Internet DRAFT - draft-birrane-dtn-amp
draft-birrane-dtn-amp
Delay-Tolerant Networking E. Birrane
Internet-Draft Johns Hopkins Applied Physics Laboratory
Intended status: Standards Track April 15, 2020
Expires: October 17, 2020
Asynchronous Management Protocol
draft-birrane-dtn-amp-08
Abstract
This document describes a binary encoding of the Asynchronous
Management Model (AMM) and a protocol for the exchange of these
encoded items over a network. This Asynchronous Management Protocol
(AMP) does not require transport-layer sessions, operates over
unidirectional links, and seeks to reduce the energy and compute
power necessary for performing network management on resource
constrained devices.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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This Internet-Draft will expire on October 17, 2020.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
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include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Protocol Scope . . . . . . . . . . . . . . . . . . . . . 3
3.2. Specification Scope . . . . . . . . . . . . . . . . . . . 4
4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Constraints and Assumptions . . . . . . . . . . . . . . . . . 4
6. Technical Notes . . . . . . . . . . . . . . . . . . . . . . . 5
7. AMP-Specific Concepts . . . . . . . . . . . . . . . . . . . . 6
7.1. Nicknames (NN) . . . . . . . . . . . . . . . . . . . . . 6
7.1.1. Motivation for Compression . . . . . . . . . . . . . 6
7.1.2. ADM Enumeration . . . . . . . . . . . . . . . . . . . 7
7.1.3. ADM Template Collection Enumeration . . . . . . . . . 8
7.1.4. Nickname Definition . . . . . . . . . . . . . . . . . 9
7.1.5. ADM Enumeration Considerations . . . . . . . . . . . 9
8. Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. CBOR Considerations . . . . . . . . . . . . . . . . . . . 10
8.2. AMM Type Encodings . . . . . . . . . . . . . . . . . . . 10
8.2.1. Primitive Types . . . . . . . . . . . . . . . . . . . 10
8.2.2. Derived Types . . . . . . . . . . . . . . . . . . . . 11
8.2.3. Collections . . . . . . . . . . . . . . . . . . . . . 14
8.3. AMM Resource Identifier (ARI) . . . . . . . . . . . . . . 19
8.3.1. Encoding ARIs of Type LITERAL . . . . . . . . . . . . 19
8.3.2. Encoding Non-Literal ARIs . . . . . . . . . . . . . . 20
8.4. ADM Object Encodings . . . . . . . . . . . . . . . . . . 23
8.4.1. Externally Defined Data (EDD) . . . . . . . . . . . . 23
8.4.2. Constants (CONST) . . . . . . . . . . . . . . . . . . 24
8.4.3. Controls (CTRL) . . . . . . . . . . . . . . . . . . . 24
8.4.4. Macros (MAC) . . . . . . . . . . . . . . . . . . . . 25
8.4.5. Operators (OPER) . . . . . . . . . . . . . . . . . . 26
8.4.6. Report Templates (RPTT) . . . . . . . . . . . . . . . 26
8.4.7. Report (RPT) . . . . . . . . . . . . . . . . . . . . 27
8.4.8. State-Based Rules (SBR) . . . . . . . . . . . . . . . 28
8.4.9. Table Templates (TBLT) . . . . . . . . . . . . . . . 30
8.4.10. Tables (TBL) . . . . . . . . . . . . . . . . . . . . 30
8.4.11. Time-Based Rules (TBR) . . . . . . . . . . . . . . . 31
8.4.12. Variables (VAR) . . . . . . . . . . . . . . . . . . . 33
9. Functional Specification . . . . . . . . . . . . . . . . . . 33
9.1. AMP Message Summary . . . . . . . . . . . . . . . . . . . 33
9.2. Message Group Format . . . . . . . . . . . . . . . . . . 34
9.3. Message Format . . . . . . . . . . . . . . . . . . . . . 35
9.4. Register Agent . . . . . . . . . . . . . . . . . . . . . 37
9.5. Report Set . . . . . . . . . . . . . . . . . . . . . . . 37
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9.6. Perform Control . . . . . . . . . . . . . . . . . . . . . 38
9.7. Table Set . . . . . . . . . . . . . . . . . . . . . . . . 38
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39
11. Security Considerations . . . . . . . . . . . . . . . . . . . 39
12. Implementation Notes . . . . . . . . . . . . . . . . . . . . 39
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 40
13.1. Informative References . . . . . . . . . . . . . . . . . 40
13.2. Normative References . . . . . . . . . . . . . . . . . . 40
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 40
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 40
1. Introduction
Network management in challenged and resource constrained networks
must be accomplished differently than the network management methods
in high-rate, high-availability networks. The Asynchronous
Management Architecture (AMA) [I-D.birrane-dtn-ama] provides an
overview and justification of an alternative to "synchronous"
management services such as those provided by NETCONF. In
particular, the AMA defines the need for a flexible, robust, and
efficient autonomy engine to handle decisions when operators cannot
be active in the network. The logical description of that autonomous
model and its major components is given in the AMA Data Model (ADM)
[I-D.birrane-dtn-adm].
The ADM presents an efficient and expressive autonomy model for the
asynchronous management of a network node, but does not specify any
particular encoding. This document, the Asynchronous Management
Protocol (AMP), provides a binary encoding of AMM objects and
specifies a protocol for the exchange of these encoded objects.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Scope
3.1. Protocol Scope
The AMP provides data monitoring, administration, and configuration
for applications operating above the data link layer of the OSI
networking model. While the AMP may be configured to support the
management of network layer protocols, it also uses these protocol
stacks to encapsulate and communicate its own messages.
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It is assumed that the protocols used to carry AMP messages provide
addressing, confidentiality, integrity, security, fragmentation/
reassembly, and other network functions. Therefore, these items are
outside of the scope of this document.
3.2. Specification Scope
This document describes the format of messages used to exchange data
models between managing and managed devices in a network. The
rationale for this type of exchange is outside of the scope of this
document and is covered in [I-D.birrane-dtn-ama]. The description
and explanation of the data models exchanged is also outside of the
scope of this document and is covered in [I-D.birrane-dtn-adm].
This document does not address specific configurations of AMP-enabled
devices, nor does it discuss the interface between AMP and other
management protocols.
4. Terminology
Note: The terms "Actor", "Agent", "Application Data Model",
"Externally Defined Data", "Variable", "Control", "Literal", "Macro",
"Manager", "Report Template", "Report", "Table", "Constant",
"Operator", "Time-Based Rule" and "State-Based Rule" are used without
modification from the definitions provided in [I-D.birrane-dtn-ama].
5. Constraints and Assumptions
The desirable properties of an asynchronous management protocol, as
specified in the AMA, are summarized here to represent design
constraints on the AMP specification.
o Intelligent Push of Information - Nodes in a challenged network
cannot guarantee concurrent, bi-directional communications. Some
links between nodes may be strictly unidirectional. AMP Agents
"push" data to Managers rather than Managers "pulling" data from
Agents.
o Small Message Sizes - Smaller messages require smaller periods of
viable transmission for communication, incur less retransmission
cost, and consume fewer resources when persistently stored en
route in the network. AMP minimizes message size wherever
practical, to include binary data representations and predefined
data definitions and templates.
o Absolute and Custom Data Identification - All data in the system
must be uniquely addressable, to include operator-specified
information. AMP provides a compact encoding for identifiers.
