Communications and Network Flashcards
1
Q
What is serial transmission?
A
- Bits sent one after the other over a single wire from source to destination
2
Q
What is parallel transmission?
A
Multiple bits are sent simultaneously over parrallel wires drom source to destination
3
Q
What is skew?
A
- Problem in parrallel transmission
- Each individual wire has slightly different properties
- Meaning different travel speeds when sends bits
- Meaning parrallel is only suitable over short distances (motherboard)
4
Q
Why would you want to use serial over parrallel
A
- Skew means parallel wires are unreliable over short distances
- Serial is reliable over longer distances
- Serial is cheaper sinse there is only one less complex cable compared to parallel
- Crosstalk can occur bettween parrallel wires where there can be interference between lines leading to corruption which increases with signal
- Serial sufferes from little freqeuncy interference meaning it can carry higher frequencies meaning more data can be carried
5
Q
What is synchronous transmission?
A
- Data transferrred at regular intervals
- Sunchronised by a clock pulse signal
- Parallel communication makes use of synchronous transmission
- Useful for real time data
6
Q
What is asynchronous transmission?
A
- Each bit is sent speratly as soon as ready
- Each character set is paired with a parity bit and a start and stop bit
- Allows for reciver to know when new data has arrived providing a ga between sets of bits delaying the next.
7
Q
What is latency?
A
The time delay before some component in a computer system responds to an instruction
- Home device
- Satelite
- Server
8
Q
What is protocals?
A
- A set of rules for communication between devices
- Both devices need to use the same protocol to communicate
Controls for : - Transmission speed and method
- Error checking method
- Data transmission format
9
Q
What is bit and baud rate?
A
Bit rate is the numebr of bits that are transferred between devices in one second
BAud rate is the number of times a signal in a commnications channel changes state
10
Q
How do you increase transmission rate?
A
- Increase baud rate
- If there is more than two voltage states to encode binary
- The bitrate would be different compared to the baud rate
- As more frequencies can be produced
11
Q
How do you calculate bit rate of a channel
A
Bit rate of a channel (Bits per second) = Baud rate x number of bits per signal
12
Q
What is bandwidth?
A
The measure of the maximum capacity of a given communication channel
- The higher the bandwidth the greater the volum of data transmission
- AKA data transfer rate
13
Q
What is a network topology? + List the different topologies
A
The wat a network and its connected devices are connected
- Bus topology
- Star topology
- Mesh topology
14
Q
What is the advantages of bus topology
A
- Cheap to install
- Does not require additional harware beyond the main cable
- Easy to add more devices to the network
15
Q
What is the disadvantages of the bus topology?
A
- If the main cables the whole network goes down
- Performance degrades heavily with more devices
- Security is poor as all computers can see all data transmission
16
Q
What is the advantages of the star topology?
A
- If a single cable fails the issue is isolated
- Easy to add new devices
- Consistent performance even under heavy load
- Less likely to have data collisions
17
Q
What is the disadvantages with the star topology?
A
- Can be costly to setup and install due to alot of caballing
- If central node goes down the whole network goes down
18
Q
How do physical and logical topologies work together?
A
- Physical topologies would pyhsically connect devices together
- A bus topology protocal could be installed on one of the computers in the network
- Allowing for that computer to see transmission of data on the network
19
Q
What is client server model
A
- All devices are connected to a central server
- Personal files, software
- Server is a point of failure
20
Q
What is a peer to peer model?
A
- No central server
- No single point of failure
- Each computer acts as a client and server
- Good for internet sharing
- If one computer goes down then those files are inaccesible to the other devices on the network
21
Q
What is WIFI + advatages
A
- A common standard for wireless network
- Cheap and easy to install and maintain
- Can transfer and handle concorrunt data and users
22
Q
What are the components for wireless networking?
