
XRT84L38
172
OCTAL T1/E1/J1 FRAMER
CAS Multi-frame
2.2.1
The CRC Multi-frame Structure
REV. 1.0.1
A CRC Multi-frame consists of 16 consecutive E1 frames, with the first of these frames being a FAS frame.
From a Frame Alignment point of view, the timeslot 0 octets of each of these E1 frames within the Multi-frame
are the most important 16 octets.
Table 32
presents the bit-format for all timeslot 0 octets within a 16 frame
CRC Multi-frame.
Table 32
has the CRC Multi-frame divided into 2 sub Multi-Frames. Sub-Multi-Frame 1 is designated as SMF1
and Sub-Multi-Frame 2 is designated as SMF2.
SMF1 consists of E1 frames 0 through 7 consisting of 4 FAS frames and 4 non-FAS frames.
There are two interesting things to note in
Table 32
. First, all of the bit-field 0 positions within each of the FAS
frames are designated as C1, C2, C3 and C4. These four bit-fields contain the CRC-4 values which has been
computed over the previous SMF. Hence, while the Transmit E1 Framer is assembling a given SMF, it
computes the CRC-4 value for that SMF and inserts these results into the C1 through C4 bit-fields within the
very next SMF. These CRC-4 values ultimately are used by the Remote Receive E3 Framer for error-detection
purposes.
N
OTE
:
This framing structure is referred to as a CRC Multi-Frame because it permits the remote receiving terminal to
locate and verify the CRC-4 bit-fields.
The second interesting thing to note regarding
Table 32
is that the bit-field 0 positions within each of the non-
FAS frames are of a fixed six (6) bit pattern: 0, 0, 1, 0, 1, 1; along with two bits, each designated at “E”. This six
bit pattern is referred to as the CRC Multi-Frame alignment pattern. This six-bit pattern will ultimately be used
by the Remote Receive E1 Framer for CRC Multi-Frame synchronization/alignment. Section discusses how
the Receive E1 Framer uses this 6-bit CRC Multi-frame alignment pattern for frame synchronization/alignment.
The "E" bits are used to indicate that the Local Receive E1 framer has detected errored sub-Multi-Frames.
2.2.2
CAS Multi-Frames and Channel Associated Signaling
T
ABLE
32: B
IT
F
ORMAT
OF
ALL
T
IMESLOT
0
OCTETS
WITHIN
A
CRC M
ULTI
-
FRAME
SMF
F
RAME
N
UMBER
0
1
B
IT
0
B
IT
1
B
IT
2
B
IT
3
B
IT
4
B
IT
5
B
IT
6
B
IT
7
1
C1
0
0
1
0
A
1
1
0
1
1
Sa4
Sa5
Sa6
Sa7
Sa8
2
3
C2
0
0
1
0
A
1
1
0
1
1
Sa4
Sa5
Sa6
Sa7
Sa8
4
5
C3
1
0
1
0
A
1
1
0
1
1
Sa4
Sa5
Sa6
Sa7
Sa8
6
7
C4
0
0
1
0
A
1
1
0
1
1
Sa4
Sa5
Sa6
Sa7
Sa8
2
8
9
C1
1
0
1
0
A
1
1
0
1
1
Sa4
Sa5
Sa6
Sa7
Sa8
10
11
C2
1
0
1
0
A
1
1
0
1
1
Sa4
Sa5
Sa6
Sa7
Sa8
12
C3
0
0
1
1
0
1
1
13
14
E
C4
1
0
A
0
Sa4
1
Sa5
1
Sa6
0
Sa7
1
Sa8
1
15
E
1
A
Sa4
Sa5
Sa6
Sa7
Sa8