Computer Science - Networks

G11

Ram: Random access memory 

• Temporary storage

• Stores data in MBS

• Volatile (Only maintains memory when the device is turned on)

• Used for normal operations

• Writing data is faster

Rom: Read only memory

• Permanent storage

• Stores data in GBS

• Non-volatile (lRetains information even when the device is powered off)

• Used for the startup process of the device

• Writing data is slower

Sram: Static ram

• Does not require refreshing

• Requires multiple transistors to store one bit

• Delivers faster access times

• Consumes less power

• Takes up more space

• Only holds a small amount of data

• Costs more than dram

• Typically used for a processors cache

Dram: Dynamic ram

Needs to be continuously refreshed

• Requires one transistor to store one bit

• Slower performance

• More power consuming

• Requires less space

• Holds much more data

• Costs less than sram

• Typically used for computer’s main memory

Explain the use of cache memory.

A type of high speed memory that is inside of the CPU. It holds frequently used data. 

Why does a computer need persistent storage?

RAM is only temporary memory and gets erased when the machine is turned off. 

Main functions of an operating system.

• Provides an interface between the user and the computer and manages application software 

• Provides user interface

• Does memory management

• Does peripheral management

• Allows multitasking

• Offers security

What role does application software play in a computer system?

Spreadsheets, email, web browsers, games, database management systems

List some common features of application software.

• Menus

• Buttons

• Toolars

• Ribbons

• Icons 

• Sliders

• Dialogue boxes

• GUI components

• Radio buttons / Checkboxes

Bit

•  Smallest unit of data in computing, represented by a 0 or a 1

Byte

•  Group of bits - 8 bits is a byte

Binary

• Computers use it to store data, BASE-2

Denary

• Decimal = Numbering system with 10 symbols (0,1,2,3,4,5,6,7,8,9) referred to as BASE 10 

Hexadecimal

• Numbering system with 16 symbols (0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F) BASE 16

How does a computer represent positive integers?

• Binary data is stored as one or more bytes.

How does a computer represent negative integers?

• “Two’s complement” = How a computer chooses to represent integers

  • 00001010 becomes 11110101 (Swaps around) 

How does a computer represent characters and words?

• By using binary code for ASCII characters

How does a computer represent pictures and graphics?

• By representing colors on a RGB scale, from 0 → -255

Lan

 Local area network (Covers the local area’s network, can only communicate with devices connected to the same network)

Wan

Wide area network (Covers a wide area of network, multiple LANS connected to each other, can range from multiple buildings, satellite links to other countries, can be wired, improved security, traffic management)

Vlan

Virtual local area network (Logical group of workstations, servers, network devices that appear to be on the same LAN despite their geographical distribution)

Wlan

Wireless local area network (Wireless distribution method for two or more devices that use high frequency radio waves and often include an access point to the internet. Allows users to move around the coverage area, often a phone or small office, while maintaining a connection, sometimes called WIFI. 

Extranet

(Controlled private network, allowing customers, partners, vendors, suppliers and other businesses to gain information, typically about a specific company or educational institution, and do so without granting access to the organization’s entire network. Private part of a website. Restricted to select users through user IDs, passwords and other authentication mechanisms on a login page.) 

Intranet

(Computer network for sharing information through, helps employees connect, communicate, collaborate and perform their roles.) 

Internet

 Network of networks (Globally connected network system that uses the TCP/IP protocols to transmit data via various types of media, network of global exchanges such as public, business, academic and government networks, connected by wired, wireless and fiber-optic technologies, not always same as WWW)

San

 Storage area network (Secure high speed data transfer network that provides access to consolidated block level storage also appears to servers as attached drives, network that stores data can be accessed by multiple computers. Each can access hard drives in the SAn as if they were local disks connected directly to the computer.) 

Vpn

Virtual private network (Allows people to log into a network remotely and encrypts the connection to THWART EAVESDROPPERS, helps bypass blocks)

Pan

Personal area network (Network covering  avery small area, usually a small room, f.eg with bluetooth) 

P2P

Peer to peer (Network model in which computers or hardware devices exchange files, “equal client” system where instead of accessing files from a server the “peer” computers just swap them amongst each other

Network

(Group of computer systems/hardware devices that are linked together through communication channels)

Importance of standards in the construction of networks.

• Play an important role

• Required for finding a common group for building their systems

• Interconnection products from various vendors would be difficult if not impossible

• General communication would also be very difficult

Protocol

• A set of rules for communication over a network / defines a format and the order of messages exchanged between two/more communicating entities as well as actions taken on the transmission. 

What is the purpose of the OSI Model?

• Open systems interconnection 

• Communication between different hardware devices was not possible

  • OSI model provides a standard way for this communication to take place

Interoperability

The ability of software and hardware on multiple machines and from multiple commercial vendors to communicate

OSI Model’s seven layers

1. Physical = Hardware, defines physical characteristics

2. Data = Physical protocol is assigned to the data

3. Network = Way the the data will be sent to the recipient device

4. Transport = Maintains flow control of data and provides error checking and recovery of data between devices

5. Session = Establishes, maintains and ends communication with the receiving device

6. Presentation = Takes data provided by the Application layer and converts it into a standard format that the other layers can understand

   1. Application = Interacts with the OS or application whenever the user chooses to transfer files/read messages or other network related activities 

Evaluate the use of a VPN.

