Mobile Ad hoc Networking (MANET) T. Clausen
Internet-Draft LIX, Ecole Polytechnique, France
Expires: September 7, 2006 C. Dearlove
BAE Systems Advanced Technology
Centre
The OLSRv2 Design Team
MANET Working Group
March 6, 2006
The Optimized Link-State Routing Protocol version 2
draft-ietf-manet-olsrv2-01
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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 is an
optimization of the classical link state algorithm tailored to the
requirements of a mobile wireless LAN.
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The key optimization of OLSRv2 is that of multipoint relays,
providing an efficient mechanism for network-wide broadcast of link-
state information. A secondary optimization is, that OLSRv2 employs
partial link-state information: each node maintains information of
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 broadcasts) and that these advertisements
contain only a subset of links (i.e. reduces the size of each
network-wide broadcast). The partial link-state information thus
obtained 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 . . . . . . . . . . . . . . . . . 7
2. Protocol Overview and Functioning . . . . . . . . . . . . . . 9
2.1 Protocol Extensibility . . . . . . . . . . . . . . . . . . 11
3. Processing and Forwarding Repositories . . . . . . . . . . . . 13
3.1 Received Message Set . . . . . . . . . . . . . . . . . . . 13
3.2 Fragment Set . . . . . . . . . . . . . . . . . . . . . . . 13
3.3 Processed Set . . . . . . . . . . . . . . . . . . . . . . 14
3.4 Forwarded Set . . . . . . . . . . . . . . . . . . . . . . 14
3.5 Relay Set . . . . . . . . . . . . . . . . . . . . . . . . 14
4. Packet Processing and Message Forwarding . . . . . . . . . . . 16
4.1 Actions when Receiving an OLSRv2 Packet . . . . . . . . . 16
4.2 Actions when Receiving an OLSRv2 Message . . . . . . . . . 16
4.3 Message Considered for Processing . . . . . . . . . . . . 16
4.4 Message Considered for Forwarding . . . . . . . . . . . . 18
5. Information Repositories . . . . . . . . . . . . . . . . . . . 21
5.1 Neighborhood Information Base . . . . . . . . . . . . . . 21
5.1.1 Link Set . . . . . . . . . . . . . . . . . . . . . . . 21
5.1.2 2-Hop Neighbor Set . . . . . . . . . . . . . . . . . . 22
5.1.3 Neighborhood Address Association Set . . . . . . . . . 23
5.1.4 MPR Set . . . . . . . . . . . . . . . . . . . . . . . 23
5.1.5 MPR Selector Set . . . . . . . . . . . . . . . . . . . 23
5.1.6 Advertised Neighbor Set . . . . . . . . . . . . . . . 23
5.2 Topology Information Base . . . . . . . . . . . . . . . . 24
5.2.1 Topology Set . . . . . . . . . . . . . . . . . . . . . 24
5.2.2 Attached Network Set . . . . . . . . . . . . . . . . . 24
5.2.3 Routing Set . . . . . . . . . . . . . . . . . . . . . 25
6. OLSRv2 Control Message Structures . . . . . . . . . . . . . . 26
6.1 General OLSRv2 Message TLVs . . . . . . . . . . . . . . . 26
6.1.1 VALIDITY_TIME TLV . . . . . . . . . . . . . . . . . . 26
6.1.2 INTERVAL_TIME TLV . . . . . . . . . . . . . . . . . . 27
6.2 Local Interface Blocks . . . . . . . . . . . . . . . . . . 28
6.3 HELLO Messages . . . . . . . . . . . . . . . . . . . . . . 28
6.3.1 HELLO Message: Message TLVs . . . . . . . . . . . . . 29
6.3.2 HELLO Message: Address Blocks TLVs . . . . . . . . . . 29
6.4 TC Messages . . . . . . . . . . . . . . . . . . . . . . . 30
7. HELLO Message Generation . . . . . . . . . . . . . . . . . . . 31
7.1 HELLO Message: Transmission . . . . . . . . . . . . . . . 33
8. HELLO Message Processing . . . . . . . . . . . . . . . . . . . 34
8.1 Populating the Link Set . . . . . . . . . . . . . . . . . 34
8.2 Populating the 2-Hop Neighbor Set . . . . . . . . . . . . 36
8.3 Populating the MPR Selector Set . . . . . . . . . . . . . 37
8.4 Neighborhood and 2-Hop Neighborhood Changes . . . . . . . 38
9. TC Message Generation . . . . . . . . . . . . . . . . . . . . 40
9.1 TC Message: Transmission . . . . . . . . . . . . . . . . . 41
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10. TC Message Processing . . . . . . . . . . . . . . . . . . . 42
10.1 Checking Freshness & Validity of a TC message . . . . . . 42
10.2 Updating the Topology Set . . . . . . . . . . . . . . . . 43
10.3 Purging Old Entries from the Topology Set . . . . . . . . 44
10.4 Updating the Attached Networks Set . . . . . . . . . . . . 44
10.5 Purging Old Entries from the Attached Network Set . . . . 45
10.6 Processing Unfragmented TC Messages . . . . . . . . . . . 45
10.7 Processing Partially or Wholly Self-Contained
Fragmented TC Messagess . . . . . . . . . . . . . . . . . 45
11. Populating the MPR Set . . . . . . . . . . . . . . . . . . . 47
12. Populating Derived Sets . . . . . . . . . . . . . . . . . . 48
12.1 Populating the Relay Set . . . . . . . . . . . . . . . . . 48
12.2 Populating the Advertised Neighbor Set . . . . . . . . . . 48
13. Populating the Neighborhood Address Association Set . . . . 49
14. Routing Table Calculation . . . . . . . . . . . . . . . . . 50
15. Proposed Values for Constants . . . . . . . . . . . . . . . 53
15.1 Message Intervals . . . . . . . . . . . . . . . . . . . . 53
15.2 Holding Times . . . . . . . . . . . . . . . . . . . . . . 53
15.3 Willingness . . . . . . . . . . . . . . . . . . . . . . . 53
15.4 Time . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
16. Representing Time . . . . . . . . . . . . . . . . . . . . . 55
17. IANA Considerations . . . . . . . . . . . . . . . . . . . . 56
17.1 Multicast Addresses . . . . . . . . . . . . . . . . . . . 56
17.2 Message Types . . . . . . . . . . . . . . . . . . . . . . 56
17.3 TLV Types . . . . . . . . . . . . . . . . . . . . . . . . 56
18. References . . . . . . . . . . . . . . . . . . . . . . . . . 57
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 58
A. Example Heuristic for Calculating MPRs . . . . . . . . . . . . 59
B. Example Algorithms for Generating Control Traffic . . . . . . 62
B.1 Example Algorithm for Generating HELLO messages . . . . . 62
B.2 Example Algorithm for Generating TC messages . . . . . . . 63
C. Protocol and Port Number . . . . . . . . . . . . . . . . . . . 65
D. Packet and Message Layout . . . . . . . . . . . . . . . . . . 66
D.1 OLSRv2 Packet Format . . . . . . . . . . . . . . . . . . . 66
E. Node Configuration . . . . . . . . . . . . . . . . . . . . . . 73
F. Security Considerations . . . . . . . . . . . . . . . . . . . 74
F.1 Confidentiality . . . . . . . . . . . . . . . . . . . . . 74
F.2 Integrity . . . . . . . . . . . . . . . . . . . . . . . . 74
F.3 Interaction with External Routing Domains . . . . . . . . 75
F.4 Node Identity . . . . . . . . . . . . . . . . . . . . . . 76
G. Flow and Congestion Control . . . . . . . . . . . . . . . . . 77
H. Sequence Numbers . . . . . . . . . . . . . . . . . . . . . . . 78
I. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 79
J. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 80
Intellectual Property and Copyright Statements . . . . . . . . 81
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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 accomodate 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).
In OLSRv2, 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
the route 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
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from HIPERLAN (a MAC layer protocol) which is standardized by ETSI
[5].
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].
Additionally, this document uses the following terminology:
node - a MANET router which implements the Optimized Link State
Routing protocol as specified in this document.
OLSRv2 interface - A network device participating in a MANET running
OLSRv2. A node may have several OLSRv2 interfaces, each interface
assigned one or more IP addresses.
neighbor - A node X is a neighbor of node Y if node Y can hear node X
(i.e., a link exists from an OLSRv2 interface on node X to an
OLSRv2 interface on node Y). A neighbor may also be called a
1-hop neighbor.
