Mobile Ad hoc Networking (MANET) T. Clausen
Internet-Draft LIX, Ecole Polytechnique, France
Intended status: Standards Track C. Dearlove
Expires: August 5, 2007 BAE Systems Advanced Technology
Centre
J. Dean
Naval Research Laboratory
The OLSRv2 Design Team
MANET Working Group
February 2007
MANET Neighborhood Discovery Protocol (NHDP)
draft-ietf-manet-nhdp-02
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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. Local Information Base . . . . . . . . . . . . . . . . . . . . 10
5.1. Local Interface Set . . . . . . . . . . . . . . . . . . . 10
6. Neighborhood Information Base . . . . . . . . . . . . . . . . 11
6.1. Link Set . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.2. Symmetric Neighbor Set . . . . . . . . . . . . . . . . . . 12
6.3. Neighborhood Address Association Set . . . . . . . . . . . 13
6.4. 2-Hop Neighbor Set . . . . . . . . . . . . . . . . . . . . 13
7. Packets and Messages . . . . . . . . . . . . . . . . . . . . . 15
7.1. HELLO Messages . . . . . . . . . . . . . . . . . . . . . . 15
7.1.1. Local Interface Block . . . . . . . . . . . . . . . . 16
7.1.2. Address Block TLVs . . . . . . . . . . . . . . . . . . 16
8. Local Information Base Changes . . . . . . . . . . . . . . . . 17
8.1. Adding a MANET Interface . . . . . . . . . . . . . . . . . 17
8.2. Removing a MANET Interface . . . . . . . . . . . . . . . . 17
8.3. Adding an Address to a MANET Interface . . . . . . . . . . 18
8.4. Removing an Address from a MANET Interface . . . . . . . . 18
8.5. Changing the Principal Address of a MANET Interface . . . 18
9. HELLO Message Generation . . . . . . . . . . . . . . . . . . . 19
9.1. HELLO Message: Transmission . . . . . . . . . . . . . . . 20
9.1.1. HELLO Message: Jitter . . . . . . . . . . . . . . . . 21
10. HELLO Message Processing . . . . . . . . . . . . . . . . . . . 22
10.1. Populating the Link Set . . . . . . . . . . . . . . . . . 22
10.2. Populating the Symmetric Neighbor Set . . . . . . . . . . 23
10.3. Populating the Neighborhood Address Association Set . . . 24
10.4. Populating the 2-Hop Neighbor Set . . . . . . . . . . . . 25
10.5. Neighborhood Changes . . . . . . . . . . . . . . . . . . . 26
11. Link Hysteresis . . . . . . . . . . . . . . . . . . . . . . . 27
11.1. Link Quality . . . . . . . . . . . . . . . . . . . . . . . 28
12. Proposed Values for Constants . . . . . . . . . . . . . . . . 29
12.1. Message Intervals . . . . . . . . . . . . . . . . . . . . 29
12.2. Holding Times . . . . . . . . . . . . . . . . . . . . . . 29
12.3. Hysteresis values . . . . . . . . . . . . . . . . . . . . 29
12.4. Jitter Times . . . . . . . . . . . . . . . . . . . . . . . 30
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12.5. Time . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
13.1. Multicast Addresses . . . . . . . . . . . . . . . . . . . 31
13.2. Message Types . . . . . . . . . . . . . . . . . . . . . . 31
13.3. TLV Types . . . . . . . . . . . . . . . . . . . . . . . . 31
13.4. LINK_STATUS and OTHER_NEIGHB Values . . . . . . . . . . . 32
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33
14.1. Normative References . . . . . . . . . . . . . . . . . . . 33
14.2. Informative References . . . . . . . . . . . . . . . . . . 33
Appendix A. Address Block TLV Combinations . . . . . . . . . . . 34
Appendix B. HELLO Message Example . . . . . . . . . . . . . . . 35
Appendix C. Time TLVs . . . . . . . . . . . . . . . . . . . . . 37
C.1. Representing Time . . . . . . . . . . . . . . . . . . . . 37
C.2. General Time TLV Structure . . . . . . . . . . . . . . . . 37
C.3. Message TLVs . . . . . . . . . . . . . . . . . . . . . . . 39
C.3.1. VALIDITY_TIME TLV . . . . . . . . . . . . . . . . . . 39
C.3.2. INTERVAL_TIME TLV . . . . . . . . . . . . . . . . . . 39
Appendix D. Message Jitter . . . . . . . . . . . . . . . . . . . 40
D.1. Jitter . . . . . . . . . . . . . . . . . . . . . . . . . . 40
D.1.1. Periodic message generation . . . . . . . . . . . . . 40
D.1.2. Externally triggered message generation . . . . . . . 41
D.1.3. Message forwarding . . . . . . . . . . . . . . . . . . 42
D.1.4. Maximum Jitter Determination . . . . . . . . . . . . . 43
Appendix E. Utilizing Link Layer Information . . . . . . . . . . 44