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o Autonomous, Stateless Operation - There is no reliable concept of
session establishment or round-trip data exchange in asynchronous
networks. AMP is designed to be stateless. Where helpful, AMP
provides mechanisms for transactional ordering of commands within
a single AMP protocol data unit, but otherwise degrades gracefully
when nodes in the network diver in their configuration.
6. Technical Notes
o Unless otherwise specified, multi-byte values in this
specification are expected to be transmitted in network byte order
(Big Endian).
o Character encodings for all text-based data types will use UTF-8
encodings.
o All AMP encodings are self-terminating. This means that, given an
indefinite-length octet stream, each encoding can be unambiguously
decoded from the stream without requiring additional information
such as a length field separate from the data type definition.
o This specification uses the term OCTETS to refer to a sequence of
one or more related BYTE values. There is no implied structure
associated with OCTETS, meaning they do not encode a length value
or utilize a terminator character. While OCTETS may contain CBOR-
encoded values, the OCTETS sequence itself is not encoded as a
CBOR structure.
o If an OCTETS sequence is included as an element of a CBOR array
then the sequence MUST be considered as a single array element
when determining the size of the array.
o Bit-fields in this document are specified with bit position 0
holding the least-significant bit (LSB). When illustrated in this
document, the LSB appears on the right.
o In order to describe the encoding of data models specified in
[I-D.birrane-dtn-adm], this specification must refer to both the
data object being encoded and to the encoding of that data object.
When discussing the encoded version of a data object, this
specification uses the notation "E(data_object)" where E() refers
to a conceptual encoding function. This notation is only provided
as a means of clarifying the text and imposes no changes to the
actual wire coding. For example, this specification will refer to
the "macro" data object as "Macro" and to the encoding of a Macro
as "E(Macro)".
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o Illustrations of fields in this specification consist of the name
of the field, the type of the field between []'s, and if the field
is optional, the text "(opt)".
Field order is deterministic and, therefore, fields MUST be
transmitted in the order in which they are specified. In cases
where an optional field is not present, then the next field will
be considered for transmission.
An example is shown in Figure 1 below. In this illustration two
fields (Field 1 and Field 2) are shown, with Field 1 of Type 1 and
Field 2 of Type 2. Field 2 is also listed as being optional.
Byte fields are shown in order of receipt, from left-to-right.
Therefore, when transmitted on the wire, Field 1 will be received
first, followed by Field 2 (if present).
+----------+----------+
| Field 1 | Field 2 |
| [TYPE 1] | [TYPE 2] |
| | (opt) |
+----------+----------+
Figure 1: Byte Field Formatting Example
When types are documented in this way, the type always refers to
the encoding of that type. The E() notation is not used as it is
to be inferred from the context of the illustration.
7. AMP-Specific Concepts
The AMP specification provides an encoding of objects comprising the
AMM. As such, AMP defines very few structures of its own. This
section identifies those data structures that are unique to the AMP
and required for it to perform appropriate and efficient encodings of
AMM objects.
7.1. Nicknames (NN)
In the AMP, a "Nickname" (NN) is used to reduce the overall size of
the encoding of ARIs that are defined in the context of an ADM. A NN
is calculated as a function of an ADM Moderated Namespace and the
type of object being identified.
7.1.1. Motivation for Compression
As identifiers, ARIs are used heavily in AMM object definitions,
particularly in those that define collections of objects. This makes
encoding ARIs an important consideration when trying to optimize the
size of AMP message.
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Additionally, the majority of ARIs are defined in the context of an
ADM. Certain AMM objects types (EDDs, OPs, CTRLs, TBLTs) can only be
defined in the context of an ADM. Other object types (VARs, CONSTs,
RPTTs) may have common, useful objects defined in an ADM as well.
The structure of an ADM, to include its use of a Moderated Namespace
and collections by object type, provide a regular structure that can
be exploited for creating a compact representation.
In particular, as specified in [I-D.birrane-dtn-adm], ARIs can be
grouped by (1) their namespace and (2) the type of AMM object being
identified. For example, consider the following ARIs of type EDD
defined in ADM1 with a Moderated Namespace of "/DTN/ADM1/".
ari:/DTN/ADM1/Edd.item_1 ari:/DTN/ADM1/Edd.item_2 ... ari:/DTN/ADM1/
Edd.item_1974
In this case, the namespace (/DTN/ADM1/) and the object type (Edd)
are good candidates for enumeration because their string encoding is
very verbose and their information follows a regular structure shared
across multiple ARIs. Separately, the string representation of
object names (item_1, item_2, etc...) may be very verbose and they
are also candidates for enumeration as they occupy a particular ADM
object type in a particular order as published in the ADM.
7.1.2. ADM Enumeration
Any ARI defined in an ADM exists in the context of a Moderated
Namespace. These namespaces provide a unique string name for the
ADM. However, ADMs can also be assigned a unique enumeration by the
same moderating entities that ensure namespace uniqueness.
An ADM enumeration is an unsigned integer in the range of 0 to
(2^64)/20. This range provides effective support for thousands of
trillions of ADMs.
The formal set of ADMs, similar to SNMP MIBs and NETCONF YANG models,
will be moderated and published. Additionally, a set of informal
ADMs may be developed on a network-by-network or on an organization-
by-organization bases.
Since informal ADMs exist within a predefined context (a network, an
organization, or some other entity) they do not have individual ADM
enumerations and are assigned the special enumeration "0". ARIs that
are not defined in formal ADMs rely on other context information to
help with their encoding (see Section 8.3).
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7.1.3. ADM Template Collection Enumeration
The ADM template presented in [I-D.birrane-dtn-adm] defines a series
of object collections for the specification of various AMM objects.
Enumerating these collections in a standard way allows for their
compressed representation in the context of nicknames for objects
stored in these collections.
The enumeration of ADM Template collections is provided in Table 1
below.
+-----------------+-------------+
| AMM Object Type | Enumeration |
+-----------------+-------------+
| CONST | 0 |
| | |
| CTRL | 1 |
| | |
| EDD | 2 |
| | |
| MAC | 3 |
| | |
| OPER | 4 |
| | |
| RPTT | 5 |
| | |
| SBR | 6 |
| | |
| TBLT | 7 |
| | |
| TBR | 8 |
| | |
| VAR | 9 |
| | |
| metadata | 10 |
| | |
| reserved | 11-19 |
+-----------------+-------------+
Table 1: ADM Type Enumerations
NOTE: Collection enumerations are different from AMM object types.
For example, the enumeration for the VAR collection (9) in an ADM is
different from the VAR object type (12).
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7.1.4. Nickname Definition
As an enumeration, a Nickname is captured as a 64-bit unsigned
integer (UVAST) calculated as a function of the ADM enumeration and
the ADM type enumeration, as follows.
