XRT7250 datasheet(353/463 Pages) EXAR

353 / 463 page

XRT7250

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DS3/E3 FRAMER IC

REV. 1.1.1

334

The first byte of this 16-byte string is a frame start

marker and is typically of the form [1, C6, C5, C4, C3,

C2, C1, C0]. The “1” in the MSB (most significant bit)

of this first byte is used to identify this byte as the

frame start marker (e.g., the first byte of the 16-byte

Trail Trace Buffer Sequence). The bits: C6 through

C0 are the results of a CRC-7 calculation over the

previous 16-byte frame. The subsequent 15 bytes

are used for the transport of 15 ASCII characters re-

quired for the E.164 numbering format.

6.1.1.4

Maintenance and Adaptation (MA) Byte

The MA byte is responsible for carrying the FERF

(Far-End Receive Failure) and the FEBE (Far-End

Block Error) status indicators from one terminal to an-

other. The MA byte-field also carries the Payload

Type, the Payload Dependent and the Timing Marker

indicators. The byte format for the MA byte is pre-

sented below.

Bit 7 - FERF (Far-End Receive Failure)

If the Receive E3 Framer block (at a Local Terminal)

is experiencing problems receiving E3 frame data

from a Remote Terminal (e.g., an LOS, OOF or AIS

condition), then it will inform the Remote Terminal

Equipment of this fact by commanding the Local

Transmit E3 Framer block to set the FERF bit-field

(within the MA byte) of an Outbound E3 frame, to “1”.

The Local Transmit E3 Framer block will continue to

set the FERF bit-field (within the subsequent Out-

bound E3 frames) to “1” until the Receive E3 Framer

block no longer experiences problems in receiving the

E3 frame data. If the Remote Terminal Equipment re-

ceives a certain number of consecutive E3 frames,

with the FERF bit-field set to “1”, then the Remote

Terminal Equipment will interpret this signaling as an

indication of a Far-End Receive Failure (e.g., a prob-

lem with the Local Terminal Equipment).

Conversely, if the Receive E3 Framer block (at a Lo-

cal Terminal Equipment) is not experiencing any

problems receiving E3 frame data from a Remote Ter-

minal Equipment, then it will also inform the Remote

Terminal Equipment of this fact by commanding the

Local Transmit E3 Framer block to set the FERF bit-

field (within the MA byte-field) of an Outbound E3

frame (which is destined for the Remote Terminal) to

“0”. The Remote Terminal Equipment will interpret

this form of signaling as an indication of a normal op-

eration.

NOTE: A detailed discussion into the practical use of the

FERF bit-field is presented in Section 5.2.4.2.

Bit 6 - FEBE (Far-End Block Error)

If a Local Receive E3 Framer block detects an error in

the EM byte, within an incoming E3 frame that it has

received from the Remote Terminal Equipment, then

it will inform the Remote Terminal Equipment of this

error by commanding the Local Transmit E3 Framer

block to set the FEBE bit-field (within the MA byte-

field) of an Outbound E3 frame (which is destined for

the Remote Terminal Equipment) to “1”. The Remote

Terminal Equipment will interpret this signaling as an

indication that the E3 frames that it is transmitting

back out to the Local Receive E3 Framer block are

erred.

Conversely, if the Local Receive E3 Framer block

does not detect any errors in the EM byte, within the

incoming E3 frame, then it will also inform the Re-

mote Terminal Equipment of this fact by commanding

the Local Transmit E3 Framer block to set the FEBE

bit-field of an Outbound E3 frame (which is destined

for the Remote Terminal Equipment) to “0”.

NOTE: A detailed discussion into the practical use of the

FEBE bit-field is presented in Section 5.2.4.2.

Bits 5 - 3 Payload Type

These bit-fields indicates to the Remote Terminal

Equipment, what kind of data is being transported in

the 530 bytes of E3 frame payload data. Some of the

defined payload type values are tabulated in Table 69.

THE MAINTENANCE AND ADAPTATION (MA) BYTE FORMAT

BIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0

FERF

FEBE

Payload Type

Payload Dependent

Timing Marker

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