1.1.7, 18.2.2, and 20.42.

    @ivar transport: Network protocol used for this leg. (Probably either "TCP"
    or "UDP".)
    @type transport: C{str}
    @ivar branch: Unique identifier for this request.
    @type branch: C{str}
    @ivar host: Hostname or IP for this leg.
    @type host: C{str}
    @ivar port: Port used for this leg.
    @type port C{int}, or None.
    @ivar rportRequested: Whether to request RFC 3581 client processing or not.
    @type rportRequested: C{bool}
    @ivar rportValue: Servers wishing to honor requests for RFC 3581 processing
    should set this parameter to the source port the request was received
    from.
    @type rportValue: C{int}, or None.

    @ivar ttl: Time-to-live for requests on multicast paths.
    @type ttl: C{int}, or None.
    @ivar maddr: The destination multicast address, if any.
    @type maddr: C{str}, or None.
    @ivar hidden: Obsolete in SIP 2.0.
    @type hidden: C{bool}
    @ivar otherParams: Any other parameters in the header.
    @type otherParams: C{dict}
    Z