Control word in review

• Layer 2 header fields may be discarded at ingress

• Control word carries variable “flag” bits

  • (FR FECN, BECN, C/R, DE, ATM CLP, EFCI, etc)

• Length required when padding small frames on links which have a minimum frame size

• Sequence number is optional. It is used to detect out of order delivery of frames.

Rsvd

bits

4

Length

8

Sequence Number

16

Control Word

Flags

4

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