2-hop neighbor - A node X is a 2-hop neighbor of node Y if node X is
a neighbor of a neighbor of node Y, but is not node Y itself.
strict 2-hop neighbor - a 2-hop neighbor which is not a neighbor of
the node, and is not a 2-hop neighbor only through a neighbor with
willingness WILL_NEVER.
multipoint relay (MPR) - A node which is selected by its 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 time to live field of the message is
greater than one.
multipoint relay selector (MPR selector, MS) - A node which has
selected its 1-hop neighbor, node X, as one of its multipoint
relays, will be called an MPR selector of node X.
link - A link is a pair of OLSRv2 interfaces from two different
nodes, where at least one interface is able to hear (i.e. receive
traffic from) the other.
symmetric link - A link where both interfaces are able to hear (i.e.
receive messages from) the other.
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asymmetric link - A link which is not symmetric.
symmetric 1-hop neighborhood - The symmetric 1-hop neighborhood of
any node X is the set of nodes which have at least one symmetric
link to node X.
symmetric 2-hop neighborhood - The symmetric 2-hop neighborhood of
node X is the set of nodes, excluding node X itself, which have a
symmetric link to the symmetric 1-hop neighborhood of X.
symmetric strict 2-hop neighborhood - The symmetric strict 2-hop
neighborhood of node X is the set of nodes in its symmetric 2-hop
neighborhood that are neither in its symmetric 1-hop neighborhood
nor reachable only through a symmetric 1-hop neighbor of node X
with willingness WILL_NEVER.
1.2 Applicability Statement
OLSRv2 is a proactive routing protocol for mobile ad hoc networks
(MANETs) [6], [7]. 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.
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 continously, 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 independant specification
[4], which is used for carrying OLSRv2 control signals. OLSRv2 is
thereby able to accommodate for extensions via "external" and
"internal" extensibility. External extensibility implies that a
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protocol extension may specify and exchange new message types which
can be forwarded and delivered correctly according to [4]. Internal
extensibility implies, that a protocol extension may define
additional attributes to be carried embedded in the OLSRv2 control
messages, detailed in this specification, while these OLSRv2 control
messages with additional attributes can still be correctly understood
by all OLSRv2 nodes.
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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 will know of all
destinations and a subset of links in the network.
More specifically, OLSRv2 consists of the following main components:
o A general and flexible signaling framework, allowing for
information exchange between OLSRv2 nodes. This framework allows
for both local information exchange (between neighboring nodes)
and global information exchange using an optimized flooding
mechanism denoted "MPR flooding".
o A specification of local signaling, denoted HELLO messages. HELLO
messages in OLSRv2 serve to:
* discover links to adjacent OLSR nodes;
* perform bidirectionality check on the discovered links;
* advertise neighbors and hence discover 2-hop neighbors;
* signal MPR selection.
HELLO messages are emitted periodically, thereby allowing nodes to
continuously track changes in their local neighborhoods.
o A specification of global signaling, denoted TC 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.
* allow nodes with multiple interface addresses to ensure that
nodes within two hops can associate these addresses with a
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single node for efficient MPR Set determination.
TC messages are emitted periodically, thereby allowing nodes to
continuously track global changes in the network.
Thus, through periodic exchange of HELLO messages, a node is able to
acquire and maintain information about its immediate neighborhood.
This includes information about immediate neighbors, as well as nodes
which are two hops away. By HELLO messages being exchanged
periodically, a node learns about changes in the neighborhood (new
nodes emerging, old nodes disappearing) without requiring explicit
mechanisms for doing so.
Based on the local topology information, acquired through the
periodic exchange of HELLO messages, an OLSRv2 node is able 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.
The idea of multipoint relays is to minimize the overhead of flooding
messages in the network by reducing redundant retransmissions in the
same region. Each node in the network selects a set of nodes in its
symmetric 1-hop neighborhood which may retransmit its messages. This
set of selected neighbor nodes is called the "Multipoint Relay" (MPR)
Set of that node. The neighbors of node N which are *NOT* in its MPR
set, receive and process broadcast messages but do not retransmit
broadcast messages received from node N. The MPR Set of a node is
selected such that it covers (in terms of radio range) all symmetric
strict 2-hop nodes. The MPR Set of N, denoted as MPR(N), is then an
arbitrary subset of the symmetric 1-hop neighborhood of N which
satisfies the following condition: every node in the symmetric strict
2-hop neighborhood of N MUST have a symmetric link towards MPR(N).
The smaller a MPR Set, the less control traffic overhead results from
the routing protocol. [7] gives an analysis and example of MPR
selection algorithms. Notice, 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 neighbors that have
selected it as MPR. This set is called the "Multipoint Relay
Selector Set" (MPR Selector Set) of a node. A node obtains this
information from periodic HELLO messages received from the neighbors.
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.
A broadcast message, intended to be diffused in the whole network,
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coming from any of the nodes in the Relay Set of node N is assumed to
be retransmitted by node N, if N has not received it yet. This set
can change over time (e.g., when a node selects another MPR Set) and
is indicated by the selector nodes in their HELLO messages.
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, TC messages, containing the
links between the node and the nodes in the Advertised Neighbor Set,
are not generated, unless needed for gateway reporting or multiple
interface address association (if the latter case only, with minimal
scope).
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 occur frequently in radio networks
due to collisions or other transmission problems.
Also, 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. Furthermore,
OLSRv2 provides support for protocol extensions such as sleep mode
operation, multicast-routing etc. Such extensions may be introduced
as additions to the protocol without breaking backwards compatibility
with earlier versions.
OLSRv2 does not require any changes to the format of IP packets.
Thus any existing IP stack can be used as is: OLSRv2 only interacts
with routing table management. OLSR sends its own control messages
using UDP.
2.1 Protocol Extensibility
This specification defines and uses two OLSRv2 message types, HELLO
and TC. As for OLSRv1 [1] extensions to OLSRv2 may define new
message types to carry additional information. This may be
considered as "external" extensibility. New message types are
divided into two ranges, those which may be added by standards
actions (with types up to 127) and those made available for private/
local use (with types 128 to 255).
All new messages must be syntactically OLSRv2 messages, as defined in
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[4]. (Some additional constraints to that specification are added
for OLSRv2 packets and messages, requiring full packet and message
headers.) Note that if it is required to include one or more blocks
of unstructured data in such a message (possibly as its only content)
this may be achieved by including each block as a single message TLV
block, with an appropriately defined message TLV. (Like message
types, TLV types are divided into those up to 127 which may be added
by standards action, and those from 128 to 255 available for private/
local use.)
A network may contain nodes both aware of, and unaware of, any new
message types. The originator of a message can control whether a
message flooded through the network is forwarded by nodes which are
unaware of the message type, thus reaching all nodes in the network,
or is only flooded by nodes which recognise the message type.
OLSRv2 also supports an alternative, and more powerful, extension
mechanism which was not supported by OLSRv1, that of adding new
information to an already defined message type, whilst still leaving
the predefined information unchanged and usable, including by a node
which does not recognise the new information. This may be considered
to be "internal" extensibility of a message.
The mechanism for this extensibility is the use of TLV (type-length-
value) structures in the message format defined in [4] to carry
information associated with either the message as a whole, or with
one or more addresses carried in the message. The messages defined
in this specification carry two types of addresses, those of the
originating node's own interfaces participating in OLSRv2, and those
of neighbouring nodes or networks to which it has a route. (New
message types may define other relationships to addresses which they
carry.) All information associated with these addresses, or the
message as a whole, in messages defined in this specification is in
TLV format; additional TLVs may be defined and added to these
messages.
Those nodes which do not recognise newly defined TLV types ignore the
added TLVs. (This is facilitated by that the TLVs defined in this
specification, or in [4], have the lowest type numbers and that TLVs
must be included in type order, as specified in [4].) It is
important that newly defined TLV types permit this behaviour.
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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 Message Set
Each node maintains, for each OLSRv2 interface it possesses, a set of
signatures of messages, which have been received over that interface,
in the form of "Received Tuples":
(RX_type, RX_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_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 record expires and *MUST* be
removed.
In a node, this is denoted the "Received Message 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 record 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_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_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 record 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_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_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 record 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_if_addr)
where:
RY_if_addr is the address of a neighbor interface for which the node
SHOULD relay flooded messages.
In a node, this is denoted the "Relay Set".
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4. Packet Processing and Message Forwarding
Upon receiving a basic packet, 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
Upon receiving a packet, a node MUST perform the following task:
1. If the packet contains no messages (i.e. the packet length is
less than or equal to the size of the packet header) or if the
packet cannot be parsed into messages, the packet MUST be
silently discarded.
