Browse Prior Art Database

State Machine for Detection of AIS Condition on 2.048 MBPS (E-1) Lines

IP.com Disclosure Number: IPCOM000109813D
Original Publication Date: 1992-Sep-01
Included in the Prior Art Database: 2005-Mar-24
Document File: 3 page(s) / 74K

Publishing Venue

IBM

Related People

Marks, LV: AUTHOR

Abstract

CCITT Recommendation 0.162 defines the Alarm Indication Signal (AIS) to be less than three zeros in 512 bits; that is, the condition of receiving 0, 1, or 2 zeros in 512 bits must be detected.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 70% of the total text.

State Machine for Detection of AIS Condition on 2.048 MBPS (E-1) Lines

       CCITT Recommendation 0.162 defines the Alarm Indication
Signal (AIS) to be less than three zeros in 512 bits; that is, the
condition of receiving 0, 1, or 2 zeros in 512 bits must be detected.

      Detecting this condition requires the ability to detect 262145
different conditions:
      .    Condition of 512 ones --- > 1 case
      .    Condition of 511 ones and 1 zero; could occur in any of
512 places --- > 512 cases
      .    Condition of 510 ones and 2 zeros; first zero could be in
any of 512 places; second in any of 511 --- > 261632 cases
      Total ---> 262145 cases

      This could require a lot of completed logic.

      The disclosed invention involves three counters (Fig. 1) that
count to 512 and 'freeze' and a mechanism that resets one of the
three counters upon receipt of a zero bit.  Each counter is reset in
turn, in round-robin fashion.  The AIS condition is detected when any
of the counters reaches a count of 512 and freezes.  If 512 bits are
received with more than two zeros, all three counters are reset.  If
two or fewer zeros are received in 512 bits, at least one of the
counters will reach 512 and freeze, indicating the AIS condition.  In
the drawing, RCLK indicates the bit clock, and ZERO indicates a data
bit of ZERO has been sampled.

      Signals A, B, C, are sequenced (Fig. 2) so that exactly one is
active at a tim...