Which tag is used in a SIP message to indicate ICE support?

The tag that denotes ICE (Interactive Connectivity Establishment) support in a SIP message is indeed "sip.ice." This tag is part of the SIP signaling that specifies how sessions can traverse NAT (Network Address Translation) devices and facilitates peer-to-peer connectivity.

Using "sip.ice," the SIP entities involved can understand that ICE methods are supported during the session establishment. ICE itself is crucial in ensuring that multimedia communications can be established reliably and efficiently across networks with varying conditions, including the presence of NAT.

The other options do not adhere to the established naming conventions used in the SIP framework or do not represent recognized tags for indicating ICE support in SIP messages. Therefore, "sip.ice" is the correct choice for representing ICE support within the context of SIP.