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Computing - A Level OCR (Paper 1) > Networks > Flashcards

Networks Flashcards

1
Q

What is a network?

A

Connected devices that can communicate, share resources and data

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2
Q

What are protocols?

A

Rules and standards that govern how networks should function and communicate

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3
Q

What is a topology?

A

Theoretical arrangement of the comments of a networks. Actual arrangement is influenced by physical factors and cost

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4
Q

Draw a ring, bus, star and mesh topology and explain the +/- of each

A

Picture can be found in photo Library
Star: + no data collisions, fast, robust, cheap +hub can be node switch etc, can be split into segments
Ring: +few collisions due to one way traffic, fast, one cable (cheap), passes through NIC of each node
- if one node fails the whole network could
Mesh: +Decentralised, wired or wireless, no single point of failure, no need for Internet and directly communicate, Good for communication
- lots of expensive cable
Bus: + simple, cheap (one cable)
- lots of collisions, if the cable breaks so does the network, slow with heavy traffic

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5
Q

What is a LAN?

A

Local Area Network. Nodes connected are geographically close

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6
Q

Benefits/properties of LAN?

A
  • organisation owns infrastructure
  • allows communication
  • Allows peripherals to be shared
  • Allows data to be shared
  • Can log on from any connected computer
  • easy upgrade and virus scans
  • Can run a program simultaneously on multiple devices
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7
Q

1) What is a WAN?

2) What is a MAN?

A

1) Wide Area Network - result of joining multiple LANs via satellite, fibre optics cables, telephone cables, or a mixture - nodes a re geographically distant
2) Metropolitan Area Networks, provide WAN services in a city

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8
Q

Properties of WAN?

A
  • infrastructure owned by 3rd party

- Same properties as WAN but it allows it at a much further distance

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9
Q

What is a SAN? Give an example

A

Storage Area Network - used for large scale storage of data in data centres
Email servers, databases and high usage file servers

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10
Q

What Is a PAN?

A

Personal Area Network - Used for transmission among devices such as computers, smartphones and tablets - can also be used to connect to high level networks or Internet

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11
Q

Advantages and disadvantages of cloud storage?

A 
\+Data moves off site
\+Maintained by third party
\+Cheaper
\+scalability
-Loss of control 
-Security issues (?)
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12
Q

What are the properties of a peer-peer network?

A
  • All nodes have = status
  • All share files and peripherals
  • each node can be accessed by another peer
  • speed decreases due to lots of collisions
  • Implemented over Internet
  • Used for legal and illegal file sharing
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13
Q

What are the properties of a client-server network?

A
  • Traditional architecture
  • Dedicated high spec machine is server
  • centralised data storage
  • Allows processing of shared files, printing, Internet access
  • manages security
  • Clients request access to services from the servers (file server, web server, printer server etc)
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14
Q

What are data centres?

A

Multiple servers stacked together

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15
Q

What are virtualised servers? +/-

A

One server is split into multiple “virtual servers” using cloud computing.
+Efficient
+Lower energy consumption

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16
Q

What is the OSI and why was it created?

A
  • Open systems interconnection evolved to create a standard of communication between different device types. Describes protocols that allow comps with different architectures to be linked together so that they can share data and communicate with each other
  • just a model
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17
Q

Describe the 7 layers of the OSI

A

Application - Network aware applications. what the user interacts with (email, web browsing etc)
Presentation - converts data between formats required for different applications +transmission over network. Eg: Compression, encryption and translation
Session - Controls communication between connected devices. Starts connections, manages them and terminates them. User login rights, file/folder perms
Transport - Guarantees end to end delivery of data. Make sure data is present and that it gets to destination
Network - Transmits and routes data via shortest possible path across network. Shortest time not distance
Data Link - decides whose turn it is to send/receive data
Physical - Physical properties of network (cable, bit encoding, transfer rates etc)

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18
Q

What is the TCP/IP stack?

A
  • A suite of protocols that describes how data is sent over a network
  • Not just a model
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19
Q

Four layers of the TCP/IP stack?