NN = ((ADM Enumeration) * 20) + (ADM Object Type Enumeration)
Considering the example set of ARIs from Section 7.1.1, assuming that
ADM1 has ADM enumeration 9 and given that objects in the example were
of type EDD, the NN for each of the 1974 items would be: (9 * 20) + 2
= 182. In this particular example, the ARI "/DTN/ADM1/Edd.item_1974"
can be encoded in 5 bytes: two bytes to CBOR encode the nickname
(182) and 3 bytes to CBOR encode the item's offset in the Edd
collection (1974).
7.1.5. ADM Enumeration Considerations
The assignment of formal ADM enumerations SHOULD take into
consideration the nature of the applications and protocols to which
the ADM applies. Those ADMs that are likely to be used in challenged
networks SHOULD be allocated low enumeration numbers (e.g. those that
will fit into 1-2 bytes) while ADMs that are likely to only be used
in well resourced networks SHOULD be allocated higher enumeration
numbers. It SHOULD NOT be the case that ADM enumerations are
allocated on a first-come, first-served basis. It is recommended
that ADM enumerations should be labeled based on the number of bytes
of the Nickname as a function of the size of the ADM enumeration.
These labels are shown in Table 2.
+-------------+--------+--------------+-----------------------------+
| ADM Enum | NN | Label | Comment |
| | Size | | |
+-------------+--------+--------------+-----------------------------+
| 0x1 - 0xCCC | 1-2 | Challenged | Constraints imposed by |
| | Bytes | Networks | physical layer and power. |
| | | | |
| 0xCCD - | 3-4 | Congested | Constraints imposed by |
| 0xCCCCCCC | Bytes | Networks | network traffic. |
| | | | |
| >=0xCCCCCCD | 5-8 | Resourced | Generally unconstrained |
| | Bytes | Networks | networks. |
+-------------+--------+--------------+-----------------------------+
Table 2: ADM Enumerations Labels
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8. Encodings
This section describes the binary encoding of logical data constructs
using the Concise Binary Object Representation (CBOR) defined in
[RFC7049].
8.1. CBOR Considerations
The following considerations act as guidance for CBOR encoders and
decoders implementing the AMP.
o All AMP encodings are of definite length and, therefore,
indefinite encodings MUST NOT be used.
o AMP encodings MUST NOT use CBOR tags. Identification mechanisms
in the AMP capture structure and other information such that tags
are not necessary.
o Canonical CBOR MUST be used for all encoding. All AMP CBOR
decoders MUST run in strict mode.
o Because AMA objects are self-delineating they can be serialized
into, or deserialized from, OCTETS. CBOR containers such as
BYTESTR and TXTSTR that encode length fields are only useful for
data that is not self-delineating, such as name fields. Encoding
self-delineating objects into CBOR containers reduced efficiency
as length fields would then be added to data that does not reqire
a length field for processing.
o Encodings MUST result in smallest data representations. There are
several cases where the AMM defines types with less granularity
than CBOR. For example, AMM defines the UINT type to represent
unsigned integers up to 32 bits in length. CBOR supports separate
definitions of unsigned integers of 8, 16, or 32 bits in length.
In cases where an AMM type MAY be encoded in multiple ways in
CBOR, the smallest data representation MUST be used. For example,
UINT values of 0-255 MUST be encoded as a uint8_t, and so on.
8.2. AMM Type Encodings
8.2.1. Primitive Types
The AMP encodes AMM primitive types as outlined in Table 3.
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+--------+-------------+--------------------------------------------+
| AMM | CBOR Major | Comments |
| Type | Type | |
+--------+-------------+--------------------------------------------+
| BYTE | unsigned | BYTEs are individually encoded as unsigned |
| | int or byte | integers unless the are defined as part of |
| | string | a byte string, in which case they are |
| | | encoded as a single byte in the byte |
| | | string. |
| | | |
| INT | unsigned | INTs are encoded as positive or negative |
| | integer or | integers from (u)int8_t up to (u)int32_t. |
| | negative | |
| | integer | |
| | | |
| UINT | unsigned | UINTs are unsigned integers from uint8_t |
| | integer | up to uint32_t. |
| | | |
| VAST | unsigned | VASTs are encoding as positive or negative |
| | integer or | integers up to (u)int64_t. |
| | negative | |
| | integer | |
| | | |
| UVAST | unsigned | VASTs are unsigned integers up to |
| | integer | uint64_t. |
| | | |
| REAL32 | floating | Up to an IEEE-754 Single Precision Float. |
| | point | |
| | | |
| REAL64 | floating | Up to an IEEE-754 Double Precision Float. |
| | point | |
| | | |
| STRING | text string | Uses CBOR encoding unmodified. |
| | | |
| BOOL | Simple | 0 is considered FALSE. Any other value is |
| | Value | considered TRUE. |
+--------+-------------+--------------------------------------------+
Table 3: Standard Numeric Types
8.2.2. Derived Types
This section provides the CBOR encodings for AMM derived types.
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8.2.2.1. Byte String Encoding
The AMM derived type Byte String (BYTESTR) is encoded as a CBOR byte
string.
8.2.2.2. Time Values (TV) and Timestamps (TS)
An TV is encoded as a UVAST. Similarly, a TS is also encoded as a
UVAST since a TS is simply an absolute TV.
Rather than define two separate encodings for TVs (one for absolute
TVs and one for relative TVs) a single, unambiguous encoding can be
generated by defining a Relative Time Epoch (RTE) and interpreting
the type of TV in relation to that epoch. Time values less than the
RTE MUST be interpreted as relative times. Time values greater than
or equal to the RTE MUST be interpreted as absolute time values.
A relative TV is encoded as the number of seconds after an initiating
event. An absolute TV (and TS) is encoded as the number of seconds
that have elapsed since 1 Jan 2000 00:00:00 (Unix Time 946684800).
The RTE is defined as the timestamp value for September 9th, 2017
(Unix time 1504915200). Since TS values are the number of seconds
since 1 Jan 2000 00:00:00, the RTE as a TS value is 1504915200 -
946684800 = 558230400.
The potential values of TV, and how they should be interpreted as
relative or absolute is illustrated below.
Potential Time values
________________________/\________________________
/ \
Relative Times Absolute Times
<------------------------><------------------------>
0 - 558,230,400 558,230,401 - 2^64
|------------------------|-------------------------|
| |
00:00:00 1 Jan 2000 00:00:00 9 Sep 2017
Unix Time 946684800 Unix Time 1504915200
For example, a time value of "10" is a relative time representing 10
seconds after an initiating event. A time value of "600,000,000"
refers to Saturday, 5 Jan, 2019 10:40:00.
NOTE: Absolute and relative times are interchangeable. An absolute
time can be converted into a relative time by subtracting the current
time from the absolute time. A relative time can be converted into
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an absolute time by adding to the relative time the timestamp of its
relative event. A pseudo-code example of converting a relative time
to an absolute time is as follows, assuming that current-time is
expressed in Unix Epoch time.
IF (time_value <= 558230400) THEN
absolute_time = (event_time - 946684800) + time_value
ELSE
absolute_time = time_value
8.2.2.3. Type-Name-Value (TNV)
TNV values are encoded as a CBOR array that comprises four distinct
pieces of information: a set of flags, a type, an optional name, and
an optional value. In the E(TNV) the flag and type information are
compressed into a single value. The CBOR array MUST have length 1,
2, or 3 depending on the number of optional fields appearing in the
encoding. The E(TNV) format is illustrated in Figure 2.
