Communication And Networking Flashcards
What is a symbol?
Pattern of bits represented by a signal
What is Baud Rate?
The number of signal changes in medium per second
1 baud = 1 symbol change per second.
What is bit rate?
Number of bits transmitted over medium per second.
Bit rate = Baud rate X Number of bits per signal.
What is bandwidth?
Range of frequencies in which a medium is capable of transmitting. - Higher bandwidth = higher bit rate.
What is latency?
Difference in time between action being initiated and it’s effect being noticed.
Usually increases with distance.
What is a protocol?
Set of rules relating to communication between devices.
Explain serial data transmission
Data sent 1 bit at a time over communication line.
Used for long distances computationally
Explain parallel data transmission
Numerous communication lines used to send multiple bits at a time
More lines used - more bits per second
What is skewing?
Data sent via parallel transmission arrives at slightly different times - each line slightly different. Over longer distances - bits may not be received together. - Long distances leads to overlapping.
What is crosstalk?
Communication lines packed to close - data can jump to another line causing data corruption.
State an advantage of serial over parallel
Doesn’t suffer crosstalk or skew - more reliable over long distances.
Cheaper than parallel to install.
What is synchronous transmission?
Clock signal shared by sender and receiver used to time when data is sent.
Often used within processor for FE cycle.
What is asynchronous transmission?
Use of start-stop bits rather than clock speed. Start-stop bits indicate duration of transmission.
Start bit always opposite stop bit.
Sender must use same baud rate and synchronise clock speed for duration of transmission.
What is a physical network topology?
Physical architecture of a network - Use of interconnected components
What is a star network topology?
Each client connected to central hub. Hub receives packet and sent to correct recipient.
Name some advantages and disadvantages of star topology.
Adv:
- Packets sent to recipient.
- Easy to add and remove clients
- no collisions - each device has own cable
- Failure of cable doesn’t affect network.
Disadv:
- Central point of failure (hub)
- Expensive to install
What is a bus topology?
Connects clients to single ‘backbone’ cable. Terminators placed at either end.
No need for central hub - just connect via backbone.
State some advantages and disadvantages of bus topology.
Adv:
- No central hub, less likely to fail.
- Cheaper to install - just cost of cable
disadv:
- packets sent via backbone - every client on network receives packets.
- High chance of collisions - 1 main cable connects many clients.
- Backbone failure brings down network
What is a logical network topology?
Flow of data packets within a network - Delivers packets to all clients on network.
What is meant by mixing topologies?
Connect clients in star topology, can run as a bus topology - sends packets to all devices.
What is client-server networking?
One or more central servers providing services to clients.
How does client-server networking work?
Clients on network request services form servers - respond with requested service.
- File storage
- Mail management
- user accounts
- print queues.
What is peer-to-peer networking?
Services provided by clients, not servers.
How does peer-to-peer networking work?
Each client has equal status
one client will be responsible for file management, another for mail storage etc.
Name a disadvantage of peer-to-peer
Each client must be running and fully operational - client responsible for files is faulty, no device can access their files.
Name some advantages of peer-to-peer.
More cost effective - no need for powerful server.
- Easier to set up and maintain.
- High performance without server.
How does wireless networking work?
Devices connect to wireless access point (WAP) which connects to network.
Allows for communications without cables.
What is WiFi?
Wireless Local Area Network (wLAN) based on international standards.
How are wireless networks secured?
Encryption. WPA or WPA2.
What is WPA?
WPA - WiFi Protected Access - requires new client enters password to connect to network.
WPA2 is slightly better than WPA with a longer password required.
What is SSID broadcast? What does disabling SSID broadcasting do?
Service Set Identifier - Name of the network.
Disabling SSID broadcast means devices need to enter the name of network to connect. `
What is a MAC address filter
MAC - Media Access Control
Filtering MAC addresses will mean only specific devices can connect to a network. MAC blacklists block specific devices connecting.
What is Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)?
Protocol used to avoid data collisions caused by simultaneous transmission.
How does CSMA/CA work?
Device listens to communication channel - check weather is idle - Only send if channel is free.
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What does CSMA/CA do if the channel is busy? What is Exponential Backoff Algorithm?
If channel busy, wait random time before checking again.
Exponential backoff algorithm - used to increase time period device waits with each check of the channel.
What is Request To Send / Clear To Send (RTS/CTS)?
Protocol which adds additional step to CSMA - Once transmitting device checked channel is idle, sends request to send (RTS) - If channel is idle, receives Clear to send (CTS). Otherwise waits before starting CSMA again.
Why is RTS/CTS required?
