Internet Engineering Task Force M. Goyal, Ed.
Internet-Draft University of Wisconsin
Intended status: Standards Track Milwaukee
Expires: January 12, 2012 E. Baccelli, Ed.
INRIA
A. Brandt
Sigma Designs
R. Cragie
Gridmerge Ltd
J. Martocci
Johnson Controls
July 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-01
Abstract
This document specifies a mechanism that enables an RPL router to
measure the quality of an existing route to another RPL router in a
low power and lossy network, thereby allowing the router 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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material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 12, 2012.
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 a Measurement Request . . . . . . . . . . . . . . 8
5. Processing a Measurement Request at an Intermediate Router . . 9
6. Processing a Measurement Request at the Target . . . . . . . . 10
7. Processing a Measurement Reply at the Origin . . . . . . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
10. Authors and Contributors . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
11.1. Normative References . . . . . . . . . . . . . . . . . . . 12
11.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
Point to point (P2P) communication between arbitrary routers 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 criteria. This mechanism, henceforth referred to as the
reactive P2P route discovery, requires the specification of routing
constraints [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 router to infer the routing
constraints 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 routes are deemed unsatisfactory but the router
does not intrinsically know the routing constraints to be used in P2P
route discovery, it may be necessary for the router to determine the
aggregated values of the routing metrics along the existing route.
This knowledge will allow the router to frame reasonable routing
constraints for use in P2P route discovery to determine a better
route. 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 the routing
constraint for use in P2P route discovery. Note that it is important
that the routing constraints are not overly strict; otherwise the P2P
route discovery may fail even though a route, much better than the
one currently being used, exists.
This document specifies a mechanism that enables an RPL router to
measure the aggregated values of the routing metrics along an
existing route to another RPL router in an LLN, thereby allowing the
router to decide if it wants to initiate the reactive discovery of a
more optimal route and determine the routing constraints 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]. The following terms, originally defined in
[I-D.ietf-roll-p2p-rpl], are redefined in the following manner.
Origin: The origin refers to the router that initiates the
measurement process defined in this document and is the start point
of the P2P route being measured.
Target: The target refers to the router at the end point of the P2P
route being measured.
Intermediate Router: A router, other than the origin and the target,
on the P2P route being measured.
2. Functional Overview
The mechanism described in this document can be used by an origin to
measure the aggregated values of the routing metrics along a P2P
route to a target 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]. The origin
sends a Measurement Request message along the route. The Measurement
Request accumulates the values of the routing metrics as it travels
towards the target. Upon receiving the Measurement Request, the
target unicasts a Measurement Reply message, carrying the accumulated
values of the routing metrics, back to the origin.
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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 | Compr |T|H|A|R| Num | Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Origin Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Target Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Address[1..Num] .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Metric Container Option(s) .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format of the Measurement Object (MO)
This document defines a new RPL Control Message type, the Measurement
Object (MO), with code 0x06 (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 being measured. If the route being measured is a source
route, this field MUST be set to 10000000 on transmission and
ignored on reception.
o SequenceNo: An 8-bit sequence number that uniquely identifies a
Measurement Request and the corresponding Measurement Reply.
o Compr: A 4-bit unsigned integer indicating the number of prefix
octets that are elided from the IPv6 addresses in Origin/Target
Address fields and the Address vector. For example, Compr value
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will be 0 if full IPv6 addresses are carried in the Origin/Target
Address fields and the Address vector.
o Type (T): This flag is set if the MO represents a Measurement
Request. The flag is cleared if the MO is a Measurement Reply.
o Hop-by-hop (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 the RPLInstanceID is a local value, the
Origin Address serving as the DODAGID. This flag is cleared if
the MO travels along a source route specified in the Address
vector. Note that, in case the P2P route being measured lies
along a non-storing DAG, an MO message may travel along a hop-by-
hop route till it reaches 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 the source route to the
destination inside the Address vector.
o Accumulate Route (A): This flag is relevant only if the MO
represents a Measurement Request that travels along a hop-by-hop
route represented by a local RPLInstanceID. When this flag is
relevant, a value 1 in the flag indicates that the Measurement
Request MUST accumulate a source route for use by the target to
send the Measurement Reply back to the origin. In this case, the
intermediate routers MUST add their IPv6 addresses (after eliding
Compr number of prefix octets) to the Address vector in the manner
specified later.
