The SIP-ETag header is used by a server (event state collector) in a 2xx
response to PUBLISH in order to convey a unique entity tag for the published
state. The client may then use this tag in a
to update previously published
A server must ignore Headers that it does not understand. A proxy must not remove or modify Headers that it does not understand.
etagthe new value of the entity-tag
java.text.ParseExceptionif the ETag syntax is invalid (not a valid token)