RFC 6130
Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)
Internet Engineering Task Force (IETF) T. Clausen Request for Comments: 6130 LIX, Ecole Polytechnique Category: Standards Track C. Dearlove ISSN: 2070-1721 BAE Systems ATC J. Dean Naval Research Laboratory April 2011 Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)Abstract
This document describes a 1-hop and symmetric 2-hop neighborhood discovery protocol (NHDP) for mobile ad hoc networks (MANETs). Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6130. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English.Table of Contents
1. Introduction .....................................................4 1.1. Motivation .................................................5 2. Terminology .....................................................6 3. Applicability Statement .........................................9 4. Protocol Overview and Functioning ..............................10 4.1. Routers and Interfaces ....................................11 4.2. Information Base Overview .................................12 4.2.1. Local Information Base .............................13 4.2.2. Interface Information Bases ........................13 4.2.3. Neighbor Information Base ..........................14 4.3. Signaling Overview ........................................14 4.3.1. HELLO Message Generation ...........................15 4.3.2. HELLO Message Content ..............................16 4.3.3. HELLO Message Processing ...........................17 4.4. Link Quality ..............................................17 5. Protocol Parameters and Constants ..............................18 5.1. Protocol and Port Numbers .................................18 5.2. Multicast Address .........................................18 5.3. Interface Parameters ......................................18 5.3.1. Message Intervals ..................................19 5.3.2. Information Validity Times .........................21 5.3.3. Link Quality .......................................22 5.3.4. Jitter .............................................22 5.4. Router Parameters .........................................23 5.4.1. Information Validity Time ..........................23 5.5. Parameter Change Constraints ..............................23 5.6. Constants .................................................24 6. Local Information Base .........................................24 6.1. Local Interface Set .......................................25 6.2. Removed Interface Address Set .............................26 7. Interface Information Bases ....................................26 7.1. Link Set ..................................................27 7.2. 2-Hop Set .................................................28 8. Neighbor Information Base ......................................28 8.1. Neighbor Set ..............................................28 8.2. Lost Neighbor Set .........................................29 9. Local Information Base Changes .................................29
9.1. Adding an Interface .......................................29
9.2. Removing an Interface .....................................30
9.3. Adding a Network Address to an Interface ..................30
9.4. Removing a Network Address from an Interface ..............31
10. Packets and Messages ..........................................32
10.1. HELLO Messages ...........................................32
10.1.1. Address Blocks ....................................33
11. HELLO Message Generation ......................................34
11.1. HELLO Message Specification ..............................35
11.2. HELLO Message Transmission ...............................37
11.2.1. HELLO Message Jitter ..............................37
12. HELLO Message Processing ......................................38
12.1. Invalid Message ..........................................38
12.2. Definitions ..............................................40
12.3. Updating the Neighbor Set ................................41
12.4. Updating the Lost Neighbor Set ...........................42
12.5. Updating the Link Sets ...................................42
12.6. Updating the 2-Hop Set ...................................44
13. Other Information Base Changes ................................45
13.1. Link Tuple Symmetric .....................................46
13.2. Link Tuple Not Symmetric .................................47
