Mobile Ad hoc Networking (MANET) T. Clausen
Internet-Draft LIX, Ecole Polytechnique, France
Expires: December 28, 2006 C. Dearlove
BAE Systems Advanced Technology
Centre
P. Jacquet
Project Hipercom, INRIA
The OLSRv2 Design Team
MANET Working Group
June 26, 2006
The Optimized Link-State Routing Protocol version 2
draft-ietf-manet-olsrv2-02
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Abstract
This document describes version 2 of the Optimized Link State Routing
(OLSRv2) protocol for mobile ad hoc networks. The protocol embodies
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an optimization of the classical link state algorithm tailored to the
requirements of a mobile wireless LAN.
The key optimization of OLSRv2 is that of multipoint relays,
providing an efficient mechanism for network-wide broadcast of link-
state information (i.e. reducing the cost of performing a network-
wide link-state broadcast). A secondary optimization is that OLSRv2
employs partial link-state information: each node maintains
information about all destinations, but only a subset of links. This
allows that only select nodes diffuse link-state advertisements (i.e.
reduces the number of network-wide link-state broadcasts) and that
these advertisements contain only a subset of links (i.e. reduces the
size of each network-wide link-state broadcast). The partial link-
state information thus obtained still allows each OLSRv2 node to at
all times maintain optimal (in terms of number of hops) routes to all
destinations in the network.
OLSRv2 imposes minimum requirements to the network by not requiring
sequenced or reliable transmission of control traffic. Furthermore,
the only interaction between OLSRv2 and the IP stack is routing table
management.
OLSRv2 is particularly suitable for large and dense networks as the
technique of MPRs works well in this context.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
1.2. Applicability Statement . . . . . . . . . . . . . . . . . 6
2. Protocol Overview and Functioning . . . . . . . . . . . . . . 8
2.1. Protocol Extensibility . . . . . . . . . . . . . . . . . . 10
3. Processing and Forwarding Repositories . . . . . . . . . . . . 11
3.1. Received Set . . . . . . . . . . . . . . . . . . . . . . . 11
3.2. Fragment Set . . . . . . . . . . . . . . . . . . . . . . . 11
3.3. Processed Set . . . . . . . . . . . . . . . . . . . . . . 12
3.4. Forwarded Set . . . . . . . . . . . . . . . . . . . . . . 12
3.5. Relay Set . . . . . . . . . . . . . . . . . . . . . . . . 12
4. Packet Processing and Message Forwarding . . . . . . . . . . . 14
4.1. Actions when Receiving an OLSRv2 Packet . . . . . . . . . 14
4.2. Actions when Receiving an OLSRv2 Message . . . . . . . . . 14
4.3. Message Considered for Processing . . . . . . . . . . . . 15
4.4. Message Considered for Forwarding . . . . . . . . . . . . 17
5. Information Repositories . . . . . . . . . . . . . . . . . . . 20
5.1. Neighborhood Information Base . . . . . . . . . . . . . . 20
5.1.1. Link Set . . . . . . . . . . . . . . . . . . . . . . . 20
5.1.2. MPR Set . . . . . . . . . . . . . . . . . . . . . . . 21
5.1.3. MPR Selector Set . . . . . . . . . . . . . . . . . . . 21
5.2. Topology Information Base . . . . . . . . . . . . . . . . 21
5.2.1. Advertised Neighbor Set . . . . . . . . . . . . . . . 21
5.2.2. ANSN History Set . . . . . . . . . . . . . . . . . . . 22
5.2.3. Topology Set . . . . . . . . . . . . . . . . . . . . . 22
5.2.4. Attached Network Set . . . . . . . . . . . . . . . . . 23
5.2.5. Routing Set . . . . . . . . . . . . . . . . . . . . . 23
6. OLSRv2 Control Message Structures . . . . . . . . . . . . . . 24
6.1. General OLSRv2 Message TLVs . . . . . . . . . . . . . . . 24
6.1.1. VALIDITY_TIME TLV . . . . . . . . . . . . . . . . . . 24
6.2. HELLO Messages . . . . . . . . . . . . . . . . . . . . . . 25
6.2.1. HELLO Message OLSRv2 Message TLVs . . . . . . . . . . 26
6.2.2. HELLO Message OLSRv2 Address Block TLVs . . . . . . . 26
6.3. TC Messages . . . . . . . . . . . . . . . . . . . . . . . 27
6.4. TC Message: OLSRv2 Address Block TLVs . . . . . . . . . . 27
7. HELLO Message Generation . . . . . . . . . . . . . . . . . . . 29
7.1. HELLO Message: Transmission . . . . . . . . . . . . . . . 29
8. HELLO Message Processing . . . . . . . . . . . . . . . . . . . 30
8.1. Populating the MPR Selector Set . . . . . . . . . . . . . 30
8.2. Symmetric Neighborhood and 2-Hop Neighborhood Changes . . 31
9. TC Message Generation . . . . . . . . . . . . . . . . . . . . 32
9.1. TC Message: Transmission . . . . . . . . . . . . . . . . . 33
10. TC Message Processing . . . . . . . . . . . . . . . . . . . . 34
10.1. Single TC Message Processing . . . . . . . . . . . . . . . 34
10.1.1. Populating the ANSN History Set . . . . . . . . . . . 35
10.1.2. Populating the Topology Set . . . . . . . . . . . . . 35
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10.1.3. Populating the Attached Network Set . . . . . . . . . 36
10.2. Completed TC Message Processing . . . . . . . . . . . . . 37
10.2.1. Purging the Topology Set . . . . . . . . . . . . . . . 37
10.2.2. Purging the Attached Network Set . . . . . . . . . . . 37
11. Populating the MPR Set . . . . . . . . . . . . . . . . . . . . 38
12. Populating Derived Sets . . . . . . . . . . . . . . . . . . . 39
12.1. Populating the Relay Set . . . . . . . . . . . . . . . . . 39
12.2. Populating the Advertised Neighbor Set . . . . . . . . . . 39
13. Routing Table Calculation . . . . . . . . . . . . . . . . . . 40
14. Proposed Values for Constants . . . . . . . . . . . . . . . . 44
14.1. Neighborhood Discovery Constants . . . . . . . . . . . . . 44
14.2. Message Intervals . . . . . . . . . . . . . . . . . . . . 44
14.3. Holding Times . . . . . . . . . . . . . . . . . . . . . . 44
14.4. Willingness . . . . . . . . . . . . . . . . . . . . . . . 44
15. Sequence Numbers . . . . . . . . . . . . . . . . . . . . . . . 45
16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46
16.1. Multicast Addresses . . . . . . . . . . . . . . . . . . . 46
16.2. Message Types . . . . . . . . . . . . . . . . . . . . . . 46
16.3. TLV Types . . . . . . . . . . . . . . . . . . . . . . . . 46
17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 48
17.1. Normative References . . . . . . . . . . . . . . . . . . . 48
17.2. Informative References . . . . . . . . . . . . . . . . . . 48
Appendix A. Example Heuristic for Calculating MPRs . . . . . . . 49
Appendix B. Heuristics for Generating Control Traffic . . . . . 52
Appendix C. Protocol and Port Number . . . . . . . . . . . . . . 53
Appendix D. Packet and Message Layout . . . . . . . . . . . . . 54
Appendix D.1. OLSRv2 Packet Format . . . . . . . . . . . . . . . . 54
Appendix E. Node Configuration . . . . . . . . . . . . . . . . . 59
Appendix F. Jitter . . . . . . . . . . . . . . . . . . . . . . . 60
Appendix G. Security Considerations . . . . . . . . . . . . . . 63
Appendix G.1. Confidentiality . . . . . . . . . . . . . . . . . . 63
Appendix G.2. Integrity . . . . . . . . . . . . . . . . . . . . . 63
Appendix G.3. Interaction with External Routing Domains . . . . . 64
Appendix G.4. Node Identity . . . . . . . . . . . . . . . . . . . 65
Appendix H. Flow and Congestion Control . . . . . . . . . . . . 66
Appendix I. Contributors . . . . . . . . . . . . . . . . . . . . 67
Appendix J. Acknowledgements . . . . . . . . . . . . . . . . . . 68
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 69
Intellectual Property and Copyright Statements . . . . . . . . . . 70
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1. Introduction
The Optimized Link State Routing protocol version 2 (OLSRv2) is an
update to OLSRv1 as published in RFC3626 [1]. Compared to RFC3626,
OLSRv2 retains the same basic mechanisms and algorithms, while
providing an even more flexible signaling framework and some
simplification of the messages being exchanged. Also, OLSRv2 takes
care to accommodate both IPv4 and IPv6 addresses in a compact
fashion.
OLSRv2 is developed for mobile ad hoc networks. It operates as a
table driven, proactive protocol, i.e. it exchanges topology
information with other nodes of the network regularly. Each node
selects a set of its neighbor nodes as "MultiPoint Relays" (MPRs).
Only nodes that are selected as such MPRs are then responsible for
forwarding control traffic intended for diffusion into the entire
network. MPRs provide an efficient mechanism for flooding control
traffic by reducing the number of transmissions required.
Nodes selected as MPRs also have a special responsibility when
declaring link state information in the network. Indeed, the only
requirement for OLSRv2 to provide shortest path routes to all
destinations is that MPR nodes declare link-state information for
their MPR selectors. Additional available link-state information may
be utilized, e.g. for redundancy.
Nodes which have been selected as multipoint relays by some neighbor
node(s) announce this information periodically in their control
messages. Thereby a node announces to the network that it has
reachability to the nodes which have selected it as an MPR. Thus, as
well as being used to facilitate efficient flooding, MPRs are also
used for route calculation from any given node to any destination in
the network.
A node selects MPRs from among its one hop neighbors with
"symmetric", i.e. bi-directional, linkages. Therefore, selecting
routes through MPRs automatically avoids the problems associated with
data packet transfer over uni-directional links (such as the problem
of not getting link-layer acknowledgments for data packets at each
hop, for link-layers employing this technique for unicast traffic).
OLSRv2 is developed to work independently from other protocols.
Likewise, OLSRv2 makes no assumptions about the underlying link-
layer. However, OLSRv2 may use link-layer information and
notifications when available and applicable.
OLSRv2, as OLSRv1, inherits the concept of forwarding and relaying
from HIPERLAN (a MAC layer protocol) which is standardized by ETSI
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[6].
1.1. 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].
MANET specific terminology is to be interpreted as described in [3]
and [4].
Additionally, this document uses the following terminology:
node - A MANET router which implements the Optimized Link State
Routing protocol version 2 as specified in this document.
OLSRv2 interface - A MANET interface, running OLSRv2.
symmetric strict 2-hop neighbor - A symmetric 2-hop neighbor which is
not a symmetric 1-hop neighbor and is not a 2-hop neighbor only
through a symmetric 1-hop neighbor with willingness WILL_NEVER.
