Mobile Ad hoc Networking (MANET) T. Clausen
Internet-Draft LIX, Ecole Polytechnique, France
Intended status: Standards Track C. Dearlove
Expires: August 13, 2007 BAE Systems Advanced Technology
Centre
J. Dean
Naval Research Laboratory
The OLSRv2 Design Team
MANET Working Group
February 9, 2007
MANET Neighborhood Discovery Protocol (NHDP)
draft-ietf-manet-nhdp-01
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Copyright (C) The IETF Trust (2007).
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Abstract
This document describes a 1-hop and symmetric 2-hop neighborhood
discovery protocol (NHDP) for mobile ad hoc networks (MANETs).
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Applicability Statement . . . . . . . . . . . . . . . . . . . 6
4. Protocol Overview and Functioning . . . . . . . . . . . . . . 7
4.1. HELLO Message Generation . . . . . . . . . . . . . . . . . 7
4.2. HELLO message content . . . . . . . . . . . . . . . . . . 8
4.3. Node Behavior . . . . . . . . . . . . . . . . . . . . . . 8
5. Neighborhood Information Base . . . . . . . . . . . . . . . . 10
5.1. Link Set . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2. Symmetric Neighbor Set . . . . . . . . . . . . . . . . . . 11
5.3. Neighborhood Address Association Set . . . . . . . . . . . 12
5.4. 2-Hop Neighbor Set . . . . . . . . . . . . . . . . . . . . 12
6. Packets and Messages . . . . . . . . . . . . . . . . . . . . . 13
6.1. HELLO Messages . . . . . . . . . . . . . . . . . . . . . . 13
6.1.1. Local Interface Block . . . . . . . . . . . . . . . . 14
6.1.2. Address Block TLVs . . . . . . . . . . . . . . . . . . 14
7. HELLO Message Generation . . . . . . . . . . . . . . . . . . . 15
7.1. HELLO Message: Transmission . . . . . . . . . . . . . . . 16
7.1.1. HELLO Message: Jitter . . . . . . . . . . . . . . . . 17
8. HELLO Message Processing . . . . . . . . . . . . . . . . . . . 18
8.1. Populating the Link Set . . . . . . . . . . . . . . . . . 18
8.2. Populating the Symmetric Neighbor Set . . . . . . . . . . 19
8.3. Populating the Neighborhood Address Association Set . . . 20
8.4. Populating the 2-Hop Neighbor Set . . . . . . . . . . . . 20
8.5. Neighborhood Changes . . . . . . . . . . . . . . . . . . . 22
9. Proposed Values for Constants . . . . . . . . . . . . . . . . 23
9.1. Message Intervals . . . . . . . . . . . . . . . . . . . . 23
9.2. Holding Times . . . . . . . . . . . . . . . . . . . . . . 23
9.3. Jitter Times . . . . . . . . . . . . . . . . . . . . . . . 23
9.4. Time . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
10.1. Multicast Addresses . . . . . . . . . . . . . . . . . . . 24
10.2. Message Types . . . . . . . . . . . . . . . . . . . . . . 24
10.3. TLV Types . . . . . . . . . . . . . . . . . . . . . . . . 24
10.4. LINK_STATUS and OTHER_NEIGHB Values . . . . . . . . . . . 25
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
11.1. Normative References . . . . . . . . . . . . . . . . . . . 26
11.2. Informative References . . . . . . . . . . . . . . . . . . 26
Appendix A. Address Block TLV Combinations . . . . . . . . . . . 27
Appendix B. HELLO Message Example . . . . . . . . . . . . . . . 28
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Appendix C. Time TLVs . . . . . . . . . . . . . . . . . . . . . 30
C.1. Representing Time . . . . . . . . . . . . . . . . . . . . 30
C.2. General Time TLV Structure . . . . . . . . . . . . . . . . 30
C.3. Message TLVs . . . . . . . . . . . . . . . . . . . . . . . 32
C.3.1. VALIDITY_TIME TLV . . . . . . . . . . . . . . . . . . 32
C.3.2. INTERVAL_TIME TLV . . . . . . . . . . . . . . . . . . 32
Appendix D. Message Jitter . . . . . . . . . . . . . . . . . . . 33
D.1. Jitter . . . . . . . . . . . . . . . . . . . . . . . . . . 33
D.1.1. Periodic message generation . . . . . . . . . . . . . 33
D.1.2. Externally triggered message generation . . . . . . . 34
D.1.3. Message forwarding . . . . . . . . . . . . . . . . . . 34
Appendix E. Utilizing Link Layer Information . . . . . . . . . . 36
Appendix F. Security Considerations . . . . . . . . . . . . . . 38
Appendix F.1. Invalid HELLO messages . . . . . . . . . . . . . . . 38
Appendix G. Flow and Congestion Control . . . . . . . . . . . . 40
Appendix H. Contributors . . . . . . . . . . . . . . . . . . . . 41
Appendix I. Acknowledgements . . . . . . . . . . . . . . . . . . 42
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 43
Intellectual Property and Copyright Statements . . . . . . . . . . 44
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1. Introduction
This document describes a neighborhood discovery protocol (NHDP) for
a mobile ad hoc network (MANET). The protocol uses an exchange of
HELLO messages in order that each node can determine its 1-hop and
symmetric 2-hop neighborhoods.
This specification describes both this HELLO message exchange, the
messages being defined as instances of the specification [1], and the
information storage required for neighborhood discovery.
This protocol makes no assumptions about the underlying link layer,
other than support of link local multicast. Link layer information
and notifications may be used if available and applicable.
This protocol is based on the neighborhood discovery process
contained in the Optimized Link State Routing Protocol (OLSR) [3].
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2. Terminology
The keywords "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 [2].
The terms "packet", "message", "address block", "TLV", and "TLV
block" in this document are to be interpreted as described in [1].
Additionally, this document uses the following terminology:
Node - A MANET router which implements this neighborhood discovery
protocol.
MANET interface - A network device participating in a MANET and
using this neighborhood discovery protocol. A node may have
several MANET interfaces, each being assigned one or more IP
addresses.
Link - A pair of MANET interfaces from two different nodes, where at
least one interface is able to receive traffic from the other.
Symmetric link - A link where both MANET interfaces are able to
receive traffic from the other.
1-hop neighbor - A node X is a 1-hop neighbor of a node Y if node Y
can hear node X (i.e. a link exists from a MANET interface on node
X to a MANET interface on node Y).
Symmetric 1-hop neighbor - A node X is a symmetric 1-hop neighbor of
a node Y if a symmetric link exists from a MANET interface on node
X to a MANET interface on node Y.
Symmetric 2-hop neighbor - A node X is a symmetric 2-hop neighbor of
a node Y if node X is a symmetric 1-hop neighbor of a symmetric
1-hop neighbor of node Y, but is not node Y itself.
1-hop neighborhood - The 1-hop neighborhood of a node X is the set
of the 1-hop neighbors of node X.
