Internet Engineering Task Force A. Cardenas
Internet-Draft Fujitsu Laboratories
Intended status: Informational S. Cespedes
Expires: January 12, 2012 U. Icesi/U. of Waterloo
T. Iwao
Fujitsu Limited
July 11, 2011
Depth-First Forwarding in Unreliable Networks
draft-cardenas-dff-01
Abstract
Routing protocols are generally composed of two independent phases,
the control plane and the data forwarding plane. The control plane
is responsible for route discovery and maintenance. The data
forwarding plane performs a table lookup operation to set the packet
on the right path. In unreliable networks, the routing process
incurs a large control overhead when is constantly repairing routes,
detecting loops, and finding alternate paths due to frequent link
failures.
This document describes the Depth-First Forwarding (DFF) protocol; a
data forwarding mechanism that can be used to minimize the burden and
control overhead of a control plane used in unreliable networks. DFF
offers reliability and low control overhead by supporting in the data
plane loop detection, updates to the routing tables, and rerouting of
data packets through alternate paths. DFF can be integrated with
different types of control plane mechanisms and can be used in mesh-
under and route-over specifications. In this draft, we describe a
sample DFF implementation as a 6LoWPAN mesh-under data forwarding
protocol.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
Cardenas, et al. Expires January 12, 2012 [Page 1]
Internet-Draft DFF July 2011
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
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Cardenas, et al. Expires January 12, 2012 [Page 2]
Internet-Draft DFF July 2011
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 5
3. Depth-First Forwarding Operation . . . . . . . . . . . . . . . 5
4. Coexistence with other packet formats . . . . . . . . . . . . 7
5. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 8
6. Data Structures . . . . . . . . . . . . . . . . . . . . . . . 9
7. Hop-by-Hop Implementation Options . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
10. Security Considerations . . . . . . . . . . . . . . . . . . . 11
11. Appendix A: Example Implementation of a Control Plane for
DFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
11.1. Data structures . . . . . . . . . . . . . . . . . . . . . 12
11.2. Route Discovery . . . . . . . . . . . . . . . . . . . . . 13
12. Appendix B: Implementing DFF without requesting new
dispatch bytes . . . . . . . . . . . . . . . . . . . . . . . . 14
13. Normative References . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
Cardenas, et al. Expires January 12, 2012 [Page 3]
Internet-Draft DFF July 2011
1. Introduction
Networks with dynamic links present a challenge for typical routing
protocols because the reliability of links may be different at the
time when the route was discovered from the time when the data is
forwarded.
In these unreliable networks, the control overhead for detecting
routing errors and for fixing paths happens often, so it is important
to avoid expensive control plane mechanisms that might overreact in
the presence of instability. Because a lightweight control plane
mechanism cannot guarantee the construction and maintenance of error-
free routes, a data forwarding protocol designed for these conditions
should be able to detect errors and find backup paths to survive link
failures.
This document describes Depth-First Forwarding (DFF), a data
forwarding mechanism that can detect loops, update the routing
tables, and reroute data packets via alternate paths. DFF is
compatible with light-weight control plane mechanisms supporting
routing tables that maintain more than one possible next hop for each
final destination.
1.1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
1.2. Terminology
Readers are expected to be familiar with all the terms and concepts
that are discussed in "Transmission of IPv6 Packets over IEEE
802.15.4 Networks" [RFC4944].
Other terms used:
Final Destination: This is the final destination of the data packet
within the mesh network.
Local destination: The local destination of the data packet refers to
the next-hop neighbor to which the packet is forwarded on its way to
the final destination.
Originator: This is the source node that created the 6lowpan data
packet.
Cardenas, et al. Expires January 12, 2012 [Page 4]
Internet-Draft DFF July 2011
2. Protocol Overview
DFF is a data forwarding mechanism responsible for detecting loops,
choosing alternate next hops, and updating the cost metrics in the
routing tables to reflect information gathered by forwarding data
packets.
DFF is intended to work in a network where nodes maintain proactively
a routing table with multiple candidate next hops for each final
destination. An example of a control plane satisfying these
conditions is described in the Appendix.