(If node Z is a symmetric 2-hop neighbor of node X then there is a
node Y such that node Z is a symmetric 1-hop neighbor of node Y
and node Y is a symmetric 1-hop neighbor of node X. If node Z is a
symmetric strict 2-hop neighbor of node X then there is such a
node Y with willingness which is not WILL_NEVER.)
symmetric strict 2-hop neighborhood - The set of the symmetric strict
2-hop neighbors of node X.
multipoint relay (MPR) - A node which is selected by its symmetric
1-hop neighbor, node X, to "re-transmit" all the broadcast
messages that it receives from node X, provided that the message
is not a duplicate, and that the hop limit field of the message is
greater than one.
MPR selector - A node which has selected its symmetric 1-hop
neighbor, node X, as one of its MPRs is an MPR selector of node X.
1.2. Applicability Statement
OLSRv2 is a proactive routing protocol for mobile ad hoc networks
(MANETs) [7], [8]. It is well suited to large and dense networks of
mobile nodes, as the optimization achieved using the MPRs works well
in this context. The larger and more dense a network, the more
optimization can be achieved as compared to the classic link state
algorithm. OLSRv2 uses hop-by-hop routing, i.e. each node uses its
local information to route packets.
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As OLSRv2 continuously maintains routes to all destinations in the
network, the protocol is beneficial for traffic patterns where the
traffic is random and sporadic between a large subset of nodes, and
where the [source, destination] pairs are changing over time: no
additional control traffic need be generated in this situation since
routes are maintained for all known destinations at all times. Also,
since routes are maintained continuously, traffic is subject to no
delays due to buffering/route-discovery. This continued route
maintenance may be done using periodic message exchange, as detailed
in this specification, or triggered by external events if available.
OLSRv2 supports nodes which have multiple interfaces which
participate in the MANET. OLSRv2, additionally, supports nodes which
have non-MANET interfaces which can serve as (if configured to do so)
gateways towards other networks.
The message exchange format, contained in previous versions of this
specification, has been factored out to an independent specification
[3], which is used for carrying OLSRv2 control signals. OLSRv2 is
thereby able to allow for extensions via "external" and "internal"
extensibility. External extensibility implies that a protocol
extension may specify and exchange new message types, formatted
according to [3], which can be forwarded and delivered correctly.
Internal extensibility implies that a protocol extension may define
additional attributes to be carried embedded in the standard OLSRv2
control messages detailed in this specification, using the TLV
mechanism specified in [3], while OLSRv2 control messages with
additional attributes can still be correctly understood by all OLSRv2
nodes.
The OLSRv2 neighborhood discovery protocol using HELLO messages has
likewise been factored out to an independent specification [4]. This
neighborhood discovery protocol serves to ensure that each OLSRv2
node has available continuously updated information repositories
describing the node's 1-hop and 2-hop neighbors. [4] uses the message
format specified in [3], and hence is extensible as described above.
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2. Protocol Overview and Functioning
OLSRv2 is a proactive routing protocol for mobile ad hoc networks.
The protocol inherits the stability of a link state algorithm and has
the advantage of having routes immediately available when needed due
to its proactive nature. OLSRv2 is an optimization over the
classical link state protocol, tailored for mobile ad hoc networks.
The main tailoring and optimizations of OLSRv2 are:
o periodic, unacknowledged transmission of all control messages;
o optimized flooding for global link-state information diffusion;
o partial topology maintenance - each node knows only a subset of
the links in the network, sufficient for a minimum hop route to
all destinations.
Using the message exchange format [3] and the neighborhood discovery
protocol [4], OLSRv2 also contains the following main components:
o a TLV, to be included within the HELLO messages of [4], allowing a
node to signal MPR selection;
o an optimized flooding mechanism for global information exchange,
denoted "MPR flooding";
o a specification of global signaling, denoted TC (Topology Control)
messages. TC messages in OLSRv2 serve to:
* inject link-state information into the entire network;
* inject addresses of hosts and networks for which they may serve
as a gateway into the entire network.
TC messages are emitted periodically, thereby allowing nodes to
continuously track global changes in the network.
The use of [4] allows a node to continuously track changes to its
local topology up to two hops away. This allows a node to make
provisions for ensuring optimized flooding, denoted "MPR flooding",
as well as injection of link-state information into the network.
This is done through the notion of MultiPoint Relays (MPRs).
The idea of MPRs is to minimize the overhead of flooding messages in
the network by reducing redundant retransmissions of messages in the
same region. Each node in the network selects an MPR Set, a set of
nodes in its symmetric 1-hop neighborhood which may retransmit its
messages. The 1-hop neighbors of a node which are not in its MPR set
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receive and process broadcast messages, but do not retransmit
broadcast messages received from that node. The MPR Set of a node X
may be any subset of its symmetric 1-hop neighborhood such that every
node in its symmetric strict 2-hop neighborhood has a symmetric link
to a node in the MPR Set of node X. The MPR Set of a node may thus be
said to "cover" the node's symmetric strict 2-hop neighborhood. The
smaller a MPR Set, the fewer times messages are forwarded and the
less resulting control traffic overhead. [8] gives an analysis and
example of MPR selection algorithms. Note that as long as the
condition above is satisfied, any algorithm selecting MPR Sets is
acceptable in terms of implementation interoperability.
Each node maintains information about the set of symmetric 1-hop
neighbors that have selected it as MPR. This set is called the MPR
Selector Set of the node. A node obtains this information from an
MPR TLV which is inserted into the HELLO message exchange of [4].
Each node also maintains a Relay Set, which is the set of nodes for
which a node is to relay broadcast traffic. The Relay Set is derived
from the MPR Selector Set in that the Relay Set MUST contain all the
nodes in the MPR Selector set and MAY contain additional nodes.
Using the MPR flooding mechanism, link-state information can be
injected into the network. For this purpose, a node maintains an
Advertised Neighbor Set which MUST contain all the nodes in the MPR
selector set and MAY contain additional nodes. If the Advertised
Neighbor Set of a node is non-empty, it is reported in TC messages
generated by that node. If the Advertised Neighbor Set is empty, TC
messages are not generated by that node, unless needed for gateway
reporting, or for a short period to accelerate the removal of
unwanted links.
OLSRv2 is designed to work in a completely distributed manner and
does not depend on any central entity. The protocol does not require
reliable transmission of control messages: each node sends control
messages periodically, and can therefore sustain a reasonable loss of
some such messages. Such losses may occur frequently in radio
networks due to collisions or other transmission problems.
OLSRv2 does not require sequenced delivery of messages. Each control
message contains a sequence number which is incremented for each
message. Thus the recipient of a control message can, if required,
easily identify which information is more recent - even if messages
have been re-ordered while in transmission.
OLSRv2 does not require any changes to the format of IP packets, any
existing IP stack can be used as is: OLSRv2 only interacts with
routing table management. OLSR sends its control messages using UDP.
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2.1. Protocol Extensibility
OLSRv2 uses the neighborhood discovery mechanism of [4], and
specifies additionally one message type, TC, and a number of TLVs.
All messages exchanged by [4] and by OLSRv2 use and comply with the
extensible message exchange format of [3], thus OLSR provides both
"external" extensibility (addition of new message types as in OLSRv1
[1]) and "internal" extensibility (addition of information to
existing messages through TLVs) as described in [3].
Those nodes which do not recognize a new message type ("external
extensibility") will ignore this message type for processing, but
will correctly forward the message, if specified in the message
header. Those nodes which do not recognize a newly defined TLV type
ignore the added TLV, but process (if the message type is recognized)
the message correctly, as well as forwards the message, if specified
in the message header.
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3. Processing and Forwarding Repositories
The following data structures are employed in order to ensure that a
message is processed at most once and is forwarded at most once per
interface of a node, and that fragmented content is treated
correctly.
3.1. Received Set
Each node maintains, for each OLSRv2 interface, a set of signatures
of messages, which have been received over that interface, in the
form of "Received Tuples":
(RX_type, RX_orig_addr, RX_seq_number, RX_time)
where:
RX_type is the received message type, or zero if the received message
sequence number is not type-specific;
RX_orig_addr is the originator address of the received message;
RX_seq_number is the message sequence number of the received message;
RX_time specifies the time at which this Received Tuple expires and
*MUST* be removed.
In a node, this is denoted the "Received Set" for that interface.
3.2. Fragment Set
Each node stores messages containing fragmented content until all
fragments are received and the message processing can be completed,
in the form of "Fragment Tuples":
(FG_message, FG_time)
where:
FG_message is the message containing fragmented content;
FG_time specifies the time at which this Fragment Tuple expires and
MUST be removed.
In a node, this is denoted the "Fragment Set".
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3.3. Processed Set
Each node maintains a set of signatures of messages which have been
processed by the node, in the form of "Processed Tuples":
(P_type, P_orig_addr, P_seq_number, P_time)
where:
P_type is the processed message type, or zero if the processed
message sequence number is not type-specific;
P_orig_addr is the originator address of the processed message;
P_seq_number is the message sequence number of the processed message;
P_time specifies the time at which this Processed Tuple expires and
*MUST* be removed.
In a node, this is denoted the "Processed Set".
3.4. Forwarded Set
Each node maintains a set of signatures of messages which have been
retransmitted/forwarded by the node, in the form of "Forwarded
Tuples":
(FW_type, FW_orig_addr, FW_seq_number, FW_time)
where:
FW_type is the forwarded message type, or zero if the forwarded
message sequence number is not type-specific;
FW_orig_addr is the originator address of the forwarded message;
FW_seq_number is the message sequence number of the forwarded
message;
FW_time specifies the time at which this Forward Tuple expires and
*MUST* be removed.
In a node, this is denoted the "Forwarded Set".
3.5. Relay Set
Each node maintains a set of neighbor interface addresses for which
it is to relay flooded messages, in the form of "Relay Tuples":
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(RY_iface_addr)
where:
RY_iface_addr is the address of a neighbor interface for which the
node SHOULD relay flooded messages. This MUST include a prefix
length.
In a node, this is denoted the "Relay Set".
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4. Packet Processing and Message Forwarding
On receiving a basic packet, as defined in [3], a node examines each
of the message headers. If the message type is known to the node,
the message is processed locally according to the specifications for
that message type. The message is also independently evaluated for
forwarding.
4.1. Actions when Receiving an OLSRv2 Packet
On receiving a packet, a node MUST perform the following tasks:
1. The packet may be fully parsed on reception, or the packet and
its messages may be parsed only as required. (It is possible to
parse the packet header, or determine its absence, without
parsing any messages. It is possible to divide the packet into
messages without even fully parsing their headers. It is
possible to determine whether a message is to be forwarded, and
to forward it, without parsing its body. It is possible to
determine whether a message is to be processed without parsing
its body. It is possible to determine if that processing may be
delayed because the message is a fragment by inspecting the first
few octets of the message body without fully parsing it.)
2. If parsing fails at any point the relevant entity (packet or
message) MUST be silently discarded, other parts of the packet
(up to the whole packet) MAY be silently discarded;
3. Otherwise if the packet header is present and it contains a
packet TLV block, then each TLV in it is processed according to
its type;
4. Otherwise each message in the packet, if any, is treated
according to Section 4.2.