13.3. Link Tuple Heard Timeout .................................48
14. Link Quality ..................................................48
14.1. Deployment without Link Quality ..........................49
14.2. Basic Principles of Link Quality .........................49
14.3. When Link Quality Changes ................................50
14.4. Updating Link Quality ....................................51
15. Proposed Values for Parameters and Constants ..................51
15.1. Message Interval Interface Parameters ....................51
15.2. Information Validity Time Interface Parameters ...........51
15.3. Information Validity Time Router Parameters ..............52
15.4. Link Quality Interface Parameters ........................52
15.5. Jitter Interface Parameters ..............................52
15.6. Constants ................................................52
16. Usage with Other Protocols ....................................52
17. Security Considerations .......................................54
17.1. Invalid HELLO Messages ...................................56
17.2. Authentication, Integrity, and Confidentiality
Suggestions ..............................................57
18. IANA Considerations ...........................................57
18.1. Expert Review: Evaluation Guidelines .....................58
18.2. Message Types ............................................58
18.3. Message-Type-Specific TLV Type Registries ................58
18.4. Address Block TLV Types ..................................59
18.5. LOCAL_IF, LINK_STATUS, and OTHER_NEIGHB Values ...........60
19. Contributors ..................................................61
20. Acknowledgments ...............................................61
21. References ....................................................62
21.1. Normative References .....................................62
21.2. Informative References ...................................62
Appendix A. Address Block TLV Combinations ........................63
Appendix B. Constraints ...........................................64
Appendix C. HELLO Message Example .................................66
Appendix D. Flow and Congestion Control ...........................69
Appendix E. Interval and Timer Illustrations ......................70
E.1. HELLO Message Generation Timing ..........................70
E.2. HELLO Message Processing Timing ..........................76
E.3. Other HELLO Message Timing ...............................77
Appendix F. Topology Pictures ....................................79
F.1. Example 1: Standard Single Interface Topology ............79
F.2. Example 2: Dual Addressed Interface on 1-Hop Neighbor ....80
F.3. Example 3: Dual Addressed Interface on 2-Hop Neighbor ....81
F.4. Example 4: Dual Addressed Interfaces .....................81
F.5. Example 5: Dual Interface on 2-Hop Neighbor ..............82
F.6. Example 6: Dual interface on 1-Hop Neighbor ..............82
F.7. Example 7: Dual Interface on 1-Hop and 2-Hop Neighbors ...83
F.8. Example 8: Dual Interface Locally and on 1-Hop Neighbor ..84
F.9. Example 9: Dual Interface on All Routers .................85
F.10. Example 10: Dual Addressed Dual Interfaces on All
Routers ......................................86
F.11. Example 11: Single Addressed Dual Interface Locally ......87
1. Introduction
This document describes a neighborhood discovery protocol (NHDP) for
a mobile ad hoc network (MANET) [RFC2501]. This protocol uses a
local exchange of HELLO messages so that each router can determine
the presence of, and connectivity to, its 1-hop and symmetric 2-hop
neighbors. Messages are defined and sent in packets according to the
specification [RFC5444].
1-hop neighborhood information is recorded for use by MANET routing
protocols to determine direct (1-hop) connectivity to neighboring
routers. 2-hop symmetric neighborhood information is recorded so as
to enable MANET routing protocols to employ flooding reduction
techniques, e.g., to select reduced relay sets for efficient network-
wide traffic dissemination.
1-hop and symmetric 2-hop neighborhood information is recorded in the
form of Information Bases. These are available for use by other
protocols, such as MANET routing protocols, that require information
regarding the local network connectivity. This protocol is designed
to maintain the information in these Information Bases even in the
presence of a dynamic network topology and wireless communication
channel characteristics.
