Is HttpWebRequest.GetResponse required to complete a POST?

For POST requests using HttpWebRequest, when I write to a request stream, at what point does the data get sent? Is it when I close the request stream or when I call GetResponse? Is the GetResponse call required?

The .net documentation does not seem to be very clear about what is really happening

Here's the code I'm curious about:

HttpWebRequest request = HttpWebRequest.Create(url) as HttpWebRequest;
request.Method = "POST";
request.ContentLength = jsonData.Length;
request.ContentType = "application/json";

Stream requestStream = request.GetRequestStream();

requestStream.Write(jsonData, 0, jsonData.Length);

requestStream.Close();

var response = request.GetResponse() as HttpWebResponse;

Thanks!