Appendix F. Security Considerations . . . . . . . . . . . . . . 46
Appendix F.1. Invalid HELLO messages . . . . . . . . . . . . . . . 46
Appendix G. Flow and Congestion Control . . . . . . . . . . . . 48
Appendix H. Contributors . . . . . . . . . . . . . . . . . . . . 49
Appendix I. Acknowledgements . . . . . . . . . . . . . . . . . . 50
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 51
Intellectual Property and Copyright Statements . . . . . . . . . . 52
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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 6.
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 12, 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 9.1, MAY be used if 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 9.1.
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 6, 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. Local Information Base
A node maintains a Local Information Base that records information
about its MANET interfaces. Each MANET interface MUST have at least
one address, and MAY have more than one address. All addresses have
an associated prefix length, which is included all addresses in the
Local Information Base. If an address otherwise does not have a
prefix length it is set equal to the address length. Two addresses
are considered equal if and only if their associated prefix lengths
are also equal.
One of the addresses of each MANET interface is denoted the principal
address of that interface. A node MAY choose which address is the
principal address in any manner; it SHOULD choose the address so as
to minimize changes of principal address. The selection of an
address as a principal address only affects how the node organizes
its information storage, it has no effect on the messages it creates
and sends.
The Local Information Base is not modified by this protocol. This
protocol may respond to changes of this Local Information Base which
MUST reflect corresponding changes in the node's status.
5.1. Local Interface Set
A node's Local Interface Set records its local MANET interfaces. It
consists of Local Interface Tuples, one per MANET interface:
(I_local_iface_addr_list)
where:
I_local_iface_addr_list is a list of the addresses of this MANET
interface, with the first of the listed addresses being considered
as the principal address of the interface.
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6. 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.
6.1. 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_list, L_SYM_time,
L_ASYM_time, L_LOST_time, L_quality, L_pending, L_lost, L_time)
where:
L_local_iface_addr is the principal address of the local MANET
interface on which the 1-hop neighbor is or was heard;
L_neighbor_iface_addr_list is a list of the addresses 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_LOST_time is the time until which the MANET interface of the 1-hop
neighbor is considered lost; if L_lost is true and L_LOST_time is
expired, then this Tuple MUST be removed;
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L_quality is a dimensionless number between 0 (included) and 1
(included) describing the quality of a link;
L_pending is a boolean flag, describing if a link is considered
pending (i.e. a candidate, but not yet established, link);
L_lost is a boolean flag, describing if a link is considered lost
due to link quality and hysteresis;
L_time specifies when this Tuple expires and MUST be removed.
The status of the link as obtained through simple message exchange,
denoted H_STATUS, can be derived based on the elements L_SYM_time and
L_ASYM_time as defined in Table 1.
+-------------+-------------+-----------+
| L_SYM_time | L_ASYM_time | H_STATUS |
+-------------+-------------+-----------+
| Expired | Expired | LOST |
| | | |
| Not Expired | Expired | SYMMETRIC |
| | | |
| Not Expired | Not Expired | SYMMETRIC |
| | | |
| Expired | Not Expired | HEARD |
+-------------+-------------+-----------+
Table 1
The status of the link, taking link quality and hysteresis into
account, denoted L_STATUS, is defined by:
1. if L_pending is true, then L_STATUS = PENDING;
2. otherwise, if L_lost is true, then L_STATUS = LOST;
3. otherwise, if L_LOST_time is not expired, then L_STATUS = LOST;
4. otherwise, L_STATUS = H_STATUS.
