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+<?xml version="1.0" encoding="latin1" ?>
+<!DOCTYPE chapter SYSTEM "chapter.dtd">
+
+<chapter>
+  <header>
+    <copyright>
+      <year>1997</year><year>2009</year>
+      <holder>Ericsson AB. All Rights Reserved.</holder>
+    </copyright>
+    <legalnotice>
+      The contents of this file are subject to the Erlang Public License,
+      Version 1.1, (the "License"); you may not use this file except in
+      compliance with the License. You should have received a copy of the
+      Erlang Public License along with this software. If not, it can be
+      retrieved online at http://www.erlang.org/.
+    
+      Software distributed under the License is distributed on an "AS IS"
+      basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+      the License for the specific language governing rights and limitations
+      under the License.
+    
+    </legalnotice>
+
+    <title>SNMP Appendix B</title>
+    <prepared></prepared>
+    <responsible></responsible>
+    <docno></docno>
+    <approved></approved>
+    <checked></checked>
+    <date></date>
+    <rev></rev>
+    <file>snmp_app_b.xml</file>
+  </header>
+
+  <section>
+    <title>Appendix B</title>
+
+    <section>
+      <title>RowStatus (from RFC1903)</title>
+      <pre>
+RowStatus ::= TEXTUAL-CONVENTION
+    STATUS       current
+    DESCRIPTION
+            "The RowStatus textual convention is used to manage the
+            creation and deletion of conceptual rows, and is used as the
+            value of the SYNTAX clause for the status column of a
+            conceptual row (as described in Section 7.7.1 in RFC1902.)
+
+            The status column has six defined values:
+
+                 - `active', which indicates that the conceptual row is
+                 available for use by the managed device;
+
+                 - `notInService', which indicates that the conceptual
+                 row exists in the agent, but is unavailable for use by
+                 the managed device (see NOTE below);
+
+                 - `notReady', which indicates that the conceptual row
+                 exists in the agent, but is missing information
+                 necessary in order to be available for use by the
+                 managed device;
+
+                 - `createAndGo', which is supplied by a management
+                 station wishing to create a new instance of a
+                 conceptual row and to have its status automatically set
+                 to active, making it available for use by the managed
+                 device;
+
+                 - `createAndWait', which is supplied by a management
+                 station wishing to create a new instance of a
+                 conceptual row (but not make it available for use by
+                 the managed device); and,
+
+                 - `destroy', which is supplied by a management station
+                 wishing to delete all of the instances associated with
+                 an existing conceptual row.
+
+            Whereas five of the six values (all except `notReady') may
+            be specified in a management protocol set operation, only
+            three values will be returned in response to a management
+            protocol retrieval operation:  `notReady', `notInService' or
+            `active'.  That is, when queried, an existing conceptual row
+            has only three states:  it is either available for use by
+            the managed device (the status column has value `active');
+            it is not available for use by the managed device, though
+            the agent has sufficient information to make it so (the
+            status column has value `notInService'); or, it is not
+            available for use by the managed device, and an attempt to
+            make it so would fail because the agent has insufficient
+            information (the state column has value `notReady').
+
+
+                                     NOTE WELL
+
+                 This textual convention may be used for a MIB table,
+                 irrespective of whether the values of that table's
+                 conceptual rows are able to be modified while it is
+                 active, or whether its conceptual rows must be taken
+                 out of service in order to be modified.  That is, it is
+                 the responsibility of the DESCRIPTION clause of the
+                 status column to specify whether the status column must
+                 not be `active' in order for the value of some other
+                 column of the same conceptual row to be modified.  If
+                 such a specification is made, affected columns may be
+                 changed by an SNMP set PDU if the RowStatus would not
+                 be equal to `active' either immediately before or after
+                 processing the PDU.  In other words, if the PDU also
+                 contained a varbind that would change the RowStatus
+                 value, the column in question may be changed if the
+                 RowStatus was not equal to `active' as the PDU was
+                 received, or if the varbind sets the status to a value
+                 other than 'active'.
+
+
+            Also note that whenever any elements of a row exist, the
+            RowStatus column must also exist.
