Delay-Tolerant Networking E. Birrane
Internet-Draft Johns Hopkins Applied Physics Laboratory
Intended status: Informational October 30, 2016
Expires: May 3, 2017
Asynchronous Management Architecture
draft-birrane-dtn-ama-04
Abstract
This document describes the motivation, desirable properties, system
model, roles/responsibilities, and component models associated with
an asynchronous management architecture (AMA) suitable for providing
application-level network management services in a challenged
networking environment. Challenged networks are those that require
fault protection, configuration, and performance reporting while
unable to provide human-in-the-loop operations centers with
synchronous feedback in the context of administrative sessions. In
such a context, networks must exhibit behavior that is both
determinable and autonomous while maintaining compatibility with
existing network management protocols and operational concepts.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Requirements Language . . . . . . . . . . . . . . . . . . 4
1.4. ORganization . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Challenged Networks . . . . . . . . . . . . . . . . . . . 7
3.2. Current Management Approaches . . . . . . . . . . . . . . 8
3.3. Limitations of Current Approaches . . . . . . . . . . . . 8
4. Service Definitions . . . . . . . . . . . . . . . . . . . . . 9
4.1. Configuration . . . . . . . . . . . . . . . . . . . . . . 9
4.2. Reporting . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3. Autonomous Parameterized Control . . . . . . . . . . . . 10
4.4. Administration . . . . . . . . . . . . . . . . . . . . . 11
5. Desirable Properties . . . . . . . . . . . . . . . . . . . . 11
5.1. Intelligent Push of Information . . . . . . . . . . . . . 12
5.2. Minimize Message Size Not Node Processing . . . . . . . . 12
5.3. Absolute Data Identification . . . . . . . . . . . . . . 12
5.4. Custom Data Definition . . . . . . . . . . . . . . . . . 13
5.5. Autonomous Operation . . . . . . . . . . . . . . . . . . 13
6. Roles and Responsibilities . . . . . . . . . . . . . . . . . 13
6.1. Agent Responsibilities . . . . . . . . . . . . . . . . . 13
6.2. Manager Responsibilities . . . . . . . . . . . . . . . . 15
7. System Model . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1. Control and Data Flows . . . . . . . . . . . . . . . . . 16
7.2. Control Flow by Role . . . . . . . . . . . . . . . . . . 16
7.2.1. Notation . . . . . . . . . . . . . . . . . . . . . . 17
7.2.2. Serialized Management . . . . . . . . . . . . . . . . 17
7.2.3. Multiplexed Management . . . . . . . . . . . . . . . 18
7.2.4. Data Fusion . . . . . . . . . . . . . . . . . . . . . 20
8. Logical Data Model . . . . . . . . . . . . . . . . . . . . . 21
8.1. Data Decomposition . . . . . . . . . . . . . . . . . . . 21
8.1.1. Groups . . . . . . . . . . . . . . . . . . . . . . . 21
8.1.2. Levels . . . . . . . . . . . . . . . . . . . . . . . 21
8.2. Data Model . . . . . . . . . . . . . . . . . . . . . . . 22
8.2.1. EDDs, VARs, and Reporting . . . . . . . . . . . . . . 23
8.2.2. Controls and Macros . . . . . . . . . . . . . . . . . 24
8.2.3. Rules . . . . . . . . . . . . . . . . . . . . . . . . 24
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8.2.4. Operators and Literals . . . . . . . . . . . . . . . 25
8.3. Application Data Model . . . . . . . . . . . . . . . . . 25
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
10. Security Considerations . . . . . . . . . . . . . . . . . . . 26
11. Informative References . . . . . . . . . . . . . . . . . . . 26
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction
This document presents an Asynchronous Management Architecture (AMA)
providing application-layer network management services over links
where delivery delays prevent timely communications between a network
operator and a managed device. These delays may be caused by long
signal propagations or frequent link disruptions (such as described
in [RFC4838]) or by non-environmental factors such as unavailability
of network operators, administrative delays, or delays caused by
quality-of-service prioritizations and service-level agreements.
1.1. Purpose
This document describes the motivation, rationale, desirable
properties, and roles/responsibilities associated with an
asynchronous management architecture (AMA) suitable for providing
network management services in a challenged networking environment.
These descriptions should be of sufficient specificity that an
implementing Asynchronous Management Protocol (AMP) in conformance
with this architecture will operate successfully in a challenged
networking environment.
An AMA is necessary as the assumptions inherent to the architecture
and design of synchronous management tools and techniques are not
valid in challenged network scenarios. In these scenarios,
synchronous approaches either patiently wait for periods of bi-
directional connectivity or require the investment of significant
time and resources to evolve a challenged network into a well-
connected, low-latency network. In some cases such evolution is
merely a costly way to over-resource a network. In other cases, such
evolution is impossible given physical limitations imposed by signal
propagation delays, power, transmission technologies, and other
phenomena. Asynchronous management of asynchronous networks enables
large-scale deployments, distributed technical capabilities, and
reduced deployment and operations costs.
1.2. Scope
It is assumed that any challenged network where network management
would be usefully applied supports basic services (where necessary)
such as naming, addressing, integrity, confidentiality,
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authentication, fragmentation, and traditional network/session layer
functions. Therefore, these items are outside of the scope of the
AMA and not covered in this document.