6.2. 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:
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N_local_iface_addr is the principal 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 N_SYM_time as defined in Table 2.
+-------------+-----------+
| N_SYM_time | N_STATUS |
+-------------+-----------+
| Expired | LOST |
| | |
| Not Expired | SYMMETRIC |
+-------------+-----------+
Table 2
6.3. 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
1-hop neighbor;
NA_time specifies when this Tuple expires and MUST be removed.
6.4. 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_list,
N2_2hop_iface_addr, N2_time)
where:
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N2_local_iface_addr is the principal address of the local MANET
interface on which this information was received;
N2_neighbor_iface_addr_list is a list of the addresses of the MANET
interface of the 1-hop neighbor from which this information was
received;
N2_2hop_iface_addr is an 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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7. 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.
7.1. 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 7.1.1.
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 7.1.2.
o Other message TLVs.
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7.1.1. 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 Local Interface Block MUST contain all of the addresses of all of
the MANET interfaces of the originating node (i.e. all addresses
appearing in an I_local_iface_addr_list). Those addresses, if any,
which correspond to MANET interfaces other than that on which the
HELLO message is transmitted MUST be associated with a corresponding
TLV with Type == OTHER_IF as specified in Section 7.1.2, addresses of
the MANET interface on which the HELLO message is transmitted MUST
NOT be associated with such a TLV. Other addresses (i.e. not of any
MANET interface of this node) which are local to this node only may
be included in the Local Interface Block, they MUST be included in
HELLO messages transmitted on all MANET interfaces, and MUST always
be associated with a TLV with Type == OTHER_IF.
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.
7.1.2. 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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8. Local Information Base Changes
The Local Information Base MUST change to respond to changes in the
node's MANET interfaces. The protocol MUST update its Neighborhood
Information Base in response to such changes, and MAY transmit HELLO
messages in response to such changes.
8.1. Adding a MANET Interface
If a MANET interface is added to the node then this is indicated by
the addition of a Local Interface Tuple to the Local Interface Set.
The Neighbor Interface Base is not changed. A HELLO message MAY be
sent on all MANET interfaces, it SHOULD be sent on the new interface.
If using scheduled messages, a message schedule MUST be established
on the new interface.
8.2. Removing a MANET Interface
If a MANET interface is removed from the node, then this MUST result
be the removal of information from the Local Information Base and the
Neighborhood Information Base as follows:
1. Identify the Local Interface Tuple from the Local Interface Set
which corresponds to the interface to be removed, and:
1. all Link Tuples whose L_local_iface_addr is included in the
I_local_iface_addr_list of that Local Interface Tuple MUST be
removed;
2. all Symmetric Neighbor Tuples whose N_local_iface_addr is
included in the I_local_iface_addr_list of that Local
Interface Tuple MUST be removed;
3. all 2-Hop Neighbor Tuples whose N2_local_iface_addr is
included in the I_local_iface_addr_list of the Local
Interface Tuple MUST be removed;
4. the Local Interface Tuple MUST be removed from the Local
Interface Set.
2. All Neighborhood Address Association Tuples for which none of the
addresses in its NA_neighbor_iface_addr_list may be found in any
L_neighbor_iface_addr_list in the Link Set SHOULD be removed.
If the removed interface is the last MANET interface of the node,
then the Neighborhood Information Base SHOULD be empty, and the node
no longer participates in the protocol.
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A HELLO message MAY be sent on all remaining MANET interfaces.
8.3. Adding an Address to a MANET Interface
If an address is added to a MANET interface then this is indicated by
the addition of an address to the appropriate
I_local_iface_addr_list. No change is made to the Neighbor
Information Base. A HELLO message MAY be sent on all MANET
interfaces.