A
- Wireless network card
- WAP
- Modem + Router
- Internet
23
Q
What is SSID’s
A
- Service set identifier (Wifi name)
- Has to be used by all devices which want to connect to the network
- Automatically broacast to any wireless device within range of the WAP
- Can be hidden and requires a password
24
Q
What does CSMA/CA and RTS/CTS stand for?
A
Carrier sense multiple access with collision avoidence
Request to send/clear to send
25
Why does overlap occur?
- Multiple channels are used by multiple people
- Causing traffic within that channel
- When devices are sending requests.
26
What is CSMA/CA without RTS/CTS
1. Data you want to send is put into a packet
2. Is the channel idle? (device to wifi network)
3. NO = Wait YES = Move on
4. Then is transmitted across the network
27
How does CSMA/CA with RTA/CTS
1. Packet assembled
2. Is channel idle (Device to netowork)
3. No=Wait Yes=Request to send (RTS)
4. Then waits for Clear to Send Signal
5. No=Wait Yes=Transmit Data
28
Why do we use CSMA/CA with RTS/CTS
- Hidden node problem
- Devices can be out of range of each other but are in range of WAP
- So they cannot communicate causing collisions
- RTS/CTS is where the WAP double checks for the devices
29
What is the internet?
- Intercontinenctal fibre optic lines
- Allowing for large amounts of data
- Collection of domain name server routers
- Mapping webaddresses to ip addresses
30
What are Routers
- Recives packets on a networks
- FOrwards to correct destination on network
- Uses algorithm to determine best method to decide on best route to the destination device on the network
31
What are gateways?
- Recives packets on a network and sends to correct address
- Able to deal with packets using different protocals between devices
- First strips header data from header info leaving raw data and then uses a new header format needed for a destination network
32
What is a packet
- A bundle of data
- Wrapped up in addtional information
- For destination information
- Error checking
33
What is packet switching?
1. Network Interface Card (NIC) recive a message to send out data
2. NIC splits the message up into equaly sized packets and number with them + Calculates each packet
3. Packets are routed to ISP + Checks for packet errors
4. Packes are routed to next node (speed and selection is effected by bandwith and conjestion)
5. Packets arrive at the ISP of the destination computer
6. Destination computer and TCP re-orders the packets into the correct sequence
7. Protocal bits are stripped from packets and origonal data is passed to the application needing it
34
What is the protocals you have to know?
- TCP/IP
- FTP
- SMTP (POP3,IMAP)
- HTTP,HTTPS
35
What is FTP used for?
- File transport system
- Used for transfering files across networks
- Ports 20,21
36
What is SMTP and the sub protocols?
- Simple mail transfer protocal
- POP3 - Downloads local copy and then destroys server copy (Port 110)
- IMAP - Syncs with the server and then downloads the email (Port 143)
37
What is HTTP and HTTPS?
- Hyper Text Markup Transfer Protocol (Secure)
- Transfer of website data such as HTML
- Port 80
37
What is HTTP and HTTPS?
- Hyper Text Markup Transfer Protocol (Secure)
- Transfer of website data such as HTML
- Port 80
38
How does firewalls work?
- Only allows certain ports to be open
- Meaning external communication can only happen through those ports
- Meaning only wanted traffic comes through onto the network
39
What do proxies do?
- Sits inbetween the device and the netowrk firewall
- Blocks websites (blacklist)
- Caches static websites for faster loading
- Security
40
What is the TCP/IP protocols
- Transfer Control Protocol / Internet Protocol
- Four layers of network protocals (application, transport, network, link)
41
What is the application layer of the TCP IP stack?
- Layer uses the appropriate protocol relating to the data transfered
- HTTPS,FTP,POP3
42
What is the transport layer of the TCP/IP stack?
- Responsible for forming end to end connection
- Connection made -> data splits into packets
- Each packet has a sequence number, total number of packets, port number
- Required for packet switching for easy reassemble
43
What is the network layer of the TCP/IP stack?
