if( len > 0xFFFF ) {
            throw new IOException( "write too large: " + len );
        } else if( off < 4 ) {
            throw new IOException( "NetBIOS socket output buffer requires 4 bytes available before off" );
        }

        off -= 4;

        b[off + 0] = (byte)SessionServicePacket.SESSION_MESSAGE;
        b[off + 1] = (byte)0x00;