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90
C
4: P
B
HAPTER
ATH
UILDER
CBR Application
A
B
C
S700 M
A
ODULE AND
PPLICATION
The CBR module consists of 4 or 8 DSX-1/E1 interfaces capable of accepting
superframe or extended superframe DS1 inputs. The DS1 signal is then mapped
over a Constant Bit Rate (CBR) virtual channel. Encapsulation of the T1 within the
ATM service is based on the ATM Forum (AF-SAA-0032.000) Circuit Emulation
Service Interoperability specification. The ATM Forum specification designates two
modes of operation:
Structured —Modeled after fractional T1. Only the timeslots which will be used
are sent.
Unstructured —Merely encapsulates the entire DS1 onto an ATM path. It allows
timing and FDL to pass through.
Structured DS1
Implement the structured service if you require DS0 midspan drop-and-insert. See
Figure 52.
Figure 52 CBR Structured DS1
A
DS0 = 5
ATM DS1
A
Channel
Bank
DS0 = 5
ATM DS1
Channel
Bank
Channel bank converts analog signal to T1; putting voice channel on DS0 5.
PathBuilder S700 puts DS0 5 on virtual circuit (VP 0/VC 35) and passes structured CBR traffic through to
the ATM network.
ATM network continues to carry CBR traffic on to another ATM network or drops the traffic (on DS0 5) to
a public switched telephone network.
Midspan drop and insert allows services such as public switched telephone service
to be inserted into the ATM link. Combining this service with Ethernet bridge
service provides you with a complete integrated communications access solution.
See Figure 53.
O
VERVIEW
DS0 5 = VP 0/VC 35
Structured CBR traffic
DS0 5 = VP 0/VC 35
Structured CBR traffic
PathBuilder S700
PathBuilder S700
B
C
ATM Network
B
C
DS0 = 5
ATM Network
Public Switched
Telephone
Network
DS0 = 5
Public Switched
Telephone
Network
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