The printers in the computer science labs (and most of the university) are network printers. One of the properties of network printers is that they function just like any other device on the network i.e. they are each assigned an ip address. The printer is a simple device, its only function is receiving files and then printing them, therefore a printer by itself doesn't have the functionality to restrict access to it by ip address or by any other method. Printers also cannot be used to run any custom software e.g. software which logs you in and charges you NetAccount for the printnig costs. This poses a problem for the university, who would like to charge users for printing files. So, in order to solve this problem, when you print from any of the lab machines, the file to be printed is not sent directly to the printer but is in fact sent to the print server (the computer next to the printer). This computer has the job of logging you in and charging you before sending the file to the printer.
The printer itself receives files in one of two ways. Either:
1. a file is sent through the ftp protocol to the printer (the printer has a simple ftp server)
2. a file is sent directly to the printer port of the printer