o Reverse (R): This flag is relevant only if the MO represents a
Measurement Request that travels along a source route, specified
in the Address vector, to the target. When this flag is relevant,
a value 1 in the flag indicates that the Address vector contains a
complete source route from the origin to the target, which can be
used, after reversal, by the target to source route the
Measurement Reply message back to the origin.
o Num: This field indicates the number of fields in the Address
vector. If the value of this field is zero, the Address vector is
not present in the MO.
o Index: If the Measurement Request is traveling along a source
route contained in the Address vector, this field indicates the
index in the Address vector of the next hop on the route. If the
Measurement Request is traveling along a hop-by-hop route with a
local RPLInstanceID and the A flag is set, this field indicates
the index in the Address vector where an intermediate router
receiving the MO message must store its IPv6 address. Otherwise,
this field MUST be set to zero on transmission and ignored on
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reception.
o Origin Address: An IPv6 address of the origin after eliding Compr
number of prefix octets. If the MO is traveling along a hop-by-
hop route and the RPLInstanceID field indicates a local value, the
Origin Address field MUST contain the DODAGID value that, along
with the RPLInstanceID, uniquely identifies the hop-by-hop route
being measured.
o Target Address: An IPv6 address of the target after eliding Compr
number of prefix octets.
o Address[1..Num]: A vector of IPv6 addresses (with Compr number of
prefix octets elided) representing a (partial) route from the
origin to the target:
* Each element in the vector has size (16 - Compr) octets.
* The total number of elements inside the Address vector is given
by the Num field.
* When the Measurement Request is traveling along a hop-by-hop
route with local RPLInstanceID and has the A flag set, the
Address vector is used to accumulate a route to be used by the
target to send the Measurement Reply back to the origin. In
this case, the route MUST be accumulated in the forward
direction, i.e., from the origin to the target. The target
router would reverse this route to obtain a source route from
itself to the origin. The IPv6 addresses in the accumulated
route MUST be accessible in the backward direction. An
intermediate router adding its address to the Address vector
MUST ensure that its address does not already exist in the
vector.
* When the Measurement Request is traveling along a source route,
the Address vector MUST contain a complete route to the target
and the IPv6 addresses in the Address vector MUST be accessible
in the forward direction, i.e., from the origin to the target.
A router (the origin or an intermediate router) specifying a
route to the target in the Address vector MUST ensure that the
vector does not contain any address more than once. The origin
may set the R flag in the MO if the route in the Address vector
represents a complete route from the origin to the target and
this route can be used after reversal by the target to send the
Measurement Reply message back to the origin.
* The origin and target addresses MUST NOT be included in the
Address vector.
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* The Address vector MUST NOT contain any multicast addresses.
o Metric Container Options: An MO MUST contain one or more Metric
Container options to accumulate routing metric values for the
route being measured.
4. Originating a Measurement Request
If an origin needs to measure the routing metric values along a P2P
route towards a target, it generates an MO message and sets its
fields in the manner described above. Specifically, the origin MUST
set the T flag to 1 to indicate that the MO represents a Measurement
Request.
If a source route is being measured, the origin MUST do the
following:
o specify the complete source route to the target inside the Address
vector;
o specify in the Num field the number of address elements in the
Address vector;
o set the Index field to value zero;
o set the R flag if the route in the Address vector can be used
after reversal by the target to source route the Measurement Reply
message back to the origin.
If a hop-by-hop route with a local RPLInstanceID is being measured
and the origin desires the MO to accumulate a source route for the
target to send the Measurement Reply message back, it MUST do the
following:
o set A flag to 1;
o include a suitably sized, empty Address vector (with all bits set
to zero) in the MO;
o specify in the Num field the number of address elements that can
fit inside the Address vector;
o set the Index field to value zero.
The origin MUST include one or more Metric Container options inside
the MO that carry the routing metric objects of interest. If
required, the origin must also initiate these routing metric objects
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by including the values of the routing metrics for the first hop on
the P2P route being measured.
After setting the MO fields as described above, the origin MUST
unicast the MO message to the next hop on the P2P route.