This protocol makes no assumptions about the underlying link layer, other than support of local broadcast or multicast for communication to 1-hop neighbor routers. Link-layer information may be used if available and applicable. This protocol is based on the neighborhood discovery process contained in the Optimized Link State Routing (OLSR) Protocol [RFC3626].1.1. Motivation
MANETs differ from more traditional wired and infrastructure-based wireless networks due to their envisioned applicability over more challenging communication channels (e.g., wireless, lossy, broadcast channels with moderate and shared bandwidth, hidden and exposed terminals, and interference from other network devices and the environment) and in more challenging topological conditions (e.g., rapid and unpredictable mobility, dynamic and non-predetermined network membership). Due to the properties of wireless transmissions, communication between two neighboring routers may not be bi-directional; even if router A is able to receive packets from router B, the converse is not guaranteed to be true. Furthermore, because of the localized nature of wireless broadcast communication, neighboring routers within the same communications channel may have different sets of neighbors. That is, when using the same communication channel, even if router A is able to exchange packets with router B, and router B is able to exchange packets with router C, this does not guarantee that router A and router C can exchange packets directly. Each router in a MANET may use more than one communication channel. In particular, between the same pair of routers, more than one distinct communication channel may exist, each with different properties. This may, for example, be the case where MANET routers are equipped with multiple distinct wireless interfaces, operating at different frequencies. For use by MANET routing protocols, as well as for establishing a router's neighbors, a router may also need to determine whether each communication channel with that neighbor is bi-directional. The set of neighbor routers of a given MANET router may be continuously changing, often due to router mobility or a changing physical environment in which the MANET is located. There is typically no information from lower layers that would enable an IP routing protocol to detect and, as appropriate, react to such changes. Such changes can often take place on a short timescale,
such as of the order of seconds, requiring MANET routing protocols to act rapidly to ensure suitable convergence properties. MANET routing protocols, for example [RFC3626] and [RFC5449], often employ relay set reductions in order to conserve network capacity when maintaining network-wide topological information, with calculation of these reduced relay sets employing up to two hop information. The neighborhood discovery protocol specified in this document provides continued tracking of neighborhood changes, link bi- directionality, and local topological information up to two hops. Combined, this allows a MANET routing protocol access to information describing link establishment/disappearance and provides the necessary topological information for reduced relay set selection and other purposes.2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. All terms introduced in [RFC5444], including "packet", "message", "Address Block", "TLV Block", "TLV", "address", "address prefix", and "address object" are to be interpreted as described therein. Additionally, this document uses the following terminology: Network Address: An address plus an associated prefix length. This may be an address with an associated maximum prefix length or an address prefix including a prefix length. A network address thus represents a range of addresses. Router: A MANET router that implements this neighborhood discovery protocol. Interface: A router's attachment to a communications medium. An interface is assigned one or more addresses. MANET interface: An interface participating in a MANET and using this neighborhood discovery protocol. A router may have several MANET interfaces.
Heard:
A MANET interface of router X is considered heard on a MANET
interface of a router Y if the latter can receive control
messages, according to this specification, from the former.
Link:
A link between two MANET interfaces exists if either can be heard
by the other.
Symmetric link:
A symmetric link between two MANET interfaces exists if both can
be heard by the other.
1-hop neighbor:
A router X is a 1-hop neighbor of a router Y if a MANET interface
of router X is heard by a MANET interface of router Y.
Symmetric 1-hop neighbor:
A router X is a symmetric 1-hop neighbor of a router Y if a
symmetric link exists between a MANET interface on router X and a
MANET interface on router Y.
2-hop neighbor:
A router X is a 2-hop neighbor of a router Y if router X is a
1-hop neighbor of a 1-hop neighbor of router Y, but is not router
Y itself.
Symmetric 2-hop neighbor:
A router X is a symmetric 2-hop neighbor of a router Y if router X
is a symmetric 1-hop neighbor of a symmetric 1-hop neighbor of
router Y, but is not router Y itself.
1-hop neighborhood:
The 1-hop neighborhood of a router X is the set of the 1-hop
neighbors of router X.
Symmetric 1-hop neighborhood:
The symmetric 1-hop neighborhood of a router X is the set of the
symmetric 1-hop neighbors of router X.
2-hop neighborhood:
The 2-hop neighborhood of a router X is the set of the 2-hop
neighbors of router X. (This may include routers in the 1-hop
neighborhood of router X.)
Symmetric 2-hop neighborhood:
The symmetric 2-hop neighborhood of a router X is the set of the
symmetric 2-hop neighbors of router X. (This may include routers
in the 1-hop neighborhood, or even in the symmetric 1-hop
neighborhood, of router X.)
Constant:
A numerical value that MUST be the same for all MANET interfaces
of all routers in the MANET, at all times.
Interface parameter:
A boolean or numerical value, specified separately for each MANET
interface of each router. A router MAY change interface parameter
values at any time, subject to some constraints.
Router parameter:
A boolean or numerical value, specified for each router, and not
specific to an interface. A router MAY change router parameter
values at any time, subject to some constraints.
