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System Processes and Performance with a Direct Connect Configuration

System Processes and Performance with a Direct Connect Configuration

This chapter describes basic system processes and the performance metrics that are captured as a result of these system processes in a Direct Connect configuration.

This chapter includes the following sections:

Overview and Purpose

System processes and performance monitoring are managed in ViewRunner for HP OpenView from the 6100 Chassis View dialog box. A right click anywhere on the chassis view allows you to view the following information:

You can access the status or configuration information to monitor the performance of any Cisco 6100 Series entity.

Bit Error Rate and Noise Margin

Bit error rate and noise margin are primary factors in achieving subscriber-designated parameters. SDSL and ADSL transceivers seek an upstream and downstream data rate that can be maintained as long as the amount of line noise does not cause a bit error rate (BER) in excess of 1 x 10-7. Line noise is a function of reach and disturbers. As reach or noise in the loop increases, upstream and downstream payload rates decrease. Also, the thinner the copper wire, the more susceptible it is to noise. Line noise is not constant, and a certain amount of line noise fluctuation does not significantly affect the trained rates. Line noise fluctuation is known as the noise margin. The noise margin must be supplied to the transceivers when you use the multiband method of training.

The SDSL Connection Process

SDSL transmission unit - central office (STU-C) modules are designed to operate within narrow parameters. These parameters use a relatively low baud rate 1 Mbps of upstream and 1 Mbps of downstream, and a fixed baud rate of 8 kbps with 16-point constellations. Such a reduction from the ADSL transmission unit-central office (ATU-C) 7 Mbps downstream and 1.5 Mbps upstream rates presents the end user, usually a single office/home office (SOHO) subscriber, with less cost and less transport capacity.

Configuring an STU-C module is similar to configuring an ATU-C module.

SDSL Upstream and Downstream Bit Rates

The STU-C module upstream and downstream rates are the same. They range from 144 kbps to 1168 kbps. The following seven rates are the fixed upstream and downstream rates for the STU-C module:

The baud rate is fixed at 8 kbps. You determine bit rates based on the number of carriers and the number of bits per carrier.

Note The STU-C module is supported by the Cisco 6130 system only.

STU-C Module Training Rates

If you are familiar with training ATU-C modules, you may notice the extended training time needed for STU-C modules. STU-C modules require at least 35 seconds to train and can take up to 3 minutes. This time frame contrasts with the 60 seconds or less that an ATU-C module needs to train.

STU-C Module Training Parameters

This section describes the trained line attributes such as receive signal quality, receiver gain, and transmit power where it applies to noise margins on the Cisco 6100 Series systems. Each of these trained line attributes displays in ViewRunner on the STU-C Module Properties dialog box Port Status tab.

As a Cisco 6100 Series system operator, you can change the noise margin (upstream and downstream) on an STU-C module for each subscriber line. Increasing this margin could cause a line that trained previously to fail to train. When you attempt to increase noise margins, ViewRunner issues a warning message that is similar to the following warning script:

Warning: Increasing noise margin could reduce the reach for a given data rate, or reduce the achievable data rate for a given reach. In some cases, it may prevent the line from training at all. Please consult product documentation for more information.

Figure 6-1 shows an STU-C Module Properties dialog box with a Service State of In Service. The various train parameters are identified in this dialog box. See the ViewRunner for HP OpenView User Guide for more information on the fields represented in this dialog box.


Figure 6-1: STU-C Module Properties Dialog Box---In Service


The ADSL Connection Process

The Carrierless Amplitude and Phase Modulation (CAP) rate-adaptive DSL (RADSL) transceivers in the Cisco ATU-Cs and ATU-Rs can train at a number of discrete settings within each of three baud rate ranges. Because the upstream and downstream data paths transmit in different frequencies, they train independently.

The transceivers in the Cisco Discrete Multi-Tone---Issue 2 (DMT-2) ATU-C modules train at one of two settings within the fixed baud rate. DMT-2 refers to the use of a single or discrete frequency. Both upstream and downstream are transmitted on the same frequency and trained in tandem.

Payload Transmission Rates

Payload data represents transmitted information that is useful to the customer, but may also include additional information such as user-requested network management and accounting information. Upstream and downstream payloads transmit in different frequency ranges; therefore, the two payload rates are established independently. Layer 2 protocol data units (PDUs) are encoded into Layer 1 (xDSL) transmission frequencies through baud rates (also known as symbol rates) and constellations. You can set different baud rates to achieve different payload rates.

