Unit 2.1 - Types and Methods of data transmission Flashcards
what are the 3 components in a data packet?
-packet header
-payload
-trailer
what does the packet header include?
-IP address of destination
-packet number
-originator’s address
-IP address of source
-sequence number of packet
-size of packets
what does the payload include?
actual data in packet
what does the trailer include?
-method of identifying the end of the packet
-form of error checking to make sure packet arrives error-free
what are the 5 steps of packet switching
-data is broken down into packets
-each packet could take a different route
-a router in each stage of transmission controls the route a packet takes
-packets may arrive out of order
-once the last packet has arrived, packets are reordered
what are the 5 methods of data transmission?
-serial
-parallel
-simplex
-half-duplex
-full-duplex
what is packet switching
message is broken up into a number of packets and each packet is sent independently, in its own path, from the start point to the end point.
what is circuit switching
Connection is made, data is transferred by packets, connection is released. each packet knows the entire fixed path which is provided by the source. Packets get sent one by one.
what are advantages of packet switching [4]
-no need to set up a single communication line
-re routing packets can overcome failed, busy, faulty lines
-easy to expand package usage
-high data transmission rate is possible (faster than circuit switching)
what are advantages of circuit switching [6]
-more reliable / secure
-dedicated pathway (consistent quality and bandwidth)
-no delay (no packet routing)
-predictable performance
-simple
-good for real time / continuous data transmission (voice calls)
what are disadvantages of packet switching [3]
-packets can be lost and need to be re-sent
-more prone to errors (real life streaming
-delay at the destination when the packets are being re-ordered
-less reliable than CS
-can’t handle real-time communication
what are disadvantages of circuit switching [5]
-INEFFICIENT RESOURCE UTILIZATION (WASTES PRODUCTS) (locks network resources even it isn’t being used)
-VULNERABILITY TO FAILURES (if one part of the circuit fails, the entire connection is lost)
-DELAY IN ESTABLISHING CONNECTIONS (setting up dedicated circuit and establishing communications takes time)
-HIGHER COST (maintaining is expensive because of dedicated channels and switches)
-outdated and no longer used
what are bouncing packets.
packets bounce from router to router and don’t reach their destination.
what are 5 differences of circuit and packet switching
-CS is physical path, PS is not
-CS packets all use the same path, PS packets travel independently
-CS reserve entire bandwidth in advance, PS doesn’t reserve
-CS bandwidth wastage, PS no bandwidth wastage
-CS no store and forward transmission, PS supports store and forward transmission
what is serial data transmission
data is sent one bit at a time, one after another as a single stream, over a single wire/channel
what is parallel data transmission
data is sent several bits at a time down several channels/wires at the same time (one channel = 1 bit)
when is serial data transmission used?
for long distances as it arrives synchronized
when is parallel data transmission used?
for short distances.
what are advantages of serial data transmission? [4]
-less risk of external interference (than parallel)
-reliable transmission over long distances
-bits won’t be out of synchronization (skewed)
-less expensive as there are fewer hardware requirements (than parallel)
what are disadvantages of parallel data transmission? [2]
-can become skewed (arrive unsynchronized) over long distances. (longer the distance, worse)
-more hardware is required so its more expensive (than serial)
what are advantages of parallel data transmission? [3]
-faster rate of data transmission (than serial)
-works well over shorter distances
-easier to program input/output operations
example of when simplex data transmission used
-computer to printer
-radio
-tv
example of when half-duplex data transmission used
-walkie talkies
example of when full-duplex data transmission used
-broadband internet connection
-video call
-telephone call
how is data transferred?
broken down into packets to be transmitted
how do you fix bouncing packets?
hopping. a hop number is added to the header of each packet and whenever the packet leaves a router, this number is reduced. there is a maximum number of hops and if the packet hasn’t reached its destination when the number runs out, the packet is deleted. the deleted packets need to be re-sent.
what is simplex data transmission
data can be sent in one direction only
what is half duplex data transmission
data can be sent in both direction but not at the same time
what is full-duplex data transmission
data can be sent in both directions at the same time
what are the disadvantages of serial data transmission? [1]
-Slow
when is packet switching used? [3]
-internet browsing
-emails / instant messaging
-file download and uploads
when is circuit switching used? [3]
-telephone calls
-voice calls
-fax lines
3 steps of when a device is plugged into a computer (USB)
-computer detects the device
-device is recognised and appropriate software is loaded up so that computer and device can communicate effectively
-if new device, computer looks for device driver that matches device. If not found, user is asked to download the appropriate software
Advantages of USB [7]
-device is detected and device drivers are loaded up automatically
-connections are one way (prevents incorrect connections)
-can support different data transmission rates
-no need for external power source
-error free data transmission (notifies transmitter to re-transmit data if errors detected)
-Easy to add more USB ports (USB hubs)
-is backward compatible (older versions are still supported)
disadvantages of USB
-standard USB supports 5m cable length, USB hubs are needed for longer
-very early USB standards (V1) may not be supported by latest computers
-data transfer rate is slower than ethernet connections