CSMA is not effective against hidden nodes - Cannot see some parts of network.
What is the Internet?
Network of interconnected computer networks - Uses end-to-end communication protocol.
Mostly wired network with cables passing under major oceans.
What is an Internet Service Provider (ISP)?
Company which provides customers with access to internet.
Largest ISP’s are national Internet Service Providers - Provide local ISP’s.
What is packet switching?
Data / message split into numerous packets, then transmitted via best possible route and assembled at recipient.
How do packets reach recipient from sender?
Packets pass through number of routers through best possible route. Each router it passes through, a ‘hop’ occurs.
What is TTL?
Time To Live
Each packet has finite number of hops it can do defined by it’s Time To live.
When TTL ends, packet is ‘dropped’ and sender resends packet.
What are the components of a packet?
Sender Address - Where packet was sent from.
Receiver address - intended recipient
Packet contents - Data packet is holding
TTL - Number of hops
Sequence number - Number of packets in a message. Identifies which position this packet is in relation to others.
What are routers and what are they used for?
Hardware which sends packets to recipient via fastest route - Lowest hops, least congested etc.
Hold tables relating to fasted routes for specific devices.
What is a gateway?
Hardware device which connects 2 networks with different protocols together.
Modifies packets so that it can travel across different protocol networks.
What is a URL?
Uniform Resource Locator
Address assigned to files on the internet.
Name the parts of the URL
Protocol - HTTP, HTTPS etc
Subdomain - Points to web server hosted at following domain - WWW .
Domain - Name of organisation - BBC
Directory - Where the file is being requested from - /news
Subdirectory - further location of file being requested - /technology
Name - What the file is called. - /index
File extension - Usually HTML
What is a domain name?
Identifies organisation or individual on internet - uses alphanumeric characters
What are fully qualified domain names?
Domain which specifies exact resource - only interpreted in one way.
https://bbc.co.uk/news/index.html
What are IP addresses?
Identifier assigned to every computer on the network.
What is a DNS?
Domain Name Server - DNS used to translate domain into corresponding IP address.
Each domain has direct relationship with IP address.
How do DNS’ work?
Table of domain names and corresponding IP stored.
If domain client is requesting doesn’t exist on certain DNS, passed onto another DNS.
What are Internet Registries?
Organisation responsible for allocation of IP addresses.
There are only 5 in the world.
What is the purpose of an internet registry?
Protect depleting pool of IP addresses.
When new IP requested, checks for prev allocated now unused before allocating brand new.
What are Firewalls?
Regulates packets passing through network.
Software or hardware, and can work as proxy server to perform packet filtering and stateful inspection.
What is packet filtering?
Method firewalls use to block or accept packets based on their source ip and the protocol they are using
What is stateful inspection?
Method used by firewalls which involves examining the contents of the packet before deciding to allow it through firewall.
Can sometimes keep track of what’s being sent - block anything not related to current activity.
What is a proxy sever?
sits between public and private network - manages every packet passing through 2 networks.
Data sent from private network adopts proxy address - some level of anonymity.
Explain how symmetric encryption works.
Both sender and receiver share same private key - used to encrypt and decrypt.
Sender and receiver exchange keys - can be vulnerable to interception.
Explain how Asymmetric encryption works.
use of 4 different keys - each device has pair of mathematically related keys ( public and private)
Message encrypted with recipients public key, corresponding private key can decrypt.
What are digital signatures?
Used to verify sender of a message - check message not tampered.
How do digital signatures work?
Digest of message created - hashing / checksum - Value depends on content of message.
Digest is encrypted with senders private key
Encrypted digest appended to message.
Message + digest encrypted with recipients public key - only decryptable by recipients private key.
Recipient receives and decrypts message and digest. - Digest matches means message was really sent by sender.
What are digital certificates?
Verifies ownership of key pair used in asymmetric encryption.
- Used to check fake key pair isn’t being used.
What is included in digital certificates?
Serial number, owners name, expiry date, owners public key and certificate authority’s digital signature.
What are worms?
Malicious software which can self-replicate within network or by users downloading infected files.
What are Trojans?
Type of malware disguised as benign file - email attachments / malicious websites
What are Viruses?
Malware requiring host file - usually executable files
How can malware be prevented?
Update software - particularly antivirus software.
Install antivirus software
Train employees about risks of opening suspicious files.
What is TCP / IP
Transmission Control Protocol / Internet Protocol - Used in all parts of the internet.
What are the 4 distinct layers in the TCP/IP stack?
Application - Selects correct protocol to transmit data.
Transport - Establishes virtual parth - end-to-end connection between sender and receiver.
