Test Equipment for BER measurement in TCP/IP?

I have a 100BaseT Ethernet Router to Ethernet Router link over several miles of fiber using TCP/IP with fixed IP addresses. Nothing in between except fiber and electrical to optical conversion.

What test equipment is recommended to measure Bit Error Rate from Ethernet port on one end to Ethernet Port on the other end? Im used to using paired PRBS generator/receiver gear to measure BER on serial links (such as Fireberd 6000a), but how is this done on a packet based link? Is there other equipment that might provide BER or other measurements of link quality for this point to point link?

Any thoughts appreciated. Thanks!

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Most Ethernet gear should provide detailed stats from the interface itself (CRC, framing, I/O errors, underruns, overruns, etc.). If you see these errors increasing, you usually need to review your physical layer (TDR, cable scanner, etc.), or, review the traffic or resources on the device itself for I/O or queuing-type errors (e.g. underruns).

TCP/IP will adjust to these errors dynamically, however, throughput will be severely impacted if the errors are consistent. Still, you don't really approach Ethernet port errors as you would a serial link (patterns, 1's density, and the like). Cisco and Juniper gear should provide enough information that you can take one of the two approaches mentioned.


Trs80 wrote:

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Good advice already. You can use tools like iperf, ttcp, netperf, to generate traffic so that you can get results in a short time. These tools will also let you know if there are lost packets.

The cisco "extended ping" is useful too. fping.exe for windows ping with "flood" option on unix.

use large packets, 1400 bytes say.

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1 point - no Ethernet measurements at packet level can give you BER, since all you can tell is whether the link managed to send a packet error free or not.

So - any errored packet can contain 1 or more bit errors and you cannot measure any closer than that. FWIW a lot of network errors tend to come in bursts, so measuring lost packets is still a useful number,

Note such a link may include Ethernet switch or bridge elements - these have the annoying tendency to do their own packet checks, and silently "eat" corrupted packets (happens with some Ethernet NTE devices, SDH muxes with Ethernet support etc). In this case the collected error stats at the routers may not include any errors detected across the link.

So - if you are really being paranoid, measure the raw fibre.

If not you should try for something like a handheld tester, which can stamp every packet and give you stats about which ones didnt make it.

Try Fluke or JDSU for some handheld testers. you might need 2 devices, with each sending to the other, or a remote acting as a mirror to swap dest + source addresses depending on how you want to test.

Work has been using some JDSU handheld units that work at layer 3 and can inject a stream of packets on a working link at a given load level. A remote unit acting as a slave will "bounce" them back and the master measures the stats involved.

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Any surplus JDSU test equipment for sale?

Don Gavin Test Equipment Connection Corporation


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