Key term
AQA A-Level Computer Science 7517
Fundamentals of Programming
Topic overviewData typesProgramming concepts and program structureArithmetic operationsRelational Operations, Constants and VariablesBoolean operationsString-handling operationsRandom numbers and exception handlingSubroutines, parameters and return valuesVariable scope and stack framesRecursive techniquesProgramming paradigms and the procedural approachClasses, Objects, Inheritance and PolymorphismAggregation, Composition, Class Diagrams and Design Principles
Fundamentals of Data Structures
Fundamentals of Algorithms
Theory of Computation
Topic overviewLogic Problems and Algorithm ConstructsPseudo-Code, Hand-Tracing and Program CorrectnessRepresentational Abstraction, Generalisation and Information HidingProcedural and Functional AbstractionData Abstraction and Problem ReductionDecomposition and CompositionAutomation and Finite State MachinesSets and Set NotationSubsets and Set OperationsRegular expressions and regular languagesBackus-Naur Form and syntax diagramsComparing Algorithms and FunctionsOrder of complexity and Big-O notationLimits of computation, tractability and heuristicsComputable problems and the Halting problemTuring machines
Fundamentals of Data Representation
Topic overviewNumber systems and the sets of numbersNumber bases: decimal, binary and hexadecimalBits, bytes and units of informationUnsigned binary and binary arithmeticSigned binary using two's complementFixed point and floating point representationNormalisation of floating point numbersRounding errors, accuracy, range and precisionCharacter coding systemsError checking and correctionBit patterns, analogue and digitalBitmapped graphicsVector graphicsDigital representation of soundMIDI and Data CompressionEncryption
Fundamentals of Computer Systems
Topic overviewHardware, Software and Its ClassificationSystem Software and the Operating SystemTranslators and the Role of the Operating SystemClassification of programming languagesTypes of program translatorLogic Gates and Their Truth TablesLogic Circuits and D-Type Flip-FlopsHalf-Adders and Full AddersBoolean algebra
Fundamentals of Computer Organisation and Architecture
Topic overviewInternal components, buses and von Neumann and Harvard architecturesThe Stored Program Concept and the ProcessorThe Fetch-Execute cycleThe processor instruction setAddressing modesMachine-Code OperationsShifts, Halting and Assembly Language ProgramsInterruptsFactors affecting processor performanceInput and output devicesSecondary storage devices
Fundamentals of Communication and Networking
Topic overviewCommunication methodsCommunication basicsNetwork Topology and Types of NetworkingWireless networkingThe Internet and Packet SwitchingRouting, URLs and Domain NamesFirewalls, Worms, Trojans and VirusesEncryption, Digital Signatures and CertificatesTCP/IPStandard application layer protocolsIP Address Structure and Subnet MaskingIP Standards and Public and Private AddressesDHCP and Network Address TranslationClient server modelThin- versus thick-client computing
Consequences of Uses of Computing
Systematic Approach to Problem Solving
Fundamentals of Databases
Big Data
Fundamentals of Communication and Networking
IP Address Structure and Subnet Masking
- 3 things to know
- Paper 2
Overview
Recall questions on how an address is structured, why it splits into network and host parts, and how a subnet mask is applied.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Apply the subnet mask 255.255.255.0 to the IP address 192.168.10.37. What is the network identifier and what is the host identifier?
Key term
Two machines have addresses 10.0.5.20 and 10.0.6.20, both with subnet mask 255.255.248.0. Are they on the same subnet?
Questions from this subtopic
Each one with the model answer underneath.
- 1
How is an IP address structured?
Model answer
An IP address is split into two parts: a network identifier and a host identifier. The network identifier part says which network the device belongs to, and the host identifier part identifies the particular device within that network. Every device on the same network shares the same network identifier and has a different host identifier.
- 2
Why is an IP address split into a network part and a host part?
Model answer
So that routing can be done in bulk. A router does not need an entry for every individual device in the world — an impossible task — only for networks. It compares the network identifier part of the destination address with its routing table, forwards the packet towards that whole network, and only the last router, the one attached to that network, needs to concern itself with the host identifier to make the final delivery.
- 3
In the address 192.168.4.27 with the network part being the first three octets, what is the network identifier and what is the host identifier?
Model answer
The network identifier is 192.168.4.0 and the host identifier is 27. Any other device whose address begins 192.168.4 is on the same network as this one.
- 4
Two devices have addresses 172.20.5.9 and 172.20.6.9, and the network part is the first two octets. Are they on the same network?
Model answer
Yes. With the first two octets forming the network identifier, both are on network 172.20.0.0; their host identifiers, 5.9 and 6.9, differ. They can communicate directly without a router.
- 5
How does a device know whether the machine it wants to reach is on its own network or a distant one?
Model answer
It compares the network identifier part of the destination address with the network identifier part of its own address. If they are the same, the destination is on the local network and the device can deliver the data directly to it. If they differ, the destination is elsewhere and the device sends the packet to its default gateway, the router that will forward it onward.
- 6
What is a subnet?
Model answer
A subnet is a smaller network created by subdividing a larger one. The host identifier part of the address range is partly given over to identifying which subdivision a device is in, so that one allocated block of addresses can be split into several separate networks.
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