3Com 3C63400-3AC-C - PathBuilder S700 Switch Reference Manual page 108

94 C 4: P B
HAPTER ATH UILDER
Data
Service
Unit
Channel
Service
Unit
S700 M A
ODULE AND PPLICATION
Figure 57 DS1 Unstructured Tunneling
T1
Unstructured
DS1 Signal Tunneled Through a PVC
Use unstructured services when DS0 midspan access is not required and end to
end DS1 service is required, for example to provide CSU or DSU end to end
connectivity. The encapsulation of unstructured DS1 occupies DS1 bandwidth on
the VCC and uses AAL 1 SAR, as shown in Figure 58.
Figure 58 AAL1 Unstructured DS1
FEC for SN/CSI
Lost Cell
Detection
Clock Recovery
ATM Header
AAL 1
VCC
5 Bytes
CSI - Convergence Sublayer Indicator
FEC - Forward Error Correction
SNP - Sequence Number Protection
SC - Sequence Count
SAR - SDU - Segmentation and Reassembly Service Data Unit
VCC - V irtual Channel Connection
O
VERVIEW
ATM Network
Unstructured DS1
DS1 Frame
Structured DS1
DS0 DS0 BLANK A & B
CSI SC SNP
1 Bit 3 Bits 4 Bits
AAL 1 Data
48 Bytes
Data
Service
Unit
Channel
Service
Unit
Signaling
A/D Converter
SAR-SDU
AAL Layer
47 Bytes
ATM Layer
SAR