Change:
The usage of no-op mechanism and RTP comfort noise mechanism for keepalives have been removed. Also, the keepalive procedures when communicating with a non-ICE peer, and when ICE is not used at all, have been removed.

Discussion:
All endpoints MUST send keepalives for each media session.  These keepalives serve the purpose of keeping NAT bindings alive for the <del> media session.  These keepalives MUST be sent even if ICE is not being utilized for the session at all.  The keepalive SHOULD be sent using a format that is supported by its peer.  ICE endpoints allow for STUN-based keepalives for UDP streams, and as such, STUN keepalives MUST be used when an agent is a full ICE implementation and is communicating with a peer that supports ICE (lite or full). If the peer does not support ICE, the choice of a packet format for keepalives is a matter of local implementation.  A format that allows packets to easily be sent in the absence of actual media content is RECOMMENDED.  Examples of formats that readily meet this goal are RTP No-Op I-D.ietf-avt-rtp-no-op, and in cases where both sides support it, RTP comfort noise RFC3389.  If the peer doesn't support any formats that are particularly well suited for keepalives, an agent SHOULD send RTP packets with an incorrect version number, or some other form of error that would cause them to be discarded by the peer. </del> <ins> media session.  The keepalives SHOULD be sent using a format that is supported by its peer.  ICE endpoints allow for STUN-based keepalives for UDP streams, and as such, STUN keepalives MUST be used when an agent is a full ICE implementation and is communicating with a peer that supports ICE (lite or full). </ins> If there has been no packet sent on the candidate pair ICE is using for a media component for Tr seconds (where packets include those defined for the component (RTP or RTCP) and previous keepalives), an <del> agent MUST generate a keepalive on that pair.  Tr SHOULD be configurable and SHOULD have a default of 15 seconds.  Tr MUST NOT be configured to less than 15 seconds.  Alternatively, if an agent has a dynamic way to discover the binding lifetimes of the intervening NATs, it can use that value to determine Tr.  Administrators deploying ICE in more controlled networking environments SHOULD set Tr to the longest duration possible in their environment. If STUN is being used for keepalives, a STUN Binding Indication is </del> <ins> agent MUST generate a keepalive on that pair.  ICE endpoints SHOULD use a Tr value of 15 seconds, but MAY use another value, e.g. based on configuration or network/NAT characteristics.  For example, if an agent has a dynamic way to discover the binding lifetimes of the intervening NATs, it can use that value to determine Tr. Administrators deploying ICE in more controlled networking environments SHOULD set Tr to the longest duration possible in their environment.  ICE endpoints MUST NOT use a Tr value smaller than 15 seconds. When STUN is being used for keepalives, a STUN Binding Indication is </ins> used RFC5389.  The Indication MUST NOT utilize any authentication mechanism.  It SHOULD contain the FINGERPRINT attribute to aid in demultiplexing, but SHOULD NOT contain any other attributes.  It is