While likely that a challenged network will eventually interface with
an unchallenged network, this document does not address the concept
of network management compatibility with synchronous approaches. An
AMP in conformance with this architecture should examine
compatibility with existing approaches as part of supporting nodes
acting as gateways between network types.
1.3. 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].
1.4. ORganization
The remainder of this document is organizaed into seven sections
that, together, describe an AMA suitable for enterprise management of
asynchronous networks: terminology, motivation, service definitions,
desirable properties, roles/responsibilities, system model, and
logical component model. The description of each section is as
follows.
o Motivation - This section provides an overall motivation for this
work as providing a novel and useful alternative to current
network management approaches. Specifically, this section
describes common network functions and how synchronous mechanisms
fail to provide these functions in an asynchronous environment.
o Service Definitions - This section defines asynchronous network
management services in terms of terminology, scope, and impact.
o Desirable Properties - This section identifies the properties to
which an AMP should adhere to effectively implement service
definitions in an asynchonous environment. These properties guide
the subsequent definition of the system and logical models that
comprise the AMA.
o Roles and Responsibilities - This section identifies the roles of
logical Actors in the AMA and their associated responsibilities.
It provides the terminology and context for discussing how network
management services interact.
o System Model - This section describes data flows amongst various
defined Actor roles. These flows capture how the AMA system works
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to provide asynchronous network management services in accordance
with defined desirable properties.
o Logical Component Model - This section describes those logical
functions that must exist in any instantiation of an AMP.
2. Terminology
This section identifies those terms critical to understanding the
proper operation of the AMA. Whenever possible, these terms align in
both word selection and meaning with their analogs from other
management protocols.
o Actor - A software service running on either managed or managing
devices for the purpose of implementing management protocols
between such devices. Actors may implement the "Manager" role,
"Agent" role, or both.
o Agent Role (or Agent) - The role associated with a managed device,
responsible for reporting performance data, enforcing
administrative policies, and accepting/performing actions. Agents
exchange information with Managers operating either on the same
device or on a remote managing device.
o Asynchronous Management Protocol (AMP) - An application-layer
protocol used to manage the Data, Controls, and other items
necessary for configuration, monitoring, and administration of
applications and protocols on a node in a challenged network.
o Application Data Model (ADM) - The set of predefined data
definitions, reports, literals, operations, and controls given to
an Actor to manage a particular application or protocol. Actors
support multiple ADMs, one for each application/protocol being
managed.
o Externally Defined Data (EDD) - Information made available to an
Agent by a managed device, but not computed directly by the Agent.
EDD definitions form the "lingua franca" for data within the AMA
and are defined by ADMs.
o Variable (VAR) - Information that is computed by an Agent,
typically as a function of EDDs and/or other Variables. A VAR is
a strongly-typed value. When a VAR is specified in an ADM, its
type and default value are immutable. When a VAR is defined
outside of an ADM, the type and default value may be changed. If
an ADM wishes to define an item whose type and value are both
immutable, that is no longer considered a Variable and should be
represented as a Literal.
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o Controls (CTRLs) - Operations that may be undertaken by an Actor
to change the behavior, configuration, or state of an application
or protocol managed by an AMP. Similar to Externally Defined
Data, Controls are defined solely in ADMs and their definition is
immutable.
o Literals (LIT) - Constants, enumerations, and other immutable
definitions.
o Macros - A named, ordered collection of Controls. When a Macro is
defined in an ADM, that definition is immutable. When a Macro is
defined outside of an ADM, that definition may be changed.
o Manager - A role associated with a managing device responsible for
configuring the behavior of, and receiving information from,
Agents. Managers interact with one or more Agents located on the
same device and/or on remote devices in the network.
o Operator (OP) - The enumeration and specification of a
mathematical function used to calculate computed data definitions
and construct expressions to calculate state. Operators are
specified in Application Data Models (ADMs) and their definition
is immutable.
o Report Entry (RPTE) - A named, typed, ordered collection of data
values gathered by one or more Agents and provided to one or more
Managers. Report entries populate report templates with values.
o Report Template (RPTT) - An ordered collection of data
identifiers. When defined in an ADM the report template
definition is immutable. When defined outside of an ADM, the
template definition may change.
o Rule - A unit of autonomous specification that provides a
stimulus-response relationship between time or state on an Agent
and the Controls to be run as a result of that time or state.
3. Motivation
Challenged networks, to include networks challenged by administrative
or policy delays, cannot guarantee capabilities required to enable
synchronous management techniques. These capabilities include high-
rate, highly-available data, round-trip data exchange, and operators
"in-the-loop". The inability of current approaches to provide
network management services in a challenged network motivates the
need for a new network management architecture focused on
asynchronous, open-loop, autonomous control of network components.
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3.1. Challenged Networks
A growing variety of link-challenged networks support packetization
to increase data communications reliability without otherwise
guaranteeing a simultaneous end-to-end path. Examples of such
networks include Mobile Ad-Hoc Networks (MANets), Vehicular Ad-Hoc
Networks (VANets), Space-Terrestrial Internetworks (STINTs), and
heterogeneous networking overlays. Links in such networks are often
unavailable due to attenuations, propagation delays, occultation, and
other limitations imposed by energy and mass considerations. Data
communications in such networks rely on store-and-forward and other
queueing strategies to wait for the connectivity necessary to
usefully advance a packet along its route.
