Based on kernel version 4.2. Page generated on 2015-09-09 12:14 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