+
+            To summarize the effect of having a conceptual row with a
+            status column having a SYNTAX clause value of RowStatus,
+            consider the following state diagram:
+
+
+                                         STATE
+              +--------------+-----------+-------------+-------------
+              |      A       |     B     |      C      |      D
+              |              |status col.|status column|
+              |status column |    is     |      is     |status column
+    ACTION    |does not exist|  notReady | notInService|  is active
+--------------+--------------+-----------+-------------+-------------
+set status    |noError    ->D|inconsist- |inconsistent-|inconsistent-
+column to     |       or     |   entValue|        Value|        Value
+createAndGo   |inconsistent- |           |             |
+              |         Value|           |             |
+--------------+--------------+-----------+-------------+-------------
+set status    |noError  see 1|inconsist- |inconsistent-|inconsistent-
+column to     |       or     |   entValue|        Value|        Value
+createAndWait |wrongValue    |           |             |
+--------------+--------------+-----------+-------------+-------------
+set status    |inconsistent- |inconsist- |noError      |noError
+column to     |         Value|   entValue|             |
+active        |              |           |             |
+              |              |     or    |             |
+              |              |           |             |
+              |              |see 2   ->D|          ->D|          ->D
+--------------+--------------+-----------+-------------+-------------
+set status    |inconsistent- |inconsist- |noError      |noError   ->C
+column to     |         Value|   entValue|             |
+notInService  |              |           |             |
+              |              |     or    |             |      or
+              |              |           |             |
+              |              |see 3   ->C|          ->C|wrongValue
+--------------+--------------+-----------+-------------+-------------
+set status    |noError       |noError    |noError      |noError
+column to     |              |           |             |
+destroy       |           ->A|        ->A|          ->A|          ->A
+--------------+--------------+-----------+-------------+-------------
+set any other |see 4         |noError    |noError      |see 5
+column to some|              |           |             |
+value         |              |      see 1|          ->C|          ->D
+--------------+--------------+-----------+-------------+-------------
+
+            (1) goto B or C, depending on information available to the
+            agent.
+
+            (2) if other variable bindings included in the same PDU,
+            provide values for all columns which are missing but
+            required, then return noError and goto D.
+
+            (3) if other variable bindings included in the same PDU,
+            provide values for all columns which are missing but
+            required, then return noError and goto C.
+
+            (4) at the discretion of the agent, the return value may be
+            either:
+
+                 inconsistentName:  because the agent does not choose to
+                 create such an instance when the corresponding
+                 RowStatus instance does not exist, or
+
+                 inconsistentValue:  if the supplied value is
+                 inconsistent with the state of some other MIB object's
+                 value, or
+
+                 noError: because the agent chooses to create the
+                 instance.
+
+            If noError is returned, then the instance of the status
+            column must also be created, and the new state is B or C,
+            depending on the information available to the agent.  If
+            inconsistentName or inconsistentValue is returned, the row
+            remains in state A.
+
+            (5) depending on the MIB definition for the column/table,
+            either noError or inconsistentValue may be returned.
+
+            NOTE: Other processing of the set request may result in a
+            response other than noError being returned, e.g.,
+            wrongValue, noCreation, etc.
+
+
+                              Conceptual Row Creation
+
+            There are four potential interactions when creating a
+            conceptual row:  selecting an instance-identifier which is
+            not in use; creating the conceptual row; initializing any
+            objects for which the agent does not supply a default; and,
+            making the conceptual row available for use by the managed
+            device.
+
+
+            Interaction 1: Selecting an Instance-Identifier
+
+            The algorithm used to select an instance-identifier varies
+            for each conceptual row.  In some cases, the instance-
+            identifier is semantically significant, e.g., the
+            destination address of a route, and a management station
+            selects the instance-identifier according to the semantics.
+
+            In other cases, the instance-identifier is used solely to
+            distinguish conceptual rows, and a management station
+            without specific knowledge of the conceptual row might
+            examine the instances present in order to determine an
+            unused instance-identifier.  (This approach may be used, but
+            it is often highly sub-optimal; however, it is also a
+            questionable practice for a naive management station to
+            attempt conceptual row creation.)
+
+            Alternately, the MIB module which defines the conceptual row
+            might provide one or more objects which provide assistance
+            in determining an unused instance-identifier.  For example,
+            if the conceptual row is indexed by an integer-value, then
+            an object having an integer-valued SYNTAX clause might be
+            defined for such a purpose, allowing a management station to
+            issue a management protocol retrieval operation.  In order
+            to avoid unnecessary collisions between competing management
+            stations, `adjacent' retrievals of this object should be
+            different.
+
+            Finally, the management station could select a pseudo-random
+            number to use as the index.  In the event that this index
+            was already in use and an inconsistentValue was returned in
+            response to the management protocol set operation, the
+            management station should simply select a new pseudo-random
+            number and retry the operation.
+
+            A MIB designer should choose between the two latter
+            algorithms based on the size of the table (and therefore the
+            efficiency of each algorithm).  For tables in which a large
+            number of entries are expected, it is recommended that a MIB
+            object be defined that returns an acceptable index for
+            creation.  For tables with small numbers of entries, it is
+            recommended that the latter pseudo-random index mechanism be
+            used.
+
+
+            Interaction 2: Creating the Conceptual Row
+
+            Once an unused instance-identifier has been selected, the
+            management station determines if it wishes to create and
+            activate the conceptual row in one transaction or in a
+            negotiated set of interactions.