8.4. Removing an Address from a MANET Interface
If an address is removed from a MANET interface then this is
indicated by the removal of an address to the appropriate
I_local_iface_addr_list. No change is made to the Neighbor
Information Base unless the removed address is the principal address
of the MANET Interface, in which case first a new principal address
of the interface is selected, as described in Section 8.5. A HELLO
message MAY be sent on all MANET interfaces.
8.5. Changing the Principal Address of a MANET Interface
If the principal address of a MANET interface of a node is changed
then this is indicated by a reordering of the appropriate
I_local_iface_addr_list. The following changes MUST be made to the
Local Information Base:
1. all Link Tuples whose L_local_iface_addr is equal to the old
first address in this I_local_iface_addr_list have that
L_local_iface_addr set equal to the new first address in this
I_local_iface_addr_list;
2. all Symmetric Neighbor Tuples whose N_local_iface_addr is equal
to the old first address in this I_local_iface_addr_list have
that N_local_iface_addr set equal to the new first address in
this I_local_iface_addr_list;
3. all 2-Hop Neighbor Tuples whose N2_local_iface_addr is equal to
the old first address in this I_local_iface_addr_list have that
N2_local_iface_addr set equal to the new first address in this
I_local_iface_addr_list.
A HELLO message SHOULD NOT be sent in response to this change.
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9. 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 9.1.1.
A HELLO message MUST include a Local Interface Block as specified in
Section 7.1.1 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 in an L_neighbor_iface_addr_list
(a neighbor address) in one or more Link Tuples whose
L_local_iface_addr is the principal address of the MANET
interface over which the HELLO message is to be sent (i.e. the
first address listed in the corresponding
I_local_iface_addr_list), and whose L_STATUS does not equal
PENDING, include the neighbor address 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:
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+ Type = OTHER_NEIGHB; AND
+ 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.
9.1. 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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9.1.1. 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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10. 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 HELLO message as specified in Appendix C;
o the "Receiving Address List" is the I_local_iface_addr_list
corresponding to the MANET interface on which the HELLO message
was received;
o the "Receiving Address" is the first address in the Receiving
Address List, i.e. is the principal address of the MANET interface
on which the HELLO message was received;
o the "Sending Address List" is the list of the addresses contained
in the Local Interface Block of the HELLO message which do not
have an associated TLV with Type == OTHER_IF;
o the word EXPIRED indicates that a timer is set to a value clearly
preceding the current time (e.g. current time - 1).
10.1. Populating the Link Set
On receiving a HELLO message, a node SHOULD update its Link Set:
1. If there is no Link Tuple such that:
* L_local_iface_addr == Receiving Address; AND
* L_neighbor_iface_addr_list contains one or more addresses in
the Sending Address List.
then create a new Link Tuple with:
* L_local_iface_addr = Receiving Address;
* L_SYM_time = EXPIRED;
* L_quality = INITIAL_QUALITY;
* L_pending = INITIAL_PENDING;
* L_lost = false;
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* L_LOST_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 any address in the Receiving Address List
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 any such address in the HELLO message 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. Otherwise if any such address in the HELLO message is
associated with a TLV with Type == LINK_STATUS and Value
== LOST then:
1. if L_STATUS == SYMMETRIC:
o L_time = current time + max(validity time,
L_HOLD_TIME),
o L_SYM_time = EXPIRED.
2. L_neighbor_iface_addr_list = Sending Address List;
3. L_ASYM_time = current time + validity time;
4. L_time = max(L_time, L_ASYM_time).
10.2. Populating the Symmetric Neighbor Set
On receiving a HELLO message, a node SHOULD update its Symmetric
Neighbor Set:
1. If any address in the Receiving Address List 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 where a corresponding link
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tuple with L_STATUS == SYMMETRIC exists in the link set:
1. If there is no Symmetric Neighbor Tuple such that:
- N_local_iface_addr == Receiving Address; AND
- N_neighbor_iface_addr == neighbor address,
then create a new Symmetric Neighbor Tuple with:
- N_local_iface_addr = Receiving Address;
- N_neighbor_iface_addr = neighbor address;
2. This Symmetric Neighbor Tuple (existing or new) is then
modified as follows:
- N_SYM_time = current time + validity time;
- N_time = N_SYM_time + N_HOLD_TIME.
