Based on kernel version 4.13.3. Page generated on 2017-09-23 13:55 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_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 ============ 104 105 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 107 provides a possibility to test and debug the stack without usage of real hardware. 108 109 See sources in drivers/net/ieee802154 folder for more details. 110 111 112 6LoWPAN Linux implementation 113 ============================ 114 115 The IEEE 802.15.4 standard specifies an MTU of 127 bytes, yielding about 80 116 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. 125 126 In September 2011 the standard update was published - [RFC6282]. 127 It deprecates HC1 and HC2 compression and defines IPHC encoding format which is 128 used in this Linux implementation. 129 130 All the code related to 6lowpan you may find in files: net/6lowpan/* 131 and net/ieee802154/6lowpan/* 132 133 To setup a 6LoWPAN interface you need: 134 1. Add IEEE802.15.4 interface and set channel and PAN ID; 135 2. Add 6lowpan interface by command like: 136 # ip link add link wpan0 name lowpan0 type lowpan 137 3. Bring up 'lowpan0' interface