Internet Engineering Task Force M. Goyal, Ed.
Internet-Draft University of Wisconsin
Intended status: Standards Track Milwaukee
Expires: October 13, 2011 E. Baccelli, Ed.
INRIA
A. Brandt
Sigma Designs
R. Cragie
Gridmerge Ltd
J. Martocci
Johnson Controls
C. Perkins
Tellabs Inc
April 11, 2011
A Mechanism to Measure the Quality of a Point-to-point Route in a Low
Power and Lossy Network
draft-ietf-roll-p2p-measurement-00
Abstract
This document specifies a mechanism that enables an RPL node to
measure the quality of an existing route to/from another RPL node in
a low power and lossy network, thereby allowing the node to decide if
it wants to initiate the discovery of a more optimal route.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on October 13, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Functional Overview . . . . . . . . . . . . . . . . . . . . . 4
3. The Measurement Object (MO) . . . . . . . . . . . . . . . . . 5
4. Originating an MO To Measure a P2P Route . . . . . . . . . . . 6
4.1. From the Origin Node to the Target Node . . . . . . . . . 7
4.2. From the Target Node to the Origin Node . . . . . . . . . 8
5. Processing a Received MO at an Intermediate Router . . . . . . 8
6. Processing a Received MO at the Target Node . . . . . . . . . 9
7. Processing a Received MO at the Origin Node . . . . . . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
11.1. Normative References . . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
Point to point (P2P) communication between arbitrary nodes in a Low
power and Lossy Network (LLN) is a key requirement for many
applications [RFC5826][RFC5867]. RPL [I-D.ietf-roll-rpl], the IPv6
Routing Protocol for LLNs, constrains the LLN topology to a Directed
Acyclic Graph (DAG) built to optimize routing costs to reach the
DAG's root and requires the P2P routes to use the DAG links only.
Such P2P routes may potentially be suboptimal and may lead to traffic
congestion near the DAG root. Additionally, RPL is a proactive
routing protocol and hence all P2P routes must be established ahead
of the time they are used.
To ameliorate situations, where RPL's P2P routing functionality does
not meet the requirements, [I-D.ietf-roll-p2p-rpl] describes a
reactive mechanism to discover P2P routes that meet the specified
performance characteristics. This mechanism, henceforth referred to
as the reactive P2P route discovery, requires the specification of
"good enough criteria", in terms of constraints on aggregated values
of the relevant routing metrics [I-D.ietf-roll-routing-metrics], that
the discovered routes must satisfy. In some cases, the application
requirements or the LLN's topological features allow a node to infer
the good enough criteria intrinsically. For example, the application
may require the end-to-end loss rate and/or latency on the route to
be below certain thresholds or the LLN topology may be such that a
router can safely assume its destination to be less than a certain
number of hops away from itself.
When the existing P2P routes are deemed unsatisfactory by the
application layer but the node does not intrinsically know the good
enough criteria, it may be necessary for the node to determine the
aggregated values of relevant routing metrics along the existing
routes. This knowledge will allow the node to frame a reasonable
good enough criteria and initiate a reactive P2P route discovery to
determine better routes. For example, if the router determines the
aggregate ETX [I-D.ietf-roll-routing-metrics] along an existing route
to be "x", it can use "ETX < x*y", where y is a certain fraction, as
a constraint in the good enough criteria. Note that it is important
that the good enough criteria is not overly strict; otherwise the
route discovery may fail even though routes, much better than the
ones being currently used, exist.
This document specifies a mechanism that enables an RPL node to
measure the aggregated values of the routing metrics along an
existing route to/from another RPL node in an LLN, thereby allowing
the node to decide if it wants to initiate the reactive discovery of
a more optimal route and determine the good enough criteria to be
used for this purpose.
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1.1. 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
[RFC2119].
Additionally, this document uses terminology from
[I-D.ietf-roll-terminology], [I-D.ietf-roll-rpl] and
[I-D.ietf-roll-p2p-rpl]. Specifically, the term node refers to an
RPL router or an RPL host as defined in [I-D.ietf-roll-rpl]. The
following terms, originally defined in [I-D.ietf-roll-p2p-rpl], are
redefined in the following manner.
Origin Node: The origin node refers to the node that initiates the
measurement process defined in this document and is one end point of
the P2P route being measured.
Target Node: The target node refers to the other end of the P2P route
being measured.
Intermediate Router: A router, other than the origin and the target
node, on the P2P route being measured.
2. Functional Overview
The mechanism described in this document can be used by an origin
node to measure the aggregated values of the routing metrics along a
P2P route to/from a target node in the LLN. Such a route could be a
source route or a hop-by-hop route established using RPL
[I-D.ietf-roll-rpl] or the reactive P2P route discovery
[I-D.ietf-roll-p2p-rpl].