Similarly, there also exist well-resourced networks that incur high
message delivery delays due to non-environmental limitations. For
example, networks whose operations centers are understaffed or where
data volume and management requirements exceed the real-time
cognitive load of operators or the associated operations console
software support. Also, networks where policy restricts user access
to existing bandwidth creates situations functionally similar to link
disruption and delay.
Independent of the reason, when a node experiences an inability to
communicate it must rely on autonomous mechanisms to ensure its safe
operation and ability to usefully re-join the network at a later
time. In cases of sparsely-populated networks, there may never be a
practical concept of "the connected network" as most nodes may be
disconnected most of the time. In such environments, defining a
network in terms of instantaneous connectivity becomes impractical or
impossible.
Specifically, challenged networks exhibit the following properties
that may violate assumptions built into current approaches to
synchronous network management.
o Links may be uni-directional.
o Bi-directional links may have asymmetric data rates.
o No end-to-end path is guaranteed to exist at any given time
between any two nodes.
o Round-trip communications between any two nodes within any given
time window may be impossible.
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3.2. Current Management Approaches
Network management tools in unchallenged networks provide mechanisms
for communicating locally-collected data from Agents to Managers,
typically using a "pull" mechanism where data must be explicitly
requested by a Manager in order to be transmitted by an Agent.
A near ubiquitous method for management in unchallenged networks
today is the Simple Network Management Protocol (SNMP) [RFC3416].
SNMP utilizes a request/response model to set and retrieve data
values such as host identifiers, link utilizations, error rates, and
counters between application software on Agents and Managers. Data
may be directly sampled or consolidated into representative
statistics. Additionally, SNMP supports a model for asynchronous
notification messages, called traps, based on predefined triggering
events. Thus, Managers can query Agents for status information, send
new configurations, and be informed when specific events have
occurred. Traps and queryable data are defined in one or more
Managed Information Bases (MIBs) which define the information for a
particular data standard, protocol, device, or application.
In challenged networks, the request/response method of data
collection is neither efficient nor, at times, possible as it relies
on sessions, round-trip latency, message retransmission, and ordered
delivery. Adaptive modifications to SNMP to support challenged
networks would alter the basic function of the protocol (data models,
control flows, and syntax) so as to be functionally incompatible with
existing SNMP installations.
The Network Configuration Protocol (NETCONF) provides device-level
configuration capabilities [RFC6241] to replace vendor-specific
command line interface (CLI) configuration software. The XML-based
protocol provides a remote procedure call (RPC) syntax such that any
exposed functionality on an Agent can be exercised via a software
application interface. NETCONF places no specific functional
requirements or constraints on the capabilities of the Agent, which
makes it a very flexible tool for configuring a homogeneous network
of devices. However, NETCONF does place specific constraints on any
underlying transport protocol: namely, a long-lived, reliable, low-
latency sequenced data delivery session. This is a fundamental
requirement given the RPC-nature of the operating concept, and it is
unsustainable in a challenged network.
3.3. Limitations of Current Approaches
Management approaches that rely on timely data exchange, such as
those that rely on negotiated sessions or other synchronized
acknowledgment, do not function in challenged network environments.
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Familiar examples of TCP/IP based management via closed-loop,
synchronous messaging does not work when network disruptions increase
in frequency and severity. While no protocol delivers data in the
absence of a networking link, protocols that eliminate or drastically
reduce overhead and end-point coordination require smaller
transmission windows and continue to function when confronted with
scaling delays and disruptions in the network.
Just as the concept of a loosely-confederated set of nodes changes
the definition of a network, it also changes the operational concept
of what it means to manage a network. When a network stops being a
single entity exhibiting a single behavior, "network management"
becomes large-scale "node management". Individual nodes must share
the burden of implementing desirable behavior without reliance on a
single oracle of configuration or other coordinating function such as
an operator-in-the-loop.
4. Service Definitions
This section identifies the services that must exist between Managers
and Agents within an AMA. These services include configuration,
reporting, parameterized control, and administration.
4.1. Configuration
Configuration services update local Agent information relating to
managed applications and protocols. This information may be
configured from ADMs, the specification of parameters associated with
these models, and as defined by operators in the network.
New configurations received by a node must be validated to ensure
that they do not conflict with other configurations at the node, or
prevent the node from effectively working with other nodes in its
region. With no guarantee of round-trip data exchange, Agents cannot
rely on remote Managers to correct erroneous or stale configurations
from harming the flow of data through a challenged network.
Examples of configuration service behavior include the following.
o Creating a new datum as a function of other well-known data:
C = A + B.
o Creating a new report as a unique, ordered collection of known
data:
RPT = {A, B, C}.
o Storing pre-defined, parameterized responses to potential future
conditions:
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IF (X > 3) THEN RUN CMD(PARM).
4.2. Reporting
Reporting services populate pre-defined Report Templates with values
collected or computed by an Agent. The resultant Report Entries are
sent to one or more Managers by the Agent. The term "reporting" is
used in place of the term "monitoring", as monitoring implies a
timeliness and regularity that cannot be guaranteed by a challenged
network. Report Entries sent by an Agent provide best-effort
information to receiving Managers.
Since a Manager is not actively "monitoring" an Agent, the Agent must
make its own determination on when to send what Report Entries based
on its own local time and state information. Agents should produce
Report Entries of varying fidelity and with varying frequency based
on thresholds and other information set as part of configuration
services.
Examples of reporting service behavior include the following.
o Generate Report Entry R1 every hour (time-based production).
o Generate Report Entry R2 when X > 3 (state-based production).