2. Otherwise, each message in the packet 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 [4], or if the originator
address of the message is an interface address of the receiving
node then the message MUST be silently discarded;
2. Otherwise:
1. If the message is of a known type then the message is
considered for processing according to Section 4.3;
2. If for the received message TTL > 0, and if either the
message is of a known type, or bit 3 of the message semantics
octet in the message header is clear, as indicated in [4],
then the message is considered for forwarding according to
Section 4.4.
4.3 Message Considered for Processing
If a message is considered for processing, the following tasks MUST
be performed:
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1. If an entry exists in the Processed Set where:
* P_type == the message type, or 0 if bit 2 of the message
semantics octet (in the message header) is clear, AND;
* P_addr == the originator address of the message, AND;
* P_seq_number == the sequence number of the message.
then the message MUST NOT be processed.
2. Otherwise:
1. Create an entry in the Processed Set with:
+ P_type = the message type, or 0 if bit 2 of the message
semantics octet (in the message header) is clear;
+ P_addr = originator address of the message;
+ P_seq_number = sequence number of the message;
+ P_time = current time + P_HOLD_TIME.
2. If the message does not contain a message TLV of type
Fragment (or if it does and the indicated number of fragments
is one) then process the message fully according to its type.
3. Otherwise:
1. If the message is "wholly or partially self-contained" as
indicated by its Fragment TLV then process the current
message as far as possible according to its type;
2. If the Fragment Set includes any messages with the same
originator address and content sequence number as the
current message, and either the same fragment number or a
different number of fragments, then remove these messages
are from the Fragment Set;
3. If the Fragment Set includes messages containing all the
remaining fragments of the same overall message as the
current message (i.e. if the number of messages in the
Fragment Set with the same originator address and content
sequence number as the current message is equal to the
current message's number of fragments, less one) then all
of these messages are removed from the Fragment Set and
processed according to their type (taking account of any
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previous processing if any or all were wholly or
partially self-contained);
4. Otherwise, the current message is added to the Fragment
Set with a FG_time of FG_HOLD_TIME (possibly replacing an
identical and previous received instance of the same
fragment of the same content).
4.4 Message Considered for Forwarding
If a message is considered for forwarding then if it is either of a
message type defined in this document, or of an unknown message type
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 there is no symmetric link in the Link Set between the
receiving interface and the sending interface (as indicated by
the source interface of the IP datagram containing the message)
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 bit 2 of the message
semantics octet (in the message header) is clear, AND;
+ RX_addr == the originator address of the received message,
AND;
+ 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:
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- RX_type = the message type, or 0 if bit 2 of the
message semantics octet (in the message header) is
clear;
- RX_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 bit 2 of the
message semantics octet (in the message header) is
clear;
- FW_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 an entry exists in the Relay Set, where
RY_if_addr == source address of the message (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 bit 2 of the
message semantics octet (in the message header) is
clear;
o FW_addr = originator address of the message;
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 the message TTL by 1;
o Increment the message hop count by 1;
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3. Transmit the message on all OLSRv2 interfaces of the
node.
Messages are retransmitted in the format specified by [4] with the
All-OLSRv2-Multicast address (see Section 17.1) 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
maintains a number of protocol sets, the information repository of
the protocol. These sets are updated, directly or indirectly, by the
exchange of messages between nodes in the network. In turn the
contents of these messages are largely determined by the contents of
a part of the information repositories, the Neighbourhood Information
Base, which contains information about the 1- and 2- hop
neighbourhoods of the node. The remaining part of the information
repository, the Topology Information Base (including the Routing Set)
contains information about the network which is not constrained to
the node's neighbourhood. The Topology Information Base is updated
by the OLSRv2 messages defined in this document, it is not used to
define their contents. The process of information exchange which
leads to the population of the Neighbourhood Information Base and the
Topology Information Base is started using only the node's own OLSRv2
interface addresses and host and network associated addresses. These
are not affected by the exchange of the OLSRv2 messages defined in
this document.
5.1 Neighborhood Information Base
The neighborhood information base stores information about links
between local interfaces and interfaces on adjacent nodes.
5.1.1 Link Set
A node records a set of "Link Tuples":
(L_local_iface_addr, L_neighbor_iface_addr,
L_SYM_time, L_ASYM_time, L_willingness, L_time).
where:
L_local_iface_addr is the interface address of the local node;
L_neighbor_iface_addr is the interface address of the neighbor node;
L_SYM_time is the time until which the link is considered symmetric;
L_ASYM_time is the time until which the neighbor interface is
considered heard;
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L_willingness is the nodes willingness to be selected as MPR;
L_time specifies when this record expires and *MUST* be removed.
+-------------+-------------+--------------+
| L_SYM_time | L_ASYM_time | L_STATUS |
+-------------+-------------+--------------+
| Expired | Expired | LOST |
| | | |
| Not Expired | Expired | SYMMETRIC |
| | | |
| Not Expired | Not Expired | SYMMETRIC |
| | | |
| Expired | Not Expired | ASYMMETRIC |
+-------------+-------------+--------------+
Table 1
The status of the link, denoted L_STATUS, can be derived based on the
fields L_SYM_time and L_ASYM_time as defined in Table 1.
In a node, the set of Link Tuples is denoted the "Link Set".
5.1.2 2-Hop Neighbor Set
A node records a set of "2-Hop Neighbor Tuples"
(N2_local_iface_addr, N2_neighbor_iface_addr, N2_2hop_iface_addr, N2_time)
describing symmetric links between its neighbors and the symmetric
2-hop neighborhood.
N2_local_iface_addr is the address of the local interface over which
the information was received;
N2_neighbor_iface_addr is the interface address of a neighbor;
N2_2hop_iface_addr is the interface address of a 2-hop neighbor with
a symmetric link to the node with interface address
N_neighbor_iface_addr;
N2_time specifies the time at which the tuple expires and *MUST* be
removed.
In a node, the set of 2-Hop Neighbor Tuples is denoted the "2-Hop
Neighbor Set".
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5.1.3 Neighborhood Address Association Set
A node maintains, for each 1-hop and 2-hop neighbor with multiple
addresses participating in the OLSRv2 network, a "Neighborhood
Address Association Tuple", representing that "these addresses belong
to the same node".
(NA_neighbor_addr_list, NA_time)
NA_neighbor_iface_addr_list is the list of interface addresses of the
1-hop or 2-hop neighbor node;
NA_time specifies the time at which the tuple expires and *MUST* be
removed.
In a node, the set of Neighborhood Address Association Tuples is
denoted the "Neighborhood Address Association Set".
5.1.4 MPR Set
A node maintains a set of neighbors which are selected as MPRs.
Their interface addresses are listed in the MPR Set.
5.1.5 MPR Selector Set
A node maintains, for each interface of an 1-hop neighbor which has
selected it as MPR, an "MPR Selector Tuple", representing the an
interface of the neighbor node which have selected it as an MPR.
(MS_neighbor_if_addr, MS_time)
MS_neighbor_if_addr specifies the interface address of a 1-hop
neighbor, which has selected the node as MPR;
MS_time specifies the time at which the tuple expires and *MUST* be
removed.
Notice that if a MPR selector node has multiple interface addresses,
the MPR Selector Set will contain one tuple for each interface
address of the MPR selector.
5.1.6 Advertised Neighbor Set
A node maintains a set of neighbor interface addresses, 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 (ASSN) is
maintained. Each time the Advertised Neighbor Set is updated, the
ASSN MUST be incremented.
5.2 Topology Information Base
The Topology Information Base stores topological information
describing the network beyond the nodes neighborhood (i.e. beyond the
Neighborhood Information Base of the node).
5.2.1 Topology Set
Each node in the network maintains topology information about the
network.
For each destination in the network, at least one "Topology Tuple"
(T_dest_iface_addr, T_last_iface_addr, T_seq, T_time)
is recorded.
T_dest_iface_addr is the interface address of a node, which may be
reached in one hop from the node with the interface address
T_last_iface_addr;
T_last_iface_addr is, conversely, the last hop towards
T_dest_iface_addr. Typically, T_last_iface_addr is a MPR of
T_dest_iface_addr;
T_seq is a sequence number, and
T_time specifies the time at which this tuple expires and *MUST* be
removed.
In a node, the set of Topology Tuples are denoted the "Topology Set".
5.2.2 Attached Network Set
Each node in the network maintains information about attached
networks.
For each attached network, at least one "Attached Network Tuple"
(AN_net_addr, AN_prefix_lenght, AN_gw_addr, AN_seq_no, AN_time)
is recorded.
