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CBR Module
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These frames are then followed by the ABCD bits of each active DS0. Two DS0’s
ABCD bits are provided in each byte after the last DS0 group. Figure 174 shows an
example of three DS0s and their ABCD bits sent in a structured encapsulation.
Figure 174
Multiframe Structure for 3x64kbit/s DS1 with CAS
Figure 175 illustrates AAL1 structured DS1.
Figure 175
AAL1 Structured DS1
AAL1 Pointer
First Transported Octet of Multiframe
Second Transported Octet of Multiframe
First 125 µsec Frame of Multiframe for
DS1
Second 125 µsec Frame of Multiframe for
DS1
Last 125 µsec Frame of Multiframe for
DS1
Signaling
Substructure
ABCD for Second
Transported Timeslot
ABCD for
Third
Transported
Timeslot
ABCD for
First
Transported
Timeslot
. . .
FEC for SN/CSI
Lost Cell
Detection
Clock Recovery
AAL Layer
ATM Layer
47 Bytes
1 Bit
3 Bits 4 Bits
CSI
SN
SNP
SAR-SDU
ATM Header
AAL 1 Data
5 Bytes
48 Bytes
CSI - Convergence Sublayer Indicator
FEC - Forward Error Correction
SNP - Sequence Number Protection
SN - Sequence Number
SAR - SDU - Segmentation and Reassembly Service Data Unit
VCC - V irtual Channel Connection
SAR
AAL 1
VCC