Multimedia Networking Flashcards
(81 cards)
What are the 3 application types of multimedia networking?
- Streaming, stored audio, video (i.e netflix youtube)
- Conversational voice/video over IP (i.e skype)
- Streaming live audio and video (i.e sports events)
What is streaming?
Video or audio can begin playout before downloading entire file
What is meant by stored audio in multimedia networking?
Audio or video that is stored at a server side, can be transmitted faster than audio/video is rendered aka there is buffering at the client.
What is jitter?
Variable network delay
In streaming if a client’s bit rate has jitter is this an issue?
No as there is a buffer so the video plays out at a constant rate to the client
Describe how client side buffering and playout interact?
- Initial fill of buffer until playout begins at t_p
- Playout begins and continues at a constant rate
- Buffer is filled at variable rate so buffer level varies
How does streaming over UDP work?
- Server sends at a rate appropriate for the client
- Sent rate = encoding rate = constant rate
In streaming over UDP how does congestion affect transmission rate?
- It does not
What is a normal length for playout delay?
2-5 seconds
What is the purpose of playout delay and in what kind of multimedia use is it for?
It removes network jitter and is used in streaming
What can be an issue with the UDP used in streaming services that are not faced by TCP HTTP
May not be allowed through firewalls, whereas TCP may be allowed through firewalls
How does streaming work with HTTP? (TCP)
- Multimedia file retrieved with HTTP GET
- Send at maximum possible rate under TCP
- Playout delay
Does the file rate fluctuate in HTTP streaming?
Yes it does, due to congestion control and retransmissions which ensure in order delivery
What is the difference between playout delay with UDP vs. HTTP (TCP) streaming?
- TCP has larger playout delay ensures more smooth TCP delivery rate than UDP
In adaptive playout delay what is the equation for packet delay estimation di?
di = (1-a)d(i-1) + a(ri - ti)
- di = delay estimate after ith packet
- a = small constant e.g 0.1
- d(i-1) = ith - 1 packet
- ri = time received
- ti = time sent
In adaptive playout delay what is the equation for average deviation of delay, vi?
vi = (1-b)v(i-1) + b|ri - ti - di|
-vi = average deviation of delay after ith packet
- b = small constant
- v(i-1) = previous average deviation after i-1th packet
- ri = time received
- ti = time sent
- di = packet delay estimation after ith packet
In adaptive playout delay what is the equation for the playout time of the first packet in a talk spurt?
Playout_time_i = ti + di + Kvi
- ti = time sent
- di = packet delay estimation after ith packet
- vi = average deviation of packet delay value
- K = some constant
What is meant by a one-size-fits all, best effort service model? and what is good about it?
Increasing link capacity so that congestion does not occur.
- Low complexity of network mechanisms
What is an issue with the one-size-fits all service model?
- High deployment cost: It is wasteful because the service will not always be busy - aka waste of money
What is an alternative to the best effort service model?
- Multiple classes of service model
What is the multiple classes of service model?
- Partition traffic into classes
- Network treats different classes of traffic differently
In the multiple classes model what 3 things should be considered to be able to maintain required QoS guarantees?
- A service level agreement is necessary (SLA)
- A policing mechanism needs to be in place
- Flows being allowed to use another flow’s unused bandwidth whenever.(SLA
What do packet classification and packet marking allow routers to do?
- Packet classification allows - router to treat different classes accordingly
- Packet marking allows router to distinguish among packets belonging to different classes of traffic
Why are policing mechanisms necessary?
- Provide a certain DEGREE of traffic isolation among classes, so that one class is not adversely affected by another traffic class that is misbehaving