module IRTF-NMRG-SMING-TYPES {

//
// $RCSfile: IRTF-NMRG-SMING-TYPES,v $
// $Revision: 1555 $
// $Author: schoenw $
// $Date: 2008-01-22 13:38:03 +0100 (Tue, 22 Jan 2008) $
//

    organization    "IRTF Network Management Research Group (NMRG),
                     Network Management Group, TU Braunschweig";

    contact         "        Frank Strauss

                     Postal: TU Braunschweig
                             Bueltenweg 74/75
                             38106 Braunschweig
                             Germany

                      Phone: +49 531 391-3266
                      EMail: strauss@ibr.cs.tu-bs.de";

    description     "Core type definitions for SMIng.";

    revision {
        date        "2000-10-19";
        description "Special semantics and default value of 8 or 11
		     zero bytes for the DateAndTime type.";
    };

    revision {
        date        "2000-02-13";
        description "SMIng grammar dropped module identity objects.";
    };

    revision {
        date        "1999-05-07";
        description "Initial Revision.";
    };

    typedef Gauge32 {
        type        Unsigned32;
        description
           "The Gauge32 type represents a non-negative integer,
            which may increase or decrease, but shall never
            exceed a maximum value, nor fall below a minimum
            value.  The maximum value can not be greater than
            2^32-1 (4294967295 decimal), and the minimum value
            can not be smaller than 0.  The value of a Gauge32
            has its maximum value whenever the information
            being modeled is greater than or equal to its
            maximum value, and has its minimum value whenever
            the information being modeled is smaller than or
            equal to its minimum value.  If the information
            being modeled subsequently decreases below
            (increases above) the maximum (minimum) value, the
            Gauge32 also decreases (increases).  (Note that
            despite of the use of the term `latched' in the
            original definition of this type, it does not
            become `stuck' at its maximum or minimum value.)";
        reference
           "RFC 2578, Sections 2. and 7.1.7.";
    };

    typedef Counter32 {
        type        Unsigned32;
        description
           "The Counter32 type represents a non-negative integer
            which monotonically increases until it reaches a
            maximum value of 2^32-1 (4294967295 decimal), when it
            wraps around and starts increasing again from zero.
               
            Counters have no defined `initial' value, and thus, a
            single value of a Counter has (in general) no
            information content.  Discontinuities in the
            monotonically increasing value normally occur at
            re-initialization of the management system, and at
            other times as specified in the description of an
            object using this type.  If such other times can
            occur, for example, the creation of an object
            instance at times other than re-initialization, then
            a corresponding object should be defined, with an
            appropriate type, to indicate the last discontinuity.
            Examples of appropriate types include: TimeStamp,
            DateAndTime or TimeTicks (other types defined in this
            module).
               
            The value of the access statement for objects with a
            type value of Counter32 should be either `readonly'
            or `notifyonly'.
               
            A default statement should not be used for objects
            with a type value of Counter32.";
        reference
           "RFC 2578, Sections 2. and 7.1.6.";
    };

    typedef Gauge64 {
        type        Unsigned64;
        description
           "The Gauge64 type represents a non-negative integer,
            which may increase or decrease, but shall never
            exceed a maximum value, nor fall below a minimum
            value.  The maximum value can not be greater than
            2^64-1 (18446744073709551615), and the minimum value
            can not be smaller than 0.  The value of a Gauge64
            has its maximum value whenever the information
            being modeled is greater than or equal to its
            maximum value, and has its minimum value whenever
            the information being modeled is smaller than or
            equal to its minimum value.  If the information
            being modeled subsequently decreases below
            (increases above) the maximum (minimum) value, the
            Gauge64 also decreases (increases).  (Note that
            despite of the use of the term `latched' in the
            original definition of this type, it does not
            become `stuck' at its maximum or minimum value.)";
    };

    typedef Counter64 {
        type        Unsigned64;
        description
           "The Counter64 type represents a non-negative integer
            which monotonically increases until it reaches a
            maximum value of 2^64-1 (18446744073709551615), when
            it wraps around and starts increasing again from zero.
               
