AODV-RPL: The Routing Protocol for Low-Power and Lossy Networks (RPL) Based on Ad Hoc On-Demand Distance Vector (AODV) Routing Blue Meadow Networks
Saratoga CA 95070 United States of America charliep@lupinlodge.com
Indian Institute of Science
Bangalore 560012 India anandsvr@iisc.ac.in
SRM University-AP
Amaravati Campus Amaravati, Andhra Pradesh 522 502 India satishnaidu80@gmail.com
Huawei Technologies
No. 156 Beiqing Rd. Haidian District Beijing 100095 China remy.liubing@huawei.com
RTG roll AODV Peer-to-Peer Route Discovery Asymmetric Route discovery for symmetric and asymmetric Peer-to-Peer (P2P) traffic flows is a desirable feature in Low-Power and Lossy Networks (LLNs). For that purpose, this document specifies AODV-RPL -- the Routing Protocol for Low-Power and Lossy Networks (RPL) based on Ad hoc On-demand Distance Vector (AODV) routing. AODV-RPL is a reactive P2P route discovery mechanism for both hop-by-hop routes and source routing. Paired instances are used to construct directional paths for cases where there are asymmetric links between source and target nodes.
Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .
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Table of Contents
  • .  Introduction
  • .  Terminology
  • .  Overview of AODV-RPL
  • .  AODV-RPL DIO Options
    • .  AODV-RPL RREQ Option
    • .  AODV-RPL RREP Option
    • .  AODV-RPL Target Option
  • .  Symmetric and Asymmetric Routes
  • .  AODV-RPL Operation
    • .  Generating RREQ
    • .  Receiving and Forwarding RREQ Messages
      • .  Step 1: RREQ Reception and Evaluation
      • .  Step 2: TargNode and Intermediate Router Determination
      • .  Step 3: Intermediate Router RREQ Processing
      • .  Step 4: Symmetric Route Processing at an Intermediate Router
      • .  Step 5: RREQ Propagation at an Intermediate Router
      • .  Step 6: RREQ Reception at TargNode
    • .  Generating RREP at TargNode
      • .  RREP-DIO for Symmetric Route
      • .  RREP-DIO for Asymmetric Route
      • .  RPLInstanceID Pairing
    • .  Receiving and Forwarding RREP
      • .  Step 1: Receiving and Evaluation
      • .  Step 2: OrigNode or Intermediate Router
      • .  Step 3: Build Route to TargNode
      • .  Step 4: RREP Propagation
  • .  Gratuitous RREP
  • .  Operation of Trickle Timer
  • .  IANA Considerations
  • . Security Considerations
  • . References
    • .  Normative References
    • .  Informative References
  • .  Example: Using ETX/RSSI Values to Determine Value of S Bit
  • .  Some Example AODV-RPL Message Flows
    • .  Example Control Message Flows in Symmetric and Asymmetric Networks
    • .  Example RREP_WAIT Handling
    • .  Example G-RREP Handling
  • Acknowledgements
  • Contributors
  • Authors' Addresses
Introduction The Routing Protocol for Low-Power and Lossy Networks (RPL) is an IPv6 distance vector routing protocol designed to support multiple traffic flows through a root-based Destination-Oriented Directed Acyclic Graph (DODAG). Typically, a router does not have routing information for destinations attached to most other routers. Consequently, for traffic between routers within the DODAG (i.e., P2P traffic), data packets either have to traverse the root in non-storing mode or traverse a common ancestor in storing mode. Such P2P traffic is thereby likely to traverse longer routes and may suffer severe congestion near the root (for more information, see , , , and ). The network environment that is considered in this document is assumed to be the same as that described in . Each radio interface/link and the associated address should be treated as an independent intermediate router. Such routers have different links, and the rules for link symmetry apply independently for each of these. The route discovery process in AODV-RPL is modeled on the analogous P2P procedure specified in AODV . The on-demand property of AODV route discovery is useful for the needs of routing in RPL-based LLNs when routes are needed but aren't yet established. P2P routing is desirable to discover shorter routes, especially when it is desired to avoid directing additional traffic through a root or gateway node of the network. It may happen that some routes need to be established proactively when known beforehand and when AODV-RPL's route discovery process introduces unwanted delay when the application is launched. AODV terminology has been adapted for use with AODV-RPL messages, namely "RREQ" for "Route Request", and "RREP" for "Route Reply". AODV-RPL currently omits some features compared to AODV -- in particular, flagging route errors, blocking the use of unidirectional links , multihoming, and handling unnumbered interfaces. AODV-RPL reuses and extends the core RPL functionality to support routes with bidirectional asymmetric links. It retains RPL's DODAG formation, RPL Instance and the associated Objective Function (OF) (defined in ), Trickle timers, and support for storing and non-storing modes. AODV-RPL adds the basic messages RREQ and RREP as part of the RPL DODAG Information Object (DIO) control message, which go in separate (paired) RPL Instances. AODV-RPL does not utilize the Destination Advertisement Object (DAO) control message of RPL. AODV-RPL uses the "P2P Route Discovery Mode of Operation" (MOP == 4) with three new options for the DIO message, dedicated to discovering P2P routes. These P2P routes may differ from routes discoverable by RPL . Since AODV-RPL uses newly defined options and a newly allocated multicast group (see ), there is no conflict with P2P-RPL , a previous document using the same MOP. AODV-RPL can be operated whether or not P2P-RPL or RPL is also running. AODV-RPL could be used for networks in which routes are needed with OFs that cannot be satisfied by routes that are constrained to traverse the root of the network or other common ancestors. P2P routes often require fewer hops and therefore consume less resources than routes that traverse the root or other common ancestors. Similar in cost to base RPL , the cost will depend on many factors such as the proximity of the OrigNode and TargNodes and distribution of symmetric/asymmetric P2P links. Experience with AODV suggests that AODV-RPL will often find routes with improved Rank compared to routes constrained to traverse a common ancestor of the source and destination nodes.
Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. AODV-RPL reuses names for messages and data structures, including Rank, DODAG, and DODAGID, as defined in RPL . This document also uses the following terms:
AODV
Ad hoc On-Demand Distance Vector .
ART option
The AODV-RPL Target option defined in this document.
Asymmetric route
The route from the OrigNode to the TargNode can traverse different nodes than the route from the TargNode to the OrigNode. An asymmetric route may result from the asymmetry of links, such that only one direction of the series of links satisfies the OF during route discovery.
Bidirectional asymmetric link
A link that can be used in both directions but with different link characteristics.
DIO
DODAG Information Object (as defined in ).
DODAG RREQ-Instance (or simply RREQ-Instance)
A RPL Instance built using the DIO with RREQ option; used for transmission of control messages from OrigNode to TargNode, thus enabling data transmission from TargNode to OrigNode.
DODAG RREP-Instance (or simply RREP-Instance)
A RPL Instance built using the DIO with RREP option; used for transmission of control messages from TargNode to OrigNode, thus enabling data transmission from OrigNode to TargNode.
Downward direction
The direction from the OrigNode to the TargNode.
Downward route
A route in the downward direction.
Hop-by-hop route
A route for which each router along the routing path stores routing information about the next hop. A hop-by-hop route is created using RPL's "storing mode".
OF
Objective Function (as defined in ).
OrigNode
The IPv6 router (originating node) initiating the AODV-RPL route discovery to obtain a route to TargNode.
Paired DODAGs
Two DODAGs for a single route discovery process between OrigNode and TargNode.
P2P
Peer-to-Peer (in other words, not constrained a priori to traverse a common ancestor).
REJOIN_REENABLE
The duration during which a node is prohibited from joining a DODAG with a particular RREQ-InstanceID, after it has left a DODAG with the same RREQ-InstanceID. The default value of REJOIN_REENABLE is 15 minutes.
