Right now, protocol mix and match is pretty hardwired. Eventually it will get changed so it's automatically figured out. This next list shows the order at which data is unwrapped from it's encapsulating protocol

  1. TCP/IP
  2. Port protocol (port 515 is LPD, port 9100 is raw byte stream)
  3. Image encoding transport (LPD job, PDF, Postscript, ESCP2, etc)
  4. CAD

Port Protocols

LPD on port 515
UNIX ™ LPD is a multi packet transaction that carries instructions for printing data.
AppSocket on port 9100
This is a raw stream of data. The socket is opened and print image data is streamed to it until the end of the image data. Closing the socket signals the end of the print job. There is no control structure. Data arrives at the printer and the printer should know how to handle it.

Image encoding transport

LPD job
LPD is not necessarily complex but is clearly capable of extensive job control and options.
PDF and Postscript
PDF is a very simple form of Postscript and should be thought of as a list of print commands. PS is a Turing complete language. PS is a fully capable programming language. Both may include 8bit content in data blocks however the rest of the document is in human readable text.
Epson ESCP2
This data arrives as simple ESC commands encoded in hex. 0x1b followed by up to a few bytes for commands which direct the printer to use particular fonts, spacing, print head movements, and more. In graphics mode, additional data arrives which is laid out in either bitstream or bitmap raster format. It is important to note that data arriving like this is entirely dependent on the printer driver in use.

CAD formats

CAD version 5 printed a simple and short paragraph of about 12 lines that was about 40 characters wide.
CAD version 6 presents nearly ½ a page of a print image with much more detail for incident information. Information is divided into a left hand side (LHS) and right hand side (RHS). The LHS is a label such as "Caller Name" and the RHS is the name of the caller.

Print driver output that can be decoded