1 2 Linux IEEE 802.15.4 implementation 3 4 5Introduction 6============ 7The IEEE 802.15.4 working group focuses on standartization of bottom 8two layers: Medium Accsess Control (MAC) and Physical (PHY). And there 9are 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 13The Linux-ZigBee project goal is to provide complete implementation 14of 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 our userspace package (see either linux-zigbee sourceforge download page 34or git tree at git://linux-zigbee.git.sourceforge.net/gitroot/linux-zigbee). 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 52MLME - MAC Level Management 53============================ 54 55Most of IEEE 802.15.4 MLME interfaces are directly mapped on netlink commands. 56See the include/net/nl802154.h header. Our userspace tools package 57(see above) provides CLI configuration utility for radio interfaces and simple 58coordinator for IEEE 802.15.4 networks as an example users of MLME protocol. 59 60 61HardMAC 62======= 63 64See the header include/net/ieee802154_netdev.h. You have to implement Linux 65net_device, with .type = ARPHRD_IEEE802154. Data is exchanged with socket family 66code via plain sk_buffs. On skb reception skb->cb must contain additional 67info as described in the struct ieee802154_mac_cb. During packet transmission 68the skb->cb is used to provide additional data to device's header_ops->create 69function. Be aware, that this data can be overriden later (when socket code 70submits skb to qdisc), so if you need something from that cb later, you should 71store info in the skb->data on your own. 72 73To hook the MLME interface you have to populate the ml_priv field of your 74net_device with a pointer to struct ieee802154_mlme_ops instance. The fields 75assoc_req, assoc_resp, disassoc_req, start_req, and scan_req are optional. 76All other fields are required. 77 78We provide an example of simple HardMAC driver at drivers/ieee802154/fakehard.c 79 80 81SoftMAC 82======= 83 84The MAC is the middle layer in the IEEE 802.15.4 Linux stack. This moment it 85provides interface for drivers registration and management of slave interfaces. 86 87NOTE: Currently the only monitor device type is supported - it's IEEE 802.15.4 88stack interface for network sniffers (e.g. WireShark). 89 90This layer is going to be extended soon. 91 92See header include/net/mac802154.h and several drivers in drivers/ieee802154/. 93 94 95Device drivers API 96================== 97 98The include/net/mac802154.h defines following functions: 99 - struct ieee802154_dev *ieee802154_alloc_device 100 (size_t priv_size, struct ieee802154_ops *ops): 101 allocation of IEEE 802.15.4 compatible device 102 103 - void ieee802154_free_device(struct ieee802154_dev *dev): 104 freeing allocated device 105 106 - int ieee802154_register_device(struct ieee802154_dev *dev): 107 register PHY in the system 108 109 - void ieee802154_unregister_device(struct ieee802154_dev *dev): 110 freeing registered PHY 111 112Moreover IEEE 802.15.4 device operations structure should be filled. 113 114Fake drivers 115============ 116 117In addition there are two drivers available which simulate real devices with 118HardMAC (fakehard) and SoftMAC (fakelb - IEEE 802.15.4 loopback driver) 119interfaces. This option provides possibility to test and debug stack without 120usage of real hardware. 121 122See sources in drivers/ieee802154 folder for more details. 123 124 1256LoWPAN Linux implementation 126============================ 127 128The IEEE 802.15.4 standard specifies an MTU of 128 bytes, yielding about 80 129octets of actual MAC payload once security is turned on, on a wireless link 130with a link throughput of 250 kbps or less. The 6LoWPAN adaptation format 131[RFC4944] was specified to carry IPv6 datagrams over such constrained links, 132taking into account limited bandwidth, memory, or energy resources that are 133expected in applications such as wireless Sensor Networks. [RFC4944] defines 134a Mesh Addressing header to support sub-IP forwarding, a Fragmentation header 135to support the IPv6 minimum MTU requirement [RFC2460], and stateless header 136compression for IPv6 datagrams (LOWPAN_HC1 and LOWPAN_HC2) to reduce the 137relatively large IPv6 and UDP headers down to (in the best case) several bytes. 138 139In Semptember 2011 the standard update was published - [RFC6282]. 140It deprecates HC1 and HC2 compression and defines IPHC encoding format which is 141used in this Linux implementation. 142 143All the code related to 6lowpan you may find in files: net/ieee802154/6lowpan.* 144 145To setup 6lowpan interface you need (busybox release > 1.17.0): 1461. Add IEEE802.15.4 interface and initialize PANid; 1472. Add 6lowpan interface by command like: 148 # ip link add link wpan0 name lowpan0 type lowpan 1493. Set MAC (if needs): 150 # ip link set lowpan0 address de:ad:be:ef:ca:fe:ba:be 1514. Bring up 'lowpan0' interface 152