4.2. Actions when Receiving an OLSRv2 Message
A node MUST perform the following tasks for each received OLSRv2
message:
1. If the received OLSRv2 message header cannot be correctly parsed
according to the specification in [3], or if the node recognizes
from the originator address of the message that the message is
one which the receiving node itself originated, then the message
MUST be silently discarded;
2. Otherwise:
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1. If the received message is of a known type then the message
is considered for processing according to Section 4.3, AND;
2. If for the received message (<hop-limit> + <hop-count>) > 1,
then the message is considered for forwarding according to
Section 4.4.
4.3. Message Considered for Processing
If a message (the "current message") is considered for processing,
the following tasks MUST be performed:
1. If an entry exists in the Processed Set where:
* P_type == the message type of the current message, or 0 if the
typedep bit in the message semantics octet (in the message
header) of the current message is cleared ('0'), AND;
* P_orig_addr == the originator address of the current message,
AND;
* P_seq_number == the message sequence number of the current
message.
then the current message MUST NOT be processed.
2. Otherwise:
1. Create an entry in the Processed Set with:
+ P_type = the message type of the current message, or 0 if
the typedep bit in the message semantics octet (in the
message header) of the current message is cleared ('0');
+ P_orig_addr = originator address of the current message;
+ P_seq_number = sequence number of the current message;
+ P_time = current time + P_HOLD_TIME.
2. If the current message does not contain a valid message TLV
with Type == FRAGMENTATION (or if it does and the indicated
number of fragments is one) then process the message fully
according to its type.
3. Otherwise:
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1. If the current message does not contain a valid message
TLV with Type == CONT_SEQ_NUM then the current message
MUST be silently discarded;
2. Otherwise if the current message is "partially or wholly
self-contained", as indicated by the notselfcont bit in
the Value field of the TLV with Type == FRAGMENTATION
being cleared ('0'), then process the current message as
far as possible according to its type;
3. If the Fragment Set includes any Fragment Tuples with:
- either the typedepseq bit in the Value field of the
TLV with Type == FRAGMENTATION in the current message
is cleared ('0') OR message type of FG_message ==
message type of current message, AND;
- originator address of FG_message == originator address
of current message, AND;
- content sequence number (the Value field of the
message TLV with Type == CONT_SEQ_NUM) of FG_message
== content sequence number of current message; AND
- either fragment number (from the Value field of the
TLV with Type == FRAGMENTATION) in FG_message ==
fragment number of current message OR number of
fragments (from the Value field of the TLV with Type
== FRAGMENTATION) of FG_message != number of fragments
of current message;
then remove these Fragment Tuples from the Fragment Set;
4. If the Fragment Set includes Fragment Tuples containing
all the remaining fragments of the same overall message
as the current message, i.e. if the number of Fragment
Tuples such that:
- either the typedepseq bit in the Value field of the
TLV with Type == FRAGMENTATION in the current message
is cleared ('0') OR message type of FG_message ==
message type of current message, AND;
- originator address of FG_message == originator address
of current message, AND;
- content sequence number (the Value field of the
message TLV with Type == CONT_SEQ_NUM) of FG_message
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== content sequence number of current message
is equal to (number of fragments of current message, less
one) then all of these Fragment Tuples are removed from
the Fragment Set and their messages processed according
to their type (taking account of any previous processing
of any which are partially or wholly self-contained);
5. Otherwise, a Fragment Tuple is added to the Fragment Set
with
- FG_message = current message;
- FG_time = current time + FG_HOLD_TIME;
possibly replacing a previously received instance of the
same fragment.
4.4. Message Considered for Forwarding
If a message is considered for forwarding, and it is either of a
message type defined in this document or of an unknown message type,
then it MUST use the following algorithm. A message type not defined
in this document MAY specify the use of this, or another algorithm.
(Such an other algorithm MAY use the Received Set for the receiving
interface, it SHOULD use the Forwarded Set similarly to the following
algorithm.)
If a message is considered for forwarding according to this
algorithm, the following tasks MUST be performed:
1. If the sending interface (as indicated by the source interface of
the IP datagram containing the message) does not match (taking
into account any address prefix of) any N_neighbor_iface_addr in
any Symmetric Neighbor Tuple, then the message MUST be silently
discarded.
2. Otherwise:
1. If an entry exists in the Received Set for the receiving
interface, where:
+ RX_type == the message type, or 0 if the typedep bit in
the message semantics octet (in the message header) is
cleared ('0'), AND;
+ RX_orig_addr == the originator address of the received
message, AND;
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+ RX_seq_number == the sequence number of the received
message.
then the message MUST be silently discarded.
2. Otherwise:
1. Create an entry in the Received Set for the receiving
interface with:
- RX_type = the message type, or 0 if the typedep bit in
the message semantics octet (in the message header) is
cleared ('0');
- RX_orig_addr = originator address of the message;
- RX_seq_number = sequence number of the message;
- RX_time = current time + RX_HOLD_TIME.
2. If an entry exists in the Forwarded Set where:
- FW_type == the message type, or 0 if the typedep bit
in the message semantics octet (in the message header)
is cleared ('0');
- FW_orig_addr == the originator address of the received
message, AND;
- FW_seq_number == the sequence number of the received
message.
then the message MUST be silently discarded.
3. Otherwise if a Relay Tuple exists whose RY_iface_addr
matches (taking into account any address prefix) the
sending interface (as indicated by the source interface
of the IP datagram containing the message):
1. Create an entry in the Forwarded Set with:
o FW_type = the message type, or 0 if the typedep
bit in the message semantics octet (in the message
header) is cleared ('0');
o FW_orig_addr = originator address of the message;
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o FW_seq_number = sequence number of the message;
o FW_time = current time + FW_HOLD_TIME.
2. The message header is modified as follows:
o Decrement <hop-limit> in the message header by 1;
o Increment <hop-count> in the message header by 1;
3. Transmit the message on all OLSRv2 interfaces of the
node.
Messages are retransmitted in the format specified by [3] with the
ALL-MANET-NEIGHBORS address (see Section 16.1) as destination IP
address.
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5. Information Repositories
The purpose of OLSRv2 is to determine the Routing Set, which may be
used to update IP's Routing Table, providing "next hop" routing
information for IP datagrams. In order to accomplish this, OLSRv2
uses a number of protocol sets: the Neighborhood Information Base,
provided by [4], is in OLSRv2 augmented by information allowing MPR
selection and signaling. Additionally, OLSRv2 specifies a Topology
Information Base, which describes the information used for and
acquired through TC message exchange - in other words: the topology
base represents the network topology graph as seen from each node.
Addresses (other than originator addresses) recorded in the
Neighborhood Information Base and the Topology Information Base MUST
all be recorded with prefix lengths, in order to allow comparison
with addresses received in HELLO and TC messages. For the Topology
Information Base this applies to A_neighbor_iface_addr,
T_dest_iface_addr, T_last_iface_addr, AN_net_addr, AN_gw_iface_addr,
R_dest_addr, R_dest_addr, R_next_iface_addr and R_local_iface_addr,
but not AH_orig_addr. For the Neighborhood Information Base see [4].
5.1. Neighborhood Information Base
The neighborhood information base stores information about links
between local interfaces and interfaces on adjacent nodes. In
addition to the sets described in [4], OLSRv2 adds an element to each
Link Tuple to allow a node to record the willingness of a 1-hop
neighbor node to be selected as an MPR. Also, OLSRv2 adds an MPR Set
and an MPR Selector Set to the Neighborhood Information Base. The
MPR Set is used by a node to record which of its symmetric 1-hop
neighbors are selected as MPRs, and the MPR Selector Set is used by a
node to record which of its symmetric 1-hop neighbors have selected
it as MPR. Thus the MPR Set is used, in addition to what is
specified in [4], when generating HELLO messages, and the MPR
Selector Set is populated, in addition to what is specified in [4]
when processing HELLO messages.
5.1.1. Link Set
The Link Tuples, specified in [4] are augmented by an element,
L_willingness:
L_willingness is the node's willingness to be selected as an MPR;
The remaining elements of the Link Tuples are as specified in [4].
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5.1.2. MPR Set
A node maintains a set of all of the OLSRv2 interface addresses with
which the node has a symmetric link and which are of 1-hop symmetric
neighbors which the node has selected as MPRs. This is denoted the
"MPR Set".
5.1.3. MPR Selector Set
A node maintains a set of "MPR Selector Tuples" containing all of the
OLSRv2 interface addresses with which the node has a symmetric link
and which are of 1-hop symmetric neighbors which have selected the
node as an MPR.
(MS_neighbor_iface_addr, MS_time)
MS_neighbor_iface_addr specifies an OLSRv2 interface address with
which the node has a symmetric link and which is of a 1-hop
symmetric neighbor which has selected the node as an MPR;
MS_time specifies the time at which this MPR Selector Tuple expires
and *MUST* be removed.
In a node, the set of MPR Selector Tuples is denoted the "MPR
Selector Set".
5.2. Topology Information Base
The Topology Information Base stores information, required for the
generation and processing of TC messages. The Advertised Neighbor
Set contains OLSRv2 interface addresses of symmetric 1-hop neighbors
which are to be reported in TC messages. The Topology Set and
Attached Network Set both record information received through TC
messages. Thus the Advertised Neighbor Set is used for generating TC
messages, while the Topology Set and Attached Network Set are
populated when processing TC messages.
Additionally, a Routing Set is maintained, derived from the
information recorded in the Neighborhood Information Base, Topology
Set and Attached Network Set.
5.2.1. Advertised Neighbor Set
A node maintains a set of OLSRv2 interface addresses of symmetric
1-hop neighbors, which are to be advertised through TC messages:
(A_neighbor_iface_addr)
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For this set, an Advertised Neighbor Set Sequence Number (ANSN) is
maintained. Each time the Advertised Neighbor Set is updated, the
ANSN MUST be incremented. The ANSN MUST also be incremented if any
locally advertised attached networks are added or removed.
5.2.2. ANSN History Set
A node records a set of "ANSN History Tuples", recording information
about the freshness of the topology information received from each
other node:
(AH_orig_addr, AH_seq_number, AH_time)
AH_orig_addr is the originator address of a received TC message;
AH_seq_number is the highest ANSN in any TC message received which
originated from AH_orig_addr;
AH_time is the time at which this ANSN History Tuple expires and
*MUST* be removed.
In a node, the set of ANSN History Tuples is denoted the "ANSN
History Set".
5.2.3. Topology Set
Each node in the network maintains topology information about the
network in the form of "Topology Tuples":
(T_dest_iface_addr, T_last_iface_addr, T_seq_number, T_time)
T_dest_iface_addr is an OLSRv2 interface address of a destination
node, which may be reached in one hop from the node with the
OLSRv2 interface address T_last_iface_addr;
T_last_iface_addr is, conversely, an OLSRv2 interface address of a
node which is the last hop on a path towards the node with OLSRv2
interface address T_dest_iface_addr. Typically, the node with
OLSRv2 interface address T_last_iface_addr is a MPR of the node
with OLSRv2 interface address T_dest_iface_addr;
T_seq_number is the highest received ANSN associated with the
information contained in this Topology Tuple;
T_time specifies the time at which this Topology Tuple expires and
*MUST* be removed.
