Chapter 9: Multimedia Networking Flashcards
Give the definition:
Rounding of values where each value is represented by bits used with multimedia audio
Quantification
Give the definition:
Sequence of images displayed at constant rate
Video
Give the definition:
Array of pixels where each pixel is represented by bits
Digital image
What type of bit rate for multimedia video is this?
Video encoding rate fixed
Constant Bit Rate (CBR)
What type of bit rate for multimedia video is this?
Video encoding rate changes as amount of spatial & temporal coding changes
Variable Bit Rate (VBR)
Give the definition:
Using redudancy within & between images to decrease the number of bits used to encode an image
Video compression
What type of video compression is this?
Within the image
Spatial
What type of video compression is this?
From one image to the next
Temporal
Give the definition:
Can begin playout before downloading the entire file
Streaming
What two things compensate for network-added delay & delay jitter in the streaming of stored video?
Client-side buffering & playout delay
Which streaming stored video challenge is this?
Once client playout begins, playback must match original timing. However network delays are variables, so will need client-side buffer to match playout requirements
Continuous playout constraint
What is the relationship between the average fill rate (x) & the playout rate (r) under playout buffering when the following is the case:
Buffer eventually empties causing freezing of video playout until buffer fills again
x < r
What is the relationship between the average fill rate (x) & the playout rate (r) under playout buffering when the following is the case:
Buffer will not empty, provided initial playout delay is large enough to absorb variability in x(t)
x >= r
Give the definition:
Buffer starvation less likely with larger delay, but larger delay until user begins watching
Initial playout delay tradeoff
Does UDP always go through firewalls?
No
Does TCP/HTTP pass easily through firewalls?
Yes
Give the definition:
Accumulation of transmission, processing & queuing delays in routers; propagation delays in links; & end-system processing delays
End-to-end delay
Which requirement for VoIP is this?
Needed to maintain “conversational” aspect. Higher delays are noticeable & impair interactivity.
VoIP end-end delay one-way requirement
What part of VoIP is this?
How the callee advertises IP address, port number & encoding algorithms
Session initialization
Give the definition:
When the time from when a packet i generated at the source until it’s received at the receiver fluctuates from packet to packet due to varying queing delays experiences by the packets in the network’s routers
Jitter
What type of loss is this?
IP datagram lost due to network congestion (router buffer overflow)
Network loss
What type of loss is this?
IP datagram arrives too late for playout at receiver
Delay loss
What type of delay is this?
Delay processing queuing in network
End-system delay
What type of VoIP playout delay is this?
Receiver attempts to playout each chunk exactly q msecs after chunk was generated
Fixed playout delay
What type of VoIP playout delay is this?
- Estimates network delay & adjusts playout delay at beginning of each talk spurt
- Silent periods compressed & elongated
- Chunks played out every 20 msecs during talk spurt
Adaptive playout delay
How does the receiver determine whether a packet is first in a talkspurt if there’s no loss & the receiver loss at successive timestamps?
Difference between successive stamps > 20 msec –> talk spurt begins
How does the receiver determine whether a packet is first in a talkspurt if loss is possible & the receiver looks at both time stamps and sequence numbers?
Difference between successive stamps > 20 msec & sequence numbers without gaps –> talk spurt begins
What type of VoIP recovery from packet loss is this?
Sending enough bits to allow recovery without retransmission
Forward Error Correction (FEC)
What type of VoIP recovery from packet loss is this?
- Audio chunks divided into smaller units
- Packet contains small units from different chunks
- If the packet’s lost, still have most of every original chunk
- No redudancy overhead, but increases playout delay
Interleaving to conceal loss
Give the definition:
Proprietary application-layer protocol that’s inferred via. reverse engineering & has encrypted messages
P2P
What’s the name of the protocol that specifies packet structure for packets carrying audio & video data?
Real-Time Protocol (RTP)
What does RTP run on top of?
UDP
Does RTP provide any mechanism to ensure QoS guarantees?
No
What does the RTP header indicated?
Type of audio encoding in each packet
What part of the RTP header is this?
Indicated type of encoding currently being used. If sender changes encoding during call, sender informs receiver via. this field.
Payload type
What part of the RTP header is this?
Increment by one for each RTP packet sent. Enables detection of packet loss & restoration of packet sequence
Sequence number
What part of the RTP header is this?
Sampling instant of first byte in this RTP data packet
Timestamp field
What part of the RTP header is this?
Identifies source of RTP stream. Each stream in RTP session has a distinct SSRC.
SSRC field
