Computer Science - Networks

• Temporary storage

• Stores data in MBS

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

• Used for normal operations

• Writing data is faster

• 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

• 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

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

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

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

• 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

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

• Menus

• Buttons

• Toolars

• Ribbons

• Icons 

• Sliders

• Dialogue boxes

• GUI components

• Radio buttons / Checkboxes

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

•  Group of bits - 8 bits is a byte

• Computers use it to store data, BASE-2

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

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

• Binary data is stored as one or more bytes.

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

  • 00001010 becomes 11110101 (Swaps around) 

• By using binary code for ASCII characters

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

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

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)

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

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. 

(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.) 

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

 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)

 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.) 

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

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

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

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

• 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

• 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. 

• Open systems interconnection 

• Communication between different hardware devices was not possible

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

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

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 

• 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

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

• 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. 

•  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. 

• 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.

•  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.

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

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

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

• 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. 

• 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.

• 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. 

• File after compression is restored fully.

  • PhotosL

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

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

Can travel long distances and can pass through walls.

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

 Cannot travel for long distances

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

• 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.

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

• 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)

• 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)

Physical Data Network Transport Session Presentation Application

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

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

Connects multiple networks

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