Download iPrint - Library Binus

CHAPTER 2
THEORITICAL FOUNDATION
Theoretical Foundation
2.1 Network
A computer network is composed of multiple connected computers that communicate
over a wired or wireless medium to share data and other resources. For instance, a home
computer network may consist of two or more computers that share files and a printer
using the network. The size and scalability of any computer network are determined both
by the physical medium of communication and by the software controlling the
communication
2.1.1 Types of Networks
Below is a list of the most common types of computer networks in order of scale.
Personal Area Network (PAN)
A personal area network (PAN) is a computer network used for
communication among computer devices. The reach of a PAN is typically a few
meters. Personal area networks may be wired with computer buses such as USB
and FireWire. A wireless personal area network (WPAN) can also be made
possible with network technologies such as IrDA and Bluetooth.
5
6
Local Area Network (LAN)
A network covering a small geographic area, like a home, office, or
building. Current LANs are most likely to be based on Ethernet technology. Hosts
can be made part of a specific LAN can be defined by setting their address to one
within the address range of the LAN subnet This can be done by manual
configuration, or by configuring DHCP (Dynamic Host Configuration Protocol)
auto-configuration to give the host an address in the appropriate range.Currently
standardized LAN technologies operate at speeds up to 10 Gbit/s. IEEE has
projects investigating the standardization of 100 Gbit/s, and possibly 40 Gbit/s.
Campus Area Network (CAN)
A network that connects two or more LANs but that is limited to a specific
and contiguous geographical area such as a college campus, industrial complex,
or a military base. Today, a campus may use a mixture of routing and bridging.
The network elements used, called "campus switches", tend to be optimized to
have many Ethernet interfaces rather than an arbitrary mixture of Ethernet and
WAN interfaces.
Wide Area Network (WAN)
A WAN is a data communications network that covers a relatively broad
geographic area (i.e. one country to another and one continent to another
7
continent) and that often uses transmission facilities provided by common
carriers, such as telephone companies.
Global Area Network (GAN)
In general, however, a GAN is a model for supporting mobile
communications across an arbitrary number of wireless LANs, satellite coverage
areas, etc. The key challenge in mobile communications is "handing off" the user
communications from one local coverage area to the next.
Internetwork
Two or more networks or network segments connected using devices that
operate at layer 3 (the 'network' layer) of the OSI Basic Reference Model, such as
a router. Any interconnection among or between p ublic, private, commercial,
industrial, or governmental networks may also be defined as an internetwork.In
modern practice, the interconnected networks use the Internet Protocol. There are
at least three variants of internetwork, depending on who administers and who
participates in them:
Intranet
An intranet is a set of interconnected networks, using the Internet Protocol
and uses IP-based tools such as web browsers, that is under the control of a single
administrative entity. That administrative entity closes the intranet to the rest of
8
the world, and allows only specific users. Most commonly, an intranet is the
internal network of a company or other enterprise.
Extranet
A extranet is network or internetwork that is limited in scope to a single
organization or entity but which also has limited connections to the networks of
one or more other usually, but not necessarily, trusted organizations or entities
(e.g., a company's customers may be provided access to some part of its intranet
thusly creating an ext ranet while at the same time the customers may not be
considered 'trusted' from a security standpoint).
"The" Internet
A specific internetwork, consisting of a worldwide interconnection of
governmental, academic, public, and private networks based upon the Advanced
Research Projects Agency Network (ARPANET) developed by ARPA of the U.S.
Department of Defense – also home to the World Wide Web (WWW) and
referred to as the 'Internet' with a capital 'I' to distinguish it from other generic
internetworks.
Participants in the Internet, or their service providers, use IP Addresses
obtained from address registries that control assignments. Service providers and
large enterprises also exchange information on the reachability of their address
ranges through the Border Gateway Protocol.
9
2.1.2 Basic Hardware Components
All networks are made up of basic hardware building blocks to interconnect
network nodes, such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and
Routers. In addition, some method of connecting these building blocks is required,
usually in the form of galvanic cable (most commonly Category 5 cable). Less common
are microwave links (as in IEEE 802.11) or optical cable ("optical fiber").
Network Interface Cards
A network card, network adapter or NIC (network interface card) is a
piece of computer hardware designed to allow computers to communicate over a
computer network. It provides physical access to a networking medium and
provides a low- level addressing system through the use of MAC addresses. It
allows users to connect to each other either by using cables or wirelessly.
Repeaters
A repeater is an electronic device that receives a signal and retransmits it
at a higher level or higher power, or onto the other side of an obstruction, so that
the signal can cover longer distances without degradation. Because repeaters work
with the actual physical signal, and do not attempt to interpret the data being
transmitted, they operate on the Physical layer, the first layer of the OSI model.
10
Hubs
A hub contains multiple ports. When a packet arrives at one port, it is
copied the packets to all the ports of the hub. When the packets are copied, the
destination address in the frame does not change to a broadcast address. It does
this in a rudimentary way; it simply copies the data to all of the Nodes connected
to the hub.
Bridges
A bridge always connects two parts of the same type of network channel –
just as a physical transport bridge always connects a road to a road and railway to
a railway. Bridges amplify the signal like a repeater, but they also have packet
filtering capabilities – only packets that have business on the other side of the
bridge (i.e. are addressed to a system that exists there) are passed over and
amplified.
