Data transmission (networking & cryptography) Flashcards
circuit-switching
establishes end-to-end connection at a fixed rate
packet-switching
many nodes inter-connected (e.g. internet) - traffic forwarded from one node to another until it reaches its destination
network protocol definition
rules to govern syntax and synchronization of communication
Protocol Data Unit (PDU) format
type | dest. add. | source add. | length | payload | error checking
OSI model layers
bottom -> top physical link network transport session presentation application
physical layer (OSI)
data encoding: how does receiver interpret frame? physical pins (which and what do they represent) Vin, digital/analog transmission
network layer
routing (routes frames across network)
subnet traffic control
logical/physical address mapping
builds headers
transport layer
ensures messages are delivered error free, in sequence, no loss (TCP)
session layer
allows two application processes on different machines to establish/use/end a session
presentation layer
“translator” of network layer and formats data to be displayed on application layer
data conversion, compression, encryption
application layer
FTP, IM, mail, printers
public-key authentication
two keys generated: both generate public keys, and Joe generates private key known only to Jill. To encrypt/deceypt, must use public key + private key.
internet model
bottom-top:
physical
network interface (MAC, ethernet, wifi)
network layer (routing, IP)
transport layer (host-host comms, UDP, TCP)
application layer (software comms, HTTP, DNS)
hash algorithm (concept)
produces short number from message of arbitrary length. Doesn’t operate in reverse.
authorization vs. authentication
authorization: enforces access rights to users, whereas authentication: verifies the message sender
CHAP (concept)
Challenge Handshake Authentication Protocol.
After the completion of the link establishment phase, the authenticator sends a “challenge” message to the peer.
The peer responds with a value calculated using a one-way hash function on the challenge and the secret combined.
The authenticator checks the response against its own calculation of the expected hash value. If the values match, the authenticator acknowledges the authentication; otherwise it should terminate the connection.
At random intervals the authenticator sends a new challenge to the peer and repeats steps 1 through 3.
Quadrature Amplitude Modulation (QAM) encodes information by changing the….
amplitude & phase
Asynchronous transmission (concept) - how are bits transmitted?
independent clock circuit out of phase with transmission- therefore must oversample 16 or more times the bit-rate. Can then count number of fractional pulses from start bit to determine first bit.
Baud rate (concept)
number of symbols transmitted per second
simplex (concept)
transmission possible in only one direction
WiMAX
think 4G
what are some challenges of WiFi?
The medium is less reliable., Interference form other spectrum users., A wireless node cannot transmit and listen at the same time., The channel is public., Hidden terminal problem., Exposed terminal problem.
If given the raw data of an ICMP request (ethernet frame), how would one tell the destination address?
First 12 hex bits
what was Aloha originally developed for?
to setup a radio network to link campuses of the University of Hawaii
how is a switch superior to a hub?
Supports full-duplex transmissions., Some collisions are avoided., Various device speeds can be mixed., Provides superficial privacy improvements., Overcomes chaining limits.
what is CIDR?
Classless Inter-Domain Routing; an IP addressing scheme that replaces the older system based on classes A, B, and C. A single IP address can be used to designate many unique IP addresses with CIDR. A CIDR IP address looks like a normal IP address except that it ends with a slash followed by a number, called the IP network prefix. CIDR addresses reduce the size of routing tables and make more IP addresses available within organizations.
IP address 10.168.10.67/25 is allocated to a system. How many hosts can be located on the same subnet?
128
ideal protocol for: byte stream guaranteed to be error-free and in sequence?
TCP
ideal protocol for: offers reliable byte stream?
TCP
ideal protocol for: data guarenteed to be error-free but out of sequence?
UDP
port (definition)
identify applications on hosts., for clients are dynamically allocated and ephemeral., for servers are fixed and well-known.
list the steps when you hit “send” on an email
- sends to SMTP server
- DNS server (translates mail@example.com to an IP address)
- encased in IP packet and send to destination via. routing
- reading of email takes place via IMAP (Internet Message Access Protocol)
pre-emptive multi-tasking (concept)
assigns time slots to processes
co-operative multi-tasking (concept)
waits for processes to return control to scheduler
what is Smart Grid and why does it matter?
a communication infrastructure that will allow all aspects of the electricity grid to talk to each other, from smart meters in houses to generation and transmission plants. This will be far more resource efficient as it will allow devices to adjust to weather/electricity supply conditions real-time!
two concepts about Smart Grid (talk about)
- WAN (Wide Area Network) - connects multiple NANs (Neighbourhood Area Network) to all components of the network - renewable generators, substations, transmission. Allows utilities to perform analytics real-time.
- ZigBee: the smart grid needs some sort of communications technology, and ZigBee offers just this: a low-cost, fast transmission tech. for short-range wireless data transfer.
