XRT84L38IB Exar Corporation, XRT84L38IB Datasheet - Page 402

• Manufacturer Part Number: XRT84L38IB
• Description: Network Controller & Processor ICs 8 Ch T1/E1 Framer
• Manufacturer: Exar Corporation

Specifications of XRT84L38IB

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

XRT84L38
OCTAL T1/E1/J1 FRAMER
Transmission of Alarm Indication Signal (AIS) or Blue Alarm by the intermediate node indicates that the
equipment is still functioning but unable to offer services. It is an all ones (except for framing bits) pattern which
can be used by the equipment further down the line to maintain clock recovery and timing synchronization.
The XRT84L38 framer can detect three types of AIS in E1 mode:
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Unframed AIS is an all ones pattern. If unframed AIS is sent, the equipment further down the line will be able to
maintain timing synchronization and be able to recover clock from the received AIS signal. However, due to the
lack of framing bits, the equipment farther down the line will not be able to maintain frame synchronization and
will declare Loss of Frame (LOF).
On the other hand, the payload portion of a framed AIS pattern is all ones. However, a framed AIS pattern still
has correct framing bits. Therefore, the equipment further down the line can still maintain frame
synchronization as well as timing synchronization. In this case, no LOF or Red alarm will be declared.
"AIS16" is an AIS alarm that only supported in E1 framing format. It is an all ones pattern in time slot 16 of each
E1 frame. As we mentioned before, time slot 16 is usually used for signaling and data link in E1, therefore, an
"AIS16" alarm is transmitted by the intermediate node to indicate that the data link channel is having a
problem. Since all the other thirty one time slots are still transmitting normal data (that is, framing information
and PCM data), therefore, the equipment further down the line can still maintain frame synchronization, timing
synchronization as well as receiving PCM data. In this case, no LOF or Red alarm will be declared by the
equipments further down the line. However, a CAS Multi-frame Yellow Alarm will be sent by the equipment
further down the line to indicate the loss of CAS Multi-frame alignment.
The Alarm indication logic within the Receive Framer block of the XRT84L38 framer monitors the incoming E1
frames for AIS (both framed and unframed) and AIS16 errors.
AIS alarm condition are detected and declared according to the following procedure:
Therefore, AIS condition has to be persisted for 104 ms before AIS alarm condition is declared by the
XRT84L38 framer.
If there is no valid AIS flag over a 4ms interval, the Alarm indication logic will decrement the flag counter. The
AIS alarm is removed when the counter reaches 0. That is, AIS alarm will be removed if in over 104 ms, there
is no valid AIS flag.
AIS16 alarm condition are detected and declared according to the following procedure:
1. The incoming E1 frames are monitored for AIS detection. AIS detection is defined as an unframed or
2. An AIS detection counter within the Receive Framer block of the XRT84L38 counts the occurrences of AIS
3. Each 4 ms interval with a valid AIS flag increments a flag counter which declares AIS alarm when 25 valid
1. The incoming E1 frames are monitored for AIS16 detection. AIS16 detection is defined as two consecutive
2. An AIS16 detection counter within the Receive Framer block of the XRT84L38 counts the occurrences of
3. Each valid AIS flag increments a flag counter which declares AIS alarm when 22 valid flags have been col-
Framed AIS
Unframed AIS
AIS16
framed pattern with less than three zeros in two consecutive frames. In the case of framed AIS, time slot 0
is excluded.
detection over a 4 ms interval. It will indicate a valid AIS flag when thirteen or more of a possible sixteen
AIS are detected.
flags have been collected.
all ones time slot 16 bytes while CAS Multi-frame alignment pattern is missing or CAS Multi-frame is out of
synchronization.
AIS16 detection.
lected.
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