DFF provides an advantage in networks where the reliability of links
changes rapidly. It assumes that the control plane mechanism cannot
guarantee up to date routing tables, nor the absence of loops.
Therefore, whenever a data packet is forwarded, DFF can keep a data
packet identifier to detect loops, update routing tables if a loop is
detected, and use alternate paths to reroute the packet around the
failed path.
DFF achieves this functionality by implementing a distributed depth-
first search over the network graph as defined by the routing table.
If the routing tables are up to date, the search only involves the
default route. However, if the routing table is not up to date and
forwarding of a data packet results in a loop, or if the link layer
fails to successfully transmit the packet to the next hop, the data
packet is then sent to an alternate next hop neighbor. A distributed
depth-first search mechanism is implemented in order to keep track of
the nodes that have participated in the forwarding of the data
packet.
Although DFF can be used without a control plane by performing a
blind (i.e., without a routing table) depth-first search of the
network, this configuration will incur in increased latency because
data packets are forwarded by intermediate nodes to a random next-hop
neighbor. Therefore, it is recommended to implement DFF in
combination with a proactive control plane protocol, in order to
efficiently guide the depth-first search by using information stored
in the routing tables.
3. Depth-First Forwarding Operation
The operation procedure described in this section relies on the
existence of a routing table in every node. This table SHOULD be
filled by a proactive control plane that stores multiple candidate
next hops for final destinations. An example of a proactive distance
vector control plane that could be integrated to DFF is provided in
Cardenas, et al. Expires January 12, 2012 [Page 5]
Internet-Draft DFF July 2011
the Appendix.
In order for an originator to send packets based on depth-first
forwarding, it first encapsulates the data packet using the standard
mesh header defined in [RFC4944] and the DFF mesh header (Figure 1).
The DFF mesh header is employed for detecting loops based on the
unique data identifier (DID) of the packet, and for rerouting packets
in the forwarding path. The originator then checks the routing table
to select the next hop with the lowest cost to reach the destination.
Before forwarding the packet, an entry is created in the loop
detection table (Figure 2), where packet's information such as the
originator's address, DID, previous hop (it points to the node itself
when the node is the originator of packet), and the selected next hop
are stored.
Upon reception of a data packet at an intermediate node (which might
be the originator if there is a loop in the path), the node checks if
an entry with the same [originator,DID] exists in the loop detection
table. If there is no such entry, the intermediate node SHOULD
create a new entry in a similar way to that described for the
originator of the data packet; however, in the Previous hop field, it
stores the address of the router from which the packet has been
received. After the entry has been created in the loop detection
table, the node forwards the packet to the selected candidate next
hop.
For those cases in which an entry already exists in the loop
detection table, the node checks which one was the last attempted
node, and poisons the routing table entry that uses that particular
node to reach the destination. By poisoning failed paths, DFF
updates the routing table based on the results from the data plane.
Then, in order to reroute the data packet, the node selects a new
next hop among the list of candidates stored in the routing table.
The selected node MUST not be registered as a previous attempt in the
list of attempted next-hops in the loop detection table. I also MUST
be a different node from that registered in the Previous Hop field.
In this way, DFF effectively makes data forwarding with loops a
depth-first search guided by the routing table stored in each node.
If the node has attempted all the candidate next hops, it turns on
the return flag in the packet's DFF mesh header and sends the packet
back to the Previous Hop. The return flag is updated hop-by-hop: it
is turned on only when a packet has been returned to the previous
node because the node has failed to forward the packet after trying
(and failing) with all the possible next hops. In any other case,
the flag is turned off by every node before forwarding the packet to
the next-hop.
Cardenas, et al. Expires January 12, 2012 [Page 6]
Internet-Draft DFF July 2011
If a node has attempted all the candidate next-hops and also founds
itself registered in the Previous Hop field of the loop detection
table (i.e., it is the originator of the packet), this means that
routing has failed; therefore, the originator must drop the packet
and delete the entry in the loop table.