            Counters have no defined `initial' value, and thus, a
            single value of a Counter has (in general) no
            information content.  Discontinuities in the
            monotonically increasing value normally occur at
            re-initialization of the management system, and at
            other times as specified in the description of an
            object using this type.  If such other times can
            occur, for example, the creation of an object
            instance at times other than re-initialization, then
            a corresponding object should be defined, with an
            appropriate type, to indicate the last discontinuity.
            Examples of appropriate types include: TimeStamp,
            DateAndTime or TimeTicks (other types defined in this
            module).
               
            The value of the access statement for objects with a
            type value of Counter64 should be either `readonly'
            or `notifyonly'.
               
            A default statement should not be used for objects
            with a type value of Counter64.";
        reference
           "RFC 2578, Sections 2. and 7.1.10.";
    };

    typedef Opaque {
        type        OctetString;
        description
           "The Opaque type is provided solely for
            backward-compatibility, and shall not be used for
            newly-defined object types.
                 
            The Opaque type supports the capability to pass
            arbitrary ASN.1 syntax.  A value is encoded using
            the ASN.1 Basic Encoding Rules into a string of
            octets.  This, in turn, is encoded as an
            OctetString, in effect `double-wrapping' the
            original ASN.1 value.
                 
            Note that a conforming implementation need only be
            able to accept and recognize opaquely-encoded data.
            It need not be able to unwrap the data and then
            interpret its contents.
                 
            A requirement on `standard' MIB modules is that no
            object may have a type value of Opaque.";
        reference
           "RFC 2578, Sections 2. and 7.1.9.";
    };

    typedef IpAddress {
        type        OctetString (4);
        status      deprecated;
        description
           "******* THIS TYPE DEFINITION IS DEPRECATED *******

            The IpAddress type represents a 32-bit internet
            IPv4 address.  It is represented as an OctetString
            of length 4, in network byte-order.
                
            Note that the IpAddress type is present for
            historical reasons. IPv4 and IPv6 addresses should
            be represented using the IpAddr type. Generic
            Network addresses should be represented using a
            pair of TDomain and TAddress types (all defined in
            this module).";
        reference
           "RFC 2578, Sections 2. and 7.1.5.";
    };

    typedef TimeTicks {
        type        Unsigned32;
        description
           "The TimeTicks type represents a non-negative
            integer which represents the time, modulo 2^32
            (4294967296 decimal), in hundredths of a second
            between two epochs.  When objects are defined which
            use this type, the description of the object
            identifies both of the reference epochs.
                 
            For example, the TimeStamp type (defined in this
            module) is based on the TimeTicks type.

            With a TimeStamp, the first reference epoch is
            defined as the time when SNMPv2-MIB::sysUpTime was
            zero, and the second reference epoch is defined as
            the current value of sysUpTime.
                 
            The TimeTicks type should not be sub-typed.";
        reference
           "RFC 2578, Sections 2. and 7.1.8.";
    };

    //
    //  The following type definitions are
    //  conversions of the textual conventions from
    //  the SNMPv2-TC module (RFC 2579), except for
    //  TAddressOrZero, which is not present in
    //  SNMPv2-TC.
    //

    typedef DisplayString {
        type        OctetString (0..255);
        format      "255a";
        description 
        "Represents textual information taken from the NVT ASCII
         character set, as defined in pages 4, 10-11 of RFC 854.
         
         To summarize RFC 854, the NVT ASCII repertoire specifies:
         
          - the use of character codes 0-127 (decimal)
         
          - the graphics characters (32-126) are interpreted as
            US ASCII
         
          - NUL, LF, CR, BEL, BS, HT, VT and FF have the special
            meanings specified in RFC 854
         
          - the other 25 codes have no standard interpretation
         
          - the sequence 'CR LF' means newline
         
          - the sequence 'CR NUL' means carriage-return
         
          - an 'LF' not preceded by a 'CR' means moving to the
            same column on the next line.
         
          - the sequence 'CR x' for any x other than LF or NUL is
            illegal.  (Note that this also means that a string may
            end with either 'CR LF' or 'CR NUL', but not with CR.)
         
