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Feb 2009 -- Due to time pressures, the ongoing development of 'rope' has been suspended temporarily.

ROPE Language Reference - "$tcp_check"

The TCP/IP protocol checksum from the packet being inspected.

RFC_793 describes this field like this.

Checksum:  16 bits

 The checksum field is the 16 bit one's complement of the one's
 complement sum of all 16 bit words in the header and text.  If a
 segment contains an odd number of header and text octets to be
 checksummed, the last octet is padded on the right with zeros to
 form a 16 bit word for checksum purposes.  The pad is not
 transmitted as part of the segment.  While computing the checksum,
 the checksum field itself is replaced with zeros.

 The checksum also covers a 96 bit pseudo header conceptually
 prefixed to the TCP header.  This pseudo header contains the Source
 Address, the Destination Address, the Protocol, and TCP length.
 This gives the TCP protection against misrouted segments.  This
 information is carried in the Internet Protocol and is transferred
 across the TCP/Network interface in the arguments or results of
 calls by the TCP on the IP.

                  +--------+--------+--------+--------+
                  |           Source Address          |
                  +--------+--------+--------+--------+
                  |         Destination Address       |
                  +--------+--------+--------+--------+
                  |  zero  |  PTCL  |    TCP Length   |
                  +--------+--------+--------+--------+

 The TCP Length is the TCP header length plus the data length in
 octets (this is not an explicitly transmitted quantity, but is
 computed), and it does not count the 12 octets of the pseudo
 header.

This is a read-only register.

This field is only relevant for TCP/IP packets, and will contain the value 0 for others types.

ROPE Language Reference - "$tcp_check"

See Also