By now

Hi

What does "by now" mean?

"The application layer software then adds a header to the front of the message and passes the resulting message across the layer 6/7 interface to the presentation layer. The presentation layer in turn adds its own header and passes the result down to the session layer, and so on. Some layers add not only a header to the front, but also a trailer to the end. When it hits bottom, the physical layer actually transmits the message, which by now might look as shown in Fig. 2-2."