Switches
Switches are a marketing term that encompasses routers and bridges, as
well as devices that may distribute traffic on load or by application content (e.g., a
Web URL identifier). Switches may operate at one or more OSI layers, including
physical, data link, network, or transport (i.e., end-to-end).
11
Routers
Routers connect different LANs together to form an intranet or connect a LAN to
a WAN, such as the internet. A router has network layer functionality that enables it to
read the network address of the packets it receives. Only packets for nodes on its network
segment are passed on. Routers do not forward broadcast messages. Unlike a bridge, a
router can link different types of network such as Ethernet and Token Ring.
2.2 WI-FI
The Wi-Fi wireless network is based on the IEEE 802.11 standard, and includes
802.11b (an 11 Mbps technology, currently the most popular form of Wi-Fi), 802.11a (a
54 Mbps technology, a newer and emerging favorite), and 802.11g (55 Mbps). The Wi-Fi
Alliance is the body responsible for promoting the term and its association with various
wireless technology standards.
Typical implementations for 802.11 wireless networking include connecting
laptops to corporate networks, and allowing home networking users to connect PCs
together without introducing new wiring. With a transmission distance of around 300 feet
and a throughput rate that tops out at 55 Mbps, Wi-Fi provides ample throughput for most
wireless applications.
Wireless Access Points
The most common form of wireless Access Point (AP) is a transceiver
connected to a wired LAN component such as a PC or a router. The AP provides
a gateway between a wired network such as a broadband cable Internet service
12
and wireless enabled devices. Any device with a compatible transceiver can
communicate with the access point if it is in range – typically 30 m in a normal
building, further if in direct line of sight. Wireless APs act like servers (of fixed
network services) to Mobile Terminals (MTs).
2.3 RADIUS
Remote Authentication Dial In User Service (RADIUS) is an AAA
(authentication, authorization and accounting) protocol for applications such as network
access or IP mobility. It is intended to work in both local and roaming situatio ns.
Many networks services (including corporate networks and public ISPs using
modem, DSL, or wireless 802.11 technologies) require you to present security credentials
(such as a username and password or security certificate) in order to connect on to the
network. Before access to the network is granted, this information is passed to a Network
Access Server (NAS) device over the link- layer protocol (for example, Point-to-Point
Protocol (PPP) in the case of many dialup or DSL providers), then to a RADIUS server
over the RADIUS protocol. The RADIUS server checks that the information is correct
using authentication schemes like PAP, CHAP or EAP. If accepted, the server will then
indicate to the NAS that you are authorized to access the network. RADIUS also allows
the authentication server to supply the NAS with additional parameters, such as
The specific IP address to be assigned to the user
The address pool from which the user's IP should be chosen
13
The maximum length that the user may remain connected
An access list, priority queue or other restrictions on a user's access
L2TP parameters
RADIUS is also commonly used for accounting purposes. The NAS can use
RADIUS accounting packets to notify the RADIUS server of events such as
The user's session start
The user's session end
Total packets transferred during the session
Volume of data transferred during the session
Reason for session ending
Radius is a common authentication protocol utilized by the 802.1X security
standard (often used in wireless networks). Although RADIUS was not initially intended
to be a wireless security authentication method, it improves the WEP encryption key
standard, in conjunction with other security methods such as EAP-PEAP.
2.4 Internet Protocols
In this context, there are three layers of protocols:
At the lower level (OSI layer 3) is IP (Internet Protocol), which defines the
datagram or packets that carry blocks of data from one node to another. The vast
majority of today's Internet uses version four of the IP protocol (i.e. IPv4, and
14
although IPv6 is standardized, it exists only as "islands" of connectivity, and there
are many ISPs without any IPv6 connectivity. [1]. ICMP (Internet Control
Message Protocol) also exists at this level. ICMP is connectionless; it is used for
control, signaling, and error reporting purposes.
TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) exist at
the next layer up (OSI layer 4); these are the protocols by which data is
transmitted. TCP makes a virtual 'connection', which gives some level of
guarantee of reliability. UDP is a best-effort, connectionless transport, in which
data packets that are lost in transit will not be re-sent.
The application protocols sit on top of TCP and UDP and occupy layers 5, 6,
and 7 of the OSI model. These define the specific messages and data formats sent
and understood by the applications running at each end of the communication.
Examples of these protocols are HTTP, FTP, and SMTP.
2.4.1 Internet Protocol Suite
The Internet protocol suite is the set of communications protocols that
implement the protocol stack on which the Internet and most commercial networks run. It
has also been referred to as the TCP/IP protocol suite, which is named after two of the
most important protocols in it: the Transmission Control Protocol (TCP) and the Internet
Protocol (IP), which were also the first two networking protocols defined.
15
The Internet Protocol suite—like many protocol suites—can be viewed as a set of
layers. Each layer solves a set of problems involving the transmission of data, and
provides a well-defined service to the upper layer protocols based on using services from
some lower layers. Upper layers are logically closer to the user and deal with more
abstract data, relying on lower layer protocols to translate data into forms that can
eventually be physically transmitted. The TCP/IP reference model consists of four layers.
2.4.2 Layers in the Internet Protocol suite
The IP suite uses encaps ulation to provide abstraction of protocols and services.
Generally a protocol at a higher level uses a protocol at a lower level to help accomplish
its aims.
DNS, TFTP, TLS/SSL, FTP, Gopher, HTTP, IMAP, IRC,
NNTP, POP3, SIP, SMTP, SNMP, SSH, TELNET, ECHO,
BitTorrent, RTP, PNRP, rlogin, ENRP
4. Application
Routing protocols like BGP, which for a variety of reasons run
over TCP, may also be considered part of the application or
network layer.
