QoS Flashcards
Why do we need QoS?
because the standard network was created to satisfy streaming apps and not interactive ones.
Multimedia apps generate a continuous data flow that needs a continuous layout with the same date profiles at the sender and at the receiver -> real time apps
Which requirements do streaming and interactive apps have to satisfy?
- streaming: constant delay, limited loss
- interactive: low response time, high transmission bandwidth, low delays
What is the biggest problem of which QoS takes care?
Delay
Which are the required resources to have QoS?
- big transmission capacity
- larger buffers at network nodes
- switching capacity
- processing capacity
Which are the delay countermeasures?
traffic classification -> sophisticated scheduling -> traffic control
What is traffic classification for QoS?
each packet is identified by its unique quintuple (transport protocol) to know which type of QoS it needs.
This phase needs specific HW: CAM, ASIC -> giving them the quintuple they return the QoS needed
In what the QoS scheduling consists?
after classification the packet is put in MULTIPLE queues in order to be served intelligently.
It cannot be a simple FIFO because packets would be put in them randomly without for example prioritization
Which are the possible queues for QoS?
- round robin
-priority queuing - classed based queuing CBQ
- Weighted Fair Queuing - WFQ -> it ensures that each packet receives the same service as it had a dedicated link between it and the destination with a given bitrate
- deadline queuing
What is the traffic control for QoS?
It can be done in different ways:
- packet level
- calls/flow level
- a priori
QoS packet level traffic control
It follows the saying and policing approaches that for example use Leaky bucket ???
QoS calls/flow level traffic control
it consistes in a signaling mechanism with resource reservation in fact it uses RSVP or UNI. In this phase we can reject or accept a connection based on the resource availability
QoS a priori traffic control
It is done with Traffic or network engineering.
Traffic: it controls the traffic distribution along the network
Network: it sizes the network based on expectations and it limits the number of users
They both do some preventive and some throughout actions:
- preventive: the network is dimensioned for the worst case thanks to statistics on user traffic + there is a traffic matrix determined by the traffic distribution
- throughout: the network state is continuously monitored and based on the results the dimension and the matrix can change
CAC for QoS
Call Admission Control
- signaling: it signals infos about the generated traffic and the required service
- resource preservation
Which are the preventive and throughout actions for traffic and network controls?
They both do some preventive and some throughout actions:
- preventive: the network is dimensioned for the worst case thanks to statistics on user traffic + there is a traffic matrix determined by the traffic distribution
- throughout: the network state is continuously monitored and based on the results the dimension and the matrix can change
Which are the principles for QoS routing?
- finding a route with required resources
- using protocols that distribute real time infos -> very dynamic
- decisions are made based on available resources and topological info’s
- not stable with connection less data transfer
- crank back