When an origin node desires to measure the aggregated values of the
routing metrics along a P2P route from itself to a target node, it
sends a Measurement Request message along that route. The
Measurement Request message accumulates the values of the relevant
routing metrics as it travels towards the target node. Upon
receiving the Measurement Request message, the target node unicasts a
Measurement Reply message, carrying the accumulated values of the
routing metrics, back to the origin node.
When an origin node desires to measure the aggregated values of the
routing metrics along a P2P route from a target node to itself, it
unicasts a Measurement Request message, specifying the routing
metrics to be measured, to the target node. On receiving the
Measurement Request message, the target node sends a Measurement
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Reply message to the origin node along the P2P route to be measured.
The Measurement Reply message accumulates the values of the relevant
routing metrics as it travels towards the origin node.
3. The Measurement Object (MO)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID | SequenceNo |T|H|I|D| Resvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Origin Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Target Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Source Route Option(*) .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Metric Container Options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format of the Measurement Object (MO)
This document defines a new RPL Control Message type, the Measurement
Object (MO) with code 0x05 (to be confirmed by IANA) that serves as
both Measurement Request and Measurement Reply. The format of an MO
is shown in Figure 1. An MO consists of the following fields:
o RPLInstanceID: Relevant only if the MO travels along a hop-by-hop
route. This field identifies the RPLInstanceID of the hop-by-hop
route.
o SequenceNo: A 16-bit sequence number that uniquely identifies a
Measurement Request and the corresponding Measurement Reply to the
origin node.
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o T: The type flag. This flag is set if the MO represents a
Measurement Request. The flag is cleared if the MO is a
Measurement Reply.
o H: This flag is set if the MO travels along a hop-by-hop route.
In that case, the hop-by-hop route is identified by the
RPLInstanceID and, if required, the Origin/Target Address serving
as the DODAGID. This flag is cleared if the MO travels along a
source route. In that case, the MO MUST contain a Source Route
option [I-D.ietf-roll-p2p-rpl]. Note that, in case of a P2P route
along a non-storing DAG, it is possible that an MO message travels
along a hop-by-hop route till the DAG's root, which then sends it
along a source route to its destination. In that case, the DAG
root will reset the H flag and also insert a Source Route option
in the MO.
o I: A flag that indicates which of the two - the Origin Address and
the Target Address - indicates the DODAGID for the hop-by-hop
route. This flag is relevant only if the MO travels along a hop-
by-hop route (i.e., H flag is set) and a local RPLInstanceID has
been specified to identify the hop-by-hop route. This flag is set
if the Origin Address indicates the DODAGID; the flag is cleared
if the Target Address indicates the DODAGID.
o D: A flag that indicates the direction of the P2P route. This
flag is set when the route to be measured is from the origin node
to the target node. Otherwise, the flag is cleared.
o Reserved: These bits are reserved for future use. These bits MUST
be set to zero on transmission and MUST be ignored on reception.
o Origin Address: The IPv6 address of the origin node.
o Target Address: The IPv6 address of the target node.
o Source Route Option: An MO MUST contain one Source Route option if
it travels along a source route.
o Metric Container Options: An MO MUST contain one or more Metric
Container options to carry the routing metric objects
[I-D.ietf-roll-routing-metrics].
4. Originating an MO To Measure a P2P Route
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4.1. From the Origin Node to the Target Node
If the origin node intends to measure the routing metric values along
a P2P route towards a target node, it generates an MO message and
sets its fields as follows:
o RPLInstanceID: If the P2P route is a hop-by-hop route, the origin
node specifies the RPLInstanceID to identify the route in this
field. This field is not relevant if the P2P route is a source
route specified in the Source Route option. This document
RECOMMENDS a value 10000000 for this field if the P2P route is a
source route.
o SequenceNo: The origin node assigns a sequence number to the MO to
uniquely identify the corresponding Measurement Reply.
o T: The T flag is set to indicate that MO represents a Measurement
Request.
o H: The H flag is set if the MO travels along a hop-by-hop route.
o I: This field in relevant only if the H flag is set and the
RPLInstanceID is a local value. The origin node sets this flag if
the Origin Address indicates the DODAGID. The origin node clears
this flag if the Target Address indicates the DODAGID.
o D: This flag is set.
o Origin Address, Target Address: These fields are set to the IPv6
addresses of the origin and target nodes respectively. If the H
flag is set and the RPLInstanceID is a local value, the Origin
Address or the Target Address MUST also indicate the DODAGID value
required to identify the hop-by-hop route.
o Source Route Option: If the P2P route is a source route (i.e., the
H flag is cleared), the Source Route option MUST be present and
MUST include a complete source route to the target node in forward
direction (excluding the addresses of the origin and target
nodes).
o Metric Container Options: The origin node MUST also include one or
more Metric Container options containing relevant routing metric
objects to accumulate the costs for these metrics along the P2P
route. The origin node also initiates the routing metric objects
by including the local values of the routing metrics for the first
hop on the P2P route.