In a node, the set of Topology Tuples is denoted the "Topology Set".
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5.2.4. Attached Network Set
Each node in the network maintains information about attached
networks in the form of "Attached Network Tuples":
(AN_net_addr, AN_gw_iface_addr, AN_seq_number, AN_time)
AN_net_addr is the network address (including prefix length) of an
attached network, which may be reached via the node with the
OLSRv2 interface address AN_gw_iface_addr;
AN_gw_iface_addr is the address of an OLSRv2 interface of a node
which can act as gateway to the network identified by AN_net_addr;
AN_seq_number is the highest received ANSN associated with the
information contained in this Attached Network Tuple;
AN_time specifies the time at which this Attached Network Tuple
expires and *MUST* be removed.
In a node, the set of Attached Network Tuples is denoted the
"Attached Network Set".
5.2.5. Routing Set
A node records a set of "Routing Tuples" describing the selected path
to each destination in the network for which a route is known:
(R_dest_addr, R_next_iface_addr, R_dist, R_local_iface_addr)
R_dest_addr is the address of the destination, either the address of
an OLSRv2 interface of a destination node, or the network address
of an attached network;
R_next_iface_addr is the OLSRv2 interface address of the "next hop"
on the selected path to the destination;
R_dist is the number of hops on the selected path to the destination;
R_local_iface_addr is the address of the local interface over which a
packet MUST be sent to reach the destination.
In a node, the set of Routing Tuples is denoted the "Routing Set".
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6. OLSRv2 Control Message Structures
Nodes using OLSRv2 exchange information through messages. One or
more messages sent by a node at the same time are combined into a
packet. These messages may have originated at the sending node, or
have originated at another node and forwarded by the sending node.
Messages with different originators may be combined in the same
packet.
The packet and message format used by OLSRv2 is defined in [3].
However this specification contains some options which are not used
by OLSRv2. In particular (using the syntactical elements defined in
the packet format specification):
o All OLSRv2 packets, not limited to those defined in this document,
include a <packet-header>.
o All OLSRv2 packets, not limited to those defined in this document,
have the pseqnum bit of <packet-semantics> cleared ('0'), i.e.
they include a packet sequence number.
o OLSRv2 packets MAY include packet TLVs, however OLSRv2 itself does
not specify any packet TLVs.
o All OLSRv2 messages, not limited to those defined in this
document, include a full <msg-header> and hence have the noorig
and nohops bits of <msg-semantics> cleared ('0').
o All OLSRv2 message defined in this document have the typedep bit,
and all reserved bits of <msg-semantics> cleared ('0').
Other options defined in [3] may be freely used, in particular any
other values of <packet-semantics> or <tlv-semantics> consistent with
its specification.
OLSRv2 messages are sent using UDP, see Appendix C.
The remainder of this section defines, within the framework of [3],
message types and TLVs specific to OLSRv2.
6.1. General OLSRv2 Message TLVs
This document specifies two message TLVs, which can be applied to any
OLSRv2 control messages, VALIDITY_TIME and INTERVAL_TIME.
6.1.1. VALIDITY_TIME TLV
All OLSRv2 messages specified in this document MUST include a
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VALIDITY_TIME TLV, specifying a period following receipt of a
message, after which 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 the originator (i.e. the <hop-count> field in the
message header as defined in [3]). Thus, a VALIDITY_TIME TLV's value
field MAY contain a sequence of pairs (time, hop limit) in increasing
hop limit order; it MUST contain a final default value.
This is an extended, and compatible, version of the VALIDITY_TIME TLV
defined in [4].
Thus, an instance of a VALIDITY_TIME TLV MAY have the following value
field:
<t_1><hl_1><t_2><hl_2> ... <t_i><hl_i> .... <t_n><hl_n><t_default>
Which would mean that the message carrying this VALIDITY_TIME TLV
would have the following validity times:
o <t_1> in the interval from 0 (exclusive) to <hl_1> (inclusive)
hops away from the originator;
o <t_i> in the interval from <hl_(i-1)> (exclusive) to <hl_i>
(inclusive) hops away from the originator;
o <t_default> in the interval from <hl_n> (exclusive) to 255
(inclusive) hops away from the originator.
The VALIDITY_TIME message TLV specification is given in Table 1.
+----------------+------+-------------------+-----------------------+
| Name | Type | Length | Value |
+----------------+------+-------------------+-----------------------+
| VALIDITY_TIME | TBD | (2*n+1) * 8 bits | {<time><hop_limit>}* |
| | | | <t_default> |
+----------------+------+-------------------+-----------------------+
Table 1
where n is the number of (time, hop_limit) pairs in the TLV (i.e. is
equal to (<length>-1)/2, where <length> is the length of the TLV
value field) and where <time> and <t_default> are represented as
specified in [3].
6.2. HELLO Messages
A HELLO message in OLSRv2 is generated as specified in [4].
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Additionally, an OLSRv2 node:
o MUST include TLV(s) with Type == MPR associated with all OLSRv2
interface addresses included in the HELLO message with a TLV with
Type == LINK_STATUS and Value == SYMMETRIC if that address is also
included in the node's MPR Set (if there is more than one copy of
the address, this applies to the specific copy of the address to
which the TLV is associated);
o MUST NOT include any TLVs with Type == MPR associated with any
other addresses;
o MAY include a message TLV with Type == WILLINGNESS, indicating the
node's willingness to be selected as MPR.
6.2.1. HELLO Message OLSRv2 Message TLVs
In a HELLO message, a node MAY include a WILLINGNESS message TLV as
specified in Table 2.
+----------------+------+-------------------+-----------------------+
| Name | Type | Length | Value |
+----------------+------+-------------------+-----------------------+
| WILLINGNESS | TBD | 8 bits | The node's |
| | | | willingness to be |
| | | | selected as MPR, any |
| | | | unused bits (based on |
| | | | the maximum |
| | | | willingness value |
| | | | WILL_ALWAYS) are |
| | | | RESERVED and SHOULD |
| | | | be set to zero. |
+----------------+------+-------------------+-----------------------+
Table 2
A node's willingness to be selected as MPR ranges from WILL_NEVER
(indicating that a node MUST NOT be selected as MPR by any node) to
WILL_ALWAYS (indicating that a node MUST always be selected as MPR).
If a node does not advertise a Willingness TLV in HELLO messages, the
node MUST be assumed to have a willingness of WILL_DEFAULT.
6.2.2. HELLO Message OLSRv2 Address Block TLVs
In a HELLO message, a node MAY include MPR address block TLV(s) as
specified in Table 3.
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+----------------+------+-------------------+-----------------------+
| Name | Type | Length | Value |
+----------------+------+-------------------+-----------------------+
| MPR | TBD | 0 bits | No value, i.e. |
| | | | novalue bit ([3]) set |
+----------------+------+-------------------+-----------------------+
Table 3
6.3. TC Messages
A TC message MUST contain:
o a message TLV with Type == CONT_SEQ_NUM, as specified in [3];
o a message TLV with Type == VALIDITY_TIME, as specified in
Section 6.1.1;
o a first address block containing all of the node's OLSRv2
interface addresses. This is similar to the Local Interface Block
specified in [4], however these addresses MUST be included in the
same order in all copies of a given TC message, regardless of
which interface it is transmitted on, and no OTHER_IF address
block TLV(s) are required;
o additional address block(s) containing all addresses in the
Advertised Address Set and Attached Network Set, the latter (only)
with associated GATEWAY address block TLV(s), as specified in
Section 6.4, both with associated PREFIX_LENGTH TLV(s), as
specified in [3], as necessary.
A TC message MAY contain:
o a message TLV INTERVAL_TIME, as specified in [4].
6.4. TC Message: OLSRv2 Address Block TLVs
In a TC message, a node MAY include GATEWAY address block TLV(s) as
specified in Table 4.
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+----------------+------+-------------------+-----------------------+
| Name | Type | Length | Value |
+----------------+------+-------------------+-----------------------+
| GATEWAY | TBD | 0 bits | No value, i.e. |
| | | | novalue bit ([3]) set |
+----------------+------+-------------------+-----------------------+
Table 4
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7. HELLO Message Generation
An OLSRv2 HELLO message is composed as defined in [4], with the
following TLVs added:
o a message TLV with Type == WILLINGNESS and Value == the node's
willingness to act as an MPR, MAY be included in the message;
o for each symmetric 1-hop neighbor OLSRv2 interface address which
is included in the HELLO message with an associated TLV with Type
== LINK_STATUS and is selected as an MPR (i.e. is present in the
MPR Set), an address TLV with Type == MPR MUST be included, this
SHOULD be associated with the same copy of the address as the TLV
with Type == LINK_STATUS;
o for each 1-hop neighbor OLSRv2 interface address which is included
in the HELLO message but is not selected as an MPR (i.e. is not
present in the MPR Set), an address TLV with Type == MPR MUST NOT
be included.
7.1. HELLO Message: Transmission
Messages are retransmitted in the packet/message format specified by
[3] with the ALL-MANET-NEIGHBORS address as destination IP address
and with TTL (IPv4) or hop limit (IPv6) equal to 1.
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8. HELLO Message Processing
Subsequent to the processing of HELLO messages, as specified in [4],
the node MUST:
1. Determine the willingness of the originating node to be an MPR
by:
* if the HELLO message contains a message TLV with Type ==
WILLINGNESS then the willingness is the value of that TLV,
ignoring the reserved bits in that field;
* otherwise the willingness is WILL_DEFAULT.
2. Update each Link Tuple whose L_neighbor_iface_addr is present in
the Local Interface Block of the HELLO message, with:
* L_willingness = the willingness of the originating node;
3. Update its MPR Selector Set, according to Section 8.1.
8.1. Populating the MPR Selector Set
On receiving a HELLO message, a node MUST:
1. If a node finds one of its own interface addresses with an
associated TLV with Type == MPR in the HELLO message (indicating
that the originator node has selected the receiving node as an
MPR), the MPR Selector Set MUST be updated as follows:
1. For each address, henceforth neighbor address, in the Local
Interface Block of the received HELLO message, where the
neighbor address is present as an N_neighbor_iface_addr in a
Symmetric Neighbor Tuple with N_STATUS == SYMMETRIC:
1. If there exists no MPR Selector Tuple with:
- MS_neighbor_iface_addr == neighbor address
then a new MPR Selector Tuple is created with:
- MS_neighbor_iface_addr = neighbor address
2. The MPR Selector Tuple (new or otherwise) with:
- MS_neighbor_iface_addr == neighbor address
is then modified as follows:
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- MS_time = current time + validity time
2. Otherwise if a node finds one of its own interface addresses with
an associated TLV with Type == LINK_STATUS and Value == SYMMETRIC
in the HELLO message (indicating, since there is no TLV with Type
== MPR, that originator node has de-selected the receiving node
as an MPR), the MPR Selector Set MUST be updated as follows:
1. All MPR Selector Tuples whose N_neighbor_iface_addr is in the
Local Interface Block of the HELLO message are removed.
