Fast Path Support for Quad-Port Flexi ATU-C Line Cards

Feature Overview

Benefits

Fast Path Support for Quad-Port Flexi ATU-C Line Cards

July 17, 2002

This feature module describes the Cisco IOS support for configuring either fast or interleave DMT paths on the quad-port flexi ATU-C (4xflexi, part number ATUC-4-FLX) line card. It includes information on new and modified commands.

This document includes the following sections:

Feature Overview

The fast path feature allows you to configure either the fast or the interleave DMT path via DSL profile configuration commands. Prior to Cisco IOS Release 12.1(5)DA, the operation of all supported DMT line cards was limited to use of the interleave path. Cisco IOS Release 12.1(5)DA supports the use of either the interleave or fast DMT paths with the 4xflexi-DMT line card provided that the CPE also supports fast path. The fast path provides improved latency characteristics for applications that cannot tolerate latency (for example, voice).

The parameters for either path are configurable using the DSL profile configuration commands. Note that while you can configure both paths, only one path will actually be enabled (dual latency is not supported at this time). Thus the maximum bit rates for the unused path must be zero. For example, to configure and use the fast path, you must specify nonzero maximum bit rates for the fast path. Once you configure the maximum bit rates for the fast path, the rates for the interleave path must be zero. The IOS software ensures that only one path is enabled at a given time.

Benefits

This section describes the benefits of the fast path feature.

This feature allows you to configure either the fast or interleaved DMT path for each flexi-DMT port.
For the fast path operation, downstream bit swapping is enabled. This helps improve line quality on certain loops when running the fast path.

Supported Platforms

This feature is supported on all NI-2 based systems (Cisco 6015, Cisco 6160, and Cisco 6260) that support the quad-port flexi ATU-C line card (4xflexi) with IOS Release 12.1(5)DA or later.

Supported Standards, MIBs, and RFCs

Standards

ANSI T1.413-1995—Network and Customer Installation Interfaces—Asymmetric Digital Subscriber Line (ADSL) Metallic Interfaces

MIBs

To obtain lists of MIBs supported by platform and Cisco IOS release and to download MIB modules, go to the Cisco MIB web site on Cisco Connection Online (CCO) at http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml.

RFCs

RFC 1695
RFC 2662

Configuration Tasks

Changing the DSL profile is the only configuration task for this feature. To reconfigure the DSL profile, follow this procedure.

Caution Before migrating from interleave mode to fast path, determine whether the deployed CPEs offer support for the feature. The Cisco 600 series CPEs currently do not support fast path.

	Command	Purpose
Step 1	`DSLAM> enable Password: <password> DSLAM#`	Enter enable mode. Enter the password. You have entered enable mode when the prompt changes to `DSLAM#`.
Step 2	`DSLAM# configure terminal`	Enter global configuration mode. You have entered global configuration mode when the prompt changes to `DSLAM (config)#`.
Step 3	`DSLAM(config)# dsl-profile test`	Select the profile that you want to attach to the selected port. Test is a profile name used as anexample.
Step 4	`DSLAM(config-dsl-profile)#dmt bitrate maximum fast downstream 8032 upstream 640`	Allow 640 kbps upstream and 8032kbpsdownstream.
Step 5	`DSLAM(config-dsl-prof)# exit`	Return to enable mode when you finish configuring interfaces.

Verifying the DSL Profile

After configuring the new DSL profile, you can perform the following tests to verify that the new profile is operating correctly.

Step 1 Enter the show dsl profile command to display the DSL profile that you changed.

Step 2 Enter the show dsl interface atm command to show the status of a port.