A

Application - Production, communication and reception of data, makes sure data in correct format
Transport - Session layer + responsible for providing constant flow
Internet - provides links to transmit datagrams across different networks
Link - Passing Datagrams to local and physical network. Allows network hardware Independence therefore allowing it to operate over any transmission medium such as copper wire, optical fibre etc

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20
Q

What does PDU mean?

A
  • Protocol Data Unit - Term used to describe data on any given layer of the stack
  • Application = data
  • Transport = Segment/Datagram
  • Internet = Datagram
  • Network access layer = frame/bits
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21
Q

What term is used to describe data on all levels instead of there associated PDU?

A

Packet

22
Q

How do each of the four layers identify the source and destination address of data?

A

Application - just data no addressing needed
Transport - Data broken into segments that use ports to identify services
Internet - Devices have unique IP address, IP datagrams use IP address to reach correct destination
Link - Ethernet splits packets into frames. Frames use MAC address of device to reach it

23
Q

What devices are used on each layer of the TCP/IP stack and OSI and what do they do?

A
  • Physical = devices that extend the physical network (repeaters/transceivers)
  • Data Link = Devices that make decisions based on MAC address of sender/recipient (bridges forwards frames to destination MAC address and switches which are bridges with multiple ports)
  • Internet/Network = devices examine data packets and make decisions based on IP address of sender/recipient (Router examines contents and finds appropriate network to route data to based on IP)
  • Transport = devices examine segments and make decision base on port number. Firewalls use port numbers
  • Application = devices examine contents of data and make decision based on content (Checking email for spam). Application layer gateway
24
Q

What is a Datagram?

A

A self contained unit of data that is the basic unit of data used in transmission. Allows data to be treated independently from one another which increases reliability

25
Q

Negatives of Datagram?

A
  • Sent without a pre defined route meaning no guarantee that it will reach destination
  • No confirmation of successful transmission
  • Order of sending/receiving not considered
26
Q

What is a domain name?

A

Name for location of resources on the Internet - unique to each site. Stored in DN server and each have a corresponding IP

27
Q

What is a domain name server?

A

Phone book of Internet - translates URLs into IP address. Easy and quick to update. No meaningful characters to remember

28
Q

Properties of circuit switching?

A
  • Data split into packets
  • Connection established via dedicated route
  • No other traffic can use route till transmission has ended
  • Packets of data all follow same route
  • continuos flow of data
  • Arrive in sent order
  • Hacker can intercept data as route is known
29
Q

Example of circuit switching?

A

Telephone calls

30
Q

Properties of packet switching?

A
  • Data broken into packets
  • Packets travel multiple routes
  • More efficient
  • No dedicated route
  • best path for packet is determined along the way by the router
  • Takes longer to assemble
  • Hackers can’t intercept
31
Q

Describe each part of a data packet?

A

Header - Contains source and destination address, sequence number and protocol
Payload - Contains data
Trailer - Contains checksum and end of packet

32
Q

What is a WAP? +/-?

A
  • Allows wireless devices to connect to a wired network
  • Uses WI-FI Bluetooth or related standards
  • usually connects to routers
  • Can rely data between wireless and wired devices
\+No physical setup 
\+Quick to add new nodes
\+Flexible deployment of nodes
\+Allows visitor access 
-Lower performance
33
Q

Advantages of private network?

A
  • Control over security
  • control over who has access to what
  • Control over what software is provided
  • Confidence of availability
34
Q

What methods are employed in order to minimise risks of private networks?

A
  • Redundancy = essential equipment is duplicated
  • Sensible backup regime = there is always a copy of essential data stored somewhere else
  • failover systems = detect abnormalities and automatically transfer operations to an alternative system
  • Disaster recovery plan =necessary so that in the event of a major failure, procedures are in place to limit the impact of the failure and remedies are applied effectively
35
Q

What is network layering?

A
  • Problems can be broken into components each of which is easier to solve than the whole
  • Example of divide and conquer
  • different aspects of the networks functionality are conceptualised and developed separately
  • Each layer concentrates on itself and only communicates with layers adjacent to it
  • Are an abstraction: solve problems by identifying common patterns in real situations
36
Q

What are the levels of domains?