DMT-2 transceivers support upstream payload rates ranging from 864 kbps to 32 kbps, and downstream payload rates ranging from 8032 kbps to 32 kbps.

CAP RADSL transceivers support one baud rate to establish upstream payload rate (136 kilobaud) and three baud rates to establish downstream payload rate (340, 680, and 952 kilobaud). These baud rates enable CAP RADSL implementations to support downstream payload rates that range from 7168 kbps to 640 kbps, and upstream data rates that range from 1088 kbps to 91 kbps.

Modifying Noise Margins

You can modify the noise margins for a subscriber line. If you set a new noise margin, a line that was training successfully might not train after you set a new margin. ViewRunner alerts you to use caution when you change the margin.

Cisco recommends that you set the margin for 6 dB upstream and 3 dB downstream to provide optimal performance. The default values for noise margin are 0 upstream and 0 downstream.

Cisco DMT-2 ATU-C module functionality supports several training options that measure and regulate subscriber traffic. You can configure these options on the Subscriber Properties DMT-2 dialog box.

DMT-2 Training Rates and Modes

DMT-2 transceivers support the following training rates:

The training mode that features the StandardTrain option supports Direct Connect lines only, specifically DMT-2 ATU-C modules. You use one setting for both the upstream and downstream rates. One option is available for the training mode, StandardTrain, which is the default.

The error message, "Reference Source Not Found," displays when ViewRunner finds a module that is incompatible with the baud rates that you have set.

CAP RADSL Training Rates

CAP RADSL transceivers support the following training rates:

These baud rates enable CAP RADSL implementations to support the following rates:

Within each baud rate range, transceivers use constellations to encode data into a frequency spectrum, and subsequently enable the discrete payload options shown in Table 6-1 and Table 6-2.

Cisco's CAP RADSL implementation supports a number of ADSL training options that you can use to control subscriber traffic. See the following section, "CAP RADSL Upstream and Downstream Constellation Combinations" for an overview of the training process.

CAP RADSL Upstream and Downstream Constellation Combinations

The concept of constellation combinations refers to the way discrete subscriber line chip sets communicate with each other. Different constellations provide different levels of data transmission accuracy.

Valid CAP RADSL constellations include 256 UC, 256, 128, 64, 32, 16, 8, and 8 extended range (er). The 128, 32, 8, and 8er constellations are not supported with downstream baud rates of 952 and 680. Because of this, some upstream-downstream payload combinations cannot be achieved.

Table 6-1 shows valid upstream and downstream constellation combinations.


Table 6-1: CAP RADSL Upstream and Downstream Constellation Combinations
Upstream

Kilobaud

136

136

136

136

136

136

136

136

Constellation

256UC

256

128

64

32

16

8

8er

Kilobaud

Const

Payload

1088

952

816

680

544

408

272

91

952

256UC

7168

X

X

X

X

D o w n s t r e a m

952

256

6272

X

X

X

X

952

64

4480

X

X

X

X

952

16

2688

X

X

X

X

680

256UC

5120

X

X

X

X

680

256

4480

X

X

X

X

680

64

3200

X

X

X

X

680

16

1920

X

X

X

X

340

256UC

2560

X

X

X

X

X

X

X

X

340

256

2240

X

X

X

X

X

X

X

X

340

128

1920

X

X

X

X

X

X

X

X

340

64

1600

X

X

X

X

X

X

X

X

340

32

1280

X

X

X

X

X

X

X

X

340

16

960

X

X

X

X

X

X

X

X

340

8

640

X

X

X

X

X

X

X

X

136

256UC

1024

X

X

X

X

X

X

X

136

256

896

X

X

X

X

X

X

X

136

128

768

X

X

X

X

X

X

X

136

64

640

X

X

X

X

X

X

X

136

32

512

X

X

X

X

X

X

X

136

16

384

X

X

X

X

X

X

X

136

8

256

X

X

X

X

X

X

X

Two entries in Table 6-1 represent the downstream rate for a payload of 4480 kbps:

The 680 kilobaud rate with a 256 constellation is the Cisco 6100 Series system and Cisco 675 default for achieving a payload rate of 4480 kbps. This rate combination supports a slightly better reach, according to 24-ISDN NEXT disturbers.

Table 6-1 also includes two entries in the downstream column for a payload of 1920 kbps:

The 340 kilobaud with a 128 constellation is the Cisco 6100 Series system and Cisco 675 default for achieving the payload rate of 1920 kbps. This rate combination is compatible with any of the upstream data rate selections. The 680 kilobaud option is limited to the 1088, 952, 680, or 408 kbps upstream payload.

