RFC 1759
Printer MIB
Network Working Group R. Smith Request for Comments: 1759 Texas Instruments Category: Standards Track F. Wright Lexmark International T. Hastings Xerox Corporation S. Zilles Adobe Systems, Inc. J. Gyllenskog Hewlett-Packard Company March 1995 Printer MIB Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Table of Contents 1. Introduction ................................................ 3 1.1 Network Printing Environment ............................... 3 1.2 Printer Device Overview .................................... 4 1.3 Categories of Printer Information .......................... 5 1.3.1 Descriptions ............................................. 5 1.3.2 Status ................................................... 5 1.3.3 Alerts ................................................... 5 2. Printer Model ............................................... 6 2.1 Overview of the Printer Model .............................. 8 2.2 Printer Sub-Units .......................................... 8 2.2.1 General Printer .......................................... 8 2.2.2 Inputs ................................................... 9 2.2.3 Media .................................................... 9 2.2.4 Outputs .................................................. 9 2.2.5 Finishers ................................................ 10 2.2.6 Markers .................................................. 10 2.2.7 Media Paths .............................................. 11 2.2.8 System Controller ........................................ 11 2.2.9 Interfaces ............................................... 11 2.2.10 Channels ................................................ 12 2.2.11 Interpreters ............................................ 12 2.2.12 Console ................................................. 12 2.2.13 Alerts .................................................. 13 2.2.13.1 Status and Alerts ..................................... 13
2.2.13.2 Overall Printer Status ................................ 13 2.2.13.2.1 Host MIB Printer Status ............................. 15 2.2.13.2.2 Sub-unit Status ..................................... 17 2.2.13.3 Alert Tables .......................................... 18 2.2.13.4 Alert Table Management ................................ 19 2.3 Read-Write Objects ......................................... 20 2.4 Enumerations ............................................... 22 2.4.1 Registering Additional Enumerated Values ................. 22 3. Objects from other MIB Specifications ....................... 22 3.1 System Group objects ....................................... 22 3.2 System Controller .......................................... 23 3.3 Interface Group objects .................................... 23 4. Textual Conventions ......................................... 23 5. The General Printer Group ................................... 27 5.1 The Cover Table ............................................ 30 5.2 The Localization Table ..................................... 31 5.3 The System Resources Tables ................................ 33 6. The Responsible Party group ................................. 35 7. The Input Group ............................................. 35 8. The Extended Input Group .................................... 41 9. The Input Media Group ....................................... 42 10. The Output Group ........................................... 44 11. The Extended Output Group .................................. 48 12. The Output Dimensions Group ................................ 49 13. The Output Features Group .................................. 51 14. The Marker Group ........................................... 52 15. The Marker Supplies Group .................................. 58 16. The Marker Colorant Group .................................. 62 17. The Media Path Group ....................................... 64 18. The Channel Group .......................................... 68 18.1 The Channel Table and its underlying structure ............ 69 18.2 The Channel Table ......................................... 70 19. The Interpreter Group ...................................... 73 20. The Console Group .......................................... 81 20.1 The Display Buffer Table .................................. 82 20.2 The Console Light Table ................................... 83 21. The Alerts Group ........................................... 85 21.1 The Alert Time Group ...................................... 92 22. Appendix A - Glossary of Terms ............................. 98 23. Appendix B - Media Size Names .............................. 101 24. Appendix C - Media Names ................................... 103 25. Appendix D - Roles of Users ................................ 107 26. Appendix E - Participants .................................. 111 27. Security Considerations .................................... 113 28. Authors' Addresses ......................................... 113
1. Introduction 1.1. Network Printing Environment The management of producing a printed document, in any computer environment, is a complex subject. Basically, the task can be divided into two overlapping pieces, the management of printing and the management of the printer. Printing encompasses the entire process of producing a printed document from generation of the file to be printed, selection of a printer, choosing printing properties, routing, queuing, resource management, scheduling, and final printing including notifying the user. Most of the printing process is outside the scope of the model presented here; only the management of the printer is covered.
