怎样计算cisco交换机端口

计算每个cisco交换机端口的流量都有一个32位或者64位的counter，我怎样才能知道每个counter从清空到查询时的时间是多少呢？？是不是用ifCounterDiscontinuityTime呢？？？？

另外哪位可以提供计算端口流量的公式呢？？

谢谢

             It is calculated as follows:

             Octets*8 + Frames*(96 + 64)
             ---------------------------
             Measurement Interval * 1,000,000 * 2

            Where:
              Measurement Interval is the amount of time over which
              the Octets and Frames were collected, in seconds.

              Measurement Interval is always one second in current
              implementation.

              Octets is the total number of octets transmitted
              or received by all network interfaces, excluding
              framing data but including FCS. This includes octets
              in frames which were partially transmitted or
              received (due to collisions, for example).

              Frames is the total number of frames transmitted
              or received by all network interfaces, including
              frames with errors.

             The number of frames is multiplied by 96 plus 64 in
             order to estimate the delay between each frame for
             Ethernet\'s IPG and preamble/SFD.

             The \'2\' in the divisor makes this a forwarding bandwidth
             counter. A frame received on one interface is typically
             forwarded out another interface. In order to avoid double-
             counting this frame\'s bandwidth, once on the receiving
             interface and once on the transmitting interface, the
             total bandwidth is divided by two.
             Since multicast and broadcast frames can be sent to multiple
             ports, the above is at best a lower bound.\"