[1] [CITE@en[RFC 3427 - Change Process for the Session Initiation Protocol (SIP)]]
([TIME[2018-04-08 17:59:02 +09:00]])
<https://tools.ietf.org/html/rfc3427>

[2] [CITE@en[RFC 6709 - Design Considerations for Protocol Extensions]]
([TIME[2018-04-05 17:00:08 +09:00]])
<https://tools.ietf.org/html/rfc6709#section-3.2.1>

[3] [CITE@en[RFC 5727 - Change Process for the Session Initiation Protocol (SIP) and the Real-time Applications and Infrastructure Area]]
([TIME[2018-04-08 17:59:09 +09:00]])
<https://tools.ietf.org/html/rfc5727#section-4>