A
  • Top level = .uk, .edu, .fr, .com
  • second level = .org, .co
  • Third level = OCR, BBC, hodder
37
Q

What is a NIC?

A
  • network interface controllers. Work on physical layer
  • Circuits that were plugged into a computers bus to produce signals that are placed on the transmission medium and also receive signals from it
  • designed to work with particular network standards (most commonly Ethernet)
  • Most computers now built with Ethernet circuitry built into their motherboards rather than requiring cards as ads-on
38
Q

What is a MAC address?

A
  • 48 bit ID allocated to a network device by the manufacturer
  • quoted in readable groups of six bytes (octets as there are 8 bits in each byte) and then converted in hexadecimal (eg; 08:01:27:0E:25:B8).
  • The first 3 octets ID the manufacturer of the equipment. The others are allocated in a way decided on by the maker too ensure each address is unique
39
Q

What is a router?

A
  • Device that connects networks
  • receives data packets from one network and forwards them to another network based on the address information in the packet
  • work out where to send a packet according to either a table of info about neighbouring networks or by using an algorithm to determine the optimum next step for the packet.
  • each router knows its closest neighbours and can therefore work out the optimum route.
40
Q

How do routers differ between needs?

A
  • home use = small routers that connect the users computer to the ISP
  • business use = powerful high speed routers which are able to direct traffic according to the needs of the moment
41
Q

What is a wireless access point?

A
  • allow temporary connection of devices to a network
  • BOYD common in business, university and public WI-FI
  • allow connection of up to 100 meters. Allows signals to be intercepted
42
Q

How does a WAP protect its ID?

A

-Hiding the SSID: A broadcast signal that ID’s a WAP, useful when network is to be used by outsiders

43
Q

How does a WAP protect its signals?

A

-Encryption: WEP (Wired equivalent privacy) uses a static key of 40/60 bits to encrypt data. Drawback is all devices have to know the key. WPA and WPA2 have replaced this. They involve once-only cryptographic keys

44
Q

What is the other way WAP protect themselves?

A

-limiting access: only allowing a certain list of MAC addresses to connect. Not practical when many new and unknown devices are likely to be connected

45
Q

What is authentication? +/-

A

Users ID themselves with a user ID and confirm they are who they say they are with a password.
-easy to obtain a users password
-can be brute forced
+Most corporate networks require additional security such as a security device
+Captchas used to prevent automated attempts to gain access

46
Q

What are Firewalls?

A
  • Hardware, software (or a combination of the two) that control the traffic into and out of a network
  • can be set up as a series of rules so that individual web addresses or specific computers can be blocked from accessing the network, or cannot be reached from within the network
  • rules can be applied that cause messages containing certain words or other streams of bits to be filtered out
47
Q

What is Packet filtering?

A
  • Used in firewalls
  • examines data packets as they pass the firewall and can reject them if they match a preset pattern.
  • Operates at the lowest 3 levels of the OSI model
  • other methods retain packets until it is established whether they are part of an existing message of the start of a new connection (check in revision textbook if this is right)
48
Q

What are proxies?

A
  • Proxy servers can act as firewalls. Computers interposed between a network and a remote resource
  • if a user on the network requests a resource such as a web page, the request is picked up by the proxy server. This then either passes on the request to the destination or does not if the resource is on a banned list.
  • The response is passed back to the proxy server, which may or may not forward it to the user.
  • Never any direct contact between the users computer and the remote resource
49
Q

What is encryption?

A
  • transformation of data in such a way that unauthorised people cannot make sense of it
  • used in networks because of risk that data might be intercepted
  • Secret key is used to transform the original data and an algorithm is applied to that key
  • critical part of VPN’s because the infrastructure is shared with a number of users
50
Q

What is special about the algorithm applied in encryption?

A
  • The algorithm is called a ciphertext
  • the receiving device needs to have access to that key to decrypt the ciphertext and restore the original plain text message
  • large keys more successful than small ones (64 bit mainly used)
  • keys often subdivided so that parts are used to produce successive stages of encryption

Computing - A Level OCR (Paper 1) (15 decks)

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