After setting the MO fields as described above, the origin node MUST
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unicast the MO message to the next hop on the P2P route. The origin
node MAY include a Record Route IPv6 Extension Header, proposed in
[I-D.thubert-6man-reverse-routing-header], in the MO message to
accumulate a reverse route that the target node can use to send the
Measurement Reply back to the origin node.
4.2. From the Target Node to the Origin Node
If the origin node intends to measure the routing metric values along
a P2P route from a target node to itself, it generates an MO message
and sets its fields as follows:
o SequenceNo: The origin node assigns a sequence number to the MO to
uniquely identify the corresponding Measurement Reply.
o T: The T flag is set to indicate that MO represents a Measurement
Request.
o D: This flag is cleared.
o Origin Address, Target Address: These fields are set to the IPv6
addresses of the origin and target nodes respectively.
o Source Route Option: In this case, the MO SHOULD NOT include any
Source Route option.
o Metric Container Options: The origin node MUST include one or more
Metric Container options containing relevant routing metric
objects to accumulate the costs for these metrics along the P2P
route. These routing metric objects MUST be empty.
The other fields in the MO are not relevant in this case and SHOULD
be set to zero. After setting the MO fields as described above, the
origin node MUST unicast the MO message to the target node.
5. Processing a Received MO at an Intermediate Router
When a node receives an MO, it examines if one of its IPv6 addresses
is listed as the Origin Address or the Target Address. If not, the
node checks if H bit is clear (i.e., the MO is traveling along a
source route). If yes, the node checks the Address[0] field inside
the Source Route Option contained in the MO. The node MUST drop the
MO with no further processing and send an ICMPv6 Destination
Unreachable error message to the source of the message (the Origin
Address if the MO is a Measurement Request; otherwise the Target
Address) if the received MO has a clear H bit but does not contain a
Source Route Option or if the Address[0] inside the Source Route
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option does not match one of the node's IPv6 address.
The node then determines the next hop on the P2P route being
measured. In case the received MO has a clear H flag, the Address[1]
field (the second element in the Address vector) inside the Source
Route Option is taken as the next hop. If the Source Route Option
does not contain Address[1] element, the node checks the T flag
inside the MO. If T flag is set, i.e., MO is a Measurement Request,
the Target Address is taken as the next hop; otherwise the Origin
Address is the next hop. If the received MO has H flag set, the node
uses the RPLInstanceID, the ultimate destination of the MO (Target
Address if T flag is set; otherwise the Origin Address) and, if
RPLInstanceID is a local value, the DODAGID (the Origin Address if I
flag is set; otherwise the Target Address) to determine the next hop
for the MO. If the H flag in the MO is set and the node is the root
of a non-storing DAG, indicated by the RPLInstanceID, the node MAY
reset the H flag and insert a Source Route option in the MO to
indicate a source route along which the MO should travel on rest of
its way to its destination. The node MUST drop the MO with no
further processing and send an ICMPv6 Destination Unreachable error
message to the source of the message if it can not determine the next
hop for the message.
After determining the next hop, the node updates the routing metric
objects, contained in the Metric Container options inside the MO,
either by updating the aggregated value for the routing metric or by
attaching the local values for the metric inside the object. The
node MUST drop the MO with no further processing and send a suitable
ICMPv6 error message to the source of the message if the node does
not know the relevant routing metric values for the next hop.
After updating the routing metrics, the node MUST unicast the MO to
the next hop. If the MO to be forwarded has a clear H flag, the node
MUST ensure that the Address vector in the Source Route option
contains the next hop address as the first element.
6. Processing a Received MO at the Target Node
When a node receives an MO, it examines if one of its IPv6 addresses
is listed as the Target Address. If yes, the node checks the T flag.
The node MUST drop the MO with no further processing and optionally
log an error if the T flag is clear (i.e. the received MO is a
Measurement Reply).
The target node then checks the D flag to determine the direction of
the P2P route to be measured. If the D flag is set (i.e., the P2P
route to be measured is from the origin node to the target node), the
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target node updates the routing metrics objects in the Metric
Container options if required, removes the Source Route Option if
present and clears the T bit thereby converting the MO into a
Measurement Reply. The target node then unicasts the updated MO back
to the origin node. For this purpose, the target node MAY use the
reverse route accumulated in the Record Route IPv6 Extension Header
[I-D.thubert-6man-reverse-routing-header] if present in the received
MO message.
