How Qos works in Transport devices?

  • QoS is Quality of Service.

  • It aims to forward traffic efficiently and perform bandwidth utilization.

  • QoS used to classify traffic and assign specific priorities and forward the traffic based on priorities.

  • It helps handling real time traffic, voice and video efficiently and even data traffic.

  • QoS works with L2 and L3 frames and packets.

  • WDM and optical devices L2 cards support Qos protocols.

  • QoS has 4 processes :

    1. Classification
    2. Mmarking / policing
    3. Queing
    4. Scheduling
  • Classification means assign forwarding class for each traffic flow depends on types of information carried by packet, we have 8 forwarding class based on importance and type of traffic.

  • Policing means control bandwidth used by each traffic flow, identify whether the income traffic is over , below or within the committed rate.

  • Policing called coloring, we have colors for the packets.

    1. Red : if the incoming packet bandwidth is greater than the peak Information rate ( in that case we have to discard )
    2. Yellow : if the rate of packet is between the peak and committed data rate , in that case we will discard the packet only if congestion occurred
    3. Green : if the bandwidth is lower than the committed rate , in that case the packet Forwarded normally
  • Queing means put the traffic in it’s specific Queue , FIFO is First in First out , move the packet from ingress to egress Ports.

  • It’s about how to order packets into the egress buffer memory.

  • Scheduling means select the SLA ( service Level agreement ) for each packet , we have different schedulers types as below.

    1. Strict priority
    2. Round robin
    3. Weighted round robin
    4. Weighted deficit round robin

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