Describe QoS considerations

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Questions derived from the 642-845 – Optimizing Converged Cisco Networks Cisco Self-Test Software Practice Test.


Objective: Describe QoS considerations
SubObjective: Explain the necessity of QoS in converged networks (e.g., bandwidth, delay, loss, etc.)


Item Number: 642-845.2.1.2
Multiple Answer, Multiple Choice


Which delay types are categorized as fixed delay? (Choose two.)



  1. Propagation delay
  2. Queuing delay
  3. Serialization delay
  4. Jitter


A. Propagation delay
C. Serialization delay


Propagation and serialization delays are examples of fixed delay. Propagation delay is the amount of time it takes to transmit the bits of a frame across the physical wire. Propagation delay is typically ignored because it is limited by the speed of light. On the contrary, serialization delay is the amount of time it takes to place the bits of a packet, encapsulated into a frame, onto the physical media. Most fixed delays are due to propagation delays whereas variable delays are due to queuing delays.


Queuing delay is the amount of time that a packet sits in a queue.


Jitter describes delay variation. Delay variation, or jitter, occurs when the end-to-end delay is changing. Voice and Video traffic can handle some delay as long as the delay is a constant number. However, if the delay from point A to point B is constantly changing, the quality of voice and video traffic will be affected.



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