Internet Printing Protocol

The Internet Printing Protocol (IPP) is an Internet protocol for communication between a print server and its clients. It allows clients to send one or more print jobs to the server and perform administration such as querying the status of a printer, obtaining the status of print jobs, or cancelling individual print jobs.

Like all IP-based protocols, IPP can run locally or over the Internet. Unlike other printing protocols, IPP also supports access control, authentication, and encryption, making it a much more capable and secure printing mechanism than older ones.

History

IPP began as a proposal by Novell for the creation of an Internet printing protocol project in 1996. The result was a draft written by Novell and Xerox called the Lightweight Document Printing Application (LDPA), derived from ECMA-140: Document Printing Application (DPA). At about the same time, Lexmark publicly proposed something called the HyperText Printing Protocol (HTPP), and both HP and Microsoft had started work on new print services for what became MS Windows 2000. Each of the companies chose to start a common Internet Printing Protocol project in the Printer Working Group (PWG) and negotiated an IPP birds-of-a-feather (BOF) session with the Application Area Directors in the Internet Engineering Task Force (IETF). The BOF session in December 1996(?) showed sufficient interest in developing a printing protocol, leading to the creation of the IETF Internet Printing Protocol (ipp) working group.

IPP/1.0 was published as a series of experimental documents (RFC 2565, RFC 2566, RFC 2567, RFC 2568, RFC 2569, and RFC 2639) in 1999. IPP/1.1 followed as a draft standard in 2000 with support documents in 2001 and 2003 (RFC 2910, RFC 2911, RFC 3196, RFC 3510). Additional extensions to IPP were published as RFCs until 2005 when the IETF IPP working group was concluded.

Work on IPP continues in the PWG with the publication of 12 candidate standards providing extensions to IPP and definition of IPP/2.0, IPP/2.1, and now IPP/2.2 representing different categories or classes of printers. A new IPP Everywhere project began in July 2010 to define an IPP profile and extensions required to support driverless printing, with a focus on non-traditional platforms such as netbooks and mobile Internet devices. The new project also expands the scope of IPP standards to include printer discovery and standard document formats.

Implementation

IPP is implemented using the Hypertext Transfer Protocol (HTTP) and inherits all of the HTTP streaming and security features. For example, authorization can take place via HTTP's Digest access authentication mechanism, GSSAPI, or via public key certificates. Encryption is provided using the SSL/TLS protocol-layer, either in the traditional always-on mode used by HTTPS or using the HTTP Upgrade extension to HTTP (RFC 2817). Streaming is supported using HTTP chunking.

IPP uses the traditional client-server model, with clients sending IPP request messages with the MIME media type "application/ipp" in HTTP POST requests to an IPP printer. IPP request messages consist of key/value pairs using a custom binary encoding followed by an "end of attributes" tag and any document data required for the request. The IPP response is sent back to the client in the HTTP POST response, again using the "application/ipp" MIME media type.

Among other things, IPP allows a client to:

1. query a printer's capabilities
2. submit print jobs to a printer
3. query the status of a printer
4. query the status of one or more print jobs
5. cancel previously submitted jobs

IPP uses TCP with port 631 as its well-known port. IPP implementations such as CUPS also use UDP with port 631 for IPP printer discovery.

Products using the Internet Printing Protocol include, among others, CUPS which is part of Apple Mac OS X and many BSD and Linux distributions and is the reference implementation for IPP/2.0 and IPP/2.1, Novell iPrint, and Microsoft Windows, starting with MS Windows 2000. MS Windows XP and Windows Server 2003 offer IPP printing via HTTPS. MS Windows Vista, Windows 7, Windows Server 2008 and 2008 R2 also support IPP printing over RPC in the "Medium-Low" security zone. For reasons unknown Microsoft dropped support of secure IPP via SSL in MS Windows Server 2008.

Standards

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See also

• Line Printer Daemon protocol
• CUPS
• Job Definition Format
• iFax/T.37 for emailing directly to a fax machine

External links

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