About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / networking / ieee802154.txt




Custom Search

Based on kernel version 4.3. Page generated on 2015-11-02 12:50 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 bottom
8	two layers: Medium Access 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 the userspace package (see either http://wpan.cakelab.org/ or the
34	git tree at https://github.com/linux-wpan/wpan-tools).
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	HardMAC
53	=======
54	
55	See the header include/net/ieee802154_netdev.h. You have to implement Linux
56	net_device, with .type = ARPHRD_IEEE802154. Data is exchanged with socket family
57	code via plain sk_buffs. On skb reception skb->cb must contain additional
58	info as described in the struct ieee802154_mac_cb. During packet transmission
59	the skb->cb is used to provide additional data to device's header_ops->create
60	function. Be aware that this data can be overridden later (when socket code
61	submits skb to qdisc), so if you need something from that cb later, you should
62	store info in the skb->data on your own.
63	
64	To hook the MLME interface you have to populate the ml_priv field of your
65	net_device with a pointer to struct ieee802154_mlme_ops instance. The fields
66	assoc_req, assoc_resp, disassoc_req, start_req, and scan_req are optional.
67	All other fields are required.
68	
69	
70	SoftMAC
71	=======
72	
73	The MAC is the middle layer in the IEEE 802.15.4 Linux stack. This moment it
74	provides interface for drivers registration and management of slave interfaces.
75	
76	NOTE: Currently the only monitor device type is supported - it's IEEE 802.15.4
77	stack interface for network sniffers (e.g. WireShark).
78	
79	This layer is going to be extended soon.
80	
81	See header include/net/mac802154.h and several drivers in
82	drivers/net/ieee802154/.
83	
84	
85	Device drivers API
86	==================
87	
88	The include/net/mac802154.h defines following functions:
89	 - struct ieee802154_dev *ieee802154_alloc_device
90	   (size_t priv_size, struct ieee802154_ops *ops):
91	   allocation of IEEE 802.15.4 compatible device
92	
93	 - void ieee802154_free_device(struct ieee802154_dev *dev):
94	   freeing allocated device
95	
96	 - int ieee802154_register_device(struct ieee802154_dev *dev):
97	   register PHY in the system
98	
99	 - void ieee802154_unregister_device(struct ieee802154_dev *dev):
100	   freeing registered PHY
101	
102	Moreover IEEE 802.15.4 device operations structure should be filled.
103	
104	Fake drivers
105	============
106	
107	In addition there is a driver available which simulates a real device with
108	SoftMAC (fakelb - IEEE 802.15.4 loopback driver) interface. This option
109	provides possibility to test and debug stack without usage of real hardware.
110	
111	See sources in drivers/net/ieee802154 folder for more details.
112	
113	
114	6LoWPAN Linux implementation
115	============================
116	
117	The IEEE 802.15.4 standard specifies an MTU of 127 bytes, yielding about 80
118	octets of actual MAC payload once security is turned on, on a wireless link
119	with a link throughput of 250 kbps or less.  The 6LoWPAN adaptation format
120	[RFC4944] was specified to carry IPv6 datagrams over such constrained links,
121	taking into account limited bandwidth, memory, or energy resources that are
122	expected in applications such as wireless Sensor Networks.  [RFC4944] defines
123	a Mesh Addressing header to support sub-IP forwarding, a Fragmentation header
124	to support the IPv6 minimum MTU requirement [RFC2460], and stateless header
125	compression for IPv6 datagrams (LOWPAN_HC1 and LOWPAN_HC2) to reduce the
126	relatively large IPv6 and UDP headers down to (in the best case) several bytes.
127	
128	In Semptember 2011 the standard update was published - [RFC6282].
129	It deprecates HC1 and HC2 compression and defines IPHC encoding format which is
130	used in this Linux implementation.
131	
132	All the code related to 6lowpan you may find in files: net/6lowpan/*
133	and net/ieee802154/6lowpan/*
134	
135	To setup 6lowpan interface you need (busybox release > 1.17.0):
136	1. Add IEEE802.15.4 interface and initialize PANid;
137	2. Add 6lowpan interface by command like:
138	   # ip link add link wpan0 name lowpan0 type lowpan
139	3. Set MAC (if needs):
140	   # ip link set lowpan0 address de:ad:be:ef:ca:fe:ba:be
141	4. Bring up 'lowpan0' interface
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.