         Any object defined using this syntax may not exceed 255
         characters in length.";
    };

    typedef PhysAddress {
        type        OctetString;
        format      "1x:";
        description 
        "Represents media- or physical-level addresses.";
    };

    typedef MacAddress {
        type        OctetString (6);
        format      "1x:";
        description 
        "Represents an 802 MAC address represented in the
         `canonical' order defined by IEEE 802.1a, i.e., as if it
         were transmitted least significant bit first, even though
         802.5 (in contrast to other 802.x protocols) requires MAC
         addresses to be transmitted most significant bit first.";
    };

    typedef TruthValue {
        type        Enumeration (true(1), false(2));
        description 
        "Represents a boolean value.";
    };

    typedef TestAndIncr {
        type        Integer32 (0..2147483647);
        description 
        "Represents integer-valued information used for atomic
         operations.  When the management protocol is used to specify
         that an object instance having this syntax is to be
         modified, the new value supplied via the management protocol
         must precisely match the value presently held by the
         instance.  If not, the management protocol set operation
         fails with an error of `inconsistentValue'.  Otherwise, if
         the current value is the maximum value of 2^31-1 (2147483647
         decimal), then the value held by the instance is wrapped to
         zero; otherwise, the value held by the instance is
         incremented by one.  (Note that regardless of whether the
         management protocol set operation succeeds, the variable-
         binding in the request and response PDUs are identical.)
         
         The value of the ACCESS clause for objects having this
         syntax is either `read-write' or `read-create'.  When an
         instance of a columnar object having this syntax is created,
         any value may be supplied via the management protocol.
         
         When the network management portion of the system is re-
         initialized, the value of every object instance having this
         syntax must either be incremented from its value prior to
         the re-initialization, or (if the value prior to the re-
         initialization is unknown) be set to a pseudo-randomly
         generated value.";
    };

    typedef AutonomousType {
        type        ObjectIdentifier;
        description 
        "Represents an independently extensible type identification
         value.  It may, for example, indicate a particular sub-tree
         with further MIB definitions, or define a particular type of
         protocol or hardware.";
    };

    typedef InstancePointer {
        type        ObjectIdentifier;
        status      obsolete;
        description 
        "A pointer to either a specific instance of a MIB object or
         a conceptual row of a MIB table in the managed device.  In
         the latter case, by convention, it is the name of the
         particular instance of the first accessible columnar object
         in the conceptual row.
         
         The two uses of this textual convention are replaced by
         VariablePointer and RowPointer, respectively.";
    };

    typedef VariablePointer {
        type        ObjectIdentifier;
        description 
        "A pointer to a specific object instance.  For example,
         sysContact.0 or ifInOctets.3.";
    };

    typedef RowPointer {
        type        ObjectIdentifier;
        description 
        "Represents a pointer to a conceptual row.  The value is the
         name of the instance of the first accessible columnar object
         in the conceptual row.
         
         For example, ifIndex.3 would point to the 3rd row in the
         ifTable (note that if ifIndex were not-accessible, then
         ifDescr.3 would be used instead).";
    };

    typedef RowStatus {
        type        Enumeration (active(1), notInService(2), 
                        notReady(3), createAndGo(4), 
                        createAndWait(5), destroy(6));
        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 of [2].)
         
         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|see 8     ->D|          ->D
--------------+--------------+-----------+-------------+-------------
set status    |inconsistent- |inconsist- |noError      |noError   ->C
column to     |         Value|   entValue|             |
notInService  |              |           |             |
              |              |     or    |             |      or
              |              |           |             |
              |              |see 3   ->C|          ->C|see 6
--------------+--------------+-----------+-------------+-------------
set status    |noError       |noError    |noError      |noError   ->A
column to     |              |           |             |      or
destroy       |           ->A|        ->A|          ->A|see 7
--------------+--------------+-----------+-------------+-------------
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.
         
         (6) the return value can indicate one of the following
         errors:
         
             wrongValue: because the agent does not support
             createAndWait, or
         
             inconsistentValue: because the agent is unable to take
             the row out of service at this time, perhaps because it
             is in use and cannot be de-activated.
         
