6LoWPAN: update documentation

This patch adds chapter to documentation which describes how to use
6lowpan technology.
Signed-off-by: Alexander Smirnov <alex.bluesman.smirnov@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ieee802154.txt

@@ -78,3 +78,30 @@ in software. This is currently WIP.
 
 See header include/net/mac802154.h and several drivers in drivers/ieee802154/.
 
+6LoWPAN Linux implementation
+============================
+
+The IEEE 802.15.4 standard specifies an MTU of 128 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 Semptember 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/ieee802154/6lowpan.*
+
+To setup 6lowpan interface you need (busybox release > 1.17.0):
+1. Add IEEE802.15.4 interface and initialize PANid;
+2. Add 6lowpan interface by command like:
+   # ip link add link wpan0 name lowpan0 type lowpan
+3. Set MAC (if needs):
+   # ip link set lowpan0 address de:ad:be:ef:ca:fe:ba:be
+4. Bring up 'lowpan0' interface