Transmission of IPv6 Packets over Bluetooth Low Energy
draft-ietf-6lowpan-btle-06

6LoWPAN Working Group                                   J. Nieminen, Ed.
Internet-Draft                                                  B. Patil
Intended status: Standards Track                           T. Savolainen
Expires: September 7, 2012                                    M. Isomaki
                                                                   Nokia
                                                               Z. Shelby
                                                               Sensinode
                                                                C. Gomez
                                              Universitat Politecnica de
                                                         Catalunya/i2CAT
                                                           March 6, 2012

         Transmission of IPv6 Packets over Bluetooth Low Energy
                       draft-ietf-6lowpan-btle-06

Abstract

   Bluetooth Low Energy is a low power air interface technology defined
   by the Bluetooth Special Interest Group (BT SIG).  The standard
   Bluetooth radio has been widely implemented and available in mobile
   phones, notebook computers, audio headsets and many other devices.
   The low power version of Bluetooth is a new specification and enables
   the use of this air interface with devices such as sensors, smart
   meters, appliances, etc.  The low power variant of Bluetooth is
   commonly specified in revision 4.0 of the Bluetooth specifications
   and commonly refered to as Bluetooth 4.0.  This document describes
   how IPv6 is transported over Bluetooth Low Energy using 6LoWPAN
   techniques.

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
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   This Internet-Draft will expire on September 7, 2012.

Copyright Notice

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   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Bluetooth Low Energy . . . . . . . . . . . . . . . . . . . . .  3
     2.1.  Bluetooth Low Energy stack . . . . . . . . . . . . . . . .  4
     2.2.  Link layer roles and topology  . . . . . . . . . . . . . .  4
     2.3.  BT-LE device addressing  . . . . . . . . . . . . . . . . .  5
     2.4.  BT-LE packets sizes and MTU  . . . . . . . . . . . . . . .  5
   3.  Specification of IPv6 over Bluetooth Low Energy  . . . . . . .  6
     3.1.  Protocol stack . . . . . . . . . . . . . . . . . . . . . .  6
     3.2.  Link model . . . . . . . . . . . . . . . . . . . . . . . .  7
       3.2.1.  Stateless address autoconfiguration  . . . . . . . . .  7
       3.2.2.  Neighbor discovery . . . . . . . . . . . . . . . . . .  8
       3.2.3.  Header compression . . . . . . . . . . . . . . . . . .  9
       3.2.4.  Unicast and Multicast address mapping  . . . . . . . .  9
     3.3.  Internet connectivity scenarios  . . . . . . . . . . . . . 10
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   6.  Additional contributors  . . . . . . . . . . . . . . . . . . . 11
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   8.  Normative References . . . . . . . . . . . . . . . . . . . . . 11
   Appendix A.  Bluetooth Low Energy fragmentation and L2CAP Modes  . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13

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1.  Introduction

   Bluetooth Low Energy (BT-LE) is a radio technology targeted for
   devices that operate with coin cell batteries or minimalistic power
   sources, which means that low power consumption is essential.  BT-LE
   is an especially attractive technology for Internet of Things
   applications, such as health monitors, environmental sensing,
   proximity applications and many others.

   Considering the potential for the exponential growth in the number of
   sensors and Internet connected devices and things, IPv6 is an ideal
   protocol due to the large address space it provides.  In addition,
   IPv6 provides tools for autoconfiguration, which is particularly
   suitable for sensor network applications and nodes which have very
   limited processing power or a full-fledged operating system.

   [RFC4944] specifies the transmission of IPv6 over IEEE 802.15.4.  The
   Bluetooth Low Energy link in many respects has similar
   characteristics to that of IEEE 802.15.4.  Many of the mechanisms
   defined in [RFC4944] can be applied to the transmission of IPv6 on
   Bluetooth Low Energy links.  This document specifies the details of
   IPv6 transmission over Bluetooth Low Energy links.

