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Based on kernel version 3.9. Page generated on 2013-05-02 23:11 EST.

1	
2			Linux IEEE 802.15.4 implementation
3	
4	
5	Introduction
6	============
7	The IEEE 802.15.4 working group focuses on standartization of bottom
8	two layers: Medium Accsess Control (MAC) and Physical (PHY). And there
9	are 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	
13	The Linux-ZigBee project goal is to provide complete implementation
14	of IEEE 802.15.4 and 6LoWPAN protocols. IEEE 802.15.4 is a stack
15	of protocols for organizing Low-Rate Wireless Personal Area Networks.
16	
17	The 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	
25	Socket API
26	==========
27	
28	int sd = socket(PF_IEEE802154, SOCK_DGRAM, 0);
29	.....
30	
31	The address family, socket addresses etc. are defined in the
32	include/net/af_ieee802154.h header or in the special header
33	in our userspace package (see either linux-zigbee sourceforge download page
34	or git tree at git://linux-zigbee.git.sourceforge.net/gitroot/linux-zigbee).
35	
36	One can use SOCK_RAW for passing raw data towards device xmit function. YMMV.
37	
38	
39	Kernel side
40	=============
41	
42	Like with WiFi, there are several types of devices implementing IEEE 802.15.4.
43	1) 'HardMAC'. The MAC layer is implemented in the device itself, the device
44	   exports MLME and data API.
45	2) '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	
49	Those types of devices require different approach to be hooked into Linux kernel.
50	
51	
52	MLME - MAC Level Management
53	============================
54	
55	Most of IEEE 802.15.4 MLME interfaces are directly mapped on netlink commands.
56	See the include/net/nl802154.h header. Our userspace tools package
57	(see above) provides CLI configuration utility for radio interfaces and simple
58	coordinator for IEEE 802.15.4 networks as an example users of MLME protocol.
59	
60	
61	HardMAC
62	=======
63	
64	See the header include/net/ieee802154_netdev.h. You have to implement Linux
65	net_device, with .type = ARPHRD_IEEE802154. Data is exchanged with socket family
66	code via plain sk_buffs. On skb reception skb->cb must contain additional
67	info as described in the struct ieee802154_mac_cb. During packet transmission
68	the skb->cb is used to provide additional data to device's header_ops->create
69	function. Be aware, that this data can be overriden later (when socket code
70	submits skb to qdisc), so if you need something from that cb later, you should
71	store info in the skb->data on your own.
72	
73	To hook the MLME interface you have to populate the ml_priv field of your
74	net_device with a pointer to struct ieee802154_mlme_ops instance. All fields are
75	required.
76	
77	We provide an example of simple HardMAC driver at drivers/ieee802154/fakehard.c
78	
79	
80	SoftMAC
81	=======
82	
83	The MAC is the middle layer in the IEEE 802.15.4 Linux stack. This moment it
84	provides interface for drivers registration and management of slave interfaces.
85	
86	NOTE: Currently the only monitor device type is supported - it's IEEE 802.15.4
87	stack interface for network sniffers (e.g. WireShark).
88	
89	This layer is going to be extended soon.
90	
91	See header include/net/mac802154.h and several drivers in drivers/ieee802154/.
92	
93	
94	Device drivers API
95	==================
96	
97	The 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	
111	Moreover IEEE 802.15.4 device operations structure should be filled.
112	
113	Fake drivers
114	============
115	
116	In addition there are two drivers available which simulate real devices with
117	HardMAC (fakehard) and SoftMAC (fakelb - IEEE 802.15.4 loopback driver)
118	interfaces. This option provides possibility to test and debug stack without
119	usage of real hardware.
120	
121	See sources in drivers/ieee802154 folder for more details.
122	
123	
124	6LoWPAN Linux implementation
125	============================
126	
127	The IEEE 802.15.4 standard specifies an MTU of 128 bytes, yielding about 80
128	octets of actual MAC payload once security is turned on, on a wireless link
129	with a link throughput of 250 kbps or less.  The 6LoWPAN adaptation format
130	[RFC4944] was specified to carry IPv6 datagrams over such constrained links,
131	taking into account limited bandwidth, memory, or energy resources that are
132	expected in applications such as wireless Sensor Networks.  [RFC4944] defines
133	a Mesh Addressing header to support sub-IP forwarding, a Fragmentation header
134	to support the IPv6 minimum MTU requirement [RFC2460], and stateless header
135	compression for IPv6 datagrams (LOWPAN_HC1 and LOWPAN_HC2) to reduce the
136	relatively large IPv6 and UDP headers down to (in the best case) several bytes.
137	
138	In Semptember 2011 the standard update was published - [RFC6282].
139	It deprecates HC1 and HC2 compression and defines IPHC encoding format which is
140	used in this Linux implementation.
141	
142	All the code related to 6lowpan you may find in files: net/ieee802154/6lowpan.*
143	
144	To setup 6lowpan interface you need (busybox release > 1.17.0):
145	1. Add IEEE802.15.4 interface and initialize PANid;
146	2. Add 6lowpan interface by command like:
147	   # ip link add link wpan0 name lowpan0 type lowpan
148	3. Set MAC (if needs):
149	   # ip link set lowpan0 address de:ad:be:ef:ca:fe:ba:be
150	4. Bring up 'lowpan0' interface
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