So yes it’s been a while since my last post. I’ve been busy going back to school working on a BS in Electrical Engineering. Additionally got a promotion at work now Sr. Network Engineer, anyway on to the reason for the post.

Bit Error Rate Test – BERT

I’m working on swing over to a new DS3 this weekend at work. This will be my first DS3 turn up and it turns out it’s just an over grown T1 for all extensive purposes. One important thing that I’ve learned to do though before moving production traffic is make sure L1 & L2 are actually functional. This is where BERT comes in.

I’ve worked with the provider to put a loop facing the new end of the DS3. On the interface I have the following config:

description Unused
bandwidth 44210
no ip address
no keepalive
dsu bandwidth 44210
framing c-bit
cablelength 10

I show the interface is UP UP so at least I know I have my RX and TX side of the cables connected correctly. To kick off the BERT we must make sure keep alives are disabled which you can see above it is.

From the system we issue the following command under the interface. (this may vary by platform):
bert pattern qrss interval

In this case I’m running the test for 12 hours as I want to be absolutely certain this circuit is ready to pass production traffic. Notice how I’ve used QRSS.

Per Wikipedia – QRSS (Quasi Random Signal Source) – A pseudorandom binary sequencer which generates every combination of a 20-bit word, repeats every 1,048,575 bits, and suppresses consecutive zeros to no more than 14. It contains high-density sequences, low-density sequences, and sequences that change from low to high and vice versa. This pattern is also the standard pattern used to measure jitter.

This is as close to real life traffic you can create with a simulated test. If it passes this I should be in good shape to go assuming L3 and up play nice but at that point it’s my problem to deal with.

From this point we can go back to enabled exec mode and check the progress by issuing:
show controllers serial 3/0/1

At the bottom we see:
BERT test result (running)
Test Pattern : 2^20 qrss, Status : Sync, Sync Detected : 1
Interval 720 minute(s), Time Remain : 11:27:40
Bit Errors (since BERT started): 0 bits,
Bits Received (since BERT started): 86115 Mbits
Bit Errors (since last sync): 0 bits
Bits Received (since last sync): 86115 Mbits
MDL transmission is disabled

As you can see we’ve been going for about 30 minutes with no errors so this is looking good.

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