Chap 2.1 - data transmission Flashcards
define data
info. translated for efficient transmission
define transmission
-movement of data from 1 device to another
define processing
-generating meaningful info.
how is a text sent
-text
-converted into binary
-arranged into data packets / datagram
-router
-internet
-person
define data packet
-data split into smaller bytes for transmission over a network
-contains header, payload, trailer
standard size of data packets
-64 KiB
what happens if data packet is small
-add 0’s
are data packets unlimited
yes
data packet structure for packet switching
-header
-payload
-trailer
what is in a header
-IP address of source device
-IP address of destination device
-sequence of packet (packet no.)
-size of packet in bytes
-total no. packets
-IP of router
-hop no.
what does sequence of data packet allow
correct reassembly of data packets
what is in payload
-data
what is in trailer
-method of identifying end of packet
-some form of error checking
max hop count
30
define packet switching
-forwarding packets form 1 router to another leading towards its destination
difference btw packet & circuit switching
packet:
-no fixed route
-diff speed for each packets
-have to reorder at arrival
-less expensive
-packets travel independently
-don’t reserve bandwidth
circuit:
-dedicated pathway
-uniform delay of packets
-packets are in order
-more expensive
-packets travel in same path
-reserve entire bandwidth
advantages for packet switching
-no single com. needed
-packet can be resent by rerouting if it fails = high speed transmission
-relatively easy to expand packet usage
-high data transmission rate possible
disadvantages of packet switching
-can be lost & need to resend
-more prone to errors for real time streaming
-delay at destination = have to reassemble
explain how packet switching works
-data is split into multiple packets
-each packet follows its own path to the destination
-routers determine the path
-rout is selected depending on no. packets in each router
-shortest path is selected
define bouncing packets
-packets move back & forth btw routers & never reach destionation
what happens after max hops
-packet is destroyed & resent
explain problems caused by bouncing packets
network could stop because lost packets mount up and ‘clog’ the system
how is an email sent
-email is broken into packets
-IP source, IP destination, sequence no., packet size, total no. packets added to header
-router checks hop no. and IP destinations of packet & determines shortest path
-packets takes diff routes and arrive at diff times
-packets are checked for errors & reassembled according to sequence no.
which form of switching is more reliable
circuit, has dedicated channel
how are the delay btw packets in circuit switching
uniform delay
how does circuit switching work
Connection establishment:
-all packets know entire path address
-data processed at source system only
-have fixed channel
Data transfer:
-delay btw packets is uniform
-resource reservation = fixed path = more wastage
Connection released
advantage of circuit switching
-dedicated pathway
-packet arrive in order
-no delay in transmission
-Ideal for certain types of traffic
disadvantage of circuit switching
-inefficient resource utilisation
-Delay when establishing channel
-higher cost = fixed channel
eg of packet switching
-internet browsing
-file download & upload
-emails & instant messages
eg of circuit switching
-traditional cell phone call
-Cellular voice call (Non-VoLTE)
-dedicated fax lines
types of transmission mode
-simplex
-half-duplex
-full-duplex
types of data transmission
-serial
-parallel
define simplex transmission mode
-data is sent from 1 direction
eg. comp - printer, radio station - person, TV - person
define half-duplex transmission mode
-data is sent from 2 direction but not at same times
eg. walkie - talkie
define full-duplex transmission mode
-data is sent from 2 directions at same time
eg. messaging at same time, live call
define serial transmission
-data sent 1 bit at a time over a single channel
eg. comp - printer via USB
define parallel transmission
-data sent in multiple bits over multiple channels
eg. internal circuit in comp
diff btw serial & parallel transmissions
serial:
-good over long distance
-data sent in correct order
-slower over short distance
parallel:
-good over short distance
-data not sent in correct order
-faster over short distance
what happens to data over long distance using parallel transmission
-parallel is better over short distance
-data is skewed
-longer the wire, more skewed
define USB
-Universal Serial Bus is a form of serial data transmission
what happens when device is plugged in comp
-comp. auto detect device from change in voltage in on data signal wire in USB cable
-device is recognised & device driver software is loaded for com.
-comp will look for device driver that match device. If not available, user is asked to download the software
advantages of USB
-devices plugged are auto detected & device drive is auto loaded up
-connection only 1 way = prevent incorrect connection
-is industry standard = considerable support available
-support diff transmission rate
-no need external power source
-error-free transmission = USB protocol notify to re-transmit if error detected
-backwards compatible
-easy to use
-high-speed data transmission
disadvantages of USB
-standard UBS support only 5m
-some early UBs may not be supported by latest comp.s
-slower data transfer rate than Ethernet
how much power does UBS cable supply
+5 V
USB types
-A
-B
-C
-mini A
-mini B
-micro A
-micro B
-micro B super speed
diff wires in USB
-black
-green
-white
-red
USB type C
-24 pin symmetrical connector
-smaller than older UBS connectors
-20V power connectivity = 10Gbps = support 4K video
-backwards compatible
how can packet switching cause errors in vid & sound
-pic & sound not in sync = packets arrive at diff times
-pauses in vid = time delay in assembling packets
-degraded vid & sound = competing traffic on con. link
-possible ‘drop out’ = packet take diff route & may get lost
note:
-when drawing serial half/ full duplex, draw 2 line - dotted & undotted
-be careful of which devices to use, eg need a web server