Figure 1 - One Printer's View of the Network
system printer asset user user user
manager operator manager
O O O O O O
/|\ /|\ /|\ /|\ /|\ /|\
/ \ / \ / \ / \ / \ / \
| | | | | |
+---------+ +-------+ +-------+ +-------+ +-----------+ +-----------+
|configur-| |printer| | asset | |printer| | user | | user |
|ator | |manager| |manager| |browser| |application| |application|
+---------+ +-------+ +-------+ +-------+ +-----------+ +-----------+
^ ^ ^ ^ | |
|R/W |R/W |R |R +-----------+ +-----------+
| | | | | spooler | | spooler |
| | | | +-----------+ +-----------+
| | | | | |
| | | | +-----------+ +-----------+
| | | | |supervisor | |supervisor |
| | | | +-----------+ +-----------+
| | | | ^ ^ ^ ^
| | | | |R |R/W |R |R/W
v v | | | | | |
================================================== | ===== |
| print| print|
|SNMP data| data|
+-----+ +-------+ PCL| PCL|
| MIB |<------>| agent | PostScript| PostScript|
+-----+ +-------+ NPAP| NPAP|
|unspecified etc.| etc.|
+=============+ +-----------------+ | |
| |--|channel/interface|<--+ |
| | +-----------------+ |
| PRINTER | |
| | +-----------------+ |
| |--|channel/interface|<----------------+
+=============+ +-----------------+
1.2. Printer Device Overview
A printer is the physical device that takes media from an input
source, produces marks on that media according to some page
description or page control language and puts the result in some
output destination, possibly with finishing applied. Printers are
complex devices that consume supplies, produce waste and have
mechanical problems. In the management of the physical printing
device the description, status and alert information concerning the
printer and its various subparts has to be made available to the
management application so that it can be reported to the end user, key operators for the replenishment of supplies or the repair or maintenance of the device. The information needed in the management of the physical printer and the management of a printing job overlap highly and many of the tasks in each management area require the same or similar information. 1.3. Categories of Printer Information Information about printers is classified into three basic categories, descriptions, status and alerts. 1.3.1. Descriptions Descriptions convey information about the configuration and capabilities of the printer and its various sub-units. This information is largely static information and does not generally change during the operation of the system but may change as the printer is repaired, reconfigured or upgraded. The descriptions are one part of the visible state of the printer where state means the condition of being of the printer at any point in time. 1.3.2. Status Status is the information regarding the current operating state of the printer and its various sub-units. Status is the rest of the visible state of the printer. As an example of the use of status, a management application must be able to determine if the various sub- units are ready to print or are in some state that prevents printing or may prevent printing in the future. 1.3.3. Alerts An Alert is the representation of a reportable event in the printer. An event is a change in the state of the printer. Some of those state changes are of interest to a management application and are therefore reportable. Typically, these are the events that affect the printer's ability to print. Alerts usually occur asynchronously to the operation of the computer system(s) to which the printer is attached. For convenience below, "alert" will be used for both the event caused by a change in the printer's state and for the representation of that event. Alerts can be classified into two basic categories, critical and non-critical. A critical alert is one that is triggered by entry into a state in which the printer is stopped and printing can not continue until the condition that caused critical alert is eliminated. "Out of paper", "toner empty" and "output bin full" are
examples of critical alerts. Non-critical alerts are triggered by those events that enter a state in which printing is not stopped. Such a non-critical state may, at some future time, lead to a state in which printing may be stopped. Examples of this kind of non- critical alerts are "input media low", "toner low" and "output bin nearly full". Or, a non-critical alert may simply provide information, such as signaling a configuration changed in the printer. Description, status and alert information about printer can be thought of as a data base describing the printer. The management application for a printer will want to view the printer data base differently depending on how and for what purposes the information in the data base is needed. 2. Printer Model In order to accomplish the management of the printer, an abstract model of the printer is needed to represent the sub-units from which the printer is composed. A printer can be described as consisting of 13 types of sub-units. It is important to note that the sub-units of a printer do not necessarily relate directly to any physically identifiable mechanism. Sub-units can also be a set of definable logical processes, such as interpreters for page description languages or command processors that set various operating modes of the printer.
Figure 2 shows a block diagram of the printer and its basic 13 sub-
units.
