# Header Compression

WinVN will now support the three styles of header compression currently in use. These protocols were developed individually by several different news providers and all use slightly incompatible formats. WinVN should be able to automatically determine the correct format to use.

Header compression provides a significant advantage to the newsreader client by being able to reduce the amount of data sent receiving article lists by up to 10x or higher (depending on content).

Three compression protocols

Giganews implemented a protocol that compresses all list data sent by the server, so group-lists, XOVER and XHDR data is all sent in compressed format. Once negotiated by the client, all list data is sent in binary GZIP compressed format. The client must enable header compression by issuing a XFEATURE command.

Astraweb uses a compression protocol when a client can ask for an article list in compressed format using the XZVER / XZHDR commands, and Astraweb will return the data as yEncoded ZLIB compressed data. It does not compress the group list.

Usenet Server/Diablo is similar to Astraweb, but sends data in GZIP compressed format instead.