RREQ
Route Request.
RREQ-DIO message
A DIO message containing the RREQ option. The RPLInstanceID in RREQ-DIO is assigned locally by the OrigNode. The RREQ-DIO message has a secure variant as noted in .
RREQ-InstanceID
The RPLInstanceID for the RREQ-Instance. The RREQ-InstanceID is formed as the ordered pair (Orig_RPLInstanceID, OrigNode-IPaddr), where Orig_RPLInstanceID is the local RPLInstanceID allocated by OrigNode and OrigNode-IPaddr is an IP address of OrigNode. The RREQ-InstanceID uniquely identifies the RREQ-Instance.
RREP
Route Reply.
RREP-DIO message
A DIO message containing the RREP option. OrigNode pairs the RPLInstanceID in RREP-DIO to the one in the associated RREQ-DIO message (i.e., the RREQ-InstanceID) as described in . The RREP-DIO message has a secure variant as noted in .
RREP-InstanceID
The RPLInstanceID for the RREP-Instance. The RREP-InstanceID is formed as the ordered pair (Targ_RPLInstanceID, TargNode-IPaddr), where Targ_RPLInstanceID is the local RPLInstanceID allocated by TargNode and TargNode-IPaddr is an IP address of TargNode. The RREP-InstanceID uniquely identifies the RREP-Instance. The RPLInstanceID in the RREP message along with the Delta value indicates the associated RREQ-InstanceID. The InstanceIDs are matched by the mechanism explained in .
Source routing
A mechanism by which the source supplies a vector of addresses towards the destination node along with each data packet .
Symmetric route
The upstream and downstream routes traverse the same routers and over the same links.
TargNode
The IPv6 router (target node) for which OrigNode requires a route and initiates route discovery within the LLN.
Upward direction
The direction from the TargNode to the OrigNode.
Upward route
A route in the upward direction.
Overview of AODV-RPL With AODV-RPL, routes from OrigNode to TargNode within the LLN do not become established until they are needed. The route discovery mechanism in AODV-RPL is invoked when OrigNode has data for delivery to a TargNode, but existing routes do not satisfy the application's requirements. For this reason, AODV-RPL is considered to be an example of an "on-demand" routing protocol. Such protocols are also known as "reactive" routing protocols since their operations are triggered in reaction to a determination that a new route is needed. AODV-RPL works without requiring the use of RPL or any other routing protocol. The routes discovered by AODV-RPL are not constrained to traverse a common ancestor. AODV-RPL can enable asymmetric communication paths in networks with bidirectional asymmetric links. For this purpose, AODV-RPL enables discovery of two routes: namely, one from OrigNode to TargNode and another from TargNode to OrigNode. AODV-RPL also enables discovery of symmetric routes along paired DODAGs, when symmetric routes are possible (see ). In AODV-RPL, routes are discovered by first forming a temporary Directed Acyclic Graph (DAG) rooted at the OrigNode. Paired DODAGs (Instances) are constructed during route formation between the OrigNode and TargNode. The RREQ-Instance is formed by route control messages from OrigNode to TargNode, whereas the RREP-Instance is formed by route control messages from TargNode to OrigNode. The route discovered in the RREQ-Instance is used for transmitting data from TargNode to OrigNode, and the route discovered in RREP-Instance is used for transmitting data from OrigNode to TargNode. Intermediate routers join the DODAGs based on the Rank as calculated from the DIO messages. AODV-RPL uses the same notion of Rank as defined in :
The Rank is the expression of a relative position within a DODAG Version with regard to neighbors, and it is not necessarily a good indication or a proper expression of a distance or a path cost to the root.
The Rank measurements provided in AODV messages do not indicate a distance or a path cost to the root. Henceforth in this document, "RREQ-DIO message" means the DIO message from OrigNode toward TargNode, containing the RREQ option as specified in . The RREQ-InstanceID is formed as the ordered pair (Orig_RPLInstanceID, OrigNode-IPaddr), where Orig_RPLInstanceID is the local RPLInstanceID allocated by OrigNode and OrigNode-IPaddr is the IP address of OrigNode. A node receiving the RREQ-DIO can use the RREQ-InstanceID to identify the proper OF whenever that node receives a data packet with Source Address == OrigNode-IPaddr and IPv6 RPL Option having the RPLInstanceID == Orig_RPLInstanceID. The D bit of the RPLInstanceID field is set to 0 to indicate that the source address of the IPv6 packet is the DODAGID. Similarly, "RREP-DIO message" means the DIO message from TargNode toward OrigNode, containing the RREP option as specified in . The RREP-InstanceID is formed as the ordered pair (Targ_RPLInstanceID, TargNode-IPaddr), where Targ_RPLInstanceID is the local RPLInstanceID allocated by TargNode and TargNode-IPaddr is the IP address of TargNode. A node receiving the RREP-DIO can use the RREP-InstanceID to identify the proper OF whenever that node receives a data packet with Source Address == TargNode-IPaddr and IPv6 RPL Option having the RPLInstanceID == Targ_RPLInstanceID along with D == 0 as above.
AODV-RPL DIO Options
AODV-RPL RREQ Option OrigNode selects one of its IPv6 addresses and sets it in the DODAGID field of the RREQ-DIO message. The address scope of the selected address MUST encompass the domain where the route is built (e.g, not link-local); otherwise, the route discovery will fail. Exactly one RREQ option MUST be present in an RREQ-DIO message; otherwise, the message MUST be dropped.
Format for AODV-RPL RREQ Option 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Option Length |S|H|X| Compr | L | RankLimit | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Orig SeqNo | | +-+-+-+-+-+-+-+-+ | | | | Address Vector (Optional, Variable Length) | . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . .
OrigNode supplies the following information in the RREQ option:
Option Type
8-bit unsigned integer specifying the type of the option (0x0B).
Option Length
8-bit unsigned integer specifying the length of the option in octets, excluding the Option Type and Option Length fields. It is variable due to the presence of the Address Vector and the number of octets elided according to the Compr value.
S
Symmetric bit indicating a symmetric route from the OrigNode to the router transmitting this RREQ-DIO. See .
H
Set to one for a hop-by-hop route. Set to zero for a source route. This flag controls both the downstream route and upstream route.
X
Reserved. This field MUST be initialized to zero and ignored upon reception.
Compr
4-bit unsigned integer. When Compr is nonzero, exactly that number of prefix octets MUST be elided from each address before storing it in the Address Vector. The octets elided are shared with the IPv6 address in the DODAGID. This field is only used in source routing mode (H=0). In hop-by-hop mode (H=1), this field MUST be set to zero and ignored upon reception.
L
2-bit unsigned integer determining the time duration that a node is able to belong to the RREQ-Instance (a temporary DAG including the OrigNode and the TargNode). Once the time is reached, a node SHOULD leave the RREQ-Instance and stop sending or receiving any more DIOs for the RREQ-Instance; otherwise, memory and network resources are likely to be consumed unnecessarily. This naturally depends on the node's ability to keep track of time. Once a node leaves an RREQ-Instance, it MUST NOT rejoin the same RREQ-Instance for at least the time interval specified by the configuration variable REJOIN_REENABLE. L is independent from the route lifetime, which is defined in the DODAG configuration option.
  • 0x00: No time limit imposed
  • 0x01: 16 seconds
  • 0x02: 64 seconds
  • 0x03: 256 seconds
RankLimit
8-bit unsigned integer specifying the upper limit on the integer portion of the Rank (calculated using the DAGRank() macro defined in ). A value of 0 in this field indicates the limit is infinity.
Orig SeqNo
8-bit unsigned integer specifying the Sequence Number of OrigNode. See .
