XRT86L30
SINGLE T1/E1/J1 FRAMER/LIU COMBO
14.0 APPENDIX A: DS-1/E1 FRAMING FORMATS
REV. 1.0.1
14.1
The E1 Framing Structure
A single E1 frame consists of 256 bits which is created 8000 times per second. This yields a bit-rate of
2.048Mbps. The 256 bits within each E1 frame are grouped into 32 octets or timeslots. These timeslots are
numbered from 0 to 31. Each timeslot is 8 bits in length and is transmitted most significant bit first, numbered
bit 0. Figure 107 presents a diagram of a single E1 frame.
FIGURE 107. SINGLE E1 FRAME DIAGRAM
E1 Frame
Timeslot 0
Timeslot 1
Timeslot 29
Timeslot 30
Timeslot 31
0
1
2
3
4
5
6
7
Not all of these timeslots are available to transmit voice or user data. For instance, timeslot 0 is always reserved for
system use and timeslot 16 is sometimes used (reserved) by the system. Hence, within each E1 frame, either 30
or 31 of the 32 timeslots are available for transporting user or voice data. In general, there are two types of E1
frames, FAS and Non-FAS. In any E1 data stream, the E1 frame begins with a FAS frame followed by Non-
FAS frame and then alternates between the two.
14.1.1
FAS Frame
Timeslot 0 within the FAS E1 frame contains a framing alignment pattern and therefore supports framing. The
bit-format of timeslot 0 is presented in Table 175. The Si bit within the FAS E1 Frame typically carries the
results of a CRC-4 calculation. The fixed framing pattern (e.g., 0, 0, 1, 1, 0, 1, 1) will be used by the Receive
E1 Framer at the Remote terminal for frame synchronization/alignment purposes.
TABLE 175: BIT
F
ORMAT OF TIMESLOT 0 OCTET WITHIN A FAS E1 FRAME
B
IT
0
1
2
3
4
5
6
7
Value
SI
0
0
1
1
0
1
1
Function
International Bit
Frame Alignment Signaling (FAS) Pattern
Description- In practice, the Si bit within the FAS E1 Frame carries the The fixed framing pattern (e.g., 0, 0, 1, 1, 0, 1, 1)
Operation results of a CRC-4 calculation, which is discussed in
greater detail in Section 14.2.1.
is used by the Receive E1 Framer at the Remote
terminal for frame synchronization/alignment
purposes.
249
EXAR [ EXAR CORPORATION ]
