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IPP
IPP (Internet Printing Protocol) is a protocol for end users’ most common
printing situations over the Internet. It allows users to find out about a printer’s
capabilities, submit print jobs to a printer, determine the status of the printer
or print job, and cancel a previously submitted print job.
For more information on using IPP, See “Printing via IPP (Internet Printing
Protocol) – Windows Server 2003/XP/2000” on page 90.
LPD/LPR
LPD/LPR (Line Printer Daemon/Line Printer Request) is a platform-
independent printing protocol that runs over TCP/IP. Originally implemented
for BSD UNIX, its use has spread into the desktop world and is now an
industry standard.
SLP
Traditionally, in order to locate services on the network, users had to supply
the host name or network address of the machine providing the desired ser-
vice. This has created many administrative problems.
However, SLP (Service Location Protocol) simplifies the discovery and use of
network resources such as printers by automating a number of network ser-
vices. It provides a framework that allows networking applications to discover
the existence, location, and configuration of networked services.
With SLP users no longer need to know the names of network hosts. Instead,
they need to know only the description of the service they are interested in.
Based on this description, SLP is able to return the URL of the desired
service.
Unicast, Multicast, and Broadcast
SLP is a unicast and a multicast protocol. This means that messages can be
sent to one agent at a time (unicast) or to all agents (that are listening) at the
same time (multicast). However, a multicast is not a broadcast. In theory,
broadcast messages are “heard” by every node on the network. Multicast
differs from broadcast because multicast messages are only “heard” by the
nodes on the network that have “joined the multicast group.”
For obvious reasons network routers filter almost all broadcast traffic. This
means that broadcasts that are generated on one subnet will not be “routed”
or forwarded to any of the other subnets connected to the router (from the
router’s perspective, a subnet is all machines connected to one of its ports).
Multicasts, on the other hand, are forwarded by routers. Multicast traffic from
a given group is forwarded by routers to all subnets that have at least one
machine that is interested in receiving the multicast for that group.