Address Vector
A vector of IPv6 addresses representing the route that the RREQ-DIO has passed. It is only present when the H bit is set to 0. The prefix of each address is elided according to the Compr field.
TargNode can join the RREQ-Instance at a Rank whose integer portion is less than or equal to the RankLimit. Any other node MUST NOT join an RREQ-Instance if its own Rank would be equal to or higher than the RankLimit. A router MUST discard a received RREQ if the integer part of the advertised Rank equals or exceeds the RankLimit.
AODV-RPL RREP Option TargNode sets one of its IPv6 addresses in the DODAGID field of the RREP-DIO message. The address scope of the selected address must encompass the domain where the route is built (e.g, not link-local). Exactly one RREP option MUST be present in an RREP-DIO message, otherwise, the message MUST be dropped. TargNode supplies the following information in the RREP option:
Format for AODV-RPL RREP Option 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Option Length |G|H|X| Compr | L | RankLimit | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Delta |X X| | +-+-+-+-+-+-+-+-+ | | | | | | Address Vector (Optional, Variable Length) | . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . .
Option Type
8-bit unsigned integer specifying the type of the option (0x0C).
Option Length
8-bit unsigned integer specifying the length of the option in octets, excluding the Option Type and Option Length fields. It is variable due to the presence of the Address Vector and the number of octets elided according to the Compr value.
G
Gratuitous RREP (see ).
H
The H bit in the RREP option MUST be set to be the same as the H bit in the RREQ option. It requests either source routing (H=0) or hop-by-hop (H=1) for the downstream route.
X
1-bit Reserved field. This field MUST be initialized to zero and ignored upon reception.
Compr
4-bit unsigned integer. This field has the same definition as in the RREQ option.
L
2-bit unsigned integer defined as in the RREQ option. The lifetime of the RREP-Instance SHOULD be no greater than the lifetime of the RREQ-Instance to which it is paired, so that the memory required to store the RREP-Instance can be reclaimed when no longer needed.
RankLimit
8-bit unsigned integer specifying the upper limit on the integer portion of the Rank, similarly to RankLimit in the RREQ message. A value of 0 in this field indicates the limit is infinity.
Delta
6-bit unsigned integer. TargNode uses the Delta field so that nodes receiving its RREP message can identify the RREQ-InstanceID of the RREQ message that triggered the transmission of the RREP (see ).
X X
2-bit Reserved field. This field MUST be initialized to zero and ignored upon reception.
Address Vector
Only present when the H bit is set to 0. The prefix of each address is elided according to the Compr field. For an asymmetric route, the Address Vector represents the IPv6 addresses of the path through the network the RREP-DIO has passed. In contrast, for a symmetric route, it is the Address Vector when the RREQ-DIO arrives at the TargNode, unchanged during the transmission to the OrigNode.
AODV-RPL Target Option The AODV-RPL Target (ART) option is based on the Target option in the core RPL specification . The Flags field is replaced by the Destination Sequence Number of the TargNode, and the Prefix Length field is reduced to 7 bits so that the value is limited to be no greater than 127. An RREQ-DIO message MUST carry at least one ART option. An RREP-DIO message MUST carry exactly one ART option. Otherwise, the message MUST be dropped. OrigNode can include multiple TargNode addresses via multiple ART options in the RREQ-DIO, for routes that share the same requirement on metrics. This reduces the cost to building only one DODAG for multiple targets.
ART Option Format for AODV-RPL 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Option Length | Dest SeqNo |X|Prefix Length| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + | | Target Prefix / Address (Variable Length) | . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . .
Option Type
8-bit unsigned integer specifying the type of the option (0x0D).
Option Length
8-bit unsigned integer specifying the length of the option in octets, excluding the Option Type and Option Length fields.
Dest SeqNo
8-bit unsigned integer. In RREQ-DIO, if nonzero, it is the Sequence Number for the last route that OrigNode stored to the TargNode for which a route is desired. In RREP-DIO, it is the Destination Sequence Number associated to the route. Zero is used if there is no known information about the Sequence Number of TargNode and not used otherwise.
X
1-bit Reserved field. This field MUST be initialized to zero by the sender and MUST be ignored by the receiver.
Prefix Length
7-bit unsigned integer. The Prefix Length field contains the number of valid leading bits in the prefix. If Prefix Length is 0, then the value in the Target Prefix / Address field represents an IPv6 address, not a prefix.
Target Prefix / Address
A variable-length field with an IPv6 destination address or prefix. The length of the Target Prefix / Address field is the least number of octets that can represent all of the bits of the Prefix, in other words, Ceil(Prefix Length/8) octets. When Prefix Length is not equal to 8*Ceil(Prefix Length/8) and nonzero, the Target Prefix / Address field will contain some initial bits that are not part of the Target Prefix. Those initial bits (if any) MUST be set to zero on transmission and MUST be ignored on receipt. If Prefix Length is zero, the Address field is 128 bits.
Symmetric and Asymmetric Routes Links are considered symmetric until indication to the contrary is received. In Figures and , BR is the Border Router, O is the OrigNode, each R is an intermediate router, and T is the TargNode. In these examples, the use of BR is only for illustrative purposes; AODV does not depend on the use of border routers for its operation. If the RREQ-DIO arrives over an interface that is known to be symmetric and the S bit is set to 1, then it remains as 1, as illustrated in . If an intermediate router sends out RREQ-DIO with the S bit set to 1, then each link en route from the OrigNode O to this router has met the requirements of route discovery, and the route can be used symmetrically.
AODV-RPL with Symmetric Instances BR /----+----\ / | \ / | \ R R R _/ \ | / \ / \ | / \ / \ | / \ R -------- R --- R ----- R -------- R / \ <--S=1--> / \ <--S=1--> / \ <--S=1--> \ / \ / <--S=1--> / \ / \ / \ O ---------- R ------ R------ R ----- R ----------- T / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ R ----- R ----------- R ----- R ----- R ----- R ---- R----- R >---- RREQ-Instance (Control: O-->T; Data: T-->O) -------> <---- RREP-Instance (Control: T-->O; Data: O-->T) -------<
Upon receiving an RREQ-DIO with the S bit set to 1, a node determines whether the link over which it was received can be used symmetrically, i.e., both directions meet the requirements of data transmission. If the RREQ-DIO arrives over an interface that is not known to be symmetric or is known to be asymmetric, the S bit is set to 0. If the S bit arrives already set to be 0, then it is set to be 0 when the RREQ-DIO is propagated (). For an asymmetric route, there is at least one hop that doesn't satisfy the OF. Based on the S bit received in RREQ-DIO, TargNode T determines whether or not the route is symmetric before transmitting the RREP-DIO message upstream towards the OrigNode O. It is beyond the scope of this document to specify the criteria used when determining whether or not each link is symmetric. As an example, intermediate routers can use local information (e.g., bit rate, bandwidth, number of cells used in 6TiSCH ), a priori knowledge (e.g., link quality according to previous communication), or averaging techniques as appropriate to the application. Other link metric information can be acquired before AODV-RPL operation, by executing evaluation procedures; for instance, test traffic can be generated between nodes of the deployed network. During AODV-RPL operation, Operations, Administration, and Maintenance (OAM) techniques for evaluating link state (see , , and ) MAY be used (at regular intervals appropriate for the LLN). The evaluation procedures are out of scope for AODV-RPL. For further information on this topic, see , , and . describes an example method using the upstream Expected Transmission Count (ETX) and downstream Received Signal Strength Indicator (RSSI) to estimate whether the link is symmetric in terms of link quality using an averaging technique.
