Networking Working Group                                     A. Tavakoli
Internet-Draft                                        S. Dawson-Haggerty
Intended status: Informational                               UC Berkeley
Expires: September 10, 2009                                       J. Hui
                                                   Arch Rock Corporation
                                                               D. Culler
                                                             UC Berkeley
                                                             Mar 9, 2009

   HYDRO: A Hybrid Routing Protocol for Lossy and Low Power Networks

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
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-

   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."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on September 10, 2009.

Copyright Notice

   Copyright (c) 2009 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
   ( 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.

Tavakoli, et al.       Expires September 10, 2009               [Page 1]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009


   HYDRO is a hybrid routing protocol for Lossy and Low power Networks
   (L2Ns) that embraces centralized and distributed routing mechanisms.
   Through the use of standard ICMP Route Advertisements and Route
   Solicitations, Node Routers build Default Routes to Border Routers.
   These routes, which maintain multiple options per each Node Router
   when available, are maintained through data-driven link estimation.
   Node Routers periodically report a high-quality subset of their
   Default Route Table to Border Routers, which then form a global view
   of the topology.  When a Node Router attempts to route to another
   Node Router in the network, if no matching entry exists in the Node
   Router's Flow Table, it forwards the packet to a Border Router, which
   then installs the correct Flow Table Entries in the network to enable
   more efficient subsequent routing.

Tavakoli, et al.       Expires September 10, 2009               [Page 2]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

Table of Contents

   1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  HYDRO Terminology  . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Data Structures  . . . . . . . . . . . . . . . . . . . . . . .  7
     5.1.  Default Route Table  . . . . . . . . . . . . . . . . . . .  7
     5.2.  Flow Table . . . . . . . . . . . . . . . . . . . . . . . .  8
     5.3.  Link Database  . . . . . . . . . . . . . . . . . . . . . .  8
   6.  Message Formats  . . . . . . . . . . . . . . . . . . . . . . .  9
     6.1.  Additional Adaptations . . . . . . . . . . . . . . . . . .  9
     6.2.  Routing Header . . . . . . . . . . . . . . . . . . . . . . 10
     6.3.  Route Install Header . . . . . . . . . . . . . . . . . . . 10
     6.4.  Router Advertisement Extension . . . . . . . . . . . . . . 11
     6.5.  Topology Report Message  . . . . . . . . . . . . . . . . . 11
     6.6.  Topology Report Package  . . . . . . . . . . . . . . . . . 12
   7.  Detailed Operation . . . . . . . . . . . . . . . . . . . . . . 12
     7.1.  Link Estimation  . . . . . . . . . . . . . . . . . . . . . 13
     7.2.  Router Discovery . . . . . . . . . . . . . . . . . . . . . 13
     7.3.  Default Route Formation  . . . . . . . . . . . . . . . . . 14
     7.4.  Global Topology Construction . . . . . . . . . . . . . . . 16
     7.5.  Node Forwarding  . . . . . . . . . . . . . . . . . . . . . 17
     7.6.  Border Router Forwarding . . . . . . . . . . . . . . . . . 19
     7.7.  Route Installation . . . . . . . . . . . . . . . . . . . . 20
     7.8.  Multicast Forwarding . . . . . . . . . . . . . . . . . . . 21
     7.9.  Multiple Border Routers  . . . . . . . . . . . . . . . . . 22
   8.  Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . 22
   9.  Configuration Parameters and Other Administrative Options  . . 23
   10. Applicability Statement  . . . . . . . . . . . . . . . . . . . 24
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 25
   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 25
   13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     14.1. Normative References . . . . . . . . . . . . . . . . . . . 26
     14.2. Informative References . . . . . . . . . . . . . . . . . . 26
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27

Tavakoli, et al.       Expires September 10, 2009               [Page 3]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

1.  Terminology

   LLN: Lossy and Low power Network

   MTU: Maximum Transmission Unit

   ROLL: Routing in Low power and Lossy Networks

   TDMA: Time Division Multiple Access

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in RFC
   2119 [RFC2119].

2.  Introduction

   The Hybrid Routing Protocol (HYDRO) for Lossy and Low Power Networks
   utilizes the two-tiered hierarchy that is used in many deployments.
   It provides point-to-point routing using a combination of centralized
   and distributed mechanisms.

   L2N networks are often deployed in two tiers: Node Routers (or Nodes
   from now on) in the network which gather data but are resource
   constrained, and Border Routers, which provide connectivity between
   the L2N subnet and another network.  The Nodes have constrained
   resources, in the form of limited energy, memory, and bandwidth.
   Consequently, a routing protocol MUST ascribe to a set of minimal
   criteria, as laid out in the IETF Roll Protocols Survey
   [I-D.ietf-roll-protocols-survey].  These requirements were culled
   from a set of application requirement documents, with the targeted
   domains including Industrial Monitoring
   [I-D.ietf-roll-indus-routing-reqs], Building Automation
   [I-D.ietf-roll-building-routing-reqs], Urban Sensing
   [I-D.ietf-roll-urban-routing-reqs], and Home Automation
   [I-D.ietf-roll-home-routing-reqs], with the requirements intended to
   provide a necessary, but not necessarily sufficient baseline.  They
   apply to low-power Node Routers, but not to the Border routers.

   The Border Routers, however, are assumed to have a relatively
   abundant supply of resources, leading to HYDRO's goal of maintaining
   as much state and complexity at the Border Routers as possible, and
   only pushing necessary functionality to the Nodes.

Tavakoli, et al.       Expires September 10, 2009               [Page 4]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

3.  Overview

   HYDRO provides point-to-point connectivity between all Nodes in a
   network, but is optimized for situations in which the number of
   network destinations in the network is far smaller than the number of
   Nodes.  Additionally, much of the traffic is typically between Node
   routers in the network and hosts on other networks.  Thus, our design
   optimizes first for this traffic pattern.  It also not uncommon for
   there to be some unicast traffic between different Node Routers; for
   instance, for control or debugging, and so we provide a second
   mechanism for optimizing this traffic.

   An underlying set of routing trees are created using IPv6 Route
   Advertisement and Route Solicitation Messages.  Each Border Router
   advertises a route with '0' cost.  Nodes process Router
   Advertisements from both Border Routers and Nodes, and add their Link
   Cost Estimate to the advertised Route Cost Estimate, and then
   themselves advertise this new cumulative Overall Route Cost.