Information Base:
A collection of information maintained by this protocol and which
is to be made available to MANET routing protocols. An
Information Base may be associated with a MANET interface or with
a router.
Furthermore, this document uses the following notational conventions:
X contains y, or y is contained in X
An unordered list membership operator. X is an unordered list and
y is an element. "X contains y" or "y is contained in X" returns
true if the unordered list X includes the element y, and returns
false otherwise.
X contains Y, or Y is contained in X
An unordered list inclusion operator. X and Y are both unordered
lists. "X contains Y" or "Y is contained in X" returns true if
the unordered list X contains all elements y which are contained
in Y, and returns false otherwise.
A overlaps B
If A and B are network addresses, and the range of addresses
represented by A and the range of addresses represented by B both
contain at least one common address. (This is only possible if
one range is a sub-range of the other.)
a := b
An assignment operator, whereby the left side (a) is assigned the
value of the right side (b). a and b may be values, network
addresses, or unordered lists (they must be of the same type).
c = d
A comparison operator, returning true if the value of the left
side (c) is equal to the value of the right side (d). c and d may
be values, network addresses, or unordered lists (they must be of
the same type). If c and d are unordered lists, then they are
considered to be equal if c contains d and d contains c (i.e.,
they contain the same set of elements, regardless of the order in
which they are recorded in the lists). If c and d are network
addresses, they are considered equal only if both addresses and
prefix lengths are equal (i.e., they represent the same).
e != f
A comparison operator, returning not (e = f), i.e., returning true
where (e = f) would have returned false, and returning false where
(e = f) would have returned true.
3. Applicability Statement
This protocol:
o Is applicable to networks, especially wireless networks, in which
unknown neighbors can be reached by local broadcast or multicast
packets.
o Is designed to work in networks with a dynamic topology, and in
which messages may be lost, such as due to collisions in wireless
networks.
o Supports routers that each have one or more participating MANET
interfaces. The set of a router's interfaces may change over
time. Each interface may have one or more associated network
addresses, and these may also be dynamically changing.
o Provides each router with current local topology information up to
two hops away, and makes this local topology information available
to MANET routing protocols in Information Bases.
o Uses the packet and message formats specified in [RFC5444]. This
includes the definition of a HELLO Message Type, used for
signaling local topology information.
o Allows "external" and "internal" extensibility as enabled by
[RFC5444].
o May interact with, and be extended by, other protocols, such as
MANET routing protocols, see Section 16.
o Can use relevant link-layer information if it is available.
o Is designed to work in a completely distributed manner, and does
not depend on any central entity.
4. Protocol Overview and Functioning
The objective of this protocol is, for each router:
o To identify 1-hop neighbors and symmetric 1-hop neighbors of this
router.
o To find the interface network addresses of the router's symmetric
2-hop neighbors.
o To record this information in Information Bases and thus make this
information available to other protocols that use this
neighborhood discovery protocol.
o To be available for use by other protocols, which MAY extend the
information in these Information Bases, including adding new Sets
to Information Bases, new elements to protocol Tuples and new TLVs
to be included in outgoing HELLO messages and processed when in
incoming HELLO messages.
These objectives are achieved using local (1-hop) signaling that:
o Advertises the presence of a router and its interface network
addresses.
o Discovers links from neighboring routers.
o Performs bi-directionality checks on the discovered links.
o Advertises discovered links, and whether each is symmetric, to its
1-hop neighbors, and hence discovers symmetric 2-hop neighbors.
This specification defines, in turn:
o Parameters and constants used by the protocol. Parameters used by
this protocol may, where appropriate, be specific to a given MANET
interface or to a MANET router. This protocol allows all
parameters to be changed dynamically, and to be set independently
for each MANET router or MANET interface, as appropriate.
o The Information Bases describing local interfaces, discovered
links and their status, current and former 1-hop neighbors, and
symmetric 2-hop neighbors.
o The format of the HELLO message that is used for local signaling.
o The generation of HELLO messages from some of the information in
the Information Bases.
o The updating of the Information Bases according to received HELLO
messages and other events.
o The response to other events, such as the expiration of
information in the Information Bases.
