4.9 - Fundamentals of communication and networking

Question 1

What are the 3 features of synchronous transmission?

Answer 1

Streams of bits are transferred over a communication channel at a constant rate

The transmitter and the receiver are synchronised using a common clock signal

No need for a start or stop bit - more information can be sent per unit of time

Question 2

What are the 2 features of asynchronous transmission?

Answer 2

There is no clock signal, so additional data (start and stop bits) is used to control the communication

Data is transmitted when it is available, rather than at specific intervals - there can be periods of time when the transmission channel is idle

Question 3

What is serial and parallel transmission?

Answer 3

Serial - data bits are sent in a sequence, one after the other, over a single wire

Parallel - several bits are sent at the same time over their own dedicated wires or printed circuit tracks

Question 4

What are the 4 advantages of serial transmission?

Answer 4

Can operate efficiently at higher bit rates - not affected by skew, and there are fewer wires in close proximity, which minimises crosstalk

Specific solutions that are not affected by interference, such as fibre-optic cables, can be used for transmitting over longer distances

Also uses fewer wires- cheaper to implement

Interfaces have fewer pins, so they are cheaper and easier to produce

Question 5

What are the 2 disadvantages of parallel transmission?

Answer 5

Only reliable over short distances and with lower bit rates than serial- mainly used inside a computer and in some early peripherals

Can be affected by skew and crosstalk when higher bit rates and longer wires are used

Question 6

What is skew and crosstalk?

Answer 6

Skew - happens when the bits that are transmitted across parallel links travel at different speeds

Crosstalk - occurs when electromagnetic interference between wires that are in proximity (such as parallel links) results in transmitting corrupted data that will need to be re-sent

Question 7

What are the 2 advantages of a bus topology?

Answer 7

Easy to connect nodes to network

Less cabling needed - cheaper to install

Question 8

What are the 3 disadvantages of a bus topology?

Answer 8

If two (or more) devices try to transmit at the same time, it will cause acollision - signals will interfere with each other

Every device attached to the bus can “read” every unencrypted message since signals are transmitted across the whole network - can be a security issue

A failure of the main bus cable will bring the whole network to a stop

Question 9

What are physical and logical toplogies?

Answer 9

Physical - the physical layout of the network

Logical - the flow of data packets around a network

Question 10

What are the 3 advantages of a star topology?

Answer 10

If one workstation fails, the rest of the network can continue to operate

New nodes can be added to the network simply by connecting them to the switch

Tends to have better performance - message is passed on to its intended node only

Question 11

What are the 2 disadvantages of a star topology?

Answer 11

Switch or hub is acentral point of failure - if it fails, none of the connected devices will be able to communicate or access network resources

Requires plenty of cable if wired - can be expensive in large networks

Question 12

What is a client and a server?

Answer 12

Client- a program that typically runs on a device used by an end-user such as a laptop or mobile phone

Server- a program on a computer that shares resources with, or provides services to, any authorised client

Question 13

How does a client-server network function? (2 points)

Answer 13

A client sends arequestto the server

The serverprocessesthe request and then sends aresponseback to the client

Question 14

What are the 2 advantages of a client-server network?

Answer 14

Servers can be located in secure rooms - easier to monitor a server room than to monitor every device on the network

Most important files are stored on servers - easier to make sure all files are backed up

Question 15

What are the 2 disadvantages of a client-server network?

Answer 15

High setup cost - servers will need to be set up and configured

If a server fails, many users will be affected

Question 16

How does a peer-to-peer network function? (4 points)

Answer 16

Every computer can be configured to share its resources - owner of each device gives permission to access some or all of the device’s resources

Peers can also share hardware such as printers or optical disc drives

Peers communicate directly with each other

Computers must be switched on to share resources

Question 17

What are the 2 advantages of a peer-to-peer network?

Answer 17

Low set-up costs - no additional devices needed

If one device fails, it has less impact - most users can carry on with their work

Question 18

What are the 2 disadvantages of a peer-to-peer network?

Answer 18

Workstations may be at multiple different locations, including at home - difficult to oversee

Individual users are likely responsible for backing up their own data

Question 19

What is WiFi and what is it used for?

Answer 19

A wireless local area network that is based on international standards

Used to enable devices to connect to a network wirelessly

Question 20

What are the 7 wireless networking components and what are their respective functions?