+---------+
| TNV |
| [ARRAY] |
+----++---+
||
||
_______________/ \________________
/ \
+------------+-----------+----------+
| Flags/Type | Name | Value |
| [BYTE] | [TXT STR] | [Varies] |
| | (opt) | (opt) |
+------------+-----------+----------+
Figure 2: E(TNV) Format
The E(TNV) fields are defined as follows.
Flags/Type
The first byte of the E(TNV) describes the type associated
with the TNV and which optional components are present. The
layout of this byte is illustrated in Figure 3.
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E(TNV) Flag/Type Byte Format
+------+---------------+
| Name | Struct |
| Flag | Type |
+------+---------------+
| 7 | 6 5 4 3 2 1 0 |
+------+---------------+
MSB LSB
Figure 3
Name Flag
This flag indicates that the TNV contains a name
field. When set to 1 the Name field MUST be present
in the E(TNV). When set to 0 the Name field MUST NOT
be present in the E(TNV).
Struct Type
This field lists the type associated with this TNV
and MUST contain one of the types defined in
[I-D.birrane-dtn-adm] with the exception that the
type of a TNV MUST NOT be a TNV.
Name
This optional field captures the human-readable name for the
TNV encoded as a CBOR text string. If there are 3 elements
in the TNV array OR there are 2 elements in the array and the
Name Flag is set, then this field MUST be present.
Otherwise, this field MUST NOT be present.
Value
This optional field captures the encoded value associated
with this TNV. The value is encoded in accordance with AMP
rules for encoding of items of the type of this TNV. If
there are 3 elements in the TNV array OR there are 2 elements
in the array and the Name Flag is not set, then this field
MUST be present. Otherwise, this field MUST NOT be present.
8.2.3. Collections
8.2.3.1. Type-Name-Value Collection (TNVC)
A TNV Collection (TNVC) is an ordered set of TNVs with special
semantics for more efficiently encoding sets of TNVs with identical
attributes.
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A TNV, defined in Section 8.2.2.3, consists of three distinct
components: a type, a name, and a value. When all of the TNVs in the
TNVC have the same format (such as they all include type information)
then the encoding of the TNVC can use this information to save
encoding space and make processing more efficient. In cases when all
TNVs have the same format, the types (if present), names (if
present), and values (if present) are separated into their own arrays
for individual processing with type information (if present) always
appearing first.
Extracting type information to the "front" of the collection
optimizes the performance of type validators. A validator can
inspect the first array to ensure that element values match type
expectations. If type information were distributed throughout the
collection, as in the case with the TNVC, a type validator would need
to scan through the entire set of data to validate each type in the
collection.
A TNVC is encoded as a sequence of at least 1 octet, where the single
required octet includes the flag BYTE representing the optional
portions of the collection that are present. If the flag BYTE
indicates an empty collection there will be no following octets.The
format of a TNVC is illustrated in Figure 4.
+----------+
| TNVC |
| [OCTETS] |
+----++----+
||
||
____________________________/ \_____________________________
/ \
+--------+---------+----------+----------+----------+----------+
| Flags | # Items | Types | Names | Values | Mixed |
| [BYTE] | [UINT] | [OCTETS] | [OCTETS] | [OCTETS] | [OCTETS] |
| | (Opt) | (Opt) | (Opt) | (Opt) | (Opt) |
+--------+---------+----------+----------+----------+----------+
Figure 4: E(TNVC) Format
The E(TNVC) fields are defined as follows.
Flags
The first byte of the E(TNVC) describes which optional
portions of a TNV will be present for each TNV in the
collection.
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If all non-reserved flags have the value 0 then the TNVC
represents an empty collection, in which case no other
information is provided for the E(TNVC).
The layout of this byte is illustrated in Figure 5.
E(TNV) Flag Byte Format
+----------+------+------+------+------+
| Reserved | Mix | Type | Name | Val |
| Flags | Flag | Flag | Flag | Flag |
+----------+------+------+------+------+
| 7-4 | 3 | 2 | 1 | 0 |
+----------+------+------+------+------+
MSB LSB
Figure 5
Mixed Flag
This flag indicates that the set of TNVs in the
collection do not all share the same properties and,
therefore, the collection is a mix of different types
of TNV. When set to 1 the E(TNVC) MUST contain the
Mixed Values field and all other flags in this byte
MUST be set to 0. When set to 0 the E(TNVC) MUST NOT
contain the Mixed Values field.
Type Flag
This flag indicates whether each TNV in the
collection has type information associated with it.
When set to 1 the E(TNVC) MUST contain type
information for each TNV. When set to 0, type
information MUST NOT be present.
Name Flag
This flag indicates whether each TNV in the
collection has name information associated with it.
When set to 1 the E(TNVC) MUST contain name
information for each TNV. When set to 0, name
information MUST NOT be present.
Value Flag
This flag indicates whether each TNV in the
collection has value information associated with it.
When set to 1 the E(TNVC) MUST contain value
information for each TNV. When set to 0, value
information MUST NOT be present.
# Items
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The number of items field lists the number of items that are
contained in the TNVC. Each of the types, names, and values
sequences (if present) MUST have exactly this number of
entries in them. This field MUST be present in the E(TNVC)
when any one of the non-reserved bits of the Flag Byte are
set to 1.
Types
The types field is encoded as an OCTETS sequence where the
Nth byte in the sequence represents the type for the Nth TNV
in the collection. This field MUST be present in the E(TNVC)
when the Type Flag is set to 1 and MUST NOT be present
otherwise. If present, this field MUST contain exactly the
same number of types as number of items in the TNVC.
Names
The names field is encoded as an OCTETS sequence containing
the names of the TNVs in the collection. Each name is
encoded as a CBOR string, with the Nth CBOR string
representing the name of the Nth TNV in the collection. This
field MUST be present in the E(TNVC) when the Names Flag is
set to 1 and MUST NOT be present otherwise. If present, this
field MUST contain exactly the same number of CBOR strings as
number of items in the TNVC.
Values
The values field is encoded as an OCTETS sequence containing
the values of TNVs in the collection.
If the Type Flag is set to 1 then each entry will be encoded
in accordance with the corresponding index in the type field.
For example, the 1st value will be encoded using the encoding
rules for the first byte in the type OCTETS sequence.
If the Type Flag is set to 0 then the values will be encoded
as native CBOR types. CBOR types do not have a one-to-one
mapping with AMP types and it is the responsibility of the
transmitting AMP actor and the receiving AMP actor to
determine how to map these to AMP types. This field MUST be
present in the E(TNVC) when the Value Flag is set to 1 and
MUST NOT be present otherwise. If present, this field MUST
contain exactly the same number of values as number of items
in the TNVC.
Mixed
The mixed field is encoded as an OCTETS sequence containing a
series of E(TNV) objects. This field MUST be present when
the Mixed Flag is set to 1 and MUST NOT be present otherwise.
If present, this field MUST contain exactly the same number
of E(TNV) objects as numnber of items in the TNVC.
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8.2.3.2. ARI Collections (AC)
An ARI collection is an ordered collection of ARI values. It is
encoded as a CBOR array with each element being an encoded ARI, as
illustrated in Figure 6.