AODV-RPL with Asymmetric Paired Instances BR /----+----\ / | \ / | \ R R R / \ | / \ / \ | / \ / \ | / \ R --------- R --- R ---- R --------- R / \ --S=1--> / \ --S=0--> / \ --S=1--> \ / \ / --S=0--> / \ / \ / \ O ---------- R ------ R------ R ----- R ----------- T / \ / \ / \ / \ / <--S=0-- / \ / \ / <--S=0-- / \ / \ / \ / \ R ----- R ----------- R ----- R ----- R ----- R ---- R----- R <--S=0-- <--S=0-- <--S=0-- <--S=0-- <--S=0-- >---- RREQ-Instance (Control: O-->T; Data: T-->O) -------> <---- RREP-Instance (Control: T-->O; Data: O-->T) -------<
As illustrated in , an intermediate router determines the S bit value that the RREQ-DIO should carry using link asymmetry detection methods as discussed earlier in this section. In many cases, the intermediate router has already made the link asymmetry decision by the time RREQ-DIO arrives. See for examples illustrating RREQ and RREP transmissions in some networks with symmetric and asymmetric links.
AODV-RPL Operation
Generating RREQ The route discovery process is initiated when an application at the OrigNode has data to be transmitted to the TargNode but does not have a route that satisfies the OF for the target of the application's data. In this case, the OrigNode builds a local RPL Instance and a DODAG rooted at itself. Then, it transmits a DIO message containing exactly one RREQ option (see ) to multicast group all-AODV-RPL-nodes. The RREQ-DIO MUST contain at least one ART option (see ), which indicates the TargNode. The S bit in RREQ-DIO sent out by the OrigNode is set to 1. Each node maintains a Sequence Number; the operation is specified in . When the OrigNode initiates a route discovery process, it MUST increase its own Sequence Number to avoid conflicts with previously established routes. The Sequence Number is carried in the Orig SeqNo field of the RREQ option. The Target Prefix / Address in the ART option can be a unicast IPv6 address or a prefix. The OrigNode can initiate the route discovery process for multiple targets simultaneously by including multiple ART options. Within an RREQ-DIO, the OF for the routes to different TargNodes MUST be the same. OrigNode can maintain different RPL Instances to discover routes with different requirements to the same targets. Using the RPLInstanceID pairing mechanism (see ), route replies (RREP-DIOs) for different RPL Instances can be generated. The transmission of RREQ-DIO obeys the Trickle timer . If the duration specified by the L field has elapsed, the OrigNode MUST leave the DODAG and stop sending RREQ-DIOs in the related RPL Instance. OrigNode needs to set the L field such that the DODAG will not prematurely timeout during data transfer with the TargNode. For setting this value, it has to consider factors such as the Trickle timer, TargNode hop distance, network size, link behavior, expected data usage time, and so on.
Receiving and Forwarding RREQ Messages
Step 1: RREQ Reception and Evaluation When a router X receives an RREQ message over a link from a neighbor Y, X first determines whether or not the RREQ is valid. If valid, X then determines whether or not it has sufficient resources available to maintain the RREQ-Instance and the value of the S bit needed to process an eventual RREP, if the RREP were to be received. If not valid, then X MUST either free up sufficient resources (the means for this are beyond the scope of this document), or drop the packet and discontinue processing of the RREQ. Otherwise, X next determines whether the RREQ advertises a usable route to OrigNode, by checking whether the link to Y can be used to transmit packets to OrigNode. When H=0 in the incoming RREQ, the router MUST drop the RREQ-DIO if one of its addresses is present in the Address Vector. When H=1 in the incoming RREQ, the router MUST drop the RREQ message if the Orig SeqNo field of the RREQ is older than the SeqNo value that X has stored for a route to OrigNode. Otherwise, the router determines whether to propagate the RREQ-DIO. It does this by determining whether or not a route to OrigNode using the upstream direction of the incoming link satisfies the Objective Function (OF). In order to evaluate the OF, the router first determines the maximum useful Rank (MaxUsefulRank). If the router has previously joined the RREQ-Instance associated with the RREQ-DIO, then MaxUsefulRank is set to be the Rank value that was stored when the router processed the best previous RREQ for the DODAG with the given RREQ-Instance. Otherwise, MaxUsefulRank is set to be RankLimit. If OF cannot be satisfied (i.e., the Rank evaluates to a value greater than MaxUsefulRank), the RREQ-DIO MUST be dropped, and the following steps are not processed. Otherwise, the router MUST join the RREQ-Instance and prepare to propagate the RREQ-DIO, as follows. The upstream neighbor router that transmitted the received RREQ-DIO is selected as the preferred parent in the RREQ-Instance.
Step 2: TargNode and Intermediate Router Determination After determining that a received RREQ provides a usable route to OrigNode, a router determines whether it is a TargNode, a possible intermediate router between OrigNode and a TargNode, or both. The router is a TargNode if it finds one of its own addresses in a Target option in the RREQ. After possibly propagating the RREQ according to the procedures in Steps 3, 4, and 5, the TargNode generates an RREP as specified in . If S=0, the determination of TargNode status and determination of a usable route to OrigNode is the same. If the OrigNode tries to reach multiple TargNodes in a single RREQ-Instance, one of the TargNodes can be an intermediate router to other TargNodes. In this case, before transmitting the RREQ-DIO to multicast group all-AODV-RPL-nodes, a TargNode MUST delete the Target option encapsulating its own address, so that downstream routers with higher Rank values do not try to create a route to this TargNode. An intermediate router could receive several RREQ-DIOs from routers with lower Rank values in the same RREQ-Instance with different lists of Target options. For the purposes of determining the intersection with previous incoming RREQ-DIOs, the intermediate router maintains a record of the targets that have been requested for a given RREQ-Instance. An incoming RREQ-DIO message having multiple ART options coming from a router with higher Rank than the Rank of the stored targets is ignored. When transmitting the RREQ-DIO, the intersection of all received lists MUST be included if it is nonempty after TargNode has deleted the Target option encapsulating its own address. If the intersection is empty, it means that all the targets have been reached, and the router MUST NOT transmit any RREQ-DIO. Otherwise, it proceeds to . For example, suppose two RREQ-DIOs are received with the same RPL Instance and OrigNode. Suppose further that the first RREQ has (T1, T2) as the targets, and the second one has (T2, T4) as targets. Then, only T2 needs to be included in the generated RREQ-DIO. The reasoning for using the intersection of the lists in the RREQs is as follows. When two or more RREQs are received with the same Orig SeqNo, they were transmitted by OrigNode with the same destinations and OF. When an intermediate node receives two RREQs with the same Orig SeqNo but different lists of destinations, that means that some intermediate nodes retransmitting the RREQs have already deleted themselves from the list of destinations before they retransmitted the RREQ. Those deleted nodes are not to be reinserted back into the list of destinations.
Step 3: Intermediate Router RREQ Processing The intermediate router establishes itself as a viable node for a route to OrigNode as follows. If the H bit is set to 1, for a hop-by-hop route, then the router MUST build or update its upward route entry towards OrigNode, which includes at least the following items: Source Address, RPLInstanceID, Destination Address, Next Hop, Lifetime, and Sequence Number. The Destination Address and the RPLInstanceID can be learned from the DODAGID and the RPLInstanceID of the RREQ-DIO, respectively. The Source Address is the address used by the router to send data to the Next Hop, i.e., the preferred parent. The lifetime is set according to DODAG configuration (not the L field) and can be extended when the route is actually used. The Sequence Number represents the freshness of the route entry; it is copied from the Orig SeqNo field of the RREQ option. A route entry with the same source and destination address and the same RPLInstanceID, but a stale Sequence Number (i.e., incoming Sequence Number is less than the currently stored Sequence Number of the route entry), MUST be deleted.