3. Transport
TCP, UDP, DCCP, SCTP, IL, RUDP
2. Internet
Routing protocols like OSPF, which run over IP, are also to be
considered part of the network layer, as they provide path
selection. ICMP and IGMP run over IP and are considered part
16
of the network layer, as they provide control information.
IP (IPv4, IPv6)
ARP and RARP operate underneath IP but above the link layer
so they belong somewhere in between.
Ethernet, Wi-Fi, token ring, PPP, SLIP, FDDI, ATM, Frame
1. Network access
Relay, SMDS
2.5 Internet Printing Protocol
Since 1996, industrial leading software and printer vendors started to form a work
group. The primary objective of this workgroup is to define a protocol which can cover
the most common situations for printing on the Internet regardless the operating
environments. The first proposed solution is Internet Printing Protocol (IPP), released
during 1999.
Internet Printing Protocol (IPP) means a mechanism to print documents over
Internet. It creates an association between a printer and a web URL address.
With IPP, documents from client machines can be readily submitted print jobs to
server machine or printers via Internet using HTTP (standard web protocol). Also, the
user can inquire about the capabilities of a printer, inquire about the status of a print job,
and cancel a job via standard web browser.
17
This mechanism facilitates greater printing flexibility, like remote printing. Also,
adopting IPP can ease the problem of integrating different printing mechanisms
implemented on different operating systems.
The design goals of IPP are:
for a user to find out about a printer's capabilities
for a user to submit print jobs to a printer
for a user to find out the status of a printer or a print job
for a user to cancel a previously submitted job
2.5.1 Current Implementation
A list of current implementations of IPP (both clients and serves) can be found in
IPP Work Group. Two major implementation may worth mentioning here:
Microsoft Windows 2000 Print Server
The Windows 2000 printing architecture has incorporated with IPP. With help
of Microsoft Internet Information Server (IIS), users can readily print documents to
Windows 2000 print server via Internet. Features provided by Windows 2000 include:
Printing documents from Windows 2000 Professional or Windows XP clients to
Windows 2000 print servers using a Uniform Resource Locator (URL).
Using Internet Explorer to manage printers, control print jobs, and view the
printer and print job's status.
18
Connecting to printers on corporate network and install printer driver via Internet
Explorer.
Common Unix Printing System
The Common UNIX Printing System (CUPS) is designed to be a crossplatform printing solution for all UNIX environments. It's design and implementation
is based on IPP.
The latest implementation supports IPP/1.1 and provides a complete, modern
printing system for UNIX. It can be extended to support new printers, devices, and
protocols while providing compatibility with existing UNIX applications.
RedHat Linux, starting from 7.3, has adopted CUPS as its native printing system
that replaces LPRng.
2.5.2 How will IPP Benefits
The immediate benefit of adopting Internet Printing in campus may be:
Network Printing Service Enhanced for notebook users
W2K/WXP users no longer need to join to domain before they can access and print to
campus network printers. (This is particularly useful to notebook users since they can just
go online, connect to campus network printer via IPP and then print the documents).
19
2.6 Photocopier
A photocopier is a machine which makes paper copies of documents and other
visual images quickly and cheaply. Most current photocopiers use a technology called
xerography, a dry process using heat. (Copiers can also use other output technologies
such as ink jet, but xerography is standard for office copying.)
Xerographic office photocopying was introduced by Xerox in the 1960s, and over
the following 20 years it gradually replaced copies made by Verifax, Photostat, carbon
paper, mimeograph machines, and other duplicating machines. The prevalence of its use
is one of the factors that prevented the development of the paperless office heralded early
in the digital revolution.
2.7 Printer
A computer printer, or more commonly a printer, produces a hard copy
(permanent human-readable text and/or graphics) of documents stored in electronic form,
usually on physical print media such as paper transparencies. Many printers are primarily
used as computer peripherals, and are attached by a printer cable to a computer which
serves as a document source. Other printers, commonly known as network printers, have
built- in network interfaces (typically wireless or Ethernet), and can serve as a hardcopy
device for any user on the network.
Printers are designed for low-volume, short-turnaround print jobs; requiring
virtually no setup time to achieve a hard copy of a given document. However, printers are
20
generally slow devices (30 pages per minute is considered fast; and many consumer
printers are far slower than that), and the cost-per-page is relatively high.
2.7.1 Modern Printing Technology
The following printing technologies are routinely found in modern printers, as of April
2006:
Toner-based printers
The most common type of toner-based printer is the laser printer, which
uses precision lasers to cause adherence. Laser printers are known for high quality
prints, good print speed, and a low (Black and White) cost-per-copy; they are the
most common printer for many general-purpose office applications. They are far
less commonly used as consumer printers due to a high initial cost.
Liquid inkjet printers
Inkjet printers consist of nozzles that produce very small ink bubbles that
turn into tiny droplets of ink. The dots formed are the size of tiny pixels. Ink-jet
printers can print high quality text and graphics. They are also almost silent in
operation. Inkjet printers have a much lower initial cost than do laser printers, but
have a much higher cost-per-copy, as the ink needs to be frequently replaced.
Solid ink printers
Solid ink printers are most commonly used as color office printers, and are
excellent at printing on transparencies and other non-porous media. Solid ink
21
printers can produce excellent results. Acquisition and operating costs are similar
to laser printers. Drawbacks of the technology include high power consumption
and long warm-up times from a cold state.
