RFC 1201 IP on ARCNET February 1991 introduces a third frame type: the exception frame. These three frame formats are shown here. Except as noted, each block represents one octet. Short Frame Long Frame Exception Frame +---------------+ +---------------+ +---------------+ | source | | source | | source | +---------------+ +---------------+ +---------------+ | destination | | destination | | destination | +---------------+ +---------------+ +---------------+ | offset | | 0 | | 0 | +---------------+ +---------------+ +---------------+ . unused . | offset | | offset | . (offset - 3 . +---------------+ +---------------+ . octets) . . unused . . unused . +---------------+ . (offset - 4 . . (offset - 4 . | protocol ID | . octets) . . octets) . +---------------+ +---------------+ +---------------+ | split flag | | protocol ID | | protocol ID | +---------------+ +---------------+ +---------------+ | sequence | | split flag | | flag: FF hex | + number + +---------------+ +---------------+ | (2 octets) | | sequence | | padding: 0xFF | +---------------+ + number + +---------------+ . . | (2 octets) | | padding: 0xFF | . client data . +---------------+ +---------------+ . (256 - offset . . . | (protocol ID) | . - 4 octets) . . . +---------------+ . . . . | split flag | +---------------+ . . +---------------+ . . | sequence | . client data . + number + . (512 - offset . | (2 octets) | . - 4 octets) . +---------------+ . . . . . . . client data . . . . (512 - offset . . . . - 8 octets) . . . . . +---------------+ +---------------+ These packet formats are presented as software would see them through ARCNET hardware. [3] refers to this as the "buffer format". The actual format of packets on the wire is a little different: the destination ID is duplicated, the padding between Provan