E(AC) Format
+---------+
| AC |
| [ARRAY] |
+----++---+
||
||
________/ \_________
/ \
+-------+ +-------+
| ARI 1 | ... | ARI N |
| [ARI] | | [ARI] |
+-------+ +-------+
Figure 6
8.2.3.3. Expressions (EXPR)
The Expression object encapsulates a typed postfix expression in
which each operator MUST be of type OPER and each operand MUST be the
typed result of an operator or one of EDD, VAR, LIT, or CONST.
The Expression object is encoded as an OCTETS sequence whose format
is illustrated in Figure 7.
E(EXPR) Format
+----------+
| EXPR |
| [OCTETS] |
+-----++---+
||
||
_________/ \_________
/ \
+---------+------------+
| Type | Expression |
| [BYTE] | [AC] |
+---------+------------+
Figure 7
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Type
The enumeration representing the type of the result of the
evaluated expression. This type MUST be defined in
[I-D.birrane-dtn-adm] as a "Primitive Type".
Expression
An expression is represented in the AMP as an ARI collection,
where each ARI in the ordered collection represents either an
operand or operator in postfix form.
8.3. AMM Resource Identifier (ARI)
The ARI, as defined in [I-D.birrane-dtn-adm], identifies an AMM
object. There are two kinds of objects that can be identified in
this scheme: literal objects (of type LIT) and all other objects.
8.3.1. Encoding ARIs of Type LITERAL
A literal identifier is one that is literally defined by its value,
such as numbers (0, 3.14) and strings ("example"). ARIs of type
LITERAL do not have issuers or nicknames or parameters. They are
simply typed basic values.
The E(ARI) of a LIT object is encoded as an OCTETS sequence and
consists of a mandatory flag BYTE and the value of the LIT.
The E(ARI) structure for LIT types is illustrated in Figure 8.
E(ARI) Literal Format
+--------+----------+
| Flags | Value |
| [BYTE] | [VARIES] |
+--------+----------+
Figure 8
These fields are defined as follows.
Flags
The Flags byte identifies the object as being of type LIT and
also captures the primitive type of the following value. The
layout of this byte is illustrated in Figure 9.
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E(ARI) Literal Flag Byte Format
+-------------------+-------------+
| VALUE TYPE OFFSET | STRUCT TYPE |
+-------------------+-------------|
| 7 6 5 4 | 3 2 1 0 |
+-------------------+-------------+
MSB LSB
Figure 9
Value Type Offset
The high nibble of the flag byte contains the offset
into the Primitive Types enumeration defined in
[I-D.birrane-dtn-adm]. An offset of 0 represents the
first defined Primitive Type. An offset of 1
represents the second defined Primitive Type, and so
on. An offset into the data types field is used to
ensure that the type value fits into a nibble.
Structure Type
The lower nibble of the flag byte identifies the type
of AMM Object being identified by the ARI. In this
instance, this value MUST be LIT, as defined in
[I-D.birrane-dtn-adm].
Value
This field captures the CBOR encoding of the value. Values
are encoded according to their Value Type as specified in the
flag byte in accordance with the encoding rules provided in
Section 8.2.1.
8.3.2. Encoding Non-Literal ARIs
All other ARIs are defined in the context of AMM objects and may
contain parameters and other meta-data. The AMP, as a machine-to-
machine binary encoding of this information removes human-readable
information such as Name and Description from the E(ARI).
Additionally, this encoding adds other information to improve the
efficiency of the encoding, such as the concept of Nicknames, defined
in Section 7.1.
The E(ARI) is encoded as an OCTETS sequence and consists of a
mandatory flag byte, an encoded object name, and optional annotations
to assist with filtering, access control, and parameterization. The
E(ARI) structure is illustrated in Figure 10.
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E(ARI) General Format
+--------+---------+-----------+---------+-----------+-----------+
| Flags | NN | Name | Parms | Issuer | Tag |
| [BYTE] | [UVAST] | [BYTESTR] | [TNVC] | [BYTESTR] | [BYTESTR] |
| | (opt) | | (opt) | (opt) | opt) |
+--------+---------+-----------+---------+-----------+-----------+
Figure 10
These fields are defined as follows.
Flags
Flags describe the type of structure and which optional
fields are present in the encoding. The layout of the flag
byte is illustrated in Figure 11.
E(ARI) General Flag Byte Format
+----+------+-----+-----+-------------+
| NN | PARM | ISS | TAG | STRUCT TYPE |
+----+------+-----+-----+-------------+
| 7 | 6 | 5 | 4 | 3 2 1 0 |
+----+------+-----+-----+-------------+
MSB LSB
Figure 11
Nickname (NN)
This flag indicates that ADM compression is used for
this E(ARI). When set to 1 the Nickname field MUST
be present in the E(ARI). When set to 0 the Nickname
field MUST NOT be present in the E(ARI). When an ARI
is user-defined, there are no semantics for Nicknames
and, therefore, this field MUST be 0 when the Issuer
flag is set to 1. Implementations SHOULD use
Nicknames whenever possible to reduce the size of the
E(ARI).
Parameters Present (PARM)
This flag indicates that this ARI can be
parameterized and that parameter information is
included in the E(ARI). When set to 1 the Parms
field MUST be present in the E(ARI). When set to 0
the Parms field MUST NOT be present in the E(ARI).
Issuer Present (ISS)
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This flag indicates that this ARI is defined in the
context of a specific issuing entity. When set to 1
the Issuer field MUST be present in the E(ARI). When
set to 0 the Issuer field MUST NOT be present in the
E(ARI).
Tag Present (TAG)
This flag indicates that the ARI is defined in the
context of a specific issuing entity and that issuing
entity adds additional information in the form of a
tag. When set to 1 the Tag field MUST be present in
the E(ARI). When set to 0 the Tag field MUST NOT be
present in the E(ARI). This flag MUST be set to 0 if
the Issuer Present flag is set to 0.
Structure Type (STRUCT TYPE)
The lower nibble of the E(ARI) flag byte identifies
the kind of structure being identified. This field
MUST contain one of the AMM object types defined in
[I-D.birrane-dtn-adm].
Nickname (NN)
This optional field contains the Nickname as calculated
according to Section 7.1.
Object Name
This mandatory field contains an encoding of the ADM object.
For elements defined in an ADM Template (e.g., where the
Issuer Flag is set to 0) this is the 0-based index into the
ADM collection holding this element. For all user-defined
ADM objects, (e.g., where the Issuer Flag is set to 1) this
value is as defined by the Issuing organization.
Parameters
The parameters field is represented as a Type Name Value
Collection (TNVC) as defined in Section 8.2.3.1. The overall
number of items in the collection represents the number of
parameters. The types of the TNVC represent the types of
each parameter, with the first listed type associated with
the first parameter, and so on. The values, if present,
represent the values of the parameters, with the first listed
value being the value of the first parameter, and so on.
Issuer
This is a binary identifier representing a predetermined
issuer name. The AMP protocol does not parse or validate
this identifier, using it only as a distinguishing bit
pattern to ensure uniqueness. This value, for example, may
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come from a global registry of organizations, an issuing node
address, or some other network-unique marking. The issuer
field MUST NOT be present for any ARI defined in an ADM.