Dye-sublimation printers
Dye-sub
printers
are
intended
primarily
for
high-quality
color
applications, including color photography; and are less well-suited for text. While
once the province of high-end print shops, dye-sublimation printers are now
increasingly used as dedicated consumer photo printers.
22
Theoretical Framework
The Printing Architecture is one of the major components from Windows
architecture. It consists of a print spooler and a set of printer drivers. The applications can
create print jobs and send them to the printers by calling device- independent Win32
printing and GDI functions. Printer drivers include a user interface component that allows
users to control a printer's selectable options (Paper Size, Number of copies, Coloration,
Pages per sheet etc.).
An application's calls to Win32 GDI functions are passed to the GDI graphics
engine, which either spools the drawing instructions as an enhanced metafile (EMF) file
or, in conjunction with a printer driver, renders a printable image that can be sent to the
spooler. Spooler components interpret EMF files, and they can insert page layout
information and job control instructions into the data stream. The spooler then sends the
data stream to the serial, parallel, or network port driver associated with the target
printer's I/O port. Spooler and driver components are designed to be replaceable.
Support for a new printer usually requires only the creation of new data files for use with
one of the Microsoft-supplied printer drivers.
Most of the device drivers work at kernel mode. Some of the device drivers or
part of the device drivers work at user mode and kernel mode. Printer drivers work at
both modes.
23
2.1 Printing Process:
The printing process is divided into three groups of steps:
Client processes
Spooler processes
Printer processes
Each process performs some operations and passes the print job to another process. For
e.g., user fires a print document from an application, the client process starts the creation
of print job by calling the GDI, and after completing the creation of print job, it sends to
the spooler. The spooler will perform some operations on that print job and sends to the
printer process. The printer processes receive the print job from the spooler process and
translate the print language into a bitmap, and then it prints.
2.1.1 Client Processes
A user sends a print job from an application. The application calls the Graphics
Device Interface (GDI). If print output is produced in RAW format, the GDI is not used.
The GDI calls the printer driver for information, which the GDI uses to create a job in
printer language. The GDI delivers the job to the spooler.
2.1.2 Spooler Processes
The client side of the spooler (Winspool.drv) makes an RPC call to the server side
spooler (Spoolsv.exe ).
Spoolsv.exe calls the print router (Spoolss.dll).
24
The router (Spoolsv.dll) sends the print job to the Local Print Provider (LPP) or
remote print server if the job is being sent to a network printer.
The LPP polls print processors to find one that can handle the data type of the job.
The LPP sends the job to the print processor, which modifies the job as required
to make it print properly.
The print processor sends the job to the page separator. A separator page is added,
as required.
The job is sent to the appropriate port print monitor. If print is bidirectional, the
job is first sent to the language monitor such as the Printer Job Language (PJL)
monitor, and then sent on to the port monitor. If the job is unidirectional, the job
is sent directly to the port monitor.
2.1.3 Printer Processes
The printer receives the print job from the print spooler.
The printer translates the print language into a bitmap, which it then prints.
2.2 Print Spooler Architecture
Print spooling is configured by users. Jobs can be sent to the spooler, or sent
directly to the printer. If jobs are sent to the spooler, they can be configured to start
printing as soon as possible or after the final page in a job has been sent to the spooler.
When you send a print job directly to the printer, your computer renders the entire job
and then transfers it directly to the printer. When you send a print job to a spooler, your
computer creates the job, including meta- information about how the job must be
25
processed, and then sends the job to the spooler. The spooler then renders the job and
sends it to the printer.
Sending a print job directly to the printer is good because you remove a potential
point of failure in printing documents, and all print job rendering is done on your
computer, affording you more control, and you don’t have to wait for other jobs to
complete, as you might if you were printing to a queue on a print server that was being
used by many users. Conversely, rendering a print job on your computer consumes
computing resources, so you might experience reduced performance or have to wait until
the print job has completed before doing anything.
Sending a print job to a spooler is good because your computer does not have to
render the print job, meaning your computer’s resources are more completely and
immediately available. Conversely, sending a print job to a spooler fails if the print server
with the spooler is unavailable, and you might have to wait for other jobs to finish
spooling before your job is processed.
The primary component of the printing interface is the print spooler. The print
spooler is an executable file that manages the printing process. Management of printing
involves retrieving the location of the correct printer driver, loading that driver, spooling
high- level function calls into a print job, scheduling the print job for printing, and so on.
The spooler is loaded at system startup and continues to run until the operating system is
shut down. Applications that print create a printer device context (DC). When an
application creates a printer DC, the spooler performs necessary tasks such as
26
determining the location of the required printer driver and then loading the appropriate
printer driver. It also determines the data type used to record the print job.
The supported data types include enhanced metafiles (EMF), ASCII text, and raw
data (all printer specific data types such as PostScript and PCL). Custom data types can
be added to the spooler when additional printer drivers and print processors are installed.
A print job is a document stored internally (by using one of the supported data types) that
may contain one or more pages of output. It may consist of multiple forms; for example,
a job may consist of one envelope and three pages of A4 paper. A print job is defined (or
bracketed) by the StartDoc and EndDoc functions.