In addition to rerouting packets when a loop is detected, nodes
reroute packets when the link layer fails to receive ACK from the
neighbor they sent the data packet to. As soon as the link layer
gives up on the transmission, DFF proceeds to reroute the packet
through a different candidate. In this case, nodes set a duplicate
detection flag in the DFF mesh header, identifying the packet as a
potential duplicate. Duplicate packets may appear in the network
when the link layer reports a failed transmission due to a failed
reception of ACKs from the recipient of the packet. This situation
is likely to happen in links that are lossy only in one direction.
Duplicate packets do not alter the depth-first search logic: if a
packet with a duplicate flag is received by a node who has already
sent a packet with the same [originator,DID] to Next Hop n (Last Next
Hop attempted), it assumes that this corresponds to a loop, and the
node then attempts to reroute the packet to Next Hop n+1 (if
available), or to send it back to Previous Hop if no other candidate
next hop are available. This, however, may correspond to a false
loop detection (i.e., the packet has not came back from a loop, but
instead, has been re-sent as a duplicate from the previous hop);
therefore, DFF does not poison entries in the routing table whenever
the forwarded packet has the duplicate flag activated. The only
exception to this rule appears for the case when the packet has the
duplicate and the returned flag both turned on. In such case, DFF
proceeds to poison the route, since this is a clear indication that
the forwarding path through the last attempted node is broken.
4. Coexistence with other packet formats
For packets encapsulated according to [RFC4944] that do not include a
DFF mesh header, the DFF node processes them with a simple forwarding
mechanism that selects the next hop with the lowest cost to reach the
final destination. In this case, the node does node create any
entries in the loop detection table, and it does not attempt to
reroute such packets through alternate paths. This forwarding option
allows for the coexistence of DFF nodes with nodes that do not follow
the message formats defined in this document (Figure 1).
A 6lowpan mesh header [RFC4944] is still required for the operation
of this basic forwarding mechanism.
Cardenas, et al. Expires January 12, 2012 [Page 7]
Internet-Draft DFF July 2011
5. Message Formats
This document assumes that multi-hop forwarding occurs in the
adaptation layer following the message format of [RFC4944].
[RFC4944] indicates that hop-by-hop processing headers with
additional mesh routing capabilities may be expressed by defining
additional headers that precede fragmentation or addressing headers.
Hence, all data packets to be forwarded using DFF MUST be preceded by
the standard mesh (L2) addressing header defined in [RFC4944], and
MAY be preceded by a header that identifies the data forwarding
mechanism (in this case DFF).
After these two headers, other LoWPAN headers such as hop-by-hop
options, header compression or fragmentation can also be included
before the actual payload. (Figure 1) shows the mesh headers of a
data frame to be forwarded with DFF.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mesh type and header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 1|Mesh Forw|D|R|x| DID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Mesh Header for DFF data frames
Field definitions are as follows:
Mesh type and header: The mesh (L2) addressing header and its
associated dispatch byte as defined in [RFC4944].
Mesh Forw: is a 6-bit identifier that allows for the use of
different mesh forwarding mechanisms. As specified in [RFC4944],
additional mesh forwarding mechanisms should use the reserved
dispatch byte values following LOWPAN_BCO; therefore, 01 SHOULD
precede Mesh Forw. A possible value to use as a mesh forwarding
identifier based on the reserved ranges defined in [RFC4944] is
010001. In this case the dispatch byte would be 01010001.
Duplicate packet flag (D): this flag is included in the DFF mesh
header to indicate that the packet has been re-sent as a
duplicate. The flag MUST be set to the value of 1 by the node
that re-sends the packet after detecting link-layer failure to
deliver through the last attempted next-hop. Once the flag is set
to 1, it MUST not be modified by intermediate nodes.
Cardenas, et al. Expires January 12, 2012 [Page 8]
Internet-Draft DFF July 2011
Return packet flag (R): this flag is included in the DFF mesh header
to indicate that the packet has been returned to the previous hop
after failure to deliver through all the available next-hops. The
flag MUST be set to the value of 1 prior to forward the packet
back to the previous hop and MUST be set to 0 prior to forward the
packet through a node in the list of candidate next-hop. This
flag is modified in a hop-by-hop basis.