Figure 2 - Printer Block Diagram
Physical Connections
|
+-----------+
| |
+-------------+ |
| Interface |-+
| (RFC1213) |
+-------------+
|
+-----------+
| |
+-------------+ | +-----------+
| Channel |-+ | Operator |
| | | Console |
+-------------+ +-----------+
|
+-----------+ +---------+
| | | |
+-----------+ +-------------+ | +-----------+ |
| General | | Interpreter |-+ | Alerts |-+
| Printer | | | | |
+-----------+ +-------------+ +-----------+
|
+-------------------------------+
| System Controller |
| (This is the Host MIB) |
+-------------------------------+
+------+ +--------+ +--------+
| | | | | |
+-------+ | +-------+ +---------+ | +-------+ +--------+ |
| Input |-+ +--------+| | Marker |-+ +--------+| | Output |-+
| |===>| |+<==>| |<==>| |+==>| |
+-------+ +--+ +--+ +---------+ +--+ +--+ +--------+
\ | || | || \
\ | || | || \
\ | || | || \
+--------+ | |+-------------------------| || +---------+
| | | +--------------------------+ || | |
+----------+ | | Media Path |+ +----------+ |
| Media |-+ +--------------------------------+ | Finisher |-+
|(optional)| |(optional)|
+----------+ +----------+
2.1. Overview of the Printer Model The model has three basic parts: (1) the flow of a print file into an interpreter and onto the marker, (2) the flow of media through the marker and (3) the auxiliary sub-units that control and facilitate the two prior flows. The flow of the print data comes through a physical connection on which some form of transport protocol stack is running. The data provided by the transport protocol (interface) appears on a channel which is the input to an interpreter. The interpreter converts the print data into a form suitable for marking on the media. The media resides in Input sub-units from which the media is selected and then transported via a Media Path first to a Marking sub-unit and then onto an Output sub-unit with (optionally) some finishing operations being performed. The auxiliary sub-units facilitate control of the printer, inquiry/control of the operator panel, reporting of alerts, and the adaptation of the printer to various natural languages and characters sets. All the software sub-units run on the System Controller which represents the processor, memory and storage systems of the Printer. Each of the sub-units is discussed in more detail below. All of the sub-units other than the Alerts report only state information, either a description or a status. The Alerts sub-unit reports event information. 2.2. Printer Sub-Units A printer is composed of 13 types of sub-units, called groups. The following sections describe the different types of sub-units. 2.2.1. General Printer The general printer sub-unit is responsible for the overall control and status of the printer. There is exactly one general printer sub- unit in a printer. The general printer sub-unit is represented by the General Printer Group in the model. In addition to the providing the status of the whole printer and allowing the printer to be reset, this Group provides information on the status of the packaging of the printer, in particular, the covers. The general printer sub-unit is usually implemented on the system controller. The localization portion of the general printer sub-unit is responsible for identifying the natural language, country, and character set in which character strings are expressed. There may be one or more localizations supported per printer. The available localizations are represented by the Localization table.
Localization is only performed on those strings in the MIB that are explicitely marked as being localized. All other character strings are returned in ASCII. The character set portion of the general printer sub-unit is responsible for identifying the possible character sets that are used by the interpreters, the operator console, and in network management requests for display objects. There may be one or more character sets per printer. The understood character sets are represented by the Character Set Table. 2.2.2. Inputs Input sub-units are mechanisms that feed media to be marked on into the printer. A printer contains one or more input sub-units. These are represented by the Input Group in the model. The model does not distinguish fixed input bins from removable trays, except to report when a removable tray has been removed. There are as many input sub-units as there are distinctly selectable input "addresses". For example, if a tray has an option for manually feeding paper as well as automatically feeding from the tray, then this is two input sub-units if these two sources can be (must be) separately selected and is one input sub-unit if putting a sheet in the manual feed slot overrides feeding from the contents of the tray; that is, in the second case there is no way to separately select or address the manual feed slot. 2.2.3. Media An input sub-unit can hold one or more instances of the media on which marking is to be done. Typically, there is a large set of possible media that can be associated with an input. The Media Group is an extension of the Input Group which represents that media that is in an input sub-unit. The Media Group only describes the current contents of each input and not the possible content of the input sub-unit. 2.2.4. Outputs Output sub-units are mechanisms that receive media that has been marked on. A printer contains one or more output mechanisms. These are represented by the Output Group in the model. The model does not distinguish fixed output bins from removable output bins, except to report when a removable bin has been removed. There are as many output sub-units as there are distinctly selectable output "addresses". Output sub-units can be addressed in two