Symmetric 1-hop neighborhood - The symmetric 1-hop neighborhood of a
node X is the set of the symmetric 1-hop neighbors of node X.
Symmetric 2-hop neighborhood - The symmetric 2-hop neighborhood of a
node X is the set of the symmetric 2-hop neighbors of node X.
(This may include nodes in the 1-hop neighborhood, or even in the
symmetric 1-hop neighborhood, of node X.)
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3. Applicability Statement
This neighborhood discovery protocol supports nodes which have one or
more interfaces participating in the MANET. It provides each node
with local topology information up to two hops away. This
information is made available to other protocols through a
Neighborhood Information Base, described in Section 5.
The protocol is designed to work in networks where messages may be
lost, such as due to collisions in wireless networks. If relevant
link layer information is available then it may be used by this
protocol.
This protocol to works in a completely distributed manner and does
not depend on any central entity. It does not require any changes to
the format of IP packets, thus any existing IP stack can be used as
is.
This protocol uses the packet and message formats specified in [1].
HELLO messages specified by this protocol may be extended using the
TLV mechanisms described in [1]. For example, if multipoint relays
(MPRs) are to be calculated similarly to as in OLSR [3] and signaled
to neighbors, then this information may be added to HELLO messages
using an address block TLV. HELLO messages can also be transmitted
in packets with messages from other protocols that also use [1].
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4. Protocol Overview and Functioning
This protocol specifies local (one hop) signaling that:
o advertises the presence of a node and its MANET interfaces;
o discovers links to adjacent nodes;
o performs bidirectionality checks on the discovered links;
o advertises discovered links and whether each is symmetric to its
1-hop neighbors and hence discover symmetric 2-hop neighbors;
o maintains an information base describing discovered links and
their status, 1-hop neighbors and their MANET interfaces,
symmetric 1-hop neighbors and symmetric 2-hop neighbors.
Signaling consists of a single type of message, known as a HELLO
message. A HELLO message identifies its originator node and that
node's MANET interfaces and addresses. As a node receives HELLO
messages and populates its information base, a list of 1-hop
neighbors' MANET interface addresses and their link status (lost,
symmetric or heard) is included in subsequent HELLO messages. Thus,
the periodic transmission allows nodes to continuously track changes
in their 1-hop and symmetric 2-hop neighborhoods. If information
about link quality is available from the link layer, then this may
also be used, see Appendix E.
4.1. HELLO Message Generation
HELLO messages may be sent:
o Proactively, at a regular interval, known as HELLO_INTERVAL.
HELLO_INTERVAL may be fixed, as suggested in Section 9, or may be
dynamic. For example HELLO_INTERVAL may be backed off due to
congestion or network stability. Note that if HELLO_INTERVAL is
dynamic, it is interpreted as the interval within which the next
HELLO message will be sent on the same MANET interface.
o As a response to a change in the node itself, or its neighborhood,
for example on first becoming active or in response to a new,
broken or changed status link.
o In a combination of these proactive and responsive mechanisms.
Jittering of HELLO message generation and transmission, as described
in Section 7.1, may be appropriate.
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HELLO messages are sent independently on each MANET interface.
4.2. HELLO message content
Each HELLO message sent over a MANET interface need not contain all
of the information appropriate to that MANET interface, however:
o A HELLO message MUST contain all of its own local interface
information.
o Within every time interval of length REFRESH_INTERVAL, HELLO
messages sent over a MANET interface MUST include all of the
information appropriate to that interface in at least one HELLO
message sent on that interface. This applies to otherwise purely
responsive nodes as well as proactive nodes.
o A HELLO message MUST include a VALIDITY_TIME message TLV that
indicates the length of time for which the message content is to
be considered valid and included in the receiving node's
Neighborhood Information Base.
o A HELLO message SHOULD include an INTERVAL_TIME message TLV that
indicates the current value of HELLO_INTERVAL.
4.3. Node Behavior
A node MUST:
o Respect a minimum interval, HELLO_MIN_INTERVAL, between successive
HELLO message transmissions over a given interface. If jitter is
used then this interval may be reduced, but only by a random value
not exceeding HP_MAXJITTER.
o Ensure that if HELLO_INTERVAL and other parameters are maintained
dynamically, changes do not invalidate the guarantees of
Section 7.1.
o Maintain, based on received HELLO messages, estimates of its 1-hop
and symmetric 2-hop neighborhoods as this protocol operates.
Formally defined in Section 5, this can be summarized as
consisting of the following sets:
Link Set - Records the status of all links from and to current
and former 1-hop neighbors.
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Symmetric Neighbor Set - Records the status of current and former
symmetric 1-hop neighbors. If any of these nodes have more
than one MANET interface then this set may record addresses
that are not in the Link Set.
Neighborhood Address Association Set - Allows the addresses of
the MANET interfaces of each 1-hop neighbor to be associated
with each other.
2-Hop Neighbor Set - Records the addresses of the MANET
interfaces of symmetric 2-hop neighbors.
The information in the Link Set and Symmetric Neighbor Set MUST be
maintained in order for a node to correctly generate HELLO
messages.
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5. Neighborhood Information Base
A node maintains a Neighborhood Information Base that records
information about its 1-hop and symmetric 2-hop neighborhoods. The
Neighborhood Information Base includes the Link Set, the Symmetric
Neighbor Set, the Neighborhood Address Association Set and the 2-Hop
Neighbor Set.
A node, X, can be present in both the 1-hop and symmetric 2-hop
neighborhoods of another node, Y, concurrently. This allows node X
to be immediately considered as a symmetric 2-hop neighbor by node Y
if the link between them fails.
All addresses MUST have an associated prefix length, which is
included in all addresses in the Neighborhood Information Base.
Prefix lengths are indicated in HELLO messages using the
PREFIX_LENGTH TLV specified in [1]; if an address has no such TLV,
then its prefix length is equal to the address length. Two addresses
are considered equal if and only if their associated prefix lengths
are also equal.
5.1. Link Set
A node's Link Set records its 1-hop neighborhood. It consists of
Link Tuples:
(L_local_iface_addr, L_neighbor_iface_addr, L_SYM_time,
L_ASYM_time, L_time)
where:
L_local_iface_addr is the address of the local MANET interface on
which the 1-hop neighbor is or was heard;
L_neighbor_iface_addr is the address of the MANET interface of the
1-hop neighbor;
L_SYM_time is the time until which the link to the 1-hop neighbor is
considered symmetric;
L_ASYM_time is the time until which the MANET interface of the 1-hop
neighbor is considered heard;
L_time specifies when this Tuple expires and MUST be removed.
The status of the link, denoted L_STATUS, can be derived based on the
fields L_SYM_time and L_ASYM_time as defined in Table 1.
