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