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AN_net_addr is the network address (prefix) of a network, which may
be reached via the node with the OLSRv2 interface address
AN_gw_addr;
AN_prefix_length is the length of the prefix of the network address
AN_net_addr;
AN_gw_addr is the address of an OLSRv2 interface of a node which can
act as gateway to the network identified by the AD_net_addr/
AD_prefix_length;
AN_seq_no is a sequence number, and;
AN_time specifies the time at which this tuple expires and *MUST* be
removed.
In a node, the set of Topology Tuples are denoted the "Topology Set".
5.2.3 Routing Set
A node records a set of "Routing Tuples":
(R_dest_iface_addr, R_next_iface_addr, R_dist, R_iface_addr)
describing the next hop and distance of the path to each destination
in the network for which a route is known.
R_dest_iface_addr is the interface address of the destination node;
R_next_iface_addr is the interface address of the "next hop" on the
path towards R_dest_iface_addr;
R_dist is the number of hops on the path to R_dest_iface_addr;
R_iface_addr is the address of the local interface over which a
packet MUST be sent to reach R_next_iface_addr.
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 [4].
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 include a <packet-header>.
o All OLSRv2 messages, not limited to those defined in this
document, include a full <msg-header> and hence have bits 0 and 1
of <msg-semantics> cleared.
o All OLSRv2 message defined in this document have all remaining
bits of <msg-semantics> cleared.
Other options defined in [4] may be freely used, in particular any
values of <tlv-semantics> consistent with its specification. An
implementation of OLSRv2 MAY take full advantage of the features of
the message specification in [4] allowing decisions relating to
whether a message should be forwarded and/or processed to be taken
parsing only the message header (plus, if a message is to be
processed but may be fragmented, only the first octets of the message
body).
OLSRv2 messages are sent using UDP, see Appendix C.
The remainder of this section defines, within the framework of [4],
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 message, VALIDITY_TIME and INTERVAL_TIME, detailed in
this section.
6.1.1 VALIDITY_TIME TLV
All OLSRv2 messages specified in this specification MUST include a
VALIDITY_TIME TLV, specifying for how long a node may, upon receiving
a message, consider the message content to be valid. The validity
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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 [4]). Thus, the VALIDITY_TIME TLV contains a sequence of
pairs (time, hop-limit) in increasing hop-limit order, followed by a
default value.
Thus, an instance of a VALIDITY_TIME TLV could have the following
value:
<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; and
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 2.
VALIDITY_TIME message TLV specification overview
+----------------+--------+-------------------+---------------------+
| Name | Type | Length | Value |
+----------------+--------+-------------------+---------------------+
| VALIDITY_TIME | TBD | (2*n+1) * 8 bits | {<time><hoplimit>}* |
| | | | <t_default> |
+----------------+--------+-------------------+---------------------+
Table 2
where <n> is the number of (time, hop_limit) pairs in the TLV, and
where <time> and <t_default> are represented as specified in section
Section 16.
6.1.2 INTERVAL_TIME TLV
OLSRv2 messages of a given type MAY include an INTERVAL_TIME message
TLV, specifying the interval at which messages of this type are being
generated by the originator node.
The INTERVAL_TIME message TLV specification is given in Table 3.
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INTERVAL_TIME TLV specification overview
+----------------+--------+-------------------+---------------------+
| Name | Type | Length | Value |
+----------------+--------+-------------------+---------------------+
| INTERVAL_TIME | TBD | 8 bits | <time> |
+----------------+--------+-------------------+---------------------+
Table 3
where <time> is the time between two successive emissions of messages
of the type, represented as specified in section Section 16.
6.2 Local Interface Blocks
The first address block, plus following TLV block in a HELLO or TC
message is known as a Local Interface Block. A Local Interface Block
is not distinguished in any way other than by being the first address
block in the message.
A Local Interface Block contains the addresses of all of the
interfaces of the originating node that support OLSRv2 and
participate in the MANET, using the standard <address-block> syntax
from [4]. In a TC message this is sufficient; in a HELLO message,
those addresses, if any, which correspond to interfaces other than
that on which the HELLO message is sent must have a corresponding
OTHER_IF TLV. In this case (only) this OTHER_IF TLV SHALL NOT have a
<value> field.
Note that a Local Interface Block may include more than one address
for each interface, and hence in a HELLO message may contain more
than one address without an OTHER_IF TLV.
6.3 HELLO Messages
A HELLO message MUST contain:
o a message TLV VALIDITY_TIME Section 6.1.1
o one or more address blocks with associated address block TLVs
The first (mandatory) address block is a Local Interface Block, as
specified in Section 6.2. Other (optional) address blocks contain
1-hop neighbors' interface addresses.
A HELLO message MAY optionally contain:
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o a message TLV INTERVAL_TIME as specified in Section 6.1.2
o a message TLV WILLINGNESS, as specified in Section 6.3.1
6.3.1 HELLO Message: Message TLVs
In a HELLO message, a node MAY include a message TLV as specified in
Table 4.
VALIDITY_TIME message TLV specification overview
+----------------+--------+-------------------+---------------------+
| Name | Type | Length | Value |
+----------------+--------+-------------------+---------------------+
| WILLINGNESS | TBD | 8 bits | <The node's |
| | | | willingness to be |
| | | | selected as MPR> |
+----------------+--------+-------------------+---------------------+
Table 4
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.
6.3.2 HELLO Message: Address Blocks TLVs
HELLO message address block TLV specification overview
+----------------+--------+-------------------+---------------------+
| Name | Type | Length | Value |
+----------------+--------+-------------------+---------------------+
| LINK_STATUS | TBD | 8 bits | One of HEARD, |
| | | | SYMMETRIC, LOST. |
| | | | |
| MPR | TBD | 0 bits | No value, i.e. |
| | | | novalue bit (see |
| | | | [4]) set |
| | | | |
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| OTHER_IF | TBD | 0 or 8 bits | In a Local |
| | | | Interface Block |
| | | | none, otherwise |
| | | | either of SYMMETRIC |
| | | | or LOST |
+----------------+--------+-------------------+---------------------+
Table 5
6.4 TC Messages
A TC message MUST contain:
o a message TLV VALIDITY_TIME Section 6.1.1
o a message TLV CONTENT_SEQUENCE_NUMBER [4]
o one or more address blocks with associated address block TLVs.
The first (mandatory) address block is a Local Interface Block, as
specified in Section 6.2. Other (optional) address blocks contain
1-hop neighbors' interface addresses and/or host or network addresses
for which this node may act as a gateway. In the latter case they
may use PREFIX_LENGTH TLV(s) as specified in [4].
A TC message MAY optionally contain:
o a message TLV INTERVAL_TIME as specified in Section 6.1.2
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7. HELLO Message Generation
An OLSRv2 HELLO message is composed of a set of message TLVs,
describing general properties of the message and the node emitting
the HELLO, and a set of address blocks (with associated TLV sets),
describing the links and their associated properties.
OLSRv2 HELLO messages are generated and transmitted per interface,
i.e. different HELLO messages are generated and transmitted per
OLSRv2 interface of a node.
OLSRv2 HELLO messages are generated and transmitted periodically,
with a default interval between two consecutive HELLO emissions on
the same interface of HELLO_INTERVAL.
This section specifies the requirements, which HELLO message
generation MUST fulfill. An example algorithm is proposed in
Appendix B.1.
For each OLSRv2 interface a node MUST generate a HELLO message with a
Local Interface Block as the first address block, as specified in
Section 6.2, followed by address blocks and address TLVs according to
Table 6.
+---------------------------+---------------------------------------+
| The set of neighbor | TLV(s) (Type = Value) |
| interfaces which are ... | |
+---------------------------+---------------------------------------+
| HEARD, but not SYMMETRIC | LINK_STATUS=HEARD |
| over the interface over | |
| which the HELLO message | |
| is being transmitted | |
| | |
| SYMMETRIC over the | LINK_STATUS=SYMMETRIC |
| interface over which the | |
| HELLO message is being | |
| transmitted | |
| | |
| LOST over the interface | LINK_STATUS=LOST |
| over which the HELLO | |
| message is being | |
| transmitted | |
| | |
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| Not SYMMETRIC over the | OTHER_IF=SYMMETRIC |
| interface over which the | |
| HELLO message is being | |
| transmitted, but | |
| SYMMETRIC over one or | |
| more other interfaces of | |
| the node | |
| | |
| Not SYMMETRIC over any | OTHER_IF=LOST |
| interface or LOST over | |
| the interface over which | |
| the HELLO message is | |
| being transmitted, but | |
| previously reported as | |
| OTHER_IF=SYMMETRIC and | |
| still HEARD or LOST over | |
| one or more interfaces of | |
| the node other than the | |
| interface over which the | |
| HELLO message is being | |
| transmitted | |
| | |
| Selected as MPR for the | MPR |
| interface over which the | |
| HELLO message is | |
| transmitted | |
+---------------------------+---------------------------------------+
Table 6
In order that an address can be reported as OTHER_IF=LOST by a node
with more than one interface participating in the MANET, such a node
MAY maintain an Other Interface Set of addresses for each interface.
