Fundamentals of Communications & Networking Flashcards
How do you calculate bit rate?
Baud rate x Number of bits per second
What is baud rate?
The number of signal changes in the medium per second
What is bit rate?
Number of bits transmitted over the medium per second
What is bandwidth?
The range of frequencies a communication range is capable of transmitting
What is the relationship between bandwidth and bit rate?
Direct relationship (directly proportional - straight line through the origin graphically)
What is latency?
The difference between an action being initiated and its effect being noticed
What is a protocol?
A set of rules relating to communication between devices.
What is serial data transmission?
Data being sent one bit at a time over one communication line.
What is serial data transmission used for?
Transmitting data medium/long distances (peripherals to computer)
What is parallel data transmission?
Numerous parallel communication lines send multiple bits between components simultaneously.
What is a skew?
(Parallel) Each medium of a communication line has different electrical properties - bits sent together may not be received together.
What is crosstalk?
(Parallel) Signals from one line can leak into another - data corruption is caused.
Serial advantages?
No skew, no crosstalk, cheaper to install, more reliable (long distances)
What is Synchronous transmission?
When the clock signal is shared between sender & receiver and times when signals are sent. Signals are sent in regular intervals and in the same order they’re sent.
What is asynchronous transmission?
No shared clock signals, you instead use start and stop bits to indicate the duration of a transmission
What are the requirements for asynchronous transmissions?
Same baud rate and synchronising their clocks (for the duration of data transmission)
What does a start bit do?
Starts the receiver clock ticking and synchronises the receiver clock to the transmitter clock.
What does the stop bit do?
Provides time for the receiver to process the received data and allows next start bit to be recognised
Physical star network advantages?
- Easy to add and remove clients from the network
- Eliminates the possibility of collisions
- Failure of 1 cable doesn’t effect network performance
- Packets sent directly to recipient
Physical star network disadvantages?
- Expensive to install due to cabling
- If hub fails, all network communication is stopped
Physical bus topology advantages
- No central hub which reduces chances of network failure
- Cheaper to install as less wiring
- Cheaper installation costs
Physical bus topology disadvantages
Client-Server Networking - what is it?
One/more servers provide services to clients
Serverd are more powerful machines
How do clients get resources and services in a client server network?
What services can be provided?
Request services from the servers which then respond to the client with the requested service.
Emails, user accounts, print queues
Advantages and disadvantages of client-server networking?
Advantages:
Centralised security via server
Management of clients via server
Disadvantages:
Requires expertise to set up and manage
Cost of server
Cost of expert
Peer-to-peer networking - what is it?
No shared server
Each client has equal status on the network, services are requested from client to client
Advantages and disadvantages of peer to peer network?
Advantages:
Cheaper to install
Less expertise
Disadvantages:
If one client goes down, whole network stops working
Digital signatures in asymmetric encryption?
What is thick-client computing?
A network with clients powerful enough to not need a server.
Advantages & disadvantages of thick client?
Advantages:
- Less risk of collisions
- No expertise needed to set up
- Less expensive set up
Disadvantages:
- Harder to maintain
- No central security/software managements
What is thin-client computing?
The majority of the networks processing power belongs to the server(s), provides services to clients.
Advantages & disadvantages of thin client computing?
Advantages:
- Easy to add new client (inexpensive)
- Greater centralised network control
Disadvantages:
- Expensive set-up and maintenance
- Needs expertise
What are routers?
Used to send packets to the recipient via the fastest route (less hops/least congested).
What are gateways?
Used when there are different protocols in play - strips away packet details other than contents & gives new sender & receiver address which complies with new protocol.
Contents of a packet?
- Senders address
- Receivers address
- Packet contents
- TTL
- Sequence number
What is packet switching?
When data is sent in packets, each is sent to the recipient via the best possible route and reassembled when it reaches the recipient.
What is a uniform resource locator?
An address assigned to files on the internet.
What is a domain name?
Used to identify an organisation or individual on the internet - easy to remember.
What is a fully qualified domain name?
A domain that specifies an exact resource - can only be interpreted 1 way. Always uses server hosts name.
What is an IP address?
Assigned to every computer on the internet - hard to remember so we use domain names.
