Linux IEEE 802.15.4 implementation


Introduction
============

The Linux-ZigBee project goal is to provide complete implementation
of IEEE 802.15.4 / ZigBee / 6LoWPAN protocols. IEEE 802.15.4 is a stack
of protocols for organizing Low-Rate Wireless Personal Area Networks.

Currently only IEEE 802.15.4 layer is implemented. We have chosen
to use plain Berkeley socket API, the generic Linux networking stack
to transfer IEEE 802.15.4 messages and a special protocol over genetlink
for configuration/management


Socket API
==========

int sd = socket(PF_IEEE802154, SOCK_DGRAM, 0);
.....

The address family, socket addresses etc. are defined in the
include/net/af_ieee802154.h header or in the special header
in our userspace package (see either linux-zigbee sourceforge download page
or git tree at git://linux-zigbee.git.sourceforge.net/gitroot/linux-zigbee).

One can use SOCK_RAW for passing raw data towards device xmit function. YMMV.


MLME - MAC Level Management
============================

Most of IEEE 802.15.4 MLME interfaces are directly mapped on netlink commands.
See the include/net/nl802154.h header. Our userspace tools package
(see above) provides CLI configuration utility for radio interfaces and simple
coordinator for IEEE 802.15.4 networks as an example users of MLME protocol.


Kernel side
=============

Like with WiFi, there are several types of devices implementing IEEE 802.15.4.
1) 'HardMAC'. The MAC layer is implemented in the device itself, the device
   exports MLME and data API.
2) 'SoftMAC' or just radio. These types of devices are just radio transceivers
   possibly with some kinds of acceleration like automatic CRC computation and
   comparation, automagic ACK handling, address matching, etc.

Those types of devices require different approach to be hooked into Linux kernel.


HardMAC
=======

See the header include/net/ieee802154_netdev.h. You have to implement Linux
net_device, with .type = ARPHRD_IEEE802154. Data is exchanged with socket family
code via plain sk_buffs. On skb reception skb->cb must contain additional
info as described in the struct ieee802154_mac_cb. During packet transmission
the skb->cb is used to provide additional data to device's header_ops->create
function. Be aware, that this data can be overriden later (when socket code
submits skb to qdisc), so if you need something from that cb later, you should
store info in the skb->data on your own.

To hook the MLME interface you have to populate the ml_priv field of your
net_device with a pointer to struct ieee802154_mlme_ops instance. All fields are
required.

We provide an example of simple HardMAC driver at drivers/ieee802154/fakehard.c


SoftMAC
=======

We are going to provide intermediate layer implementing IEEE 802.15.4 MAC
in software. This is currently WIP.

See header include/net/mac802154.h and several drivers in drivers/ieee802154/.

6LoWPAN Linux implementation
============================

The IEEE 802.15.4 standard specifies an MTU of 128 bytes, yielding about 80
octets of actual MAC payload once security is turned on, on a wireless link
with a link throughput of 250 kbps or less.  The 6LoWPAN adaptation format
[RFC4944] was specified to carry IPv6 datagrams over such constrained links,
taking into account limited bandwidth, memory, or energy resources that are
expected in applications such as wireless Sensor Networks.  [RFC4944] defines
a Mesh Addressing header to support sub-IP forwarding, a Fragmentation header
to support the IPv6 minimum MTU requirement [RFC2460], and stateless header
compression for IPv6 datagrams (LOWPAN_HC1 and LOWPAN_HC2) to reduce the
relatively large IPv6 and UDP headers down to (in the best case) several bytes.

In Semptember 2011 the standard update was published - [RFC6282].
It deprecates HC1 and HC2 compression and defines IPHC encoding format which is
used in this Linux implementation.

All the code related to 6lowpan you may find in files: net/ieee802154/6lowpan.*

To setup 6lowpan interface you need (busybox release > 1.17.0):
1. Add IEEE802.15.4 interface and initialize PANid;
2. Add 6lowpan interface by command like:
   # ip link add link wpan0 name lowpan0 type lowpan
3. Set MAC (if needs):
   # ip link set lowpan0 address de:ad:be:ef:ca:fe:ba:be
4. Bring up 'lowpan0' interface