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CCNP Practical Studies: Using DSL to Access a Central Site

Chapter Description

This sample chapter focuses on Digital Subscriber Line (DSL) technology, one of the most popular broadband access methods and a new topic on the CCNP exam.

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.

Figure 02Figure 8-2 Cisco 6160 DSLAM Chassis


You can install line cards of two or more different types in a single Cisco 6160 chassis. However, mixing different types of cards (Flexi ADSL, SDSL, and/or IDSL) on the same side of the chassis might result in decreased performance.

Basic Cisco 6160 DSLAM Configuration

In this section, you will learn all the necessary information to successfully configure the Cisco 6160 DSLAM.

Interface Numbering

Before you begin the configuration, it is important to know the interface numbering scheme used by the Cisco IOS software in the 6160. Interfaces whose names begin with ATM0 (ATM0/0, ATM0/1, and so forth) are NI-2 card WAN interfaces. ATM0/0 is the ATM switch's interface with the processor. There is no need to configure ATM0/0 unless you plan to use in-band management. ATM0/1 is the trunk port. ATM0/2 and ATM0/3, if present, are subtending interfaces.

Table 8-2 illustrates the interface numbering scheme for Cisco 6160 DSLAM.

Table 8-2 Cisco 6160 DSLAM Interface Numbering




The ATM switch's interface


Trunk interface




A = 1 to 34 (slot); B = 1 to 4 (port)


Management Ethernet port

As shown in Table 8-2, interfaces whose names begin with ATM1 through ATM34 are line card interfaces. Ethernet0/0 is the interface for the LAN that connects the Cisco 6160 to its management system. For line card interfaces, the number before the slash indicates the slot number. The number after the slash indicates the interface or port number. For example, ATM5/4 is port 4 in slot 5.

Configuring Line Cards

Before you can use the Flexicard, you need to configure a slot for a specific card type. Use this command:

slot slot# cardtype

slot# is the slot number; the range is 1 to 34. cardtype is the card type for which you want to configure the slot. You must indicate the type of card. To configure the Quad Flexicard in slot 1 to use DMT modulation, you would enter the following:

lab-6160(config)#slot 1 ATUC-4FLEXIDMT


You can use show hardware command to find out which cards are installed in the Cisco 6160 DSLAM.

Creating DSL Profiles

Except for a few dynamic operational modes, port configuration takes place through a configuration profile rather than by direct configuration. A profile is a named list of configuration parameters with a value assigned to each parameter. You can change the value of each parameter in the profile. To configure a subscriber, you need only attach the desired profile to that subscriber. When you change a parameter in a profile, you change the value of that parameter on all ports using that profile. If you want to change a single port or a subset of ports, you can copy the profile, change the desired parameters, and then assign the new profile to the desired ports. Multiple ports can share the same profile, but one port cannot have more than one profile. If you modify an existing profile, that change takes effect on every ADSL port linked to that profile.

Every port is attached to a special profile named "default" by default. You can modify the default profile (but not delete it). This is useful when you want to modify one or two default parameters and apply this to every port in the system (rather than creating a new profile with minor changes and attaching it to every port in the system).

When you create a profile, it inherits all the configuration settings of the default profile at the time of creation. If you subsequently modify the special profile default, the new changes to the default do not propagate to the previously created profiles.

To create a DSL profile, or to select an existing profile for modification, use the following command:

dsl-profile profile-name

To delete a DSL profile, use the following command:

no dsl-profile profile-name

In both examples, profile-name is the name of the profile you want to create, or an existing profile you want to delete or modify. To create a DSL profile called ccnp, you would enter the following:

lab-6160#configure terminal
lab-6160(config)#dsl-profile ccnp

After the DSL profiles are created, you can customize them with the following parameters:

  • Bit rate

  • DMT margin

  • Check bytes

  • Interleaving delay

  • Training mode

The following sections discuss these parameters in more detail.

Setting the Bit Rate

To set the maximum and minimum allowed bit rates for the fast-path and interleaved-path profile parameters, use the following command:

dmt bitrate max interleaved downstream dmt-bitrate upstream dmt-bitrate

dmt-bitrate is a multiple of 32 kbps. If you enter a nonmultiple of 32 kbps, the Cisco IOS software aborts the command.

In Example 8-1, the command sets the maximum interleaved-path bit rate of the ccnp profile to 8032 kbps downstream and 832 kbps upstream.

Example 8-1 Setting the Bit Rate

lab-6160#configure terminal
lab-6160(config)#dsl-profile ccnp
lab-6160(config-dsl-prof)#dmt bitrate interleaved-path downstream 8032
 upstream 832

Setting the Margins

To set upstream and downstream signal-to-noise ratio (SNR) DMT margins, use the following command:

dmt margin downstream dmt-margin upstream dmt-margin

dmt-margin is equal to the upstream and downstream SNR margins in decibels. Values must be nonnegative integers. The range is from 0 to 127 dB.


Research has shown that the optimum margins for DMT service are 6 dB downstream and 6 dB upstream.

In Example 8-2, the command sets the DMT SNR margins of the ccnp profile to 6 dB upstream and 3 dB downstream.

Example 8-2 Setting the Margin

lab-6160#configure terminal
lab-6160(config)#dsl-profile ccnp
lab-6160(config-dsl-prof)#dmt margin downstream 3 upstream 6

Setting Check Bytes

Check bytes are also called FEC bytes. They are added to the user data stream to improve error correction, but they slow performance. To set upstream and downstream check bytes, use the following command:

dmt check-bytes interleaved downstream bytes upstream bytes

bytes values can be 0, 2, 4, 6, 8, 10, 12, 14, and 16. The default is 16 in each direction.

In Example 8-3, the command sets the interleaved check bytes for the ccnp profile to 6 upstream and 12 downstream.

Example 8-3 Setting the Check Bytes

lab-6160#configure terminal
lab-6160(config)#dsl-profile ccnp
lab-6160(config-dsl-prof)#dmt check-bytes interleaved
downstream 12 upstream 6

Setting Interleaving Delay

To set the interleaving delay parameter, use this command:

dmt interleaving-delay downstream delay-in-_secs upstream delay-in-_secs

delay-in-μsecs specifies the interleaving delay in microseconds. The default value is 16000 microseconds in each direction. Allowable values are 0, 500, 1000, 2000, 4000, 8000, and 16000 microseconds.

In Example 8-4, the command sets the interleaving delay of the ccnp profile to 2000 microseconds downstream and 4000 microseconds upstream.

Example 8-4 Setting the Interleaving Delay

lab-6160#configure terminal
lab-6160(config)#dsl-profile ccnp
lab-6160(config-dsl-prof)#dmt interleaving-delay downstream 2000 upstream 4000

Setting the Training Mode

Two training modes are available—standard and quick. Standard train relates to a training procedure specified in ANSI standards document T1.413, which is considered the standards reference for DMT ADSL. Quick train, also called fast train, uses a vendor-specific training sequence that is shorter than the standard training sequence.

To modify the training mode in a DMT profile, use the following command:

dmt training-mode {standard / quick}

In Example 8-5, the command sets the ccnp profile's training mode to quick.

Example 8-5 Setting the Training Mode

lab-6160#configure terminal
lab-6160(config)#dsl-profile ccnp
lab-6160(config-dsl-prof)#dmt training-mode quick
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