The Other Interface Set for an interface is updated when a HELLO
message is to be transmitted over that interface, and used to
determine which addresses are reported as OTHER_IF=LOST in that
message. The Other Interface Set of addresses is updated and used as
follows:
1. Each address that the HELLO message is to include with a
corresponding TLV with Type=LINK_STATUS and Value=SYMMETRIC is
removed from the set.
2. Each address that the HELLO message is to include with a
corresponding TLV with Type=OTHER_IF and Value=SYMMETRIC is added
to the set if not already present.
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3. Each other address in the set (not included in the HELLO message
with a corresponding TLV with Type=OTHER_IF and Value=SYMMETRIC)
1. Is removed if the HELLO message is to include it with a
corresponding TLV with Type=LINK_STATUS and Value=LOST.
2. Is removed if it is not HEARD or LOST over an interface other
than the interface over which the HELLO message is to be
transmitted.
3. Otherwise is included in the HELLO message with a TLV with
Type=OTHER_IF and Value=LOST. (Note that the address may
also have a corresponding TLV with Type=LINK_STATUS and
Value=HEARD if appropriate.)
7.1 HELLO Message: Transmission
Messages are retransmitted in the packet/message format specified by
[4] with the All-OLSRv2-Multicast address as destination IP address
and with a TTL=1.
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8. HELLO Message Processing
Upon receiving a HELLO message, a node will update its local link
information base according to the specification given in this
section.
For the purpose of this section, please notice the following:
o the "validity time" of a message is calculated from the VALIDITY-
TIME TLV of the message as specified in Section 6.1.1;
o the "Source Address" is the source address as indicated by the
source interface of the IP datagram containing the message;
o a HELLO message MUST neither be forwarded nor be recorded in the
Processing and Forwarding Repositories;
o the address blocks considered exclude the Local Interface Block,
unless explicitly specified;
o a HELLO message is only valid when, for each address listed in the
address blocks:
* the address is associated with a TLV with Type=Link Status OR a
TLV with Type=Other Interface Status OR both, the latter either
when the TLV with Type=Link Status has Value=HEARD, or when the
the TLV with Type=Link Status has Value=LOST and the TLV with
Type=Other Interface Status has Value=SYMMETRIC, AND
* if the address is associated with a TLV with Type=MPR, then it
MUST also be associated with a TLV with Type=Link Status and
Value=SYMMETRIC.
Invalid HELLO messages are not processed.
8.1 Populating the Link Set
Upon receiving a HELLO message, a node SHOULD update its Link Set
with the information contained in the HELLO. Thus, for the Local
Interface Block (see Section 6.2) the Neighbor Address Association
Set is updated as specified by Section 13. For each address, listed
in the subsequent HELLO message address blocks (see Section 6):
1. if there exists no link tuple with:
* L_neighbor_iface_addr == Source Address
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a new tuple is created with
* L_neighbor_iface_addr = Source Address;
* L_local_iface_addr = Address of the interface which
received the HELLO message;
* L_SYM_time = current time - 1 (expired);
* L_time = current time + validity time.
2. The tuple (existing or new) with L_neighbor_iface_addr == Source
Address is then modified as follows:
1. if the node finds the address of the interface, which
received the HELLO message, in one of the address blocks
included in message, then the tuple is modified as follows:
1. if the occurrence of L_local_iface_addr in the HELLO
message is:
- associated with a TLV with (Type == "LINK_STATUS",
Value == LOST)
then
- L_SYM_time = current time - 1 (i.e., expired)
2. else if the occurrence of L_local_iface_addr in the HELLO
message:
- is associated with:
o a TLV with (Type == "LINK_STATUS", Value ==
SYMMETRIC);
OR;
o a TLV with (Type == "LINK_STATUS", Value == HEARD);
then
- L_SYM_time = current time + validity time,
- L_time = L_SYM_time + L_HOLD_TIME.
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2. L_ASYM_time = current time + validity time;
3. L_time = max(L_time, L_ASYM_time)
3. Additionally, the willingness field is updated as follows:
If a TLV with Type=="WILLINGNESS" is present in the message
TLVs, then:
+ L_willingness = Value of the TLV
otherwise:
+ L_willingness = WILL_DEFAULT
The rule for setting L_time is the following: a link losing its
symmetry SHOULD still be advertised in HELLOs (with the remaining
status as defined by Table 1) during at least the duration of the
"validity time". This allows neighbors to detect the link breakage.
Thus, the Local Link Set must maintain information, also about LOST
links, until the link would otherwise expire.
8.2 Populating the 2-Hop Neighbor Set
Upon receiving a HELLO message from a symmetric neighbor interface, a
node SHOULD update its 2-hop Neighbor Set.
If the Source Address is the L_local_iface_addr from a link tuple
included in the Link Set with L_STATUS equal to SYMMETRIC (in other
words: if the Source Address is a symmetric neighbor interface) then
the 2-hop Neighbor Set SHOULD be updated as follows:
1. for each address (henceforth: 2-hop neighbor address), listed in
the HELLO message:
1. if the 2-hop neighbor address is an interface address of the
receiving node silently discard the 2-hop neighbor address
(in other words: a node is not its own 2-hop neighbor).
2. else if the 2-hop neighbor address has a TLV with:
+ (Type=LINK_STATUS, Value == SYMMETRIC); OR
+ (Type=OTHER_IF, Value=SYMMETRIC);
a 2-hop tuple is created with:
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+ N2_local_iface_addr = address of the interface over
which the HELLO message was received;
+ N2_neighbor_iface_addr = source address of the message;
+ N2_2hop_iface_addr = 2-hop neighbor address;
+ N2_time = current time + validity time.
This tuple may replace an older similar tuple with the same
N2_local_iface_addr, N2_neighbor_iface_addr and
N2_2hop_iface_addr values.
3. else if the 2-hop neighbor address has a TLV with:
+ (Type == LINK_STATUS, Value == LOST); OR
+ (Type == OTHER_IF, Value == LOST),
then any 2-hop tuple with:
+ N2_local_iface_addr equal to the address of the interface
over which the HELLO message was received; AND
+ N2_neighbor_iface_addr equal to the source address of the
message; AND
+ and N2_2hop_iface_addr equal to the 2-hop neighbour
address
MUST be deleted.
8.3 Populating the MPR Selector Set
Upon receiving a HELLO message, if a node finds one of its own
interface addresses, listed with an MPR TLV (indicating that the
originator node has selected one of the receiving node's interfaces
as MPR), the MPR Selector Set SHOULD be updated as follows:
For each address in the Local Interface Block of the received
message:
1. If there exists no MPR Selector tuple with:
* MS_if_addr == that address
then a new tuple is created with:
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* MS_if_addr = that address
2. The tuple (new or otherwise) with:
* MS_if_addr == that address
is then modified as follows:
* MS_time = current time + validity time.
MPR Selector tuples are removed upon expiration of MS_time, or upon
link breakage as described in Section 8.4.
8.4 Neighborhood and 2-Hop Neighborhood Changes
A change in the neighborhood is detected when:
o Link Loss: the L_SYM_time field of a link tuple expires (either
due to time out, or as a result of processing a TLV (Type ==
LINK_STATUS, Value == LOST)).
o Link Acquisition: a new link tuple is inserted in the Link Set
with a non expired L_SYM_time or a tuple with expired L_SYM_time
is modified so that L_SYM_time becomes non-expired. This is
considered as a link acquisition if there was previously no such
link tuple.
o Neighbor Loss: all links to a neighbor node have have been lost.
A change in the 2-hop neighborhood is detected when a 2-Hop Neighbor
Tuple expires or is deleted according to section Section 8.2.
