client polling

Michael Sweet mike at
Wed Aug 17 07:13:32 PDT 2005

angelb at 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"

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 (

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

Michael Sweet, Easy Software Products           mike at easysw dot com
Internet Printing and Document Software

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