1xx is an informational status code. It indicates that the request has been recieved and not rejected by the server and the process is continuing.
100 - The client shouldcontinue with its request. This interim response is used to inform the client that the initial part of the request has been received and has not yet been rejected by the server.
101 - The server understands and is willing to comply with the client's request, via the Upgrade message header field, for a change in the application protocol being used on this connection. The server will switch protocols to those defined by the response's Upgrade header field immediately after the empty line which terminates the 101 response.