The following processing occurs when changes in the neighborhood or
the 2-hop neighborhood are detected:
o In case of link loss, all 2-Hop Neighbor Tuples with
* N2_local_iface_addr == interface address of the node where the
link was lost
* N2_neighbor_iface_addr == interface address of the neighbor
MUST be deleted.
o In case of neighbor loss, all MPR Selector tuples associated with
that neighbor are deleted. More precisely:
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* all MPR selector tuples with MS_iface_addr == interface address
of the neighbor MUST be deleted, along with any interface
addresses associated in the Neighbor Address Association Set.
o The MPR Set MUST be re-calculated when a link acquisition or loss
is detected, or when a change in the 2-hop neighborhood is
detected.
o An additional HELLO message MAY be sent when the MPR Set or the
neighborhood changes.
Additionally, proper update of the sets describing local topology
should be made when a Neighbor Association Address Tuple has a list
of addresses which is modified.
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9. TC Message Generation
TC messages are, in OLSRv2, transmitted with the purpose of
populating the Topology Set, the Attached Network Set and the
Neighborhood Address Association Set:
o Topology Discovery: ensure that information is present in each
node describing all destinations and a sufficient subset of links
in order to provide least-hop paths to all destinations.
o Multiple Interface Declaration: ensure that nodes, up to two hops
away from the originator, are aware of the interface configuration
of the originator node.
Thus, nodes with a non-empty Advertised Neighbor Set, or which are
specifically reporting an empty Advertised Neighbor Set (for a period
of T_HOLD_TIME following reporting a non-empty Advertised Neighbor
Set) or with more than one interface which supports OLSRv2 and
participates in the MANET, MUST generate TC messages, according to
the following:
1. The node includes, in its first address block of the TC message,
a Local Interface Block as specified in Section 6.2
2. If the node has a non-empty Advertised Neighbor Set or is
specifically reporting an empty Advertised Neighbor Set, or it
has a one or more attached non-OLSRv2 networks, to which it
wishes to advertise routes to the network, it furthermore:
1. includes a message TLV (Type = CONTENT_SEQ_NUMBER TLV, Value
= the Advertised Neighbor Set Sequence Number);
2. includes address blocks, containing its Advertised Neighbor
Set (if non-empty);
3. includes address blocks and PREFIX_LENGTH TLVs, describing
attached non-OLSRv2 networks;
4. sets the TTL of the message to the network diameter.
3. Otherwise, the node:
1. sets the TTL of the message to 2.
OLSRv2 TC messages are generated and transmitted periodically, with a
default interval between two consecutive TC emissions by the same
node of TC_INTERVAL.
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9.1 TC Message: Transmission
Messages are retransmitted in the packet/message format specified by
[4] with the All-OLSRv2-Multicast address as destination IP address
and is forwarded according to the specification in section
Section 4.4. If fragmentation is necessary, a FRAGMENTATION TLV MUST
be included, and each fragment SHOULD be flagged as partially or
wholly self contained as specified in [4].
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10. TC Message Processing
Upon receiving a TC message, a node MUST update its topology
information base according to the specification given in this
section.
For the purpose of this section, note the following:
o the "validity time" of a message is calculated from the
VALIDITY_TIME message TLV according to the specification in
Section 16;
o the "originator address" refers to the address, contained in the
"originator address" field of the OLSRv2 message header specified
in [4];
o the ASSN of the node, originating the TC message, is recovered as
the value of the CONTENT_SEQ_NO message TLV in the TC message, if
any.
10.1 Checking Freshness & Validity of a TC message
In order to be able to ensure that only valid and fresh information
is recorded in the Topology Set, each node maintains an ASSN History
Set, recording the highest ASSN received from each node in the
network, in the form of a "ASSN History Tuples":
(AS_Address, AS_seq, AS_time)
AS_Address is the originator address of a received TC message;
AS_seq is the highest received ASSN seen in a TC message from
AS_Address;
AS_time is the time at which this tuple expires and MUST be removed.
Upon receiving a TC message, a node MUST check if the TC message is
fresh and valid as follows:
1. If the TC message has more than one address block (i.e. not just
a Local Interface Block) and does not contain a message-TLV of
type CONTENT_SEQ_NO. then the message MUST be discarded;
2. otherwise, if the ASSN History Set contains a tuple where:
* AS_Address == Originator Address of the TC message; AND
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* AS_seq > the ASSN recovered from the TC message,
then the TC message MUST be discarded;
3. otherwise a tuple is inserted in the ASSN History Set with:
* AS_Address = Originator Address in the message;
* AS_seq = The ASSN, extracted from the message;
* AS_time = current time + AS_HOLD_TIME.
possibly replacing an existing tuple with the same AS_Address.
10.2 Updating the Topology Set
A node SHOULD update its Topology Set as follows:
1. For each address, LocAddr, from the Local Interface Block in the
TC message:
1. For each advertised neighbor address, listed in an address
block other than the Local Interface Block in the TC message,
which does NOT have an associated PREFIX_LENGTH TLV:
1. if there exists a tuple in the Topology Set where:
T_dest_iface_addr == advertised neighbor address; AND
T_last_iface_addr == LocAddr.
then the tuple is updated as follows:
T_time = current time + validity time
T_seq = ASSN
2. Otherwise, a new topology tuple is created with:
T_dest_iface_addr = advertised neighbor address, AND
T_last_iface_addr = LocAddr; AND
T_seq = ASSN.
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10.3 Purging Old Entries from the Topology Set
Old entries from the Topology Set MUST be purged as follows:
1. For each address, LocAddr, from the Local Interface Block in the
TC message:
1. all tuples in the Topology Set where:
T_last_iface_addr == LocAddr AND
T_seq < ASSN
MUST be removed.
10.4 Updating the Attached Networks Set
A node SHOULD update its Attached Networks Set as follows:
1. For each address, LocAddr, from the Local Interface Block in the
TC message:
1. For each advertised neighbor address, listed in an address
block other than the Local Interface Block in the TC message,
which does have an associated PREFIX_LENGTH TLV:
1. if there exists a tuple in the Attached Networks Set
where:
AN_net_addr == advertised neighbor address; AND
AN_prefix_length == the prefix length as recoveredf from
the PREFIX_LENGTH TLV; AND
AN_gw_addr == LocAddr.
then the tuple is updated as follows:
AN_time = current time + validity time
AN_seq = ASSN
2. Otherwise, a new topology tuple is created with:
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AN_net_addr == advertised neighbor address; AND
AN_prefix_length == the prefix length as recoveredf from
the PREFIX_LENGTH TLV; AND
AN_gw_addr == LocAddr.
AN_time = current time + validity time
AN_seq = ASSN
10.5 Purging Old Entries from the Attached Network Set
TBD
10.6 Processing Unfragmented TC Messages
If an unfragmented TC message, i.e. a TC message without a
FRAGMENTATION message TLV, is received, it MUST be processed as
follows:
1. Verify freshness and validity of the TC message (see
Section 10.1). If the message is not discarded, then continue;
2. Update the Topology Set (see Section 10.2);
3. Purge old entries from the Topology Set (see Section 10.3);
4. Update the Attached Networks Set (see Section 10.4;
5. Purge old entries from the Attached Networks Set (see
Section 10.5);
6. Update the Neighborhood Address Association Set (see Section 13).
10.7 Processing Partially or Wholly Self-Contained Fragmented TC
Messagess
If a TC message contains a FRAGMENTATION message TLV which indicates
that the fragment is a partially or wholly self-contained message,
then the following processing SHOULD be carried out immediately upon
receipt of each received fragment (if not then it MUST be carried out
for each fragment once all fragments have been received):
1. Verify freshness and validity of the TC message (see
Section 10.1). If the message is not discarded, then continue;
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2. Update the Topology Set (see Section 10.2);
3. Update the Neighborhood Address Association Set (see Section 13).
4. Update the Attached Networks Set (see Section 10.4;
Once all fragments have been received, the following processing MUST
be carried out once:
1. Purge old entries from the Topology Set (see Section 10.3);
2. Purge old entries from the Attached Networks Set (see
Section 10.5);
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11. Populating the MPR Set
Each node MUST select, from among its one-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 MPR nodes, will
be received by all nodes 2 hops away.
Each node selects its MPR Set individually, utilizing the information
in the Link Set, 2-Hop Neighbor Set and 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 Link Set, 2-Hop Neighbor Set or 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.
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 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 the addresses of the MPR Selector set (i.e. all
addresses, associated with a MPR selector through the Neighborhood
Address Association Set). This set MAY contain additional neighbor
addresses.
12.2 Populating the Advertised Neighbor Set
The Advertised Neighbor Set contains the set of neighbor addresses,
to which a node advertises links through TC messages. This set
SHOULD at least contain the addresses of the MPR Selector Set (i.e.
all addresses, associated with a MPR selector through the
Neighborhood Address Association Set). This set MAY contain
additional neighbor addresses.