Step 4: Symmetric Route Processing at an Intermediate Router If the S bit of the incoming RREQ-DIO is 0, then the route cannot be symmetric, and the S bit of the RREQ-DIO to be transmitted is set to 0. Otherwise, the router MUST determine whether the downward direction (i.e., towards the TargNode) of the incoming link satisfies the OF. If it does, the S bit of the RREQ-DIO to be transmitted is set to 1. Otherwise, the S bit of the RREQ-DIO to be transmitted is set to 0. When a router joins the RREQ-Instance, it also associates within its data structure for the RREQ-Instance the information about whether or not the RREQ-DIO to be transmitted has the S bit set to 1. This information associated to RREQ-Instance is known as the S bit of the RREQ-Instance. It will be used later during the RREP-DIO message processing (see ). Suppose a router has joined the RREQ-Instance, the H bit is set to 0, and the S bit of the RREQ-Instance is set to 1. In this case, the router MAY optionally include the Address Vector of the symmetric route back to OrigNode as part of the RREQ-Instance data. This is useful if the router later receives an RREP-DIO that is paired with the RREQ-Instance. If the router does NOT include the Address Vector, then it has to rely on multicast for the RREP. The multicast can impose a substantial performance penalty.
Step 5: RREQ Propagation at an Intermediate Router If the router is an intermediate router, then it transmits the RREQ-DIO to the multicast group all-AODV-RPL-nodes; if the H bit is set to 0, the intermediate router MUST append the address of its interface receiving the RREQ-DIO into the Address Vector. In addition, if the address of the router's interface transmitting the RREQ-DIO is not the same as the address of the interface receiving the RREQ-DIO, the router MUST also append the transmitting interface address into the Address Vector.
Step 6: RREQ Reception at TargNode If the router is a TargNode and was already associated with the RREQ-Instance, it takes no further action and does not send an RREP-DIO. If TargNode is not already associated with the RREQ-Instance, it prepares and transmits an RREP-DIO, possibly after waiting for RREP_WAIT_TIME, as detailed in ().
Generating RREP at TargNode When a TargNode receives an RREQ message over a link from a neighbor Y, TargNode first follows the procedures in . If the link to Y can be used to transmit packets to OrigNode, TargNode generates an RREP according to Sections and . Otherwise, TargNode drops the RREQ and does not generate an RREP. If the L field is not 0, the TargNode MAY delay transmitting the RREP-DIO for the duration RREP_WAIT_TIME to await a route with a lower Rank. The value of RREP_WAIT_TIME is set by default to 1/4 of the duration determined by the L field. For L == 0, RREP_WAIT_TIME is set by default to 0. Depending upon the application, RREP_WAIT_TIME may be set to other values. Smaller values enable quicker formation for the P2P route. Larger values enable formation of P2P routes with better Rank values. The address of the OrigNode MUST be encapsulated in the ART option and included in this RREP-DIO message along with the SeqNo of TargNode.
RREP-DIO for Symmetric Route If the RREQ-Instance corresponding to the RREQ-DIO that arrived at TargNode has the S bit set to 1, there is a symmetric route, both of whose directions satisfy the OF. Other RREQ-DIOs might later provide better upward routes. The method of selection between a qualified symmetric route and an asymmetric route that might have better performance is implementation specific and out of scope. For a symmetric route, the RREP-DIO message is unicast to the Next Hop according to the Address Vector (H=0) or the route entry (H=1); the DODAG in RREP-Instance does not need to be built. The RPLInstanceID in the RREP-Instance is paired as defined in . If the H bit is set to 0, the Address Vector from the RREQ-DIO MUST be included in the RREP-DIO.
RREP-DIO for Asymmetric Route When an RREQ-DIO arrives at a TargNode with the S bit set to 0, the TargNode MUST build a DODAG in the RREP-Instance corresponding to the RREQ-DIO rooted at itself, in order to provide OrigNode with a downstream route to the TargNode. The RREP-DIO message is transmitted to multicast group all-AODV-RPL-nodes.
RPLInstanceID Pairing Since the RPLInstanceID is assigned locally (i.e., there is no coordination between routers in the assignment of RPLInstanceID), the tuple (OrigNode, TargNode, RPLInstanceID) is needed to uniquely identify a discovered route. It is possible that multiple route discoveries with dissimilar OFs are initiated simultaneously. Thus, between the same pair of OrigNode and TargNode, there can be multiple AODV-RPL route discovery instances. So that OrigNode and TargNode can avoid any mismatch, they MUST pair the RREQ-Instance and the RREP-Instance in the same route discovery by using the RPLInstanceID. When preparing the RREP-DIO, a TargNode could find the RPLInstanceID candidate for the RREP-Instance is already occupied by another RPL Instance from an earlier route discovery operation that is still active. This unlikely case might happen if two distinct OrigNodes need routes to the same TargNode, and they happen to use the same RPLInstanceID for RREQ-Instance. In such cases, the RPLInstanceID of an already active RREP-Instance MUST NOT be used again for assigning RPLInstanceID for the later RREP-Instance. If the same RPLInstanceID were reused for two distinct DODAGs originated with the same DODAGID (TargNode address), intermediate routers could not distinguish between these DODAGs (and their associated OFs). Instead, the RPLInstanceID MUST be replaced by another value so that the two RREP-Instances can be distinguished. In the RREP-DIO option, the Delta field of the RREP-DIO message () indicates the value that TargNode adds to the RPLInstanceID in the RREQ-DIO that it received, to obtain the value of the RPLInstanceID it uses in the RREP-DIO message. 0 indicates that the RREQ-InstanceID has the same value as the RPLInstanceID of the RREP message. When the new RPLInstanceID after incrementation exceeds 255, it rolls over starting at 0. For example, if the RREQ-InstanceID is 252 and incremented by 6, the new RPLInstanceID will be 2. Related operations can be found in . RPLInstanceID collisions do not occur across RREQ-DIOs; the DODAGID equals the OrigNode address and is sufficient to disambiguate between DODAGs.
Receiving and Forwarding RREP Upon receiving an RREP-DIO, a router that already belongs to the RREP-Instance SHOULD drop the RREP-DIO. Otherwise, the router performs the steps in the following subsections.
Step 1: Receiving and Evaluation If the OF is not satisfied, the router MUST NOT join the DODAG; the router MUST discard the RREP-DIO and does not execute the remaining steps in this section. An intermediate router MUST discard an RREP if one of its addresses is present in the Address Vector and does not execute the remaining steps in this section. If the S bit of the associated RREQ-Instance is set to 1, the router MUST proceed to . If the S bit of the RREQ-Instance is set to 0, the router MUST determine whether the downward direction of the link (towards the TargNode) over which the RREP-DIO is received satisfies the OF and whether the router's Rank would not exceed the RankLimit. If these are true, the router joins the DODAG of the RREP-Instance. The router that transmitted the received RREP-DIO is selected as the preferred parent. Afterwards, other RREP-DIO messages can be received; AODV-RPL does not specify any action to be taken in such cases.
Step 2: OrigNode or Intermediate Router The router updates its stored value of the TargNode's Sequence Number according to the value provided in the ART option. The router next checks if one of its addresses is included in the ART option. If it is included, this router is the OrigNode of the route discovery. Otherwise, it is an intermediate router.
Step 3: Build Route to TargNode If the H bit is set to 1, then the router (OrigNode or intermediate) MUST build a downward route entry towards TargNode that includes at least the following items: OrigNode Address, RPLInstanceID, TargNode Address as destination, Next Hop, Lifetime, and Sequence Number. For a symmetric route, the Next Hop in the route entry is the router from which the RREP-DIO is received. For an asymmetric route, the Next Hop is the preferred parent in the DODAG of RREP-Instance. The RPLInstanceID in the route entry MUST be the RREQ-InstanceID (i.e., after subtracting the Delta field value from the value of the RPLInstanceID). The source address is learned from the ART option, and the destination address is learned from the DODAGID. The lifetime is set according to DODAG configuration (i.e., not the L field) and can be extended when the route is actually used. The Sequence Number represents the freshness of the route entry and is copied from the Dest SeqNo field of the ART option of the RREP-DIO. A route entry with the same source and destination address and the same RPLInstanceID, but a stale Sequence Number, MUST be deleted.