   HYDRO allows for multiple Border Routers to manage a network.  We
   detail the mechanisms for setting up and managing such a topology in
   later sections, but for ease of understanding frame our discussion in
   the context of networks with only a single Border Router.  Such a
   simplification does not alter the functionality of Nodes.

   Each Node maintains information about multiple potential next-hops to
   the Border Router, which form a set of Default Routes.  The ordering
   of these choices, is based on a combination of the Overall Route
   Cost, the Confidence in the Link Cost Estimate (which is a component
   of that Overall Route Cost), and a Node's Willingness To Route
   (Willingness).  Confidence MAY be measured by the number of packets
   over which the Link Cost Estimate is formed, both of which are
   provided by the link layer.

   Each Node periodically reports a high-quality subset of its Default
   Route Table, as well as any requested Node Attributes, whether static
   or dynamic, in the form of Topology Reports to a Border Router.
   Using this information, the Border Routers create a global view of
   the topology of the subnet.

   When a Node needs to route a packet, either as its originator or a
   forwarder, it attempts to classify a packet against its Flow Table
   (which is initially empty).  If an entry matches the packet, then the
   packet is forwarded according to the rules specified by the entry.
   Otherwise, the Node forwards the packet along a Default Route to the
   Border Router.

   When a data packet destined for a Node Router, with a destination

Tavakoli, et al.       Expires September 10, 2009               [Page 5]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   address within the subnet reaches a Border Router, the Border Router
   determines the best route, according to its global topology view and
   a user-specified routing policy (e.g. lowest cost).  It then forwards
   the packet to the destination by inserting a source routing header
   into the packet and forwarding it to the first hop in the source
   route.  It SHOULD additionally generate a Route Install Header for
   either the source or destination of the packet, instructing it to
   install the necessary Flow Table Entries to route future similar
   packets more efficiently.  This header may be set in a new packet or
   added to the original data packet.

   HYDRO mechanisms require the frequent transmission (or exchange) of
   IPv6 addresses.  Because full 128-bit addresses in this setting are
   not practical, we assume that all Nodes are associated with a locally
   unique 16-bit short identifier, and furthermore that all Border
   Routers have access to the mapping between 16-bit and 64-bit
   interface identifiers.  This 16-bit identifier should be equivalent
   to the 16-bit form of compressed address specified by [RFC4944].  The
   mapping may be static or dynamic, using mechanisms like DHCPv6 but is
   beyond the scope of this document.  All routing takes place using 16-
   bit short identifiers

4.  HYDRO Terminology

   Border Router: A device with relatively abundant resources and
   multiple interfaces, including an interface (the 'L2N Interface')
   that shares a link type with Nodes.

   L2N Network: A network with a single IPv6 prefix encompassing both a
   set of Border Routers and Node.  Multiple types of links connect
   these routers, and the Border Routers are all in a single link-local
   multicast domain.  All interfaces on this network share a single
   prefix (the L2N prefix).

   L2N Interface: The interface which the Border Router uses to
   communicate with devices on the subnet.

   Secondary Interface: A second interface the Border Router uses to
   communicate with other Border Routers.  Examples include an Ethernet
   or 802.11 mesh.

   Default Route: A route leading to a Border Router from a Node,
   composed of a locally maintained next-hop link.

   Default Route Table: A Node's table which contains information about
   a set of Default Routes and their associated next-hop Nodes,
   including the cost of communicating with a Border Router using that

Tavakoli, et al.       Expires September 10, 2009               [Page 6]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   particular Default Route.

   Flow Table: A table with a (Classification, Action) format, in which
   'Classification' helps categorize which packets an entry applies to,
   and 'Action' describes how to forward a matching packet.

   Neighbor: A Node or Border Router within a single IP-hop.

   Node Attributes: Information about a Node, either static (e.g.
   bandwidth, resources), or dynamic (e.g. energy left).

   Node Router (Node): Any node in the network that serves as a router,
   but not as a Border Router.  Typically a constrained device.

   Overall Route Cost: The cumulative cost of a particular Default Route
   option, obtained by summing the Route Cost Estimate advertised by the
   associated next-hop Node, and the Link Cost Estimate of communicating
   with that Node.

   Primary Default Route: The Default Route that a Node attempts to use
   before all other potential Default Routes.  Typically the top entry
   in the Default Route Table, but we detail mechanisms that allow other
   entries in the Default Route Table to also periodically serve as the
   Primary Default Route.

   Route Install Message: A message containing the bidirectional path
   between two Nodes.  The message also dictates installation type.

   Topology Report: Includes a subset of information about a subset of
   Default Route next-hops from the Default Route Table, as well as
   requested Node Attributes.

   Willingness To Route (Willingness): An advertised value that
   indicates a Node's willingness to route packets for other Nodes.
   Setting the value of this metric is policy-driven and outside the
   scope of this document.

5.  Data Structures

5.1.  Default Route Table

   Each Node maintains a Default Route Table, whose entries contain the
   following fields:

   Neighbor Address: 16-bit short IPv6 address of the neighboring Node
   or Border Router.

Tavakoli, et al.       Expires September 10, 2009               [Page 7]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   Route Hops: The distance to a Border Router in hops using the
   specified Neighbor as the next-hop.

   Route Cost Estimate: Route cost advertised by the next-hop Node for
   this entry.

   Willingness: The Willingness to Route advertised by the next-hop Node
   for this entry.

   There are also certain fields associated with a Default Route Entry
   that MUST be provided by the Link Layer, but are used by HYDRO for
   Default Route Table seeding and maintenance.  These fields are:

   Link Cost Estimate: Estimate of the link cost to communicate with the
   next-hop Node for this entry.  The link layer MAY need multiple
   packet transmissions and acknowledgements to provide this estimate.

   Link Quality: Last recorded link quality measurement.  The link layer
   MUST be able to provide this value based on a single packet
   reception.  The metric and scale of this field is likely hardware-

   Confidence: The Confidence of the link layer in the Link Cost
   Estimate it provides.

   The size of the Default Route Table is dictated by

5.2.  Flow Table

   Each Node maintains a Flow Table, whose entries are composed of two

   Flow Match: The Flow Match contains information against which packets
   can be checked.  Flow Match MUST include a Packet Destination field,
   and MAY contain certain additional fields, such as Packet Source.