   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 RFC 2119 [RFC2119].

   The terms 6LN, 6LR and 6LBR are defined as in [I-D.ietf-6lowpan-nd].

2.  Bluetooth Low Energy

   BT-LE is designed for transferring small amounts of data infrequently
   at modest data rates at a very low cost per bit.  Bluetooth SIG has
   introduced two trademarks, Bluetooth Smart for single-mode devices (a
   device that only supports BT-LE) and Bluetooth Smart Ready for dual-
   mode devices.  In the rest of the draft, the term BT-LE refers to
   both types of devices.

   BT-LE is an integral part of the BT 4.0 specification [BTCorev4.0].
   Devices such as mobile phones, notebooks, tablets and other handheld
   computing devices which include BT 4.0 chipsets also have the low-
   energy functionality of Bluetooth.  BT-LE is also included in many
   different types of accessories that collaborate with mobile devices
   such as phones, tablets and notebook computers.  An example of a use
   case for a BT-LE accessory is a heart rate monitor that sends data
   via the mobile phone to a server on the Internet.

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2.1.  Bluetooth Low Energy stack

   The lower layer of the BT-LE stack consists of the Physical (PHY) and
   the Link Layer (LL).  The Physical Layer transmits and receives the
   actual packets.  The Link Layer is responsible for providing medium
   access, connection establishment, error control and flow control.
   The upper layer consists of the Logical Link Control and Adaptation
   Protocol (L2CAP), Generic Attribute protocol (GATT) and Generic
   Access Profile (GAP) as shown in Figure 1.  GATT and BT-LE profiles
   together enable the creation of applications in a standardized way
   without using IP.  L2CAP provides multiplexing capability by
   multiplexing the data channels from the above layers.  L2CAP also
   provides fragmentation and reassembly for large data packets.

           +----------------------------------------+------------------+
           |              Applications                                 |
           +----------------------------------------+------------------+
           |        Generic Attribute Profile       |  Generic Access  |
           +----------------------------------------+     Profile      |
           | Attribute Protocol |Security Manager   |                  |
           +--------------------+-------------------+------------------+
           |              Logical Link Control and Adaptation          |
           +--------------------+-------------------+------------------+
           |              Host Controller Interface                    |
           +--------------------+-------------------+------------------+
           |           Link Layer       |      Direct Test Mode        |
           +--------------------+-------------------+------------------+
           |              Physical Layer                               |
           +--------------------+-------------------+------------------+

                      Figure 1: BT-LE Protocol Stack

2.2.  Link layer roles and topology

   BT-LE defines two Link Layer roles: the Master Role and the Slave
   Role.  A device in the Master Role, which is called master, can
   manage multiple simultaneous connections with a number of devices in
   the Slave Role, called slaves.  A slave can only be connected to a
   single master.  Hence, a BT-LE network (i.e. a BT-LE piconet) follows
   a star topology.

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                 [BTLE-Slave]-----\                /-----[BTLE-Slave]
                                   \              /
                  [BTLE-Slave]-----/[BTLE-Master]/-----[BTLE-Slave]
                                   /              \
                 [BTLE-Slave]-----/                \-----[BTLE-Slave]

                       Figure 2: BT-LE Star Topology

   A master is assumed to be less constrained than a slave.  Hence,
   master and slave can correspond with 6LoWPAN Border Router (6LBR) and
   host, respectively.

   In BT-LE, communication only takes place between a master and a
   slave.  Hence, in a BT-LE network using IP, a radio hop is equivalent
   to an IP link and vice versa.

2.3.  BT-LE device addressing

   Every BT-LE device is identified by a unique 48 bit Bluetooth Device
   Address (BD_ADDR).  A Bluetooth Smart device such as a sensor may use
   a public (obtained from IEEE Registration Authority) or a random
   device address (generated internally).  The public address is created
   according to the IEEE 802-2001 standard [IEEE802-2001] and using a
   valid Organizationally Unique Identifier (OUI) obtained from the IEEE
   Registration Authority.  This specification mandates that the
   Bluetooth Device Address MUST be a public address.