CAP modules support 136-kilobaud training rates, which can be allowed or disallowed when the system controller module software supports this feature and the subscriber is locked.

If the system controller module supports per-subscriber provisionable 136 kilobaud or does not support ATUCPARMS, the Allow 136K Baud toggle in the Cisco 6100 Series Properties dialog box is disabled. If the system controller module supports ATUCPARMS, but does not support per-subscriber 136 kilobaud, the toggle is enabled.

The valid upstream and downstream rates shown in Table 6-2 somewhat simplify data rate selection.

.
Table 6-2: Valid Rate Combinations for Upstream and Downstream Rates
Upstream Rate (kbps)
Downstream Rate (kbps) 1088 952 816 680 544 408 272 91

7168

X1

X

X

X

6272

X

X

X

X

5120

X

X

X

X

4480

X

X

X

X

3200

X

X

X

X

2688

X

X

X

X

2560

X

X

X

X

X

X

X

X

2240

X

X

X

X

X

X

X

X

1920

X

X

X

X

X

X

X

X

1600

X

X

X

X

X

X

X

X

1280

X

X

X

X

X

X

X

X

1024

X

X

X

X

X

X

X

960

X

X

X

X

X

X

X

X

896

X

X

X

X

X

X

X

768

X

X

X

X

X

X

X

640

X

X

X

X

X

X

X

X

512

X

X

X

X

X

X

X

384

X

X

X

X

X

X

X

256

X

X

X

X

X

X

X

1x = valid, empty cell = invalid

The actual training procedure is a function of transceiver-controlled parameter exchange and algorithms designed by Cisco to place parameters around valid data rate selections from Table 6-2.

ADSL Training Process

The following guidelines apply to the ADSL training sequence:

This setting means that control of the downstream data rate is relinquished to the ATU-C module; that is, the ATU-C module controls the upstream data rate setting by default.

By using the preceding guidelines, the ATU-C module has complete control over upstream and downstream data rate selection. You can select valid upstream and downstream data rate combinations on the GUI. ViewRunner communicates these rates to the ATU-C module. This process is accomplished as follows:
Figure 6-2: Subscriber Properties Dialog Box---Choosing Data Rates



Figure 6-3: Module Properties Dialog Box---Data Rate Combination


ATU-C Module Training Parameters

This section describes the trained line attributes including receive signal quality, receiver gain, and transmit power, where applicable to noise margins on the Cisco 6100 Series systems. Each of these trained-line attributes displays in ViewRunner on the ATU-C Module Properties dialog box Port Status tab.

You can modify the noise margin (upstream and downstream) on an ATU-C module for each subscriber line, but if you increase this margin, a line that trained previously could fail to train. When you attempt to increase noise margins, ViewRunner issues an alert that is similar to the following message:

Warning: Increasing noise margin could reduce the reach for a given data rate, or reduce the achievable data rate for a given reach. In some cases, it may prevent the line from training at all. Please consult product documentation for more information.

Figure 6-4 shows a CAP ATU-C Module Properties dialog box in which a session is in progress (Service State field reads In Service). The various training parameters are identified on this dialog box. See the ViewRunner for HP OpenView User Guide for more information on the fields represented in this dialog box.


Figure 6-4: ATU-C Module Properties Dialog Box---In Service


Receive Signal Quality

The receive signal quality is a measure of the signal quality for the upstream channel (from the ATU-R, in the case of the Cisco 675). This value is represented in decibels.

Receiver Gain

Receiver gain is a measure of loop attenuation over the entire DSL frequency spectrum. The ATU-C or STU-C module uses an algorithm to boost receiver gain so that attenuation can be corrected for proper support of a given receive data rate.

The ATU-C or STU-C module algorithm attempts to keep gain to a minimum to prevent NEXT. However, if loop conditions warrant, the algorithm must boost gain enough to ensure that the required minimum signal level is received.

CAP modules support 136 kilobaud training rates, which you can allow or disallow when the system controller module software supports this feature and the subscriber is locked. If the system controller module supports per-subscriber provisionable 136 kilobaud or does not support ATUCPARMS, the Allow 136K Baud toggle in the Cisco 6100 Series Properties dialog box is disabled. If the system controller module supports ATUCPARMS, but does not support per-subscriber 136 kilobaud, the toggle is enabled.

