Huawei This specification clarifies "Capabilities Update" in OPEN state defined in RFC 3588bis. Capabilities update in OPEN state can reuse commands CER/CEA commands for re-negotiation between Diameter peers when one of them changes its capabilities.It is a very important function in Diameter. However, RFC 3588 has defined a mechanism of containing capabilities list both in CER and CEA commands and the peer should update its local database whenever it receives CER/CEA. This makes the process complex and redundant when they are used in OPEN state. So this draft proposes a simpler solution based on CER/CEA commands to deal with this problem.