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+-------------+-------------+-----------+
| L_SYM_time | L_ASYM_time | L_STATUS |
+-------------+-------------+-----------+
| Expired | Expired | LOST |
| | | |
| Not Expired | Expired | SYMMETRIC |
| | | |
| Not Expired | Not Expired | SYMMETRIC |
| | | |
| Expired | Not Expired | HEARD |
+-------------+-------------+-----------+
Table 1
5.2. Symmetric Neighbor Set
A node's Symmetric Neighbor Set records its symmetric 1-hop
neighborhood. It consists of Symmetric Neighbor Tuples:
(N_local_iface_addr, N_neighbor_iface_addr, N_SYM_time, N_time)
where:
N_local_iface_addr is the address of the local MANET interface to
which the 1-hop neighbor has or had a symmetric link;
N_neighbor_iface_addr is an address of a MANET interface of a 1-hop
neighbor which is or was a symmetric 1-hop neighbor of this node;
N_SYM_time is the time until which the 1-hop neighbor is considered
to be a symmetric 1-hop neighbor;
N_time specifies when this Tuple expires and MUST be removed.
The status of the 1-hop neighbor, denoted N_STATUS, can be derived
based on the field L_SYM_time as defined in Table 2.
+-------------+-----------+
| N_SYM_time | N_STATUS |
+-------------+-----------+
| Expired | LOST |
| | |
| Not Expired | SYMMETRIC |
+-------------+-----------+
Table 2
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5.3. Neighborhood Address Association Set
A node's Neighborhood Address Association Set records the MANET
interface configuration of its 1-hop neighbors. It consists of
Neighborhood Address Association Tuples:
(NA_neighbor_iface_addr_list, NA_time)
where:
NA_neighbor_iface_addr_list is a list of interface addresses of a
single 1-hop neighbor;
NA_time specifies when this Tuple expires and MUST be removed.
5.4. 2-Hop Neighbor Set
A node's 2-Hop Neighbor Set records its symmetric 2-hop neighborhood.
It consists of 2-Hop Neighbor Tuples:
(N2_local_iface_addr, N2_neighbor_iface_addr, N2_2hop_iface_addr,
N2_time)
where:
N2_local_iface_addr is the address of the local MANET interface on
which this information was received;
N2_neighbor_iface_addr is the address of the MANET interface of a
symmetric 1-hop neighbor;
N2_2hop_iface_addr is the address of a MANET interface of a
symmetric 2-hop neighbor which has a symmetric link (using any
MANET interface) to the indicated symmetric 1-hop neighbor;
N2_time specifies the time at which this Tuple expires and MUST be
removed.
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6. Packets and Messages
The packet and message format used by this neighborhood discovery
protocol is defined in [1], which is used with the following
considerations:
o this protocol specifies one message type, the HELLO message;
o HELLO message header options may be used as specified by the
protocol which uses this neighborhood discovery protocol;
o HELLO messages MUST NOT be forwarded;
o HELLO messages may be included in multi-message packets as
specified in [1];
o packet header options may be used as specified by the protocol
which uses this neighborhood discovery protocol.
6.1. HELLO Messages
A HELLO message MUST contain:
o A VALIDITY_TIME message TLV as specified in Appendix C,
representing time value (at distance one hop) H_HOLD_TIME, which
MUST NOT be less than REFRESH_INTERVAL. If HELLO messages may be
lost then H_HOLD_TIME SHOULD be a multiple of REFRESH_INTERVAL.
o An address block, and associated TLV block, known as the Local
Interface Block, as specified in Section 6.1.1.
A HELLO message which is transmitted at a regular interval SHOULD
contain, and otherwise MAY contain:
o An INTERVAL_TIME message TLV as specified in Appendix C,
representing time value (at distance one hop) HELLO_INTERVAL.
A HELLO message MAY contain:
o One or more address blocks, with associated address block TLVs,
containing current or former 1-hop neighbors' MANET interface
addresses. Other addresses (i.e. addresses of non-neighbor nodes)
MAY be included in these address blocks, but MUST NOT be
associated with any of the TLVs specified in Section 6.1.2.
o Other message TLVs.
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6.1.1. Local Interface Block
The first address block, plus following TLV block, in a HELLO message
is known as the Local Interface Block. The Local Interface Block is
not distinguished in any way other than by being the first address
block in the message.
The first address of the Local Interface Block MUST be the used
address of the MANET interface over which the HELLO message is
transmitted.
The Local Interface Block MUST contain all of the addresses of all of
the MANET interfaces of the originating node, and no other addresses.
Those addresses, if any, which correspond to MANET interfaces other
than that on which the HELLO message is transmitted MUST have a
corresponding OTHER_IF TLV as specified in Section 6.1.2, other
addresses (i.e. those of the MANET interface on which the HELLO
message is transmitted) MUST NOT use this TLV.
Note that a Local Interface Block MAY include more than one address
for each MANET interface, and hence a HELLO message MAY contain more
than one address without an OTHER_IF TLV.
6.1.2. Address Block TLVs
The three address block TLVs used in HELLO messages are specified in
Table 3.
+----------------+------+-------------------+-----------------------+
| Name | Type | Length | Value |
+----------------+------+-------------------+-----------------------+
| OTHER_IF | TBD | 0 bits | Not Applicable |
| | | | |
| LINK_STATUS | TBD | 8 bits | One of LOST, |
| | | | SYMMETRIC or HEARD |
| | | | |
| OTHER_NEIGHB | TBD | 8 bits | One of LOST or |
| | | | SYMMETRIC |
+----------------+------+-------------------+-----------------------+
Table 3
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7. HELLO Message Generation
HELLO messages MUST be generated and transmitted independently on
each MANET interface. If using the HELLO message interval
HELLO_INTERVAL then, following a HELLO message transmission on a
MANET interface, another HELLO message MUST be sent on the same
interface after an interval not greater than HELLO_INTERVAL. Two
successive HELLO message transmissions on the same MANET interface
MUST be separated by at least HELLO_MIN_INTERVAL, except as noted in
Section 7.1.1.
A HELLO message MUST include a Local Interface Block as specified in
Section 6.1.1 as its first address block.
Other addresses which MUST be included in HELLO messages are:
o addresses of 1-hop neighbors from the Link Set;
o addresses of 1-hop neighbors from the Symmetric Neighbor Set.
These addresses MUST NOT be included in the Local Interface Block.
These addresses MAY be included in any HELLO messages sent on the
appropriate MANET interface. These addresses, and their associated
TLVs, are:
1. For each address which appears as an L_neighbor_iface_addr in one
or more Link Tuples whose L_local_iface_addr is an address of the
MANET interface over which the HELLO message is to be sent,
include that L_neighbor_iface_addr with an associated TLV with:
* Type = LINK_STATUS; AND
* Value = L_STATUS.
2. For each address which appears as an N_neighbor_iface_addr in one
or more Symmetric Neighbor Tuples:
1. if this address has already been included with an associated
TLV with Type == LINK_STATUS and Value == SYMMETRIC, do not
add an associated TLV with Type == OTHER_NEIGHB;
2. otherwise if, for one or more of these Symmetric Neighbor
Tuples, N_STATUS == SYMMETRIC, then include this
N_neighbor_iface_addr with an associated TLV with:
+ Type = OTHER_NEIGHB; AND
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+ Value = SYMMETRIC.
