atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services T1's, CSU's and DSU's Trouble shooting tips?

Soneplex and Adtran HDSL T1's consists of a C unit in the CO and an R unit at the Remote or customer. It may or may not have a line regenerators called "doubblers" because they double the distance the circuit can be deployed. Because each is made by the same manufactuer, they talk to each other constently and gather Performance Monitoring Information for use in OAMP or Operations, Administration, Maintenence and Provisioning.

Line coding:

Conventional T1: Bipolar pulses AMI. Alternate mark Inversion.

Soneplex HDSL T1: 2B1Q

Adtran T1: Started out with TC Pam and in the new versions 2B1Q (because Adtran bought out Soneplex from ADC).

The type of T1 your dealing with will determine what tests you perform, what impairments to look for.

John,

Does 2B1Q = B8ZS ?

I've been installing T-1s for quite a few years, and have never heard of term "2B1Q"...

Sheer curioisity on my part.

Always willing to learn from older and wiser cats...

2B1Q = 2 binary one quadnary. Simply put: For a voltage of +1 volt it equals the binary code of 00. +3v = 01. -1 volt = 01 and -3 volts = 11.

So an 8 bit byte or "word" can be represented by 4 voltage level changes.

In effect the frequency of an HDSL T1 is reduced to 1/4th that of a conventional T1 allowing it to be deployed 12kft without regeneration. A conventional T1 must be regenerated at 6kft intervals.
PS: dont quote me on the volts vs bits I'm trying to do it from memory.

B8ZS = Binary eight zero substituation.

It only really really means something to a convential T1.

The requirement calls for a substituted special pattern to be inserted and transmitted in the case where 8 zeroes in a row are supposed to be transmitted on the T1.

Digital circuits do not like to see zeros, it screws up timing and syncronization circuitry of regenerative sections of equipment.

8 7 6 5 4 3 2 1 Bit position

0 0 0 0 0 0 0 0 T1 is suposed to transmit

0 +1 0 +1 -1 0 0 -1 substituted bit pattern

There are deliberate Bipolar violations in the 4th and 7th bit positions which tells any equipment capable of detecting BPV's that this is a substituted bit patteren for 8 zeros and don't flag it as a BPV.

At the receiving end the substituted pattern is removed and the 8 zeroes are reinserted.

At the receiving end the substituted pattern is removed and the 8 zeroes are reinserted.

The T1 will transmit in a Bipolar (AMI) format under normal operation. If 8 zeros are to be transmitted the trannsmitter will insert the substituted B8ZS pattern until such time that the transmission of 8 consecutive zeros ends. Then it returns to sending in the Bipolar (AMI) line code format.