Reserved flag (x): this bit is reserved for future flag definitions.
DID: this is the data packet identifier. It is a sequence number
generated by the originator. The originator address concatenated
with the DID sequence number form an identifier of previously seen
data packets.
6. Data Structures
The loop detection option is based on the idea of storing the DID and
originator-ID of a data packet, so that if a packet containing the
same DID identifier and originator is received, DFF detects it as a
loop.
After the loop is detected, DFF follows a distributed depth-first
search for the destination through the candidate next hops kept in
the routing table. In order to do a Depth-First search, nodes need
to keep a list of their children (i.e., the candidate next hops that
have been used to forward the packet), and the previous hop (the node
who sent the data packet for the first time to the current router).
A Loop Detection Table (Figure 2) needs to be kept by the nodes to
support the loop detection functionality. The candidate next hop
field does not need to be pre-stored, it can be filled dynamically as
soon as the node attempts to send the packet to a next-hop neighbor.
Cardenas, et al. Expires January 12, 2012 [Page 9]
Internet-Draft DFF July 2011
+---------+-------------------------------------------------------+
|Parameter| Description |
+---------+-------------------------------------------------------+
|(O,DID) | Source Address concatenated with a sequential |
| | number. Used to identify previously seen data packets |
+---------+-------------------------------------------------------+
|Previous | Address of the router who sent the data packet for the|
|Hop | first time to the current router. If forwarding fails,|
| | return data packet to this router |
+---------+-------------------------------------------------------+
|TTL | Time to live for the current DID entry |
+---------+-------------------------------------------------------+
|Next Hop | First neighbor selected to forward the packet |
| 1 | |
+---------+-------------------------------------------------------+
| ... | ... |
+---------+-------------------------------------------------------+
|Next hop | Neighbor selected the k-th time |
| K | |
+---------+-------------------------------------------------------+
Figure 2: Basic Elements of a Loop Detection Table
7. Hop-by-Hop Implementation Options
While DFF can be used in a route-over or mesh-under protocol, this
document provides a sample implementation of a mesh-under forwarding
solution for 6LoWPAN networks; therefore, all addresses referenced in
this document are either 16-bit short or EUI-64 link layer addresses.
DFF requires the use of hop-by-hop options, and this document
describes how these hop-by-hop options can be implemented by
allocating a new dispatch byte from the reserved values for mesh
forwarding in [RFC4944].
To avoid the request of a new dispatch byte, the appendix describes a
way to implement DFF by overloading the fragmentation header in
[RFC4944]. This implementation has the advantage of using headers
already defined by the standard; however, the implementation by
overloading the fragmentation header only allows rerouting a packet
on loop detection and not when a link fails. The reason behind this
loss of functionality is that rerouting when a link fails requires
the use of a duplicate flag in the header of the packet. This is a
hop-by-hop option that can be set by intermediate nodes, and the
fragmentation header of [RFC4944] cannot be changed by intermediate
nodes.
Cardenas, et al. Expires January 12, 2012 [Page 10]
Internet-Draft DFF July 2011
Similarly, a route over implementation of DFF would need to obtain
new fields in the hop-by-hop options of IPv6 packets.
8. Acknowledgements
Ganesh Venkatesh, and Geoff Mulligan provided useful discussions
which helped shape this document.
9. IANA Considerations
This memo includes the request of a new dispatch byte to identify DFF
headers. In the Appendix there is an implementation that avoids the
use of new dispatch bytes.
10. Security Considerations
The security of a mesh forwarding protocol depends on the integrity,
authentication, and confidentiality of the messages. The security
mechanisms for protecting the network can be provided by link-layer
technologies. Further details are presented in the Security
Considerations section of [RFC4944].