Step 4: RREP Propagation If the receiver is the OrigNode, it can start transmitting the application data to TargNode along the path as provided in RREP-Instance, and processing for the RREP-DIO is complete. Otherwise, the RREP will be propagated towards OrigNode. If H=0, the intermediate router MUST include the address of the interface receiving the RREP-DIO into the Address Vector. If H=1, according to the previous step, the intermediate router has set up a route entry for TargNode. If the intermediate router has a route to OrigNode, it uses that route to unicast the RREP-DIO to OrigNode. Otherwise, in the case of a symmetric route, the RREP-DIO message is unicast to the Next Hop according to the Address Vector in the RREP-DIO (H=0) or the local route entry (H=1). Otherwise, in the case of an asymmetric route, the intermediate router transmits the RREP-DIO to multicast group all-AODV-RPL-nodes. The RPLInstanceID in the transmitted RREP-DIO is the same as the value in the received RREP-DIO.
Gratuitous RREP In some cases, an intermediate router that receives an RREQ-DIO message MAY unicast a Gratuitous RREP-DIO (G-RREP-DIO) message back to OrigNode before continuing the transmission of the RREQ-DIO towards TargNode. The Gratuitous RREP (G-RREP) allows the OrigNode to start transmitting data to TargNode sooner. The G bit of the RREP option is provided to distinguish the G-RREP-DIO (G=1) sent by the intermediate router from the RREP-DIO sent by TargNode (G=0). The G-RREP-DIO MAY be sent out when the intermediate router receives an RREQ-DIO for a TargNode and the router has a pair of downward and upward routes to the TargNode that also satisfy the OF and for which the Destination Sequence Number is at least as large as the Sequence Number in the RREQ-DIO message. After unicasting the G-RREP to the OrigNode, the intermediate router then unicasts the RREQ towards TargNode, so that TargNode will have the advertised route towards OrigNode along with the RREQ-InstanceID for the RREQ-Instance. An upstream intermediate router that receives such a G-RREP MUST also generate a G-RREP and send it further upstream towards OrigNode. In case of source routing, the intermediate router MUST include the Address Vector between the OrigNode and itself in the G-RREP. It also includes the Address Vector in the unicast RREQ-DIO towards TargNode. Upon reception of the unicast RREQ-DIO, the TargNode will have a route Address Vector from itself to the OrigNode. Then, the router MUST include the Address Vector from the TargNode to the router itself in the G-RREP-DIO to be transmitted. For establishing hop-by-hop routes, the intermediate router MUST unicast the received RREQ-DIO to the Next Hop on the route. The Next Hop router along the route MUST build new route entries with the related RPLInstanceID and DODAGID in the downward direction. This process repeats at each node until the RREQ-DIO arrives at the TargNode. Then, the TargNode and each router along the path towards OrigNode MUST unicast the RREP-DIO hop-by-hop towards OrigNode as specified in .
Operation of Trickle Timer RREQ-Instance/RREP-Instance multicast uses Trickle timer operations to control RREQ-DIO and RREP-DIO transmissions. The Trickle control of these DIO transmissions follows the procedures described in entitled "DIO Transmission". If the route is symmetric, the RREP-DIO does not need the Trickle timer mechanism.
IANA Considerations AODV-RPL uses the "P2P Route Discovery Mode of Operation" (MOP == 4), with new options as specified in this document. This document has been added as an additional reference for "P2P Route Discovery Mode of Operation" in the "Mode of Operation" registry within the "Routing Protocol for Low Power and Lossy Networks (RPL)" registry group. IANA has assigned the three new AODV-RPL options described in in the "RPL Control Message Options" registry within the "Routing Protocol for Low Power and Lossy Networks (RPL)" registry group. AODV-RPL Options
Value Meaning Reference
0x0B RREQ RFC 9854
0x0C RREP RFC 9854
0x0D ART RFC 9854
IANA has allocated the permanent multicast address with link-local scope in for nodes implementing this specification. This allocation has been made in the "Local Network Control Block (224.0.0.0 - 224.0.0.255 (224.0.0/24))" registry within the "IPv4 Multicast Address Space Registry" registry group. Permanent Multicast Address with Link-Local Scope
Address(es) Description References
224.0.0.69 all-AODV-RPL-nodes RFC 9854
Security Considerations The security considerations for the operation of AODV-RPL are similar to those for the operation of RPL (as described in Section of the RPL specification ). Sections and of describe RPL's optional security framework, which AODV-RPL relies on to provide data confidentiality, authentication, replay protection, and delay protection services. Additional analysis for the security threats to RPL can be found in . A router can join a temporary DAG created for a secure AODV-RPL route discovery only if it can support the security configuration in use (see ), which also specifies the key in use. It does not matter whether the key is preinstalled or dynamically acquired. The router must have the key in use before it can join the DAG being created for secure route discovery. If a rogue router knows the key for the security configuration in use, it can join the secure AODV-RPL route discovery and cause various types of damage. Such a rogue router could advertise false information in its DIOs in order to include itself in the discovered route(s). It could generate bogus RREQ-DIO and RREP-DIO messages carrying bad routes or maliciously modify genuine RREP-DIO messages it receives. A rogue router acting as the OrigNode could launch denial-of-service attacks against the LLN deployment by initiating fake AODV-RPL route discoveries. When rogue routers might be present, RPL's preinstalled mode of operation, where the key to use for route discovery is preinstalled, SHOULD be used. When an RREQ-DIO message uses the source routing option by setting the H bit to 0, a rogue router may populate the Address Vector field with a set of addresses that may result in the RREP-DIO traveling in a routing loop. If a rogue router is able to forge a G-RREP, it could mount denial-of-service attacks.
