XRT86VL38
PRELIMINARY
xr
OCTAL T1/E1/J1 FRAMER/LIU COMBO
REV. P1.0.6
413
13.2
The E1 Multi-frame Structure
There are two types of E1 Multi-frame structures, CRC Multi-frame and CAS Multi-frame. The CAS Multi-
frame can be considered a subset of the CRC Multi-frame, in that CAS is an option to carry signaling
information within the CRC Multi-frame structure.
13.2.1
The CRC Multi-frame Structure
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, timeslot 0 of each of these E1 frames within the Multi-frame are the
most important 16 octets. Table 188 presents the bit-format for all timeslot 0 octets within a 16 frame CRC
Multi-frame.
The CRC Multi-frame is divided into 2 sub Multi-Frames. Sub-Multi-Frame 1 is designated as SMF1 and Sub-
Multi-Frame 2 is designated as SMF2. SMF1 and SMF2 each consist of 8 E1 frames having 4 FAS frames and
4 non-FAS frames. There are two interesting things to note in Table 188. First, all of the bit-field 0 positions
within each of the FAS frames (within each SMF) are designated as C1, C2, C3 and C4. These four bit-fields
contain the CRC-4 values which have 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 E1 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 188 is that the bit-field 0 positions within each of the non-
FAS frames (within the entire MF) are of a fixed 6-bit pattern 0, 0, 1, 0, 1, 1 along with two bits, each
designated as “E”. This 6-bit pattern is referred to as the CRC Multi-Frame alignment pattern, which can
ultimately be used by the Remote Receive E1 Framer for CRC Multi-Frame synchronization/alignment. The
"E" bits are used to indicate that the Local Receive E1 framer has detected errored sub-Multi-Frames.
T
ABLE
188: B
IT
F
ORMAT
OF
ALL
T
IMESLOT
0
OCTETS
WITHIN
A
CRC M
ULTI
-
FRAME
SMF
F
RAME
N
UMBER
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
0
C1
0
0
1
1
0
1
1
1
0
1
A
Sa4
Sa5
Sa6
Sa7
Sa8
2
C2
0
0
1
1
0
1
1
3
0
1
A
Sa4
Sa5
Sa6
Sa7
Sa8
4
C3
0
0
1
1
0
1
1
5
1
1
A
Sa4
Sa5
Sa6
Sa7
Sa8
6
C4
0
0
1
1
0
1
1
7
0
1
A
Sa4
Sa5
Sa6
Sa7
Sa8
2
8
C1
0
0
1
1
0
1
1
9
1
1
A
Sa4
Sa5
Sa6
Sa7
Sa8
10
C2
0
0
1
1
0
1
1
11
1
1
A
Sa4
Sa5
Sa6
Sa7
Sa8
12
C3
0
0
1
1
0
1
1
13
E
1
A
Sa4
Sa5
Sa6
Sa7
Sa8
14
C4
0
0
1
1
0
1
1
15
E
1
A
Sa4
Sa5
Sa6
Sa7
Sa8