How Qos works in Transport devices?

[Mohamed.Saeed]

• 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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