(P2) Fundamentals of Communication And Networks Flashcards
Describe what thin client computing is.
Thin client computing are programs that are executed on an application server.
Explain two reasons why a thin client system is better than a thick client system.
Clients are cheaper as they have lower hardware specifications. Easier to add new clients. Simpler to update software.
Describe the relationship between bitrate and bandwidth.
Greater the bandwidth, the higher the bit rate. They are directly proportional.
Describe the difference of operation between of serial and parallel transmission.
Serial sends one bit at a time, but parallel sends multiple bits at the same time.
Explain why a laser printer with a built in wireless network adapter is likely to be a suitable choice for a small office.
Laser printer: cheaper than buying ink. Cheaper per page.
Wireless: Cheaper as no cabling. All devices can use it.
State one reason why IPv6 has been introduced to replace IPv4.
Not enough unique addresses in IPv4.
Explain how the CSMA/CA protocol with RTS/CTS is used.
- Computer with data to send monitors data signals.
- If data signal is present, then continue to wait.
- When no signal presents, computer sends Request To Send (RTS).
- Two computers could start transmitting at the same time if they both detect no data signal.
- Wireless Access Point (WAP) responds to RTS with Clear To Send (CTS) signal.
- RTS/CTS signal blocks any other transmission from nodes for specific time.
- When CTS received then start to transmit.
- If CTS not received, continue to wait.
- Reciever sends acknowledgement.
- After transmitting, the transmitter waits to recieve acknowledgement packet.
- If no acknowledgement then wait and listen again.
- Acknowledgement notifies other computers they can transmit again.
- Collisions cannot be detected by transmitter.
State two reasons why JSON is better than XML.
Less lines of code so take up less storage/ memory.
Easier for humans to read and debug.
State one advantage of using DHCP.
No requirements to manually assign IP addresses. Facilitates efficient use of a limited pool of IP addresses.
Explain how two or more computers connected to the Internet can have the same IP address and still communicate with each other.
Computers have private IP addresses. Network address translation (NAT) will be performed so that computers can communicate on the Internet.
Explain four different ways that a firewall can protect computers on a LAN.
Block specific protocols. Block certain types of packets. Firewall maintains information about current connections and only allows packets relevant to these connections through. Acts as proxy server.
Explain how Computer A will use a subnet mask to determine whether or not it can send the packet directly to Computer B across the LAN or if the packet must be send via the Internet.
AND operation of subnet mask with Computer A’s and B’s IP address. Result of each AND operation is the subnet ID. Subnet ID compared, if they are different packets, then must be sent through Internet.
Explain how packets are routed across the Internet.
Hierarchical organisation of routers. Path to take selected by each router. Route may change as a result of congestion. Route determined using the IP address. Router decrementing “time to live” of packet. Source and destination MAC address changed at each router.
Explain how the checksum can be used to determine if the recieved packets has been changed during transmission.
Checksum produced when packet transmitted. Checksum calculated from packet content. MOD operation used to limit magnitude of checksum. Recalculated checksum and compare. If these match, data is accurate.
State the name of two application protocols and their use.
SMTP- Send/ transmit emails
IMAP- Send and recieve emails
Explain how the transport layer of TCP/IP stack determines which application layer software on the server should deal with the received request.
It uses the port to determine which server should deal with the request.
Describe one function of the network layer of the TCP/IP stack.
Adds source IP address. Adds destination IP address.
Explain the difference between asynchronous and synchronous communication.
Asynchronous: The receiver and transmitter are not synchronised by a common clock.
Synchronous: The reciever and transmitter are synchronised by a common clock.
In asynchronous data transmittion, where are the stop, start and parity bit located?
Left to Right:
Stop. Parity. Start.
A message is to be sent from Computer A to B and will be encrypted using asymmetric encryption. To enable Computer B to authenticate that the message was sent by Computer A, a digital signature will also be sent with the message.
Explain how Computer B will decrypt the message and verify that it was sent by Computer A.
Receiver’s private key is used to decrypt message. Hash is calculated from the message. Sender’s public key is used to decrypt the digital signature. If both hashs match then the sender then the sender can be authenticated.
Explain why the DCHP system is used.
Reduces the need for expert knowledge when configuring a host. Facilities efficient use of a pool of IP addresses. Content of communication: Host sends to discover a DHCP server. DHCP server offers configuration to host. Host accepts offer of configuration from DHCP server by echoing the accepted to host.
What is the purpose of DHCP system?
To auntomate the configuration of hosts connecting to a TCP/IP network.
What is the key exchange problem with a symmetric cipher?
How to pass the key from sender to reciever as the key can be intercepted if transmitted.
Explain how External Routers are configured so that web servers can be accessed by computers outside of the network.
Trafiic arriving on the HTTPS port must be forwarded by the external router to the IP address on the Web Server.
Describe two security measures to keep a wireless access point secure and explain how these measures will make ut more secure.
Disable broadcast of SSID so that you must know the SSID to connect.