MPR Selector Tuples are also removed upon expiration of MS_time, or
upon symmetric link breakage as described in Section 8.2.
8.2. Symmetric Neighborhood and 2-Hop Neighborhood Changes
A node MUST also perform the following:
1. If a Link Tuple with L_STATUS == SYMMETRIC is removed, or its
L_STATUS changes from SYMMETRIC to HEARD or LOST, and if that
Link Tuple's L_neighbor_iface_addr is an MS_iface_addr of an MPR
Selector Tuple, then that MPR Selector Tuple MUST be removed.
2. If any of:
* a Link Tuple is added with L_STATUS == SYMMETRIC, OR;
* a Link Tuple with L_STATUS == SYMMETRIC is removed, or its
L_STATUS changes from SYMMETRIC to HEARD or LOST, or vice
versa, OR;
* a 2-Hop Neighbor Tuple is added or removed, OR;
* the Neighbor Address Association Set is changed such that the
subset of any NA_neighbor_iface_addr_list consisting of those
addresses which are the L_neighbor_iface_addr of a Link Tuple
with L_STATUS == SYMMETRIC is changed, including the cases of
removal or addition of a Neighbor Address Association Tuple
containing any such addresses;
then the MPR Set MUST be recalculated.
An additional HELLO message MAY be sent when the MPR Set changes, in
addition to the cases specified in [4], and subject to the same
constraints.
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9. TC Message Generation
A node with one or more OLSRv2 interfaces, and with a non-empty
Advertised Neighbor Set or which acts as a gateway to an associated
network which is to be advertised in the MANET, MUST generate TC
messages. A node with an empty Advertised Neighbor Set and which is
not acting as such a gateway SHOULD also generate "empty" TC messages
for a period A_HOLD_TIME after it last generated a non-empty TC
message. TC messages (non-empty and empty) are generated according
to the following:
1. the TC message MUST contain a message TLV with Type ==
CONT_SEQ_NUM and Value == ANSN from the Advertised Neighbor Set;
2. the TC message MUST contain a message TLV with Type ==
VALIDITY_TIME and Value == T_HOLD_TIME as specified in
Section 6.1.1;
3. the TC message MAY contain a message TLV with Type ==
INTERVAL_TIME and Value == TC_INTERVAL as specified in [4];
4. the TC message MUST contain the addresses of all of its OLSRv2
interfaces in its first address block, note that the TC message
generated on all OLSRv2 interfaces MUST be identical (including
having identical message sequence number) and hence these
addresses are not ordered or otherwise identified according to
the interface on which the TC message is transmitted;
5. the TC message MUST contain, in address blocks other than its
first:
1. A_neighbor_iface_addr from each Advertised Neighbor Tuple;
2. the addresses of all associated hosts and networks for which
this node is to act as a gateway and which is to be
advertised in the MANET, each associated with a TLV with Type
== GATEWAY.
6. the TC message MAY be fragmented, only by its originator. It
SHOULD be fragmented only if necessary; if the TC message is
fragmented, a FRAGMENTATION TLV MUST be included, and each
fragment SHOULD be indicated as "partially or wholly self
contained" in it, and MUST indicate that the content sequence
number (ANSN) is message type specific.
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9.1. TC Message: Transmission
TC messages are generated and transmitted periodically on all OLSRv2
interfaces, with a default interval between two consecutive TC
emissions by the same node of TC_INTERVAL. TC messages MAY be
generated in response to a change of contents (a change in ANSN, due
to a change in the Advertised Neighbor Set or the advertised locally
attached networks) but a node must respect a minimum interval of
TC_MIN_INTERVAL between generated TC messages.
TC messages SHOULD be generated with a message hop limit [3] greater
than or equal to the expected network diameter (by default with a hop
limit of 255).
TC messages are transmitted with the ALL-MANET-NEIGHBORS multicast
address as destination IP address and are forwarded according to the
specification in Section 4.4.
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10. TC Message Processing
When according to Section 4.3 a TC message is to be processed
according to its type, this means that processing is carried out
according to Section 10.1 and Section 10.2. The timing of this
processing depends on whether the TC message is a fragment, and if so
whether it is "partially or wholly self-contained":
o if the message is not a fragment, then first Section 10.1 and then
Section 10.2 are carried out when the message is received;
o if the message is a fragment which is "partially or wholly self-
contained", then processing according to Section 10.1 is carried
out when the message is received, and processing according to
Section 10.2 is carried out when all matching fragments have been
received and all processing according to Section 10.1 has been
carried out;
o if the message is a fragment which is not "partially or wholly
self-contained", then processing according to Section 10.1 is
carried out when all matching fragments have been received, and
processing according to Section 10.2 is carried out when all
matching fragments have been received and all processing according
to Section 10.1 has been carried out.
For all processing purposes, "ANSN" is defined as being the value of
the message TLV with Type == CONT_SEQ_NUM in the TC message. If a TC
message has no such TLV then the processing of Section 10.1 and
Section 10.2 MUST NOT be carried out. (Note that if the message is a
fragment it will have already been discarded according to
Section 4.3.) If more than one TC message is processed according to
Section 10.2 then these must have the same ANSN to be recognized as
fragments of the same message.
10.1. Single TC Message Processing
For the purpose of this section, note the following:
o "validity time" is calculated from the VALIDITY_TIME message TLV
in the TC message according to the specification in Section 6.1.1;
o "originator address" refers to the originator address in the TC
message header;
o comparisons of sequence numbers are carried out as specified in
Section 15.
The TC message is processed as follows:
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1. the ANSN History Set is updated according to Section 10.1.1; if
the TC message is indicated as discarded in that processing then
the following steps are not carried out;
2. the Topology Set is updated according to Section 10.1.2;
3. the Attached Network Set is updated according to Section 10.1.3.
10.1.1. Populating the ANSN History Set
The node MUST update its ANSN History Set as follows:
1. if there is an ANSN History Tuple with:
* AH_orig_addr == originator address; AND
* AH_seq_number > ANSN
then the TC message MUST be discarded;
2. otherwise create a new ANSN History Tuple with:
* AH_orig_addr = originator address;
* AH_seq_number = ANSN;
* AH_time = current time + validity time.
possibly replacing an existing ANSN History Tuple with the same
AH_orig_addr.
10.1.2. Populating the Topology Set
The node SHOULD update its Topology Set as follows:
1. for each address, henceforth local address, in the first address
block in the TC message:
1. for each address, henceforth advertised address, in an
address block other than the first in the TC message, and
which does not have an associated TLV with Type == GATEWAY:
1. if there is a Topology Tuple with:
T_dest_iface_addr == advertised address; AND
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T_last_iface_addr == local address
then update this Topology Tuple to have:
T_seq_number = ANSN;
T_time = current time + validity time
2. otherwise create a new Topology Tuple with:
T_dest_iface_addr = advertised address;
T_last_iface_addr = local address;
T_seq_number = ANSN;
T_time = current time + validity time.
10.1.3. Populating the Attached Network Set
The node SHOULD update its Attached Network Set as follows:
1. for each address, henceforth gateway address, in the first
address block in the TC message:
1. for each address, henceforth network address, in an address
block other than the first in the TC message, and which has
an associated TLV with Type == GATEWAY:
1. if there is a Attached Network Tuple with:
AN_net_addr == network address; AND
AN_gw_iface_addr == gateway address
then update this Attached Network Tuple to have:
AN_seq_number = ANSN;
AN_time = current time + validity time
2. otherwise create a new Attached Network Tuple with:
AN_net_addr = network address;
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AN_gw_iface_addr = gateway address
AN_seq_number = ANSN;
AN_time = current time + validity time
10.2. Completed TC Message Processing
The TC message(s) are processed as follows:
1. the Topology Set is updated according to Section 10.2.1;
2. the Attached Network Set is updated according to Section 10.2.2.
10.2.1. Purging the Topology Set
The Topology Set MUST be updated as follows:
1. for each address, henceforth local address, in the first address
block of any of the TC messages, all Topology Tuples with:
T_last_iface_addr == local address; AND
T_seq_number < ANSN
MUST be removed.
10.2.2. Purging the Attached Network Set
The Attached Network Set MUST be updated as follows:
1. for each address, henceforth local address, in the first address
block of any of the TC messages, all Attached Network Tuples
with:
AN_gw_iface_addr == local address; AND
AN_seq_number < ANSN
MUST be removed.
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11. Populating the MPR Set
Each node MUST select, from among its symmetric 1-hop neighbors, a
subset of nodes as MPRs. This subset MUST be selected such that a
message transmitted by the node, and retransmitted by all its MPRs,
will be received by all of its symmetric strict 2-hop neighbors.
Each node selects its MPR Set individually, utilizing the information
in the Symmetric Neighbor Set, the 2-Hop Neighbor Set and the
Neighborhood Address Association Set. Initially these sets will be
empty, as will be the MPR Set. A node SHOULD recalculate its MPR Set
when a relevant change is made to the Symmetric Neighbor Set, the
2-Hop Neighbor Set or the Neighborhood Address Association Set.
More specifically, a node MUST calculate MPRs per interface, the
union of the MPR Sets of each interface make up the MPR Set for the
node. All OLSRv2 interfaces of nodes selected as MPRs with which the
node has a symmetric link MUST be added to the MPR Set. Also
symmetric 1-hop neighbor nodes with willingness WILL_NEVER (as
recorded in the Link Set) MUST NOT be considered as MPRs.
MPRs are used to flood control messages from a node into the network
while reducing the number of retransmissions that will occur in a
region. Thus, the concept of MPR is an optimization of a classical
flooding mechanism. While it is not essential that the MPR Set is
minimal, it is essential that all symmetric strict 2-hop neighbors
can be reached through the selected MPR nodes. A node MUST select an
MPR Set such that any strict 2-hop neighbor is "covered" by at least
one MPR node. A node MAY select additional MPRs beyond the minimum
set. Keeping the MPR Set small ensures that the overhead of OLSRv2
is kept at a minimum.
Appendix A contains an example heuristic for selecting MPRs.
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12. Populating Derived Sets
The Relay Set and the Advertised Neighbor Set of OLSRv2 are denoted
derived sets, since updates to these sets are not directly a function
of message exchanges, but rather are derived from updates to other
sets, in particular the MPR Selector Set.
12.1. Populating the Relay Set
The Relay Set contains the set of neighbor addresses, for which a
node is supposed to relay broadcast traffic. This set SHOULD at
least contain all addresses in the MPR Selector Set. This set MAY
contain additional symmetric 1-hop neighbor addresses.
12.2. Populating the Advertised Neighbor Set
The Advertised Neighbor Set contains the set of OLSRv2 interface
addresses of those 1-hop neighbors to which a node advertises a
symmetric link in TC messages. This set SHOULD at least contain all
of the OLSRv2 interface addresses of the nodes in the MPR Selector
Set (i.e. all addresses associated with an MPR Selector node through
the Neighborhood Address Association Set, that is, appearing in the
same NA_neighbor_iface_addr_list as any MS_neighbor_iface_addr).