+
+            Interaction 2a: Creating and Activating the Conceptual Row
+
+            The management station must first determine the column
+            requirements, i.e., it must determine those columns for
+            which it must or must not provide values.  Depending on the
+            complexity of the table and the management station's
+            knowledge of the agent's capabilities, this determination
+            can be made locally by the management station.  Alternately,
+            the management station issues a management protocol get
+            operation to examine all columns in the conceptual row that
+            it wishes to create.  In response, for each column, there
+            are three possible outcomes:
+
+                 - a value is returned, indicating that some other
+                 management station has already created this conceptual
+                 row.  We return to interaction 1.
+
+                 - the exception `noSuchInstance' is returned,
+                 indicating that the agent implements the object-type
+                 associated with this column, and that this column in at
+                 least one conceptual row would be accessible in the MIB
+                 view used by the retrieval were it to exist. For those
+                 columns to which the agent provides read-create access,
+                 the `noSuchInstance' exception tells the management
+                 station that it should supply a value for this column
+                 when the conceptual row is to be created.
+
+                 - the exception `noSuchObject' is returned, indicating
+                 that the agent does not implement the object-type
+                 associated with this column or that there is no
+                 conceptual row for which this column would be
+                 accessible in the MIB view used by the retrieval.  As
+                 such, the management station cannot issue any
+                 management protocol set operations to create an
+                 instance of this column.
+
+            Once the column requirements have been determined, a
+            management protocol set operation is accordingly issued.
+            This operation also sets the new instance of the status
+            column to `createAndGo'.
+
+            When the agent processes the set operation, it verifies that
+            it has sufficient information to make the conceptual row
+            available for use by the managed device.  The information
+            available to the agent is provided by two sources:  the
+            management protocol set operation which creates the
+            conceptual row, and, implementation-specific defaults
+            supplied by the agent (note that an agent must provide
+            implementation-specific defaults for at least those objects
+            which it implements as read-only).  If there is sufficient
+            information available, then the conceptual row is created, a
+            `noError' response is returned, the status column is set to
+            `active', and no further interactions are necessary (i.e.,
+            interactions 3 and 4 are skipped).  If there is insufficient
+            information, then the conceptual row is not created, and the
+            set operation fails with an error of `inconsistentValue'.
+            On this error, the management station can issue a management
+            protocol retrieval operation to determine if this was
+            because it failed to specify a value for a required column,
+            or, because the selected instance of the status column
+            already existed.  In the latter case, we return to
+            interaction 1.  In the former case, the management station
+            can re-issue the set operation with the additional
+            information, or begin interaction 2 again using
+            `createAndWait' in order to negotiate creation of the
+            conceptual row.
+
+                                     NOTE WELL
+
+                 Regardless of the method used to determine the column
+                 requirements, it is possible that the management
+                 station might deem a column necessary when, in fact,
+                 the agent will not allow that particular columnar
+                 instance to be created or written.  In this case, the
+                 management protocol set operation will fail with an
+                 error such as `noCreation' or `notWritable'.  In this
+                 case, the management station decides whether it needs
+                 to be able to set a value for that particular columnar
+                 instance.  If not, the management station re-issues the
+                 management protocol set operation, but without setting
+                 a value for that particular columnar instance;
+                 otherwise, the management station aborts the row
+                 creation algorithm.
+
+            Interaction 2b: Negotiating the Creation of the Conceptual
+            Row
+
+            The management station issues a management protocol set
+            operation which sets the desired instance of the status
+            column to `createAndWait'.  If the agent is unwilling to
+            process a request of this sort, the set operation fails with
+            an error of `wrongValue'.  (As a consequence, such an agent
+            must be prepared to accept a single management protocol set
+            operation, i.e., interaction 2a above, containing all of the
+            columns indicated by its column requirements.)  Otherwise,
+            the conceptual row is created, a `noError' response is
+            returned, and the status column is immediately set to either
+            `notInService' or `notReady', depending on whether it has
+            sufficient information to make the conceptual row available
+            for use by the managed device.  If there is sufficient
+            information available, then the status column is set to
+            `notInService'; otherwise, if there is insufficient
+            information, then the status column is set to `notReady'.
+            Regardless, we proceed to interaction 3.
+
+            Interaction 3: Initializing non-defaulted Objects
+
+            The management station must now determine the column
+            requirements.  It issues a management protocol get operation
+            to examine all columns in the created conceptual row.  In
+            the response, for each column, there are three possible
+            outcomes:
+
+                 - a value is returned, indicating that the agent
+                 implements the object-type associated with this column
+                 and had sufficient information to provide a value.  For
+                 those columns to which the agent provides read-create
+                 access (and for which the agent allows their values to
+                 be changed after their creation), a value return tells
+                 the management station that it may issue additional
+                 management protocol set operations, if it desires, in
+                 order to change the value associated with this column.