4.1. Routers and Interfaces
In order for a router to participate in a MANET, it MUST have at
least one, and possibly more, MANET interfaces.
Each MANET interface:
o Is configured with one or more network addresses. Each address in
the range of addresses represented by that network address MUST
satisfy the following properties:
o It MUST be unique to this router, i.e., it MUST NOT be assigned
to any interface of any other router.
o If assigned to other MANET interfaces, on the same router,
these MANET interfaces MUST be isolated, i.e., addresses may
only be assigned to different interfaces on the same router if
no MANET interface on another router can communicate with both.
For example, interfaces using distinct radio "channels" MAY be
assigned the same address.
o Has a set of interface parameters, defining the behavior of this
MANET interface. Each MANET interface MAY be individually
parameterized.
o Has an Interface Information Base, recording information regarding
links to this MANET interface and symmetric 2-hop neighbors that
can be reached through such links.
o Generates and processes HELLO messages.
In addition to a set of MANET interfaces as described above, each
router has:
o A Local Information Base, containing the network addresses of the
interfaces (MANET and non-MANET) of this router. The contents of
this Information Base are not changed by signaling.
o A Neighbor Information Base, recording information regarding
current and recently lost 1-hop neighbors of this router.
A router may have both MANET interfaces and non-MANET interfaces.
Interfaces of both of these types are recorded in a router's Local
Information Base, which is used, but not updated, by the signaling of
this protocol.
4.2. Information Base Overview
Each router maintains protocol state using Information Bases,
described in the following sections. Each Information Base consists
of a number of Protocol Sets. Each Protocol Set contains a number of
Protocol Tuples.
An implementation of this protocol MAY maintain this information in
the indicated form, or in any other organization that offers access
to this information. In particular, note that it is not necessary to
remove Protocol Tuples from Protocol Sets at the exact time
indicated, only to behave as if the Protocol Tuples were removed at
that time.
Information in the Local Information Base is defined locally and
included in HELLO messages. Information in the Interface Information
Base and the Neighbor Information Base is determined from received
HELLO messages; some of this information may also be included in
transmitted HELLO messages. Such information has a limited duration
in which it is considered valid. This duration is determined from
the VALIDITY_TIME TLV in the HELLO message in which the information
is received, which in turn is set by the router that originated the
HELLO message, using its corresponding interface parameter
H_HOLD_TIME.
Appendix E illustrates the relationship between message reception,
included VALIDITY_TIME TLVs, and the duration for which information
received in a HELLO message is considered valid. Appendix F
illustrates some example topologies and how they correspond to
information in the Information Bases.
4.2.1. Local Information Base
Each router maintains a Local Information Base, which contains the router's local configuration information, specifically: o The Local Interface Set, which consists of Local Interface Tuples, each of which represents an interface (MANET or non-MANET) of the router. o The Removed Interface Address Set, which consists of Removed Interface Address Tuples, each of which records a recently used network address of an interface (MANET or non-MANET) of the router. The Local Interface Set is used for generating HELLO messages, specifically for determining which interface network addresses are to be included and identified as local interfaces. The Removed Interface Address Set is used to avoid incorrectly recording a formerly used network address as a symmetric 2-hop neighbor's network address. The Local Information Base is used for generating signaling, but is not itself updated by signaling specified in this document. Updates to the Local Information Base are due to changes of the router configuration, and may be allowed to trigger signaling.4.2.2. Interface Information Bases
Each router maintains, for each of its MANET interfaces, an Interface Information Base, which contains 1-hop neighborhood and symmetric 2-hop neighborhood information collected from this MANET interface, specifically: o A Link Set, which records information about current and recently lost links between this MANET interface and MANET interfaces of 1-hop neighbors. The Link Set consists of Link Tuples, each of which contains information about a single link. Link quality information (see Section 14), when used, is recorded in Link Tuples. o A 2-Hop Set, which records the existence of symmetric links between symmetric 1-hop neighbors of this MANET interface and other routers (symmetric 2-hop neighbors). The 2-Hop Set consists of 2-Hop Tuples, each of which records a network address of a symmetric 2-hop neighbor, and all network addresses of the corresponding symmetric 1-hop neighbor.