The default data type for a print job is the enhanced metafile. An EMF record is a
compact structure used to store text output commands, raster graphics commands, and so
on. When an application calls
StartDoc,
the spooler creates a spool file and a data file
and begins storing EMF records in the spool file. The spool and data files are created in
an operating system directory. The spooler uses the spool file to store EMF records, and
uses the data file to record the type of form, the data type for the print job, the target
printer, and so on. The spooler deletes these files when the job has successfully printed.
The Microsoft Windows print spooler is made up of a set of Microsoft-supplied and
optional vendor-supplied components, with responsibilities that include:
Determining whether a print job should be handled locally or across a network.
Accepting a data stream created by GDI, in conjunction with a printer driver, for
output on a particular type of printer.
27
Spooling the data to a file (if spooling is enabled).
Selecting the first available physical printer in a logical printer queue.
Converting a data stream from a spooled format (such as enhanced metafile
(EMF)) to a format that can be sent to printer hardware (such as printer control
language (PCL)).
Sending a data stream to printer hardware.
Maintaining a registry-based database for spooler components and printer forms.
Windows print spooler support for Directory Services consists of:
Publishing print queues.
Maintaining three registry keys.
Allowing access to spooler- maintained registry keys.
Returning a print queue's publication state.
2.3 Spooler Components
The primary components of the Microsoft Windows print spooler are illustrated in the
following diagram. The print spooler consists of a group of components that include the
print router, the local and remote print provider, the print processor, and the language and
port monitors.
Application: The print application creates a print job by calling GDI functions.
28
GDI: The Graphics Device Interface (GDI) includes both user-mode and kernelmode components. The user- mode component, Win32 GDI, is used by Win32
applications that require graphics support. The kernel- mode component, the
graphics engine (or graphics rendering engine), exports services and functions
that graphics device drivers can use.
Winspool.drv : Winspool.drv is the client interface into the spooler. It exports the
functions that make up the spooler's Win32 API, and provides RPC stubs for
accessing the server. (GDI is the primary client, but applications also call some of
its Win32 functions.)
Spoolsv.exe : Spoolsv.exe is the spooler's API server. It is implemented as a
Windows 2000 (or later) service that is started when the operating system is
started. This module exports an RPC interface to the server side of the spooler's
Win32 API. Clients of spoolsv.exe
include winspool.drv (locally) and
Win32spl.dll (remotely). The module implements some API functions, but most
function calls are passed to a print provider by means of the router (spoolss.dll).
Router: The router, spoolss.dll, determines which print provider to call, based on
a printer name or handle supplied with each function call, and passes the function
call to the correct provider.
Print Provider: The print provider that supports the specified print device.
Print Monitor: Windows XP supports two types of print monitors: language
monitors, and port monitors.
If printer hardware is local to the system on which the application is running, the "client"
and "server" are the same system (although this is not evident in the diagram).
29
2.4 Print Providers
Print providers are responsible for directing print jobs to local or remote print
devices. They are also responsible for print queue management operations, such as
starting, stopping, and enumerating a server's print queues. Print providers define a highlevel, machine- independent, Operating System- independent view of a print server. All
print providers implement a common set of print provider capabilities. These capabilities
are defined by a set of API functions, which are called by the spooler's router
(spoolss.dll).
2.4.1 Print Provider Flow Paths
When viewing the diagram, you should consider the following points:
If the printer is managed by the client system, the print job is handled by the local
print provider (localspl.dll). Printers managed by localspl.dll do not have to be
physically local to the client; they can be directly connected to network cards.
If the printer is located on a NT-based-operating system server, the network
provider (win32spl.dll) uses RPC to redirect calls from the client's router to the
server's spoolsv.exe process. Because the printer is local to the server, the server's
local print provider will handle the print job.
If the printer is located on some other type of server, it can be accessed by either
the local print provider or by a network print provider that supports that server
type, using data formats and network protocols supported by the server.
For the local print provider to access a remote printer, it must contain a port
monitor that can use network protocols recognized by the remote printer or server.
30
2.4.2 Print Provider Capabilities
By supporting predefined sets of API functions, Windows print providers can supply the
following capabilities:
Print Queue Manageme nt: Adding, deleting, opening, closing, enumerating, and
setting parameters for print queues. Also, providing notification of changes to a
print queue's state.
Printer Driver Management : Adding, deleting, enumerating, and specifying a
directory for printer drivers.
Print Job Creation: Starting and ending a document, starting and ending a
document page, writing the job's data stream to a port, reading printer status
information.
Print Job Scheduling : Scheduling, enumerating, and setting parameters for a
print job.
Forms Management: Adding, deleting, enumerating, and setting parameters for
print forms.
Print Processor Management : Adding, deleting, enumerating, specifying a
directory for and the data types supported by print processors.
Print Monitor Management : Adding, deleting, and enumerating print monitors.
Port Management: Adding, deleting, configuring, enumerating, and setting
parameters for printer ports.
Registry Management: Creating, deleting, and enumerating registry keys and
values associated with a print provider.
31
Other Capabilities: Displaying a message box, shutting down the print provider,
reading a memory mapped spool file, providing a communication path between
port monitor UI DLLs and port monitor server DLLs.