3. otherwise if, for all of these Symmetric Neighbor Tuples,
N_STATUS == LOST, and this address has not already been
included with an associated TLV with Type == LINK_STATUS and
Value == LOST, then include this N_neighbor_iface_addr with
an associated TLV with:
+ Type = OTHER_NEIGHB; AND
+ Value = LOST.
On each of its MANET interfaces, for each specified 1-hop neighbor
address and associated TLV, the address and associated TLV MUST be
included in at least one HELLO message in every interval of length
REFRESH_INTERVAL.
If an address is specified with more than one associated TLV, then
these TLVs MAY be independently included or excluded from each HELLO
messages as long as each such TLV is included associated with that
address in a HELLO message sent on that MANET interface in every
interval of length REFRESH_INTERVAL.
TLVs associated with the same address included in the same HELLO
message MAY be applied to the same or different copies of that
address.
7.1. HELLO Message: Transmission
Messages are transmitted in the packet/message format specified by
[1] using the ALL-MANET-NEIGHBORS multicast address as destination IP
address, and with the HELLO message hop limit = 1.
If the parameters of the protocol are changed, then guarantees given
for the old values of the parameters MUST still be respected. In
particular:
o If HELLO_INTERVAL is increased, then a HELLO message MUST be sent
within the old HELLO_INTERVAL of the previous HELLO message sent
on each MANET interface.
o If REFRESH_INTERVAL is increased, then all information (addresses
and associated TLVs) must be sent again on each MANET interface
within the old REFRESH_INTERVAL of the previous HELLO message that
included that information.
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7.1.1. HELLO Message: Jitter
HELLO messages MAY be sent using periodic message generation or
externally triggered message generation. If using data link and
physical layers which are subject to packet loss due to collisions,
HELLO messages SHOULD be jittered as described in Appendix D.
Internally triggered message generation MAY be treated as if
externally generated message generation, or MAY be not jittered.
HELLO messages MUST NOT be forwarded, and thus message forwarding
jitter does not apply to HELLO messages.
Each form of jitter described in Appendix D requires a parameter
MAXJITTER. These parameters may be dynamic, and are specified by:
o For periodic message generation: HP_MAXJITTER, which MUST be
significantly less than HELLO_INTERVAL.
o For externally triggered message generation: HT_MAXJITTER. If
HELLO messages are also periodically generated then HT_MAXJITTER
also MUST be significantly less than HELLO_INTERVAL.
When HELLO message generation is delayed in order that a HELLO
message is not sent within HELLO_MIN_INTERVAL of the previous HELLO
message on the same MANET interface, then HELLO_MIN_INTERVAL SHOULD
be reduced by jitter, with maximum reduction HP_MAXJITTER. In this
case HP_MAXJITTER MUST NOT be greater than HELLO_MIN_INTERVAL.
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8. HELLO Message Processing
On receiving a HELLO message, a node MUST update its neighborhood
information base.
For the purpose of this section, note the following definitions:
o the "validity time" of a message is calculated from the
VALIDITY_TIME TLV of the message as specified in Appendix C;
o the "Source Address" is the first address, including prefix
length, of the Local Interface Block in the HELLO message;
o the "Receiving Address" is the address, including prefix length,
of the MANET interface on which the HELLO message was received;
o the word EXPIRED indicates that a timer is set to a value clearly
preceding the current time (e.g. current time - 1).
8.1. Populating the Link Set
On receiving a HELLO message, a node SHOULD update its Link Set:
1. If there is no Link Tuple with:
* L_local_iface_addr == Receiving Address; AND
* L_neighbor_iface_addr == Source Address,
then create a new Link Tuple with
* L_local_iface_addr = Receiving Address;
* L_neighbor_iface_addr = Source Address;
* L_SYM_time = EXPIRED;
* L_time = current time + validity time.
2. This Link Tuple (existing or new) is then modified as follows:
1. If the node finds the Receiving Address in one of the address
blocks included in the HELLO message, other than the Local
Interface Block, then the Link Tuple is modified as follows:
1. If the Receiving Address in that address block is
associated with a TLV with Type == LINK_STATUS and Value
== LOST then:
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1. if L_STATUS == SYMMETRIC:
o L_time = current time + max(validity time,
L_HOLD_TIME),
o L_SYM_time = EXPIRED.
2. Otherwise if the Receiving Address in that address block
is associated with a TLV with Type == LINK_STATUS and
(Value == HEARD or Value == SYMMETRIC) then:
- L_SYM_time = current time + validity time;
- L_time = L_SYM_time + L_HOLD_TIME.
2. L_ASYM_time = current time + validity time;
3. L_time = max(L_time, L_ASYM_time).
8.2. Populating the Symmetric Neighbor Set
On receiving a HELLO message, a node SHOULD update its Symmetric
Neighbor Set:
1. If the Receiving Address is in an address block of the HELLO
message, other than the Local Interface Block, with an associated
TLV with Type == LINK_STATUS and (Value == HEARD or Value ==
SYMMETRIC) then:
1. For each address (henceforth neighbor address) in the HELLO
message's Local Interface Block:
1. If there is a Symmetric Neighbor Tuple with:
- N_local_iface_addr == Receiving Address; AND
- N_neighbor_iface_addr == neighbor address,
then update this Symmetric Neighbor Tuple to have:
- N_SYM_time = current time + validity time;
- N_time = N_SYM_time + N_HOLD_TIME.
2. Otherwise create a new Symmetric Neighbor Tuple with:
- N_local_iface_addr = Receiving Address;
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- N_neighbor_iface_addr = neighbor address;
- N_SYM_time = current time + validity time;
- N_time = N_SYM_time + N_HOLD_TIME.
2. Otherwise if the Receiving Address is in an address block of the
HELLO message, other than the Local Interface Block, with an
associated TLV with Type == LINK_STATUS and Value == LOST, then:
1. For each address (henceforth neighbor address) in the HELLO
message Local Interface Block, if there exists a Symmetric
Neighbor Tuple with:
+ N_local_iface_addr == Receiving Address; AND
+ N_neighbor_iface_addr == neighbor address,
update this Symmetric Neighbor Tuple to have:
+ N_SYM_time = EXPIRED;
+ N_time = min(N_time, current time + N_HOLD_TIME).
8.3. Populating the Neighborhood Address Association Set
On receiving a HELLO message, the node SHOULD update its Neighborhood
Address Association Set:
1. Remove all Neighborhood Address Association Tuples where:
* NA_neighbor_iface_addr_list contains at least one address
which is contained in the Local Interface Block of the
received HELLO message,
and create a new Neighborhood Address Association Tuple with:
* NA_neighbor_iface_addr_list = list of all addresses contained
in the Local Interface Block of the received HELLO message;
* NA_time = current time + validity time.
