Class of Service

1. Layer 2 Marking - CoS (Class of Service)
   1. There is a 3-bit field in the Layer 2 802.1q frame header which is used to carry the CoS QoS marking
   2. A value of 0-7 can be set (higher is better)
      1. The default value is 0, which is designated as Best Effort traffic
      2. CoS 6 and 7 are reserved for network use
      3. IP phones mark their call signaling traffic as CoS 3 and their voice payload as CoS 5

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OSI or TCP/IP Layer

CCNA Exam Topic

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