client polling

angelb at angelb at
Wed Aug 17 08:02:32 PDT 2005

> > 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 (
> 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.

Thank you Mike for the reply. It helps. I appreciate it very much.


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