This set MAY also contain OLSRv2 interface addresses of other
symmetric 1-hop neighbors.
Whenever an address is removed from the Advertised Neighbor Set, the
ANSN MUST be incremented. Whenever an address is added to the
Advertised Neighbor Set, the ANSN MUST be incremented.
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13. Routing Table Calculation
The Routing Set is updated when a change (an entry appearing or
disappearing, or changing between SYMMETRIC and LOST) is detected in:
o the Link Set, OR;
o the Neighbor Address Association Set, OR;
o the 2-Hop Neighbor Set, OR;
o the Topology Set, OR;
o the Attached Network Set.
Note that some changes to these sets do not necessitate a change to
the Routing Set, in particular changes to the Link Set which do not
involve Link Tuples with L_STATUS == SYMMETRIC (either before or
after the change), similar changes to the Neighbor Address
Association Set. A node MAY avoid updating the Routing Set in such
cases.
Updates to the Routing Set does not generate or trigger any messages
to be transmitted. The state of the Routing Set SHOULD, however, be
reflected in the IP routing table by adding and removing entries from
the routing table as appropriate.
To construct the Routing Set of node X, a shortest path algorithm is
run on the directed graph containing
o the arcs X -> Y where there exists a Link Tuple with Y as
L_neighbor_iface_addr and L_STATUS == SYMMETRIC (i.e. Y is a
symmetric 1-hop neighbor of X), AND;
o the arcs Y -> Z where Y is added as above and the Link Tuple with
Y as L_neighbor_iface_addr has L_willingness not equal to
WILL_NEVER, and there exists a 2-Hop Neighbor Tuple with Y as
N2_neighbor_iface_addr and Z as N2_2hop_iface_addr (i.e. Z is a
symmetric 2-hop neighbor of Z through Y, which does not have
willingness WILL_NEVER), AND;
o the arcs U -> V, where there exists a Topology Tuple with U as
T_last_iface_addr and V as T_dest_iface_addr (i.e. this is an
advertised link in the network).
The graph is complemented with:
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o arcs Y -> W where there exists a Link Tuple with Y as
L_neighbor_iface_addr and L_STATUS == SYMMETRIC and a Neighborhood
Address Association Tuple with Y and W both contained in
NA_neighbor_iface_addr_list (i.e. Y and W are both addresses of
the same symmetric 1-hop neighbor), AND;
o arcs U -> T where there exists an Attached Network Tuple with U as
AN_net_addr and T as AN_gw_iface_addr (i.e. U is a gateway to
network T).
The following procedure is given as an example for (re-)calculating
the Routing Set using a variation of Dijkstra's algorithm. Thus:
1. All Routing Tuples are removed.
2. For each Link Tuple with L_STATUS == SYMMETRIC, a new Routing
Tuple is added with:
* R_dest_addr = L_neighbor_iface_addr of the Link Tuple;
* R_next_iface_addr = L_neighbor_iface_addr of the Link Tuple;
* R_dist = 1;
* R_local_iface_addr = L_local_iface_addr of the Link Tuple.
3. For each Neighbor Address Association Tuple, for which two
addresses A1 and A2 are in NA_neighbor_iface_addr_list where:
* there is a Routing Tuple with:
+ R_dest_addr == A1
* and there is no Routing Tuple with:
+ R_dest_addr == A2
then a Routing Tuple is added with:
* R_dest_addr = A2;
* R_next_iface_addr = R_next_iface_addr of the Routing Tuple in
which R_dest_addr == A1;
* R_dist = 1;
* R_local_iface_addr = R_local_iface_addr of the Routing Tuple
in which R_dest_addr == A1.
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4. The following procedure, which adds Routing Tuples for
destination nodes h+1 hops away, MUST be executed for each value
of h, starting with h=2 and incrementing by 1 for each iteration.
The execution MUST stop if no new Routing Tuples are added in an
iteration.
1. For each Topology Tuple, if
+ T_dest_iface_addr is not equal to R_dest_addr of any
Routing Tuple, AND;
+ T_last_iface_addr is equal to R_dest_addr of a Routing
Tuple whose R_dist == h;
then a new Routing Tuple MUST be added, with:
+ R_dest_addr = T_dest_iface_addr;
+ R_next_iface_addr = R_next_iface_addr of the Routing Tuple
whose R_dest_addr == T_last_iface_addr;
+ R_dist = h+1;
+ R_local_iface_addr = R_local_iface_addr of the Routing
Tuple whose R_dest_addr == T_last_iface_addr.
Several Topology Tuples may be used to select a next hop
R_next_iface_addr for reaching the address R_dest_addr. When
h == 1, ties should be broken such that nodes with highest
willingness are preferred, and between nodes of equal
willingness, MPR selectors are preferred over non-MPR
selectors.
2. After the above iteration has completed, if h == 1, for each
2-Hop Neighbor Tuple where:
+ N2_2hop_iface_addr is not equal to R_dest_addr of any
Routing Tuple, AND;
+ N2_neighbor_iface_addr has a willingness (i.e. the
L_willingness of the Link Tuple of which
L_neighbor_iface_addr == N2_neighbor_iface_addr) which is
not equal to WILL_NEVER;
a Routing Tuple is added with:
+ R_dest_addr = N2_2hop_iface_addr of the 2-Hop Neighbor
Tuple;
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+ R_next_iface_addr = R_next_iface_addr of the Routing Tuple
in which R_dest_addr == N2_neighbor_iface_addr;
+ R_dist = 2;
+ R_local_iface_addr = R_local_iface_addr of the Routing
Tuple in which R_dest_addr == N2_neighbor_iface_addr.
5. For each Attached Network Tuple, if
* AN_net_addr is not equal to R_dest_addr of any Routing Tuple,
AND;
* AN_gw_iface_addr is equal to R_dest_addr of a Routing Tuple;
then a new Routing Tuple MUST be added, with:
* R_dest_addr = AN_net_addr;
* R_next_iface_addr = R_next_iface_addr of the Routing Tuple
whose R_dest_addr == AN_gw_iface_addr;
* R_dist = R_dist of the Routing Tuple whose R_dest_addr ==
AN_gw_iface_addr;
* R_local_iface_addr = R_local_iface_addr of the Routing Tuple
whose R_dest_addr == AN_gw_iface_addr.
If more than one Attached Network Tuple has the same AN_net_addr,
then more than one Routing Tuple MUST NOT be added, and the added
Routing Tuple MUST have minimum R_dist.
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14. Proposed Values for Constants
This section list the values for the constants used in the
description of the protocol.
14.1. Neighborhood Discovery Constants
The constants HELLO_INTERVAL, REFRESH_INTERVAL, HELLO_MIN_INTERVAL,
H_HOLD_TIME, L_HOLD_TIME, N_HOLD_TIME and C are used as in [4].
14.2. Message Intervals
o TC_INTERVAL = 5 seconds
o TC_MIN_INTERVAL = TC_INTERVAL/4
14.3. Holding Times
o T_HOLD_TIME = 3 x TC_INTERVAL
o A_HOLD_TIME = T_HOLD_TIME
o P_HOLD_TIME = 30 seconds
o FG_HOLD_TIME = 30 seconds
o RX_HOLD_TIME = 30 seconds
o FW_HOLD_TIME = 30 seconds
14.4. Willingness
o WILL_NEVER = 0
o WILL_DEFAULT = 3
o WILL_ALWAYS = 7
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15. Sequence Numbers
Sequence numbers are used in OLSRv2 with the purpose of discarding
"old" information, i.e. messages received out of order. However with
a limited number of bits for representing sequence numbers, wrap-
around (that the sequence number is incremented from the maximum
possible value to zero) will occur. To prevent this from interfering
with the operation of OLSRv2, the following MUST be observed when
determining the ordering of sequence numbers.
The term MAXVALUE designates in the following one more than the
largest possible value for a sequence number. For a 16 bit sequence
number (as are those defined in this specification) MAXVALUE is
65536.
The sequence number S1 is said to be "greater than" the sequence
number S2 if:
o S1 > S2 AND S1 - S2 <= MAXVALUE/2 OR
o S2 > S1 AND S2 - S1 > MAXVALUE/2
Thus when comparing two messages, it is possible - even in the
presence of wrap-around - to determine which message contains the
most recent information.
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16. IANA Considerations
16.1. Multicast Addresses
A well-known multicast address, ALL-MANET-NEIGHBORS, must be
registered and defined for both IPv6 and IPv4. The addressing scope
is link-local, i.e. this address is similar to the all nodes/routers
multicast address of IPv6 in that it targets all OLSRv2 capable nodes
adjacent to the originator of an IP datagram.
16.2. Message Types
OLSRv2 defines one message type, which must be allocated from the
"Assigned Message Types" repository of [3]
+--------------------+-------+--------------------------------------+
| Mnemonic | Value | Description |
+--------------------+-------+--------------------------------------+
| TC | TBD | Topology Control (global signaling) |
+--------------------+-------+--------------------------------------+
Table 5
16.3. TLV Types
OLSRv2 defines one Message TLV type, which must be allocated from the
"Assigned message TLV Types" repository of [3]
+--------------------+-------+--------------------------------------+
| Mnemonic | Value | Description |
+--------------------+-------+--------------------------------------+
| WILLINGNESS | TBD | Specifies a node's willingness to |
| | | act as a relay and to partake in |
| | | network formation |
+--------------------+-------+--------------------------------------+
Table 6
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OLSRv2 defines one Address Block TLV type, which must be allocated
from the "Assigned address block TLV Types" repository of [3]
+--------------------+-------+--------------------------------------+
| Mnemonic | Value | Description |
+--------------------+-------+--------------------------------------+
| MPR | TBD | Specifies that a given address is |
| | | selected as MPR |
+--------------------+-------+--------------------------------------+
Table 7
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17. References
17.1. Normative References
[1] Clausen, T. and P. Jacquet, "The Optimized Link State Routing
Protocol", RFC 3626, October 2003.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, BCP 14, March 1997.
[3] Clausen, T., Dean, J., Dearlove, C., and C. Adjih, "Generalized
MANET Packet/Message Format", work in
progress draft-ietf-manet-packetbb-01.txt, June 2006.
[4] Clausen, T., Dean, J., and C. Dearlove, "MANET Neighborhood
Discovery Protocol (NHDP)", work in
progress draft-ietf-manet-nhdp-00.txt, June 2006.
17.2. Informative References
[5] Atkins, D., Stallings, W., and P. Zimmermann, "PGP Message
Exchange Formats", RFC 1991, August 1996.
[6] ETSI, "ETSI STC-RES10 Committee. Radio equipment and systems:
HIPERLAN type 1, functional specifications ETS 300-652",
June 1996.
[7] Jacquet, P., Minet, P., Muhlethaler, P., and N. Rivierre,
"Increasing reliability in cable free radio LANs: Low level
forwarding in HIPERLAN.", 1996.
[8] Qayuum, A., Viennot, L., and A. Laouiti, "Multipoint relaying:
An efficient technique for flooding in mobile wireless
networks.", 2001.
