Networks and internet Flashcards
[PPQ] How are checksums used during communication?
The checksum is calculated from the data in the packet before it is transmitted, and is sent along with the packet. The checksum is recalculated at the receiving end, and if the two checksums do not match then the data has been corrupted
[PPQ] Why can parallel communication not be used at long ranges?
High risk that data skew will occur, and there could be interference between the multiple wires
What are the advantages of ring topologies?
Using a ring topology reduces the risk of packet collisions. The speed of data transfer also decreases less under heavy load
What are the advantages of bus topologies?
Cheaper, easier to install
What is a protocol?
A set of rules that govern how devices or programs should communicate
[PPQ] Explain the differences between the ways in which parallel and serial communication
is carried out.
Serial sends one bit at a time whereas
parallel sends multiple bits simultaneously. Serial uses a single wire whereas parallel uses several.
[PPQ] Why do peripherals use serial communication?
Parallel communication can only be used over short distances because of data skew (where bits travel at different speeds and arrive at different speeds)
[PPQ] What is baud rate?
Number of signal changes per second
What is a packet?
A container in which data is transmitted over networks. It contains the addresses of the recipient and the sender
What is a packet switched network?
A network in which data is set in packets. One message is split into multiple packets, each of which is sent to the recipient by the best possible route, before being reassembled with other packets
What happens to a packet as it goes through a network?
It passes through a number of routers before reaching its destination. A router uses the recipient address on a packet to determine where to send the packet. Every time that a packet passes through a router, a hop is said to occur.
What is a packet’s “time to live”?
The number of hops it can do before it’s deleted by the router
What are the primary components of a packet?
Sender’s address, receiver’s address, packet contents, time to live, sequence number
What are gateways?
Network devices that allow two networks to communicate using different protocols. It modifies packets by stripping away everything but the contents, and giving them new metadata which complies with the new protocol
What is the meaning of the “https://” part in a URL?
The protocol being used to acceess the file
What is the meaning of “www” in a URL?
Subdomain
What is a FQDN (Fully Qualified Domain Name)?
A domain name that specifies an exact resource and can only be interpreted in one way
What are IP addresses?
They are addresses that are assigned to every device connected to the internet. Since they are not user-friendly, easily-recognisable domain names map to IP addresses
What is a DNS (domain name server)?
A server that translates domain names into their corresponding IP addresses. DNSs contain large tables mapping domain names to IP addresses. If the website the user is trying to access is obscure or rarely visited, the DNS might not have it in its records, and will have to pass on the request to another DNS, meaning small websites sometimes take longer to load
What is an internet registry?
An organisation responsible for the allocation of IP addresses. They protect the depleting pool of unallocated IP addresses, When a new IP address is requested, an internet registry will first
look for a previously allocated IP address that has become unused rather than allocate a brand new IP address straight away.
What is a firewall?
Software or hardware that monitors incoming internet traffic and blocks it if it deems it to be malicious, based on its source IP address or the protocol it’s using
What is stateful inspection?
Examining the contents of a packet before deciding whether to allow it through the firewall
What is a proxy server?
A server that sits between a public network and a private network is called a proxy server. These devices manage every packet that passes between the two networks. Firewalls can be said to act as proxy servers. When a device in a private network sends a packet through a firewall and into a public network, the packet’s “sender” address is that of the firewall, rather than the device’s
private IP address. This provides some degree of anonymity.
What is a digest?
The value of the digest depends on the content of the message and will not be the same if the message is changed
How do digital signatures work [PPQ]?
- A digest of the message is created
- This digest is encrypted with the sender’s private key and appended to the message
- The message and appended digest are encrypted
with the recipient’s public key, meaning that only the
recipient can decrypt the information. - When the recipient receives the message, they first
decrypt it using their private key - The recipient creates a new digest from the message
- The digest is decrypted using the sender’s public key, to produce the original digest
- If the two digests match, the receiver knows the message was sent by the sender
What is a digital certificate?
A digital certificate verifies ownership of a key pair used in asymmetric encryption and can be used to check that a fake key pair isn’t being used by an impostor. Issued by certificate authorities, these files contain: a serial number, the owner’s name, an expiry date, the owner’s public key and the certificate authority’s digital signature.
What is CSMA/CA?
A protocol that allows multiple devices to transmit data at high speeds without interfering with each other
How does CSMA/CA with RTS/CTS work?
Computer with data to send monitors/listens for data signal
If another transmission in progress then continue to wait
When no signal present computer sends a Request to Send
Two computers could start transmitting simultaneously if they both detect there is no data signal
Teceiver/WAP responds (to RTS) with a CTS signal, which blocks any other transmissions from nodes in range
When CTS received then start to transmit. If CTS not received continue to wait (until transmission ends)
After transmitting the transmitter waits to receive acknowledgement packet (to confirm data received and not corrupted, notifies other computers that they can transmit again)
If no acknowledgement received, wait a random time period and listen again / retransmit.