Tag
A value used to disambiguate multiple ARIs with the same
Issuer. The definition of the tag is left to the discretion
of the Issuer. The Tag field MUST be present if the Tag Flag
is set in the flag byte and MUST NOT be present otherwise.
8.4. ADM Object Encodings
The autonomy model codified in [I-D.birrane-dtn-adm] comprises
multiple individual objects. This section describes the CBOR
encoding of these objects.
Note: The encoding of an object refers to the way in which the
complete object can be encoded such that the object as it exists on a
Manager may be re-created on an Agent, and vice-versa. In cases
where both a Manager and an Agent already have the definition of an
object, then only the encoded ARI of the object needs to be
communicated. This is the case for all objects defined in a
published ADM and any user-defined object that has been synchronized
between an Agent and Manager.
8.4.1. Externally Defined Data (EDD)
Externally defined data (EDD) are solely defined in the ADMs for
various applications and protocols. EDDs represent values that are
calculated external to an AMA Agent, such as values measured by
firmware.
The representation of these data is simply their identifying ARIs.
The representation of an EDD is illustrated in Figure 12.
E(EDD) Format
+-------+
| ID |
| [ARI] |
+-------+
Figure 12
ID
This is the ARI identifying the EDD. Since EDDs are always
defined solely in the context of an ADM, this ARI MUST NOT
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have an ISSUER field and MUST NOT have a TAG field. This ARI
may be defined with parameters.
8.4.2. Constants (CONST)
Unlike Literals, a Constant is an immutable, typed, named value.
Examples of constants include PI to some number of digits or the UNIX
Epoch.
Since ADM definitions are preconfigured on Agents and Managers in an
AMA, the type information for a given Constant is known by all actors
in the system and the encoding of the Constant needs to only be the
name of the constant as the Manager and Agent can derive the type and
value from the unique Constant name.
The format of a Constant is illustrated in Figure 13.
E(CONST) Format
+-------+
| ID |
| [ARI] |
+-------+
Figure 13
ID
This is the ARI identifying the Constant. Since Constant
definitions are always provided in an ADM, this ARI MUST NOT
have an ISSUER field and MUST NOT have a TAG field. The ARI
MUST NOT have parameters.
8.4.3. Controls (CTRL)
A Control represents a pre-defined and optionally parameterized
opcode that can be run on an Agent. Controls in the AMP are always
defined in the context of an AMA; there is no concept of an operator-
defined Control. Since Controls are pre-configured in Agents and
Managers as part of ADM support, their representation is the ARI that
identifies them, similar to EDDs.
The format of a Control is illustrated in Figure 14.
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E(CTRL) Format
+-------+
| ID |
| [ARI] |
+-------+
Figure 14
ID
This is the ARI identifying the Control. This ARI MUST NOT
have an ISSUER field and MUST NOT have a TAG field. This ARI
may have parameters.
8.4.4. Macros (MAC)
Macros in the AMP are ordered collections of ARIs (an AC) that
contain Controls or other Macros. When run by an Agent, each ARI in
the AC MUST be run in order.
Any AMP implementation MUST allow at least 4 levels of Macro nesting.
Implementations MUST prevent recursive nesting of Macros.
The ARI associated with a Macro MAY contain parameters. Each
parameter present in a Macro ARI MUST contain type, name, and value
information. Any Control or Macro encapsulated within a
parameterized Macro MAY also contain parameters. If an encapsulated
object parameter contains only name information, then the parameter
value MUST be taken from the named parameter provided by the
encapsulating Macro. Otherwise, the value provided to the object
MUST be used instead.
The format of a Macro is illustrated in Figure 15.
E(MAC) Format
+-------+------------+
| ID | Definition |
| [ARI] | [AC] |
+-------+------------+
Figure 15
ID
This is the ARI identifying the Macro. When a Macro is
defined in an ADM this ARI MUST NOT have an ISSUER field and
MUST NOT have a TAG field. When the Macro is defined outside
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of an ADM, the ARI MUST have an ISSUER field and MAY have a
TAG field.
Definition
This is the ordered collection of ARIs that identify the
Controls and other Macros that should be run as part of
running this Macro.
8.4.5. Operators (OPER)
Operators are always defined in the context of an ADM. There is no
concept of a user-defined operator, as operators represent
mathematical functions implemented by the firmware on an Agent.
Since Operators are preconfigured in Agents and Managers as part of
ADM support, their representation is simply the ARI that identifies
them.
The ADM definition of an Operator MUST specify how many parameters
are expected and the expected type of each parameter. For example,
the unary NOT Operator ("!") would accept one parameter. The binary
PLUS Operator ("+") would accept two parameters. A custom function
to calculate the average of the last 10 samples of a data item should
accept 10 parameters.
Operators are always evaluated in the context of an Expression. The
encoding of an Operator is illustrated in Figure 16.
E(OP) Format
+-------+
| ID |
| [ARI] |
+-------+
Figure 16
ID
This is the ARI identifying the Operator. Since Operators
are always defined solely in the context of an ADM, this ARI
MUST NOT have an ISSUER field and MUST NOT have a TAG field.
8.4.6. Report Templates (RPTT)
A Report Template is an ordered collection of identifiers that
describe the order and format of data in any Report built in
compliance with the template. A template is a schema for a class of
reports. It contains no actual values and may be defined in a formal
ADM or configured by users in the context of a network deployment.
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The encoding of a RPTT is illustrated in Figure 17.
E(RPTT) Format
+-------+----------+
| ID | Contents |
| [ARI] | [AC] |
+-------+----------+
Figure 17
ID
This is the ARI identifying the report template.
Contents
This is the ordered collection of ARIs that define the
template.
8.4.7. Report (RPT)
A Report is a set of data values populated using a given Report
Template. While Reports do not contain name information, they MAY
contain type information in cases where recipients wish to perform
type validation prior to interpreting the Report contents in the
context of a Report Template. Reports are "anonymous" in the sense
that any individual Report does not contain a unique identifier.
Reports can be differentiated by examining the combination of (1) the
Report Template being populated, (2) the time at which the Report was
populated, and (3) the Agent producing the report.
A Report object is comprised of the identifier of the template used
to populate the report, an optional timestamp, and the contents of
the report. A Report is encoded as a CBOR array with either 2 or 3
elements. If the array has 2 elements then the optional Timestamp
MUST NOT be in the Report encoding. If the array has 3 elements then
the optional timestamp MUST be included in the Report encoding. The
Report encoding is illustrated in Figure 18.
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E(RPT) Format
+---------+
| RPT |
| [ARRAY] |
+---++----+
||
||
_____________/ \______________
/ \
+----------+-----------+----------+
| Template | Timestamp | Entries |
| [OCTETS: | [TS] | [OCTETS: |
| ARI] | (opt) | TNVC] |
+----------+-----------+----------+
Figure 18
Template
This is the ARI identifying the template used to interpret
the data in this report.
This ARI may be parameterized and, if so, the parameters MUST
include a name field and have been passed-by-name to the
template contents when constructing the report.
Timestamp
The timestamp marks the time at which the report was created.
This timestamp may be omitted in cases where the time of the
report generation can be inferred from other information.