   Flow Path: The Flow Path indicates the path a packet should take.
   This can either be a full source route, or simply the next-hop to
   which the packet should be sent to.

5.3.  Link Database

   Each Border Router maintains a Link Database, whose entries have
   several parts:

   Link <n1,n2>: a link between Node 'n1' and 'n2', reported in a
   Topology Report by 'n1'.

Tavakoli, et al.       Expires September 10, 2009               [Page 8]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   Sequence Number: The sequence number contained in the Topology Report
   which last reported this edge.

   Metric: The Metric associated with this edge in the last Topology

   Confidence: The Confidence associated with this edge in the last
   Topology Report

   Attributes: Any Node Attributes contained in the last Topology
   Report, such as Willingness to route

6.  Message Formats

6.1.  Additional Adaptations

   The 6lowpan working group has defined an adaptation layer for IPv6
   datagrams, when carried over Low Power and Lossy links.  This is
   necessary due to the small link MTU.  We suggest an additional
   function of the adaptation layer involving extension headers, which
   is necessary to use these header efficiently.  The generalized IPv6
   extension header format is defined in [RFC2460], and is reproduced

       |  Next Header  |  Hdr Ext Len  |                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
       |                                                               |
       .                                                               .
       .                            Options                            .
       .                                                               .
       |                                                               |

   The "Hdr Ext Len" is specified in units of 8-octet chunks, not
   including the first 8 octets.  A similar layout is used for TLV-
   encoded options, except the 'Next Header' field is named the 'Option
   Type' field.  We suggest that the 6lowpan working group may wish to
   define, as part of the adaptation layer, lengths in units of single
   octets; we will assume for the rest of this document that such a
   modification is in effect.  Although this limits the length of
   extension headers and options to 255 bytes, we feel that this is not
   a significant limitation and the payload savings resulting from
   removing unnecessary padding are significant.

   This recommendation applies specifically to Hop-by-hop, Destination,
   and Routing extension headers (with 'next header' values 0, 60, and

Tavakoli, et al.       Expires September 10, 2009               [Page 9]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   43, respectively).  It also applies to TLV-encoded sub-headers as
   specified in [RFC2460].

6.2.  Routing Header

   IPv6 Routing extension headers are defined in [RFC2460].  However,
   the loose source routing they define is not appropriate for this
   setting since (a) it uses 128-bit addresses, and (b) it is deprecated
   by [RFC5095].  Source routing is a critical facility in this class of
   network, and so we define a new routing type.  Alternatively, we may
   consider this a routing type 0 header, with adaptations.

       |  Next Header  |  Hdr Ext Len  | Routing Type=0| Segments Left |
       |            Address[1]         |      Address[2]               |
       .                               .                               .
       .                               .                               .
       .                               .                               .
       |          Address[n-1]         |         Address[n]            |

   The addresses in this header are stored in compressed 16-bit form, as
   specified by [RFC4944] (or later).

6.3.  Route Install Header

   A Route Install Header may be placed either as a Destination option
   or a Hop-by-hop option, depending on the method of install.
   Processing of this header will depend on which of these is in effect.

       |  Option Type  |  Option  Len  | M Len | |R| M |   Path Len    |
       |         Flow Match (D)        |         Address[1]            |
       |            Address[2]         |         Address[3]            |
       .                               .                               .
       .                               .                               .
       .                               .                               .
       |     Address[Path Len - 1]     |       Address[Path Len]       |

   Option Type: the TLV dispatch value TBD.

Tavakoli, et al.       Expires September 10, 2009              [Page 10]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   M Len : 'match length'.  The length of the flow match in octets.
   MUST be at least 2, but MAY be extended in future drafts.

   R : 'reverse'. if set, indicates that the reverse path should also be

   M : 'method'. 00 is HOP_BY_HOP and 01 is FULL_PATH.  Other values are

   Path Len: the number of addresses contained in the list.  If zero,
   indicates that an IPv6 routing header should be consulted for the
   path to D.

   Flow Match (D): the destination address of this flow.

   Address[...]: a list of intermediate Nodes on a path from a source
   address to D. The source must be the destination of the IPv6 datagram
   the header is carried in; that source address must not be included in
   the path, and Address[n] = D.

6.4.  Router Advertisement Extension

   In order to carry the Total Path Cost in a router advertisement, we
   define a new extension header to the Router Advertisement message
   defined in [RFC2461].

       |  Option Type  |  Option  Len  |            Metric             |
       |  Willingness  |

   Option type: the TLV value for this header TBD.

   Option length: The option length, in octets (4).

   Metric: the Overall Route Cost from a Node to the original
   advertising router, the Border Router.  If this extension is not
   present, a cost of zero should be assumed.

   Willingness: a value indicating the Node's willingness or capacity to
   route traffic for other Nodes.

6.5.  Topology Report Message

   Topology Reports are carried as an IPv6 hop-by-hop option inserted in
   outgoing packets.

Tavakoli, et al.       Expires September 10, 2009              [Page 11]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

       |  Option Type  |  Option  Len  |  AL   |  Sequence Number      |
       |                         (Attributes)                          |
       |   Metric[1]   | Confidence[1] |         Address[1]            |
       .                               .                               .
       .                               .                               .
       .                               .                               .
       |   Metric[N]   | Confidence[N] |         Address[N]            |

   Sequence Number: a monotonically increasing identifier of this
   topology report

   AL: "Attribute Length": the length of the "Attributes" field in
   octets.  If the length is zero, no Node Attributes are carried.  If
   the length is one, a single octet follows the Sequence Number field,
   which is the "Willingness" value.  Other values of AL are reserved.

   Attributes: Node Attributes which may be used to make routing
   decisions; defined outside of the HYDRO protocol

   Metric[i] : a Link Cost Estimate

   Confidence[i] : the link estimator's Confidence in Metric[i]

   Address[i] : a compressed IPv6 address indicating the Node or Border
   Router Metric[i] and Confidence[i] refer to.

   There is no explicit field specifying the number of entries;
   implementations should infer this value from the Option Length field
   and the Attribute Length field.

6.6.  Topology Report Package

   A Topology Report Package is used for transmitting a collection of
   Topology Report Messages between Border Routers.  This message is
   formed by suffixing the Topology Report with the 2-octet address of
   its originator.  Multiple Topology Report Messages may be
   concatenated into a single Topology Report Package.