Use a MAC address whitelist so that only devices with an address on the list can connect.
Explain how the CSMA/CA access method with RTS/CYS will be used during thia transmission.
Computer with data to send listens for data signal. If data signal is present then continue to wait. When no data signal present, computer sends a Request to Send. Two computers could start transmitting at the same time if they both detect there is no signal. WAP responds to Request to Send with Clear to Send. RTS/CTS signal blocks any other transmission from nodes in range. When CTS is recieved, then start to transmit. If CTS not recieved continue to wait. Reciever sends acknowledgement. After transmitting, the transmitter waits to recieve acknowledgement packet. If no acknowledgement, wait a period of time. The acknowledgement also notifies other computers that they can transmit again. Waiting periods are often random. Collisions cannot be detected by transmitter.
Explain the difference between a symmetric and an asymmetric cipher system.
Symmetric: same key used to encrypt and decrypt.
Asymmetric: different but related keys are used for encryption and decryption.
Explain why serial communication is more appropriate than parallel communication when sending data over long distances.
Skew can occur where data arrives in the wrong order, which is likely to happen over long distances.
Bit transmitted together don’t arrive together.
Explain the difference between a physical topology and a logical topology.
Physical: the layout of the wiring between devices.
Logical: how data flows around a network.
Explain the difference between client-server and peer-to-peer networking.
Client-server: All data and resources are stored on the server. Setup requires greater expertise. Administration is easier.
Peer-to-peer: All devices have equal status. Resources are stored on each individual device. Any device can share resources with any other device on the network. A device can act as both client and server. Devices communicate directly with each other. No dependence on a server.
State one difference between HTTP and HTTPS.
HTTPS uses encryption to make it secure.
Identify the TCP/IP layer that is concerned with ports and explain how a client port and a well-known port are used when retrieving a web page.
Transport layer. Client port allocated to web browser by transport layer. Well Known Port: web server uses Well Known Port so that client is able to contact it to initate.
What is the purpose of a Domain Name System (DNS) server?
To take a required FQDN and return an IP address.
Describe two situations when a DNS query will not be sent to a DNS server.
The local computer already has a copy of the needed IP address in a host’s file.
The local computer has a cache of recent DNS queries.
What is encryption?
Using an algorithm to convert a message into a form that is not understandable without the key to decrypt it.
State two purposes of the addition of a digital signature to a message.
Verfiy the sender.
Detect if message has been tampered with.
Explain how a thin-client works.
Most processing is done by the central server. Work stations are just interfaces. Applications are not installed on thin client workstations.
Explain how choosing to use a thin-client network will affect the selection of hardware used by the system.
Higher bandwidth network connection required. Network must use switch not hub.
Explain what is meant by an IP address.
A numerical value assigned to a device.
State what is meant by the term protocol.
A set of rules for communication between devices.
Explain what a virus is and the diferenfes between a virus and a worm.
Virus is a program that attachs itself to another program. Self-replicating. Has malicious purposes. Viruses need human interaction to spread, and worms do not. Viruses are a sub-class of worm. Worms duplicate by exploiting a network security weakness.
Describe the steps that would be involved in producing a digital signature for a message before it is transmitted by a computer.
Digest calculated from message contents. Sender’s private key is used for hash encryption. Digital signature is appended to message.
Explain what asynchronous data transmission is and why stop and start bits are required when asynchronous data transmission is used.
Transmission of data without use of external clock signal.
Start but locks reciever and transmitter in phase.
Stop bit allows start bit to be recognised.
What is Baud Rate?
The number of signal changes in the medium per second.
What is Bit Rate?
Number of bits that are transmitted over the medium per second.
State the equation for bit rate.
Bit rate = Baud rate × No. of Bits per signal
What are the units for Bandwidth?
Hertz.
What is bandwidth?
Range of frequencies that a communication medium is capable of transmitting.
What is the relationship between bandwidth and bit rate?
Direct relationship.
What are the units for latency?
Milliseconds.
What is Latency?
The difference in time between an action being initiated and its effect being noticed.
Explain how serial data transmission works.
Data is sent one bit at a time over one communication line.
When is serial transmission usually used?
Over medium to long distances (e.g. mouse to computer).
Explain how parallel data transmission works.
The transimssion uses numerous parallel communication lines in order to send multiple bits between components in a computer simultaneously.
How is skew caused?
Communication lines that form part of a parallel communication medium will have slightly different electrical properties, meaning that the time taken for one bit to be transferred will differ slightly from line to line. Therefore, bits sent together may not arrive together.
State when skew is worse and explain what can happen as a result of this.
Worse over long distances.
Bits from different pulses overlapping, causing a corruption of data.
Describe a disadvantage of parallel data transmission.
More expensive because of their use of multiple lines.
Describe when parallel data transmission is likely to be used.
Over short distances. (Between parts of the processor and within RAM)
What is crosstalk and when does it occur?
Occur over parallel data transmission. When communication lines are tightly packed, signals from one line can ‘leak’ into another, causing corruption of data.