2.4.  BT-LE packets sizes and MTU

   Maximum size of the payload in the BT-LE data channel PDU is 27
   bytes.  Depending on the L2CAP mode in use, the amount of data
   available for transporting IP bytes in the single BT-LE data channel
   PDU ranges between 19 and 27 octets.  For power efficient
   communication between two BT-LE devices, data and its header should
   fit in a single BT-LE data channel PDU.  MTU larger than 27 bytes can
   be supported by the L2CAP specification.  The Basic L2CAP Mode allows
   a maximum payload size (i.e.  IP datagram size) of 65535 bytes per
   L2CAP PDU.  The rest of the L2CAP modes allow a maximum payload size
   that ranges between 65527 and 65533 bytes per L2CAP PDU.

   The maximum payload size of a BT-LE data channel PDU is 27 bytes,
   from which L2CAP headers may consume additional bytes.  However, data
   packets may be much larger (e.g.  IPv6 requires support for an MTU of
   1280 bytes).  Fragmentation and Recombination (FAR) functionality is
   an inherent function of the BT-LE L2CAP layer.  Larger L2CAP packets
   can be transferred with the assistance of the FAR functionality.

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   Appendix A describes FAR operation and five L2CAP Modes.  This
   specification requires that FAR functionality MUST be provided in the
   L2CAP layer up to the IPv6 minimum MTU of 1280 bytes.  The
   corresponding L2CAP Mode MUST be Basic Mode.  Since FAR in BT-LE is a
   function of the L2CAP layer, fragmentation functionality as defined
   in [RFC4944] MUST NOT be used in BT-LE networks.

3.  Specification of IPv6 over Bluetooth Low Energy

   BT-LE technology sets strict requirements for low power consumption
   and thus limits the allowed protocol overhead. 6LoWPAN standard
   [RFC4944], [I-D.ietf-6lowpan-nd] and [RFC6282] provides useful
   generic functionality like header compression, link-local IPv6
   addresses, Neighbor Discovery and stateless IP-address
   autoconfiguration for reducing the overhead in 802.15.4 networks.
   This functionality can be partly applied to BT-LE.

   A significant difference between IEEE 802.15.4 and BT-LE is that the
   former supports both star and mesh topology (and requires a routing
   protocol), whereas BT-LE does not currently support the formation of
   multihop networks.  In consequence, the mesh header defined in
   [RFC4944] for mesh under routing MUST NOT be used in BT-LE networks.
   In addition, a BT-LE device MUST NOT play the role of a 6LoWPAN
   Router (6LR).

3.1.  Protocol stack

   In order to enable transmission of IPv6 packets over BT-LE, a new
   fixed L2CAP channel ID MUST be reserved for IPv6 traffic by the BT-
   SIG.  A request for allocation of a new fixed channel ID for IPv6
   traffic by the BT-SIG should be submitted through the liaison process
   or formal communique from the 6lowpan chairs and respective area
   directors.  Until a channel ID is allocated by BT-SIG, the channel ID
   0x0007 is recommended for experimentation.  Once the channel ID is
   allocated, the allocated value MUST be used.  Figure 3 illustrates
   IPv6 over BT-LE stack.

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                  +-------------------+
                  |    UDP/TCP        |
                  +-------------------+
                  |      IPv6         |
                  +-------------------+
                  | 6LoWPAN adapted   |
                  |     to BT-LE      |
                  +-------------------+
                  |  BT-LE L2CAP      |
                  +-------------------+
                  |  BT-LE Link Layer |
                  +-------------------+
                  |  BT-LE Physical   |
                  +-------------------+

                      Figure 3: IPv6 over BT-LE Stack

3.2.  Link model

   The concept of IP link (layer 3) and the physical link (combination
   of PHY and MAC) needs to be clear and the relationship has to be well
   understood in order to specify the addressing scheme for transmitting
   IPv6 packets over the BT-LE link.  [RFC4861] defines a link as "a
   communication facility or medium over which nodes can communicate at
   the link layer, i.e., the layer immediately below IP."