If the D flag in the received MO message is clear (i.e., the P2P
route to be measured is from the target node to the origin node), the
target node selects the P2P route to be measured and modifies the
following MO fields:
o RPLInstanceID: If the P2P route is a hop-by-hop route, the target
node specifies in this field the RPLInstanceID associated with the
route. This field is not relevant if the P2P route is a source
route. This document RECOMMENDS a value 10000000 for this field
if the P2P route is a source route.
o T: The T flag is cleared to indicate that MO represents a
Measurement Reply.
o H: The H flag is set if the P2P route is a hop-by-hop one.
o I: If the H flag is set and the RPLInstanceID is a local value,
the target node sets this flag if the Origin Address indicates the
DODAGID. The target node clears this flag if the Target Address
indicates the DODAGID.
o D: This flag is cleared.
o Source Route Option: If the P2P route is a source route, the
Source Route option MUST be present and MUST include a complete
source route from the target node to the origin node (excluding
the addresses of the target and origin nodes).
o Metric Container Options: The target node MUST initiate the
routing metric objects inside the Metric Container options by
including the local values of the routing metrics for the first
hop on the P2P route.
The target node need not modify the other fields in the received MO.
After these modifications, the target node MUST unicast the MO
message to the next hop on the P2P route.
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7. Processing a Received MO at the Origin Node
When a node receives an MO, it examines if one of its IPv6 addresses
is listed as the Origin Address. If yes, the node checks the T flag.
The node MUST drop the MO with no further processing and optionally
log an error if the T flag is set (i.e. the received MO is a
Measurement Request) or if the node has no recollection of sending a
Measurement Request with the sequence number listed in the received
MO.
If the D flag in the received MO is clear (i.e., the P2P route to be
measured is from the target node to the origin node), the origin node
MUST update the routing metrics objects in the Metric Container
options if required.
The origin node can now examine the routing metric objects inside the
Metric Container options to evaluate the quality of the measured P2P
route. If a routing metric object contains local metric values
recorded by enroute nodes, the origin node MAY aggregate these local
values into an end-to-end value as per the aggregation rules for the
metric.
8. Security Considerations
TBA
9. IANA Considerations
TBA
10. Acknowledgement
Authors gratefully acknowledge the contributions of Pascal Thubert,
Richard Kelsey and Zach Shelby in the development of this document.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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11.2. Informative References
[I-D.ietf-roll-p2p-rpl]
Goyal, M., Baccelli, E., Brandt, A., Cragie, R., Martocci,
J., and C. Perkins, "Reactive Discovery of Point-to-Point
Routes in Low Power and Lossy Networks",
draft-ietf-roll-p2p-rpl-02 (work in progress),
February 2011.
[I-D.ietf-roll-routing-metrics]
Vasseur, J., Kim, M., Pister, K., Dejean, N., and D.
Barthel, "Routing Metrics used for Path Calculation in Low
Power and Lossy Networks",
draft-ietf-roll-routing-metrics-19 (work in progress),
March 2011.
[I-D.ietf-roll-rpl]
Winter, T., Thubert, P., Brandt, A., Clausen, T., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., and J.
Vasseur, "RPL: IPv6 Routing Protocol for Low power and
Lossy Networks", draft-ietf-roll-rpl-19 (work in
progress), March 2011.
[I-D.ietf-roll-terminology]
Vasseur, J., "Terminology in Low power And Lossy
Networks", draft-ietf-roll-terminology-05 (work in
progress), March 2011.
[]
Thubert, P., "Reverse Routing Header",
draft-thubert-6man-reverse-routing-header-01 (work in
progress), December 2010.
[RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation
Routing Requirements in Low-Power and Lossy Networks",
RFC 5826, April 2010.
[RFC5867] Martocci, J., De Mil, P., Riou, N., and W. Vermeylen,
"Building Automation Routing Requirements in Low-Power and
Lossy Networks", RFC 5867, June 2010.
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Authors' Addresses
Mukul Goyal (editor)
University of Wisconsin Milwaukee
3200 N Cramer St
Milwaukee, WI 53211
USA
Phone: +1 414 2295001
Email: mukul@uwm.edu
Emmanuel Baccelli (editor)
INRIA
Phone: +33-169-335-511
Email: Emmanuel.Baccelli@inria.fr
URI: http://www.emmanuelbaccelli.org/
Anders Brandt
Sigma Designs
Emdrupvej 26A, 1.
Copenhagen, Dk-2100
Denmark
Phone: +45-29609501
Email: abr@sdesigns.dk
Robert Cragie
Gridmerge Ltd
89 Greenfield Crescent
Wakefield WF4 4WA
UK
Phone: +44-1924910888
Email: robert.cragie@gridmerge.com
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Jerald Martocci
Johnson Controls
507 E Michigan St
Milwaukee, WI 53202
USA
Phone: +1 414-524-4010
Email: jerald.p.martocci@jci.com
Charles Perkins
Tellabs Inc
Email: charliep@computer.org
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