Explain two advantages of serial data transmission.
Doesn’t suffer from crosstalk or skew, which makes it more reliable, especially over long distances.
Uses just one line, so are cheaper to install than parallel mediums.
When is synchronous data transmission used?
Within busses of a computer’s processor in the fetch-execute cycle.
Explain why synchronous data transmission is more suitable for transmitting data in real-time systems.
Signals are sent at regular intervals, which will be recieved in the same order that they were sent.
Why does asynchronous data transmission not need a clock signal to work?
The start and stop bits indicate the duration of transmittion.
Explain how the start and stop bit are related.
The start bit must be a 1 or 0, and the stop bit has to be the opposite.
State two requirements for asynchronous data transmission between a sender and receiver.
Use the same Baud Rate.
Synchronise their clocks for the duration of data transmission.
Describe a physical star topology.
Each client has its own direct connection to the central hub
In a physical star toplogy, what is the hub responsible for?
Recieving packets for all of the clients connected to it and is responsible for delivering them to the correct recipient.
Give 4 advantages of a star topology.
- Packets are sent directly to their recipient, over a cable and so other clients cannot see packets that aren’t meant for them.
- Easy to add and remove clients to and from the network.
- Each cable has just one device communicating over it, eliminating the possibility of collisions.
- Failure of one cable does not affect rest of the network.
Give 2 disadvantages of a physical star topology.
- Should central hub fail, all communication over the network is stopped.
- Expensive to install due to amount of cable required.
Describe the components of a physical bus topology.
Clients are connected to a single cable called a backbone.
A device called a terminator is placed at either end of the backbone.
No need for a central hub.
Give two advantages for a physical bus topology.
- No central hub, so reduces chances of a network failure and decreases cost of installation.
- Inexpensive to install as a minimum length of a cable is required.
Give 3 disadvantages of a physical bus topology.
- Packets are sent through shared backbone, allowing every client on the network to see packets that aren’t mesnt for them.
- Backbone is used for communication by multiple clients, introducing the risk of collisions.
- Should the backbone fail, the entire network becomes unusable.
Describe a logical bus topology.
Network delivers packets to all clients on the network.
Describe a logical star topology.
Network delivers packets only to the intended user.
Explain what a host is.
A hostbis device on a network that provides services. They provide services such as file storage, printer sharing and internet access.
Explain what two components are needed for a wireless network to function.
Wireless access point, which can connect to a wired network.
Wireless network adapter in the devices that connect to the wireless network.
Explain how wireless networks are secured: WPA.
By encrypting transmitted data using WPA (WiFi Protected Access) or WPA2.
WPA requires that a new wireless client enters a password in order to connect to a network.
Explain a method of securing a wireless network: SSID.
Disabling SSID (Service Set Identifier) broadcast so wireless devices in range of the network can’t see the network is available, allowing only those who know the SSID to connect.
Explain a way of securing a wireless network: MAC.
Set up a MAC (Media Access Control) address filter. MAC address whitelists can be created to allow only specific devices to connect to a network. Or use a MAC address blacklist to block specific devices from connecting to a network.
What does CSMA/CA stand for?
Carrier Sense Multiple Access with Collision Avoidance.
What is CSMA/CA?
A protocol hsed in wireless networks to avoid data collisions caused by multiple devices communicating simultaneously.
Describe the process of CSMA/CA WITHOUT RTS/CTS.
- When a device is ready to transmit, it listens to its communication channel to check whether it is idle.
- If so, then data is transmitted.
- If the channel is busy, the device waits for a random period of time before checking the channel again.
How can a CSMA/CA waiting time period be increased?
Using an exponential backoff algorithm.
State a disadvantage of CSMA/CA.
Cannot overcome hidden nodes.
A problem that arises when the device checking for an idle channel cannot see some parts of the network on which there might be communication happening.
What does RTS/CTS stand for?
Request to send / Clear to send.
State the method of aolving the hidden node problem.
RTS/CTS
Describe the process of RTS/CTS.
- Once the transmitting device has checked whether the channel is idle, it sends a Request to Send message to the server.
- If the server is idle, it will respond with a Clear to Send message at which point the transmitting device can begin communication with the server.
- If no Clear to Send message is recieved, the server is busy communicating with a hidden node and the transmitting device must wait.
Define the Internet.
A network of inter-connected computer networks which use an end-to-end communication protocol.
What protocol is used by the Internet?
TCP/IP
What is a packet?
A container in which data is transmitted over networks.
Explain what a packet switched network is.
One in which data is sent in packets. One message is frequently split into multiple packets, each of which is sent to its recipient via the best possible route before being reassembled with other packets by its recipient.
When a packet is sent through a network, what does it have to pass through?
A number of routers before reaching its destination.
How does a router know where to send a packet?
Uses the recipient address on the packet to determine where to send the packet.
Define the term ‘hop’?
Hop refers to every time a packet passes through a router.