   In the case of BT-LE, L2CAP is an adaptation layer that supports the
   transmission of IPv6 packets.  L2CAP also provides multiplexing
   capability in addition to FAR functionality.  This draft assumes the
   same common IPv6 header values as those assumed in [RFC 6282].  It is
   also assumed that the IPv6 payload length can be inferred from the
   L2CAP header length and also assumes that IPv6 addresses assigned to
   6LoWPAN interfaces are formed with an IID derived directly from the
   48-bit Bluetooth device addresses, as described in subsection 3.2.1.

   The BT-LE link between two communicating nodes can be considered to
   be a point-to-point or point-to-multipoint link.  When one of the
   communicating nodes is in the role of a master, then the link can be
   viewed as a point-to-multipoint link.

   When a host connects to another BT-LE device the link is up and IP
   address configuration and transmission can occur.

3.2.1.  Stateless address autoconfiguration

   A BT-LE 6LN performs stateless address autoconfiguration as per
   [RFC4862].  The 64 bit Interface Identifier (IID) for a BT-LE

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   interface is formed from the 48-bit unique public Bluetooth device
   address [REF Sec 2.3] as per the "IPv6 over Ethernet" specification
   [RFC2464].  A BT-LE 6LN SHOULD utilize this EUI-64 address for
   stateless address autoconfiguration.  The 48-bit public bluetooth
   address is globally unique and provided by the IEEE registration
   authority.  Hence the "Universal/Local" (U/L) bit MUST be set to 0.

   The IPv6 link-local address [RFC4291] for a BT-LE node is formed by
   appending the IID, as defined above, to the prefix FE80::/64, as
   depicted in Figure 4.

   The tool for a gateway to obtain an IPv6 prefix for numbering the
   BT-LE network is out of scope of this document, but can for example
   be accomplished via DHCPv6 Prefix Delegation.  The used IPv6 prefix
   may change due to the gateway^1s movement.

3.2.2.  Neighbor discovery

   [I-D.draft-ietf-6lowpan-nd] describes the neighbor discovery approach
   for 6loWPAN nodes.  BT-LE does not support mesh networks and hence
   only those aspects of the [I-D.draft-ietf-6lowpan-nd] that apply to a
   star topology are considered.

   The following aspects of 6lowpan-nd are applicable to BT-LE 6LNS:

   1.  A BT-LE 6LN MUST register its address with the router by sending
   a NS message with the ARO option and process the NA accordingly.  The
   NA with the ARO option SHOULD be sent irrespective of whether the IID
   is derived from the unique 48 bit BT-LE device address or the IID is
   a random value that is generated as per the privacy extensions for
   stateless address autoconfiguration [RFC4941].

   2.  Sending a Router solicitation (RS) and processing Router
   advertisements by BT-LE 6LNs MUST follow Sections 5.3 and 5.4
   respectvely of [I-D.draft-ietf-6lowpan-nd].

                     10 bits        54 bits             64 bits
                   +----------+-----------------+----------------------+
                   |1111111010|       zeros     | Interface Identifier |
                   +----------+-----------------+----------------------+

                Figure 4: IPv6 link-local address in BT-LE

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3.2.3.  Header compression

   This document assumes [RFC6282], which specifies the compression
   format for IPv6 datagrams on top of IEEE 802.15.4, as the basis for
   IPv6 header compression on top of BT-LE.  It is required that all
   headers MUST be compressed according to HC base encoding.  In BT-LE
   the star topology structure can be exploited in order to provide a
   mechanism for IID compression.  The following text describes the
   principles of IPv6 address compression on top of BT-LE.

