client polling

[Michael Sweet]

angelb at bugarin.us wrote:
> Hi all.
> 
> I've searched the documentations for information about client
> polling but I have not found the answer I'm looking for.
> 
> What does the client actually do when it "polls" the server for
> information? How big is the data being asked, what method of
> communication(UDP?), and what effort(cpu, memory) on the server
> side when a client polls it?

cups-polld sends CUPS_GET_PRINTERS and CUPS_GET_CLASSES requests
to the server every BrowseInterval seconds; these requests go over
TCP (standard IPP request over HTTP + TCP) and are roughly
equivalent to the overhead of doing a "lpstat -h server -p -c"
command.

Once it has the printer/class data, is sends it to the local
cupsd via UDP on the browse port (usually 631), which the client's
cupsd sees as coming from the local loopback interface (127.0.0.1)

The data is throttled to prevent overwhelming the client's cupsd,
basically by sending groups of N = (# printers/classes) / interval)
browse packets once every second until all of the packets have been
sent.

-- 
______________________________________________________________________
Michael Sweet, Easy Software Products           mike at easysw dot com
Internet Printing and Document Software          http://www.easysw.com