Multimedia Networks Flashcards
What are the 3 application types of multimedia networking?
- streaming stored
audio/video - Conversational voice/video
over IP - streaming live audio/video
What is client-side buffering?
- initial fill of buffer
- playout begins (at t_p)
- buffer fill level varies over
time (fill rate x(t) varies and
playout rate r is constant)
Why is HTTP used for streaming multimedia?
- file retrieved via HTTP GET
- send at max rate under TCP
- fill rate fluctuates due to TCP
congestion - larger playout delay = smooth
TCP delivery rate
Why is UDP used for streaming multimedia?
- server sends at rate
appropriate for client - short payout delay to remove
network jitter - error recovery at application
level
What is the equation for playout time for first packet in talk spurt?
playout time_i = t_i +d_i + Kdv_i
how does a one size fits all service model work?
increase link capacity so congestion doesn’t occur
what are the disadvantages of a one-size fits all service model?
- low complexity of network
mechanisms - high deployment costs
What is a multiple classes of service model?
- partition traffic into classes
- network treats different
classes differently
What are the 4 principle QoS guarantees for network mechanisms
Service Level Agreement
Policing mechanism
Unused bandwidth
Call admission
Why do we need an SLA (service level agreement)?
packet classification = router treat different traffic classes accordingly
packet marking = router can distinguish packets belong to different classes
Why do we need a policing mechanism?
- provide degree of traffic isolation among classes
- one class not adversely affected by another that’s misbehaving
Why do we need an unused bandwidth mechanism?
- whilst providing isolation between flows, want to use resources efficiently
- flows allow use of another flow’s unused bandwidth at any time
Why do we need call admission?
- sufficient resources not always available
- before accepting new call, flows declare QoS requirements
- network can deny if cannot meet needs
What is priority queuing?
multiple queues to classify as high/low priority
What is weighted fair queueing?
- generalized round robin
- each class gets weighted amount of service in each cycle
What are the tasks of queue management?
- remove packets from a queue on request from packet scheduler
- discard/remark packets if queue full/saturated
- proactively avoid queue becoming congested
What is packet removal/discard policy and what are some examples?
if packet arrives to full queue what do we do?
- tail drop = drop arriving packet
- priority = drop on priority basis
- random = drop randomly
What is random early detection (RED)?
- drop packets randomly from selected flows
- when queue length exceeds threshold
What is a 2 queue length threshold?
- if buffer average below min threshold, no congestion
- if buffer above max threshold, drop packets with p= 1
- if buffer between min and max, drop packets with p = p
What is random early detection with in/out (RIO)?
- assumes edge router marking of packets conforming to SLA
- conforming packets in profile
- non-conforming out of profile
- out of profile packets dropped first if core router has congestion
What is the goal of a policing mechanism?
shape traffic so it doesn’t exceed declared/agreed parameters
What are the 3 commonly used criteria for policing mechanisms?
- Average rate: packets sent per unit time
- Peak rate
- Burst size: max no of packets sent consecutively
What do combine token/leaky bucket and weighted fair queueing provide?
Upper bound on delay
What are the 2 approaches on internet quality of service?
Fina grained approach
- provide QoS for individual applications or flows
Coarse grained approach
- provide QoS to large classes of data or aggregate traffic