7.  Detailed Operation

   This section describes in greater detail the HYDRO protocol.  We

Tavakoli, et al.       Expires September 10, 2009              [Page 12]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   begin by describing the interaction of HYDRO with the link layer, and
   the Router Advertisement mechanism.  We then explain how these
   primitives are used to form Default Routes, report topology, and
   route back into the network.  Finally, we detail how Border Routers
   may insert Flow Table Entries into the network to improve inefficient

7.1.  Link Estimation

   A critical design element for good performance in L2N networks is
   good link estimation; low power wireless links exhibit significant
   temporal and spatial variations in quality due to a number of
   physical and environmental phenomenon.  This poses a challenge to
   traditional IP link abstraction since any protocol must account for
   this behavior.

   The link layer MUST provide an additive link metric for potential
   links to the routing layer, such that the cost of a path C[A -> B ->
   C] = C[A -> B] + C[B -> C].  Examples of such a metric are Expected
   Transmissions (ETX) or Expected Transmission Time (ETT).
   Additionally, the link layer MUST provide an estimate of its
   Confidence in each Link Cost Estimate.  These estimates MAY be binary
   or integer valued.

   The link layer must also provide a mechanism for 'local broadcast';
   the 802.15.4 broadcast address (0xffff) is such a mechanism.  It MAY
   be advantageous to replace this mechanism with a dedicated discovery
   component in the future.

7.2.  Router Discovery

   Router Advertisement and Router Solicitation messages and the
   associated protocol have been standardized for IPv6 in [RFC2461].
   While many of the mechanisms can be applied directly in L2Ns, some
   require modification for efficiency or performance.  The 6lowpan
   working group has created a team to investigate these necessary
   modifications; once their work is complete HYDRO SHOULD be modified
   to used those mechanisms.

   We do not alter the Router Solicitation or Router Advertisement
   packet formats.  We do define a new Router Advertisement extension,
   the Multihop extension, which allows Nodes to advertise their Overall
   Route Cost value.  Router Advertisements without this extension are
   assumed to have a Total Route Cost of zero.  In addition, another
   extension allows Router Advertisements to specify a Node's
   Willingness value.

   When an event triggers the generation of Router Solicitation or

Tavakoli, et al.       Expires September 10, 2009              [Page 13]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   Router Advertisement messages, a binary exponential timer is started.
   Each time the timer fires, a new Router Solicitation or Advertisement
   is generated and sent to the IPv6 all-routers link-local multicast
   address (ff02::2), using the link broadcast facility.

   There are two conditions which cause a reset of the Router
   Solicitation timer, and thus the transmission of new Router

   1.  Boot

   2.  No valid Default Route is present in the Default Route Table.

   There are two conditions which cause the Router Advertisement timer
   to be started, if it is not running, and thus the transmission of
   Router Advertisements:

   1.  Reception of a Router Solicitation, and the Primary Default Route
   is valid.

   2.  The Total Route Cost of the Primary Default Route changes by more
   then a threshold, ROUTE_COST_NOTIF_DIFF.

7.3.  Default Route Formation

   The Border Router is manually configured with an IPv6 address,
   including a full 64-bit network prefix on its L2N Interface; all
   Border Routers on the same L2N Subnet have L2N Interfaces with
   addresses on the same prefix.  A Node automatically transmits Router
   Solicitations on boot, and nearby Nodes with a valid Primary Default
   Route will reply with Router Advertisements.  This section specifies
   processing rules for these Router Advertisements.  The result is an
   ordered table of potential next-hops towards the Border Router.

   A Node that receives a Router Advertisement from a Potential Default
   Route Neighbor (PNeighbor) first checks if a Default Route entry for
   PNeighbor exists in its Default Route Table.  If an entry for
   PNeighbor does not exist, it begins processing the Route
   Advertisement to determine if an entry for PNeighbor should be

   The Default Route Table is sorted based on a combination of Overall
   Route Cost, which is the sum value of the Route Cost Estimate
   advertised by the next-hop Neighbor and the Link Cost Estimate, the
   Confidence, and the Willingness advertised by an entry's next-hop
   Node.  The Confidence and Link Cost Estimate MUST be provided by the
   link layer.

Tavakoli, et al.       Expires September 10, 2009              [Page 14]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   Processing begins by checking whether the link layer Link Quality
   Metric exceeds the necessary threshold (LINK_ADMIT_THRESH) to be
   considered.  The exact metric is implementation specific, and MAY NOT
   be the Link Cost Estimate ultimately used for Default Route
   maintenance.  For instance, implementations may use a link
   measurement like RSSI or LQI, along with a static or dynamic
   threshold to reject poor links.  The rationale is that estimators
   like ETX require multiple packets before they can be trusted, whereas
   the routing layer must evaluate a flood of Router Advertisements for
   possible use as Default Routes.

   A Node next checks if an empty spot exists in the Default Route
   table.  If a spot exits, then HYDRO determines where in the table to
   insert an entry for PNeighbor.  The algorithm begins by creating a
   new Default Route entry at the bottom of the Default Route table.  It
   then repeatedly compares the new Default Route entry with the entry
   in the spot above it.  If the higher spot is empty, or if the entry
   also has a '0' Confidence value and its advertised Route Cost
   Estimate is greater than the PNeighbor's advertised Route Cost
   Estimate, the two entries' positions are swapped.  The iteration
   stops when this condition fails, or the algorithm reaches the top of
   the Default Route Table.

   If the Default Route Table is full, then HYDRO determines whether the
   bottom Default Route Table entry should be evicted to create room for
   PNeighbor.  If the bottom entry is not Mature, meaning that its
   Confidence value is less than CONF_EVICT_THRESHOLD, or its Route Hops
   value is less than PNeighbor's Route Hops value, we leave the Default
   Route Table as is and discard the Route Advertisement.

   Otherwise, if PNeighbor's Route Cost Estimate is lower than the
   existing Default Route Entry's Route Cost Estimate by at least
   PATH_COST_DIFF_THRESH, or if the absolute value of the difference
   between the two Route Cost Estimates is less than
   PATH_COST_DIFF_THRESH and PNeighbor's Link Quality Estimate is
   greater than the existing Default Route Entry's Link Quality Estimate
   by at least LINK_QUALITY_DIFF_THRESH, than the existing bottom
   Default Route Table Entry is evicted to make room for PNeighbor's

   If an entry slot is found for PNeighbor, the field values are set
   according to the Router Advertisement.  If an entry previously
   existed for PNeighbor, then the field values are simply updated.