The Link Set for a MANET interface is used for generating HELLO messages. Specifically, the Link Set information is included to both allow other routers to identify symmetric links and to populate the 2-Hop Set. Recently lost links are recorded in the Link Set for a MANET interface so that they can be advertised in HELLO messages, accelerating their removal from relevant 1-hop neighbors' Link Sets. The Link Set for a MANET interface is itself updated on receiving a HELLO message, including recording symmetric links as indicated above. The 2-Hop Set for a MANET interface is updated as indicated above, and is not itself used in generating HELLO messages.4.2.3. Neighbor Information Base
Each router maintains a Neighbor Information Base, which contains collected information about current and recently lost 1-hop neighbors, specifically: o The Neighbor Set consists of Neighbor Tuples, each of which records all network addresses of a single 1-hop neighbor. Neighbor Tuples are maintained as long as there are corresponding Link Tuples. o The Lost Neighbor Set consists of Lost Neighbor Tuples, each of which records a network address of a recently lost symmetric 1-hop neighbor. The Neighbor Set associates all network addresses of each 1-hop neighbor. These network addresses may be included when generating a HELLO message, so that other symmetric 1-hop neighbors can record this information in a 2-Hop Set. The Neighbor Set can be updated on receiving a HELLO message. The Lost Neighbor Set is used to determine which network addresses are to be included in a HELLO message as being lost (of a recently symmetric 1-hop neighbor). The Lost Neighbor Set can itself be updated on receiving a HELLO message.4.3. Signaling Overview
This protocol contains a signaling mechanism for maintaining the Interface Information Bases and the Neighbor Information Base. If information from the link layer, or any other source, is available and appropriate, it may also be used to update these Information Bases. Such updates are subject to the constraints specified in Appendix B.
Signaling consists of a single type of message, known as a HELLO
message. Each router generates HELLO messages on each of its MANET
interfaces. HELLO messages are generated independently on each MANET
interface of a MANET router; the content of a given HELLO message
depends on the MANET interface for which it has been generated.
Each HELLO message:
o Identifies, as far as is required, the MANET interface for which
it is generated and transmitted; this allows recipients of that
HELLO message to identify that MANET interface from among those it
may hear.
o Reports the network addresses of other interfaces (MANET and non-
MANET) of the router; this allows recipients of that HELLO message
to associate a set of network addresses with a single 1-hop
neighbor.
o Includes 1-hop neighbor information from the Information Bases;
this allows detection of local symmetric links, and symmetric
2-hop neighbors.
HELLO message generation, and the validity of the information
recorded as a consequence of processing a HELLO message, is affected
by timers and validity information included in HELLO messages through
TLVs. The relationship between message timers and intervals is
illustrated in Appendix E.
4.3.1. HELLO Message Generation
HELLO messages are generated by a router for each of its MANET
interfaces, and MAY be sent:
o Proactively, at a regular interval, known as HELLO_INTERVAL.
HELLO_INTERVAL may be fixed, or may be dynamic. For example,
HELLO_INTERVAL may be backed off due to congestion or network
stability.
o As a response to a change in the router itself, or its 1-hop
neighborhood, for example, on first becoming active or in response
to a new, lost, or changed status link.
o In a combination of these proactive and responsive mechanisms.
Jittering of HELLO message generation and transmission SHOULD be used
as described in Section 11.2, unless the medium access control
mechanism in use prevents any simultaneous transmissions by
potentially interfering routers.
