+1 to Katleen's comment about optional data channel protection.

[duzongpeng] At the security aspect, we suggest using the IPSec to protect the data tunnel between WTP and AR. [/duzongpeng]

In 3.3. IEEE 802.11 WTP Alternate Tunnel Failure Indication

Length == 4, but should it be >4 due to IPv4/IPv6 address at the end?

[duzongpeng] Change to >4, Thanks. [/duzongpeng]