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1 Hardware Description 78-5296-02 10/02/98
Cisco 6200 User Guide1-14
The NTC STM-1 also transmits upstream data back to the service provider via ATM on the STM-1
physical layer.
The Cisco 6200 uses a fixed mapping of permanent virtual channels (PVCs) between trunk and
subscriber ports. This means that no configuration of these circuits is required. Thirty-one PVCs link
each subscriber port to the trunk port on the NTC. These subscriber traffic PVCs are assigned virtual
channel identifiers (VCIs) 33 through 63. VCIs 0 through 31 are reserved for control traffic. All of
these VCs use virtual path identifier (VPI) 0. See the Cisco 6200 User Guide for instructions on
using the command show dsl vcmap to display the VCIs assigned to a particular slot or port.
The NTC STM-1 collects ATM cell counts, which are accessible through the 6200 Management
Information Base (MIB). These cell count include:
• Number of nonidle cells transmitted upstream
• Number of nonidle downstream cells received with good or correctable header checksums
• Number of downstream cells received with uncorrectable header checksums
The NTC STM-1 provides bidirectional adaptation between serial ATM cells within the STM-1 fiber
and the 16-bit-parallel format on the backplane’s 160-Mbps H-bus. Three basic circuits perform this
adaptation process:
• Optical interface
• Upstream data transfer
• Downstream data transfer
Figure 1-7 shows how the three circuits interact.
Figure 1-7 NTC STM-1 Application
The optical interface performs the optical-to-electrical and electrical-to-optical conversions. Its
other tasks include clock recovery, cell delineation, and diagnostic information retrieval.
Cisco
6200
NTC
14270
ATM on
STM-1
Optical
interface
Downstream
data
transfer
Upstream
data
transfer
Line
module