2. Otherwise if any address in the Receiving Address List 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,
then update this Symmetric Neighbor Tuple to have:
+ N_SYM_time = EXPIRED;
+ N_time = min(N_time, current time + N_HOLD_TIME).
10.3. 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:
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* 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.
10.4. Populating the 2-Hop Neighbor Set
On receiving a HELLO message the node SHOULD update its 2-Hop
Neighbor Set:
1. If there exists a Link Tuple with L_local_iface_addr == Source
Address and for which 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 in any I_local_iface_addr_list
(i.e. is not an address of a MANET interface 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 such that:
- N2_local_iface_addr == Receiving Address;
- N2_neighbor_iface_addr_list contains one or more
addresses in the Sending Address List; AND
- N2_2hop_iface_addr == 2-hop neighbor address.
then create a 2-Hop Neighbor Tuple with:
- N2_local_iface_addr = Receiving Address;
- N2_2hop_iface_addr = 2-hop neighbor address.
This 2-Hop Neighbor Tuple (existing or new) is then
modified as follows:
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- N2_neighbor_iface_addr_list = Sending Address List;
- 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_list contains one or more
addresses in the Sending Address List; AND
- N2_2hop_iface_addr == 2-hop neighbor address.
10.5. Neighborhood Changes
If L_STATUS of a Link Tuple changes from SYMMETRIC to any other
status, due to any of:
o L_SYM_time expires;
o L_SYM_time is set to EXPIRED as result of processing a TLV with
Type == LINK_STATUS and Value == LOST;
o A change in L_quality resulting in L_quality < HYST_REJECT
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_list contains one or more addresses in the
L_neighbor_iface_addr_list 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 9.
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11. Link Hysteresis
Link hysteresis allows associating a L_quality value with a link.
Using this L_quality in conjunction with two thresholds, HYST_ACCEPT
and HYST_REJECT, as well as for each link a L_pending and a L_lost
flag, Section 6.1 allows determining the L_STATUS of a link.
The basic principles of link hysteresis are as follows:
o A node does not advertise a neighbor interface in any state until
L_quality is acceptable. If INITIAL_PENDING == true, this is such
that L_quality >= HYST_ACCEPT, otherwise this is such that
L_quality >= HYST_REJECT; to ensure the latter a node MUST NOT
define INITIAL_PENDING == false and INITIAL_QUALITY < HYST_REJECT.
(A node also MUST NOT define INITIAL_PENDING == true and
INITIAL_QUALITY >= HYST_ACCEPT.) A link which is not yet
advertised has L_pending == true.
o Once L_quality >= HYST_ACCEPT, the L_pending flag is set false,
indicating that the link can be advertised.
o A link for which L_pending == false is advertised until its
L_quality drops below HYST_REJECT.
o If a link has L_pending == false and L_quality < HYST_REJECT, the
link is LOST and is advertised as such. This link is not
reconsidered as a candidate HEARD or SYMMETRIC link until
L_quality >= HYST_ACCEPT.
o A link which has an acceptable quality may be advertised as HEARD,
SYMMETRIC or LOST according to the exchange of HELLO messages.
If L_quality for a link changes, the following actions MUST be taken:
1. if L_quality >= HYST_ACCEPT then the corresponding Link Tuple is
modified by:
* L_pending = false;
* L_lost = false;
* L_LOST_time = EXPIRED.
2. if L_quality < HYST_REJECT then the corresponding Link Tuple is
modified by:
* L_lost = true
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* L_LOST_time = current time + L_HOLD_TIME
Any corresponding Tuples in the Symmetric Neighbor Set and 2-Hop
Neighbor Set MUST be removed.
If L_quality for a link is updated based on HELLO message reception,
or on reception of a packet including a HELLO message, then L_quality
MUST be updated prior to the HELLO processing described in
Section 10. (If the receipt of the HELLO message, or the packet
containing it, creates the Link Tuple then instead the Link Tuple
MUST be created with the updated L_quality value.)
