When the Keep-Alive connection-token has been transmitted with a request or a response, a Keep-Alive header field MAY also be included. The Keep-Alive header field takes the following form:
Keep-Alive-header = "Keep-Alive" ":" 0# keepalive-param
keepalive-param = param-name "=" value
The Keep-Alive header itself is optional, and is used only if a parameter is being sent. HTTP/1.1 does not define any parameters.
If the Keep-Alive header is sent, the corresponding connection token MUST be transmitted. The Keep-Alive header MUST be ignored if received without the connection token.