QoS Flashcards
What is meant with Quality of Servivce (QoS)
“A set of service requirements to
be met by the network while transporting a
flow”
For what type of applicationss is QoS particularly important?
for interactive and
latency-sensitive applications (telephony,
gaming, video streaming, …)
What happens to the traffic with QoS applied?
certain packets get treated differently, its more fair
Explain QoS deterministic service guarantees
network guarantees a
parameter is kept below/above some threshold for certain
application data
Explain QoS statistical service guarantees
network guarantees a
some percentage of traffic is kept below/above some threshold
What four things are required for achieving QoS?
- Service Level Specifications
- Classification
- Input control
- Scheduling
What is the difference between short and large buffer w.r.t. losses and delay?
- Short buffers, shorter delay, larger loss
- Large buffers, longer delay, smaller loss
What are some basic assumptions about QoS loss sensitive scheduling?
- 2 Priotities classes (high and low)
- Packets in same classare served in FIFO order
- Buffer has k postions
What is HoL and how does it work?
Head of the Line;
It is similar to FIFO, but it prioritises the high over the low packets
What is PBS and how does it work?
Partial Buffer Sharing;
Above threshold T, only high priority packets are placed in the queue, low are discarded. Below T it works like FIFO; no high over low.
What is POB and how does it work?
Push-Out Buffer;
An incomming high priority packet is allowed to push out a low priority packet from the queue
What are the variants of POB?
LIFO POB: last-
R POB: random-
FIFO POB: First-
low prio class is replaced
What is the contracted rate?
The maximum/optimal rate at which packets can be admitted.
Which elements guard the contracted rate?
QoS Input control
What happens to packets if token bucket is empty.
They either get tagged or discarded.