5. Processing a Measurement Request at an Intermediate Router
When a router receives an MO, it examines if one of its IPv6
addresses is listed as the Origin or the Target Address. If not, the
router processes the received message in the following manner.
An intermediate router MUST discard the packet with no further
processing if the received MO is not a Measurement Request.
The router then determines the next hop on the P2P route being
measured. In case the received MO has a clear H flag, the router
increments the Index field and uses the Address[Index] element as the
next hop. If this element does not exist, the router uses the Target
Address as the next hop.
If the received MO has H flag set to 1, the router uses the
RPLInstanceID, the Target Address and, if RPLInstanceID is a local
value, the DODAGID (same as the Origin Address) to determine the next
hop for the MO. Also,
o If the RPLInstanceID of the hop-by-hop route is a local value and
the A flag is set, the router MUST store one of its IPv6 addresses
(after eliding Compr bytes and making sure that the Address vector
does not already contains one of its IPv6 addresses) at location
Address[Index] and then increments the Index field.
o If the router is the root of the non-storing DAG along which the
received MO message has been traveling, the router MUST do the
following:
* reset the H, A and R flags;
* insert a source route to the target inside the Address vector;
* specify in the Num field the number of address elements in the
Address vector;
* set the Index field to value zero;
The router MUST drop the MO with no further processing and send an
ICMPv6 Destination Unreachable error message to the source of the
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message if it can not determine the next hop for the message.
After determining the next hop, the router 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
router MUST drop the MO with no further processing and send a
suitable ICMPv6 error message to the source of the message if the
router does not know the relevant routing metric values for the next
hop.
After updating the routing metrics, the router MUST unicast the MO to
the next hop.
6. Processing a Measurement Request at the Target
When a router receives an MO, it examines if one of its IPv6
addresses is listed as the Target Address. If yes, the router
processes the received message in the following manner.
An intermediate router MUST discard the packet with no further
processing if the received MO is not a Measurement Request.
The target then updates the routing metrics objects in the Metric
Container options if required and generates a Measurement Reply
message. The received Measurement Request message can be trivially
converted into the Measurement Reply by reseting the T flag to zero.
The target MAY remove the Address vector from the Measurement Reply
if desired. The target then unicasts the Measurement Reply back to
the origin:
o If the Measurement Request traveled along a DAG with a global
RPLInstanceID, the Measurement Reply MAY be unicast back to the
origin along the same DAG.
o If the Measurement Request traveled along a hop-by-hop route with
a local RPLInstanceID and the A flag inside the received message
is set, the target MAY reverse the source route contained in the
Address vector and use it to send the Measurement Reply back to
the origin.
o If the Measurement Request traveled along a source route and the R
flag inside the received message it set, the target MAY reverse
the source route contained in the Address vector and use it to
send the Measurement Reply back to the origin.
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7. Processing a Measurement Reply at the Origin
When a router receives an MO, it examines if one of its IPv6
addresses is listed as the Origin Address. If yes, the router
processes the received message in the following manner.
The origin MUST discard the packet with no further processing if the
received MO is not a Measurement Reply or if the origin has no
recollection of sending a Measurement Request with the sequence
number listed in the received MO.
The origin then examines 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 routers, the origin 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. Authors and Contributors
In addition to the editors, the authors of this document include the
following individuals (listed in alphabetical order).
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, Wakefieldm WF4
4WA, UK. Phone: +44 1924910888; Email: robert.cragie@gridmerge.com
Jerald Martocci, Johnson Controls, Milwaukee, WI 53202, USA. Phone:
+1 414 524 4010; Email:jerald.p.martocci@jci.com
Charles Perkins, Tellabs Inc., USA. Email:charliep@computer.org
Authors gratefully acknowledge the contributions of Richard Kelsey
and Zach Shelby in the development of this document.
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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.
11.2. Informative References
[I-D.ietf-roll-p2p-rpl]
Goyal, M., Baccelli, E., Brandt, A., Cragie, R., and J.
Martocci, "Reactive Discovery of Point-to-Point Routes in
Low Power and Lossy Networks", draft-ietf-roll-p2p-rpl-03
(work in progress), May 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.
[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
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