Configuration Example

The following example shows a profile named test being created. The profile uses the default profile values for any parameters not specified.

fxp_6160#configure terminal

fxp_6160(config)#dsl-profile test

fxp_6160(cfg-dsl-profile)#dmt bitrate maximum fast downstream 8032 upstream 640

warning: Interleave path has been disabled with max rates set to 0 kbps
fxp_6160(cfg-dsl-profile)#exit
 
fxp_6160#show dsl profile test

 
01:04:08: %SYS-5-CONFIG_I: Configured from console by console
fxp_6160#show dsl profile test
 
dsl profile test:
      Alarms Enabled: NO
      ATM Payload Scrambling: Enabled
 
 DMT profile parameters
      Maximum Bitrates:
         Interleave Path:   downstream:     0 kb/s,   upstream:     0 kb/s
         Fast Path:         downstream:  8032 kb/s,   upstream:   640 kb/s
      Minimum Bitrates:
         Interleave Path:   downstream:     0 kb/s,   upstream:     0 kb/s
         Fast Path:         downstream:     0 kb/s,   upstream:     0 kb/s
      Margin:               downstream:     6 dB,     upstream:     6 dB
      Interleaving Delay:   downstream: 0 usecs,  upstream: 0 usecs
      Check Bytes (FEC):
         Interleave Path:   downstream:    16,        upstream:    16
         Fast Path:         downstream:     0,        upstream:     0
      R-S Codeword Size:    downstream:  auto,        upstream:  auto
      Trellis Coding:         Disabled
      Overhead Framing:       Mode 3
      Operating Mode:         Automatic
      Training Mode:          Quick
 
 SDSL profile parameters
      Maximum Bitrates: 784 kbps
 
 CAP profile parameters
      Maximum Bitrates:     downstream:   640 kb/s,   upstream:    91 kb/s
      Minimum Bitrates:     downstream:     0 kb/s,   upstream:     0 kb/s
      Margin:               downstream:     3 dB,     upstream:     6 dB
      PSDM:                 downstream:   -40 dBm/Hz, upstream:   -38 dBm/Hz
      Interleaving Delay:     Long (Reed-Solomon enabled)
      136K Baud DS Rates:     Enabled
      68K Baud US Rates:      Disabled
      17K Baud US Rates:      Disabled
      CPE Signature:          0
 
 IDSL profile parameters
      Bitrate:              128 kbit/sec
      Encapsulation:        llc-ppp
      Frame Relay parameters:
         UPC intent:           pass
         Bc default:           32768 bytes
         LMI type:             cisco
         lmi-n392dce:          2 events
         lmi-n393dce:          2 events
         lmi-t392dce:          15 seconds

Command Reference

This section documents the new and modified commands that are specific to the fast path feature. All other commands used with this feature are documented in the Command Reference for Cisco DSLAMS with NI-2 document. For information on other Cisco IOS commands that can be used on the NI-2 DSL systems, see the Cisco ATM Switch Router Command Reference Guide.

dmt bitrate

To set the maximum and minimum allowed bit rates for the fast or interleaved DMT profile parameters, use the dmt-bitrate profile configuration command. To reset this command to the default value, use the no form of this command.

dmt bitrate maximum {fast | interleaved} downstream dmt-bitrate upstream dmt-bitrate

dmt bitrate minimum {fast | interleaved} downstream dmt-bitrate upstream dmt-bitrate

Syntax Description


dmt-bitrate	The DMT bit rate is given as a multiple of 32 kbps. If you enter a nonmultiple of 32 kbps, the system rejects and aborts the command. See the allowed ranges and default values in Usage Guidelines.
fast	Specify the DMT fast latency path.
interleaved	Specify the DMT interleaved latency path.

Defaults

The default no dmt bitrate maximum interleaved sets the maximum downstream and upstream interleaved bitrate to 640 and 128 kbps respectively. This command causes the port to retrain.
The default no dmt bitrate maximum fast sets both the maximum downstream and upstream fastpath bitrate to zero. This command causes the port to retrain.
The default no dmt bitrate minimum interleaved sets both the minimum downstream and upstream interleaved bitrates to zero. This command does not cause the port to retrain.
The default no dmt bitrate minimum fast sets both the minimum downstream and upstream fastpath bitrate to zero. This command does not cause the port to retrain.

Command Modes

Profile configuration.

Command History


Release	Modification
12.0(5)DA	This command was introduced in a previous release.
12.1(5)DA	The fast keyword was added.

Usage Guidelines

Only the alarm subsystem uses the minimum bitrate settings. Cisco IOS asserts an alarm if the line card trains at a rate below the configured minimum bitrate. However, no alarm is generated when alarms are disabled. See alarms in the Command Reference for Cisco DSLAMS with NI-2, for more information on enabling and disabling alarms.