different ways: (1) as a set of "mailboxes" which are addressed by a specific mailbox selector such as a bin number or a bin name, or (2) as a set of "slots" into which multiple copies are collated. Sometimes both modes of using the output sub-units can be used on the same printer. All that is important from the viewpoint of the model is that the output units can be separately selected. 2.2.5. Finishers A finisher is a sub-unit that performs some operations on the media other than marking. The finisher sub-units are represented by the Finisher Group in the model. Some examples of finishing processes are stapling, punching, binding, inserting, or folding. Finishing processes may have supplies asssociated with the process. Stapling, binding, and punching are examples of processes that have supplies. A printer may have more than one finishing sub-unit and each finishing sub-unit may be associated with one or more output sub-units. Finishers are not described in this MIB. The exact interaction and sequencing between an output device and its associated finisher is not specified by the model. It depends on the type of finishing process and the exact implementation of the printer system. This standard allows for the logical association of a finishing process with an output device but does not put any restrictions on the exact sequence or interaction with the associated output device. The output and finisher sub-units may or may not be separate identifiable physical mechanisms depending on the exact implementation of a printer. In addition, a single output device may be associated with multiple finishing sub-units and a single finishing sub-unit may be associated with multiple output devices. 2.2.6. Markers A marker is the mechanism that produces marks on the print media. The marker sub-units and their associated supplies are represented by the Marker Group in the model. A printer can contain one or more marking mechanisms. Some examples of multiple marker sub-units are: a printer with separate markers for normal and magnetic ink or an imagesetter that can output to both a proofing device and final film. Each marking device can have its own set of characteristics associated with it, such as marking technology and resolution. In this model the marker sub-unit is viewed as very generalized and encompasses all aspects of a marking process. For example, in a xero-graphic process, the marking process as well as the fusing process would be included in the generalized concept of the marker. With the generalized concept of a marking process, the concept of multiple marking supplies associated with a single marking sub-unit
results. For example, in the xerographic process, there is not only a supply of toner, but there can also be other supplies such as a fuser supply that can be consumed and replaced separately. In addition there can be multiple supplies of toner for a single marker device, as in a color process. 2.2.7. Media Paths The media paths encompass the mechanisms in the printer that move the media through the printer and connect all other media related sub- units: inputs, outputs, markers and finishers. A printer contains one or more media paths. These are represented by the Media Path Group in the model. The Media Path group has some objects that apply to all paths plus a table of the separate media paths. In general, the design of the media paths determines the maximum speed of the printer as well as the maximum media size that the printer can handle. Media paths are complex mechanisms and can contain many different identifiable sub-mechanisms such as media movement devices, media buffers, duplexing units and interlocks. Not all of the various sub-mechanisms reside on every media path. For example, one media path may provide printing only on one surface of the media (a simplex path) and another media path may have a sub- mechanism that turns the media over and feeds it a second time through the marker sub-unit (a duplex path). The duplex path may even have a buffer sub-mechanism that allows multiple copies of the obverse side to be held before the reverse side of all the copies are marked. 2.2.8. System Controller The System Controller is the sub-unit upon which the software components of the Printer run. The System Controller is represented in the model by the Host MIB. This MIB allows for the specification of the processor(s), memory, disk storage, file system and other underlying sub-mechanisms of the printer. The controller can range from simple single processor systems to multiprocessor systems. In addition, controllers can have a full range of resources such as hard disks. The printer is modeled to have one system controller even though it may have more than one processor and multiple other resources associated with it. 2.2.9. Interfaces An interface is the communications port and associated protocols that are responsible for the transport of data to the printer. A printer has one or more interface sub-units. The interfaces are represented by the Interfaces Group of MIB-II (RFC 1213). Some examples of