4.3. Autonomous Parameterized Control
Controls represent a function that can be run by an Agent to affect
its behavior or otherwise change its internal state. In this
context, a Control may refer to a single function or an ordered set
of functions run in sequence (e.g., a macro). The set of Controls
understood by an Agent define the functions available to affect the
behavior of applications and protocols managed by the Agent.
Since there is no guarantee that a Manager will be in contact with an
Agent at any given time, the decisions of whether and when a Control
should be run must be made locally and autonomously by the Agent.
Two types of automation triggers are identified in the AMA: triggers
based on the general state of the Agent and, more specifically,
triggers based on an Agent's notion of time. As such, the autonomous
execution of Controls can be viewed as a stimulus-response system,
where the stimulus is the positive evaluation of a state or time
based predicate and the response is the Control to be executed.
The autonomous nature of Control execution by an Agent implies that
the full suite of information necessary to run a Control may not be
known by a Manager in advance of running the Control on an Agent. To
address this situation, Controls in the AMA MUST support a
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parmeterization mechanism so that required data can be provided at
the time of execution on the Agent rather than at the time of
definition/configuration by the Manager.
Autonomous, parameterized control provides a powerful mechanism for
Managers to "manage" an Agent asynchronously during periods of no
communication by pre-configuring responses to events that may be
encountered by the Agent at a future time.
Examples of potential control service behavior include the following.
o Updating local routing information based on instantaneous link
analysis.
o Managing storage on the device to enforce quotas.
o Applying or modifying local security policy.
4.4. Administration
Administration services enforce the potentially complex mapping of
configuration, reporting, and control services amongst Agents and
Managers in the network. Fine-grained access control specifying
which Managers may apply which services to which Agents may be
necessary in networks dealing with multiple administrative entities
or overlay networks crossing multiple administrative boundaries.
Whitelists, blacklists, key-based infrastructures, or other schemes
may be used for this purpose.
Examples of administration service behavior include the following.
o Agent A1 only Sends reports for Protocol P1 to Manager M1.
o Agent A2 only accepts a configurations for Application Y from
Managers M2 and M3.
o Agent A3 accepts services from any Manager providing the proper
authentication token.
Note that the administrative enforcement of access control is
different from security services provided by the networking stack
carrying AMP messages.
5. Desirable Properties
This section describes those design properties that are desireable
when defining an architecture that must operate across challenged
links in a network. These properties ensure that network management
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capabilities are retained even as delays and disruptions in the
network scale. Ultimately, these properties are the driving design
principles for the AMA.
5.1. Intelligent Push of Information
Pull management mechanisms require that a Manager send a query to an
Agent and then wait for the response to that query. This practice
implies a control-session between entities and increases the overall
message traffic in the network. Challenged networks cannot guarantee
timely roundtrip data-exchange and, in extreme cases, are comprised
solely of uni-directional links. Therefore, pull mechanisms must be
avoided in favor of push mechanisms.
Push mechanisms, in this context, refer to Agents making their own
determinations relating to the information that should be sent to
Managers. Such mechanisms do not require round-trip communications
as Managers do not request each reporting instance; Managers need
only request once, in advance, that information be produced in
accordance with a pre-determined schedule or in response to a pre-
defined state on the Agent. In this way information is "pushed" from
Agents to Managers and the push is "intelligent" because it is based
on some internal evaluation performed by the Agent.
5.2. Minimize Message Size Not Node Processing
Protocol designers must balance message size versus message
processing time at sending and receiving nodes. Verbose
representations of data simplify node processing whereas compact
representations require additional activities to generate/parse the
compacted message. There is no asynchronous management advantage to
minimizing node processing time in a challenged network. However,
there is a significant advantage to smaller message sizes in such
networks. Compact messages require smaller periods of viable
transmission for communication, incur less re-transmission cost, and
consume less resources when persistently stored en-route in the
network. AMPs should minimize PDUs whenever practical, to include
packing and unpacking binary data, variable-length fields, and pre-
configured data definitions.
5.3. Absolute Data Identification
Elements within the management system must be uniquely identifiable
so that they can be individually manipulated. Identification schemes
that are relative to system configuration make data exchange between
Agents and Managers difficult as system configurations may change
faster than nodes can communicate.
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Consider the following SNMP technique for approximating an
associative array lookup. A manager wishing to do an associative
lookup for some key K1 will (1) query a list of array keys from the
agent, (2) find the key that matched K1 and infer the index of K1
from the returned key list, and (3) query the discovered index on the
agent to retrieve the desired data.
Ignoring the inefficiency of two pull requests, this mechanism fails
when the Agent changes its key-index mapping between the first and
second query. Rather than construting an artificial mapping from K1
to an index, an AMP must provide an absolute mechanism to lookup the
value K1 without an abstraction between the Agent and Manager.
5.4. Custom Data Definition
Custom definition of new data from existing data (such as through
data fusion, averaging, sampling, or other mechanisms) provides the
ability to communicate desired information in as compact a form as
possible. Specifically, an Agent should not be required to transmit
a large data set for a Manager that only wishes to calculate a
smaller, inferred data set. The Agent should calculate the smaller
data set on its own and transmit that instead. Since the
identification of custom data sets is likely to occur in the context
of a specific network deployment, AMPs must provide a mechanism for
their definition.