For example, if a report is included in a message group such
that the timestamp of the message group is equivalent to the
timestamp of the report, the report timestamp may be omitted
and the timestamp of the included message group used instead.
Entries
This is the collection of data values that comprise the
report contents in accordance with the associated Report
Template.
8.4.8. State-Based Rules (SBR)
A State-Based Rule (SBR) specifies that a particular action should be
taken by an Agent based on some evaluation of the internal state of
the Agent. A SBR specifies that starting at a particular START time
an ACTION should be run by the Agent if some CONDITION evaluates to
true, until the ACTION has been run COUNT times. When the SBR is no
longer valid it may be discarded by the agent.
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Examples of SBRs include:
Starting 2 hours from receipt, whenever V1 > 10, produce a Report
for Report Template R1 no more than 20 times.
Starting at some future absolute time, whenever V2 != V4, run
Macro M1 no more than 36 times.
An SBR object is encoded as an OCTETS sequence as illustrated in
Figure 19.
E(SBR) Format
+----------+
| SBR |
| [OCTETS] |
+----++----+
||
||
_______________________/ \_______________________
/ \
+-------+-------+--------+--------+--------+--------+
| ID | START | COND | EVALS | FIRES | ACTION |
| [ARI] | [TV] | [EXPR] | [UINT] | [UINT] | [AC] |
+-------+-------+--------+--------+--------+--------+
Figure 19
ID
This is the ARI identifying the SBR. If this ARI contains
parameters they MUST include a name in support of pass-by-
name to each element of the Action AC.
START
The time at which the SBR condition should start to be
evaluated. This will mark the first evaluation of the
condition associated with the SBR.
CONDITION
The Expression which, if true, results in the SBR running the
associated action. An EXPR is considered true if it
evaluates to a non-zero value.
EVALS
The number of times the SBR condition can be evaluated. The
special value of 0 indicates there is no limit on how many
times the condition can be evaluated.
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FIRES
The number of times the SBR action can be run. The special
value of 0 indicates there is no limit on how many times the
action can be run.
ACTION
The collection of Controls and/or Macros to run as part of
the action. This is encoded as an AC in accordance with
Section 8.2.3.2 with the stipulation that every ARI in this
collection MUST be of type CTRL or MAC.
8.4.9. Table Templates (TBLT)
A Table Template (TBLT) describes the types, and optionally names, of
the columns that define a Table.
Because TBLTs are only defined in the context of an ADM, their
definition cannot change operationally. Therefore, a TBLT is encoded
simply as the ARI for the template. The format of the TBLT Object
Array is illustrated in Figure 20.
E(TBLT) Format
+-------+
| ID |
| [ARI] |
+-------+
Figure 20
The elements of the TBLT array are defined as follows.
ID
This is the ARI of the table template encoded in accordance
with Section 8.3.
8.4.10. Tables (TBL)
A Table object describes the series of values associated with a
Table Template.
A Table object is encoded as a CBOR array, with the first element of
the array identifying the Table Template and each subsequent element
identifying a row in the table. The format of the TBL Object Array
is illustrated in Figure 21.
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E(TBL) Format
+---------+
| TBL |
| [ARRAY] |
+---++----+
||
||
______________/ \_______________
/ \
+---------+--------+ +--------+
| TBLT ID | Row 1 | | Row N |
| [ARI] | [TNVC] | ... | [TNVC] |
+---------+--------+ +--------+
Figure 21
The TBL fields are defined as follows.
Template ID (TBLT ID)
This is the ARI of the table template describing the format
of the table and is encoded in accordance with Section 8.3.
Row
Each row of the table is represented as a series of values
with optional type information to aid in type checking table
contents to column types. Each row is encoded as a TNVC and
MAY include type information. AMP implementations should
consider the impact of including type information for every
row on the overall size of the encoded table.
Each TNVC representing a row MUST contain the same number of
elements as there are columns in the referenced
Table Template.
8.4.11. Time-Based Rules (TBR)
A Time-Based Rule (TBR) specifies that a particular action should be
taken by an Agent based on some time interval. A TBR specifies that
starting at a particular START time, and for every PERIOD seconds
thereafter, an ACTION should be run by the Agent until the ACTION has
been run for COUNT times. When the TBR is no longer valid it MAY BE
discarded by the Agent.
Examples of TBRs include:
Starting 2 hours from receipt, produce a Report for Report
Template R1 every 10 hours ending after 20 times.
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Starting at the given absolute time, run Macro M1 every 24 hours
ending after 365 times.
The TBR object is encoded as an OCTETS sequence as illustrated in
Figure 22.
E(TBR) Format
+----------+
| TBR |
| [OCTETS] |
+----++----+
||
||
___________________/ \___________________
/ \
+-------+-------+--------+--------+--------+
| ID | START | PERIOD | COUNT | ACTION |
| [ARI] | [TV] | [UINT] | [UINT] | [AC] |
+-------+-------+--------+--------+--------+
Figure 22
ID
This is the ARI identifying the TBR and is encoded in
accordance with Section 8.3. If this ARI contains parameters
they MUST include a name in support of pass-by-name to each
element of the Action AC.
START
The time at which the TBR condition should start to be
evaluated.
PERIOD
The number of seconds to wait between running the action
associated with the TBR.
COUNT
The number of times the TBR action can be run. The special
value of 0 indicates there is no limit on how many times the
action can be run.
ACTION
The collection of Controls and/or Macros to run as part of
the action. This is encoded as an ARI Collection in
accordance with Section 8.2.3.2 with the stipulation that
every ARI in this collection MUST represent either a Control
or a Macro.
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8.4.12. Variables (VAR)
Variable objects are transmitted in the AMP without the human-
readable description.
Variable objects are encoded as an OCTETS sequence whose format is
illustrated in Figure 23.
E(VAR) Format
+-----------+
| Variable |
| [OCTETS] |
+-----++----+
||
||
______/ \_____
/ \
+-------+-------+
| ID | Value |
| [ARI] | [TNV] |
+-------+-------+
Figure 23
ID
This is the ARI identifying the VAR and is encoded in
accordance with Section 8.3. This ARI MUST NOT include
parameters.
Value
This field captures the value (and optionally the type and
name) of the variable, encoded as a TNV.
9. Functional Specification
This section describes the format of the messages that comprise the
AMP protocol.
9.1. AMP Message Summary
The AMP message specification is limited to three basic
communications:
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+------------+-------------+----------------------------------------+
| Message | Enumeration | Description |
+------------+-------------+----------------------------------------+
| Register | 0 | Add Agents to the list of managed |
| Agent | | devices known to a Manager. |
| | | |
| Report Set | 1 | Receiving a Report of one or more |
| | | Report Entries from an Agent. |
| | | |
| Perform | 2 | Sending a Macro of one or more |
| Control | | Controls to an Agent. |
| | | |
| Table Set | 3 | Receiving one or more tables from an |
| | | Agent. |
+------------+-------------+----------------------------------------+
Table 4: ADM Message Type Enumerations
The entire management of a network can be performed using these three
messages and the configurations from associated ADMs.
