6LoWPAN Working Group J. Nieminen, Ed.
Internet-Draft B. Patil
Intended status: Standards Track T. Savolainen
Expires: February 27, 2012 M. Isomaki
Nokia
Z. Shelby
Sensinode
C. Gomez
Universitat Politecnica de
Catalunya/i2CAT
August 26, 2011
Transmission of IPv6 Packets over Bluetooth Low Energy
draft-ietf-6lowpan-btle-02
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
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."
This Internet-Draft will expire on February 27, 2012.
Copyright Notice
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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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Bluetooth Low Energy . . . . . . . . . . . . . . . . . . . . . 4
2.1. Protocol stack . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Link layer roles and topology . . . . . . . . . . . . . . 5
2.3. LE device addressing . . . . . . . . . . . . . . . . . . . 5
2.4. 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. IPv6 Address configuration . . . . . . . . . . . . . . 7
3.2.2. Header compression . . . . . . . . . . . . . . . . . . 8
3.2.3. Unicast and Multicast address mapping . . . . . . . . 9
3.3. Internet connectivity scenarios . . . . . . . . . . . . . 9
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. Additional contributors . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
8. Normative References . . . . . . . . . . . . . . . . . . . . . 10
Appendix A. Bluetooth Low Energy basics . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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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 the Internet of Things
applications, such as health monitors, environmental sensing,
proximity applications and many others.
Considering the expected explosion 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.
1.1. Requirements Language
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].
1.2. Terminology
Bluetooth Low Energy
Bluetooth Low Energy is a low power air interface technology
specified by the Bluetooth Special Interest Group (SIG). BT-LE is
specified in Revision 4.0 of the Bluetooth specifications (BT
4.0).
Gateway
Network element connecting the BT-LE sensors to the Internet. Can
be e.g a home gateway or a mobile device.
6LR and 6LBR
These terms correspond to those defined in [I-D.ietf-6lowpan-nd]
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2. Bluetooth Low Energy
BT-LE is designed for transferring small amounts of data (in most
cases less than 10 bytes) infrequently (e.g. every 500 ms) at modest
data rates (e.g. 300 kbps) at a very low cost per bit.
BT-LE is an integral part of the BT 4.0 specification. Devices such
as mobile phones, notebooks, tablets and other handheld computing
devices which will include BT 4.0 chipsets in the near future will
have the low-energy functionality of Bluetooth. BT-LE will also be
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.
2.1. Protocol 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 Access Profile |
+----------------------------------------+
| Generic Attribute Profile |
+----------------------------------------+
| Attribute Protocol |Security Manager |
+--------------------+-------------------+
| Logical Link Control and Adaptation |
+--------------------+-------------------+
| Host Controller Interface |
+--------------------+-------------------+
| Link Layer | Direct Test Mode |
+--------------------+-------------------+
| Physical Layer |
+--------------------+-------------------+
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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.
[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. LE device addressing
Every LE device is identified by a unique 48 bit Bluetooth Device
Address (BD_ADDR). An LE-only device such as a sensor may use a
public (obtained from IEEE Registration Authority) or a random device
address (generated internally). When LE devices are in a connection
they are addressed by an Access Address, a 32 bit address generated
at the time of the connection set up. The access address identifies
a connection between a slave and a master.
2.4. LE packets sizes and MTU
Maximum size of the payload in an LE packet at the baseband is 31
bytes which means that at the L2CAP layer this equals to 23 octets
MTU. For power efficient communication between a sensor and a client
the sensor data and its header should fit in 23 octet payload. MTU
longer than 23 octets can be supported by the LE specification.
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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 [I-D.ietf-6lowpan-hc] 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 the 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. On the other
hand, a BT-LE device MUST NOT play the role of a 6LoWPAN Router
(6LR).
When BT-LE is applied in sensors, generated data may fit into one
Link Layer packet (23 bytes, maximum L2CAP payload size) that is
transferred to the collector device periodically. However, IP data
packets may be much larger and hence MTU size should be the size of
the IP data packet. Segmentation and reassembly (SAR) functionality
is an inherent function of the BT-LE link layer. Larger L2CAP
packets can be transferred with the assistance of the SAR
functionality provided by the link layer. This specification
requires that SAR functionality MUST be provided in the link layer up
to the IPv6 minimum MTU of 1280 bytes. Since SAR functionality in
BT-LE is a function of the link layer, fragmentation functionality as
defined in [RFC4944] SHOULD NOT be used in BT-LE neworks.
