3Com 3C63400-3AC-C - PathBuilder S700 Switch, Справочное руководство

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94 C
HAPTER
4: P
ATH
B
UILDER
S700 M
ODULE AND
A
PPLICATION
O
VERVIEW
Figure 57 DS1 Unstructured Tunneling
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
ATM Network
Data
Service
Unit
Channel
Service
Unit
Data
Service
Unit
Channel
Service
Unit
T1
Unstructured
DS1 Signal Tunneled Through a PVC
PathBuilder S700 PathBuilder S700
FEC for SN/CSI
Lost Cell
Detection
Clock Recovery
A/D Converter
AAL Layer
ATM Layer
47 Bytes 1 Bit 3 Bits 4 Bits
CSI SC SNP
SAR-SDU
ATM Header AAL 1 Data
5 Bytes 48 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
DS0 DS0 BLANK A & B
Signaling
Structured DS1
DS1 Frame
Unstructured DS1
SAR
AAL 1
VCC