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Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.

1	
2			Linux IEEE 802.15.4 implementation
3	
4	
5	Introduction
6	============
7	The IEEE 802.15.4 working group focuses on standardization of the bottom
8	two layers: Medium Access Control (MAC) and Physical access (PHY). And there
9	are mainly two options available for upper layers:
10	 - ZigBee - proprietary protocol from the ZigBee Alliance
11	 - 6LoWPAN - IPv6 networking over low rate personal area networks
12	
13	The goal of the Linux-wpan is to provide a complete implementation
14	of the 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 data
20	   messages and a special protocol over netlink 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 the userspace package (see either http://wpan.cakelab.org/ or the
34	git tree at https://github.com/linux-wpan/wpan-tools).
35	
36	
37	Kernel side
38	=============
39	
40	Like with WiFi, there are several types of devices implementing IEEE 802.15.4.
41	1) 'HardMAC'. The MAC layer is implemented in the device itself, the device
42	   exports a management (e.g. MLME) and data API.
43	2) 'SoftMAC' or just radio. These types of devices are just radio transceivers
44	   possibly with some kinds of acceleration like automatic CRC computation and
45	   comparation, automagic ACK handling, address matching, etc.
46	
47	Those types of devices require different approach to be hooked into Linux kernel.
48	
49	
50	HardMAC
51	=======
52	
53	See the header include/net/ieee802154_netdev.h. You have to implement Linux
54	net_device, with .type = ARPHRD_IEEE802154. Data is exchanged with socket family
55	code via plain sk_buffs. On skb reception skb->cb must contain additional
56	info as described in the struct ieee802154_mac_cb. During packet transmission
57	the skb->cb is used to provide additional data to device's header_ops->create
58	function. Be aware that this data can be overridden later (when socket code
59	submits skb to qdisc), so if you need something from that cb later, you should
60	store info in the skb->data on your own.
61	
62	To hook the MLME interface you have to populate the ml_priv field of your
63	net_device with a pointer to struct ieee802154_mlme_ops instance. The fields
64	assoc_req, assoc_resp, disassoc_req, start_req, and scan_req are optional.
65	All other fields are required.
66	
67	
68	SoftMAC
69	=======
70	
71	The MAC is the middle layer in the IEEE 802.15.4 Linux stack. This moment it
72	provides interface for drivers registration and management of slave interfaces.
73	
74	NOTE: Currently the only monitor device type is supported - it's IEEE 802.15.4
75	stack interface for network sniffers (e.g. WireShark).
76	
77	This layer is going to be extended soon.
78	
79	See header include/net/mac802154.h and several drivers in
80	drivers/net/ieee802154/.
81	
82	
83	Device drivers API
84	==================
85	
86	The include/net/mac802154.h defines following functions:
87	 - struct ieee802154_hw *
88	   ieee802154_alloc_hw(size_t priv_data_len, const struct ieee802154_ops *ops):
89	   allocation of IEEE 802.15.4 compatible hardware device
90	
91	 - void ieee802154_free_hw(struct ieee802154_hw *hw):
92	   freeing allocated hardware device
93	
94	 - int ieee802154_register_hw(struct ieee802154_hw *hw):
95	   register PHY which is the allocated hardware device, in the system
96	
97	 - void ieee802154_unregister_hw(struct ieee802154_hw *hw):
98	   freeing registered PHY
99	
100	 - void ieee802154_rx_irqsafe(struct ieee802154_hw *hw, struct sk_buff *skb,
101	                              u8 lqi):
102	   telling 802.15.4 module there is a new received frame in the skb with
103	   the RF Link Quality Indicator (LQI) from the hardware device
104	
105	 - void ieee802154_xmit_complete(struct ieee802154_hw *hw, struct sk_buff *skb,
106	                                 bool ifs_handling):
107	   telling 802.15.4 module the frame in the skb is or going to be
108	   transmitted through the hardware device
109	
110	The device driver must implement the following callbacks in the IEEE 802.15.4
111	operations structure at least:
112	struct ieee802154_ops {
113		...
114		int	(*start)(struct ieee802154_hw *hw);
115		void	(*stop)(struct ieee802154_hw *hw);
116		...
117		int	(*xmit_async)(struct ieee802154_hw *hw, struct sk_buff *skb);
118		int	(*ed)(struct ieee802154_hw *hw, u8 *level);
119		int	(*set_channel)(struct ieee802154_hw *hw, u8 page, u8 channel);
120		...
121	};
122	
123	 - int start(struct ieee802154_hw *hw):
124	   handler that 802.15.4 module calls for the hardware device initialization.
125	
126	 - void stop(struct ieee802154_hw *hw):
127	   handler that 802.15.4 module calls for the hardware device cleanup.
128	
129	 - int xmit_async(struct ieee802154_hw *hw, struct sk_buff *skb):
130	   handler that 802.15.4 module calls for each frame in the skb going to be
131	   transmitted through the hardware device.
132	
133	 - int ed(struct ieee802154_hw *hw, u8 *level):
134	   handler that 802.15.4 module calls for Energy Detection from the hardware
135	   device.
136	
137	 - int set_channel(struct ieee802154_hw *hw, u8 page, u8 channel):
138	   set radio for listening on specific channel of the hardware device.
139	
140	Moreover IEEE 802.15.4 device operations structure should be filled.
141	
142	Fake drivers
143	============
144	
145	In addition there is a driver available which simulates a real device with
146	SoftMAC (fakelb - IEEE 802.15.4 loopback driver) interface. This option
147	provides a possibility to test and debug the stack without usage of real hardware.
148	
149	See sources in drivers/net/ieee802154 folder for more details.
150	
151	
152	6LoWPAN Linux implementation
153	============================
154	
155	The IEEE 802.15.4 standard specifies an MTU of 127 bytes, yielding about 80
156	octets of actual MAC payload once security is turned on, on a wireless link
157	with a link throughput of 250 kbps or less.  The 6LoWPAN adaptation format
158	[RFC4944] was specified to carry IPv6 datagrams over such constrained links,
159	taking into account limited bandwidth, memory, or energy resources that are
160	expected in applications such as wireless Sensor Networks.  [RFC4944] defines
161	a Mesh Addressing header to support sub-IP forwarding, a Fragmentation header
162	to support the IPv6 minimum MTU requirement [RFC2460], and stateless header
163	compression for IPv6 datagrams (LOWPAN_HC1 and LOWPAN_HC2) to reduce the
164	relatively large IPv6 and UDP headers down to (in the best case) several bytes.
165	
166	In September 2011 the standard update was published - [RFC6282].
167	It deprecates HC1 and HC2 compression and defines IPHC encoding format which is
168	used in this Linux implementation.
169	
170	All the code related to 6lowpan you may find in files: net/6lowpan/*
171	and net/ieee802154/6lowpan/*
172	
173	To setup a 6LoWPAN interface you need:
174	1. Add IEEE802.15.4 interface and set channel and PAN ID;
175	2. Add 6lowpan interface by command like:
176	   # ip link add link wpan0 name lowpan0 type lowpan
177	3. Bring up 'lowpan0' interface
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