If alarms are enabled for the profile, setting the DMT bit rate to 0 disables the associated minimum DMT bit rate alarm.

Table 1 lists the allowable DMT bit rate ranges and default values.

Table 1: Allowable Ranges and Default Values for DMT Bit Rates

		Downstream		Upstream
Configuration Parameter	Data Path	Path Range (kbps)	Path Default (kbps)	Path Range (kbps)	Path Default (kbps)
dmt bitrate max	fast	8032 to 32	0	864 to 0	0
dmt bitrate min	fast	8032 to 0	0	864 to 0	0
dmt bitrate max	Interleaved	8032 to 32	640	864 to 0	128
dmt bitrate min	Interleaved	8032 to 0	0	864 to 0	0

Caution When you change the value of the bit rate parameter, the dmt bitrate command causes the port to retrain.

Setting a parameter to its current value does not cause a retrain. If a port is training when you change the parameter, the port untrains and retrains to the new parameter.

Examples

In this example, the command sets the maximum fast bit rate of the default profile to 8032 kbps downstream and 864 kbps upstream.

DSLAM# configure terminal

DSLAM(config)# dsl-profile default

DSLAM(config-dsl-prof)# dmt bitrate maximum fast downstream 8032 upstream 864

In this example, the command sets the maximum interleaved bit rate of the default profile to 3200 kbps downstream and 640 kbps upstream:

DSLAM# configure terminal

DSLAM(config)# dsl-profile default

DSLAM(config-dsl-prof)# dmt bitrate maximum interleaved downstream 3200 upstream 640

Related Commands


Command	Description
show dsl profile	Display a specific profile, all ports to which the profile is currently attached, and those port settings.

Glossary

C
CBOS	Cisco Broadband Operating System. An operating system that users access to configure and operate Cisco products.
CCO	Cisco Connection Online.
chassis	The card cage (housing) where modules are placed.
Cisco Connection Online	See CCO.

D
DDTS	Cisco Distributed Defect Tracking System.
digital signal level 3	See DS3.
Distributed Defect Tracking System	See DDTS.
DMT	Discrete Multitone.
downstream rate	The line rate for return messages or data transfers from the network machine to the user's CPE.
DS3	digital signal level 3. A framing specification used for transmitting digital signals at 44.736 Mbps on a T3 facility.
DSL	Digital Subscriber Line.
DSLAM	Digital Subscriber Line Access Multiplexer. Concentrates and multiplexes digital subscriber line signals at the telephone service provider location to the broadband wide area network. Replaces ADSLAM.

G
g.832 ADM	ITU-T framing standard that defines the mapping of ATM cells into the physical medium.

I
IP	Internet Protocol. The network layer protocol for the Internet Protocol suite.
IP address	The 32-bit address assigned to hosts that want to participate in a TCP/IP Internet connection.

M
Management Information Base	See MIB.
MIB	Management Information Base. A collection of objects that can be accessed via a network management protocol, such as SNMP and CMIP (Common Management Information Protocol).

N
NI-2	A second generation network interface card.

O
OC-3	optical carrier level 3. Physical protocol, defined for SONET optical signal transmissions.

S
Simple Network Management Protocol	See SNMP.
slot	A numbered location within a chassis, which is capable of housing a module.
SNMP	Simple Network Management Protocol. The network management protocol of choice for TCP/IP-based internet connections.

U
UNI	User-Network Interface.
UNI signaling	User-Network Interface signaling for ATM communications.
upstream rate	The line rate for message or data transfer from the source machine to a destination machine on the network. Also see downstream rate.

V
VC	virtual circuit. A logical circuit created to ensure reliable communication between two network devices. A virtual circuit is defined by a VPI/VCI pair, and can be either permanent (PVC) or switched (SVC). In ATM, a virtual circuit is called a virtual channel. Sometimes abbreviated VC.
virtual circuit	See VC.
VPI	virtual path identifier. An 8-bit field in the header of an ATM cell. The VPI, together with the VCI, is used to identify the next destination of a cell as it passes through the network. See also VCI.

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