linux/Documentation/networking/ieee802154.txt
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   1
   2                Linux IEEE 802.15.4 implementation
   3
   4
   5Introduction
   6============
   7The IEEE 802.15.4 working group focuses on standartization of bottom
   8two layers: Medium Accsess Control (MAC) and Physical (PHY). And there
   9are mainly two options available for upper layers:
  10 - ZigBee - proprietary protocol from ZigBee Alliance
  11 - 6LowPAN - IPv6 networking over low rate personal area networks
  12
  13The Linux-ZigBee project goal is to provide complete implementation
  14of IEEE 802.15.4 and 6LoWPAN protocols. IEEE 802.15.4 is a stack
  15of protocols for organizing Low-Rate Wireless Personal Area Networks.
  16
  17The stack is composed of three main parts:
  18 - IEEE 802.15.4 layer;  We have chosen to use plain Berkeley socket API,
  19   the generic Linux networking stack to transfer IEEE 802.15.4 messages
  20   and a special protocol over genetlink for configuration/management
  21 - MAC - provides access to shared channel and reliable data delivery
  22 - PHY - represents device drivers
  23
  24
  25Socket API
  26==========
  27
  28int sd = socket(PF_IEEE802154, SOCK_DGRAM, 0);
  29.....
  30
  31The address family, socket addresses etc. are defined in the
  32include/net/af_ieee802154.h header or in the special header
  33in our userspace package (see either linux-zigbee sourceforge download page
  34or git tree at git://linux-zigbee.git.sourceforge.net/gitroot/linux-zigbee).
  35
  36One can use SOCK_RAW for passing raw data towards device xmit function. YMMV.
  37
  38
  39Kernel side
  40=============
  41
  42Like with WiFi, there are several types of devices implementing IEEE 802.15.4.
  431) 'HardMAC'. The MAC layer is implemented in the device itself, the device
  44   exports MLME and data API.
  452) 'SoftMAC' or just radio. These types of devices are just radio transceivers
  46   possibly with some kinds of acceleration like automatic CRC computation and
  47   comparation, automagic ACK handling, address matching, etc.
  48
  49Those types of devices require different approach to be hooked into Linux kernel.
  50
  51
  52MLME - MAC Level Management
  53============================
  54
  55Most of IEEE 802.15.4 MLME interfaces are directly mapped on netlink commands.
  56See the include/net/nl802154.h header. Our userspace tools package
  57(see above) provides CLI configuration utility for radio interfaces and simple
  58coordinator for IEEE 802.15.4 networks as an example users of MLME protocol.
  59
  60
  61HardMAC
  62=======
  63
  64See the header include/net/ieee802154_netdev.h. You have to implement Linux
  65net_device, with .type = ARPHRD_IEEE802154. Data is exchanged with socket family
  66code via plain sk_buffs. On skb reception skb->cb must contain additional
  67info as described in the struct ieee802154_mac_cb. During packet transmission
  68the skb->cb is used to provide additional data to device's header_ops->create
  69function. Be aware, that this data can be overriden later (when socket code
  70submits skb to qdisc), so if you need something from that cb later, you should
  71store info in the skb->data on your own.
  72
  73To hook the MLME interface you have to populate the ml_priv field of your
  74net_device with a pointer to struct ieee802154_mlme_ops instance. All fields are
  75required.
  76
  77We provide an example of simple HardMAC driver at drivers/ieee802154/fakehard.c
  78
  79
  80SoftMAC
  81=======
  82
  83The MAC is the middle layer in the IEEE 802.15.4 Linux stack. This moment it
  84provides interface for drivers registration and management of slave interfaces.
  85
  86NOTE: Currently the only monitor device type is supported - it's IEEE 802.15.4
  87stack interface for network sniffers (e.g. WireShark).
  88
  89This layer is going to be extended soon.
  90
  91See header include/net/mac802154.h and several drivers in drivers/ieee802154/.
  92
  93
  94Device drivers API
  95==================
  96
  97The include/net/mac802154.h defines following functions:
  98 - struct ieee802154_dev *ieee802154_alloc_device
  99   (size_t priv_size, struct ieee802154_ops *ops):
 100   allocation of IEEE 802.15.4 compatible device
 101
 102 - void ieee802154_free_device(struct ieee802154_dev *dev):
 103   freeing allocated device
 104
 105 - int ieee802154_register_device(struct ieee802154_dev *dev):
 106   register PHY in the system
 107
 108 - void ieee802154_unregister_device(struct ieee802154_dev *dev):
 109   freeing registered PHY
 110
 111Moreover IEEE 802.15.4 device operations structure should be filled.
 112
 113Fake drivers
 114============
 115
 116In addition there are two drivers available which simulate real devices with
 117HardMAC (fakehard) and SoftMAC (fakelb - IEEE 802.15.4 loopback driver)
 118interfaces. This option provides possibility to test and debug stack without
 119usage of real hardware.
 120
 121See sources in drivers/ieee802154 folder for more details.
 122
 123
 1246LoWPAN Linux implementation
 125============================
 126
 127The IEEE 802.15.4 standard specifies an MTU of 128 bytes, yielding about 80
 128octets of actual MAC payload once security is turned on, on a wireless link
 129with a link throughput of 250 kbps or less.  The 6LoWPAN adaptation format
 130[RFC4944] was specified to carry IPv6 datagrams over such constrained links,
 131taking into account limited bandwidth, memory, or energy resources that are
 132expected in applications such as wireless Sensor Networks.  [RFC4944] defines
 133a Mesh Addressing header to support sub-IP forwarding, a Fragmentation header
 134to support the IPv6 minimum MTU requirement [RFC2460], and stateless header
 135compression for IPv6 datagrams (LOWPAN_HC1 and LOWPAN_HC2) to reduce the
 136relatively large IPv6 and UDP headers down to (in the best case) several bytes.
 137
 138In Semptember 2011 the standard update was published - [RFC6282].
 139It deprecates HC1 and HC2 compression and defines IPHC encoding format which is
 140used in this Linux implementation.
 141
 142All the code related to 6lowpan you may find in files: net/ieee802154/6lowpan.*
 143
 144To setup 6lowpan interface you need (busybox release > 1.17.0):
 1451. Add IEEE802.15.4 interface and initialize PANid;
 1462. Add 6lowpan interface by command like:
 147   # ip link add link wpan0 name lowpan0 type lowpan
 1483. Set MAC (if needs):
 149   # ip link set lowpan0 address de:ad:be:ef:ca:fe:ba:be
 1504. Bring up 'lowpan0' interface
 151
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