         (7) the return value can indicate the following error:
         
         
             inconsistentValue: because the agent is unable to
             remove the row at this time, perhaps because it is in
             use and cannot be de-activated.
         
         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 can not 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 can not 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' or `inconsistentValue'.
         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.";
    };

    typedef TimeStamp {
        type        TimeTicks;
        description 
        "The value of the sysUpTime object at which a specific
         occurrence happened.  The specific occurrence must be
         defined in the description of any object defined using this
         type.  When the specific occurrence occurred prior to the
         last time sysUpTime was zero, then the TimeStamp value is
         zero.  Note that this requires all TimeStamp values to be
         reset to zero when the value of sysUpTime reaches 497+ days
         and wraps around to zero.";
    };

    typedef TimeInterval {
        type        Integer32 (0..2147483647);
        description 
        "A period of time, measured in units of 0.01 seconds.";
    };

    typedef DateAndTime {
        type        OctetString (8 | 11);
	default     0x0000000000000000000000;
        format      "2d-1d-1d,1d:1d:1d.1d,1a1d:1d";
        description 
        "A date-time specification.
         
         field  octets  contents                  range
         -----  ------  --------                  -----
          1      1-2   year*                     0..65536
          2       3    month                     1..12
          3       4    day                       1..31
          4       5    hour                      0..23
          5       6    minutes                   0..59
          6       7    seconds                   0..60
                       (use 60 for leap-second)
          7       8    deci-seconds              0..9
          8       9    direction from UTC        '+' / '-'
          9      10    hours from UTC*           0..13
         10      11    minutes from UTC          0..59
         
         * Notes:
         - the value of year is in big-endian encoding
         - daylight saving time in New Zealand is +13
         
         For example, Tuesday May 26, 1992 at 1:30:15 PM EDT would be
         displayed as:
         
                         1992-5-26,13:30:15.0,-4:0
         
         Note that if only local time is known, then timezone
         information (fields 8-10) is not present.

	 The two special values of 8 or 11 zero bytes denote an
	 unknown date-time specification.";
    };

    typedef StorageType {
        type        Enumeration (other(1), volatile(2), 
                        nonVolatile(3), permanent(4), 
                        readOnly(5));
        description 
        "Describes the memory realization of a conceptual row.  A
         row which is volatile(2) is lost upon reboot.  A row which
         is either nonVolatile(3), permanent(4) or readOnly(5), is
         backed up by stable storage.  A row which is permanent(4)
         can be changed but not deleted.  A row which is readOnly(5)
         cannot be changed nor deleted.
         
         If the value of an object with this syntax is either
         permanent(4) or readOnly(5), it cannot be modified.
         Conversely, if the value is either other(1), volatile(2) or
         nonVolatile(3), it cannot be modified to be permanent(4) or
         readOnly(5).  (All illegal modifications result in a
         'wrongValue' error.)
         
         Every usage of this textual convention is required to
         specify the columnar objects which a permanent(4) row must
         at a minimum allow to be writable.";
    };

    typedef TDomain {
        type        ObjectIdentifier;
        description
        "Denotes a kind of transport service.

         Some possible values, such as snmpUDPDomain, are defined
         in the SNMPv2-TM MIB module.  Other possible values are
         defined in other MIB modules.";
        reference
        "The SNMPv2-TM MIB module is defined in RFC 1906.";
    };

    typedef TAddressOrZero {
        type        OctetString (0..255);
        description
        "Denotes a transport service address.

         A TAddress value is always interpreted within the context
         of a TDomain value.  Thus, each definition of a TDomain
         value must be accompanied by a definition of a textual
         convention for use with that TDomain.  Some possible
         textual conventions, such as SnmpUDPAddress for
         snmpUDPDomain, are defined in the SNMPv2-TM MIB module.
         Other possible textual conventions are defined in
         other MIB modules.

         A zero-length TAddress value denotes an unknown transport
         service address.";
        reference
        "The SNMPv2-TM MIB module is defined in RFC 1906.";
    };

    typedef TAddress {
        type        TAddressOrZero (1..255);
        description
        "Denotes a transport service address.

         This type does not allow a zero-length TAddress value.";
    };

};