8.4. Populating the 2-Hop Neighbor Set
On receiving a HELLO message the node SHOULD update its 2-Hop
Neighbor Set:
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1. If there exists a Link Tuple with L_local_iface_addr == Source
Address and L_STATUS == SYMMETRIC then:
1. For each address (henceforth 2-hop neighbor address) in an
address block of the HELLO message, other than the Local
Interface Block, which is not an interface address of the
receiving node:
1. If the 2-hop neighbor address has an associated TLV with:
- Type == LINK_STATUS and Value == SYMMETRIC; OR
- Type == OTHER_NEIGHB and Value == SYMMETRIC,
then, if there is no 2-Hop Neighbor Tuple with:
- N2_local_iface_addr == Receiving Address;
- N2_neighbor_iface_addr == Source Address;
- N2_2hop_iface_addr == 2-hop neighbor address;
create a 2-Hop Neighbor Tuple with:
- N2_local_iface_addr = Receiving Address; AND
- N2_neighbor_iface_addr = Source Address; AND
- N2_2hop_iface_addr = 2-hop neighbor address.
This 2-Hop Neighbor Tuple (existing or new) is then
modified as follows:
- N2_time = current time + validity time.
2. Otherwise if the 2-hop neighbor address has a TLV with:
- Type == LINK_STATUS and (Value == LOST or Value ==
HEARD); OR
- Type == OTHER_NEIGHB and Value == LOST;
then remove all 2-Hop Neighbor Tuples with:
- N2_local_iface_addr == Receiving Address; AND
- N2_neighbor_iface_addr == Source Address; AND
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- N2_2hop_iface_addr == 2-hop neighbor address.
8.5. Neighborhood Changes
If the L_SYM_time field of a Link Tuple expires (either due to timing
out, or as a result of processing a TLV with Type == LINK_STATUS and
Value == LOST) then all 2-Hop Neighbor Tuples with:
o N2_local_iface_addr == L_local_iface_addr from the Link Tuple,
AND;
o N2_neighbor_iface_addr == L_neighbor_iface_addr from the Link
Tuple,
MUST be deleted.
In this, or any other case of neighborhood change, a node MAY send a
HELLO message reporting updated information, subject to the
constraints in Section 7.
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9. Proposed Values for Constants
This section lists proposed values for the constants used in the
specification of the protocol.
9.1. Message Intervals
o HELLO_INTERVAL = 2 seconds
o REFRESH_INTERVAL = HELLO_INTERVAL
o HELLO_MIN_INTERVAL = HELLO_INTERVAL/4
9.2. Holding Times
o H_HOLD_TIME = 3 x REFRESH_INTERVAL
o L_HOLD_TIME = H_HOLD_TIME
o N_HOLD_TIME = H_HOLD_TIME
9.3. Jitter Times
o HP_MAXJITTER = HELLO_INTERVAL/4
o HT_MAXJITTER = HELLO_INTERVAL/4
9.4. Time
o C = 0.0625 second (1/16 second)
In order to achieve interoperability, C MUST be the same on all
nodes.
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10. IANA Considerations
10.1. Multicast Addresses
A well-known link-local multicast address, ALL-MANET-NEIGHBORS, must
be registered and defined for both IPv6 and IPv4.
10.2. Message Types
This specification defines one message type, which must be allocated
from the "Assigned Message Types" repository of [1].
+--------------------+-------+--------------------------------------+
| Mnemonic | Value | Description |
+--------------------+-------+--------------------------------------+
| HELLO | TBD | Local signaling |
+--------------------+-------+--------------------------------------+
Table 4
10.3. TLV Types
This specification defines two Message TLV types, which must be
allocated from the "Assigned Message TLV Types" repository of [1].
+--------------------+-------+--------------------------------------+
| Mnemonic | Value | Description |
+--------------------+-------+--------------------------------------+
| VALIDITY_TIME | TBD | The time (in seconds) from receipt |
| | | of the message during which the |
| | | information contained in the message |
| | | is to be considered valid |
| | | |
| INTERVAL_TIME | TBD | The maximum time (in seconds) |
| | | between two successive transmissions |
| | | of messages of the appropriate type |
+--------------------+-------+--------------------------------------+
Table 5
This specification defines three Address Block TLV types, which must
be allocated from the "Assigned Address Block TLV Types" repository
of [1].
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+--------------------+-------+--------------------------------------+
| Mnemonic | Value | Description |
+--------------------+-------+--------------------------------------+
| OTHER_IF | TBD | Specifies that the address, in the |
| | | Local Interface Block of the |
| | | message, is an address associated |
| | | with a MANET interface other than |
| | | the one on which the message is |
| | | transmitted |
| | | |
| LINK_STATUS | TBD | Specifies the status of the link to |
| | | the indicated address (LOST, |
| | | SYMMETRIC or HEARD) |
| | | |
| OTHER_NEIGHB | TBD | Specifies that the address is |
| | | (SYMMETRIC) or was (LOST) of a MANET |
| | | interface of a symmetric 1-hop |
| | | neighbor of the node transmitting |
| | | the HELLO message, but does not have |
| | | a matching or better LINK_STATUS TLV |
+--------------------+-------+--------------------------------------+
Table 6
10.4. LINK_STATUS and OTHER_NEIGHB Values
The values which the LINK_STATUS TLV can use are the following:
o LOST = 0
o SYMMETRIC = 1
o HEARD = 2
The values which the OTHER_NEIGHB TLV can use are the following:
o LOST = 0
o SYMMETRIC = 1
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11. References
11.1. Normative References
[1] Clausen, T., Dearlove, C., Dean, J., and C. Adjih, "Generalized
MANET Packet/Message Format", Work In
Progress draft-ietf-manet-packetbb-03.txt, January 2007.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, BCP 14, March 1997.
11.2. Informative References
[3] Clausen, T. and P. Jacquet, "The Optimized Link State Routing
Protocol", RFC 3626, October 2003.
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Appendix A. Address Block TLV Combinations
The algorithm for generating HELLO messages in Section 7 specifies
which addresses MAY be included in the address blocks after the Local
Interface Block, and with which associated TLVs. These TLVs may have
Type == LINK_STATUS or Type == OTHER_NEIGHB, or both. TLVs with Type
== LINK_STATUS may have three possible values (Value == HEARD, Value
== SYMMETRIC or Value == LOST), and TLVs of TYPE == OTHER_NEIGHB may
have two possible values (Value == SYMMETRIC or Value == LOST). When
both TLVs are associated with the same address only certain
combinations of these TLV values are necessary, and are the only
combinations generated by the algorithm in Section 7. These
combinations are indicated in Table 7.
Cells labeled with "Yes" indicate the possible combinations which are
generated by the algorithm in Section 7. Cells labeled with "No"
indicate combinations not generated by the algorithm in Section 7,
but which are correctly parsed and interpreted by the algorithm in
Section 8.
