Bit Oriented Framing( Flags) a flag is some fixed string of bits to indicate the start and end of a packet a single flag can be used to indicate both the start and the end of a packet In principle, any string could be used, but appearance of flag must be prevented somehow in data Standard protocols use the 8-bit string 01111110 as a flag Use 01111111..1110(<16 bits) as abort under error conditions Constant flags or 1's is considered an idle state Thus 0111111 is the actual bit string that must not appear in data INVENTED- 1970 by IBM for SDLC (synchronous data link protocol)Bit Oriented Framing (Flags) • A flag is some fixed string of bits to indicate the start and end of a packet – A single flag can be used to indicate both the start and the end of a packet • In principle, any string could be used, but appearance of flag must be prevented somehow in data – Standard protocols use the 8-bit string 01111110 as a flag – Use 01111111..1110 ( <16 bits) as abort under error conditions – Constant flags or 1's is considered an idle state • Thus 0111111 is the actual bit string that must not appear in data • INVENTED ~ 1970 by IBM for SDLC (synchronous data link protocol) Eytan Modiano Slide 8