   In a link-local communication, both the IPv6 source and destination
   addresses MUST be elided, since the device knows that the packet is
   destined for it even if the packet does not have destination IPv6
   address.  On the other hand, a node SHALL learn the IID of the other
   endpoint of each L2CAP connection it participates in.  By exploiting
   this information, a node that receives a data channel PDU containing
   an IPv6 packet (or a part of it) can infer the corresponding IPv6
   source address.  The device MUST maintain a Neighbor Cache, in which
   the entries include both the IID of the neighbor and the Device
   Address that identifies the neighbor.

   When a BT-LE slave transmits an IPv6 packet to a remote destination
   using global IPv6 addresses, the slave MUST elide the IPv6 source
   address, if a context is defined for the prefix of the IPv6 source
   address.  In this case, the 6LBR/master can infer the elided IPv6
   source address since 1) the master/6LBR has previously assigned the
   prefix to the slaves; and 2) the master/6LBR maintains a Neighbor
   Cache that relates the Device Address and the IID of the
   corresponding slave.  If a context is defined for the IPv6
   destination address, the slave MUST also elide the prefix of the
   destination IPv6 address.  In that case, the 6LBR/master can infer
   the elided destination prefix by using the context.

   When a master/6LBR receives an IPv6 packet sent by a remote node
   outside the BT-LE network, and the destination of the packet is a
   slave, the master/6LBR MUST elide the IPv6 destination address of the
   packet before forwarding it to the slave.  The slave can infer that
   the IPv6 destination address of the packet is its own IPv6 address.
   If a context is defined for the prefix of the IPv6 source address,
   the master/6LBR MUST elide that prefix as well.

3.2.4.  Unicast and Multicast address mapping

   The BT-LE link layer does not support multicast.  Hence traffic is
   always unicast between two BT-LE devices.  Even in the case where a
   master is attached to multiple slave BT-LE devices, the master device
   cannot do a multicast to all the connected slave devices.  If the
   master device needs to send a multicast packet to all its slave

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   devices, it has to replicate the packet and unicast it on each link.
   However, this may not be energy-efficient and particular care must be
   taken if the master is battery-powered.  In the opposite direction, a
   slave can only transmit data to a single destination (i.e. the
   master).  Hence, if a slave transmits an IPv6 multicast packet, the
   slave can unicast the corresponding BT-LE packet to the master.  It
   is required that the master MUST provide a table for mapping
   different types of multicast addresses (all-nodes, all-routers and
   solicited-node multicast addresses) to the corresponding IIDs and
   Device Addresses.

3.3.  Internet connectivity scenarios

   In a typical scenario, BT-LE network is connected to the Internet.

                        h           ____________
                         \         /            \
                   h ---- 6LBR --- |  Internet  |
                         /         \____________/
                        h
                                           h:      host
                 <-- BT-LE -->             6LBR:   6LoWPAN Border Router

             Figure 5: BT-LE network connected to the Internet

   In some scenarios, the BT-LE network may transiently or permanently
   be an isolated network.

                        h       h           h:     host
                         \     /            6LBR:  6LoWPAN Border Router
                    h --- 6LBR -- h
                         /    \
                        h      h

                     Figure 6: Isolated BT-LE network

   Host-to-master and master-to-host communication MUST use the same
   mechanisms as would be used in global IPv6 communications.  The
   gateway is used to route the packets to one of its slaves.

4.  IANA Considerations

   While there are no actions for IANA, we do expect BT SIG to allocate

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   an L2CAP channel ID (see Section 3.1).

5.  Security Considerations

   The transmission of IPv6 over BT-LE links has similar requirements
   and concerns for security as for IEEE 802.15.4.  IPv6 over BT-LE
   SHOULD be protected by using BT-LE Link Layer security.

