what byte/bytes do you send to conclude a HTTP server response?
There is no marker -- rather, in the HTTP response header there is a Content-Length field describing the length of the response body
If you're interested in examining and learning about the HTTP protocol, I would download the tool Fiddler at http://www.fiddler2.com/fiddler2/
You can then look "behind the scenes" at what happens when you visit a web page and see the request and response text.
From RFC 2616(HTTP 1.1)
HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all protocol elements except the entity-body (see appendix 19.3 for tolerant applications). The end-of-line marker within an entity-body is defined by its associated media type, as described in section 3.7.
There is no such byte. The connection may be terminated by either side.
There is the optional Content-Length header, but it's a kind of hint for the client to know the size of the response.
The response length is determined by closing the connection (HTTP/1.0), the Content-Length response header, or the use of Chunked Encoding.