+
+                 - the exception `noSuchInstance' is returned,
+                 indicating that the agent implements the object-type
+                 associated with this column, and that this column in at
+                 least one conceptual row would be accessible in the MIB
+                 view used by the retrieval were it to exist. However,
+                 the agent does not have sufficient information to
+                 provide a value, and until a value is provided, the
+                 conceptual row may not be made available for use by the
+                 managed device.  For those columns to which the agent
+                 provides read-create access, the `noSuchInstance'
+                 exception tells the management station that it must
+                 issue additional management protocol set operations, in
+                 order to provide a value associated with this column.
+
+                 - the exception `noSuchObject' is returned, indicating
+                 that the agent does not implement the object-type
+                 associated with this column or that there is no
+                 conceptual row for which this column would be
+                 accessible in the MIB view used by the retrieval.  As
+                 such, the management station cannot issue any
+                 management protocol set operations to create an
+                 instance of this column.
+
+            If the value associated with the status column is
+            `notReady', then the management station must first deal with
+            all `noSuchInstance' columns, if any.  Having done so, the
+            value of the status column becomes `notInService', and we
+            proceed to interaction 4.
+
+            Interaction 4: Making the Conceptual Row Available
+
+            Once the management station is satisfied with the values
+            associated with the columns of the conceptual row, it issues
+            a management protocol set operation to set the status column
+            to `active'.  If the agent has sufficient information to
+            make the conceptual row available for use by the managed
+            device, the management protocol set operation succeeds (a
+            `noError' response is returned).  Otherwise, the management
+            protocol set operation fails with an error of
+            `inconsistentValue'.
+
+
+                                     NOTE WELL
+
+                 A conceptual row having a status column with value
+                 `notInService' or `notReady' is unavailable to the
+                 managed device.  As such, it is possible for the
+                 managed device to create its own instances during the
+                 time between the management protocol set operation
+                 which sets the status column to `createAndWait' and the
+                 management protocol set operation which sets the status
+                 column to `active'.  In this case, when the management
+                 protocol set operation is issued to set the status
+                 column to `active', the values held in the agent
+                 supersede those used by the managed device.
+
+            If the management station is prevented from setting the
+            status column to `active' (e.g., due to management station
+            or network failure) the conceptual row will be left in the
+            `notInService' or `notReady' state, consuming resources
+            indefinitely.  The agent must detect conceptual rows that
+            have been in either state for an abnormally long period of
+            time and remove them.  It is the responsibility of the
+            DESCRIPTION clause of the status column to indicate what an
+            abnormally long period of time would be.  This period of
+            time should be long enough to allow for human response time
+            (including `think time') between the creation of the
+            conceptual row and the setting of the status to `active'.
+            In the absence of such information in the DESCRIPTION
+            clause, it is suggested that this period be approximately 5
+            minutes in length.  This removal action applies not only to
+            newly-created rows, but also to previously active rows which
+            are set to, and left in, the notInService state for a
+            prolonged period exceeding that which is considered normal
+            for such a conceptual row.
+
+
+                             Conceptual Row Suspension
+
+            When a conceptual row is `active', the management station
+            may issue a management protocol set operation which sets the
+            instance of the status column to `notInService'.  If the
+            agent is unwilling to do so, the set operation fails with an
+            error of `wrongValue'.  Otherwise, the conceptual row is
+            taken out of service, and a `noError' response is returned.
+            It is the responsibility of the DESCRIPTION clause of the
+            status column to indicate under what circumstances the
+            status column should be taken out of service (e.g., in order
+            for the value of some other column of the same conceptual
+            row to be modified).
+
+
+                              Conceptual Row Deletion
+
+            For deletion of conceptual rows, a management protocol set
+            operation is issued which sets the instance of the status
+            column to `destroy'.  This request may be made regardless of
+            the current value of the status column (e.g., it is possible
+            to delete conceptual rows which are either `notReady',
+            `notInService' or `active'.)  If the operation succeeds,
+            then all instances associated with the conceptual row are
+            immediately removed."
+
+
+    SYNTAX       INTEGER {
+                     -- the following two values are states:
+                     -- these values may be read or written
+                     active(1),
+                     notInService(2),
+
+                     -- the following value is a state:
+                     -- this value may be read, but not written
+                     notReady(3),
+
+                     -- the following three values are
+                     -- actions: these values may be written,
+                     --   but are never read
+                     createAndGo(4),
+                     createAndWait(5),
+                     destroy(6)
+                 }
+      </pre>
+    </section>
+  </section>
+</chapter>
+