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02cf2286 SL |
1 | |
2 | Linux IEEE 802.15.4 implementation | |
3 | ||
4 | ||
5 | Introduction | |
6 | ============ | |
6bf0d84d SS |
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 | |
dd456d45 | 9 | are mainly two options available for upper layers: |
29cd5ddc SS |
10 | - ZigBee - proprietary protocol from the ZigBee Alliance |
11 | - 6LoWPAN - IPv6 networking over low rate personal area networks | |
02cf2286 | 12 | |
6bf0d84d | 13 | The goal of the Linux-wpan is to provide a complete implementation |
29cd5ddc | 14 | of the IEEE 802.15.4 and 6LoWPAN protocols. IEEE 802.15.4 is a stack |
02cf2286 SL |
15 | of protocols for organizing Low-Rate Wireless Personal Area Networks. |
16 | ||
dd456d45 | 17 | The stack is composed of three main parts: |
18 | - IEEE 802.15.4 layer; We have chosen to use plain Berkeley socket API, | |
6bf0d84d SS |
19 | the generic Linux networking stack to transfer IEEE 802.15.4 data |
20 | messages and a special protocol over netlink for configuration/management | |
dd456d45 | 21 | - MAC - provides access to shared channel and reliable data delivery |
22 | - PHY - represents device drivers | |
02cf2286 SL |
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 | |
48a2f112 | 32 | include/net/af_ieee802154.h header or in the special header |
b251d4de LB |
33 | in the userspace package (see either http://wpan.cakelab.org/ or the |
34 | git tree at https://github.com/linux-wpan/wpan-tools). | |
02cf2286 | 35 | |
02cf2286 | 36 | |
02cf2286 SL |
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 | |
6bf0d84d | 42 | exports a management (e.g. MLME) and data API. |
02cf2286 SL |
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 | ||
48a2f112 | 53 | See the header include/net/ieee802154_netdev.h. You have to implement Linux |
02cf2286 | 54 | net_device, with .type = ARPHRD_IEEE802154. Data is exchanged with socket family |
a0aea577 DES |
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 | |
c17cb8b5 | 58 | function. Be aware that this data can be overridden later (when socket code |
a0aea577 DES |
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. | |
02cf2286 SL |
61 | |
62 | To hook the MLME interface you have to populate the ml_priv field of your | |
56aa091d WA |
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. | |
02cf2286 | 66 | |
02cf2286 SL |
67 | |
68 | SoftMAC | |
69 | ======= | |
70 | ||
dd456d45 | 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. | |
02cf2286 | 78 | |
b251d4de LB |
79 | See header include/net/mac802154.h and several drivers in |
80 | drivers/net/ieee802154/. | |
a0aea577 | 81 | |
dd456d45 | 82 | |
83 | Device drivers API | |
84 | ================== | |
85 | ||
86 | The include/net/mac802154.h defines following functions: | |
87 | - struct ieee802154_dev *ieee802154_alloc_device | |
88 | (size_t priv_size, struct ieee802154_ops *ops): | |
89 | allocation of IEEE 802.15.4 compatible device | |
90 | ||
91 | - void ieee802154_free_device(struct ieee802154_dev *dev): | |
92 | freeing allocated device | |
93 | ||
94 | - int ieee802154_register_device(struct ieee802154_dev *dev): | |
95 | register PHY in the system | |
96 | ||
97 | - void ieee802154_unregister_device(struct ieee802154_dev *dev): | |
98 | freeing registered PHY | |
99 | ||
100 | Moreover IEEE 802.15.4 device operations structure should be filled. | |
101 | ||
102 | Fake drivers | |
103 | ============ | |
104 | ||
b251d4de LB |
105 | In addition there is a driver available which simulates a real device with |
106 | SoftMAC (fakelb - IEEE 802.15.4 loopback driver) interface. This option | |
6bf0d84d | 107 | provides a possibility to test and debug the stack without usage of real hardware. |
dd456d45 | 108 | |
b251d4de | 109 | See sources in drivers/net/ieee802154 folder for more details. |
dd456d45 | 110 | |
111 | ||
63ce40e4 | 112 | 6LoWPAN Linux implementation |
113 | ============================ | |
114 | ||
b251d4de | 115 | The IEEE 802.15.4 standard specifies an MTU of 127 bytes, yielding about 80 |
63ce40e4 | 116 | octets of actual MAC payload once security is turned on, on a wireless link |
117 | with a link throughput of 250 kbps or less. The 6LoWPAN adaptation format | |
118 | [RFC4944] was specified to carry IPv6 datagrams over such constrained links, | |
119 | taking into account limited bandwidth, memory, or energy resources that are | |
120 | expected in applications such as wireless Sensor Networks. [RFC4944] defines | |
121 | a Mesh Addressing header to support sub-IP forwarding, a Fragmentation header | |
122 | to support the IPv6 minimum MTU requirement [RFC2460], and stateless header | |
123 | compression for IPv6 datagrams (LOWPAN_HC1 and LOWPAN_HC2) to reduce the | |
124 | relatively large IPv6 and UDP headers down to (in the best case) several bytes. | |
125 | ||
6bf0d84d | 126 | In September 2011 the standard update was published - [RFC6282]. |
63ce40e4 | 127 | It deprecates HC1 and HC2 compression and defines IPHC encoding format which is |
128 | used in this Linux implementation. | |
129 | ||
b251d4de LB |
130 | All the code related to 6lowpan you may find in files: net/6lowpan/* |
131 | and net/ieee802154/6lowpan/* | |
63ce40e4 | 132 | |
6bf0d84d SS |
133 | To setup a 6LoWPAN interface you need: |
134 | 1. Add IEEE802.15.4 interface and set channel and PAN ID; | |
63ce40e4 | 135 | 2. Add 6lowpan interface by command like: |
136 | # ip link add link wpan0 name lowpan0 type lowpan | |
6bf0d84d | 137 | 3. Bring up 'lowpan0' interface |