Multi-length packet format including check sequence(s)

Details Multi-length packet format including check sequence(s) Multi-length packet format including check sequence(s)

1989-06-23

1990-10-09

Olms, Douglas W.

Multiplex communications

Wide area network

Packet switching

370 60, H04J 0324

Patent

active

049624989

ABSTRACT:
A unique packet transport word, i.e., header, format is disclosed which is advantageously employed to delimit the corresponding packet and to verify data fields in the transport word. An at least first parity check is employed in conjunction with a packet length indicator to delimit the corresponding packet. The at least first parity check is formed by computing a predetermined number of parity check bits from bits in predetermined bit positions of the transport word. These parity check bits are inserted into predetermined bit positions in the transport word. Similarly, bits representing the packet length indicator are also inserted into predetermined bit positions of the transport word. In a specific embodiment, a plurality of parity checks is employed to achieve increased robustness. The plurality of parity checks is formed such that each of the bits in predetermined bit positions of the transport word is used in computing at least two different parity check bits. In one embodiment, a first prescribed parity check is formed by computing parity over bits from predetermined bit positions in one or more groups of bit positions in the transport word and a second prescribed parity check is formed by computing parity over bits from predetermined similar bit positions in the groups of bit positions in the transport word. In one example the transport word includes a plurality of bytes each of which includes a predetermined number of bit positions forming columns and rows. Parity check bits forming the first prescribed parity check are obtained by computing parity from bits in predetermined bit positions in the transport word columns and parity check bits forming the second prescribed parity check are obtained by computing parity from bits in predetermined bit positions in the transport word rows. In this example, the first and second parity checks are obtained by so-called "group" processing and are adequate to both delimit the packets and verify the transport word data fields. These verified fields include, among others, the packet length and necessary information for delivery and "billing" of the packet.

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