Congestion Control and Quality of Service Study Notes

  • The average data rate, peak data rate, maximum burst size, and effective band width are qualitative values that describe a data flow.
  • A data flow can have a constant bit rate, a variable bit rate, or traffic that is bursty.
  • Congestion control refers to the mechanisms and techniques to control congestion and keep the load below capacity.
  • Delay and throughput measure the performance of a network.
  • Open-loop congestion control prevents congestion; closed-loop congestion control removes congestion.
  • TCP avoids congestion through the use of two strategies: the combination of slow start and additive increase, and multiplicative decrease.
  • Frame Relay avoids congestion through the use of two strategies: backward explicit congestion notification (BECN) and forward explicit congestion notification (FECN).
  • A flow can be characterized by its reliability, delay, jitter, and bandwidth.
  • Scheduling, traffic shaping, resource reservation, and admission control are techniques to improve quality of service (QoS).
  • FIFO queuing, priority queuing, and weighted fair queuing are scheduling techniques.
  • Leaky bucket and token bucket are traffic shaping techniques.
  • Integrated Services is a flow-based QoS model designed for IP.
  • The Resource Reservation Protocol (RSVP) is a signaling protocol that helps IP create a flow and makes a resource reservation.
  • Differential Services is a class-based QoS model designed for IP.
  • Access rate, committed burst size, committed information rate, and excess burst size are attributes to control traffic in Frame Relay.
  • Quality of service in ATM is based on service classes, user-related attributes, and network-related attributes.


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