SIP-URL         = "sip:" [ userinfo "@" ] hostport
                    url-parameters [ headers ]
  url-parameters  = *( ";" url-parameter )
  url-parameter   = transport-param | user-param
                  | ttl-param | maddr-param | tag-param | other-param
  transport-param = "transport=" ( "udp" | "tcp" )
  ttl-param       = "ttl=" ttl
  ttl             = 1*3DIGIT       ; 0 to 255
  maddr-param     = "maddr=" maddr
  maddr           = IPv4address    ; multicast address
  user-param      = "user=" ( "phone" )
  tag-param       = "tag=" UUID
  other-param     = *uric
  headers         = "?" header *( "&" header )
  header          = hname "=" hvalue
  hname           = *uric
  hvalue          = *uric
  digits          = 1*DIGIT