interfaces are serial ports (with little or no protocol) and EtherNet ports on which one might run InterNet IP, Novell IPX, etc. 2.2.10. Channels The channel sub-units identify the independent sources of print data (here print data is the information that is used to construct printed pages and may have both data and control aspects). A printer may have one or more channels. The channel sub-units are represented by the Channel Group in the Model. Each channel is typically identified by the electronic path and service protocol used to deliver print data to the printer. A channel sub-unit may be independently enabled (allowing print data to flow) or disabled (stopping the flow of print data). It has a current Control Language which can be used to specify which interpreter is to be used for the print data and to query and change environment variables used by the interpreters (and SNMP). There is also a default interpreter that is to be used if an interpreter is not explicitly specified using the Control Language. Channel sub-units are based on an underlying interface. 2.2.11. Interpreters The interpreter sub-units are responsible for the conversion of a description of intended print instances into images that are to be marked on the media. A printer may have one or more interpreters. The interpreter sub-units are represented by the Interpreter Group in the Model. Each interpreter is generally implemented with software running on the System Controller sub-unit. The Interpreter Table has one entry per interpreter where the interpreters include both Page Description Language (PDL) Interpreters and Control Language Interpreters. 2.2.12. Console Many printers have a console on the printer, the operator console, that is used to display and modify the state of the printer. The console can be as simple as a few indicators and switches or as complicated as full screen displays and keyboards. There can be at most one such console. This console sub-unit is represented by the Console Group in the model. Although most of the information displayed there is also available in the state of the printer as represented by the various Groups, it is useful to be able to query and modify the operator console remotely. For example, a management application might like to display to its user the current message on the operator console of the remote printer or the management application user might like to modify the current message on the operators console of the remote printer. As another example, one might have a remote application that puts up a pseudo console on a
workstation screen. Since the rules by which the printer state is mapped onto the console and vice versa are not standardized, it is not possible to reproduce the console state or the action of console buttons and menus. Therefore, the Console Group provides access to the console. The operator console is usually implemented on the system controller with additional hardware for input and display. 2.2.13. Alerts The alert sub-unit is responsible for detecting reportable events, making an entry in the alert table and, if and only if the event is a critical event, initiating a trap. The alert sub-unit is represented by the Alerts Group and, in particular, the Alert Table. This table contains information on the severity, sub-unit, detailed location within the sub-unit, alert code and description of each critical alert that is currently active within the printer. Each reportable event causes an entry to be made in the Alert Table. 2.2.13.1. Status and Alerts Summary information about the state of the printer is reported at three separate levels: (1) there is the status of the printer as a whole reported in the Host MIB, (2) there is the status of various sub-units reported in the principle table of the Group that represents the sub-unit, and (3) there are alert codes reported in the Alert Table. 2.2.13.2. Overall Printer Status Of the many states a printer can be in, certain states are more "interesting" because of the distinct actions they are likely to provoke in the administrator. These states may be applied to the printer as a whole, or to a particular sub-unit of the printer. These named states are: Non Critical Alert Active - For the printer this means that one or more sub-units have a non-critical alert active. For a sub-unit, this means that the sub-unit has a non-critical alert active. Critical Alert Active - For the printer this means that one or more sub-units have a critical alert active. For a sub-unit, this means that the sub-unit has a critical alert active. Unavailable - The printer or sub-unit is unavailable for use (this is the same as "broken" or "down" in other terminologies). A trained service person is typically necessary to make it available.
Busy / Temporarily Unavailable - The printer or sub-unit is
operational but currently occupied with a request for activity. The
sub-unit will become available without the need of human interaction.
Moving on-line or off-line - The printer is either off-line, in the
process of moving off-line or in the process of moving back on-line;
for example on high end printers reloading paper involves a
transition to off-line to open the paper bin, it is then filled and,
finally, there is a transition back to on-line as the paper bin is
repositioned for printing.
Standby - The printer or sub-unit is unavailable for use because it
is partially powered down and may need some period of time to become
fully operational again. A unit in Standby state shall respond to
network management requests.