11.1. Link Quality
A node MAY never update link quality (L_quality). In this case the
node MUST define:
o INITIAL_PENDING = false;
o INITIAL_QUALITY >= HYST_REJECT (there is no reason not to define
INITIAL_QUALITY = 1).
A node MAY update link quality based on any information available to
it. Particular cases that MAY be used include:
o Link layer information, see Appendix E.
o Receipt or loss of packets. Provided packets include a packet
sequence number as defined in [1], packets on a link SHOULD have
sequential packet sequence numbers, whether or not they include
HELLO messages. Link quality can be updated when a packet is
received based on, for example, whether the last N out of M
packets on the link were received, or a "leaky integrator"
tracking packets.
o Receipt or loss of HELLO messages. If the maximum interval
between HELLO messages is known (possibly by inclusion of a
message TLV with Type == INTERVAL_TIME as defined in Appendix C.2
in HELLO messages) then the loss of HELLO messages can be
determined without the need to receive a HELLO message. Note that
if this case is combined with the previous case then care must be
taken to avoid "double counting" a lost HELLO message in a lost
packet.
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12. Proposed Values for Constants
This section lists proposed values for the constants used in the
specification of the protocol.
12.1. Message Intervals
o HELLO_INTERVAL = 2 seconds
o REFRESH_INTERVAL = HELLO_INTERVAL
o HELLO_MIN_INTERVAL = HELLO_INTERVAL/4
12.2. Holding Times
o H_HOLD_TIME = 3 x REFRESH_INTERVAL
o L_HOLD_TIME = H_HOLD_TIME
o N_HOLD_TIME = H_HOLD_TIME
12.3. Hysteresis values
If link quality is not changed then:
o HYST_ACCEPT = 1
o HYST_REJECT = 0
o INITIAL_QUALITY = 1
o INITIAL_PENDING = false
Otherwise, i.e. if link quality is changed, then these parameters
will be dependent on the link quality process used. Example possible
parameters are:
o HYST_ACCEPT = 0.75
o HYST_REJECT = 0.25
o INITIAL_QUALITY = 0.5
o INITIAL_PENDING = true
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12.4. Jitter Times
o HP_MAXJITTER = HELLO_INTERVAL/4
o HT_MAXJITTER = HELLO_INTERVAL/4
12.5. 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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13. IANA Considerations
13.1. Multicast Addresses
A well-known link-local multicast address, ALL-MANET-NEIGHBORS, must
be registered and defined for both IPv6 and IPv4.
13.2. 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
13.3. 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
13.4. 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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14. References
14.1. 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.
14.2. 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 9 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 9. These
combinations are indicated in Table 7.
Cells labeled with "Yes" indicate the possible combinations which are
generated by the algorithm in Section 9. Cells labeled with "No"
indicate combinations not generated by the algorithm in Section 9,
but which are correctly parsed and interpreted by the algorithm in
Section 10.
+----------------+----------------+----------------+----------------+
| | 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. 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.
Each of these cases uses a parameter, denoted MAXJITTER, for the
maximum timing variation that it introduces. If more than one of
these cases is used by a protocol, it MAY use the same or a different
value of MAXJITTER for each case. It also MAY use the same or
different values of MAXJITTER according to message type, and under
different circumstances - in particular if other parameters (such as
message interval) vary.
Issues relating to the value of MAXJITTER are considered in
Appendix D.1.4.
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
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.
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Subtraction of the random value from the message interval ensures
that the message interval never exceeds MESSAGE_INTERVAL, and does
not adversely affect timeouts or other mechanisms which may be based
on message late arrival or failure to arrive. By basing the message
transmission time on the previous transmission time, rather than by
jittering a fixed clock, nodes can become completely desynchronized,
which minimizes their probability of repeated collisions. This is
particularly useful when combined with externally triggered message
generation and rescheduling.
The jitter value SHOULD be taken from a uniform distribution between
zero and MAXJITTER.