+----------------+----------------+----------------+----------------+
| | Type == | Type == | Type == |
| | OTHER_NEIGHB | OTHER_NEIGHB, | OTHER_NEIGHB, |
| | (absent) | Value == | Value == LOST |
| | | SYMMETRIC | |
+----------------+----------------+----------------+----------------+
| Type == | No | Yes | Yes |
| LINK_STATUS | | | |
| (absent) | | | |
| | | | |
| Type == | Yes | Yes | Yes |
| LINK_STATUS, | | | |
| Value == HEARD | | | |
| | | | |
| Type == | Yes | No | No |
| LINK_STATUS, | | | |
| Value == | | | |
| SYMMETRIC | | | |
| | | | |
| Type == | Yes | Yes | No |
| LINK_STATUS, | | | |
| Value == LOST | | | |
+----------------+----------------+----------------+----------------+
Table 7
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Appendix B. HELLO Message Example
An example HELLO message, sent by an originator node with a single
MANET interface, is as follows. The message uses IPv4 (four octet)
addresses without prefix TLVs. The message is sent with a full
message header (message semantics octet is 0) with a hop limit of 1
and a hop count of 0. The overall message length is 50 octets.
The message contains a message TLV block with content length 8 octets
containing two message TLVs, of types VALIDITY_TIME and
INTERVAL_TIME. Each uses a TLV with semantics value 4, indicating
that no start and stop indexes are included, and each has a value
length of 1 octet. The values included (0x68 and 0x50) are time
codes representing the default values of parameters H_HOLD_TIME and
HELLO_INTERVAL, respectively (6 seconds and 2 seconds).
The first address block contains 1 local interface address. The
semantics octet value 2 indicates no address tail, and the head
length of 4 octets indicates no address mid sections. This address
block has no TLVs (TLV block content length 0 octets).
The second, and last, address block contains 4 neighbor interface
addresses. The semantics octet value 2 indicates no address tail,
the head length of 3 octets indicates address mid sections of one
octet each. The following TLV block (content length 7 octets)
includes one LINK_STATUS TLV which reports the link status values of
all reported neighbors in a single multivalue TLV: the first two
addresses are HEARD, the third address is SYMMETRIC and the fourth
address is LOST. The TLV semantics value of 20 indicates, in
addition to that this is a multivalue TLV, that no start and stop
indexes are included, since values for all addresses are included.
The TLV value length of 4 octets indicates one octet per value per
address.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HELLO |0 0 0 0 0 0 0 0|0 0 0 0 0 0 0 0 0 0 1 1 0 0 1 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 1|0 0 0 0 0 0 0 0| Message Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0| VALIDITY_TIME |0 0 0 0 0 1 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 1|0 1 1 0 1 0 0 0| INTERVAL_TIME |0 0 0 0 0 1 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 1|0 1 0 1 0 0 0 0|0 0 0 0 0 0 0 1|0 0 0 0 0 0 1 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 1 0 0| Head |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Head (cont) |0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0|0 0 0 0 0 1 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 1 0|0 0 0 0 0 0 1 1| Head |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Head (cont) | Mid | Mid | Mid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mid |0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1| LINK_STATUS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1 0 1 0 0|0 0 0 0 0 1 0 0| HEARD | HEARD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SYMMETRIC | LOST |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Appendix C. Time TLVs
This appendix specifies a general time TLV structure for expressing
either single time values or a set of time values with each value
associated with a range of distances. Furthermore, using this
general time TLV structure, this document specifies the INTERVAL_TIME
and VALIDITY_TIME TLVs, which are used by NHDP.
C.1. Representing Time
This document specifies a TLV structure in which time values are each
represented in an 8 bit time code, one or more of which may be used
in a TLV's value field. Of these 8 bits, the least significant four
bits represent the mantissa (a), and the most significant four bits
represent the exponent (b), so that:
o time value = (1 + a/16) * 2^b * C
o time code = 16 * b + a
All nodes in the network MUST use the same value of C, which will be
specified in seconds, hence so will be all time values. Note that
ascending values of the time code represent ascending time values,
time values may thus be compared by comparison of time codes.
An algorithm for computing the time code representing the smallest
representable time value not less than the time value t is:
1. find the largest integer b such that t/C >= 2^b;
2. set a = 16 * (t / (C * 2^b) - 1), rounded up to the nearest
integer;
3. if a == 16 then set b = b + 1 and set a = 0;
4. if a and b are in the range 0 and 15 then the required time value
can be represented by the time code 16 * b + a, otherwise it can
not.
The minimum time value that can be represented in this manner is C.
The maximum time value that can be represented in this manner is
63488 * C.
C.2. General Time TLV Structure
A Time TLV may be a packet, message or address block TLV. If it is a
packet or message TLV then it must be a single value TLV as defined
in [1]; if it is an address block TLV then it may be single value or
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multivalue TLV. The specific Time TLVs specified in this document,
in Appendix C.3 are message, and hence single value, TLVs. Note that
even a single value Time TLV may contain a multiple octet <value>
field.
The purpose of a single value Time TLV is to allow a single time
value to be determined by a node receiving an entity containing the
Time TLV, based on its distance from the entity's originator. The
Time TLV may contain information that allows that time value to be a
function of distance, and thus different receiving nodes may
determine different time values. If a receiving node will not be
able to determine its distance from the originating node, then the
form of this Time TLV with a single time code in a <value> field (or
single value subfield) SHOULD be used.
The <value> field of a single value Time TLV is specified, using the
regular expression syntax of [1], by:
<value> = {<time><distance>}*<time>
where:
<time> is an 8 bit field containing a time code as defined in
Appendix C.1.
<distance> is an 8 bit field specifying a distance from the message
originator, in hops.
A single value <value> field thus consists of an odd number of
octets; with a repetition factor of n in the regular expression
syntax it contains 2n+1 octets, thus the <length> field of a single
value Time TLV, which MUST always be present, is given by:
o <length> = 2n+1
A single value <value> field may be thus represented by:
<t_1><d_1><t_2><d_2> ... <t_i><d_i> ... <t_n><d_n><t_default>
<d_1>, ... <d_n>, if present, MUST be a strictly increasing sequence.
Then, at the receiving node's distance from the originator node, the
time value indicated is that represented by the time code:
o <t_1>, if n > 0 and distance <= <d_1>;
o <t_i+1>, if n > 1 and <d_i> < distance <= <d_i+1> for some i such
that 1 <= i < n;
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o <t_default> otherwise, i.e. if n == 0 or distance > <d_n>.
In a multivalue Time TLV, each single value subfield of the
multivalue Time TLV is defined as above. Note that [1] requires that
each single value subfield has the same length (i.e. the same value
of n) but they need not use the same values of <d_1> to <d_n>.
C.3. Message TLVs
Two message TLVs are defined, for signaling message validity time
(VALIDITY_TIME) and message interval (INTERVAL_TIME).
