Cisco 6200 - Manual (Page 9)

78-5296-02 10/02/98 Hardware Description
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Cisco 6200 User Guide 1-9
1.3 Network Trunk Cards (NTCs)
This section describes the OC-3c and STM-1 network trunk cards (NTCs). The NTC module resides
in slot 1 of the Cisco 6200 chassis.
1.3.1 What is the NTC OC-3?
The NTC is a service interface module that concentrates the data traffic from all Cisco 6200
subscriber ports and connects the node to a single trunk line from the service-providing ATM
network. This full-duplex channel unit carries data both downstream (to the subscriber) and
upstream (from the subscriber).
In Release 1, the trunk is a full-duplex OC-3c fiber optic channel. One OC-3c channel terminates at
a single NTC.
The OC3 NTC is available in both single-mode and multimode versions. Multimode fiber is
LED-driven and is designed for distances up to 2 kilometers (1.2 miles). Longer distances (up to
15 kilometers or 9.2 miles) require laser-driven single-mode fiber.
In the downstream direction, the OC3 NTC accepts ATM cells at the OC-3c rate (155.52 Mbps) and
adapts these cells to the Cisco 6200 internal bus.
The OC3 NTC also transmits upstream data back to the service provider via ATM on the OC-3c
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 chapter “Command Reference” for instructions
on using the command show dsl vcmap to display the VCIs assigned to a particular slot or port.
The OC3 NTC 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 OC3 NTC provides bidirectional adaptation between serial ATM cells within the OC-3c 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 1-5 shows how the three circuits interact.