The MIB module to configure and perform Bit Error Rate Testing
(BERT) on DS3, DS1/E1 and DS0/DS0Bundle interfaces.
Bit error rate testing and loopbacks are used by carriers
and ISPs to aid in problem resolution as well as for
testing the quality of T1/E1 or T3/E3 links.  Tests can
be run on a full T1/E1 line or can be run on a fractional
T1/E1 such as single DS0 or a group of DS0s.  By using BERT,
poor quality links could be detected early.
BERT enables the user to test the quality of links by directly
comparing a pseudo-random or repetitive test pattern with
an identical locally generated test pattern. 
        
Terminology:
        
BERT: Bit Error Rate Testing (BERT) involves generating a known
data sequence into a transmission device and examining the
received sequence at the same device or a remote device
for errors.
        
The use of BERT results in the computation of a bit error rate
(BER), which is
        		
		bits received in error
	BER = ------------------------
		number of bits transmitted
        
To perform a bit error rate test using one tester, 
communications equipment must be placed into a loop-back
mode of operation and the BERT test can then be used to 
determine if equipment is operating correctly.
        
When running a BERT, system expects to receive the same pattern
that is transmitting.  To help ensure this, two common options
are available.
        
- Use loopback somewhere in the link or network.  This can
 be accomplished by putting the line in loop up mode;
 send the pattern; find the BER.
        
- configure remote testing equipment to transmit the Same BERT
  pattern at the same time.
        
Typical Sequence in Performing Bit Error Rate Test by the 
device is given below:
        
- Loop Up:
The tester issues special code to force the far end (CPE) into 
loopback.  Upon recognition of the loop activation request code
the CPE enters a loop mode in which it returns the port data
back to the tester.
        
- Send Pattern:
After a loop has been established, the tester can generate 
test pattern toward the CPE and monitor the incoming data.
           
- Loop Down:
The tester issues a special code (loop down command) to 
release the far end from the loopback.
        
Terminology Used:
CPE - Customer's premise equipment.  At CPE, following equipment
is required:
DSU
CSU
Usually DSU and CSU functions are incorporated by vendors
into a single CSU/DSU unit.
OCU - Office Channel Unit
CSU - Channel Service Unit
A CSU contains the last signal regenerator on the line 
before DTE and mechanism to put the line into loopback
for testing from the central office.
DSU - Data Service Unit.