5.5. Autonomous Operation
AMA network functions must be achievable using only knowledge local
to the Agent. Rather than directly controlling an Agent, a Manager
configures the autonomy engine of the Agent to take its own action
under the appropriate conditions in accordance with the Agent's
notion of local state and time.
6. Roles and Responsibilities
By definition, Agents reside on managed devices and Managers reside
on managing devices. This section describes how these roles
participate in the network management functions outlined in the prior
section.
6.1. Agent Responsibilities
Application Data Model (ADM) Support
Agents MUST collect all data, execute all Controls, populate
all Report Templates and run operations required by each ADM
which the Agent claims to support. Agents MUST report
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supported ADMs so that Managers in a network understands what
information is understood by what Agent.
Local Data Collection
Agents MUST collect from local firmware (or other on-board
mechanisms) and report all Externally Defined Data defined in
all ADMs for which they have been configured.
Autonomous Control
Agents MUST determine, without Manager intervention, whether
a configured Control should be invoked. Agents MUST
periodically evaluate the conditions associated with
configured Controls and invoke those Controls based on local
state. Agents MAY also invoke Controls on other devices for
which they act as proxy.
User Data Definition
Agents MUST provide mechanisms for operators in the network
to use configuration services to create customized Variables,
Report Templates, Macros and other information in the context
of a specific network or network use-case. Agents MUST allow
for the creation, listing, and removal of such definitions in
accordance with whatever security models are deployed within
the particular network.
Where applicable, Agents MUST verify the validity of these
definitions when they are configured and respond in a way
consistent with the logging/error-handling policies of the
Agent and the network.
Autonomous Reporting
Agents MUST determine, without real-time Manager
intervention, whether and when to populate and transmit a
given Report Entry targeted to one or more Managers in the
network.
Consolidate Messages
Agents SHOULD produce as few messages as possible when
sending information. For example, rather than sending
multiple Report Entry messages to a Manager, an Agent SHOULD
prefer to send a single message containing multiple Report
Entries.
Regional Proxy
Agents MAY perform any of their responsibilities on behalf of
other network nodes that, themselves, do not have an Agent.
In such a configuration, the Agent acts as a proxy for these
other network nodes.
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6.2. Manager Responsibilities
Agent/ADM Mapping
Managers MUST understand what ADMs are supported by the
various Agents with which they communicate. Managers should
not attempt to request, invoke, or refer to ADM information
for ADMs unsupported by an agent.
Data Collection
Managers MUST receive information from Agents by
asynchronously configuring the production of data reports and
then waiting for, and collecting, responses from Agents over
time. Managers MAY try to detect conditions where Agent
information has not been received within operationally
relevant timespans and react in accordance with network
policy.
Custom Definitions
Managers should provide the ability to define custom
definitions. Any custom definitions MUST be transmitted to
appropriate Agents and these definitions MUST be remembered
to interpret the reporting of these custom values from Agents
in the future.
Data Translation
Managers should provide some interface to other network
management protocols, such as the SNMP. Managers MAY
accomplish this by accumulating a repository of push-data
from high-latency parts of the network from which data may be
pulled by low-latency parts of the network.
Data Fusion
Managers MAY support the fusion of data from multiple Agents
with the purpose of transmitting fused data results to other
Managers within the network. Managers MAY receive fused
reports from other Managers pursuant to appropriate security
and administrative configurations.
7. System Model
This section describes the notional data flows and control flows that
illustrate how Managers and Agents within an AMA cooperate to perform
network management services.
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7.1. Control and Data Flows
The AMA identifies three significant data flows: control flows from
Managers to Agents, reports flows from Agents to Managers, and fusion
reports from Managers to other Managers. These data flows are
illustrated in Figure 1.
AMA Control and Data Flows
+---------+ +------------------------+ +---------+
| Node A | | Node B | | Node C |
| | | | | |
|+-------+| |+-------+ +-------+| |+-------+|
|| ||=====>>||Manager|====>>| ||====>>|| ||
|| ||<<=====|| B |<<====|Agent B||<<====|| ||
|| || |+--++---+ +-------+| ||Manager||
|| Agent || +---||-------------------+ || C ||
|| A || || || ||
|| ||<<=========||==========================|| ||
|| ||===========++========================>>|| ||
|+-------+| |+-------+|
+---------+ +---------+
Figure 1
In this data flow, the Agent on node A receives Controls from
Managers on nodes B and C, and replies with Report Entries back to
these Managers. Similarly, the Agent on node B interacts with the
local Manager on node B and the remote Manager on node C. Finally,
the Manager on node B may fuse Report Entries received from Agents at
nodes A and B and send these fused Report Entries back to the Manager
on node C.
From this figure it is clear that there exist many-to-many
relationships amongst Managers, amongst Agents, and between Agents
and Managers. Note that Agents and Managers are roles, not
necessarily differing software applications. Node A may represent a
single software application fulfilling only the Agent role, whereas
node B may have a single software application fulfilling both the
Agent and Manager roles. The specifics of how these roles are
realized is an implementation matter.
7.2. Control Flow by Role
This section describes three common configurations of Agents and
Managers and the flow of messages between them. These configurations
involve local and remote management and data fusion.
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7.2.1. Notation
The notation outlined in Table 1 describes the types of control
messages exchanged between Agents and Managers.