   If the Route Cost in the Route Advertisement is set to MAX_ROUTE_COST
   and PNeighbor was already present in the Default Route Table, the
   existing PNeighbor entry is evicted.

Tavakoli, et al.       Expires September 10, 2009              [Page 15]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   The top entry in the Default Route Table is the Primary Default
   Route.  We define the Overall Node Route Cost at any given time to be
   the Overall Route Cost of the Primary Default Route, and Overall
   Route Hops to be the Route Hops Value of the Primary Default Route.
   If no Primary Default Route exists, these are set to MAX_ROUTE_COST
   and MAX_HOPS, respectively.

   At the end of each period, as determined by PERIOD_LENGTH, each Node
   reevaluates its Default Route Table.  If the Default Route Table is
   empty (implying that no Primary Default Route exits), a Router
   Solicitation is sent out, requesting Router Advertisements from
   neighboring Nodes.  In addition, if the absolute difference between
   the Node's Overall Node Route Cost at the end of the last period, and
   the current Overall Node Route Cost is greater than
   ROUTE_COST_NOTIF_DIFF, or the Overall Route Hops has changed since
   the end of the last period, the Node sends a Routing Advertisement.

   After each Router Solicitation, if after SOLICITATION_PERIOD time, no
   Primary Default Route exists, another Router Solicitation is sent
   out.  This SHOULD be modified to use a Trickle or Exponential Backoff

7.4.  Global Topology Construction

   Each Border Router maintains a view of the topology of the entire L2N
   Subnet using information obtained from the Topology Reports created
   by each Node.

   Each Node prepares a Topology Report periodically, with period length
   determined by TOP_REPORT_PERIOD.  The Node then holds off on sending
   the report for TOP_REPORT_WAIT time, in an attempt to piggyback the
   report on a data packet.  This Topology Report is added to an IP
   datagram as an IPv6 hop-by-hop options header using a new TLV
   dispatch value.

   For each entry within the top DEFAULT_TOP_THRESH slots (inclusive),
   if the slot is not empty, the entry is flagged as Mature (Confidence
   >= CONF_EVICT_THRESH), or it is set as the Primary Default Route,
   then its Address, Link Cost Estimate, and Confidence are inserted
   into the Topology Report.

   In addition to Default Route information, the Node SHOULD include
   requested Node Attribute values, which are defined outside of HYDRO
   by the application, and SHOULD include its Willingness value

   The Topology Report is then sent to the Border Router.  The report
   MAY be added to an outgoing data packet destined to the Border
   Router, or in a new message generated by the Node.  Topology reports

Tavakoli, et al.       Expires September 10, 2009              [Page 16]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   SHOULD NOT be inserted into messages where a Flow Match is available
   in the Flow Entry Table.

   The Border Router maintains a graph of the entire network.  When it
   receives a Topology Report from a Node, it first compares the
   Sequence Number contained in the Topology Report against the last
   received sequence number (LSN) from that Node.  If the Sequence
   Number is greater than the LSN, or if it is less then LSN -
   SEQ_ROLLOVER_THRESH, or if this is the first report from this Node
   Router, the Border Router removes the edges created by previous
   Topology Report from the same Node, and inserts edges based on the
   information in the latest Topology Report.  Edge costs are determined
   by policy.  One option is to use the Link Cost Estimates from the
   Topology Report.  In addition, the Node Attributes can be associated
   with the appropriate graph vertices.

7.5.  Node Forwarding

   For any given packet at a Node, whether it originated there or is
   simply being forwarded, a series of steps are taken in order to
   determine how to send the packet.  HYDRO SHOULD specify multiple
   next-hops for any particular packet when available.  If transmission
   to the first next-hop fails, HYDRO will attempt to use the next next-
   hop, until all choices provided have failed.  The link layer MUST use
   link-layer acknowledgements in order to determine transmission
   success or failure, and SHOULD retry failed transmissions.  This
   section describes how the ordered list of potential next-hops is
   constructed for a particular packet.

   1.  If the packet contains an IPv6 Routing Header, the address of the
   next-hop is determined using that route, and the 'Segments remaining'
   field of the routing header is decremented.  The address from the
   routing header is provided as the first choice next-hop.  If a router
   receives a packet containing a routing header where the segments
   remaining field is zero but the router is not the destination, the
   router SHOULD ignore the routing header.

   2.  If no routing header exists, HYDRO examines the Flow Table to
   determine if a matching entry exists.  The matching process depends
   on the particular instantiation of the Flow Match data structure.

   2.1.  If the matching entry indicates the Flow Path Type is
   FULL_PATH, then this indicates the Flow Path is a full Source Route.
   If the packet was locally generated, a new routing header is inserted
   into the packet and the next hop of that path provided as the first
   choice next-hop.

   2.2.  If the matching entry indicates the Flow Path Type is

Tavakoli, et al.       Expires September 10, 2009              [Page 17]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   NEXT_HOP_PATH, then this indicates the Flow Path is a next hop
   address, with each Node along the path expected to have a similar
   entry.  This Node address is provided as the first next-hop choice.
   The NEXT_HOP_PATH data structure MAY store multiple potential next
   hops, in an ordered list, specified by NUM_HOP_CHOICES.  More then
   one potential next hop MAY be provided using this list.

   3.  Finally, HYDRO uses the Default Route Table to choose a next-hop,
   and forwards the packet towards the Border Router.  HYDRO will
   attempt to send to the Primary Default Route first, followed by the
   top entries of the Default Routing Table.

   The number of next-hops that HYDRO attempts to use when forwarding a
   particular packet is determined by NUM_NEXT_CHOICES.  In addition, a
   packet that is being forwarded MUST NOT select its previous-hop Node
   as the next-hop Node.  If an entry specifies such a case, it is
   ignored and the process described above continues.