11. Appendix A: Example Implementation of a Control Plane for DFF
There are many route discovery protocols compatible with DFF. The
final selection of which control plane to use depends on the resource
considerations of the nodes in the network. If nodes have tight
memory constraints and the network is large, managing the size of the
routing table is important. Therefore, a control plane that builds a
network with a routing table that grows at a slower rate than the
size of the network--e.g., hierarchical routing, or clustering--is
important. If minimizing the routing stretch of the network is a
priority, and if nodes have enough memory to accommodate a routing
table of the size of the network, then a routing protocol that stores
a routing entry for each destination can be implemented.
The only condition of a control plane that will leverage an
implementation of DFF is that for each final destination, each node
should be able to maintain a number of alternate routes being
advertised by multiple neighbors, which would be used if a selected
route were to fail.
While a number of routing protocols satisfy the above constraint,
they tend to include extra overhead for preventing loops or dealing
Cardenas, et al. Expires January 12, 2012 [Page 11]
Internet-Draft DFF July 2011
with routing inconsistencies or failures. One of the primary goals
of DFF is to avoid the use of these extra control messages. This
appendix presents a basic control plane compatible with DFF. It is a
distance vector protocol that assumes no other control message other
than periodic routing updates.
This reference implementation requires two data structures: a link
table and a routing table. Both data structures are updated by means
of periodic control messages that include information about the
announcing neighbor and the destinations stored by the announcing
neighbor in its routing table.
11.1. Data structures
Link Table
The Link Table is used to maintain a list of neighbors and the
quality of their links. The structure of the link table depends of
the implementation; however, some key fields are shown in (Figure 3).
+---------+-----------------------------------------------------+
|Parameter| Description |
+---------+-----------------------------------------------------+
|Next Hop | The address of the neighbor |
+---------+-----------------------------------------------------+
|Link | The cost as defined by the metric. If the ETX |
|Cost | metric is used, then the Link Cost is the ETX to |
| | reach this neighbor |
+---------+-----------------------------------------------------+
|TTL | A time to live value used to delete this entry if no|
| | new control messages from the neighbor are received |
| | before the TTL timer expires. |
+---------+-----------------------------------------------------+
|Transmit | The forward quality of the link. If ETX metric is |
|quality | used, this field keeps an estimate of the likelihood|
| | that a packet successfully arrives at the neighbor |
+---------+-----------------------------------------------------+
|Receiving| The reverse delivery ratio of the link.If ETX metric|
|quality | is used, it keeps an estimate of the likelihood that|
| | a packet from this neighbor is successfully received|
+---------+-----------------------------------------------------+
|One Way | If the current node does not see itself in the list |
|Link | of destinations announced by this neighbor, then |
| | this field is true to indicate it is one-way link |
+---------+-----------------------------------------------------+
Figure 3: Elements of a Link Table
Cardenas, et al. Expires January 12, 2012 [Page 12]
Internet-Draft DFF July 2011
Routing Table
The Routing Table contains up to K candidate next hops for each final
destination.
The structure of the routing table is implementation dependent;
however the routing table must contain at least the fields shown in
(Figure 4) per entry.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Local DST Address 1 | Cost | TTL |
+ Final DST Address | ... | ... ~
| | Local DST Address K | Cost | TTL |
+---------------------------------------------------------------+
:
:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Local DST Address 1 | Cost | TTL |
+ Final DST Address | ... | ... ~
| | Local DST Address K | Cost | TTL |
+---------------------------------------------------------------+
Figure 4: Routing Table Format
Final DST Address: The address of the target destination.
Local DST Address 1: The address of the first next-hop candidate.
The Local DST candidates are sorted based on their cost to reach
the destination, with Local DEST Address 1 being the next hop for
the best route, and Local DEST Address K (if available) being the
next hop for the Kth optimal route.
TTL: A time to live value used to delete this entry if the timer
expires.
Cost: The cost to reach the destination through a next hop.
11.2. Route Discovery
A route discovery mechanism compatible with DFF needs to be based on
distance vector, maintain a routing table, and support multiple
alternate next hops per destination.
This sample implementation is based on a proactive distance vector
routing algorithm, where routing table messages are used to exchange
reachability information among neighboring nodes.