+-------------+--------------------------------------+--------------+
| Term | Definition | Example |
+-------------+--------------------------------------+--------------+
| EDD# | EDD definition, from ADM. | EDD1 |
| | | |
| V# | Custom data definition. | V1 = EDD1 + |
| | | V0. |
| | | |
| DEF([ACL], | Define id from expression. Allow | DEF([*], V1, |
| ID,EXPR) | managers in access control list | EDD1 + EDD2) |
| | (ACL) to request this id. | |
| | | |
| PROD(P,ID) | Produce ID according to predicate P. | PROD(1s, |
| | P may be a time period (1s) or an | EDD1) |
| | expression (EDD1 > 10). | |
| | | |
| RPT(ID) | A report identified by ID. | RPT(EDD1) |
+-------------+--------------------------------------+--------------+
Table 1: Terminology
7.2.2. Serialized Management
This is a nominal configuration of network management where a Manager
interacts with a set of Agents. The control flows for this are
outlined in Figure 2.
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Serialized Management Control Flow
+----------+ +---------+ +---------+
| Manager | | Agent A | | Agent B |
+----+-----+ +----+----+ +----+----+
| | |
|-----PROD(1s, EDD1)--->| | (1)
|----------------------------PROD(1s, EDD1)-->|
| | |
| | |
|<-------RPT(EDD1)------| | (2)
|<----------------------------RPT(EDD1)-------|
| | |
| | |
|<-------RPT(EDD1)------| |
|<----------------------------RPT(EDD1)-------|
| | |
| | |
|<-------RPT(EDD1)------| |
|<----------------------------RPT(EDD1)-------|
| | |
In a simple network, a Manager interacts with multiple Agents.
Figure 2
In this figure, the Manager configures Agents A and B to produce EDD1
every second in (1). At some point in the future, upon receiving and
configuring this message, Agents A and B then build a Report Entry
containing EDD1 and send those reports back to the Manager in (2).
7.2.3. Multiplexed Management
Networks spanning multiple administrative domains may require
multiple Managers (for example, one per domain). When a Manager
defines custom Report Templates/Variables to an Agent, that
definition may be tagged with an access control list (ACL) to limit
what other Managers will be privy to this information. Managers in
such networks should synchronize with those other Managers granted
access to their custom data definitions. When Agents generate
messages, they MUST only send messages to Managers according to these
ACLs, if present. The control flows in this scenario are outlined in
Figure 3.
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Multiplexed Management Control Flow
+-----------+ +-------+ +-----------+
| Manager A | | Agent | | Manager B |
+-----+-----+ +---+---+ +-----+-----+
| | |
|---DEF(A,V1,EDD1*2)-->|<-DEF(B, V2, EDD2*2)--| (1)
| | |
|---PROD(1s, V1)------>|<---PROD(1s, V2)------| (2)
| | |
|<--------RPT(V1)------| | (3)
| |--------RPT(V2)------>|
|<--------RPT(V1)------| |
| |--------RPT(V2)------>|
| | |
| |<---PROD(1s, V1)------| (4)
| | |
| |---ERR(V1 no perm.)-->|
| | |
|--DEF(*,V3,EDD3*3)--->| | (5)
| | |
|---PROD(1s, V3)------>| | (6)
| | |
| |<----PROD(1s, V3)-----|
| | |
|<--------RPT(V3)------|--------RPT(V3)------>| (7)
|<--------RPT(V1)------| |
| |--------RPT(V2)------>|
|<-------RPT(V3)-------|--------RPT(V3)------>|
|<-------RPT(V1)-------| |
| |--------RPT(V2)------>|
Complex networks require multiple Managers interfacing with Agents.
Figure 3
In more complex networks, any Manager may choose to define custom
Report Templates and Variables, and Agents may need to accept such
definitions from multiple Managers. Variable definitions may include
an ACL that describes who may query and otherwise understand these
definitions. In (1), Manager A defines V1 only for A while Manager B
defines V2 only for B. Managers may, then, request the production of
Report Entries containing these definitions, as shown in (2). Agents
produce different data for different Managers in accordance with
configured production rules, as shown in (3). If a Manager requests
the production of a custom definition for which the Manager has no
permissions, a response consistent with the configured logging policy
on the Agent should be implemented, as shown in (4). Alternatively,
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as shown in (5), a Manager may define custom data with no
restrictions allowing all other Managers to request and use this
definition. This allows all Managers to request the production of
Report Entries containing this definition, shown in (6) and have all
Managers receive this and other data going forward, as shown in (7).
7.2.4. Data Fusion
In some networks, Agents do not individually transmit their data to a
Manager, preferring instead to fuse reporting data with local nodes
prior to transmission. This approach reduces the number and size of
messages in the network and reduces overall transmission energy
expenditure. The AMA supports fusion of NM reports by co-locating
Agents and Managers on nodes and offloading fusion activities to the
Manager. This process is illustrated in Figure 4.
Data Fusion Control Flow
+-----------+ +-----------+ +---------+ +---------+
| Manager A | | Manager B | | Agent B | | Agent C |
+---+-------+ +-----+-----+ +----+----+ +----+----+
| | | |
|--DEF(A,V0,EDD1+AD2)->| | | (1)
|--PROD(EDD1&AD2,V0)-->| | |
| | | |
| |--PROD(1s,EDD1)->| | (2)
| |------------------PROD(1s, EDD2)->|
| | | |
| |<---RPT(EDD1)----| | (3)
| |<------------------RPT(EDD2)------|
| | | |
|<-----RPT(A,V0)-------| | | (4)
| | | |
Data fusion occurs amongst Managers in the network.
