Contact           = ( "Contact" | "m" ) ":" 
                       ("*" | (1# (( name-addr | addr-spec )
                       *( ";" contact-params ))))
   name-addr         = [ display-name ] "<" addr-spec ">"
   addr-spec         = SIP-URL | URI
   display-name      = *token | quoted-string
   contact-params    = "q"       "=" qvalue
                     | "action"  "=" "proxy" | "redirect"
                     | "expires" "=" delta-seconds | <"> SIP-date <">
                     | contact-extension
   contact-extension = generic-param
   qvalue            = ("0" ["." 0*3DIGIT]) 
                     | ("1" ["." 0*3("0")])