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Appendix A. Example Heuristic for Calculating MPRs
The following specifies a proposed heuristic for selection of MPRs.
In graph theory terms, MPR computation is a "set cover" problem,
which is a difficult optimization problem, but for which an easy and
efficient heuristics exist: the so-called "Greedy Heuristic", a
variant of which is described here. In simple terms, MPR computation
constructs an MPR Set that enables a node to reach any symmetric
2-hop neighbors by relaying through an MPR node.
There are several peripheral issues that the algorithm needs to
address. The first one is that some nodes have some willingness
WILL_NEVER. The second one is that some nodes may have several
interfaces.
The algorithm hence can be summarized by:
o All 1-hop neighbor nodes with willingness equal to WILL_NEVER MUST
ignored in the following algorithm: they are not considered as
1-hop neighbors (hence not used as MPRs).
o Because link sensing is performed by interface, the local network
topology is best described in terms of links: hence the algorithm
is considering 1-hop neighbor OLSRv2 interfaces, and 2-hop
neighbor OLSRv2 interfaces (and their addresses). Additionally,
asymmetric links are ignored. This is reflected in the
definitions below.
o MPR computation is performed on each interface of the node: on
each interface I, the node MUST select some neighbor interfaces,
so that all 2-hop neighbor interfaces are reached.
From now on, MPR calculation will be described for one interface I on
the node, and the following terminology will be used in describing
the heuristics:
neighbor interface (of I) - An OLSRv2 interface of a 1-hop neighbor
to which there exist a symmetric link using interface I.
N - the set of such neighbor interfaces
2-hop neighbor interface (of I) An interface of a symmetric strict
2-hop neighbor which can be reached from a neighbor interface for
I.
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N2 - the set of such 2-hop neighbor interfaces
D(y): - the degree of a 1-hop neighbor interface y (where y is a
member of N), is defined as the number of symmetric neighbor
interfaces of node y which are in N2
MPR Set - the set of the neighbor interfaces selected as MPRs.
The proposed heuristic selects iteratively some interfaces from N as
MPRs in order to cover 2-hop neighbor interfaces from N2, as follows:
1. Start with an MPR Set made of all members of N with L_willingness
equal to WILL_ALWAYS
2. Calculate D(y), where y is a member of N, for all interfaces in
N.
3. Add to the MPR Set those interfaces in N, which are the *only*
nodes to provide reachability to an interface in N2. For
example, if interface B in N2 can be reached only through a
symmetric link to interface A in N, then add interface B to the
MPR Set. Remove the interfaces from N2 which are now covered by a
interface in the MPR Set.
4. While there exist interfaces in N2 which are not covered by at
least one interface in the MPR Set:
1. For each interface in N, calculate the reachability, i.e.,
the number of interfaces in N2 which are not yet covered by
at least one node in the MPR Set, and which are reachable
through this neighbor interface;
2. Select as an MPR the interface with highest L_willingness
among the interfaces in N with non-zero reachability. In
case of multiple choice select the interface which provides
reachability to the maximum number of interfaces in N2. In
case of multiple interfaces providing the same amount of
reachability, select the interface as MPR whose D(y) is
greater. Remove the interfaces from N2 which are now covered
by an interface in the MPR Set.
Other algorithms, as well as improvements over this algorithm, are
possible. For example:
o Assume that in a multiple interface scenario there exists more
than one link between nodes 'a' and 'b'. If node 'a' has selected
node 'b' as MPR for one of its interfaces, then node 'b' can be
selected as MPR with minimal performance loss by any other
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interfaces on node 'a'.
o In a multiple interface scenario MPRs are selected for each
interface of the selecting node, providing full coverage of all
2-hop nodes accessible through that interface. The overall MPR
Set is then the union of these sets. These sets do not however
have to be selected independently, if a node is selected as an MPR
for one interface it may be automatically added to the MPR
selection for other interfaces.
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Appendix B. Heuristics for Generating Control Traffic
A node creates HELLO messages and TC messages as specified in
Section 7 and Section 9, the former being a modification of the
specification in [4]. The heuristics for creation of HELLO messages
in [4] remain applicable, with the division of the address TLVs with
Type == LINK_STATUS and Value == SYMMETRIC into separate ranges with
and without an associated TLV with Type == MPR. The heuristics for
collection of addresses are also generally applicable to TC messages,
excepting that the first address block is not sorted as the Local
Interface Block of a HELLO message is, and that other addresses
recorded in TC messages are divided into those with and without a TLV
with Type == GATEWAY. These should be ordered so that the range of
addresses without that TLV is continuous (and it is suggested that
the range without is also continuous).
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Appendix C. Protocol and Port Number
Packets in OLSRv2 are communicated using UDP. Port 698 has been
assigned by IANA for exclusive usage by the OLSR (v1 and v2)
protocol.
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Appendix D. Packet and Message Layout
This section specifies the translation from the abstract descriptions
of packets employed in the protocol specification, and the bit-layout
packets actually exchanged between the nodes.
Appendix D.1. OLSRv2 Packet Format
The basic layout of an OLSRv2 packet is as described in [3]. However
the following points should be noted.
OLSRv2 uses only packets with a packet header including a packet
sequence number, either with or without a packet TLV block. Thus all
OLSRv2 packets have the layout of either
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0| Reserved |0|0| Packet Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Message + Padding |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
: ... :
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Message + Padding |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
or
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0| Reserved |1|0| Packet Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Packet TLV Block |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Message + Padding |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
: ... :
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Message + Padding |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The reserved bits marked Resv SHOULD be cleared ('0'). The octets
indicated as Padding are optional and MAY be omitted; if not omitted
they SHOULD be used to pad to a 32 bit boundary and MUST all be zero.
OLSRv2 uses only messages with a complete message header. Thus all
OLSRv2 messages, plus padding if any, have the following layout.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Type | Resv |N|0|0| Message Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hop Limit | Hop Count | Message Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Message Body |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The reserved bits marked Resv SHOULD be cleared ('0'). In standard
OLSRv2 messages (HELLO and TC) the type dependent sequence number bit
marked N SHOULD also be cleared ('0').
The layouts of the message body, address block, TLV block and TLV are
as in [3], allowing all options. Standard (HELLO and TC) messages
contain a first address block which contains local interface address
information, all other address blocks contain neighbor interface
address information (or for a TC message address information for
which it is a gateway) specific to the message type.
An example HELLO message, using IPv4 (four octet) addresses is as
follows. The overall message length is 56 octets (it does not need
padding). The message has a hop limit of 1 and a hop count of 0, as
sent by its originator.
The message has a message TLV block with content length 12 octets
containing three message TLVs. These TLVs represent message validity
time, message interval time and willingness. Each uses a TLV with
semantics value 4, indicating no start and stop indexes are included,
and each has a value length of 1 octet.
The first address block contains a 1 local interface address, with
head length 4. This is equal to the address length, thus no tail or
mid sections of the address are included. This address block has no
TLVs (the TLV block content length is 0 octets).
The second, and last, address block reports 4 neighbor interface
addresses, with address head length 3 octets, and no tail octet (zero
tail length). Thus each mid address section is of length one octet.
The following address TLV block (content length 11 octets) includes
two TLVs.
The first of these TLVs reports the link status of all four neighbors
in a single multivalue TLV, the first two addresses are HEARD, the
last two addresses are SYMMETRIC. The TLV semantics value of 12
indicates, in addition to that this is a multivalue TLV, that no
start index and stop index are included, hence values for all
addresses are included. The TLV value length of 4 octets indicates
one octet per value per address.
The second of these TLV indicates that the last address (start index
3, stop index 3) is an MPR. This TLV has no value, or value length,
fields, as indicated by its semantics octet being equal to 1.
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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 1 0 0 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 1 0 0| VALIDITY_TIME |0 0 0 0 0 1 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 1| Value | INTERVAL_TIME |0 0 0 0 0 1 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 1| Value | WILLINGNESS |0 0 0 0 0 1 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 1| Value |0 0 0 0 0 0 0 1|0 0 0 0 0 1 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Head |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|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 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Head | Mid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mid | Mid | Mid |0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 1 0 1 1| LINK_STATUS |0 0 0 0 1 1 0 0|0 0 0 0 0 1 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HEARD | HEARD | SYMMETRIC | SYMMETRIC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPR |0 0 0 0 0 0 0 1|0 0 0 0 0 0 1 1|0 0 0 0 0 0 1 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An example TC message, using IPv4 (four octet) addresses, is as
follows. The overall message length is 64 octets, it also does not
need padding.
The message has a message TLV block with content length 13 octets
containing three TLVs. The first TLV is a content sequence number
TLV used to carry the 2 octet ANSN. The semantics value is 4
indicating that no index fields are included. The other two TLVs are
validity and interval times as for the HELLO message above.
The message has three address blocks. The first address block
contains 3 local interface addresses (with common head length 2
octets) and has a TLV block with content length 0 octets.
The other two address blocks contain neighbor interface addresses.
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The first contains 3 addresses and has an empty TLV block (content
length 0 octets). The second contains 1 address. The head octet
(hex 82) indicates a head length of two octets and the presence of a
tail octet. The tail octet (hex 82) indicates a tail length of two
octets, all zero bits and not included. The following TLV block
(content length 6 octets) includes two TLVs, the first (semantics
value 4 indicating no indexes are needed) indicates that the address
has a netmask, with length given by the value (of length 1 octet) of
16. Thus this address is Head.0.0/16. The second TLV indicates that
the originating node is a gateway to this network, the TLV semantics
value of 5 indicates that neither indexes nor value are needed.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TC |0 0 0 0 0 0 0 0|0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hop Limit | Hop Count | Message Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 1| CONT_SEQ_NUM |0 0 0 0 0 1 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 1 0| Value (ANSN) | VALIDITY_TIME |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 1 0 0|0 0 0 0 0 0 0 1| Value | INTERVAL_TIME |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 1 0 0|0 0 0 0 0 0 0 1| Value |0 0 0 0 0 0 1 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 1 0| Head | Mid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mid (cont) | Mid | Mid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mid (cont) |0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0|0 0 0 0 0 0 1 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 1 0| Head | Mid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mid (cont) | Mid | Mid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mid (cont) |0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0|0 0 0 0 0 0 0 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 0 0 0 0 0 1 0| Head |1 0 0 0 0 0 1 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0| PREFIX_LENGTH |0 0 0 0 0 1 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 1|0 0 0 1 0 0 0 0| GATEWAY |0 0 0 0 0 1 0 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Appendix E. Node Configuration
OLSRv2 does not make any assumption about node addresses, other than
that each node is assumed to have at least one a unique and routable
IP address for each interface that it has which participates in the
MANET.
When applicable, a recommended way of connecting an OLSRv2 network to
an existing IP routing domain is to assign an IP prefix (under the
authority of the nodes/gateways connecting the MANET with the routing
domain) exclusively to the OLSRv2 area, and to configure the gateways
statically to advertise routes to that IP sequence to nodes in the
existing routing domain.