Figure 4
In this example, Manager A requires the production of a Variable V0,
from node B, as shown in (1). The Manager role understands what data
is available from what agents in the subnetwork local to B,
understanding that EDD1 is available locally and EDD2 is available
remotely. Production messages are produced in (2) and data collected
in (3). This allows the Manager at node B to fuse the collected
Report Entries into V0 and return it in (4). While a trivial
example, the mechanism of associating fusion with the Manager
function rather than the Agent function scales with fusion
complexity, though it is important to reiterate that Agent and
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Manager designations are roles, not individual software components.
There may be a single software application running on node B
implementing both Manager B and Agent B roles.
8. Logical Data Model
This section identifies the different kinds of information present in
an asynchronously-managed network and describes how this information
should be communicated in the context of an ADM.
8.1. Data Decomposition
8.1.1. Groups
The AMA supports four basic groups of information: Data, Actions,
Literals, and Operators:
Data Data values consist of information collected by an Agent and
reported to Managers. This includes definitions from an ADM,
derived data values as configured from Managers, and Report
Entries which are collections of data elements.
Actions Actions are invoked on Agents and Managers to change behavior
in response to some external event (such as local state
changes or time). Actions include application-specific
functions specified as part of an ADM and macros which are
collections of these controls.
Literals Literals are constant numerical values that may be used in
the evaluation of expressions and predicates.
Operators Operators are those mathematical functions that operate on
series of Data and Literals, such as addition, subtraction,
multiplication, and division.
8.1.2. Levels
The AMA defines three levels that describe the origins and
multiplicity of data groups within the system. These classifications
are atomic, computed, and collection.
Atomic
The Atomic level contains items computed or defined
externally to the AMA and, thus, cannot be changed or
otherwise decomposed by Actors within the AMA. These items
are described in the context of an ADM and implemented in the
context of firmware or software running on an Agent. The
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identification of Atomic items MUST be globally unique and
should be managed by a registration authority.
Computed
The Computed level contains items whose definition/value are
specified/computed within the scope of an Actor in the AMA.
Items at the computed level may be formally specified in an
ADM (and therefore have definitions that are not subject to
change) or may be defined dynamically on Agents by Managers
and therefore have definitions that are subject to change in
accordance with configuration services. In either case the
definition of a Computed level item may reference other
Computed level items and other Atomic level items if such
inclusion does not result in a circular reference. When
defined in the context of an ADM, a Computed level item MUST
be globally unique and should be managed by a registration
authority.
Collection
The Collection level contains items representing groups of
other items, including other Collection level items. When a
Collection level item definition references another
Collection level item, circular references MUST be prevented.
When defined in the context of an ADM, a Collection level
item MUST be globally unique and should be managed by a
registration authority.
8.2. Data Model
Each component of the AMA data model can be identified as a
combination of group and level, as illustrated in Table 2. In this
table, group/level combinations that are unsupported are listed as N/
A. In this context, N/A indicates that the AMA does not require
support for groups of data at a particular level for compliance.
+------------+----------------------+---------+----------+----------+
| | Data | Action | Literals | Operator |
+------------+----------------------+---------+----------+----------+
| Atomic | Externally Defined | Control | Literal | Operator |
| | Data | | | |
| | | | | |
| Computed | Variable | Rule | N/A | N/A |
| | | | | |
| Collection | Report Entry | Macro | N/A | N/A |
+------------+----------------------+---------+----------+----------+
Table 2
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The eight elements of the AMA logical data model are described as
follows.
8.2.1. EDDs, VARs, and Reporting
Fundamental to any performance reporting function is the ability to
measure the state of the Agent. Measurement may be accomplished
through direct sampling of hardware, query against in-situ data
stores, or other mechanisms that provide the initial quantification
of state.
EDDs serve as the "lingua franca" of the management system: the unit
of information that cannot be otherwise created. As such, this
information serves as the basis for any user-defined (Variable)
values in the system.
AMPs MAY consider the concept of the confidence of the EDD as a
function of time. For example, to understand at which point a
measurement should be considered stale and need to be re-measured
before acting on the associated data.
While EDDs provide the full, raw set of information available to
Managers and Agents there is a performance optimization to pre-
computed re-used combinations of these values. Computing new values
as a function of measured values simplifies operator specifications
and prevents Agent implementations from continuously re-calculating
the same value each time it is used in a given time period.
For example, consider a sensor node which wishes to report a
temperature averaged over the past 10 measurements. An Agent may
either transmit all 10 measurements to a Manager, or calculate
locally the average measurement and transmit the "fused" data.
Clearly, the decision to reduce data volume is highly coupled to the
nature of the science and the resources of the network. For this
reason, the ability to define custom computations per deployment is
necessary.
Periodically, or in accordance with local state changes, Agents must
collect a series of measured values and computed values and
communicate them back to Managers. This ordered collection of value
information is noted in this architecture as a Report Entry which
populates either a pre-defined or ad-hoc Report Template. In support
of hierarchical definitions, Report Entries may, themselves, contain
other Report Entries. It would be incumbent on an AMP implementation
to guard against circular reference in Report Template definitions.