   HYDRO receives feedback from the link layer following each
   transmission about which Default Route next-hops the link was able to
   successfully use.  If the number of consecutive failures of the
   Primary Default Route is greater than MAX_CONSEC_FAILURES, HYDRO
   initiates a search for a new Primary Default Route.  If another
   Default Route Table entry exists whose Route Hops is less than the
   Primary Default Route's Route Hops, and its Route Cost Estimate is
   less than the Primary Default Route's Route Cost Estimate, then one
   of these candidates is selected at random (if multiple choices exist)
   to be the new Primary Default Route (although the table is not
   reordered).  If no such candidate is found, then the Route Hops
   comparison is dropped and the same search is performed again with
   only Route Cost Estimate comparisons.  If again no candidate is
   found, then the Primary Default Route remains unchanged.

   In addition, at the end of each period, with probability
   NEW_PRIMARY_ROUTE_PROB, this same exploration for an alternate
   Primary Default Route occurs, allowing HYDRO an opportunity to
   increase the Confidence in other Default Route Entry Link Cost

   As a final task at the end of each period, if a Node that is a single
   hop away from a Border Router determines that it has failed to
   successfully transmit a single packet to a Border Router (while at
   least making one attempt), it determines that the link to the Border
   Router is gone, and SHOULD broadcast a Router Advertisement
   advertising an Overall Route Cost of MAX_ROUTE_COST, and Overall
   Route Hops of MAX_HOPS.  Not broadcasting such a message MAY lead to
   longer convergence times in networks with multiple Border Routers
   that may fail or be mobile.

Tavakoli, et al.       Expires September 10, 2009              [Page 18]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   After each forwarding attempt, HYDRO reorders the Default Route Table
   using updated link statistics from the recent attempt.  If the packet
   was transmitted successfully (using Node 'A' as the next-hop) and the
   entry (A) is not the top entry in the Default Route Table, it swaps
   positions with the entry above it (B) if its Confidence is greater
   than CONF_PROM_THRESHOLD and one of the following three conditions

   1.  Overall Route Cost of A + WILLINGNESS_COST_THRESH < Overall Route
   Cost of B.

   2.  Overall Route Cost of A is less than the Overall Route Cost of B,
   or greater than it by less than PATH_COST_DIFF_THRESH, and the
   absolute value of the difference between the Willingness of A and the
   Willingness of B is less than or equal to WILLINGNESS_THRESH.

   3.  A's Overall Route Cost is within WILLINGNESS_COST_THRESH of B's
   Overall Route Cost, and A's Willingness > B's Willingness +

7.6.  Border Router Forwarding

   Border Routers will receive packets from Nodes in the L2N in the
   course of normal operation, since Nodes will forward packets to a
   Border Router when they do not have a matching Flow Table Entry for a
   packet.  The Border Router should process packets which originated on
   its L2N interface as follows:

   NOTE: Some of the following steps assume multiple Border Routers
   exist in a network.  We describe the setup and maintenance of such a
   topology in a later section.

   1.  If the destination address is a global unicast address, normal
   IPv6 processing rules apply; the packet will be routed according to
   the IPv6 Routing Table Entry for that destination.

   2.  If the packet contains an IPv6 Routing Header and the first hop
   of that route is another Border Router, the packet is dropped.

   3.  If the destination is a unicast address within the L2N subnet and
   the Border Router does not have a route in its route database, the
   packet is dropped.  It MAY generate an ICMPv6 Host Unreachable
   message in this case, but implementers SHOULD take care to limit the
   rate of message generation; it MAY be advantageous in many cases not
   to generate this message.

   4.  Otherwise, the Border Router has a stored route to the
   destination (in the L2N subnet):

Tavakoli, et al.       Expires September 10, 2009              [Page 19]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   4.1 If the Border Router has a route to the destination and the next-
   hop is another Border Router, the packet is forwarded to that Border
   Router without modification.

   4.2.  If the Border Router has a route to the destination and the
   next-hop is a Node, the Border Router inserts an IPv6 Routing Header
   containing the source route to the destination, and transmits the
   packet to the first hop of this route.

7.7.  Route Installation

   In the course of forwarding a packet as described in the 'Border
   Router Forwarding' section, a Border Router may determine that it is
   not on the best path between the source and destination Node (where
   'best' is defined by a user-specified routing policy, such as lowest
   cost).  Alternatively, there may be administratively configured
   routes between Nodes in the network.  HYDRO SHOULD install routes to
   enable more efficient routing, but in any case, the exact policy for
   determining when and what routes are installed is not part of the
   HYDRO protocol; what is required is that HYDRO Nodes process
   installation messages as described.

   Two types of routes may be installed: hop-by-hop and full path
   routes.  For a hop-by-hop route from Node A to Node B, each
   intermediate Node N_i on the path P=[A,N_1,N_2...N_i,B] from A to B
   adds a Flow Table Entry indicating that packets destined to B (and
   also potentially originating from A) have next hop N_i+1.  A full
   path install of this same route would place the entire path P into
   the Flow Table of Node A; outgoing packets from A destined to B use
   the path to insert an IPv6 Routing Header containing the route.  If
   the reverse option is selected, intermediate Nodes would have to
   create Flow Table entries for the reverse direction as well for hop-
   by-hop route installs, and the full reverse path would have to be
   installed at B for full path route installs.

   Suppose a Border Router R wishes to install a route between Nodes A
   and B. A Route Install Header is created and placed into the IPv6
   Destination Options header.  The 'method' field is set to either
   HOP_BY_HOP or FULL_PATH, and the 'reverse' field is set to indicate
   whether or not the path from B to A should also be installed.  The
   Flow Match is initialized to indicate that the destination address of
   the Flow is B. This header is placed either in a new packet addressed
   to Node A, or in the header of an existing packet which is destined
   to Node A.

   When Node A receives the Route Install Message, it processes it as
   part of its processing of the Destination Options extension headers.
   Regardless of the method of install, the router searches its Flow

Tavakoli, et al.       Expires September 10, 2009              [Page 20]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   Table using the Flow Match in the routing header.  If one is present,
   it replaces it with the new information (if the 'method' is
   FULL_PATH).  If the 'method' is HOP_BY_HOP, since there can be
   NUM_FLOW_CHOICES for each Flow Table entry, if the same next-hop Node
   already exists, it is brought to the top of the list.  Otherwise, the
   bottom next-hop in the list is evicted, and the new next-hop is
   placed at the top of the list.