These capabilities are implemented as a set of functions defined by print providers. There
are many functions supported to define a print provider. Functions are divided into the
following groups:
Initialization Functions
Print Queue Management Functions
Printer Driver Management Functions
Print Job Creation Functions
Print Job Scheduling Functions
Forms Management Functions
Print Processor Management Functions
Print Monitor Management Functions
Port Management Functions
Registry Management Functions
Other Functions
2.4.3 Local Print Provider
The local print provider for Windows provides job control and printer
management capabilities for all printers that are accessed through the local print
provider's port monitors. (A client administrator sets up access to such printers by
32
selecting the Local Printer option when using the Add Printer Wizard.) Such printers
include those connected to the local system's serial and parallel ports. They can also
include devices connected to other I/O channels, such as SCSI ports, along with printers
connected to remote non-NT-based-operating system servers.
Control Flow in Local Printer Provider
As the diagram shows, an application creates a print job by calling the Graphics
Driver Interface (GDI). Regardless of whether the print job's initial output format is
EMF, the local print provider's job creation API creates a spool file. Later, when the job
is scheduled, the spool file is read and, if the format is EMF, the EMF print processor
sends the job back to GDI for conversion to RAW format, with the help of a printer
graphics DLL. The converted data stream can then be sent back through the local print
provider to the printer (without being re-spooled).
2.5 Printer Driver
Printer drivers contain information that is specific to the printer that is used.
Printer drivers reside on user’s computers and are used by the GDI to render print jobs. A
printer driver is a software program that understands how to communicate with printers
and plotters. Printer drivers translate the information a user sends from the computer into
commands that the printer understands. Various drivers must be installed on the print
server to support different hardware and operating systems. For example, an
administrator running Windows 2000 Server who shares a printer with clients running
33
Windows 95 and Windows 98 might want to install the appropriate drivers so the users
won't be prompted to install the missing drivers. The printer driver sends the printersetting information, including the specifications needed to produce each character of the
document, to the GDI. It also transmits helper services or utilities required to make the
output print correctly.
Printer drivers are composed of three separate files:
1. A printer graphics driver (for example, PSCRIPT.DLL, RASDD.DLL, or
PLOTTER.DLL). Graphics drivers are responsible for print rendering (converting
GDI commands from the graphics engine into printer commands that a printer can
understand). Each graphics driver handles different printer languages. For
example:
o
PSCRIPT.DLL: deals with the PostScript printer language.
o
PLOTTER.DLL: deals with the HPGL/2 language used by many plotters.
o
RASDD.DLL: deals
with
printer
languages
based
on
raster
(bitmap) images, including PCL and most dot matrix printer languages.
2. A printer interface driver (for example, PSCRPTUI.DLL, RASDDUI.DLL, or
PLOTUI.DLL). This dynamic- link library (DLL) includes the user interface you
see when you configure a printer in Print Manager. It is called by the client side of
the router (WINSPOOL.DRV).
3. Characterization files: Characterization data files provide model-specific
information about print devices.
34
2.5.1 Printer Driver Components
All Windows printer drivers consist of the following components:
A printer graphics DLL that assists GDI in rendering a print job, and sends the
rendered data stream to the print spooler.
A printer interface DLL that provides both a user interface to the driver's
configuration parameters, and an interface the spooler can call to notify the driver
of print-related system events.
2.6 Print Processors
The print processor is a dynamic- link library (DLL) which calls the printer driver.
An application has tried to use a print processor which has not been installed on your
computer. The spooler monitors the current print jobs and the target printer to determine
an appropriate time to print a job. Once the spooler determines that a job should be
printed, it calls the print processor. The print processor works together with the printer
driver to move the spooled print jobs from the hard disk.
Print processors are user- mode DLLs that are responsible for converting a print
job's spooled data into a format that can be sent to a print monitor. They are also
responsible for handling application requests to pause, resume and cancel print jobs.
35
The print job's spooled data is contained in a spool file. The print processor reads
the file, performs conversion operations on the data stream, and writes the converted data
to the spooler. The spooler then sends the data stream to the appropriate print monitor.
Microsoft Windows 2000 and later includes the print processors listed in the following
table.
Print Processor Input Data Types Output Data Types
EMF
localspl.dll *
RAW
RAW
TEXT
sfmpsprt.dll
PSCRIPT1
RAW
* Beginning with Windows 2000, localmon.dll and winprint.dll are included in
localspl.dll.
For information about the data types, see the following topics:
EMF Data Type RAW
Data Type TEXT Data
Type PSCRIPT1 Data
Type
You can create a customized print processor to support a data type that is not
supported by Windows 2000 or later operating system versions. You can also provide a
customized print processor that supports one or more of the supported data types, thus
36
allowing you to modify the capabilities provided by the supplied print processors. Print
processors are associated with printer drivers during driver installation, so multiple print
processors supporting the same data type can coexist.
Difference Between EMF and RAW Data Formats?
RAW is data formatted exactly how the print er needs it. Depending on the printer
concerned, it could be fully rendered to a dot-by-dot page image or, on more
sophisticated printers, incorporate vector elements. A PostScript printer, for example,
expects a page to be described by a set of PostScript commands. This is essentially a
vector format and that's what the RAW data would contain. EMF (Enhanced Metafile)
describes the page in a vector format specific to Windows. EMF is actually a capture of
the GDI (Graphics Device Interface) commands that programs use to tell Windows how
to draw what you see on the output device, normally the screen. Because EMF is
Windows' native image description language, capturing the commands into a spool file is
a relatively quick and simple process. Immediately converting data to RAW format
involves more processing and may produce a larger quantity of data than the equivalent
EMF. Therefore, when printing from an application, EMF gets the immediate business of
generating the print job over as soon as possible before returning control to the user.