C.3.1. VALIDITY_TIME TLV
A VALIDITY TIME TLV is a message TLV that defines the validity time
of the information carried in the message in which the TLV is
contained. After this time the receiving node MUST consider the
message content to no longer be valid (unless repeated in a later
message). The validity time of a message MAY be specified to depend
on the distance from its originator. (This is appropriate if
messages are sent with different hop limits, so that receiving nodes
at greater distances receive information less frequently and must
treat is as valid for longer.)
A VALIDITY_TIME TLV is an example of a Time TLV specified as in
Appendix C.1.
C.3.2. INTERVAL_TIME TLV
An INTERVAL_TIME TLV is a message TLV that defines the maximum time
before another message of the same type as this message from the same
originator should be received. This interval time MAY be specified
to depend on the distance from the originator. (This is appropriate
if messages are sent with different hop limits, so that receiving
nodes at greater distances have an increased interval time.)
An INTERVAL_TIME TLV is an example of a Time TLV specified as in
Appendix C.1.
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Appendix D. Message Jitter
Since NHDP employs periodic message transmission in order to detect
neighborhoods, and since NHDP is a building block for MANET routing
protocols employing other triggered or periodic message exchanges,
this appendix presents global concerns pertaining to jittering of
MANET control traffic.
D.1. Jitter
In order to prevent nodes in a MANET from simultaneous transmission,
whilst retaining the MANET characteristic of maximum node autonomy, a
randomization of the transmission time of packets by nodes, known as
jitter, may be employed. Note that while jitter may resolve the
problem of simultaneous transmissions, the delays it introduces will
otherwise only have a negative impact on a well-designed protocol.
Thus jitter parameters should always be minimized, subject to their
acceptably achieving their intent. Three jitter mechanisms, which
target different aspects of this problem, may be employed, with the
aim of reducing the likelihood of simultaneous transmission, and, if
it occurs, preventing it from continuing.
Three cases exist:
o Periodic message generation;
o Externally triggered message generation;
o Message forwarding.
D.1.1. Periodic message generation
When a node generates a message periodically, two successive messages
will be separated by a well-defined interval, denoted here
MESSAGE_INTERVAL. A node may maintain more than one such interval,
e.g. for different message types or in different circumstances (such
as backing off transmissions to avoid congestion). Jitter may be
applied by reducing this delay by a random amount, so that the delay
between consecutive transmissions of a messages of the same type is
equal to (MESSAGE_INTERVAL - jitter), where jitter is the random
value.
Subtraction of the random value from the message interval ensures
that the message interval never exceeds the nominal message interval,
and does not adversely affect timeouts or other mechanisms which may
be based on message late arrival or failure to arrive. Note that by
basing the message transmission time on the previous transmission
time, rather than by jittering a fixed clock, nodes can become
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completely desynchronized, which minimizes their probability of
collisions.
It is appropriate and convenient for the jitter value to be taken
from a uniform distribution between zero and a maximum value, denoted
here MAXJITTER. MAXJITTER must be significantly less than the
current value of MESSAGE_INTERVAL. MAXJITTER may be a single fixed
parameter (in which case it must be significantly less than all
values of MESSAGE_INTERVAL) or be based on MESSAGE_INTERVAL (for
example it may be a fixed proportion of MESSAGE_INTERVAL).
Note that a node will know its own MESSAGE_INTERVAL value and can
readily ensure that any MAXJITTER value used is appropriate.
D.1.2. Externally triggered message generation
When a node responds to an externally triggered change in
circumstances which is likely to also affect other nodes by
generating a message, that message may be jittered by delaying it by
a random duration. If this message is of a type which is
periodically transmitted then it may be appropriate to restart its
schedule of these messages, this should be based on this delayed
time. In some cases there may be a minimum interval between such
messages, in this case it may be appropriate to jitter that minimum
interval time.
The normal delay on a triggered message may be generated uniformly in
an interval between zero and a maximum delay, denoted here MAXJITTER.
Selection of MAXJITTER will be protocol specific. In some cases the
delay may be fixed, or fixed according to the message type. In the
case of a regularly scheduled message, at an interval denoted here
MESSAGE_INTERVAL, MAXJITTER must be significantly less than
MESSAGE_INTERVAL. This may require prior agreement as to the value
(or minimum value) of MESSAGE_INTERVAL, be by inclusion of
MESSAGE_INTERVAL (the time until the next relevant message, rather
than the time since the last) in the message, or use any other
protocol specific mechanism.
D.1.3. Message forwarding
When a node forwards a message it may be jittered by delaying it by a
random time. The normal delay on a triggered message may be
generated uniformly in an interval between zero and a maximum delay,
denoted here MAXJITTER. The value of MAXJITTER will be protocol
specific and may in some cases be fixed, possibly by message type.
However in the case of a regularly scheduled message, at an interval
denoted here MESSAGE_INTERVAL, MAXJITTER must be significantly less
than MESSAGE_INTERVAL. This may require prior agreement as to the
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value (or minimum value) of MESSAGE_INTERVAL, may be by inclusion in
the message of MESSAGE_INTERVAL (the time until the next relevant
message, rather than the time since the last message) or be by any
other protocol specific mechanism. The choice of MAXJITTER may also
take into account the expected number of times that the message may
be forwarded.
For several possible reasons (differing parameters, message
rescheduling, extreme random values) a node may receive a message
while still waiting to forward an earlier message of the same type
originating from the same node. This is possible without jitter, but
may occur more often with it. The appropriate action to take is
protocol specific (typically to discard the earlier message or to
forward both, possible modifying timing to maintain message order).
In many cases, including [3] and protocols using the full
functionality of [1], messages are transmitted hop by hop in
potentially multi-message packets, and some or all of those messages
may need to be forwarded. For efficiency this should be in a single
packet, and hence the forwarding jitter of all messages received in a
single packet should be the same. For this to have the intended
distribution it is necessary to choose a single random jitter for all
messages. It is not appropriate to give each message a random jitter
and then using the smallest of these jitter values, as that produces
a jitter with a reduced mean value.
In addition, the protocol may permit messages received in different
packets to be combined, possibly also with locally generated messages
(scheduled or triggered). However in this case the purpose of the
jitter will be accomplished by choosing any of the independently
scheduled times for these events as the single forwarding time; this
may have to be the earliest time to achieve all constraints. This is
because without combining messages, a transmission was due at this
time anyway.
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Appendix E. Utilizing Link Layer Information
The interface between NHDP and any protocol(s) using NHDP is through
the Neighborhood Information Base as defined in Section 5. The
message exchange and associated processing specified in Section 7 and
Section 8 allow fully maintaining this Neighborhood Information Base.
Different link layers, and even different implementations of the same
link layer, may make varying amount of information available
describing local connectivity. If present, such link layer
information MAY be used to supplement, or replace, elements of NHDP
as follows:
No link layer information - Absent any link layer information on a
MANET interface, NHDP MUST be employed for populating all sets of
the Neighborhood Information Base as defined in this
specification.
