1 2 Linux IEEE 802.15.4 implementation 3 4 5Introduction 6============ 7The IEEE 802.15.4 working group focuses on standardization of bottom 8two layers: Medium Access Control (MAC) and Physical (PHY). And there 9are 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 13The linux-wpan project goal is to provide a complete implementation 14of the IEEE 802.15.4 and 6LoWPAN protocols. IEEE 802.15.4 is a stack 15of protocols for organizing Low-Rate Wireless Personal Area Networks. 16 17The 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 25Socket API 26========== 27 28int sd = socket(PF_IEEE802154, SOCK_DGRAM, 0); 29..... 30 31The address family, socket addresses etc. are defined in the 32include/net/af_ieee802154.h header or in the special header 33in the userspace package (see either http://wpan.cakelab.org/ or the 34git tree at https://github.com/linux-wpan/wpan-tools). 35 36One can use SOCK_RAW for passing raw data towards device xmit function. YMMV. 37 38 39Kernel side 40============= 41 42Like with WiFi, there are several types of devices implementing IEEE 802.15.4. 431) 'HardMAC'. The MAC layer is implemented in the device itself, the device 44 exports MLME and data API. 452) '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 49Those types of devices require different approach to be hooked into Linux kernel. 50 51 52HardMAC 53======= 54 55See the header include/net/ieee802154_netdev.h. You have to implement Linux 56net_device, with .type = ARPHRD_IEEE802154. Data is exchanged with socket family 57code via plain sk_buffs. On skb reception skb->cb must contain additional 58info as described in the struct ieee802154_mac_cb. During packet transmission 59the skb->cb is used to provide additional data to device's header_ops->create 60function. Be aware that this data can be overridden later (when socket code 61submits skb to qdisc), so if you need something from that cb later, you should 62store info in the skb->data on your own. 63 64To hook the MLME interface you have to populate the ml_priv field of your 65net_device with a pointer to struct ieee802154_mlme_ops instance. The fields 66assoc_req, assoc_resp, disassoc_req, start_req, and scan_req are optional. 67All other fields are required. 68 69 70SoftMAC 71======= 72 73The MAC is the middle layer in the IEEE 802.15.4 Linux stack. This moment it 74provides interface for drivers registration and management of slave interfaces. 75 76NOTE: Currently the only monitor device type is supported - it's IEEE 802.15.4 77stack interface for network sniffers (e.g. WireShark). 78 79This layer is going to be extended soon. 80 81See header include/net/mac802154.h and several drivers in 82drivers/net/ieee802154/. 83 84 85Device drivers API 86================== 87 88The 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 102Moreover IEEE 802.15.4 device operations structure should be filled. 103 104Fake drivers 105============ 106 107In addition there is a driver available which simulates a real device with 108SoftMAC (fakelb - IEEE 802.15.4 loopback driver) interface. This option 109provides possibility to test and debug stack without usage of real hardware. 110 111See sources in drivers/net/ieee802154 folder for more details. 112 113 1146LoWPAN Linux implementation 115============================ 116 117The IEEE 802.15.4 standard specifies an MTU of 127 bytes, yielding about 80 118octets of actual MAC payload once security is turned on, on a wireless link 119with a link throughput of 250 kbps or less. The 6LoWPAN adaptation format 120[RFC4944] was specified to carry IPv6 datagrams over such constrained links, 121taking into account limited bandwidth, memory, or energy resources that are 122expected in applications such as wireless Sensor Networks. [RFC4944] defines 123a Mesh Addressing header to support sub-IP forwarding, a Fragmentation header 124to support the IPv6 minimum MTU requirement [RFC2460], and stateless header 125compression for IPv6 datagrams (LOWPAN_HC1 and LOWPAN_HC2) to reduce the 126relatively large IPv6 and UDP headers down to (in the best case) several bytes. 127 128In Semptember 2011 the standard update was published - [RFC6282]. 129It deprecates HC1 and HC2 compression and defines IPHC encoding format which is 130used in this Linux implementation. 131 132All the code related to 6lowpan you may find in files: net/6lowpan/* 133and net/ieee802154/6lowpan/* 134 135To setup 6lowpan interface you need (busybox release > 1.17.0): 1361. Add IEEE802.15.4 interface and initialize PANid; 1372. Add 6lowpan interface by command like: 138 # ip link add link wpan0 name lowpan0 type lowpan 1393. Set MAC (if needs): 140 # ip link set lowpan0 address de:ad:be:ef:ca:fe:ba:be 1414. Bring up 'lowpan0' interface 142