Which FTP transfer mode reduces data size during transmission to improve…

FTP (File Transfer Protocol, RFC 959) supports three data transmission modes:

1. Stream mode — the file is sent as a continuous stream of bytes, exactly as stored, with no extra processing. This is the default mode.

2. Block mode — the file is sent as a series of data blocks, each preceded by a header that carries a byte count and descriptor codes.

3. Compressed mode — the data is compressed before transmission. It uses run-length encoding: a run of n identical data bytes is replaced by a short two-byte code, and long strings of filler bytes are collapsed into a single byte.

Only the compressed (compression) mode reduces the size of the data during transmission, which increases bandwidth efficiency on large transfers at a small extra CPU cost. Encapsulation, multiplexing and fragmentation are general networking concepts, not FTP transmission modes, and none of them compresses the data.

Hence the correct answer is Compression Mode.