Protocols 1
What is FTP used for?
For transmitting and downloading files over a network.
What is meant by a protocol? [2]
A set of standard rules and guidelines which allow two or more devices to communicate over a network.
What is the purpose of TLS? [3]
Provides encryption, authentication and data integrity
What is a DMA? [2]
-Allows certain hardware to access RAM independently of the process.
-Initiate Data Transfer
— Processor is free to continue processing without being interrupted by the certain hardware (frees up the CPU to continue other tasks)
Define polymorphism.
- Redefine methods for different derived classes
- Allows the same method to take up different behaviours depending on which class is instantiated.
What is the difference between POP3 and IMAP?
Imap sends a copy of the email on the server to the client while pop send the deletes the original.
Imap is bi directional while pop3 is unidirectional.
What computational thinking skill is used to create the layers for TCP/IP?
Decomposition.
Explain what is meant by non-repudiation
Non-repudiation is that neither the sender nor the recipient should be able to deny that they were part of the data transmission which just took place
What conditions are needed to enter running state from blocked state?
You can't. You have to enter the ready state first and for that the required I/O operation needs to be completed for the blocked process.
Apart from a stack. which data structure could be used to evaluate an RPN expression.
A binary tree - it allows the use of both in-fix, post-fix notation.
What are the TLS and SSL protocols? [3]
Protocols used to authenticate other device in communication.
provide encryption.
ensure confidentiality and integrity of data.
Describe how the TCP/IP protocol can be viewed as a stack. [4]
Protocol is split into layers.
Each layer is pushed into the stack in this order Application-Transport, Internet, Data Link/Network Layer.
On the receiving end, each layer is popped out from the stack using LIFO so the first to be popped out is Data Link/Network Layer.
How can a message be sent using asymmetric encryption?
Both sender and receiver use an algorithm to generate their own pair of keys which they stored it on their computers.
The receiver will send the sender their public key and the sender uses the receiver’s public key to encrypt the document and then sends the encrypted document to the receiver. The receiver now uses their private key to unlock the document and decrypt it.
What is the difference between low-level and high-level scheduling? [4]
low-level:
-system assigns process to task based on priority level
-schedules which process are to be put from ready state to running state based on priority.
-Maximising efficiency of the system’s use of burst time and response time.
high-level scheduling
-chooses which tasks are to be process but not how
-loads task into ready queue
Explain the need for scheduling in process management. [4]
- More than one task can appear to be executed simultaneously
- High priority jobs can be completed first
- CPU is kept busy all the time
- Leads to highly efficient process execution
- Fair access to the CPU/prevents starvation
How does CSMA/CD resolve collision? [6]
Detect changes in voltage over a line
Indicates that there is a collision
Send out a jamming signal to all node to stop sending data
Every node will set a random time
Check if the line is free and retry its transmission
If transmission count is high then abort transmission
Describe the application of the Transport layer in the safe transmission of packets [4]
The transport layer ensures that packets arrive in sequence, without errors, by swapping acknowledgements and retransmitting packets if they become lost or corrupted.
It uses positive acknowledgement with re- transmission (PAR) which means it automatically re-sends a data packet if it has not received a positive acknowledgement.
Compare digital certificate and digital signature
Similarities: both used for authentication, both are unique to the owner, uses owner’s public key, make use of hash algorithm.
Differences: certificate obtained from issuing authority/signature created from a message, certificate provides authentication of owner/signature used to authenticate messages that are sent by the owner, certificate remains unchanged whilst it is valid/new signature created for every message, only certificate provides extra information, only signature makes use of a private key
What is the function of a PCB within processing states? [5]
Process Control Block is created in memory when data needs to be retrieved during execution time
current process state (ready, running and blocked)
process privileges
register values
process priority
amount of CPU time needed for process to be complete
unique process ID
Explain how an interpreter executes a program without producing a complete translated version of it.
Examines code line by line
Checks for errors
if no errors, executes the statement
if error, halts execution and reports the error
Repeated for every iteration present and also every time the program is run.
Explain CSMA/CA. [4]
CSMA/CA is effective before a collision.
CSMA/CA is generally used in wireless networks.
CSMA/CA minimises the risk of collision and is useful to avoid collisions as it works before data is transmitted.
CSMA/CA initially transmits the intent to send the data. Once an acknowledgment is received, the sender sends the data.
TCP is known as the host to host connection protocol. Explain how the process will work between two hosts: Host X and Host Y. [4]
Hosts can include clients and servers that send/receive data, provide services or apps.
Host ‘X’ will first of all send host ‘Y’ a segment (packet) which will include synchronisation sequence bits so that segments will be received in the correct order.
Host ‘Y’ will now respond by sending back its own segment (containing an acknowledgement together with its own synchronisation sequence bits).
Host ‘X’ now sends out its own acknowledgement that the segment from ‘Y’ was received.
Transmission of data between ‘X’ and ‘Y’ can now take place.
Describe the process of quantum key distribution [6]
The sender uses a light source to generate photons. The photons are sent through four random polarisers. The polarised photon travels along a fiber optic cable to its destination.
At the destination, there are two beam splitters (diagonal splitter and vertical splitter).
The beam splitter are chosen at random and the photon detectors are read, this is repeated until the whole of encryption key has been transmitted.
The recipient sends back the sequence of beam splitters that were used to the sender.
The sender now compares this sequence to the polarisation sequence used at the sending station.
The sender now informs the recipient where in the sequence the correct beam splitters were used.
This now ensures that the sender and recipient are fully synchronised.
This encryption key can be sent and received safely
How do processes access data when using virtual memory? [4]
Process executes the load process with Virtual Address (VA)
The OS/computer translates the address to a Physical address (PA) in memory
If PA is not in memory, the OS loads it from the HDD
The computer then reads RAM using PA and returns data to the program
Explain the different names for packets at each layer of TCP/IP and what they include
Different names are used as each layer adds its own header to the packet
Packets are known as frames at the data-link layer, Datagrams at the internet layer and segments at the transport layer.
Segments include sender/receiver port numbers, packet number and checksum
Datagrams include IP addresses (sender and receiver)
Frames include MAC addresses (source and destination), frame length along with checksum