What is the DNS system?
Stores a table of FQDN and the corresponding IP addresses, a distributed database of mappings.
How are DNS servers organised?
Into a hierarchy
How do DNS servers support load distribution?
Returning 1 IP address from a list.
What are internet registries?
An organisation responsible for the allocation of IP addresses, only 5
What is a part of the internet registries work?
Protect the pool of unallocated IP addresses. When an IP address is requested, it looks for an unused one rather than a new one.
What are worms?
Pieces of malicious software that self-replicate between computers.
What are trojans?
Disguised as a benign file - spread as email attachments usually.
What are viruses?
Executable files that lie dormant until ran, spread over anything - priv network, the internet or flash drives.
How do we prevent malware?
- Good code quality
- Up to date software
- Have an anti-virus (which is utility software), scan the files and remove suspicious.
- Train employees about the risks of suspicious mail attachments.
What is WiFi?
Provides wireless networks, based on international standards.
How are wireless networks encrypted?
WPA or WPA2 - means a new client enters a password when logging into a new network.
How do you secure wireless network with SSID?
Disable the SSID broadcast so that only those who know it can connect, those in range who don’t know it can’t see it.
How do you secure wireless network using MAC address filter?
Whitelist - only allow specific devices to connect to a network.
Blacklist - block specific devices from connecting to a network.
Steps of CSMA/CA?
- Computer with data to send listens if channel is idle
- If not idle then wait
- When no data, sends a request to send
- receiver responds to RTS with clear to send
- RTS/CTS blocks any other transmissions
- sender transmits
- receiver acknowledges after all data is sent
- if no acknowledgment then resend after a random waiting period
IP address split into 2 parts..
Network identifier- Smaller networks have diff, each device on network has same
Host identifier- Different for each individual device
More bits on network identifier?
More different subnets.
More bits on host identifier?
More devices can be connected simultaneously.
IPv4?
- Has 32 bits
- Dotted quad numbers, 4 parts
- Each of the 4 parts has one byte
- 256^4 different IPv4 addresses
- Short supply
Why have we got IPv6?
Short supply of IPv4, num of devices that need this increasing so rapidly.
IPv6?
- 8 blocks
- Each has 4 hex characters
- 10^37 permutations
- Has 128 bits
Public IP addresses (routable)
Globally unique.
Most home addresses have 1.
Global authorities assign.
Private IP addresses (non-routable)
Millions of devices can have the same (has to be 1 per network though)
Packets are sent to this IP address.
DHCP?
Assigns IP addresses to devices (from a pool of available), once a device leaves the network the IP address is back in the pool.
NAT?
- Sends packets through the router (makes record of packet)
- Replaces private IP address of the computer with routers routable IP address
- (RESPONSE) sent to routers public ip address, forwarded to correct private IP address (using the record)
What is port forwarding?
Used when client needs to communicate with a server
- Client sends packet to public IP address of router
- Packets sent by client contain port num of application running on server that client wants
- private network router forwards packets to server using NAT
What is the client-server model?
Client sends request messages to server, server responds with response messages containing requested information.
What is an API?
A set of protocols relating to how different applications communicate with each other. Defines how interaction between the applications should be carried out.
JSON vs XML?
JSON is more compact, easier to read, easier to create and faster for computers to process.
XML is more flexible than JSON.
Port number for FTP?
20 and 21
Port number for SSH?
22
Port number for HTTP?
80
Port number for HTTPS?
443
Port number for POP3?
110 & 995
Port number for SMTP?
25, 587 & 465
What happens at the receiving end of TCP/IP stack?
Reverses!!
- Link layer: Removes MAC addresses
- Network layer: removes IP addresses
- Transport layer: uses port num to send to application, uses sequence num to see if it’s in right place
- Application layer: recieves packets & displays info
How do firewalls work?
Regulates the packets passing through a device & the internet
- can be software or hardware & be proxy server
Packet filtering?
Used by firewalls to accept/reject packets based on source IP address/protocol used
Stateful inspection?
Examines packets contents before deciding if it can enter the firewall.
Proxy server?
Sits between public & private network - manages packets moving between them
TCP/IP in order with protocols?