The Host MIB provides three status objects that can be used to
describe the status of a printer: (1) hrDeviceStatus in the entry in
the Host MIB hrDeviceTable; (2) hrPrinterStatus in the
hrPrinterTable; and (3) hrPrinterDetectedErrorState in the
hrPrinterTable. These objects describe many of the states that a
printer can be in. The following table shows how the "interesting"
states named above can be recognized by inspecting the values of the
three printer-related objects in the Host MIB:
Printer hrDeviceStatus hrPrinterStatus hrPrinterDetectedErrorState
Status
Normal running(2) idle(3) none set
Busy/ running(2) printing(4)
Temporarily
Unavailable
Non Critical warning(3) idle(3) or could be: lowPaper,
Alert Active printing(4) lowToner, or
serviceRequested
Critical down(5) other(1) could be: jammed,
Alert Active noPaper, noToner,
coverOpen, or
serviceRequested
Unavailable down(5) other(1)
Moving off- warning(3) idle(3) or offline
line printing(4)
Off-line down(5) other(1) offline Moving down(5) warmup(5) on-line Standby running(2) other(1) These named states are only a subset of the possible states - they are not an exhaustive list of the possible states. Nevertheless, several things should be noted. When using these states, it is not possible to detect when both critical and non-critical alerts are pending - if both are pending, the Critical Alert Active state will prevail. In addition, a printer in the Standby state will be represented in the Host MIB with a device status of running(2) and a printer status of other(1), a set of states that don't uniquely distinguish this important printer state. Although the above mapping is workable, it would be improved with a few additions to hrDeviceStatus and hrPrinterStatus in the Host Resources MIB. In particular, it would be appropriate to add a "standby" enumeration to hrDeviceStatus. Similarly, it would be useful to add the following states to hrPrinterStatus: "offline" to indicate that reason for the printer being down (instead of having to use "other") which allows both "warning" and "offline" to indicate going offline and "down" and "offline" to indicate offline and "notApplicable" to cover cases, such as "standby", where the device state completely describes the state of the device. Detailed status per sub-unit is reported in the sub-unit status fields. 2.2.13.2.1. Host MIB Printer Status For completeness, the definitions of the Printer Status objects of the Host MIB are given below: hrDeviceStatus OBJECT-TYPE SYNTAX INTEGER { unknown(1), running(2), warning(3), testing(4), down(5) } ACCESS read-only STATUS mandatory DESCRIPTION "The current operational state of the device
described by this row of the table. A value
unknown(1) indicates that the current state of the
device is unknown. running(2) indicates that the
device is up and running and that no unusual error
conditions are known. The warning(3) state
indicates that agent has been informed of an
unusual error condition by the operational software
(e.g., a disk device driver) but that the device is
still 'operational'. An example would be high
number of soft errors on a disk. A value of
testing(4), indicates that the device is not
available for use because it is in the testing
state. The state of down(5) is used only when the
agent has been informed that the device is not
available for any use."
::= { hrDeviceEntry 5 }
hrPrinterStatus OBJECT-TYPE
SYNTAX INTEGER {
other(1),
unknown(2),
idle(3),
printing(4),
warmup(5)
}
ACCESS read-only
STATUS mandatory
DESCRIPTION
"The current status of this printer device. When
in the idle(1), printing(2), or warmup(3) state,
the corresponding hrDeviceStatus should be
running(2) or warning(3). When in the unknown
state, the corresponding hrDeviceStatus should be
unknown(1)."
::= { hrPrinterEntry 1 }
hrPrinterDetectedErrorState OBJECT-TYPE
SYNTAX OCTET STRING
ACCESS read-only
STATUS mandatory
DESCRIPTION
"This object represents any error conditions
detected by the printer. The error conditions are
encoded as bits in an octet string, with the
following definitions:
Condition Bit # hrDeviceStatus
lowPaper 0 warning(3)
noPaper 1 down(5)
lowToner 2 warning(3)
noToner 3 down(5)
doorOpen 4 down(5)
jammed 5 down(5)
offline 6 down(5)
serviceRequested 7 warning(3)
If multiple conditions are currently detected and
the hrDeviceStatus would not otherwise be
unknown(1) or testing(4), the hrDeviceStatus shall
correspond to the worst state of those indicated,
where down(5) is worse than warning(3) which is
worse than running(2).
Bits are numbered starting with the most
significant bit of the first byte being bit 0, the
least significant bit of the first byte being bit
7, the most significant bit of the second byte
being bit 8, and so on. A one bit encodes that
the condition was detected, while a zero bit
encodes that the condition was not detected.
This object is useful for alerting an operator to
specific warning or error conditions that may
occur, especially those requiring human
intervention."