References Normative References Key words for use in RFCs to Indicate Requirement Levels In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. The Trickle Algorithm The Trickle algorithm allows nodes in a lossy shared medium (e.g., low-power and lossy networks) to exchange information in a highly robust, energy efficient, simple, and scalable manner. Dynamically adjusting transmission windows allows Trickle to spread new information on the scale of link-layer transmission times while sending only a few messages per hour when information does not change. A simple suppression mechanism and transmission point selection allow Trickle's communication rate to scale logarithmically with density. This document describes the Trickle algorithm and considerations in its use. [STANDARDS-TRACK] RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks Low-Power and Lossy Networks (LLNs) are a class of network in which both the routers and their interconnect are constrained. LLN routers typically operate with constraints on processing power, memory, and energy (battery power). Their interconnects are characterized by high loss rates, low data rates, and instability. LLNs are comprised of anything from a few dozen to thousands of routers. Supported traffic flows include point-to-point (between devices inside the LLN), point-to-multipoint (from a central control point to a subset of devices inside the LLN), and multipoint-to-point (from devices inside the LLN towards a central control point). This document specifies the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL), which provides a mechanism whereby multipoint-to-point traffic from devices inside the LLN towards a central control point as well as point-to-multipoint traffic from the central control point to the devices inside the LLN are supported. Support for point-to-point traffic is also available. [STANDARDS-TRACK] Routing Metrics Used for Path Calculation in Low-Power and Lossy Networks Low-Power and Lossy Networks (LLNs) have unique characteristics compared with traditional wired and ad hoc networks that require the specification of new routing metrics and constraints. By contrast, with typical Interior Gateway Protocol (IGP) routing metrics using hop counts or link metrics, this document specifies a set of link and node routing metrics and constraints suitable to LLNs to be used by the Routing Protocol for Low-Power and Lossy Networks (RPL). [STANDARDS-TRACK] Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References Ad-hoc On-demand Distance Vector Routing Advanced Development Group, Sun MicroSystems Laboratories, Inc., Menlo Park, CA, USA
Advanced Development Group, Sun MicroSystems Laboratories, Inc., Menlo Park, CA, USA
Proceedings WMCSA'99. Second IEEE Workshop on Mobile Computing Systems and Applications, pp. 90-100 Co-iOAM: In-situ Telemetry Metadata Transport for Resource Constrained Networks within IETF Standards Framework
2018 10th International Conference on Communication Systems & Networks (COMSNETS), pp. 573-576 The Contiki Open Source OS for the Internet of Things (Contiki Version 2.7) commit 7635906 Contiki-NG: The OS for Next Generation IoT Devices (Contiki-NG Version 4.6) commit 3b0bc6a Cooja Simulator for Wireless Sensor Networks (Contiki/Cooja Version 2.7) commit 7635906 An empirical study of asymmetry in low-power wireless links
IEEE Communications Magazine, vol. 50, no. 7, pp. 137-146 On Link Asymmetry and One-way Estimation in Wireless Sensor Networks
ACM Transactions on Sensor Networks, vol. 6, no. 2, pp. 1-25 An empirical study of low-power wireless
ACM Transactions on Sensor Networks, vol. 6, no. 2, pp. 1-49 Ad hoc On-Demand Distance Vector (AODV) Routing The Ad hoc On-Demand Distance Vector (AODV) routing protocol is intended for use by mobile nodes in an ad hoc network. It offers quick adaptation to dynamic link conditions, low processing and memory overhead, low network utilization, and determines unicast routes to destinations within the ad hoc network. It uses destination sequence numbers to ensure loop freedom at all times (even in the face of anomalous delivery of routing control messages), avoiding problems (such as "counting to infinity") associated with classical distance vector protocols. This memo defines an Experimental Protocol for the Internet community. Performance Evaluation of the Routing Protocol for Low-Power and Lossy Networks (RPL) This document presents a performance evaluation of the Routing Protocol for Low-Power and Lossy Networks (RPL) for a small outdoor deployment of sensor nodes and for a large-scale smart meter network. Detailed simulations are carried out to produce several routing performance metrics using these real-life deployment scenarios. Please refer to the PDF version of this document, which includes several plots for the performance metrics not shown in the plain-text version. This document is not an Internet Standards Track specification; it is published for informational purposes. Reactive Discovery of Point-to-Point Routes in Low-Power and Lossy Networks This document specifies a point-to-point route discovery mechanism, complementary to the Routing Protocol for Low-power and Lossy Networks (RPL) core functionality. This mechanism allows an IPv6 router to discover "on demand" routes to one or more IPv6 routers in a Low-power and Lossy Network (LLN) such that the discovered routes meet specified metrics constraints. A Mechanism to Measure the Routing Metrics along a Point-to-Point Route in a Low-Power and Lossy Network This document specifies a mechanism that enables a Routing Protocol for Low-power and Lossy Networks (RPL) router to measure the aggregated values of given routing metrics along an existing route towards another RPL router, thereby allowing the router to decide if it wants to initiate the discovery of a better route. An Overview of Operations, Administration, and Maintenance (OAM) Tools Operations, Administration, and Maintenance (OAM) is a general term that refers to a toolset for fault detection and isolation, and for performance measurement. Over the years, various OAM tools have been defined for various layers in the protocol stack. This document summarizes some of the OAM tools defined in the IETF in the context of IP unicast, MPLS, MPLS Transport Profile (MPLS-TP), pseudowires, and Transparent Interconnection of Lots of Links (TRILL). This document focuses on tools for detecting and isolating failures in networks and for performance monitoring. Control and management aspects of OAM are outside the scope of this document. Network repair functions such as Fast Reroute (FRR) and protection switching, which are often triggered by OAM protocols, are also out of the scope of this document. The target audience of this document includes network equipment vendors, network operators, and standards development organizations. This document can be used as an index to some of the main OAM tools defined in the IETF. At the end of the document, a list of the OAM toolsets and a list of the OAM functions are presented as a summary. A Security Threat Analysis for the Routing Protocol for Low-Power and Lossy Networks (RPLs) This document presents a security threat analysis for the Routing Protocol for Low-Power and Lossy Networks (RPLs). The development builds upon previous work on routing security and adapts the assessments to the issues and constraints specific to low-power and lossy networks. A systematic approach is used in defining and evaluating the security threats. Applicable countermeasures are application specific and are addressed in relevant applicability statements. Management of Networks with Constrained Devices: Use Cases This document discusses use cases concerning the management of networks in which constrained devices are involved. A problem statement, deployment options, and the requirements on the networks with constrained devices can be found in the companion document on "Management of Networks with Constrained Devices: Problem Statement and Requirements" (RFC 7547). Routing for RPL (Routing Protocol for Low-Power and Lossy Networks) Leaves This specification provides a mechanism for a host that implements a routing-agnostic interface based on IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Neighbor Discovery to obtain reachability services across a network that leverages RFC 6550 for its routing operations. It updates RFCs 6550, 6775, and 8505. An Architecture for IPv6 over the Time-Slotted Channel Hopping Mode of IEEE 802.15.4 (6TiSCH) This document describes a network architecture that provides low-latency, low-jitter, and high-reliability packet delivery. It combines a high-speed powered backbone and subnetworks using IEEE 802.15.4 time-slotted channel hopping (TSCH) to meet the requirements of low-power wireless deterministic applications.
Example: Using ETX/RSSI Values to Determine Value of S Bit The combination of the downstream Received Signal Strength Indicator (RSSI) and the upstream Expected Transmission Count (ETX) has been tested to determine whether a link is symmetric or asymmetric at intermediate routers. We present two methods to obtain an ETX value from RSSI measurement.
Method 1:
In the first method, we constructed a table measuring RSSI versus ETX using the Cooja simulation setup in the Contiki OS environment . We used Contiki-2.7 running the 6LoWPAN/RPL protocol stack for the simulations. For approximating the number of packet drops based on the RSSI values, we implemented simple logic that drops transmitted packets with certain predefined ratios before handing over the packets to the receiver. The packet drop ratio is implemented as a table lookup of RSSI ranges mapping to different packet drop ratios with lower RSSI ranges resulting in higher values. While this table has been defined for the purpose of capturing the overall link behavior, in general, it is highly recommended to conduct physical radio measurement experiments. By keeping the receiving node at different distances, we let the packets experience different packet drops as per the described method. The ETX value computation is done by another module that is part of RPL OF implementation. Since the ETX value is reflective of the extent of packet drops, it allowed us to prepare a useful table correlating ETX and RSSI values (see ). ETX and RSSI values obtained in this way may be used as explained below:
Communication Link from Source to Destination Source -------> NodeA -------> NodeB -----> Destination
Selection of S Bit Based on Expected ETX Value
RSSI at NodeA for NodeB Expected ETX at NodeA for NodeB->NodeA
> -60 150
-70 to -60 192
-80 to -70 226
-90 to -80 662
-100 to -90 3840
Method 2:
One could also make use of the function guess_etx_from_rssi() defined in the 6LoWPAN/RPL protocol stack of Contiki-ng OS to obtain RSSI-ETX mapping. This function outputs an ETX value ranging between 128 and 3840 for -60 <= rssi <= -89. The function description is beyond the scope of this document.