Failed data delivery - If link layer information is available on a
MANET interface, identifying when data delivery to a presumed
directly connected node has failed, NHDP MUST be employed for
populating all sets of the Neighborhood Information Base as
defined in this specification. The link layer information MAY be
used to degrade a presumed directly connected node from being
considered as SYMMETRIC to being considered HEARD or LOST. A
HELLO message reflecting these changes MAY be generated,
respecting the considerations in Section 7.
Link quality information - The link layer may make available "soft"
information (possibly derived from the physical layer) relating to
the link quality. NHDP MAY be able to use this information, in a
normalized form, to adjust the link status between LOST, HEARD and
SYMMETRIC.
Local (1-hop) connectivity - If link layer information is available
on a MANET interface, identifying the local (1-hop) connectivity
via that interface, then this information MAY be used as follows
when generating HELLO messages over that interface:
* Step 1 in Hello Message Generation (Section 7) MAY be ignored.
This implies that local connectivity verification over that
MANET interface is not performed by NHDP, but is using the link
layer information.
* All other steps in Hello Message Generation (Section 7) MUST be
carried out, such that Neighborhood Address Association Sets
and 2-Hop Neighbor Sets can be populated correctly.
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* All MANET interfaces which do not have local (1-hop)
connectivity information available MUST employ the message
exchange as detailed in this specification.
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Appendix F. Security Considerations
The objective of this protocol is to allow each node in the network
to acquire information describing its 1-hop and symmetric 2-hop
neighborhoods. This is acquired through message exchange between
neighboring nodes. The information is made available through a
collection of sets, describing the node's 1-hop neighborhood and
symmetric 2-hop neighborhood.
Under normal circumstances, the information recorded in these sets is
correct - i.e. corresponds to the actual network topology, apart from
any changes which have not (yet) been tracked by the HELLO message
exchanges.
If some node for some reason, malice or malfunction, injects invalid
HELLO messages, incorrect information may be recorded in the sets
maintained. The exact consequence of this inexactness depends on the
use of these sets, and MUST be explicitly reflected in the
specification of protocols which use information provided by NHDP.
This appendix, therefore, only outlines the ways in which correctly
formed, but still invalid, HELLO messages may appear.
Appendix F.1. Invalid HELLO messages
A correctly formed, but still invalid, HELLO message may take any of
the following forms:
A node may lie about its own identity:
* The Local Interface Block of the HELLO message may contain
addresses which do not correspond to addresses of MANET
interfaces of the local node which transmits the HELLO message;
* The Local Interface Block of the HELLO message may omit
addresses of MANET interfaces of the local node which transmits
the HELLO message;
* The Local Interface Block may contain OTHER_IF TLVs, indicating
incorrectly that an address is associated with a MANET
interface other than the one over which the HELLO message is
being transmitted;
* The Local Interface Block may omit OTHER_IF TLVs, thereby
indicating incorrect addresses associated with the MANET
interface over which the HELLO message is being transmitted;
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A node may lie about the identity of other nodes:
* A present or absent address in an address block, other than in
the Local Interface Block, does not in and by itself cause a
problem. It is the presence, absence or incorrectness of
associated LINK_STATUS and OTHER_NEIGHB TLVs that cause
problems;
* A present LINK_STATUS TLV may, incorrectly, identify an address
as being of a node which is or was in the sending node's 1-hop
neighborhood;
* A consistently absent LINK_STATUS TLV may, incorrectly, fail to
identify an address as being of a node which is or was in the
sending node's 1-hop neighborhood;
* A present OTHER_NEIGHB TLV may, incorrectly, identify an
address as being of a node which is or was in the sending
node's symmetric 1-hop neighborhood;
* A consistently absent OTHER_NEIGHB TLV may, incorrectly, fail
to identify an address as being of a node which is or was in
the sending node's symmetric 1-hop neighborhood;
* The value of a LINK_STATUS or OTHER_NEIGHB TLV may incorrectly
indicate the status (LOST, SYMMETRIC, HEARD) of a 1-hop
neighbor.
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Appendix G. Flow and Congestion Control
This document specifies one message type, the HELLO message. The
size of each complete HELLO message is proportional to the size of
the originating node's 1-hop neighborhood; some or all of this
information on each of the node's MANET interfaces. HELLO messages
MUST NOT be forwarded.
A node MUST report its 1-hop neighborhood in HELLO messages on each
of its MANET interfaces at least each REFRESH_INTERVAL. Thus, this
puts a lower bound on the control traffic generated by each node in
the network employing this neighborhood discovery protocol.
A node MUST ensure that two successive HELLO messages sent on the
same MANET interface are separated by at least HELLO_MIN_INTERVAL.
(If using jitter then this may be reduced to a mean minimum value of
HELLO_MIN_INTERVAL - HP_MAXJITTER/2.) Thus, this puts an upper bound
on the control traffic generated by each node in the network
employing this neighborhood discovery protocol.
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Appendix H. Contributors
This specification is the result of the joint efforts of the
following contributors -- listed alphabetically.
o Brian Adamson, NRL, USA, <adamson@itd.nrl.navy.mil>
o Cedric Adjih, INRIA, France, <Cedric.Adjih@inria.fr>
o Emmanuel Baccelli, Hitachi Labs Europe, France,
<Emmanuel.Baccelli@inria.fr>
o Thomas Heide Clausen, PCRI, France, <T.Clausen@computer.org>
o Justin Dean, NRL, USA, <jdean@itd.nrl.navy.mil>
o Christopher Dearlove, BAE Systems, UK,
<Chris.Dearlove@baesystems.com>
o Philippe Jacquet, INRIA, France, <Philippe.Jacquet@inria.fr>
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Appendix I. Acknowledgements
The authors would like to acknowledge the team behind OLSRv1,
specified in RFC3626, for their contributions.
The authors would like to gratefully acknowledge the following people
for intense technical discussions, early reviews and comments on the
specification and its components: Joe Macker (NRL), Alan Cullen (BAE
Systems), and the entire IETF MANET working group.
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Authors' Addresses
Thomas Heide Clausen
LIX, Ecole Polytechnique, France
Phone: +33 6 6058 9349
Email: T.Clausen@computer.org
URI: http://www.lix.polytechnique.fr/Labo/Thomas.Clausen/
Christopher M. Dearlove
BAE Systems Advanced Technology Centre
Phone: +44 1245 242194
Email: chris.dearlove@baesystems.com
URI: http://www.baesystems.com/ocs/sharedservices/atc/
Justin W. Dean
Naval Research Laboratory
Phone: +1 202 767 3397
Email: jdean@itd.nrl.navy.mil
URI: http://pf.itd.nrl.navy.mil/
The OLSRv2 Design Team
MANET Working Group
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Clausen, et al. Expires August 13, 2007 [Page 44]