Performance Train Counters Overview

The Cisco 6100 Series system includes the following train counters for capturing system performance statistics in a Direct Connect configuration:

ViewRunner uses counters to display individual subscriber and CAP ATU-C, DMT-2 ATU-C, and STU-C modem port statistics.

After the Cisco 6100/6130 establishes the connection, the training sequence begins that is described in the "ADSL Training Process" section.

If the CAP ATU-C, DMT-2 ATU-C, STU-C, and ATU-R modems train, a successful train counter increments for these modems. If the xTU-C modem and ATU-R modem fail to train, a failed train counter increments for the xTU-C modem. You can view train counter statistics on the Performance Management dialog box.

Getting Information about Subscriber Line Performance

The following sections describe how to get information about subscriber line performance from the Performance Management dialog box.

Using the Performance Management Dialog Box

To check the performance of an xTU-C module in a dedicated configuration, right-click the chassis to access the Chassis menu and choose 6100 Performance. The Performance Management dialog box for an xTU-C module opens, shown in Figure 6-5. The Performance Management dialog box has two top-level tabs, the xTUC tab and the Cell Counts tab.


Figure 6-5: Performance Management Dialog Box---xTU-C Ports Tab


Table 6-3 describes the Performance Management dialog box xTU-C Port tab fields and buttons.


Table 6-3: Performance Management Fields
Field Description

xTU-C Port

Lists the chassis, slot, and port number of an xTU-C module.

Successful Trains

Lists the number of times the associated module has trained successfully.

Failed Trains

Displays the number of times the associated module has failed to train successfully.

Port Statistics

The following line statistics display, at the bottom of the dialog box, showing the number of:

  • Line ports

  • Successful trains

  • Failed trains

  • Ports failing to train

If a module fails to train, you may have provisioned it incorrectly. See "Provisioning Subscribers for a Direct Connect Configuration," for more information on provisioning.

Viewing Training Data Graphically

To view training data graphically, you can select a line of the table for a DMT-2 ATU-C or CAP ATU-C module, and click on the Successful Trains or Failed Trains columns. Doing this displays a graphical representation of the bit allocation, signal-to-noise ratio, and receiver gain for that module. You can refresh the graph or close it by using the Refresh and Close buttons. The range of the training statistics that display is the same as that specified in the MIB.

Using the Cell Counts Tab

When you click the Cell Counts tab, two new tabs appear, the PVC tab and the ATM tab. You can get cell or packet count data by using these tabs, which are described in the following sections.

Checking PVC Performance Management

To monitor PVC performance, you use the Cell Counts PVC tab on the Performance Management dialog box, shown in Figure 6-6.


Figure 6-6: Performance Management Dialog Box Cell Counts---PVC Tab


Table 6-4 describes the fields and buttons on this dialog box.


Table 6-4: Cell Counts PVC Tab Field Descriptions

All PVCs group box

Lists the PVCs that are set up on the node. Displays the Subscriber ID, Subscriber VPI/VCI, and Network VPI/VCI assignments for each PVC.

Monitored PVCs group box

Lists the PVCs that are being monitored. Displays the Subscriber ID and the PVC, Subscriber Ingress, Subscriber Egress, Network Ingress, and Network Egress for each PVC. PVCs that are listed here do not show up in the All PVCs group box.

Add >> button

Use this button to move one PVC at a time to the Monitored PVCs group box when you want to monitor the performance of that PVC.

<< Del button

Use this button to delete a PVC from the Monitored PVCs group box. Doing this does not delete the PVC. It only removes that PVC from the performance monitoring area.

All >> button

Use this button to move all of the subscribers that are listed in the Subscriber ID column to the Monitored PVCs group box where you can monitor their performance.

<< All button

Use this button to move all of the PVCs in the Monitored PVCs group box out of that group box and returns them to the All PVCs group box.

Transit PVCs checkbox

Select this field to include transit PVCs.

Time since reset

Displays the approximate time in seconds (00:00:00) since the last counter reset.

Reset Counters button

Click this button to reset all counters in the Monitored PVCs group box to zero (0).

Refresh Counters button

Click this button to update line data after you click Reset Counters.

Steps for Monitoring PVC Performance

To check the PVC performance status for a subscriber line, you need to move that PVC from the All PVCs group box to the Monitored PVCs group box. Follow these steps:

Step 1 Click the Cell Counts tab and then click the PVC tab on the Performance Management dialog box.

Doing this opens the Cell Counts PVC tab, shown in Figure 6-6.

