XRT84L38 Datasheet, PDF (191/451 Pages) Exar Corporation – OCTAL T1/E1/J1 FRAMER

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XRT84L38
OCTAL T1/E1/J1 FRAMER
REV. 1.0.0
SMF
1
2
TABLE 32: BIT FORMAT OF ALL TIMESLOT 0 OCTETS WITHIN A CRC MULTI-FRAME
FRAME
NUMBER
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
BIT 0
C1
0
C2
0
C3
1
C4
0
C1
1
C2
1
C3
E
C4
E
BIT 1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
BIT 2
0
A
0
A
0
A
0
A
0
A
0
A
0
A
0
A
BIT 3
1
Sa4
1
Sa4
1
Sa4
1
Sa4
1
Sa4
1
Sa4
1
Sa4
1
Sa4
BIT 4
1
Sa5
1
Sa5
1
Sa5
1
Sa5
1
Sa5
1
Sa5
1
Sa5
1
Sa5
BIT 5
0
Sa6
0
Sa6
0
Sa6
0
Sa6
0
Sa6
0
Sa6
0
Sa6
0
Sa6
BIT 6
1
Sa7
1
Sa7
1
Sa7
1
Sa7
1
Sa7
1
Sa7
1
Sa7
1
Sa7
BIT 7
1
Sa8
1
Sa8
1
Sa8
1
Sa8
1
Sa8
1
Sa8
1
Sa8
1
Sa8
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 com-
putes 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 pur-
poses.
NOTE: 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
CAS Multi-Frames are only relevant if the user is using CAS or Channel Associated Signaling. If the user is im-
plementing Common Channel Signaling then the CAS Multi-Frame is not available. The exact role of CAS
Multi-Frames is discussed in some detail in the next section.
2.2.2.1 Channel Associated Signaling
If the user operates an E1 channel in Channel Associated Signaling (CAS) mode, then the timeslot 16 octets
within each E1 frame will be reserved for signaling. Such signaling would convey information such as On-Hook,
Off-Hook conditions, call set-up, control, etc. In CAS, this type of signaling data that is associated with a partic-
ular voice channel will be carried within timeslot 16 of a particular E1 frame within a CAS Multi-Frame.
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