Each time an address is removed from the Advertised Neighbor Set, the
ASSN MUST be incremented. When an address is added to the Advertised
Neighbor Set, the ASSN MUST be incremented.
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13. Populating the Neighborhood Address Association Set
All OLSRv2 messages containing a Local Interface Block (including
HELLO and TC messages) SHOULD be used to update the Neighborhood
Address Association Set as follows:
1. If there is a Neighborhood Address Association Tuple, any of
whose addresses are in the Local Interface Block being processed,
then discard that tuple.
2. A tuple is added to the Neighborhood Address Association Set,
where:
* NA_neighbor_addr_list = all addresses from the Local Interface
Block;
* NA_time = current time + NA_HOLD_TIME.
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14. Routing Table Calculation
The Routing Set is updated when a change (an entry appearing/
disappearing) is detected in:
o the Link Set,
o the Neighbor Address Association Set,
o the 2-hop Neighbor Set,
o the Topology Set,
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 the arcs X -> Y where Y is any
symmetric neighbor of X (with Link Type equal to SYM), the arcs Y ->
Z where Y is a neighbor node with willingness different of WILL_NEVER
and there exists an entry in the 2-hop Neighbor Set with Y as
N2_neighbor_iface_addr and Z as N2_2hop_iface_addr, and the arcs U ->
V, where there exists an entry in the Topology Set with V as
T_dest_iface_addr and U as T_last_iface_addr. The graph is
complemented with the arcs W0 -> W1 where W0 and W1 are two addresses
of interfaces of a same neighbor (in a neighbor address association
tuple).
The following procedure is given as an example for (re-)calculating
the Routing Set (with a breadth-first algorithm):
1. All the tuples from the Routing Set are removed.
2. The new routing tuples are added starting with the symmetric
neighbors (h=1) as the destinations. Thus, for each tuple in the
Link Set where:
* L_STATUS == SYMMETRIC (L_STATUS is calculated as
indicated in Table 1)
a new routing tuple is recorded in the Routing Set with:
* R_dest_iface_addr = L_neighbor_iface_addr, of the link tuple;
* R_next_iface_addr = L_neighbor_iface_addr, of the link tuple;
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* R_dist = 1;
* R_iface_addr = L_local_iface_addr of the link tuple.
3. for each neighbor address association tuple, for which two
addresses A1 and A2 exist in I_neighbor_iface_addr_list where:
* there exists a routing tuple with:
+ R_dest_iface_addr == A1
* there is no routing tuple with:
+ R_dest_iface_addr == A2
then a tuple in the Routing Set is created with:
* R_dest_iface_addr = A2;
* R_next_iface_addr = R_next_iface_addr of the route tuple of
A1;
* R_dist = R_dist of the route tuple of A1 (e.g. 1);
* R_iface_addr = R_iface_addr of the route tuple of A1.
4. for each symmetric strict 2-hop neighbor where the
N2_neighbor_iface_addr has a willingness different from
WILL_NEVER a tuple in the Routing Set is created with:
* R_dest_iface_addr = N2_2hop_iface_addr of the 2-hop neighbor;
* R_next_iface_addr = the R_next_iface_addr of the route tuple
with:
+ R_dest_iface_addr == N2_neighbor_iface_addr of the 2-hop
tuple;
* R_dist = 2;
* R_iface_addr = the R_iface_addr of the route tuple with:
+ R_dest_iface_addr == N2_neighbor_iface_addr of the 2-hop
tuple;
5. The new route tuples for the destination nodes h+1 hops away are
recorded in the routing table. The following procedure MUST be
executed for each value of h, starting with h=2 and incrementing
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by 1 for each iteration. The execution will stop if no new tuple
is recorded in an iteration.
1. For each topology tuple in the Topology Set, if its
T_dest_iface_addr does not correspond to R_dest_iface_addr of
any route tuple in the Routing Set AND its T_last_iface_addr
corresponds to R_dest_iface_addr of a route tuple whose
R_dist is equal to h, then a new route tuple MUST be recorded
in the Routing Set (if it does not already exist) where:
+ R_dest_iface_addr = T_dest_iface_addr;
+ R_next_iface_addr = R_next_iface_addr of the route tuple
where:
- R_dest_iface_addr == T_last_iface_addr
+ R_dist = h+1; and
+ R_iface_addr = R_iface_addr of the route tuple where:
- R_dest_iface_addr == T_last_iface_addr.
2. Several topology tuples may be used to select a next hop
R_next_iface_addr for reaching the node R_dest_iface_addr.
When h==1, ties should be broken such that nodes with highest
willingness and MPR selectors are preferred as next hop.
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15. Proposed Values for Constants
This section list the values for the constants used in the
description of the protocol.
15.1 Message Intervals
o HELLO_INTERVAL = 2 seconds
o REFRESH_INTERVAL = 2 seconds
o TC_INTERVAL = 5 seconds
15.2 Holding Times
o L_HOLD_TIME = 3 x HELLO_INTERVAL
o N2_HOLD_TIME = 3 x REFRESH_INTERVAL
o NA_HOLD_TIME = 3 x TC_INTERVAL
o T_HOLD_TIME = 3 x TC_INTERVAL
o RX_HOLD_TIME = 30 seconds
o FW_HOLD_TIME = 30 seconds
o P_HOLD_TIME = 30 seconds
o FG_HOLD_TIME = 30 seconds
15.3 Willingness
o WILL_NEVER = 0
o WILL_LOW = 1
o WILL_DEFAULT = 3
o WILL_HIGH = 6
o WILL_ALWAYS = 7
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15.4 Time
o C = 0.0625 seconds (1/16 second)
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16. Representing Time
OLSRv2 specifies several TLVs, where time, in seconds, is to be
represented via an 8 bit field.
Of these 8 bits, the highest four bits represent the mantissa (a) and
the four lowest bits represent the exponent (b), yielding that:
o time = C*(1+a/16)* 2^b [in seconds]
where a is the integer represented by the four highest bits of the
time field and b the integer represented by the four lowest bits of
the time field. The proposed value of the scaling factor C is
specified in Section 15. All nodes in the network MUST use the same
value of C.
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17. IANA Considerations
17.1 Multicast Addresses
A well-known multicast address, All-OLSRv2-Multicast, 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.
17.2 Message Types
OLSRv2 defines two message types, which must be allocated from the
"Assigned Message Types" repository of [4]
+--------------------+--------+-------------------------------------+
| Mnemonic | Value | Description |
+--------------------+--------+-------------------------------------+
| HELLOv2 | TBD | Local Signaling |
| | | |
| TCv2 | TBD | Global Signaling |
+--------------------+--------+-------------------------------------+
Table 7
17.3 TLV Types
OLSRv2 defines three Message TLV types, which must be allocated from
the "Assigned message TLV Types" repository of [4]
+--------------------+--------+-------------------------------------+
| Mnemonic | Value | Description |
+--------------------+--------+-------------------------------------+
| VALIDITY_TIME | TBD | The time (in seconds) from receipt |
| | | of the message during which the |
| | | information contained in a message |
| | | is to be valid |
| | | |
| INTERVAL_TIME | TBD | The time (in seconds) between two |
| | | successive transmissions of |
| | | messages of a given type |
| | | |
| WILLINGNESS | TBD | Specifies a node's willingness |
| | | [0-7] to act as a relay and to |
| | | partake in network formation |
+--------------------+--------+-------------------------------------+
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Table 8
OLSRv2 defines three Address Block TLV types, which must be allocated
from the "Assigned address block TLV Types" repository of [4]
+--------------------+--------+-------------------------------------+
| Mnemonic | Value | Description |
+--------------------+--------+-------------------------------------+
| OTHER_IF | TBD | Specifies that an address is |
| | | associated to an interface other |
| | | than the one where the message is |
| | | transmitted, and may specify its |
| | | status (verified bidirectional or |
| | | lost) |
| | | |
| LINK_STATUS | TBD | Specifies a given link's status |
| | | (asymmetric, verified |
| | | bidirectional, lost) |
| | | |
| MPR | TBD | Specifies that a given address is |
| | | selected as MPR |
+--------------------+--------+-------------------------------------+
Table 9
18. References
[1] Clausen, T., "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] Atkins, D., Stallings, W., and P. Zimmermann, "PGP Message
Exchange Formats", RFC 1991, August 1996.
[4] Clausen, T., Dean, J., and C. Dearlove, "Generalized MANET
Packet/Message Format", Work In
Progress draft-ietf-manet-packetbb-00.txt, February 2006.