- Uses the IP protocol
- Adds the source and destination IP to the packet
- This info is used by routers
- Sockets are formed from IP and Port
44
What is the Link layer of TCP/IP stack?
- Physical connection
- Adds the MAC addres of the source an destination devices as well as the destination router
45
What is a MAC address?
- 12 digit hex code
- Hardcoded during manufacturing of the NIC card
- Never changes and unquily identifies the device
46
What is the stucture of the URL
47
What are interet registers?
- Five org that governed by Internet coporationn for assigned names and numbers
- Hold database of all domain names
48
How are domain names organised?
- Domain names are structured into a hierachy fashion
- Smaller domains appearing lower down
- When written outyou go from bottom up
49
What is a Full Qualified Domain Name?
The host name as well as the domain name
www.codekuma.co.uk
50
What is a DNS?
- Domain Name System
- Internationally agreed strucutre which classifies the area an iternet resource resides
- Which is structured into a heirachy
51
What is a IP Address?
- Internet protcal address
- Unquie address given to a single network device
52
What are the steps in loading a website?
1. URL request by brower from user www.codekuma.co.uk/index.js
2. Browerser extracts FQDN and sends to DNS server
3. Local DNS server maps the FQDN to an IP and returns to brower
4. If DNS lookup table doesnt have the FQDN it passes the request to a regional DNS which has larger lookup table
5. If the regional DNS doesnt have the IP then the request is sent to the NSPand DNS which has even bigger tabels and is garenteed to have the address and is sent to user and to local ISP for future
6. GET request is sent to webserver
7. File returend to browser from server
53
What are the three methods of securing a network?
1. Firewalls
2. Prozy servers
3. Encryption
54
How do firewalls work?
- Filter communication into and out of a server
- Can be software or hardware or both
- Rules are set on the network like blacklists and whitelists
- Statefull packet insepction peaks into incoming packets and checks for patterns like virus
55
How do proxies work?
- Pyhsical computer between a network anda known source (webserver)
- All traffic passes in and out of a network
- Uses blacklists and whitelists and caches websites
- Ensures there is no single connection other than itself to the internet
56
What is encryption?
The process of encoding messages so that it ca be read only by the sender and the intended recipient
57
How does ceasar cipher work
- Shift the characters in a message
- By x number of places in the algorithm
58
What is symmetric encryption?
- Same key is used for encryption and decryption
- Vunerable to key interception or key duplication
- Senstive data transfers uses asynetric instead
59
What is asymetric encryption?
- Two keys are used to ecryption and decryption
- Form a key pair where one is a public and private key
- Pubic key stored on a key server
- Private key is kept secret
60
What are the steps inasymetric encryption
1. Public keys are exchanged between two people
2. Person 1 uses Person 2's public key to encrpt message
3. Person 1 also uses thier private key to encrpt again creating a combined key
4. Person 2 can then use thier own private key and Person 1's public key to decrypt the message
61
What can asymetric encryption allow for?
1. No one can read the mesage
2. No one else can change the message and is authentic as both keys are required
62
What are digital signatures and certificates used for?
- Additional methods to ensure data sent and recives is authentic
- Which is checked by a certification authority (trusted org that checks and approves digital certificates)
63
What is a digital signature?
- Uses a mathmatical function with a public and private key
- Creating a unique signature which is attached to the message before being sent
64
What are digital certificates?
- Method of making sure that an encrypted message is from trusted source
- The source will havea certificate from a certification authority
65
What are the steps in using digital signatures?
1. Hash function used on plaintext to produce a message digest which changes if message changes
2. Craig uses private key to encrypt digital signature and attaches to plaintext message
3. This is then encrypted using Daves pulic key and send to Dave
4. Encrypted message is decrypted by using Dave using his private key
5. Digital signiture is then extracted and decrypted using daves public key giving a message digest
6. Message digest then is regenerated applying hash function to plaintext mesage
7. Compare decrypted digest to regenerated digest to see if the message came from craig and is unchanged
66
How do viruses work?
