如何使用分光器

如何连接分光器

1常见问题

在部署探针及分光器时，常见的问题有二个：极性问题和光功率问题。

1.1 极性

下图示例说明了分光器与DTE、DCE网络设备的连接原理。分光器只能对TX信号进行正确地分光，本图说明了采用正确的极性进行连接。DCE Tx(DTE Rx)数据连接到探针采用蓝色标记，DTE Tx(DCE Rx)数据连接到探针的采用红色标记。

如果光缆在双向都接反了（即混合极性，mixed-polarity），用户原有的链路还可正常工作(DTE-Tx to DCE-Rx and DTE-Tx to DCE-Rx)，但是分光器有时不能正常工作，探针可能接收到较低光功率的光信号或接收不到光信号（低于探针的光功率范围）。

一个不影响原有链路正常工作并检测混合极性的方法是测量分光器输出到探针的光功率。若光功率非常低，多达-30db to -40db，就有可能是采用混合极性的连接方法。

若已经确认是混合极性问题，或想确认是否采用了混合极性接法，可采用以下方法：

[警告-此操作可能导致链路的中断]

1 –同时颠倒分光器A、B端口的连接，可能发生如下结果：

A: 探针接受到光功率增强，探针可以监控到数据[这表时原来是混全极性连接，现在是正确的连接方式]

或者

B: 探针接受到的光功率更弱了(现在是错误的混合极性连接)

恢复原来的连接方式并检查光缆的衰减，是否光接头有污或损坏的光缆。

2 –测量连接分光器的每根光缆和二根光缆的光功率：

A: 断开连接分光器的所有光缆并记录下连接的方式.

B: Take a light reading off of the Network “A” cable, then plug it into the tap in the same orientation as it was before and get the readings off the probe connections. [One will be "0" the other will have a value]

C: Now disconnect Network “A” , and repeat the above procedure with the cable from Network “B” - again you will get a valid reading and a "0".

D: Now connect BOTH cables and take a reading off of the probe-connectors

If the light level at the probe connectors is about the same as it was in A: and B: then you are connected correctly. If, however, you see a much greater difference (-15db or more) at the probe connectors when both cables are connected than with either side alone, then you have a mixed-polarity connection and should reverse the cables.

These polarity issues will not come up if you are using cables with polarized connectors at both ends of the cable.

1.2 光功率

2Netscout Probes的光学参数

NetScout makes a line of Fiber Optics probes for most mainstream circuits. The following tables reflect the light sensitivity of our different probes.

It should be noted that, as stated previously, there is a difference between the …typical‟ light level ranges that are found usable in a test laboratory environment and that of a production network where any downtime and/or failure are not acceptable. We therefore differentiate between the absolute range of light figures supplied from the vendors under which the optical receivers on the NICs are known to function, as opposed to the range of light under which we are confident of 100% performance and reliability. We list the minimum values for each probe, both the typical value and our own recommended value from field and customer experience.

It is this latter range that we strongly suggest be used and that readings on the …edge‟ of this suggested range be considered marginal. For example, we would consider a light reading for the 9100 model ATM OC3/OC12 probe of -26dBm to be a marginal level and would suggest raising it to –25dBm or better to insure reliable operation of the probe. Even though the manufacturer of the NIC receiver would suggest –30dBm is appropriate, we have found quite often that field experience does not bear this out when not in a lab. A 1dBM rise will equate to a 22% increase in light.

2.1 Netscout OC3 and OC12 ATM Probes:

Maximum light level NetScout Probe Model Typical Minimum range / Field

value suggested

8110 Multimode -30 to –31dBm / -26dBm -14dBm

8110 Singlemode ** -30 to –31dBm / -26dBm -14dBm

9110 Multimode -26 to –30dBm / -26dBm -14dBm

9110 Singlemode -28 to –31.5dBm / -26dBm -8dBm

-20dBm / -17dBm +4dBm

Gigabit (8900 and 9900

series)

Fast Ethernet (8213, 8243) -30dBm / -28dBm -10dBm

**Note: The 8110 Single-mode Probe uses a special Tap-to-Probe cable that