Note that a node will know its own MESSAGE_INTERVAL value and can
readily ensure that any MAXJITTER value used satisfies the conditions
in Appendix D.1.4.
D.1.2. Externally triggered message generation
An internal or external condition or event MAY trigger message
generation by a node. Depending upon the protocol, this condition
MAY trigger generation of a single message, initiation of a new
periodic message schedule, or rescheduling of existing periodic
messaging. Collision between externally triggered messages is made
more likely if more than one node is likely to respond to the same
event. To reduce this likelihood, an externally triggered message
MAY be jittered by delaying it by a random duration; an internally
triggered message MAY also be so jittered if appropriate. This delay
SHOULD be generated uniformly in an interval between zero and
MAXJITTER. If periodically transmitted messages are rescheduled,
then this SHOULD be based on this delayed time, with subsequent
messages treated as described in Appendix D.1.1.
When messages are triggered, whether or not they are also
periodically transmitted, a protocol MAY impose a minimum interval
between messages of the same type, denoted MESSAGE_MIN_INTERVAL. It
is however appropriate to also allow this interval to be reduced by
jitter, so that when a message is transmitted the next message is
allowed after a time (MESSAGE_MIN_INTERVAL - jitter), where jitter
SHOULD be generated uniformly in an interval between zero and
MAXJITTER (using a value of MAXJITTER appropriate to periodic message
transmission). This is because otherwise, when external triggers are
more frequent than MESSAGE_MIN_INTERVAL, it takes the role of
MESSAGE_INTERVAL and the arguments applying to jittering of the
latter also apply to the former. This also permits
MESSAGE_MIN_INTERVAL to equal MESSAGE_INTERVAL even when jitter is
used.
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D.1.3. Message forwarding
When a node forwards a message, it may be jittered by delaying it by
a random duration. This delay SHOULD be generated uniformly in an
interval between zero and MAXJITTER.
Unlike the cases of periodically generated and externally triggered
messages, a node is not automatically aware of the message
originator's value of MESSAGE_INTERVAL, which is required to select a
value of MAXJITTER which is known to be valid. This may require
prior agreement as to the 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, which may include estimation of the value of
MESSAGE_INTERVAL based on received message times.
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. (This also requires that a single
value of MAXJITTER is used in this case.) For this to have the
intended uniform 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 to use the smallest of these jitter
values, as that produces a jitter with a non-uniform distribution and
a reduced mean value.
In addition, the protocol may permit messages received in different
packets to be combined, possibly also with locally generated messages
(periodically generated 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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D.1.4. Maximum Jitter Determination
In considering how the maximum jitter (one or more instances of
parameter MAXJITTER) may be determined, the following points may be
noted:
o While jitter may resolve the problem of simultaneous
transmissions, the timing changes (in particular the delays) it
introduces will otherwise only have a negative impact on a well-
designed protocol. Thus MAXJITTER should always be minimized,
subject to acceptably achieving its intent.
o When messages are periodically generated, all of the following
that are relevant apply to each instance of MAXJITTER:
* it MUST NOT be greater than MESSAGE_INTERVAL/2;
* it SHOULD be significantly less than MESSAGE_INTERVAL;
* it MUST NOT be greater than MESSAGE_MIN_INTERVAL;
* it SHOULD NOT be greater than MESSAGE_MIN_INTERVAL/2.
o As well as the decision as to whether to use jitter being
dependent on the medium access control and lower layers, the
selection of the MAXJITTER parameter should be appropriate to
those mechanisms.
o As jitter is intended to reduce collisions, greater jitter, i.e.
an increased value of MAXJITTER, is appropriate when the chance of
collisions is greater. This is particularly the case with
increased node density, where node density should be considered
relative to (the square of) the interference range rather than
useful signal range.
o The choice of MAXJITTER used when forwarding messages may also
take into account the expected number of times that the message
may be sequentially forwarded, up to the network diameter in hops.
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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 6. The
message exchange and associated processing specified in Section 9 and
Section 10 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 9.
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 9) 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 9) 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 provide false information 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 provide false information 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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Full Copyright Statement
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