domain immediately, made it become the standard that it is... ...People who suggest I make SIGNIFICANT changes to the protocol, such as 'full duplex', 'multiple outstanding blocks', 'multiple destinations', etc etc don't understand that the incredible simplicity of the protocol is one of the reasons it survived. Batch Transfers Another problem with XMODEM was that it required the transfer to be user-driven rather than automated. Typically this meant the user would navigate on the sender's system to select the file they wanted, and then use a command to put that system into the "ready to send" mode. They would then trigger the transfer from their end using a command in their terminal emulator. If the user wanted to transfer another file, they would have to repeat this process again. For automated transfers between two sites, a number of add-ons to the XMODEM protocol were implemented over time. These generally assumed the sender would continue sending file after file, with the receiver attempting to trigger the next file by sending a NAK as normal at the start of a transfer. When the NAKs timed out, it could be assumed that either there were no more files, or the link was broken anyway. MODEM7 MODEM7, also known as MODEM7 batch or Batch XMODEM, was the first known extension of the XMODEM protocol. A normal XMODEM file transfer starts with the receiver sending a single NAK character to the sender, which then starts sending a single SOH to indicate the start of the data, and then packets of data. MODEM7 changed this behavior only slightly, by sending the filename, in 8.3 filename format, before the <SOH>. Each character was sent individually and had to be echoed by the receiver as a form of error correction. For a non-aware XMODEM implementation, this data would simply be ignored while it waited for the SOH to arrive, so the characters would not be echoed and the implementation could fall back to conventional XMODEM. With "aware" software, the file name could be used to save the file locally. Transfers could continue with another <NAK>, each file is saved under the name being sent to the receiver. Jerry Pournelle in 1983 described MODEM7 as "probably the most popular microcomputer communications program in existence". TeLink MODEM7 sent the filename as normal text, which meant it could be corrupted by the same problems that XMODEM was attempting to avoid. This