Answer 20

NIC (Network Interface Controller) - connects a device to a network

Hub - simply repeats messages to all connected devices

Switch - only sends a message to its intended destination device

Router - required to connect two separate networks when communication happens

Modem - modulates electrical signals so that they can be sent through a cable that uses a different technology

Network access device - makes it easier for home devices to connect to the Internet

Gateway - allows the transmission of data between dissimilar networks

Question 21

What are the 3 types of network encryption?

Answer 21

WEP - uses a symmetric encryption algorithm (same key is used to encrypt and decrypt data) to secure a network

WPA - generates new encryption key for each data packeted

WPA2 - encrypts each message several times depending on key size

Question 22

What does a router do and what are the 4 types?

Answer 22

Forwards data packets between computer networks

Types:
Edge routers -link one network to another

Subscriber routers- routers provided to homes and small businesses

Enterprise routers- routers that connect large businesses and ISP networks to the internet

Core routers- routers that are part of the Internet backbone

Question 23

What does a regular firewall do? (2 points)

Answer 23

Monitors both incoming and outgoing network traffic

Will attempt to prevent malicious traffic entering the network

Question 24

What is static filtering?

Answer 24

The process of a firewall checking the headers of the packets arriving from the untrusted network against a set of rules orpacket filtersdefined by the network administrator

Question 25

What is stateful inspection? (3 points)

Answer 25

Continuously monitoring incoming and outgoing traffic after a connection is established Analysing packet types, looking inside the payload of the packet rather than just the header, and checking for suspicious activity Requires the firewall to maintain a connection table (or state table), which keeps track of all of the conversations going on between the trusted and untrusted networks

Question 26

What does a proxy server do? (3 points)

Answer 26

Sits between the client device and the firewall Provides anonymity to the clients, keeping their true IP addresses hidden Can also keep a cache of websites and serve them from the cache wherever possible - speeds up user access and reduces network traffic

Question 27

What are the 7 steps of a digital signature being used?

Answer 27

1. Sender runs hash function against plaintext message to produce a digest/hash total 2. Sender encrypts digest with their private key 3. Sender attaches the ‘signature’ to their message 4. Sender encrypts the whole thing with receiver’s public key 5. Receiver uses their private key to decrypt it so they can read the message. 6. Receiver then uses sender’s public key to decrypt the digest 7. Receiver runs hash function on the plaintext and checks whether the digests match.

Question 28

What are the 4 layers in the TCP/IP protocol stack and their respective functions?

Answer 28

Application - selects appropriate protocol for the communication and interacts with the user via appropriate application software Transport - establishes end-to-end communication and splits application data into segments (TCP) or datagrams (UDP) Internet - prepares packets for the Internet by supplying IP addresses for appropriate source and destination Link - receives packets and adds MAC addresses

Question 29

What are the 2 other functions of the Transport layer?

Answer 29

Assigns sequence numbers and source and destination port numbers to the segment header Keeps a record of the incoming sequence numbers at the receiving end

Question 30

Define 'socket'.

Answer 30

A combination of an IP address and a port number; a TCP endpoint

Question 31

What are the 4 steps of DHCP (Dynamic Host Configuration Protocol)?

Answer 31

1. Discovery - device broadcasts out a discover message for a DHCP server when it starts up 2. Offer - when a DHCP server receives a request, it reserves an IP address for the client and sends an offer message to the client including the address, subnet mask, lease duration and address of server 3. Request - in response to the DHCP offer, the client broadcasts a request message with the details of the server from which it has accepted the offer 4. Acknowledgement - a packet is sent to the client that includes any other configuration information that the client requested

Question 32

What is thin and thick client computing?

Answer 32

Thin-client - a device that has limited main memory, limited secondary storage, and only basic processing capability Thick-client - a device that does most of its own processing and storage

Question 33

What are the 4 advantages of thin-client computing?

Answer 33

Cheaper to buy Software is always kept up-to-date by the provider - often available at no cost Arguably more secure - data not held locally Responsibility for backup is with the company storing the data

Question 34

What are the 2 disadvantages of thin-client computing?

Answer 34

Needs to be connected to the Internet Requirement for a decent amount of bandwidth as more data is transferred between client and server

Question 35

What are the 3 advantages of thick-client computing?

Answer 35

More robust and reliable - greater “up time” and availability of services Preferred solution when running heavy-duty/resource-hungry software applications Can be operated without reliance on constant connection to a central server

Question 36

What are the 3 disadvantages of thick-client computing?

Answer 36

Often more expensive - higher-spec client computers required Every client needs its own software installed - increases time and effort on part of network administrators More prone to integrity issues - due to non-centralised and distrusted nature