[5] ETSI, "ETSI STC-RES10 Committee. Radio equipment and systems:
HIPERLAN type 1, functional specifications ETS 300-652",
June 1996.
[6] Jacquet, P., Minet, P., Muhlethaler, P., and N. Rivierre,
"Increasing reliability in cable free radio LANs: Low level
forwarding in HIPERLAN.", 1996.
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[7] Qayuum, A., Viennot, L., and A. Laouiti, "Multipoint relaying:
An efficient technique for flooding in mobile wireless
networks.", 2001.
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
The OLSRv2 Design Team
MANET Working Group
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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 2-hop
interfaces by relaying through an MPR node.
There are several peripheral issues that the algorithm need 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 need to be precised in the following way:
o All neighbor nodes with willingness equal to WILL_NEVER MUST
ignored in the following algorithm: they are not considered as
neighbors (hence not used as MPRs), nor as 2-hop neighbors (hence
no attempt to cover them is made).
o Because link sensing is performed by interface, the local network
topology, is best described in terms of links: hence the algorithm
is considering neighbor interfaces, and 2-hop neighbor 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 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 interface of a neighbor to which there
exist a symmetrical link on interface I.
N - the set of such neighbor interfaces
2-hop neighbor interface (of I) An interface of a symmetric strict
2-hop neighbor and 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 N_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 N_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 Some 2-hop neighbors may have several interfaces. The described
algorithm attempts to reach every such interface of the nodes.
However, whenever information that several 2-hop interfaces are,
in fact, interfaces of the same 2-hop neighbor, is available, it
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can be used: only one of the interfaces of the 2-hop neighbor
needs to be covered. This information is provided in the
Neighborhood Address Association Set.
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
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. Example Algorithms for Generating Control Traffic
The proposed generation of the control messages proceeds in four
steps. HELLO messages and TC messages both essentially consist of a
list of advertised addresses of neighbors (some part of the
topology).
Hence, a first step is to collect the set of relevant addresses which
are to be advertised. Because there are a number of TLVs which can
be associated with each address (including mandatory ones), this step
results in a list of addresses, each associated with a certain number
of TLVs.
The second step is then to regroup the addresses which share exactly
the same TLVs (same Type and same Value), into an address block which
will be associated with a list of TLVs.
The third step is to pack the message header and message TLVs into a
sequence of octets.
The fourth step consists of packing every address block obtained in
the second step by finding the longest common prefix of the addresses
in the address block (the head), then, packing the list of the tails
of the addresses into a sequence of octets, followed by the TLVs of
the address block.
This generation method can be used for TC generation and HELLO
generation: in each case, all what need to be specified is the
message headers, message TLVs, and the list of each address with its
associated TLVs.
The Local Interface Block MUST include all of the participating
interface addresses of the node (including the one of chosen as the
node's originator address and included in the message header).
Appendix B.1 Example Algorithm for Generating HELLO messages
This section proposes an algorithm for generating HELLO messages.
Periodically, on each interface I, the node generates a HELLO message
specific to that interface, as follows:
1. First, the list of the links of the interface is collected. It
is the list of the Link Tuples where:
* L_local_iface_addr == address of the interface
Each corresponding address L_neighbor_iface_addr is then
advertised with the following TLVs:
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* Type="LINK-STATUS", Value=L_STATUS, the status of the link
(see Section 5.1.1);
* Type="OTHER_IF", if and only if as specified in Section 7);
* Type="MPR", if and only of the address L_neighbor_iface_addr
is an interface address in the MPR Set.
2. Second, if the node has more than one interface, for each address
which was not previously advertised and for which there exists a
Link Tuple on another interface where:
* L_local_iface_addr is different from address of the interface
I; AND
* L_STATUS == SYMMETRIC
the corresponding address L_neighbor_iface_addr is advertised
with the following TLV:
* Type="OTHER_IF", Value=SYMMETRIC.
3. Third, if the node has more than one interface, for each
interface address which is to be reported as LOST as specified in
Section 7) the interface address is advertised with the following
TLV:
* Type="OTHER_IF", Value=LOST.
4. Then a HELLO message is generated using the previous method, with
the specified headers and TLVs:
* a message TLV with Type="VALIDITY_TIME" and Value=encoding of
L_HOLD_TIME, SHALL be added
* a message TLV with Type="INTERVAL_TIME" and Value=encoding of
HELLO_INTERVAL, SHOULD be added
* a message TLV with Type="WILLINGNESS" and Value=the
willingness of the node. This SHOULD NOT be included if this
value is WILL_DEFAULT, it SHALL be included otherwise.
Appendix B.2 Example Algorithm for Generating TC messages
Periodically, the node generates TC messages, broadcast on all the
interfaces of the node, as follows:
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1. Each A_iface_addr in the Advertised Neighbor Set, SHALL be
included in the TC message.
2. The TC message is generated with the proper headers, and (except
where the Advertised Neighbor Set is empty and the TC message is
not specifically reporting this, see Section 9) including the
message TLV, Type="CONTENT_SEQUENCE_NUMBER", Value=the current
ASSN of the node.
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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 [4]. However
the following points should be noted.
OLSRv2 uses only packets with a packet header. Thus all OLSRv2
packets 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0| Reserved | Packet Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Message |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
: ... :
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Message |
| |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
All reserved bits are also unset (zero).
OLSRv2 uses only packets with a complete message header. Thus all
OLSRv2 messages 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 |U|N|0|0| Message Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time To Live | Hop Count | Message Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Message Body + Padding |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In standard OLSRv2 messages (HELLO and TC) the U and N bits are also
unset(zero). In all OLSRv2 messages the reserved bits marked Resv
above are also unset (zero).
The layouts of the message body, address block, TLV block and TLV are
as in [4], allowing all options. Standard (HELLO and TC) messages
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contain a first address block which contains local interface
addresses, all other address blocks contain information specific to
the message type. Except by being first, the local interface address
block is not distinguished in any way.
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 TTL 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 single local interface address,
with head length 4; thus although 1 tail is indicated, no tail octets
are included. This address block has no TLVs (TLV block content
length 0 octets).
The second, and last, address block reports 4 neighbour interface
addresses, with address head length 3 octets. The following TLV
block (content length 11 octets) includes two TLVs.
The first of these TLVs reports the link status of all four
neighbours 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, since 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.
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|
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 1 0 0| Head |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Head (cont) |0 0 0 0 0 0 0 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0|0 0 0 0 0 0 1 1| Head |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Head (cont) |0 0 0 0 0 1 0 0| Tail |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tail | Tail | Tail |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 |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 67 octets, the final octet is
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 4 octets containing a
single TLV with semantics value 1, indicating that the TLV has no
value field, or length thereof. This TLV indicates that the second
and third of these addresses (indexes 1 to 2) are for other
interfaces than the one on which this TC message is transmitted.
The other two address blocks contain neighbour interface addresses,
with head lengths 2 and 4 respectively. The first of these, with 3
addresses, has an empty TLV block (content length 0 octets). The
second, which contains 1 address, has a TLV block (content length 4
octets) with a single TLV (semantics value 4 indicating no indexes
needed) indicating that this is a network address with the given
prefix length (itself with length 1 octet).
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 1 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Originator Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live | 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 (ASSN) | 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 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Head |0 0 0 0 0 0 1 1| Tail |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tail (cont) | Tail | Tail |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tail (cont) |0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0| OTHER_IF |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 1|0 0 0 0 0 0 0 1|0 0 0 0 0 0 1 0|0 0 0 0 0 0 1 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Head |0 0 0 0 0 0 1 1| Tail |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tail (cont) | Tail | Tail |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Tail (cont) |0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0|0 0 0 0 0 1 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Head |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 1|0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0| PREFIX-LENGTH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 1 0 0|0 0 0 0 0 0 0 1|Value (Length) |0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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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. 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 F.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 [3] 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 F.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 F.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 F.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 G. Flow and Congestion Control
TBD
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Appendix H. Sequence Numbers
Sequence numbers are used in OLSR 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.
The term MAXVALUE designates in the following the largest possible
value for a sequence number.
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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Appendix I. Contributors
This specification is the result of the joint efforts of the
following contributers -- 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, 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) 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: Kenichi Mase (Niigata University),
Li Li (CRC), Louise Lamont (CRC), Joe Macker (NRL), Alan Cullen (BAE
Systems), Philippe Jacquet (INRIA), Khaldoun Al Agha (LRI), Richard
Ogier (?), Song-Yean Cho (Samsung Software Center), Shubhranshu Singh
(Samsung AIT) and the entire IETF MANET working group.
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