9.2. Message Group Format
Individual messages within the AMP are combined into a single group
for communication with another AMP Actor. Messages within a group
MUST be received and applied as an atomic unit. The format of a
message group is illustrated in Figure 24. These message groups are
assumed communicated amongst Agents and Managers as the payloads of
encapsulating protocols which should provide additional security and
data integrity features as needed.
A message group is encoded as a CBOR array with at least 2 elements,
the first being the time the group was created followed by 1 or more
messages that comprise the group. The format of the message group is
illustrated in Figure 24.
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AMP Message Group Format
+---------------+
| Message Group |
| [ARRAY] |
+------++-------+
||
____________________||___________________
/ \
+-----------+-----------+ +-----------+
| Timestamp | Message 1 | ... | Message N |
| [TS] | [BYTESTR] | | [BYTESTR] |
+-----------+-----------+ +-----------+
Figure 24
Timestamp
The creation time for this messaging group. Individual
messages may have their own creation timestamps based on
their type, but the group timestamp also serves as the
default creation timestamp for every message in the group.
This is encoded in accordance with Table 3.
Message N
The Nth message in the group.
9.3. Message Format
Each message identified in the AMP specification adheres to a common
message format, illustrated in Figure 25, consisting of a message
header, a message body, and an optional trailer.
Each message in the AMP is encode as an OCTETS sequence formatted in
accordance with Figure 25.
AMP Message Format
+--------+----------+----------+
| Header | Body | Trailer |
| [BYTE] | [VARIES] | [VARIES] |
| | | (opt.) |
+--------+----------+----------+
Figure 25
Header
The message header BYTE is shown in Figure 26. The header
identifies a message context and opcode as well as flags that
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control whether a Report should be generated on message
success (Ack) and whether a Report should be generated on
message failure (Nack).
AMP Common Message Header
+----------+-----+------+-----+----------+
| Reserved | ACL | Nack | Ack | Opcode |
+----------+-----+------+-----+----------+
| 7 6 | 5 | 4 | 3 | 2 1 0 |
+----------+-----+------+-----+----------+
MSB LSB
Figure 26
Opcode
The opcode field identifies which AMP message is
being represented.
ACK Flag
The ACK flag describes whether successful application
of the message must generate an acknowledgment back
to the message sender. If this flag is set (1) then
the receiving actor MUST generate a Report
communicating this status. Otherwise, the actor MAY
generate such a Report based on other criteria.
NACK Flag
The NACK flag describes whether a failure applying
the message must generate an error notice back to the
message sender. If this flag is set (1) then the
receiving Actor MUST generate a Report communicating
this status. Otherwise, the Actor MAY generate such
a Report based on other criteria.
ACL Used Flag
The ACL used flag indicates whether the message has a
trailer associated with it that specifies the list of
AMP actors that may participate in the Actions or
definitions associated with the message. This area
is still under development.
Body
The message body contains the information associated with the
given message.
Trailer
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An OPTIONAL access control list (ACL) may be appended as a
trailer to a message. When present, the ACL for a message
identifiers the agents and managers that can be affected by
the definitions and actions contained within the message.
The explicit impact of an ACL is described in the context of
each message below. When an ACL trailer is not present, the
message results may be visible to any AMP Actor in the
network, pursuant to other security protocol implementations.
9.4. Register Agent
The Register Agent message is used to inform an AMP Manager of the
presence of another Agent in the network.
The body of this message is the name of the new agent, encoded as
illustrated in Figure 27.
Register Agent Message Body
+-----------+
| Agent ID |
| [BYTESTR] |
+-----------+
Figure 27
Agent ID
The Agent ID MUST represent the unique address of the Agent
in whatever protocol is used to communicate with the Agent.
9.5. Report Set
The Report Set message contains a set of 1 or more Reports produced
by an AMP Agent and sent to an AMP Manager.
The body of this message contains information on the recipient of the
reports followed by one or more Reports. The body is encoded as
illustrated in Figure 28.
Report Set Message Body
+----------+----------+
| RX Names | Reports |
| [ARRAY] | [ARRAY] |
+----------+----------+
Figure 28
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RX Names
This field captures the set of Managers that have been sent
this report set. This is encoded as a CBOR array that MUST
have at least one entry. Each entry in this array is encoded
as a CBOR text string.
Reports
This field captures the set of reports being sent. This is
encoded as a CBOR array that MUST have at least one entry.
Each entry in this array is encoded as a RPT in accordance
with Section 8.4.7.
9.6. Perform Control
The perform control message causes the receiving AMP Actor to run one
or more preconfigured Controls provided in the message.
The body of this message is the start time for the controls followed
by the controls themselves, as illustrated in Figure 29.
Perform Control Message Body
+-------+-----------+
| Start | Controls |
| [TV] | [AC] |
+-------+-----------+
Figure 29
Start
The time at which the Controls/Macros should be run.
Controls
The collection of ARIs that represent the Controls and/or
Macros to be run by the AMP Actor. Every ARI in this
collection MUST be either a Control or a Macro.
9.7. Table Set
The Table Set message contains a set of 1 or more TBLs produced by an
AMP Agent and sent to an AMP Manager.
The body of this message contains information on the recipient of the
tables followed by one or more TBLs. The body is encoded as
illustrated in Figure 30.
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Table Set Message Body
+----------+----------+
| RX Names | Tables |
| [ARRAY] | [ARRAY] |
+----------+----------+
Figure 30
RX Names
This field captures the set of Managers that have been sent
this table set. This is encoded as a CBOR array that MUST
have at least one entry. Each entry in this array is encoded
as a CBOR text string.
Tables
This field captures the set of tables being sent. This is
encoded as a CBOR array that MUST have at least one entry.
Each entry in this array is encoded as a TBL in accordance
with Section 8.4.10.
10. IANA Considerations
A Nickname registry needs to be established.
11. Security Considerations
Security within the AMP exists in two layers: transport layer
security and access control.
Transport-layer security addresses the questions of authentication,
integrity, and confidentiality associated with the transport of
messages between and amongst Managers and Agents. This security is
applied before any particular Actor in the system receives data and,
therefore, is outside of the scope of this document.
Finer grain application security is done via ACLs provided in the AMP
message headers.
12. Implementation Notes
A reference implementation of this version of the AMP specification
is available in the 3.6.2 release of the ION open source code base
available from sourceforge at https://sourceforge.net/projects/ion-
dtn/.
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13. References
13.1. Informative References
[I-D.birrane-dtn-ama]
Birrane, E., "Asynchronous Management Architecture",
draft-birrane-dtn-ama-07 (work in progress), June 2018.
13.2. Normative References
[I-D.birrane-dtn-adm]
Birrane, E., DiPietro, E., and D. Linko, "AMA Application
Data Model", draft-birrane-dtn-adm-02 (work in progress),
June 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>.
Appendix A. Acknowledgements
The following participants contributed technical material, use cases,
and useful thoughts on the overall approach to this protocol
specification: Jeremy Pierce-Mayer of INSYEN AG contributed the
concept of the typed data collection and early type checking in the
protocol. David Linko and Evana DiPietro of the Johns Hopkins
University Applied Physics Laboratory contributed appreciated review
and type checking of various elements of this specification.
Author's Address
Edward J. Birrane
Johns Hopkins Applied Physics Laboratory
Email: Edward.Birrane@jhuapl.edu
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