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. This specification defines the use of channel ID 0x07 for
this purpose. Figure 3 illustrates IPv6 over BT-LE stack.
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+-------------------+
| UDP/TCP |
+-------------------+
| IPv6 over 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 relation 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 SAR functionality.
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. IPv6 Address configuration
The Interface Identifier (IID) for a BT-LE interface MUST be formed
from the 48-bit public device Bluetooth address as per the "IPv6 over
Ethernet" specification [RFC2464]. An IPv6 prefix used for stateless
autoconfiguration [RFC4862] of a BT-LE interface MUST have a length
of 64 bits.
The IPv6 link-local address [RFC4291] for a BT-LE interface is formed
by appending the IID, as defined above, to the prefix FE80::/64, as
depicted in Figure 4.
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10 bits 54 bits 64 bits
+----------+-----------------+----------------------+
|1111111010| zeros | Interface Identifier |
+----------+-----------------+----------------------+
Figure 4: IPv6 link-local address in BT-LE
3.2.2. Header compression
This document assumes [I-D.ietf-6lowpan-hc], 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. However, whereas
IEEE 802.15.4 frames contain source and destination MAC layer
addresses, BT-LE data channel PDUs contain the Access Address, which
identifies the connection between a master and a slave. 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 can be elided. In fact, the node that receives a data
channel PDU through a Link Layer connection MAY infer that the IPv6
destination address of the packet is its own IPv6 address. If a node
knows the IID of the other endpoint of the Link Layer connection, the
IPv6 source address MAY also be elided. A device MAY learn the IID
of the other endpoint of a Link Layer connection e.g. from the RS/RA/
NS/NA Neighbor Discovery (ND) message exchange. The device MAY
maintain a Neighbor Cache, in which the entries include both the IID
of the neighbor and the Access Address that identifies the Link Layer
connection with the neighbor. A device MAY also derive the IID of
the other endpoint of a Link Layer connection from the Link Layer
connection establishment messages. The device MAY maintain a
Neighbor Cache, in which the entries include both the IID of the
neighbor and the Access Address that identifies the Link Layer
connection with the neighbor.
When a BT-LE slave transmits an IPv6 packet to a remote destination
using global IPv6 addresses, the slave MAY elide the IPv6 source
address. This is possible 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 Access Address of each Link Layer
connection and the IID of the corresponding slave. The slave MAY
also elide the prefix of the destination IPv6 address if a context is
defined for the IPv6 destination address.
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
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slave, the master/6LBR MAY elide the IID of the IPv6 destination
address by exploiting the information contained in the table
mentioned above. The prefixes of the IPv6 destination and source
addresses MAY also be elided if a context is defined for them.
3.2.3. Unicast and Multicast address mapping
In BT-LE, address resolution should be used for finding the Access
Address of the Link Layer connection with the target node. 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 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. There should
be a table for mapping different types of multicast addresses to the
access address in the master.
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
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Figure 6: Isolated BT-LE network
4. IANA Considerations
While there are no actions for IANA, we do expect BT SIG to allocate
an L2CAP channel ID.
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
Erik Nordmark has provided valuable feedback for this draft.
8. Normative References
[I-D.ietf-6lowpan-hc]
Hui, J. and P. Thubert, "Compression Format for IPv6
Datagrams in Low Power and Lossy Networks (6LoWPAN)",
draft-ietf-6lowpan-hc-15 (work in progress),
February 2011.
[I-D.ietf-6lowpan-nd]
Shelby, Z., Chakrabarti, S., and E. Nordmark, "Neighbor
Discovery Optimization for Low Power and Lossy Networks
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(6LoWPAN)", draft-ietf-6lowpan-nd-17 (work in progress),
June 2011.
[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.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[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.
[RFC4994] Zeng, S., Volz, B., Kinnear, K., and J. Brzozowski,
"DHCPv6 Relay Agent Echo Request Option", RFC 4994,
September 2007.
Appendix A. Bluetooth Low Energy basics
This section will provide background material on the basics of
bluetooth low energy.
Authors' Addresses
Johanna Nieminen (editor)
Nokia
Itaemerenkatu 11-13
FI-00180 Helsinki
Finland
Email: johanna.1.nieminen@nokia.com
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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
Carles Gomez
Universitat Politecnica de Catalunya/i2CAT
C/Esteve Terradas, 7
Castelldefels 08860
Spain
Email: carlesgo@entel.upc.edu
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