::= { hrPrinterEntry 2 }
2.2.13.2.2. Sub-unit Status
Sub-unit status is reported in the entries of the principle table in
the Group that represents the sub-unit. For sub-units that report a
status, there is a status column in the table and the value of this
column is always an integer formed in the following way.
The SubUnitStatus is an integer that is the sum of 5 distinct values,
Availability, Non-Critical, Critical, On-line, and Transitioning.
These values are:
Availability value
Available and Idle 0 000'b
Available and Standby 2 010'b
Available and Active 4 100'b
Available and Busy 6 110'b
Unavailable and OnRequest 1 001'b
Unavailable because Broken 3 011'b
Unknown 5 101'b
Non-Critical
No Non-Critical Alerts 0
Non-Critical Alerts 8
Critical
No Critical Alerts 0
Critical Alerts 16
On-Line
Intended state is On-Line 0
Intended state is Off-Line 32
Transitioning
At intended state 0
Transitioning to intended state 64
For example, an input (tray) that jammed on the next to the last page
may show a status of 27 (unavailable because broken (3) + a critical
state (16), jammed, and a noncritical state (8), low paper).
2.2.13.3. Alert Tables
The Alert Group consists of a single table in which all active alerts
are represented. This section provides and overview of the table and
a description of how it is managed. The basic content of the alert
table is the severity (critical or non-critical) of the alert, the
Group and entry where a state change caused the alert, additional
information about the alert (a more detailed location, an alert code,
and a description), and an indication of the level of training needed
to service the alert.
The Alert Table contains some information that is redundant, for
example that an event has occurred, and some information that is only
represented in the Alert Table, for example the additional
information. A single table was used because a single entry in a
Group could cause more than one alert, for example paper jams in more
than one place in a media path. Associating the additional
information with the entry in the affected group would only allow one
report where associating the additional information with the alert
makes multiple reports possible.
Every time an alert occurs in the printer, the printer makes one or more entries into the Alert Table. The printer determines if an event is to be classified as critical or non-critical. If the severity of the Alert is "critical", the printer sends a trap or event notification to the host indicating that the table has changed. Whether or not a trap is sent, the management application is expected to poll the printer on a regular basis and to read and parse the table to determine what conditions have changed, in order to provide reliable information to the management application user. 2.2.13.4. Alert Table Management The alert tables are sparsely populated tables. This means the tables will only contain entries of the alerts that are currently active and the number of rows, or entries in the table will be dynamic. More than one event can be added or removed from the event tables at a time depending on the implementation of the printer. There are basically two kinds of events that produce alerts: binary change events and simple change events. Binary change events come in pairs: the leading edge event and the trailing edge event. The leading edge event enters a state from which there is only one exit; for example, going from running to stopped with a paper jam. The only exit from this state is fixing the paper jam and it is clear when that is accomplished. The trailing edge event is the event which exits the state the was entered by the leading edge event; in the example above fixing the paper jam is the trailing edge event. It is relatively straightforward to manage binary change events in the Alert Table. Only the leading edge event makes an entry in the alert table. This entry persists in the Alert Table until the trailing edge event occurs at which point this event is signal by the removal of the leading edge event entry in the Alert Table. That is, a trailing edge event does not create an entry; it removes the corresponding leading edge event. With binary events it is possible to compute the maximum number that can occur at the same time and construct an Alert Table that would hold that many events. There would be no possibility of table overflow and no information about outstanding events would be lost. Unfortunately, there are some events that are not binary changes. This other category of event, the simple change event, is illustrated by the configuration change event. With this kind of event the state of the machine has changed, but to a state which is (often) just as valid as the state that was left and from which no return is necessary. For example, an operator may change the paper that is in the primary input source from letter to legal. At some time in the future the paper may be changed back to letter, but it
might be changed to executive instead. This is where the problem
occurs. It is not obvious how long to keep simple change event
entries in the Alert Table. It they were never removed, the Alert
Table would continue to grow indefinitely.