When the print spooler is ready to send a buffered page to the printer, RAW data
can be passed straight through whereas EMF commands must first be rendered into RAW
format. This is done as a background process which means you can continue working. On
a well-specified PC and/or printer, the effect on overall performance of this background
processing may not be noticeable.
37
That's the theory, but it doesn't always hold true. And you would think print
quality should be the same in either case, but I have avoided describing a lot of behindthe-scenes complications. Odd problems can sometimes be solved by switching from
EMF to RAW, or occasionally vice-versa. In fact, RAW is the manufacturer's preferred
format for some printers. There isn't much you can do about the speed, but make sure the
computer has enough memory to avoid excessive use of the swap file and ensure the disk
is defragmented. You might also try the spool setting 'Print directly to the printer'. This is
not an option when a printer is shared over a network. Your application will take longer
to return control to you, but printing time may be reduced, because the job is not being
spooled to disk.
2.7 Processing a Print Job
When the spooler is ready to send a print job to a print processor, it calls the print
processor's
activities
OpenPrintProcessor
and
returns
a
PrintDocumentOnPrintProcessor ,
function.
handle.
This
The
function
spooler
performs
can
initialization
then
call
which is the print processor function that converts
the data stream from the input format to the output format and returns the converted
stream to the spooler. If the input format is NT-based-operating system EMF, the
PrintDocumentOnPrintProcessor
function can control the playback of the EMF
records by using the functions listed in Using GDI Functions in Print Processors. These
functions provide an interface between the print processor and the printer driver. This
interface allows print processors to control the physical layout of printer pages, and thus
38
facilitates implementing such features as printing multiple document pages per physical
page ("N - up" printing), printing pages in reverse order, and printing multiple copies of
each page.
A print processor's output data stream must be returned to the spooler. Typically,
if the data conversion requires interaction with the printer driver's printer graphics DLL
(as is the case for EMF input data), the graphics DLL returns the stream to the spooler by
calling
EngWritePrinter.
On the other hand, if the conversion does not call the printer
graphics DLL (as is the case for RAW input data), then the print processor calls
WritePrinter.
The
PrintDocumentOnPrintProcessor
function can be interrupted by
asynchronous calls from the spooler to the print processor's
ControlPrintProcessor
function. This function implements an application's ability to pause, resume, or cancel a
print job. After
PrintDocumentOnPrintProcessor
finishes converting the data stream
and returns, the spooler calls the print processor's ClosePrintProcessor function.
2.8 Installing a Print Processor
To install a print processor, an installation application must call the spooler's
AddPrintProcessor
function. To associate a print processor with a print queue, list its
file name in an INF file in a
PrintProcessor
entry. This entry must be included for
every print queue to which the print processor is to be associated. For more information,
see Printer INF Files. When an installation application calls the spooler's
AddPrinter
39
function, using a
PRINTER_INFO_2
structure as an input argument, it specifies the print
processor name (obtained from the INF file) as a structure member.
Associating a Print Processor with a PnP-installed Print Queue
If the PnP manager detects and installs a print queue on a system running either
Windows 2000 or Windows XP, and if the INF file used to install the print queue
contains a
WinPrint,
PrintProcessor
entry other than the default Windows print processor,
the print processor will not be associated with the print queue. However, the
print processor will be installed. (Note that if you install the print queue using the Add
Printer wizard, the print processor is correctly associated with the print queue. Note also
that the PnP manager in Microsoft Windows Server™ 2003 and later correctly associates
a print processor with the print queue.)
To associate the print processor with the print queue for Plug and Play
installations
on
Windows 2000
PRINTER_EVENT_INITIALIZE
and
Windows XP,
case in the printer interface DLL's
include
a
DrvPrinterEvent
function. For Microsoft Windows Server™ 2003 and later, it is not necessary to add a
PRINTER_EVENT_INITIALIZE
case in the DrvPrinterEvent function.
2.9 Print Monitor
Print monitors are responsible for directing a print data stream from the print
spooler to an appropriate port driver. Two types of print monitors are defined —
language monitors and port monitors.
40
2.10 Language Monitors
Language monitors are user- mode DLLs that serve two purposes:
They provide a full duplex communications path between the print spooler and
bidirectional printers that are capable of providing software-accessible status
information.
They add printer control information, such as commands defined by a printer job
language, to the data stream.
Microsoft provides a language monitor, pjlmon.dll, which supports printer job language
(PJL), and provides bidirectional communication for PJL printers. This monitor is
included in the DDK as the sample language monitor.
Customized language monitors can be written to support other job control languages, for
unidirectional or bidirectional printers.
Language monitors are optional and only associated with a particular printer type if
included in the printer's INF file, as described in Installing a Print Monitor.
If a language monitor is associated with a printer, the language monitor receives the
printer's data stream from the print processor, modifies it, and passes it to the printer's
port monitor.
41
2.11 Port Monitors
Port monitors consist of user-mode DLLs. They are responsible for providing a
communications path between the user- mode print spooler and the kernel- mode port
drivers that access I/O port hardware. A port monitor typically uses the
WriteFile, ReadFile,
and
DeviceIOControl
CreateFile,
functions, described in the Platform SDK
documentation, to communicate with kernel- mode port drivers. Port monitors are also
responsible for management and configuration of a server's printer ports, as described in
Managing a Port.
