Protocol choices:

<X>    Xmodem checksum
<C>    Xmodem CRC
<K>    Kermit
<Y>    Ymodem (also known as Xmodem-1K)
<YB>   Ymodem Batch (also known as "true" Ymodem)
<Z>    Zmodem
<ZZ>   ZedZap (Zmodem variant, max 8kB block size)
<H>    HYDRA  (bidirectional with chat, this is the best)
<SZ>   Slow-Zmodem  (for non-8bit links, like Telnet)
<SH>   Slow-HYDRA   (for non-8bit links, like Telnet)