HELLO messages MAY be scheduled independently for each MANET interface, or, interface parameters permitting, using the same schedule for all MANET interfaces of a router.4.3.2. HELLO Message Content
The content of a HELLO message MUST satisfy the following: o A HELLO message MUST contain all of the network addresses in the Local Interface Set of the router on which the HELLO message is being generated. This includes: o At least one network address of each MANET interface of the router. o Network addresses that include all source addresses of any IP datagrams sent by the router on any MANET interface. o All other network addresses of the router that are to be made known to any other router for any reason. o For each MANET interface, within every time interval equal to the corresponding REFRESH_INTERVAL, sent HELLO messages MUST collectively include all of the relevant information in the corresponding Link Set and the Neighbor Information Base. Note that when determining whether to include information in a HELLO message, the sender MUST consider all times up to the latest time when it may send its next HELLO message on this MANET interface. o For each MANET interface, within every time interval equal to the corresponding REFRESH_INTERVAL, sent HELLO messages MUST collectively include all of the relevant information in the corresponding Link Set and the Neighbor Information Base. o When determining whether to include a given piece of neighbor information in a HELLO message, it is not sufficient to consider whether that information has been sent in the interval of length REFRESH_INTERVAL up to the current time. Instead, the router MUST consider the interval of length REFRESH_INTERVAL that will end at the latest possible time at which the next HELLO message will be sent on this MANET interface. (Normally, this will be HELLO_INTERVAL past the current time, but MAY be earlier if this router elects to divide its neighbor information among more than one HELLO message in order to reduce the size of its HELLO messages.) All neighbor information MUST be sent in this interval, i.e., the router MUST ensure that this HELLO message includes all neighbor information that has not already been included in any HELLO messages sent since the start of this
interval (normally, the current time - (REFRESH_INTERVAL -
HELLO_INTERVAL)).
o A HELLO message MUST include exactly one VALIDITY_TIME Message
TLV, as specified in [RFC5497], that indicates the length of time
for which the message content is to be considered valid, and is
therefore to be included in the receiving router's Interface
Information Base.
o A periodically generated HELLO message SHOULD include exactly one
INTERVAL_TIME Message TLV, as specified in [RFC5497], that
indicates the current value of HELLO_INTERVAL for that MANET
interface, i.e., the period within which a further HELLO message
is guaranteed to be sent on that MANET interface.
4.3.3. HELLO Message Processing
HELLO messages received by a router are used to update the Interface
Information Base for the MANET interface over which that HELLO
message was received, as well as the Neighbor Information Base of the
router. Specifically:
o The router ensures that there is a single Neighbor Tuple
corresponding to the originator of that HELLO message.
o The router ensures that there is a Link Tuple, with appropriate
status (heard or symmetric) and advertised duration, corresponding
to the link between the MANET interfaces on which that HELLO
message was sent and received. One or more Lost Neighbor Tuples
may be created if the HELLO message reports that the link was
lost.
o If the link between the MANET interfaces on which the HELLO
message was sent and received is symmetric, then the router
ensures that there are the appropriate 2-Hop Tuples, with
advertised duration.
The processing defined in this specification handles any unexpected
and erroneous information in a HELLO message, maintaining the
constraints on Information Base contents specified in Appendix B.
4.4. Link Quality
Some links in a MANET may be marginal, e.g., due to adverse wireless
propagation. In order to avoid using such marginal links, a link
quality value is recorded in each Link Tuple. A MANET router
considers links for which an insufficient link quality is recorded as
lost. Modifying the recorded link quality in a Link Tuple is
OPTIONAL. If link quality is not to be modified, it MUST be set to indicate an always usable quality link. Note that link quality is a "link admittance" mechanism, allowing a router to determine that a given link is too unstable to even consider for use. It is specifically not a link metric nor is it a substitute for one. Link quality information is only used locally and is not used in signaling. Routers may interoperate whether they are using the same, different, or no link quality information. Link quality information is thus not equivalent to a link metric. Link quality information is defined in this specification as a normalized, dimensionless value in the interval zero to one, inclusive, where the greater the value, the better the link quality. See Section 14 for further details.
(page 18 continued on part 2)