The agent needs to have an algorithm implemented for the management
of the alert table, especially in the face of combinations of binary
and simple alerts that would overflow the storage capaciity of the
table. When the table is full and a new alert needs to be added, an
old alert needs to be deleted. The alert to be deleted should be
chosen using the following rules:
1. Find a non-critical simple alert and delete it. If there are
multiple non-critical simple alerts, it is suggested that the
oldest one be chosen. If there are no non-critical simple
alerts, then,
2. Find a non-critical binary alert and delete it. If there are
multiple non-critical binary alerts, it is suggested that the
oldest one be chosen. If there are no non-critical binary
alerts, then,
3. Find a critical (binary) alert and delete it. If there are
multiple critical alerts, it is suggested that the
oldest one be chosen. Agent implementors are encouraged to
provide at least enough storage space for the maximum number
of critical alerts that could occur simultaneously. Note that
all critical alerts are binary.
Note that because the Alert Index is a monotonically increasing
integer there will be gaps in the values in the table when an alert
is deleted. Such gaps can be detected by the management application
to indicate that the management application may want to re-acquire
the Printer state and check for state changes it did not observe in
the Alert Table.
2.3. Read-Write Objects
Some of the objects in the printer MIB report on the existence of or
amount of a given resource used with the printer. Some examples of
such resources are the size and number of sheets of paper in a paper
tray or the existence of certain output options. On some printers
there are sensors that allow these resources to be sensed. Other
printers, however, lack sensors that can detect (all of) the
properties of the resource. Because the printer needs to know of the
existence or properties of these resources for the printer to
function properly some other way of providing this information is
needed. The chosen way to solve this problem is to allow a
management application to write into objects which hold the
descriptive or existence values for printers that cannot sense the
values. Thus many of the objects in the MIB are given read-write
access, but a printer implementation might only permit a management
operation to change the value if the printer could not sense the
value itself. Therefore, the ability to change the value of a read-
write object may depend on the implementation of the agent. Note
that even though some objects explicitely state the behaviour of
conditional ability to change values, any read-write object may act
that way.
Generally, an object is given read-write access in the Printer MIB
specification if:
1.The object involves installation of a resource that some
printers cannot themselves detect. Therefore, external means are
needed to inform the printer of the installation. (Here external
means include using the operator console, or remote management
application) and
2.The printer will behave differently if the installation of the
resource is reported than the printer would if the installation
were not reported; that is, the object is not to be used
as a place to put information not used by the printer, i.e., not a
"PostIt". Another way of saying this is that the printer believes
that information given it and acts as if the information were
true. For example, on a printer that cannot sense the size, if
one paper size is loaded, but another size is set into the paper
size object, then the printer will use the size that was
set as its current paper size in its imaging and paper handling.
The printer may get hints that it may not know about the existence or
properties of certain resources. For example, a paper tray may be
removed and re-inserted. When this removal and insertion happens,
the printer may either assume that a property, such as the size of
paper in the tray, has not changed or the printer may change the
value of the associated object to "unknown", as might be done for the
amount of paper in the tray. As long as the printer acts according
to the value in the object either strategy is acceptable.
It is an implementation-specific matter as to whether or not MIB
object values are persistent across power cycles or cold starts. It
is particularly important that the values of the prtMarkerLifeCount
object persist throughout the lifetime of the printer. Therefore, if
the value of any MIB object persists across power cycles, then the
prtMarkerLifeCount object must also persist.
2.4. Enumerations Enumerations (enums) are sets of symbolic values defined for use with one or more objects. Some common enumeration sets are assigned a symbolic data type name (textual convention). These enumerations are listed at the beginning of this specification. 2.4.1. Registering Additional Enumerated Values This working group has defined several type of enumerations. These enumerations differ in the method employed to control the addition of new enumerations. Throughout this document, references to "enumeration (n)", where n can be 1, 2 or 3 can be found in the various tables. The definitions of these types of enumerations are: enumeration (1) All the values are defined in the Printer MIB specification (RFC for the Printer MIB). Additional enumerated values require a new RFC. enumeration (2) An initial set of values are defined in the Printer MIB specification. Additional enumerated values are registered after review by this working group. The initial versions of the MIB will contain the values registered so far. After the MIB is approved, additional values will be registered through IANA after approval by this working group. enumeration (3) An initial set of values are defined in the Printer MIB specification. Additional enumerated values are registered without working group review. The initial versions of the MIB will contain the values registered so far. After the MIB is approved, additional values will be registered through IANA without approval by this working group.
(page 22 continued on part 2)