   BT-LE Link Layer supports encryption and authentication by using the
   Counter with CBC-MAC (CCM) mechanism [RFC3610] and a 128-bit AES
   block cipher.  Upper layer security mechanisms may exploit this
   functionality when it is available.  (Note: CCM does not consume
   bytes from the maximum per-packet L2CAP data size, since the link
   layer data unit has a specific field for them when they are used.)

   Key management in BT-LE is provided by the Security Manager Protocol
   (SMP).

6.  Additional contributors

   Kanji Kerai, Jari Mutikainen, David Canfeng-Chen and Minjun Xi from
   Nokia have contributed significantly to this document.

7.  Acknowledgements

   Samita Chakrabarti and Erik Nordmark have provided valuable feedback
   for this draft.

8.  Normative References

   [BTCorev4.0]
              "Bluetooth Core Specification v4.0, http://
              www.bluetooth.org/Technical/Specifications/adopted.htm".

   [I-D.ietf-6lowpan-nd]
              Shelby, Z., Chakrabarti, S., and E. Nordmark, "Neighbor
              Discovery Optimization for Low Power and Lossy Networks
              (6LoWPAN)", draft-ietf-6lowpan-nd-18 (work in progress),
              October 2011.

   [IEEE802-2001]
              "IEEE 802-2001 standard,
              http://standards.ieee.org/findstds/standard/
              802-2001.html".

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

   [RFC2464]  Crawford, M., "Transmission of IPv6 Packets over Ethernet
              Networks", RFC 2464, December 1998.

   [RFC3610]  Whiting, D., Housley, R., and N. Ferguson, "Counter with
              CBC-MAC (CCM)", RFC 3610, September 2003.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

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

   [RFC6282]  Hui, J. and P. Thubert, "Compression Format for IPv6
              Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
              September 2011.

Appendix A.  Bluetooth Low Energy fragmentation and L2CAP Modes

   This section provides an overview of Fragmentation and Recombination
   (FAR) method and L2CAP modes in Bluetooth Low Energy.  FAR is an
   L2CAP mechanism, in which an L2CAP entity can take the (large) upper
   layer PDU, prepend the L2CAP header (4 bytes in the Basic L2CAP mode)
   and break the resulting L2CAP PDU into fragments which can then be
   directly encapsulated into Data channel PDUs.  There are bits in the
   Data channel PDUs which identify whether the payload is a complete
   L2CAP PDU or the first of a set of fragments, or one of the rest of
   the fragments.

   There are five L2CAP modes defined in the BT 4.0 spec.  These modes
   are: Retransmission Mode (a Go-Back-N mechanism is used), Enhanced
   Retransmission Mode (includes selective NAK among others), Flow
   Control Mode (PDUs are numbered, but there are no retransmissions),
   Streaming Mode (PDUs are numbered, but there are no ACKs of any kind)
   and Basic L2CAP Mode.

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Authors' Addresses

   Johanna Nieminen (editor)
   Nokia
   Itaemerenkatu 11-13
   FI-00180 Helsinki
   Finland

   Email: johanna.1.nieminen@nokia.com

   Basavaraj Patil
   Nokia
   6021 Connection drive
   Irving, TX  75039
   USA

   Email: basavaraj.patil@nokia.com

   Teemu Savolainen
   Nokia
   Hermiankatu 12 D
   FI-33720 Tampere
   Finland

   Email: teemu.savolainen@nokia.com

   Markus Isomaki
   Nokia
   Keilalahdentie 2-4
   FI-02150 Espoo
   Finland

   Email: markus.isomaki@nokia.com

   Zach Shelby
   Sensinode
   Hallituskatu 13-17D
   FI-90100 Oulu
   Finland

   Email: zach.shelby@sensinode.com

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   Carles Gomez
   Universitat Politecnica de Catalunya/i2CAT
   C/Esteve Terradas, 7
   Castelldefels  08860
   Spain

   Email: carlesgo@entel.upc.edu

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