After the client has received the server's greeting, which includes the server's PVN, the client then responds by sending its own greeting. Like the server's greeting, the client's greeting also includes a PVN and a vendor string:
ODSIMSrequested_version[(vendor_string)]
The client's greeting differs from the server's greeting, however, in that rather than sending its best supported PVN, the client instead sends its requested PVN, based on an evaluation of the server's stated PVN and the clients knowledge of its own capabilities.
If the client and server have the same capabilities, then the client simply issues the same PVN as the server.
If the client is newer than the server, then the client simply settles for the server's PVN and a reduced feature set.
If the client is older than the server, then the client issues its best support PVN and hopes the server will be willing to support an older protocol..
The vendor string is any string preferred by the client vendor that identifies the client. The server operator may use this string to collect statistics about the connecting clients. This field is completely optional, and if omitted, the parenthesis should also be omitted, rather than sending empty parenthesis.