layer selects protocols relating to the application being used to transmit data over a network, usually the Internet. If this application is a browser, for example, then it would select an appropriate higher-level protocol for communication such as HTTP, POP3, or FTP.
Transport Layer:
Uses the TCP protocol to establish an end-to-end connection with the recipient computer. Protocols use port numbers to track sessions and add info to the header. Once the connection has been made, the data is split into packets. It will then add the Number/Sequence, the total number of packets, and the port number packets should use. The packets are numbered so that they can be reassembled in the correct order.
Internet
Uses the IP part of the stack and adds to each packet the destination IP address and the source IP address. All routers operate at this layer and use the IP address to find out where packets are heading. The addition of the IP address and port number forms a socket like 127.56.87.2:80. The socket specifies which device the packet must be sent to and the application being used on that device.
Link
This is the physical connection between the network nodes and the unique Media Access Control (MAC) addresses identifying the Network Interface Cards (NICs) of the source and destination computers. These mean that once the packet finds the correct network using the IP address, it can then locate the correct peice of hardware. The destination MAC address is that of the device that the packet is being sent to next. Unless the two computers are on the same network, the destination MAC address will initially be the MAC address of the first router that the packet will be sent to.
Circuit switching
Creates a direct link between the two devices for the duration of the communication.
Advantages:
- Exclusive creation is created between the two devices for the duration of the communication, data segments arrive in the same order.
Disadvantages:
- Bandwidth is wasted when no data is being sent.
- The two connected devices must have the same transfer rate otherwise they cannot transfer any data.
Packet switching
Breaks down streams of data into smaller blocks, each sent independently of one another.
Advantages:
- At each node, packets are sent via whichever route the node deems least congested, maximising bandwidth
- It is more affordable and efficient than circuit switching because all the bandwidth can be used at once, but requires less complex infrastructure and easily respond if parts of the network fail.
Disadvantages:
- Even though sending data down the least congested route maximises bandwidth, it may not guarantee the quality of the data being sent.
- The data may be out of order once sent, however, this can be eliminated using Cyclical Redundancy Checks or Checksums.
DNS
The DNS is a system used to name and organise internet resources. It is a hierarchy in which each smaller domain is separated from the larger domain by a full stop.
TLD = Top Level Domain
2LD = 2nd level domain.
Domain names are much easier to remember than IP addresses, which is why they are used to link servers across the world. The role of the DNS server is to translate these domain names into IP addresses when we wish to access a website.
Client Server
Client-server networks consist of terminals known as clients connected to a server.
- Controls access and security for a shared file store.
- Manages access to the internet.
- Manages printing jobs.
- Provides email services.
- Client can make a request to the server for data, connections and all other services.
Advantages:
- Easier to manage file security due to the centralized architecture. So access controls like login requirements ensure that authorised users can access data.
- Easier to backup shared data because they can be controlled centrally by the network administrator so the process of creating and managing backups is streamlined.
- Easier to install software updates to all computers on the network because of all the information and resources are stored on a central server, meaning that when it comes to software updates, the centralisation will simplify the process significantly,
Disadvantages:
- Can be expensive to set up and maintain as the servers, and the software which needs to be licensed can get quite expensive. As well as that, the cost of storage, RAM, processors which can handle multiple tasks at the same time is quite significant.
- IT specialists are required in order to maintain the server because of how much maintenance is required for all the parts in the server.
- As the server is the single point of failure, clients can risk losing network access if the server fails.
Client servers are mainly used by large organisations such as schools which have multiple clients as well as computers which need to access to the same information.
Peer to Peer Server
- Peer is connected to eachother through a logical connection.
- There is no central server.
- Each peer is responsible for their own files, backups and updates.
- In the case of a printer,peers usually have their own printer, however, one peer can send print jobs to another peer to process but they must be switched on to communicate with the printer.
Advantages:
- Very easy to maintain because there is no central server, meaning no IT specialists are needed.
- Cheaper to set up as there is no expensive hardware.
Disadvantages:
- Network is less secure seeing as there is no central server which provides security to the computers connected to it.
- Users need to manage their own backups so if their client gets damaged and they have not backed it up, they risk losing files and important information.
Suitable for smaller organisations with fewer computers.
Relational databases
Recognises the differences between entities by creating different tables for each entity.
Flat file
Database that consists of a single file. Most likely based around a single entity and its attributes.
Usually written as: Entity1(Attribute1,Attribute2,Attribute3…)
Primary Key
Unique identifier for each record in the table. Primary key is shown by underlining it.
Foreign Key
Attribute which links two tables together. Exits in one table as the primary key, and acts as the foreign key in another. Shown using an asterik (*)
Secondary key
Allows a database to be searched quickly. In a database full of names and ID Numbers for example, the patient may not know their ID but know their surname. Therefore a secondary index is set up on the surname attribute, making it possible to order and search by surname which makes it easier to find specific people in a database.
Types of entity relationship models.
- On-to-one: Each entity can only be linked to one other entity. E.g., One husband, one wife.
- One-to-many: One table can be associated with many other tables. E.g., One mother, multiple children and can be done in vice versa (Many children to one mother).
- Many to many: One entity can be associated with many other identities and the same applies to the other way around. E.g. One students can enrol into many courses and vice versa.
Ways of capturing data
- Manually entering data into a database: E.g., Amount of pedestrians participating in a survey.
- Magnetic Ink Character Recognition (MCIR): E.g., Cheques. Banks use this to scan them, all the details excluding the amount are printed in a special magnetic ink recognised bt a computer but the amount must be entered manually.
- Optical Mark Recognition: Used for multiple choice questions on a test.
- Optical Character Recognition: Can also be used on multiple choice questions as well as convert images into a machine readable format.
Selecting and Managing Data
Selecting Data:
- Can be collected in SQL or QBE (Microsoft Access)
Managing Data:
- Can be managed in Database Management Language (DML).
