Motorola T1/E1 manual Alternate Mark Inversion AMI, 1 in 15 Requirement AMI

Canopy T1/E1 Multiplexer	September 2004
	T1/E1 Multiplexer FPGA Version 3.4

For E1 mode, the Canopy T1/E1 Multiplexer supports the following:

◦Transparent support of the E1 channel

◦AMI

◦HDB3

◦up to three ports

Alternate Mark Inversion (AMI)

The template of the DS-1 signal is bipolar. This means that a plus voltage, a zero voltage, and a minus voltage are important to the coding of the signal. The code that is used in T1 is called Alternate Mark Inversion (AMI). The requirement is that if a “1” (or Mark) is coded as a positive voltage, the very next “1” must be coded as a minus voltage or the result will be a bipolar violation (BPV). Another one of the requirements of the coding sequence is that a “1” bit is sent to maintain the timing synchronization. A signal that is sending all “0s” would be a constant zero voltage line. The eventual result would be that the system’s timing would be lost. In order to overcome the potential situation where a string of “0s” causes a loss of the system’s timing, a number of zero suppression techniques have been designed. Common techniques are used to handle zero suppression requirements are:

◦1 in 15 Requirement

◦B8ZS.

◦HDB3

The Canopy T1/E1 Multiplexer fulfills the role of a transparent T1/E1 extender. As such, it is compatible with either AMI, B8ZS, or HDB3 coding of signals. The endpoints determine which of the zero suppression techniques will be applied to the signal. The Canopy T1/E1 Multiplexer must be set to match the zero suppression settings at the endpoints of the signal.

The 1 in 15 Requirement (AMI)

The 1 in 15 requirement stipulates that no more than 15 “0s” may be sent be for every “1” that is transmitted. The easiest approach is to make every bit 8 a “1” and to use only the lower 7 bits for data transmission. This 7/8 mode yields a rate of 56 kbps instead of the standard DS-0 rate of 64 kbps. This technique also prevents the use of signaling bits since bit 8 is now used for a different purpose.

Configuring the Canopy T1/E1 Multiplexer to AMI accommodates the stipulations for bit handling identified in the 1 in 15 requirement.

Binary Eight Zero Substitution Coding

The limitations imposed by the 1 in 15 requirement led to the development of Binary Eight Zero Substitution (B8ZS) coding. This signal coding technique takes advantage of BPVs in the data stream to be decoded as signal. With B8ZS coding, each block of eight consecutive zeros is replaced with the B8ZS code word. The transmitted bit stream will contain two AMI violations.

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