   If the Flow Table is full, HYDRO evicts an entry using a Least
   Recently Used policy.  The Node then adds the route contained in the
   routing header to the Flow Table: it copies into the Flow Path either
   the entire route, if the method is FULL_PATH, or the next hop, if the
   method is HOP_BY_HOP.

   If the method is HOP_BY_HOP, or if the method is FULL_PATH and the
   reverse bit is set, the router generates a new packet.  The new
   packet contains an IPv6 Routing Header with the route specified in
   the Route Install Header.  If the method was HOP_BY_HOP, the router
   adds an IPv6 hop-by-hop option extension containing a new routing
   header.  This new hop-by-hop routing header does not contain the
   route since that information is present in the IPv6 Routing Header,
   and so the path_len field is zero.

   If a Node receives a Route Install Header in a hop-by-hop option, the
   method MUST be HOP_BY_HOP.  If this is the case, it inserts a new
   Flow Table entry using the Flow Match contained in the Route Install
   Header, and consults the routing header to determine the next-hop
   address to install.  The next hop address is the one obtained by
   following normal processing rules for the source header when
   forwarding the packet.

7.8.  Multicast Forwarding

   In this so-called "route-over" design, the link-local multicast
   address is mapped directly to link-local broadcast at the link layer.
   Thus any packet destined to a link-local multicast group should be
   send by the originator using the links local broadcast facility;
   these packets clearly MUST NOT be forwarded or retransmitted by any
   non-origin Node.

   Additionally, it is often desirable for Nodes to send packets to all
   Nodes in a subnet, regardless of whether or not they are within a
   link-local broadcast domain.  For this purpose, we use the IPv6 site-
   local scope.  First, we define the well-known address ff05::XXXX to
   correspond to a subnet-wide flood.  Nodes receiving packets destined
   to this address SHOULD forward these packets using the link-local
   broadcast address; this may be done using a mechanism like Trickle to
   reduce dependency on network density; more details about this

Tavakoli, et al.       Expires September 10, 2009              [Page 21]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   forwarding is elided from this document.

7.9.  Multiple Border Routers

   It is often desirable for multiple Border Routers to be present on
   single L2N subnet to provide a diversity of routing options and
   failover connectivity.  If more than one Border Router is present,
   layer 2 connectivity between them will be assumed, for example using
   Ethernet, 802.11 mesh, or virtual tunneled IP links (something
   similar to [RFC2003]).  The interface the Border Routers use to
   connect directly to the other Border Routers is named the Secondary

   The multiple Border Routers assign themselves unique address on the
   L2N subnet prefix using their Secondary Interface via manual
   configuration.  On startup, the Border Routers join a link-local
   multicast group ff02::XXXX on their secondary interface and begin
   listening for messages on UDP port XXXX.

   When a Border Router receives a Topology Report from a Node Router,
   the Topology Report should be appended to a Topology Report Package
   header and transmitted to the link-local multicast group.  Border
   Routers receiving Topology Report Packages should process the
   contained Topology Reports identically to locally received reports.

   When Border Routers receive a Topology Report Package, they must
   annotate the previous hop of the message in their Link Database to
   indicate if it is a Border Router; that way, they can determine when
   the next hop to a Node is another Border Router.  Furthermore, the
   transmission of Topology Report messages to other Border Routers
   ensures that all Border Routers maintain a consistent view of the

8.  Extensions

   The protocol specified in this draft addresses many of the unique
   demands of this space and the routing requirements spelled out in the
   IETF Roll Protocols Survey [I-D.ietf-roll-protocols-survey].
   However, there are certain limitations of the design that are left
   for future revisions of the draft.

   First, routing from a Border Router to a Node relies on source
   routing.  Also, the FULL_PATH route install method uses source
   routing.  For paths longer then 5-10 hops, the per-packet overhead of
   this mechanism becomes unacceptable, as does the state at each Node
   that must maintain these paths.  There are many methods of fixing or
   ameliorating this problem.  Using the current design, deploying

Tavakoli, et al.       Expires September 10, 2009              [Page 22]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   additional Border Routers to decrease the network depth may be an
   option in some situations.  Alternatively, a later protocol
   specification could include a mechanisms for loose source routing
   between landmarks, which might be determined by Border Routers.  This
   would serve as a hybrid of the source routing and hop-by-hop route
   install options.  The need to test the efficiency and functionality
   of these adaptations, particularly in the face of multiple link
   failures, preclude their full specification at this point in the

   Another issue is that of network numbering.  The current draft
   requires that Border Routers with two interfaces to assign themselves
   different address on the same L2N prefix to both of these interfaces.
   This also occurs in the (experimental) design for IPv6 Neighbor
   Discovery Proxies [RFC4389], but seems to the authors to be somewhat
   inelegant.  It may be possible to devise a better solution.

9.  Configuration Parameters and Other Administrative Options

   CONF_EVICT_THRESHOLD: Setting of this MAY be dependent on the data
   rate (because that determines how long it takes to get a Mature
   entry).  Initial implementations use '5'.

   CONF_PROM_THRESHOLD: Threshold for being able to promote an entry in
   the Default Route Table.  Dependent on link layer.

   DEFAULT_TOP_THRESH: The maximum number of Default Route Entries (from
   the top) that MAY be included in a Topology Report.  Recommended
   value is 4.

   LINK_ADMIT_THRESH: This value depends on the availability of hardware
   based link quality metrics, (such as LQI for CC2420-Based Hardware
   Platforms), and the setting of the threshold may depend on the actual
   deployment environment as well.

   LINK_QUALITY_DIFF_THRESH: Will vary based on link quality metric
   used.  For CC2420 LQI, 10 is the recommended value.

   MAX_CONSEC_FAILURES: Maximum number of consecutive failures after
   which a new Primary Default Route SHOULD be used.  Recommended value
   is 20 (if link layer retransmissions are included).

   MAX_HOPS: Upper bound value to denote invalid entry.

   MAX_ROUTE_COST: Upper bound value to denote invalid entry.

   NEW_PRIMARY_ROUTE_PROB: Probability of looking for another Primary

Tavakoli, et al.       Expires September 10, 2009              [Page 23]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   Default Route at the end of a period.  Recommended value is 25%.

   NUM_DEFAULT_ENTRIES: The size of the Default Route Table, recommended
   to be '8'.

