TFRA08C13-DB AGERE [Agere Systems], TFRA08C13-DB Datasheet - Page 53

• Manufacturer Part Number: TFRA08C13-DB
• Description: TFRA08C13 OCTAL T1/E1 Framer
• Manufacturer: AGERE [Agere Systems]

Preliminary Data Sheet
October 2000
Lucent Technologies Inc.
Lucent Technologies Inc.
Frame Formats
CRC-4 Multiframe Alignment Search Algorithm with
400 ms Timer
The CRC-4 multiframe alignment with 400 ms timer
mode is enabled by setting FRM_PR9 to 0XXX1XX1
(binary). This receive CRC-4 multiframe reframe mode
is the modified CRC-4 multiframe alignment algorithm
described in ITU Rec. 706 Annex B, where it is referred
to as CRC-4-to-non-CRC-4 equipment interworking. A
flow diagram of this algorithm is illustrated in
Figure 14. When the interworking algorithm is enabled,
it supersedes the 100 ms algorithm described on
page 51 and in Figure 13. This algorithm assumes that
a valid basic frame alignment signal is consistently
present, but the CRC-4 multiframe alignment cannot be
achieved by the end of the total CRC-4 multiframe
alignment search period of 400 ms, if the distant end is
a non-CRC-4 equipment. In this mode, the following
consequent actions are taken:
This algorithm allows the identification of failure of
CRC-4 multiframe alignment generation/detection, but
with correct basic framing, when interworking between
each piece of equipment having the modified CRC-4
multiframe alignment algorithm.
As described in ITU Rec. G.706 Section B.2.3:
An indication that there is no incoming CRC-4 multi-
frame alignment signal.
All CRC-4 processing on the receive 2.048 Mbits/s
signal is inhibited.
CRC-4 data is transmitted to the distant end with
both E bits set to 0.
A 400 ms timer is triggered on the initial recovery of
the primary basic frame alignment.
The 400 ms timer reset if and only if:
— The criteria for loss of basic frame alignment as
described in ITU Rec. G.706 Section 4.1.1 is
achieved.
(continued)
— If 915 out of 1000 errored CRC-4 blocks are
— On-demand reframe is requested.
— The receive framer is programmed to the non-
The loss of basic frame alignment checking process
runs continuously, irrespective of the state of the
CRC-4 multiframe alignment process below it.
A new search for frame alignment is initiated if
CRC-4 multiframe alignment cannot be achieved in
8 ms, as described in ITU Rec. G.706 Section 4.2.
This new search for basic frame alignment will not
reset the 400 ms timer or invoke consequent actions
associated with loss of the primary basic frame align-
ment. In particular, all searches for basic frame align-
ment are carried out in parallel with, and
independent of, the primary basic frame loss check-
ing process. All subsequent searches for CRC-4 mul-
tiframe alignment are associated with each basic
framing sequence found during the parallel search.
During the search for CRC-4 multiframe alignment,
traffic is allowed through, upon, and to be synchro-
nized to, the initially determined primary basic frame
alignment.
Upon detection of the CRC-4 multiframe before the
400 ms timer elapsing, the basic frame alignment
associated with the CRC-4 multiframe alignment
replaces, if necessary, the initially determined basic
frame alignment.
If CRC-4 multiframe alignment is not found before
the 400 ms timer elapses, it is assumed that a condi-
tion of interworking between equipment with and
without CRC-4 capability exists and the actions
described above are taken.
If the 2.048 Mbits/s path is reconfigured at any time,
then it is assumed that the (new) pair of path termi-
nating equipment will need to re-establish the com-
plete framing process, and the algorithm is reset.
detected resulting in a loss of basic frame align-
ment as described in ITU Rec. G.706 Section
4.3.2.
CRC-4 mode.
TFRA08C13 OCTAL T1/E1 Framer
53