• Encryption

  • Encodes data so that only a computer with the right decoder can read and use it

• Tunneling  

  • Involves establishing and maintaining a logical network connection

Data packet

Contains data traveling over a network. A very basic binary unit for communication over a digital network.

(Ensure) Data integrity

• Refers to the overall completeness, accuracy and constituency of data. Must be imposed when sending data through a network. Can be achieved by error checking/correction protocols. 

(Manage) Flow control

•  Used to manage flow of data among two different network devices, especially in cases where the sending device can send data much faster than the receiver can digest. 

  • Router: Built to manage a lot of data, whereas a desktop at the receiving end has far less sending or receiving abilities. Xon-Xoff is an example that syncs the sender with the receiver. 

(Prevent) Deadlock

• A situation where two nodes or processes are trying to access the same node at the exact same moment causing neither to be able to proceed. It is up to the relevant protocol to stop both and re queue them so they can happen sequentially.      

  • (Manage/control) Congestion = Refers to a network state where a node or link carries so much data that it may deteriorate network service quality resulting in queuing delay, frame or data packet loss and the blocking of new connections.

(Perform) Error checking

•  Refers to the techniques used to detect noise (interference) or other impairments introduced into data while it is transmitted from source to destination. Often makes use of parity bits, bits at the end of a packet that are calculated to be either a 0/1.

Redundancy

• Central concept in detecting or directing eros. A redundancy check is extra data added to a message for the purpose of error detection. 

Parity checking

The parity checking protocol determines whether bits in a transmission have been corrupted

Checksum

•  Method of verifying the integrity of digitally transmitted data. Can be computed in many ways, using different algorithms. 

Explain why protocols are necessary.

• Because without them, it is impossible to communicate between different networks. Without them, computers do not know how to interpret the signals coming through the networks. 

 Explain why the speed of data transmission across a network can vary.

• Data transmitted over a network is packaged and transported in small pieces of data. 

• Causes of data lag = Length of route, type of media, network congestion, traffic load, time of day, weather, infrastructure

  • More traffic = Slower data transfer on a particular connection.

Explain why compression of data is often necessary when transmitting across a network.

• Data compression = Involves encoding information to use fewer bits than the original data entity. Takes up less storage space and less bandwidth for transmission. The more compressed, the faster the sending. Consequence is that the data can be disseminated more rapidly. 

Lossless

• File after compression is restored fully.

  • PhotosL

Lossy

• Reduces a file permanently, eliminating certain information, especially redundant information. 

  • Never a TEXT. file or a file that cannot risk to be degraded

Radio wave

Can travel long distances and can pass through walls.

Microwave

Cannot penetrate into walls, used for one to one communication between sender and receiver

Infrared

 Cannot travel for long distances

Packet

• Unit of data that is routed between an origin and a destination on the Internet/any other packet switched network.

Packet switching

• Type of network in which relatively small units of data called packets are routed through a network based on the destination address contained within each packet. 

  • Network technology that breaks up messages into smaller packets.

Circuit switching

• Establishing a dedicated path between a sender and a receiver. Once the connection is established, it will exist until the connection is terminated. 

Advantages of a wireless network

• Uses unlicensed radio spectrum (Doesn’t cost anything)

• LANs can be set up without cabling (Does not take space/time to lay the cables)

• WiFi can support roaming between access points (People can switch from router to router automatically depending on the best connection)

• Global standards (eg. 802.11n)

• Setup costs are minimal (Many types are available on the market and they are affordable) 

• Convenience (Can have a connection everywhere)

• Mobility (Can access the internet outside their normal work environment)

• Productivity (Work can be accomplished from any convenient location) 

• Deployment (Reuires less than one access point)

• Expandability (Wireles networks can serve a suddenly increased number of clients with existing equipment)

  • Cost (It is not expensive)

Disadvantages of wireless network

• Interference (2.4GHz spectrum is often crowded with other devices)

• Limited range

• WEP (Easy to hack and WPA2 has solved this problem)

• Access Points (Can be used to steal data)

• Health concerns

• Security (Known to have weaknesses)

• Range (Additional access points must be purchased for wider range)

• Reliability (Wireless networking signals are subject to a wide variety of interference)

• Speed (Can be slow but modern ones are becoming faster)

  • Social (Led to changes in working patterns, social activities and raised health issues)

Please do not throw sausage pizza away

Physical Data Network Transport Session Presentation Application

Client

Computer system that requests services from a serve connected to another network

Server

A computer system that provides a service to other systems on the same network

Router

Connects multiple networks

VPN advantages

Tunneling (Data can be secured) Authentication (passwords etc)