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Appendix F. Jitter
In a wireless network, simultaneous packet transmission by nearby
nodes is undesirable as, depending on the medium access control and
other lower layer mechanisms, the interference between these messages
may cause at best increased delay, and at worst complete packet loss
by both nodes. This is often particularly true when using a
broadcast mechanism, such as is used by OLSRv2 packets.
The problems of simultaneous packet transmission in OLSRv2 are
increased by the following features of the protocol:
o If two nodes send packets containing regularly scheduled messages
of the same type at the same time, then if, as is typical, they
are using the same message interval, further transmissions of
these messages will also be at the same time, and will also
interfere. This node synchronization could even result in
complete operational failure of these nodes.
o OLSRv2 allows nodes to respond to changes in their circumstances,
usually changes in the neighborhood, with immediate messages of
appropriate types. Nearby nodes will have overlapping
neighborhoods, and may respond to the same change in
circumstances. For example a single link failure can result in a
node having to change its MPR Set, and then two or more of its
neighbors having changed MPR status responding simultaneously with
revised TC messages, whose packets may interfere.
o When a node sends such a responsive message, there is no apparent
reason why it should not restart its message schedule of the
appropriate type of message. This results in nodes responding to
the same change not just sending single simultaneous packets, but
becoming synchronized.
o Nodes also forward messages they receive from other nodes. Two
nearby nodes will thus commonly receive and forward the same
message. The consequent packet transmissions can easily interfere
with each other.
Because interference can easily occur, is self-reinforcing, and is
anything from undesirable to catastrophic, mechanisms to minimize it,
and to break synchronization of nodes, SHOULD be used in OLSRv2.
These all make a deliberate adjustment to the timing, known as
"jitter". Three cases exist:
o When a node generates a control message periodically, it would
normally wait for a delay equal to MESSAGE_INTERVAL (e.g.
HELLO_INTERVAL for HELLO messages or TC_INTERVAL for TC messages)
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between two transmissions of messages of that type. This delay
SHOULD be mitigated by subtracting a jitter time, so that the
delay between consecutive transmissions of a messages of the same
type SHOULD be equal to MESSAGE_INTERVAL - jitter, where jitter is
a random value whose generation is discussed below. Note that
this is a deliberately asymmetric process. It ensures that the
message interval does not exceed MESSAGE_INTERVAL (which leaves
MESSAGE_INTERVAL an appropriate value for reporting in an
INTERVAL_TIME message TLV) and also allows different nodes to
become completely desynchronized as each interval is based on the
previous actual transmission time, not on a fixed clock of period
MESSAGE_INTERVAL.
o When a node responds to an externally triggered change in
circumstances, it SHOULD delay the transmission of a message in
response by a random jitter time. It MAY restart its schedule of
messages of the appropriate type based on that new time. If such
a message is delayed due to the need to respect the appropriate
MESSAGE_MIN_INTERVAL (e.g. HELLO_MIN_INTERVAL for HELLO messages
or TC_MIN_INTERVAL for TC messages) then the node MAY reduce this
minimum interval by a jitter time as the normal message interval
is reduced (thus allowing MESSAGE_MIN_INTERVAL to equal
MESSAGE_INTERVAL even when using jitter).
o When a node forwards a message, it SHOULD delay the message
retransmission by a random jitter time.
In the first and second cases above, the maximum jitter time may be
specified by a parameter MAXJITTER. It is necessary only that this
be significantly less than each MESSAGE_INTERVAL, and less than each
MESSAGE_MIN_INTERVAL. Normally the actual value of the jitter
(reduction in message interval or delay of responsive message) SHOULD
be uniformly generated in the interval 0 <= jitter <= MAXJITTER,
however this may be modified as indicated below.
In the third case above, a message SHOULD be delayed by a jitter
value which is significantly less than the originating node's message
interval. This MAY be available in an INTERVAL_TIME message TLV in
the message to be forwarded. If not so available, a node MAY
estimate an acceptable maximum jitter by any other means available to
it, which may be by use of its own MAXJITTER parameter for as long as
this works. In a network in which this is likely to be unsuccessful,
nodes SHOULD include an INTERVAL_TIME message TLV in messages which
are to be forwarded.
In all cases, as well as constraints imposed by message intervals and
message minimum intervals, the maximum jitter delay SHOULD only be as
large as is required to achieve the required objective of minimizing
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interference due to synchronization. This is because all jitter, and
forwarding jitter in particular, is undesirable for otherwise ideal
functioning of the network.
Because of differing parameters, or due to responsive messages with a
small minimum message interval, a node may receive a message from an
originating node while still waiting to forward an earlier message of
the same type originating from the same node. The forwarding node
SHOULD NOT allow forwarding jitter delay to reorder these messages.
A node MAY discard the earlier message, transmitting the later
message no later than the earlier message was due to be
retransmitted, if, and only if, it can guarantee that this will not
have any adverse effect.
OLSRv2 messages are transmitted in potentially multi-message packets.
Whilst a packet is a hop by hop construct and it is the messages in
it which are forwarded, if a number of messages are received in the
same packet, they SHOULD (if their maximum jitter delays are
compatible) be permitted to be forwarded in the same new packet.
This may be accomplished by generating the same random delay for all
messages received in a single packet. Furthermore, the opportunity
to combine messages to be forwarded from different sources, and
locally generated messages in a single packet SHOULD be allowed even
when this means adjusting (forwards or backwards) the strictly
uniformly generated random jitter times, however these SHOULD NOT be
allowed to exceed their maximum value, nor allow a message interval
to be exceeded, nor compromise the purpose of jitter. (It is for
this reason that messages in the same packet should be given the same
random jitter, as giving them independent jitter values but then, for
example, allowing all to be sent with the earliest would reduce the
mean jitter delay.)
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Appendix G. Security Considerations
Currently, OLSRv2 does not specify any special security measures. As
a proactive routing protocol, OLSRv2 makes a target for various
attacks. The various possible vulnerabilities are discussed in this
section.
Appendix G.1. Confidentiality
Being a proactive protocol, OLSRv2 periodically diffuses topological
information. Hence, if used in an unprotected wireless network, the
network topology is revealed to anyone who listens to OLSRv2 control
messages.
In situations where the confidentiality of the network topology is of
importance, regular cryptographic techniques, such as exchange of
OLSRv2 control traffic messages encrypted by PGP [5] or encrypted by
some shared secret key, can be applied to ensure that control traffic
can be read and interpreted by only those authorized to do so.
Appendix G.2. Integrity
In OLSRv2, each node is injecting topological information into the
network through transmitting HELLO messages and, for some nodes, TC
messages. If some nodes for some reason, malicious or malfunction,
inject invalid control traffic, network integrity may be compromised.
Therefore, message authentication is recommended.
Different such situations may occur, for instance:
1. a node generates TC messages, advertising links to non-neighbor
nodes;
2. a node generates TC messages, pretending to be another node;
3. a node generates HELLO messages, advertising non-neighbor nodes;
4. a node generates HELLO messages, pretending to be another node;
5. a node forwards altered control messages;
6. a node does not forward control messages;
7. a node does not select multipoint relays correctly;
8. a node forwards broadcast control messages unaltered, but does
not forward unicast data traffic;
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9. a node "replays" previously recorded control traffic from another
node.
Authentication of the originator node for control messages (for
situations 2, 4 and 5) and on the individual links announced in the
control messages (for situations 1 and 3) may be used as a
countermeasure. However to prevent nodes from repeating old (and
correctly authenticated) information (situation 9) temporal
information is required, allowing a node to positively identify such
delayed messages.
In general, digital signatures and other required security
information may be transmitted as a separate OLSRv2 message type,
thereby allowing that "secured" and "unsecured" nodes can coexist in
the same network, if desired, or signatures and security information
may be transmitted within the OLSRv2 HELLO and TC messages, using the
TLV mechanism.
Specifically, the authenticity of entire OLSRv2 control messages can
be established through employing IPsec authentication headers,
whereas authenticity of individual links (situations 1 and 3) require
additional security information to be distributed.
An important consideration is, that all control messages in OLSRv2
are transmitted either to all nodes in the neighborhood (HELLO
messages) or broadcast to all nodes in the network (TC messages).
For example, a control message in OLSRv2 is always a point-to-
multipoint transmission. It is therefore important that the
authentication mechanism employed permits that any receiving node can
validate the authenticity of a message. As an analogy, given a block
of text, signed by a PGP private key, then anyone with the
corresponding public key can verify the authenticity of the text.
Appendix G.3. Interaction with External Routing Domains
OLSRv2 does, through the use of TC messages, provide a basic
mechanism for injecting external routing information to the OLSRv2
domain. Appendix E also specifies that routing information can be
extracted from the topology table or the routing table of OLSRv2 and,
potentially, injected into an external domain if the routing protocol
governing that domain permits.
Other than as described in Appendix E, when operating nodes,
connecting OLSRv2 to an external routing domain, care MUST be taken
not to allow potentially insecure and untrustworthy information to be
injected from the OLSRv2 domain to external routing domains. Care
MUST be taken to validate the correctness of information prior to it
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being injected as to avoid polluting routing tables with invalid
information.
A recommended way of extending connectivity from an existing routing
domain to an OLSRv2 routed MANET is to assign an IP prefix (under the
authority of the nodes/gateways connecting the MANET with the exiting
routing domain) exclusively to the OLSRv2 MANET area, and to
configure the gateways statically to advertise routes to that IP
sequence to nodes in the existing routing domain.
Appendix G.4. Node Identity
OLSRv2 does not make any assumption about node addresses, other than
that each node is assumed to have at least one a unique and routable
IP address for each interface that it has which participates in the
MANET.
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Appendix H. Flow and Congestion Control
TBD
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Appendix I. Contributors
This specification is the result of the joint efforts of the
following contributors -- listed alphabetically.
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 Satoh Hiroki, Hitachi SDL, Japan, <h-satoh@sdl.hitachi.co.jp>
o Philippe Jacquet, INRIA, France, <Philippe.Jacquet@inria.fr>
o Monden Kazuya, Hitachi SDL, Japan, <monden@sdl.hitachi.co.jp>
o Kenichi Mase, Niigata University, Japan, <mase@ie.niigata-u.ac.jp>
o Ryuji Wakikawa, KEIO University, Japan, <ryuji@sfc.wide.ad.jp>
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Appendix J. Acknowledgements
The authors would like to acknowledge the team behind OLSRv1,
specified in RFC3626, including Anis Laouiti, Pascale Minet, Laurent
Viennot (all at INRIA, France), and Amir Qayuum (Center for Advanced
Research in Engineering, Pakistan) 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: Li Li (CRC), Louise Lamont (CRC),
Joe Macker (NRL), Alan Cullen (BAE Systems), Philippe Jacquet
(INRIA), Khaldoun Al Agha (LRI), Richard Ogier (SRI), Song-Yean Cho
(Samsung Software Center), Shubhranshu Singh (Samsung AIT) 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/
Philippe Jacquet
Project Hipercom, INRIA
Phone: +33 1 3963 5263
Email: philippe.jacquet@inria.fr
URI: http://hipercom.inria.fr/test/Jacquet.htm
The OLSRv2 Design Team
MANET Working Group
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