Cisco 6200 User Manual page 27

78-5296-02 10/02/98
1.5.4 What is the SLC 8DMT?
The eight-port DMT version of the SLC (SLC 8DMT) is a hot-swappable line module that provides
data communication between the Cisco 6200 node and up to eight subscribers. Modems on the SLC
8DMT use discrete multitone (DMT) modulation, a common method for encoding asymmetric
digital subscriber line (ADSL) transmissions. The SLC 8DMT transmits high-speed data through an
external POTS splitter to subscribers over existing, telephone-grade segments of copper wire. Figure
1-12 illustrates SLC operation.
Figure 1-12
The SLC 8DMT transports data at speeds up to 8 Mbps downstream (from the service provider to
the subscriber) and receives at speeds up to 800 kbps upstream (from the subscriber to the service
provider). The SLC supports upstream and downstream passband channels for subscriber data.
Baseband plain old telephone service (POTS) is unused by the SLC; voice and data are added by the
external POTS splitter.
How the SLC 8DMT Handles Traffic
In the downstream direction, the SLC receives ATM cells from the Cisco 6200 backplane bus. The
cell filter discards cells whose virtual path/virtual channel IDs (VPI/VCIs) do not pertain to a
particular subscriber's channel. (Each port has a fixed set of 31 VCIs, numbered 33 to 63, which are
permanently assigned to VCIs on the NTC.) The cell filter buffers cells, and the DMT transceiver
transmits the outbound cells. The SLC sends the cells out to an external POTS splitter, which inserts
baseband POTS traffic (if any such traffic is provided) before sending the downstream ADSL and
POTS signals across standard unshielded twisted pair copper wire to the subscriber.
SLC 8DMT Operation
Contention
arbitration
NTC
ATM
Cisco
6200
Cell
filter
Port 1
DMT
and
transceiver
Port 2
Port 3
Port 8
Hardware Description
Public
telephone
network
SLC
POTS
splitter
POTS
splitter
Cisco 6200 User Guide
1
ADSL
modem
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