- Attaches to host program
- Host file has to be opened
- Becomes resident in memory
- Infect other files via copying itself
- Spreads through lack of awareness
67
How do worms work?
- Subclass of virus
- Can spread without human interaction
- Self replicate and send to people via email
- Spreads through lack of awareness
- Exploits out of data systems
68
What are trojans?
- Disguised as trusted programs
- Creates backdoors to system
- Which allows unauthorised acess
- Doesn't infect or selfreplicate
- Exploits lack of awareness
69
How can you protect against malware?
70
What is a routable IP adress?
- IP adresses assigned to devices connected to internet
- Assigned by IANA ensuring te are unique and identified on a world wide scale
71
What are non-routable IP addresses?
- Assingned internally to devices on a private network
- Routers or global internet will reject them as they are in the private range
- Non-routable as no router will forward them on
72
What is DHCP?
- Dynamic host confiuration protocol
- A DHCP server is a device which is responsible for automatically ssigning a dynamic IPP adress
- On both Public and Private netowrks
- Solving shortabge of IPv addresses
73
What are the steps in connecting a phone to a wireless network?
1. DHCP discover message sent to router on a special IP
2. DHCP offer message sent from router on th special IP and gives an IP and the time its able to lease the IP
3. DHCP requests message sent from phone to ask to use that IP
4. DHCP ACK message approves and assigns the IP to the Phone
74
What is NAT?
- Network address translation
- Responsible for converting IP addresses as they pass over the boundry between public and private address spaces
- Via a router which has a public and private IP
75
What are the steps in NAT and Port Forwarding?
1. Computer on local network sends request to router with source and destination IP
2. Router then stores computer IP in the NAT translaion table and create a random port number and attaches onto router public IP
3. Request is sent to webserver from router with its own public IP and the given destination IP
4. Reponse is sent from the webserver to the route with the destination and source
5. Router then forwards the data to the private address of the computer in the network
76
What is an API?
- Application programming interface
- Set of protocols which define how two applications that can interact with each other
77
What is the websocket protocol?
- Modern API used for communication with a webserver
- Provides a modern, always open,bidirectional ,fast, real time interaction communication stream
- Saves transmission time, bandwidth speed and cost
- Used in games and instant messaging
78
What is a CRUD application?
- Create
- Retrive
- Update
- Delete
- Fundemental operations for any database or content management system
79
What is a REST API?
- Respresentational state transfer
- Client sends HTTPS request to webserver
- Allows for javascript to send a call a HTTPS request to server on webserver to database server (Where SQL quieries are sent)
- And a JSON or XML reponses given to the web server
- Webserver then passes on response to client browser
80
What are the different HTTP request methods and the related CRUD and SQL database function?
81
What is JSON
- Like XML which are both standards fortransfering data between a server and an application
JSON prefered due to:
- Syntax is simpler
- Morecompact due to not needing tags like XML
- Easier to understand
- Easier to process using a javascript fuction with less issues between numeric values and characters
82
What is client thickness?
Refers to the amount of processing and strorage that a client does compared to the server
83
What is Thick-client computing?
- Majority of processing and storage on client
- Little processing and storage done on server
84
What is thin-client computing
- Very little processing and stroage done on client
- Majority of processin and storage done on server
85
What are the advantages of Thick client computing?
- More robust and reliable meaning greater uptime and avaliability of services
- Prefered for heavy applications
- Doesnt rely on connection to server independent operation
86
What are the disadvanages of thick client computing?
- More expensive with higher spec needed
- Every client needs its own software installed and maintained - time consuming
- More prone to integrity issues due to being non centralised
87
What are the advanages of thin client computing?
- Software upadates done once and applied to every computer
- Easy to setup and configure
- Secure data stored on only server
88
What are the disadvanages of thin client computing?
- Relient on server, if server goes down computer is unusable
- Requires expensive powerful server
- Higher demand on bandwidth
