SEAlink was not expected to operate over X.25 or similar links, and thus did not perform escaping. This was also needed so the zero packet would work properly, as this standard used the SYN character that WXmodem had re-purposed. On top of these changes, it added an "Overdrive" mode for half duplex links. This suppressed ACKs for packets that were successfully transferred, in effect making the window of infinite size. This mode was indicated by a flag in the zero block.