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Cisco 6160 DSLAM Overview 179

Other sources of interference include the following:

• Impedance changes

• Bridged taps

• Crosstalk

• Impulse hits

Techniques to Solve Interference

Several techniques exist for adjusting to interference:

• Rate-Adaptive DSL (RADSL)—Used to adjust the transmission rate.

• Reed-Solomon Forward Error Correction (FEC)—The process of correcting errors

mathematically at the receiving end of a transmission path rather than calling for a

retransmission.

• Bit interleaving—Used to avoid having consecutive errors delivered to the FEC

algorithm at the receiving end of the circuit.

• Trellis coding—A modulation error-correction technique to improve error performance

during reception.

Cisco 6160 DSLAM Overview

This section provides an overview of the Cisco 6160 DSLAM system and hardware components

and discusses basic Cisco DSLAM conﬁguration.

System and Hardware Components

The Cisco 6160 can be operated as a carrier class DSLAM with ADSL, SDSL, and Integrated

Services Digital Network DSL (IDSL) interfaces. The Cisco 6160 is intended for use in North

American central ofﬁce facilities. The Cisco 6160 DSLAM can support up to 256 subscribers

and concentrate trafﬁc onto a single high-speed WAN trunk.

Examine Figure 8-2. The chassis has 32 short slots for line cards and two double-length slots

for Network Interface (NI-2) cards. Slots 10 and 11 hold the NI-2 cards. Slots 1 to 9 and 12 to 34

hold the line cards. Some of the essential functions the NI-2 card provides are ATM switching,

WAN interface, and subtending.

WAN interfaces can be either OC-3c or DS3 and can be used for trunking or subtending.

Subtending allows up to 12 other chassis to be subtended to a single host DSLAM system,

aggregating the subtended systems through a single network uplink.

DSL line cards come in several varieties. In this chapter, the Quad Flexicard is used. It supports

four ADSL connections and can be conﬁgured with CAP, DMT2, or G.lite line coding.

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