We tested the operations in this specification by making the following experiment, using the above parameters. In our experiment, a communication link is considered as symmetric if the ETX value of NodeA->NodeB and NodeB->NodeA (see ) are within, say, a 1:3 ratio. This ratio should be understood as determining the link's symmetric/asymmetric nature. NodeA can typically know the ETX value in the direction of NodeA->NodeB, but it has no direct way of knowing the value of ETX from NodeB->NodeA. Using physical testbed experiments and realistic wireless channel propagation models, one can determine a relationship between RSSI and ETX representable as an expression or a mapping table. Such a relationship, in turn, can be used to estimate the ETX value at NodeA for link NodeB->NodeA from the received RSSI from NodeB. Whenever NodeA determines that the link towards the NodeB is bidirectional asymmetric, then the S bit is set to 0. Afterwards, the link from NodeA to Destination remains designated as asymmetric, and the S bit remains set to 0. Determination of asymmetry versus bidirectionality remains a topic of lively discussion in the IETF.
Some Example AODV-RPL Message Flows This appendix provides some example message flows showing RREQ and RREP establishing symmetric and asymmetric routes. Also, examples for the use of RREP_WAIT and G-RREP are included. In the examples, router (O) is to be understood as performing the role of OrigNode. Router (T) is to be understood as performing the role of TargNode. Routers (R) are intermediate routers that are performing AODV-RPL functions in order to discover one or more suitable routes between (O) and (T).
Example Control Message Flows in Symmetric and Asymmetric Networks In the following diagram, RREQ messages are multicast from router (O) in order to discover routes to and from router (T). The RREQ control messages flow outward from (O). Each router along the way establishes a single RREQ-Instance identified by RREQ-InstanceID even if multiple RREQs are received with the same RREQ-InstanceID. In the top half of the diagram, the routers are able to offer a symmetric route at each hop of the path from (O) to (T). When (T) receives an RREQ, it is then able to transmit data packets to (O). Router (T) then prepares to send an RREP along the symmetric path that would enable router (O) to send packets to router (T).
AODV-RPL RREQ Message Flow Example When Symmetric Path Available (R) ---RREQ(S=1)--->(R) ---RREQ(S=1)--->(R) ^ | | | RREQ(S=1) RREQ(S=1) | | | v (O) --------->(R) --------->(R)-------->(T) / \ RREQ RREQ RREQ ^ | \ (S=1) (S=0) (S=0) | | \ / RREQ | \ RREQ (S=1) RREQ (S=0) (S=0) | \ / v \ RREQ (S=0) / (R) ---->(R)------>(R)----.....--->(R)
In the following diagram, which results from the above RREQ message transmission, a symmetric route is available from (T) to router (O) via the routers in the top half of the diagram. RREP messages are sent via unicast along the symmetric route. Since the RREP message is transmitted via unicast, no RREP messages are sent by router (T) to the routers in the bottom half of the diagram.
AODV-RPL RREP Message Flow Example When Symmetric Path Available (R)<------RREP----- (R)<------RREP----- (R) | ^ | | RREP RREP | | v | (O) ----------(R) ----------(R) --------(T) / \ | | \ | | \ (no RREP messages sent) / | \ / | \ / | \ / (R) -----(R)-------(R)----.....----(R)
In the following diagram, RREQ messages are multicast from router (O) in order to discover routes to and from router (T) as before. As shown, no symmetric route is available from (O) to (T).
AODV-RPL RREQ Message Flow When Symmetric Path Unavailable (R) ---RREQ(S=0)--->(R) ---RREQ(S=0)--->(R) ^ | | | RREQ(S=1) RREQ(S=0) | | | v (O) --------->(R) --------->(R)-------->(T) ^ \ RREQ RREQ RREQ | \ | \ (S=1) (S=0) (S=0) | | | \ / | | RREQ (S=1) RREQ (S=0) / (R) | \ / | | \ RREQ (S=0) / / (R) ---->(R)------>(R)----.....----->(R)---
Upon receiving the RREQ in , router (T) then prepares to send an RREP that would enable router (O) to send packets to router (T). In , since no symmetric route is available from (T) to router (O), RREP messages are sent via multicast to all neighboring routers.
AODV-RPL RREQ and RREP-Instances for Asymmetric Links (R)<------RREP----- (R)<------RREP----- (R) | | | | RREP RREP | | | | v v (O)<--------- (R)<--------- (R)<------- (T) ^ \ RREP RREP RREP | \ | \ | |RREP | \ / | RREP | \ RREP RREP / (R) | \ / | | \ / / (R)<----- (R)<----- (R)<---.....---- (R)< - RREP RREP RREP RREP
Example RREP_WAIT Handling In , the first RREQ arrives at (T). This triggers TargNode to start the RREP_WAIT_TIME timer.
TargNode Starts RREP_WAIT (O) --------->(R) --------->(R)-------->(T) RREQ RREQ RREQ (S=1) (S=0) (S=0)
In , another RREQ arrives before the RREP_WAIT_TIME timer is expired. It could be preferable compared the previously received RREP that caused the RREP_WAIT_TIME timer to be set.
Waiting TargNode Receives Preferable RREQ (O) (T) / \ ^ | \ | | \ / RREQ | \ RREQ (S=1) RREQ (S=0) (S=0) | \ / v \ RREQ (S=0) / (R) ---->(R)------>(R)----.....--->(R)
In , the RREP_WAIT_TIME timer expires. TargNode selects the path with S=1.
RREP_WAIT Expires at TargNode (R) ---RREQ(S=1)--->(R) ---RREQ(S=1)--->(R) ^ | | | RREQ(S=1) RREQ(S=1) | | | v (O) (T)
Example G-RREP Handling In , R* has upward and downward routes to TargNode (T) that satisfy the OF of the RPL Instance originated by OrigNode (O), and the Destination Sequence Number is at least as large as the Sequence Number in the RREQ message.
RREP Triggers G-RREP at Intermediate Node (R) ---RREQ(S=1)--->(R) ---RREQ(S=0)--->(R) ^ | | | RREQ(S=1) RREQ(S=0) | | | v (O) --------->(R) --------->(R)-------->(T) / \ RREQ RREQ RREQ ^ | \ (S=1) (S=0) (S=0) | | \ / RREQ | \ RREQ (S=1) / (S=0) | \ / v \ v (R) ---->(R*)<------>(R)<----....--->(R)
In , R* transmits the G-RREP-DIO back to OrigNode (O) and forwards the incoming RREQ towards (T).
Intermediate Node Initiates G-RREP (O) (T) \ ^ \ | \ (RREQ) / \ G-RREP-DIO / \ / \ (RREQ) (RREQ) / (R*)------>(R)----....--->(R)
Acknowledgements The authors thank , , and for their support and valuable input. The authors specially thank for implementing AODV-RPL in Contiki and conducting extensive simulation studies. The authors would like to acknowledge the reviews, feedback, and comments from the following people, in alphabetical order: , , , , , , , , , , , , , , and .
Contributors Wenzhou-Kean University
88 Daxue Rd, Ouhai Wenzhou Zhejiang Province, 325060 China Kean University 1000 Morris Avenue Union, New Jersey 07083 United States of America sangi_bahrian@yahoo.com
Indian Institute of Science
Bangalore 560012 India malati@iisc.ac.in
Huawei Technologies
No. 156 Beiqing Rd. Haidian District Beijing 100095 China zhangmingui@huawei.com
Authors' Addresses Blue Meadow Networks
Saratoga CA 95070 United States of America charliep@lupinlodge.com
Indian Institute of Science
Bangalore 560012 India anandsvr@iisc.ac.in
SRM University-AP
Amaravati Campus Amaravati, Andhra Pradesh 522 502 India satishnaidu80@gmail.com
Huawei Technologies
No. 156 Beiqing Rd. Haidian District Beijing 100095 China remy.liubing@huawei.com