Cardenas, et al. Expires January 12, 2012 [Page 13]
Internet-Draft DFF July 2011
An important configuration parameter is the number of possible next
hops kept for each destination. By default the number of possible
next hops for each final destination in the routing table is a
maximum of 3. Having more than one possible next hop improves the
reliability of the protocol by allowing the depth-first search
algorithm to use alternate routes in case using preferred next hop
results in a loop, or if the preferred next hop does not acknowledge
reception of the data packet.
Routing table updates are transmitted as configured by the
administrator; they can be periodic or dynamic. One of the main
characteristics of DFF is that it does not need an up to date routing
table because the loop detection and depth-first search mechanism
attempts to find alternate routes even when the routing table
contains stale information.
Routing table updates should include the following fields:
Destination Addr: The Address of the destination in the routing
table entry.
Cost to DST: The total cost to reach DST. This value depends on the
metric used. A popular metric is ETX.
Based on the information received in the routing table updates, each
node updates its routing table to be later used by the DFF forwarding
mechanism.
12. Appendix B: Implementing DFF without requesting new dispatch bytes
DFF can be implemented as a full standard conforming to [RFC4944]
without requesting any new dispatch bytes. In this way, nodes
implementing DFF can interoperate with other nodes that only
implement headers defined in [RFC4944].
A possible way to avoid the DFF mesh header is by overloading the
datagram_tag and datagram_offset fields of the fragmentation header
defined in [RFC4944].
Because each source maintains a sequence number for the datagram_tag,
and the datagram_offset can be used to differentiate between
fragmented packets with the same value in datagram_tag, the DID value
required by DFF can be generated by the concatenation of the
datagram_tag and datagram_offset values of a fragmented data frame.
Nonetheless, an implementation of DFF that avoids the request of a
new dispatch byte will prevent the use of flags, and without the
Cardenas, et al. Expires January 12, 2012 [Page 14]
Internet-Draft DFF July 2011
existence of a duplicate flag, duplicate packets will not be
detected. Therefore, it is RECOMMENDED that nodes that implement DFF
by using the datagram_tag and datagram_offset fields for storing the
DID value, do not reroute on link-layer ACK failures, but only on
loop detections. In this case, all previously seen [originator,DID]
values can be assumed to correspond to loop detections, and the
routing table cost to reach the final destination via the last
attempted neighbor can be safely poisoned, without the risk of
poisoning valid routes taken by duplicate packets.
This implementation of DFF assumes the existence of fragmentation
headers within the LoWPAN encapsulation. This works well if data
packets are fragmented, but if the entire payload datagram fits
within a single 802.15.4 frame, then [RFC4944] states that the LoWPAN
encapsulation should not contain a fragmentation header. However,
the use of a fragmentation header for a packet that does not need to
be fragmented should, in principle, not affect the operation of nodes
implementing [RFC4944]. Therefore, even if a packet does not need to
be fragmented, the originator node can append the fragmentation
header so DFF nodes can use it for extracting the DID identifier.
The control plane used to populate the routing tables can also avoid
the need to request a new dispatch byte by encapsulating routing
updates in UDP packets.
13. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, September 2007.
Authors' Addresses
Alvaro A. Cardenas
Fujitsu Laboratories
1240 E. Arques Avenue, M/S 345
Sunnyvale, CA 94085
US
Phone: +1 408 530-4516
Email: alvaro.cardenas-mora@us.fujitsu.com
Cardenas, et al. Expires January 12, 2012 [Page 15]
Internet-Draft DFF July 2011
Sandra L. Cespedes
U. Icesi/U. of Waterloo
Calle 18 No. 122-135 Pance
Cali, Valle
Colombia
Phone: +1 (519) 8884567 x37448
Email: slcesped@bbcr.uwaterloo.ca
Tadashige Iwao
Fujitsu Limited
Shiodome City Center, 5-2, Higashi-shimbashi 1-chome, Minato-ku
Tokyo,
JP
Phone: +81-3-6252-2283
Email: smartnetpro-iwao_std@ml.css.fujitsu.com
Cardenas, et al. Expires January 12, 2012 [Page 16]