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8.2.2. Controls and Macros
Just as traditional network management approaches provide well-known
identifiers for values, the AMA provides well-known identifiers for
Actions. Whereas several low-latency, high-availability approaches
in networks can use approaches such as remote procedure calls (RPCs),
challenged networks cannot provide a similar function - Managers
cannot be in the processing loop of an Agent when the Agent is not in
communication with the Manager.
Controls in a system are the combination of a well-known operation
that can be taken by an Agent as well as any parameters that are
necessary for the proper execution of that function. For specific
applications or protocols, a control specification (as a series of
opcodes) can be published such that any implementing AMP accepts
these opcodes and understands that sending the opcodes to an Agent
supporting the application or protocol will properly execute the
associated function. Parameters to such functions are provided in
real-time by either Managers requesting that a control be run, pre-
configured, or auto-populated by the Agent in-situ.
Often, a series of controls must be executed in concert to achieve a
particular function, especially when controls represent more
primitive operations for a particular application/protocol. In such
scenarios, an ordered collection of controls can be specified as a
Macro. In support of the hierarchical build-up of functionality,
Macros may, themselves, contain other Macros, through it would be
incumbent on an AMP implementation to guard against excessive
recursion or other resource-intensive nesting.
8.2.3. Rules
Stimulus-response autonomy systems provide a way to pre-configure
responses to anticipated events. Such a mapping from responses to
events is advantageous in a challenged network for a variety of
reasons, as listed below.
o Distributed Operation - The concept of pre-configuration allows
the Agent to operate without regular contact with Managers in the
system. Configuration opportunities will be sporadic in any
challenged network making bootstrapping of the system difficult,
but this is a fundamental problem in any network scenario and any
autonomy approach.
o Deterministic Behavior - Where the mapping of stimulus to response
is stable, the behavior of the Agent to a variety of in-situ state
also remains stable. This stable behavior is necessary in
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critical operational systems where the actions of a platform must
be well understood even in the absence of an operator in the loop.
o Engine-Based Behavior - Several operational systems are unable to
deploy "mobile code" based solutions due to network bandwidth,
memory or processor loading, or security concerns. The benefit of
engine-based approaches is that the configuration inputs to the
engine can be flexible without incurring a set of problematic
requirements or concerns.
The logical unit of stimulus-response autonomy proposed in the AMA is
a Rule of the form:
IF stimulus THEN response
Where the set of such rules, when evaluated in some prioritized
sequence, provides the full set of autonomous behavior for an Agent.
Stimulus in such a system would either be a function of relative
time, absolute time, or some mathematical expression comprising one
or more values (measurement values or computed values).
Notably, in such a system, stimuli and responses from multiple
applications and protocols may be combined to provide an expressive
capability.
8.2.4. Operators and Literals
Computing values or evaluating expressions requires applying
mathematical operations to data known to the management system.
Operators in the AMA represent enumerated mathematical operations
applied to primitive and computed values in the AMA for the purpose
of creating new values. Operations may be simple binary operations
such as "A + B" or more complex functions such as sin(A) or
avg(A,B,C,D).
Literals represent pre-configured constants in the AMA, such as well-
known mathematical numbers (e.g., PI, E), or other useful data such
as Epoch times. Literals also represent asserted Primitive Values
used in expressions. For example, considering the expression (A = B
+ 10), A would be a Variable, B would be either a Variable or EDD, +
would be an Operator, and 10 would be a Literal.
8.3. Application Data Model
Application data models (ADMs) specify the data associated with a
particular application/protocol. The purpose of the ADM is to
provide a published interface for the management of an application or
protocol independent of the nuances of its software implementation.
In this respect, the ADM is conceptually similar to the Managed
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Information Base (MIB) used by SNMP, but contains additional
information relating to command opcodes and more expressive syntax
for automated behavior.
An ADM MUST define all well-known items necessary to manage the
specific application or protocol. This includes the definitions of
EDDs, Variables, Report Templates, Controls, Macros, Rules, Literals,
and Operators.
9. IANA Considerations
At this time, this protocol has no fields registered by IANA.
10. Security Considerations
Security within an AMA MUST exist 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 in the AMA. 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 which are defined
via configuration messages and implementation specific.
11. Informative References
[BIRRANE1]
Birrane, E. and R. Cole, "Management of Disruption-
Tolerant Networks: A Systems Engineering Approach", 2010.
[BIRRANE2]
Birrane, E., Burleigh, S., and V. Cerf, "Defining
Tolerance: Impacts of Delay and Disruption when Managing
Challenged Networks", 2011.
[BIRRANE3]
Birrane, E. and H. Kruse, "Delay-Tolerant Network
Management: The Definition and Exchange of Infrastructure
Information in High Delay Environments", 2011.
[I-D.irtf-dtnrg-dtnmp]
Birrane, E. and V. Ramachandran, "Delay Tolerant Network
Management Protocol", draft-irtf-dtnrg-dtnmp-01 (work in
progress), December 2014.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3416] Presuhn, R., Ed., "Version 2 of the Protocol Operations
for the Simple Network Management Protocol (SNMP)",
STD 62, RFC 3416, DOI 10.17487/RFC3416, December 2002,
<http://www.rfc-editor.org/info/rfc3416>.
[RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst,
R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant
Networking Architecture", RFC 4838, April 2007.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<http://www.rfc-editor.org/info/rfc6241>.
Author's Address
Edward J. Birrane
Johns Hopkins Applied Physics Laboratory
Email: Edward.Birrane@jhuapl.edu
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