chapter 9 - multimedia Flashcards
(22 cards)
How is analog audio digitized?
Sample at fixed rate
quantize each sample
encode to bits
How is video size reduced?
removing redundency inside each image to compress frames
Use spatial and temporal redundancy
playout buffering
client buffers incoming data so they send in the right order and at the right pace
What are the 3 types of multimedia apps?
Streaming stored video
Conversational voice/video
Live streaming
Why is playout buffering needed?
smooth out delay jitter
ensure continuous playback
When is UDP used for streaming?
When low latency is needed
error recovery is done in the app
Why use TCP/HTTP for streaming?
Easier firewall traversal, reliable delivery
What’s the max tolerable end-to-end delay for VoIP?
400
What is interleaving in VoIP?
Instead of sending voice chunks in order, interleaving mixes them before sending
technique used to reduce the impact loss
What’s the difference between fixed and adaptive playout?
Fixed: play each packet after a fixed amount of time
Adaptive: calculates the delay dynamically based on network conditions - adjust time
What is voice over IP(VoIP)?
technology that lets you make voice calls over the Internet using IP
What does forward error correction(FEC) do?
adds redundancy so lost data can be fixed without resending anything
What is real-time protocol (RTP) used for?
Carries audio/video data with info like sequence numbers, timestamps, and payload type
What is an RTP timestamp?
tells us when media sample was created to help sync playback
What does Real-Time Control Protocol (RTCP) do?
Sends control reports to help apps adjust transmission quality
How does RTCP help sync audio and video?
Maps RTP timestamps to real clock time using sender reports
Does RTP guarantee delivery or timing?
No – routers treat RTP packets as best effort
What is a token bucket?
way to control the rate at which data is sent on a network
Why is (packet)policing needed?
To prevent traffic from exceeding bandwidth and harming other flows
What is Per-Hop Behavior (PHB) in DiffServ?
how each router along a packet’s path should treat that packet
What is DiffServ? - differentiated services
r providing different levels of Quality of Service (QoS) to different types of traffic on IP networks
marks packets with a DSCP field in the IP header
DSCP value tells routers what kind of service to give the packet
What’s the difference between RTP and RTCP?
RTP: carries media data
RTCP: carries control info (feedback, stats)