   NUM_FLOW_CHOICES: The maximum number of next-hop choices for a
   HOP_BY_HOP Flow Table Entry.  Recommended value is 1.

   NUM_NEXT_CHOICES: The maximum number of next-hop choices to be used
   when attempting to send a packet.

   PATH_COST_DIFF_THRESH: Threshold for determining whether two Route
   Costs are similar.  Depends on Metric used for Route Costs, but if
   ETX (Expected Transmissions) are used, the recommended value is 1.

   PERIOD_LENGTH: Application dependent, will affect control traffic
   rate and convergence rate, potentially.

   ROUTE_COST_NOTIF_DIFF: Difference in the route cost that merits a
   Route Advertisement.  Route Cost is metric dependent, but if ETX is
   used, then a recommended value is 0.5.

   SOLICITATION_PERIOD: Tradeoff between control traffic generated and
   route formation.

   TOP_REPORT_PERIOD: To meet the ROLL requirements, this should be
   lower bounded by the inverse of the data rate.

   TOP_REPORT_WAIT: This should be set to the variance in data reporting

   WILLINGNESS_COST_THRESH: The buffer in Overall Route Cost that SHOULD
   be traded for a more willing Node to route packets.  This is
   dependent on a particular application's tolerance for routing stretch
   to reduce load on certain Nodes.

   WILLINGNESS_THRESH: The difference in Willingness that is necessary
   for promoting a Default Route Entry that gives up less Overall Route
   Cost than WILLINGNESS_COST_THRESH but more than
   PATH_COST_DIFF_THRESH.  Is dependent on the range in Willingness.

10.  Applicability Statement

   HYDRO is designed for use in L2Ns that are composed of a two-tiered
   hierarchy in which a set of Nodes are supported by a much smaller set
   of more capable Border Routers.  In other words, HYDRO was designed
   for scenarios laid out by the ROLL working group, as detailed in the

Tavakoli, et al.       Expires September 10, 2009              [Page 24]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   Protocols Survey [I-D.ietf-roll-protocols-survey].  As such, we now
   provide a brief analysis of HYDRO's performance relative to the five
   quantified metrics, demonstrating that it passes all five criteria.

   Table Scalability: The size of the Default Route Table is limited by
   a constant, NUM_DEFAULT_ENTRIES, and as such is O(1).  The Flow Table
   scales with the number of destinations, and so the total amount of
   routing state is O(D), which meets the criteria.

   Loss Response: In the case that a link fails, this is only detected
   when trying to send a data packet over the link.  In such a case, the
   data packet is then forwarded over another path, potentially leading
   to the installation of a new route in the network.  The updated
   quality of the link is reported with the next Topology Report.  This
   limits the scope of the loss response only to the active path,
   achieving a pass.

   Control Cost: The three forms of control cost are route formation,
   Topology Reports, and Route Install Messages.  Route Advertisement
   messages initiated by the Border Router can be turned down to
   arbitrarily low frequencies, and Route Solicitation messages by Nodes
   are only of single-hop scope and triggered by failure of all Default
   Routes.  Route Install Messages are a product of data traffic, and so
   subsequently HYDRO meets the requirement of being bound by the data
   rate plus a small constant.

   Link Cost: Link qualities play an integral part of routing in HYDRO.

   Node Cost: Each Node can report the desired Node Attributes as part
   of its Topology Reports, as well as its Willingness, and the
   objective function for calculating routes at the Border Router can
   incorporate these.

11.  Security Considerations

12.  IANA Considerations

   This document includes no request to IANA.

13.  Acknowledgements

   Special thanks to members of the ROLL working group for helpful
   comments and discussion that aided in the design of HYDRO.

Tavakoli, et al.       Expires September 10, 2009              [Page 25]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

14.  References

14.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

14.2.  Informative References

              Martocci, J., Riou, N., Mil, P., and W. Vermeylen,
              "Building Automation Routing Requirements in Low Power and
              Lossy Networks", draft-ietf-roll-building-routing-reqs-05
              (work in progress), February 2009.

              Porcu, G., "Home Automation Routing Requirements in Low
              Power and Lossy Networks",
              draft-ietf-roll-home-routing-reqs-06 (work in progress),
              November 2008.

              Networks, D., Thubert, P., Dwars, S., and T. Phinney,
              "Industrial Routing Requirements in Low Power and Lossy
              Networks", draft-ietf-roll-indus-routing-reqs-04 (work in
              progress), January 2009.

              Tavakoli, A., Dawson-Haggerty, S., and P. Levis, "Overview
              of Existing Routing Protocols for Low Power and Lossy
              Networks", draft-ietf-roll-protocols-survey-06 (work in
              progress), February 2009.

              Dohler, M., Watteyne, T., Winter, T., Barthel, D.,
              Jacquenet, C., Madhusudan, G., and G. Chegaray, "Urban
              WSNs Routing Requirements in Low Power and Lossy
              Networks", draft-ietf-roll-urban-routing-reqs-04 (work in
              progress), February 2009.

   [RFC2003]  Perkins, C., "IP Encapsulation within IP", RFC 2003,
              October 1996.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC2461]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor
              Discovery for IP Version 6 (IPv6)", RFC 2461,

Tavakoli, et al.       Expires September 10, 2009              [Page 26]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

              December 1998.

   [RFC4389]  Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
              Proxies (ND Proxy)", RFC 4389, April 2006.

   [RFC4944]  Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
              "Transmission of IPv6 Packets over IEEE 802.15.4
              Networks", RFC 4944, September 2007.

   [RFC5095]  Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
              of Type 0 Routing Headers in IPv6", RFC 5095,
              December 2007.

Authors' Addresses

   Arsalan Tavakoli
   UC Berkeley
   Soda Hall, UC Berkeley
   Berkeley, CA  94720


   Stephen Dawson-Haggerty
   UC Berkeley
   Soda Hall, UC Berkeley
   Berkeley, CA  94720


   Jonathan W. Hui
   Arch Rock Corporation
   501 2nd St. Ste. 410
   San Francisco, CA  94107


Tavakoli, et al.       Expires September 10, 2009              [Page 27]

Internet-Draft           draft-tavakoli-hydro-01                Mar 2009

   David Culler
   UC Berkeley
   Soda Hall, UC Berkeley
   Berkeley, CA  94720


Tavakoli, et al.       Expires September 10, 2009              [Page 28]