An NT-based-operating system user's view of a "printer" is really a print queue, to
which one or more physical printer devices can be connected. A port is the physical
connection between the print queue and a single printer device. Each port monitor
supports one or more instances of one or more types of ports. For example, localmon.dll,
the sample port monitor, can support all of a server's local COM and LPT ports. (The
print folder assigns ports to port monitors by calling the Platform SDK documentation's
AddPrinter
function.)
For print queues representing multiple printer devices (through multiple ports),
the spooler sends each print job to the first available port. If the port monitor indicates
that a specified port is busy or has encountered an error, the spooler resubmits the job to
the queue, specifying another port supported by the port monitor.
Besides localmon.dll, Windows 2000 and later operating system versions provide
several additional port monitors. The Windows 2000 Server Resource Kit describes each
42
of these port monitors. Customized port monitors can be written to support additional
types of I/O port hardware.
For Windows 2000 and later, each port monitor is divided into two DLLs:
Port Monitor UI DLL: A port monitor's user interface DLL contains user
interface functionality and executes on print client systems. This DLL must reside
in the client system's System32 subdirectory.
Port Monitor Server DLL: A port monitor's server DLL contains port
communications functionality and executes on print servers. It must not display a
user interface.
2.12 Initializing a Print Monitor
When the spooler calls
immediately calls the DLL's
entry point function to call
LoadLibrary
DllEntryPoint
to load a print monitor DLL, the system
function. It is generally a good idea for the
DisableThreadLibraryCalls ,
described in the Platform
SDK documentation, so the DLL is not unnecessarily notified when threads are created
and deleted.
Each DLL exports an initialization function, which the spooler calls after calling
LoadLibrary.
Language monitor DLLs and port monitor server DLLs export an
InitializePrintMonitor2
InitializePrintMonitorUI
function.
function.
Port
monitor
UI
DLLs
export
an
43
These two initialization functions are responsible for returning pointers to the rest
of the functions defined by print monitors, so the spooler can call them. The initialization
functions can also perform load-time initialization
InitializePrintMonitor2
operations. The monitor's
function returns a monitor instance handle. The monitor
should allocate local memory to store instance-specific information, and use the monitor
handle as an identifier for the allocated memory.
When the spooler is first started, it loads all of the monitor DLLs that have been
installed. After calling all monitor initialization functions, the spooler calls each port
monitor's
EnumPorts
function, which enumerates the ports supported by the monitor. (A
monitor supports a port if the port has been added to the monitor's database, as described
in Adding a Port.) Each suppor ted port is then opened, as described in Opening and
Closing a Port.
2.13 Opening and Closing a Port
After a port has been added, as described in Adding a Port, the spooler can open it
by calling the appropriate language monitor's OpenPortEx function.
The language monitor uses the
OpenPortEx
function to create and return a port
handle. Typically, a language monitor calls its associated port monitor's
OpenPort
function, and the language monitor just returns the handle obtained from the port
monitor's OpenPort.
44
If a language monitor is not associated with a port, the spooler calls the port
monitor's OpenPort function directly.
The spooler does not allow more than one path to a port to be enabled at one time.
Thus, after it has called
OpenPortEx
(or
OpenPort)
in a particular monitor, it does not
attempt to open the same port again before closing it.
After a port has been opened, the spooler can call additional functions to print a
job, as described in Printing a Print Job, using the port handle as an input argument. A
monitor should be written so that, after a port has been opened, the spooler can send
multiple print jobs before closing the port.
The spooler closes a port if a job must be sent through a different language
monitor, if no print queues are associated with a port, or when the system shuts down. To
close a port, the spooler calls a language monitor's
ClosePort
function. The function
invalidates the handle that was created when the port was opened. A language monitor
typically calls the ClosePort function defined by its associated port monitor.
If a language monitor is not associated with a port, the spooler calls the port monitor's
ClosePort
function directly.
2.14 Printing a Print Job
After a port has been opened, as described in Opening and Closing a Port, the spooler can
send print jobs to the port.
45
Each print job is delimited by spooler calls to a language or port monitor's
StartDocPort
and
EndDocPort
processor calls the spooler's
functions. The spooler calls these functions when a print
StartDocPrinter
and
EndDocPrinter
functions, which are
described in the Platform SDK documentation. Within the scope of a set of
StartDocPort
and
EndDocPort
WritePort, ReadPort,
functions, unlimited spooler calls to a monitor's
and GetPrinterDataFromPort functions can occur.
Each of these functions requires the port handle returned by
OpenPort)
OpenPortEx
(or
to be specified as an input argument. Typically, a language monitor
implements each of the functions by calling the like- named function in its associated port
monitor.
When the spooler calls a language monitor's
WritePort
function to send a data
stream to the port, the function generally adds language-specific information, such as PJL
commands, to the received data stream before passing it to the associated port monitor's
WritePort
The
function.
ReadPort
function is used for obtaining status information from bidirectional
printer hardware, which a language monitor might send to the spooler by calling
SetPort,
described in the Platform SDK documentation. The spooler does not call the
ReadPort
function.
If printing hardware is bidirectional, both its language monitor and its port
monitor should support a
GetPrinterDataFromPort
GetPrinterDataFromPort
function. A language monitor's
function should accept a registry value name as input, obtain
46
a value for that name (generally by calling associated port monitor's
ReadPort
WritePort
and
functions), and return the value to the caller. A port monitor's
GetPrinterDataFromPort
DeviceIoControl
function should accept an I/O control code as input, call
(described in the Platform SDK documentation) to pass the control
code to the port driver, and return the result.