diff options
Diffstat (limited to 'Documentation/networking/ieee802154.txt')
| -rw-r--r-- | Documentation/networking/ieee802154.txt | 177 |
1 files changed, 177 insertions, 0 deletions
diff --git a/Documentation/networking/ieee802154.txt b/Documentation/networking/ieee802154.txt new file mode 100644 index 000000000..e74d8e1da --- /dev/null +++ b/Documentation/networking/ieee802154.txt @@ -0,0 +1,177 @@ + + Linux IEEE 802.15.4 implementation + + +Introduction +============ +The IEEE 802.15.4 working group focuses on standardization of the bottom +two layers: Medium Access Control (MAC) and Physical access (PHY). And there +are mainly two options available for upper layers: + - ZigBee - proprietary protocol from the ZigBee Alliance + - 6LoWPAN - IPv6 networking over low rate personal area networks + +The goal of the Linux-wpan is to provide a complete implementation +of the IEEE 802.15.4 and 6LoWPAN protocols. IEEE 802.15.4 is a stack +of protocols for organizing Low-Rate Wireless Personal Area Networks. + +The stack is composed of three main parts: + - IEEE 802.15.4 layer; We have chosen to use plain Berkeley socket API, + the generic Linux networking stack to transfer IEEE 802.15.4 data + messages and a special protocol over netlink for configuration/management + - MAC - provides access to shared channel and reliable data delivery + - PHY - represents device drivers + + +Socket API +========== + +int sd = socket(PF_IEEE802154, SOCK_DGRAM, 0); +..... + +The address family, socket addresses etc. are defined in the +include/net/af_ieee802154.h header or in the special header +in the userspace package (see either http://wpan.cakelab.org/ or the +git tree at https://github.com/linux-wpan/wpan-tools). + + +Kernel side +============= + +Like with WiFi, there are several types of devices implementing IEEE 802.15.4. +1) 'HardMAC'. The MAC layer is implemented in the device itself, the device + exports a management (e.g. MLME) and data API. +2) 'SoftMAC' or just radio. These types of devices are just radio transceivers + possibly with some kinds of acceleration like automatic CRC computation and + comparation, automagic ACK handling, address matching, etc. + +Those types of devices require different approach to be hooked into Linux kernel. + + +HardMAC +======= + +See the header include/net/ieee802154_netdev.h. You have to implement Linux +net_device, with .type = ARPHRD_IEEE802154. Data is exchanged with socket family +code via plain sk_buffs. On skb reception skb->cb must contain additional +info as described in the struct ieee802154_mac_cb. During packet transmission +the skb->cb is used to provide additional data to device's header_ops->create +function. Be aware that this data can be overridden later (when socket code +submits skb to qdisc), so if you need something from that cb later, you should +store info in the skb->data on your own. + +To hook the MLME interface you have to populate the ml_priv field of your +net_device with a pointer to struct ieee802154_mlme_ops instance. The fields +assoc_req, assoc_resp, disassoc_req, start_req, and scan_req are optional. +All other fields are required. + + +SoftMAC +======= + +The MAC is the middle layer in the IEEE 802.15.4 Linux stack. This moment it +provides interface for drivers registration and management of slave interfaces. + +NOTE: Currently the only monitor device type is supported - it's IEEE 802.15.4 +stack interface for network sniffers (e.g. WireShark). + +This layer is going to be extended soon. + +See header include/net/mac802154.h and several drivers in +drivers/net/ieee802154/. + + +Device drivers API +================== + +The include/net/mac802154.h defines following functions: + - struct ieee802154_hw * + ieee802154_alloc_hw(size_t priv_data_len, const struct ieee802154_ops *ops): + allocation of IEEE 802.15.4 compatible hardware device + + - void ieee802154_free_hw(struct ieee802154_hw *hw): + freeing allocated hardware device + + - int ieee802154_register_hw(struct ieee802154_hw *hw): + register PHY which is the allocated hardware device, in the system + + - void ieee802154_unregister_hw(struct ieee802154_hw *hw): + freeing registered PHY + + - void ieee802154_rx_irqsafe(struct ieee802154_hw *hw, struct sk_buff *skb, + u8 lqi): + telling 802.15.4 module there is a new received frame in the skb with + the RF Link Quality Indicator (LQI) from the hardware device + + - void ieee802154_xmit_complete(struct ieee802154_hw *hw, struct sk_buff *skb, + bool ifs_handling): + telling 802.15.4 module the frame in the skb is or going to be + transmitted through the hardware device + +The device driver must implement the following callbacks in the IEEE 802.15.4 +operations structure at least: +struct ieee802154_ops { + ... + int (*start)(struct ieee802154_hw *hw); + void (*stop)(struct ieee802154_hw *hw); + ... + int (*xmit_async)(struct ieee802154_hw *hw, struct sk_buff *skb); + int (*ed)(struct ieee802154_hw *hw, u8 *level); + int (*set_channel)(struct ieee802154_hw *hw, u8 page, u8 channel); + ... +}; + + - int start(struct ieee802154_hw *hw): + handler that 802.15.4 module calls for the hardware device initialization. + + - void stop(struct ieee802154_hw *hw): + handler that 802.15.4 module calls for the hardware device cleanup. + + - int xmit_async(struct ieee802154_hw *hw, struct sk_buff *skb): + handler that 802.15.4 module calls for each frame in the skb going to be + transmitted through the hardware device. + + - int ed(struct ieee802154_hw *hw, u8 *level): + handler that 802.15.4 module calls for Energy Detection from the hardware + device. + + - int set_channel(struct ieee802154_hw *hw, u8 page, u8 channel): + set radio for listening on specific channel of the hardware device. + +Moreover IEEE 802.15.4 device operations structure should be filled. + +Fake drivers +============ + +In addition there is a driver available which simulates a real device with +SoftMAC (fakelb - IEEE 802.15.4 loopback driver) interface. This option +provides a possibility to test and debug the stack without usage of real hardware. + +See sources in drivers/net/ieee802154 folder for more details. + + +6LoWPAN Linux implementation +============================ + +The IEEE 802.15.4 standard specifies an MTU of 127 bytes, yielding about 80 +octets of actual MAC payload once security is turned on, on a wireless link +with a link throughput of 250 kbps or less. The 6LoWPAN adaptation format +[RFC4944] was specified to carry IPv6 datagrams over such constrained links, +taking into account limited bandwidth, memory, or energy resources that are +expected in applications such as wireless Sensor Networks. [RFC4944] defines +a Mesh Addressing header to support sub-IP forwarding, a Fragmentation header +to support the IPv6 minimum MTU requirement [RFC2460], and stateless header +compression for IPv6 datagrams (LOWPAN_HC1 and LOWPAN_HC2) to reduce the +relatively large IPv6 and UDP headers down to (in the best case) several bytes. + +In September 2011 the standard update was published - [RFC6282]. +It deprecates HC1 and HC2 compression and defines IPHC encoding format which is +used in this Linux implementation. + +All the code related to 6lowpan you may find in files: net/6lowpan/* +and net/ieee802154/6lowpan/* + +To setup a 6LoWPAN interface you need: +1. Add IEEE802.15.4 interface and set channel and PAN ID; +2. Add 6lowpan interface by command like: + # ip link add link wpan0 name lowpan0 type lowpan +3. Bring up 'lowpan0' interface |