Step 2 Select the PVC whose performance you want to monitor; be sure to place your cursor on the Subscriber or Network VPI/VCI column.

Note If you click a PVC with your cursor in the Subscriber ID column, the Subscriber Properties dialog box for that subscriber opens. Therefore, click the PVC from either the Subscriber VPI/VCI column or the Network VPI/VCI column to move that PVC to the monitoring area.

Step 3 After you have clicked the PVC you want to monitor, click Add >>.

Doing this moves that PVC to the Monitored PVCs list. Under the Monitor PVCs group box columns, you can monitor subscriber-side and network-side channel transmissions to identify bottlenecks.

Initially, when you move a PVC to the Monitored PVCs list, the counters display a hyphen.

Step 4 Click Reset Counters to begin monitoring the performance of that PVC.

Doing this sets the base time and displays 00:00:00 in the Time since reset field. The counters are set to zero (0). When you click Reset Counters, the Refresh Counters button is enabled.

Step 5 Click Refresh Counters to display the difference in value since the time you reset the counters. The time displays in the Time since reset field.

Step 6 To monitor the PVC performance of all PVCs, click All >>.

Step 7 To remove a PVC from the Monitored PVCs list, highlight that PVC and click << Del.

Step 8 To remove all of the PVCs from the Monitored PVCs list, click << All.

Checking ATM Performance

To check the port status for subscribers who are using ATM, click the Cell Counts tab and then click the ATM tab on the Performance Management dialog box of an xTU-C module. Doing this opens the Cell Counts ATM tab, shown in Figure 6-7.


Figure 6-7: Performance Management Dialog Box---Cell Counts ATM Tab


Note Use the Reset Counters and Refresh Counters buttons as you use them on the Cell Counts PVC tab.

Table 6-5 describes the fields on the Cell Counts ATM tab.


Table 6-5: Performance Management Cell Count ATM Tab Fields
Field Description

Port Index

Displays the chassis slot number for the port whose performance management you are accessing.

Received Cell Count

Displays the number of cells being received.

Transmitted Cell Count

Displays the number of cells being transmitted.

Header Control Errors

Displays the number of errors accumulated in the header control.

Section Bit Interleave Parity

Displays interleave parity counts by section bits.

Line Far End Block Error

Displays far end block errors from the subscriber line.

Line Bit Interleaved Parity

Displays interleave parity counts by line bit.

Path Far End Block Error

Displays counts of far end block errors.

Path Bit Interleaved Parity

Displays interleaved parity by path bit.

Time since reset

Displays the time in seconds (00:00:00) since the last counter reset.

Reset Counters button

Click this button to reset all counters to zero (0).

Refresh Counters button

Click this button to update data after you click Reset Counters.

Current Connection Activity

Two current connection activity displays are provided.

These two connection displays are described in the following sections.

Module Properties Dialog Box Port Status Tab

For ATU-Cs or STU-Cs in a dedicated configuration, the Module Properties dialog box Port Status tab (Figure 6-8 and Figure 6-9) displays state information.


Figure 6-8: ATU-C Module Properties Dialog Box Port tab and Status tab



Figure 6-9: STU-C Module Properties Dialog Box Port tab and Status tab


Active Connections Dialog Box

The Active Connections dialog box lists data about all of the currently active connections in the Cisco 6100 Series system. To open the Active Connections dialog box, right-click the Cisco 6100/6130 chassis and select Active Connections from the menu. Figure 6-10 and Figure 6-11 present the Active Connections dialog box first in the far-left position, then scrolling right for the last figure.


Figure 6-10: Active Connections Dialog Box---Left Side



Figure 6-11: Active Connections Dialog Box---Right Side


You can use the logical, service-oriented navigation to go directly to an entity by clicking any blue hyperlink in the Active Connections dialog box.

Table 6-6 describes the columns on the Active Connections dialog box.


Table 6-6: Active Connections Columns
Column Description

Subscriber ID

Displays the identifier by which the subscriber is known.

ATU-C or STU-C Port

Displays the chassis, slot number, and port number to which the line port is connected.

Modem Status

Indicates whether the modem is trained or training.

Actual Up

Displays the actual upstream train rate at which the subscriber is training. This rate can never be higher than the value of the Provisioned Up column.

Actual Down

Displays the actual downstream train rate at which the subscriber is training. This rate can never be higher than the value of the Provisioned Down column.

Rx SNR

Signal-to-noise ratio for the ADSL upstream (receive side) data channel.

Provisioned Up

Displays the upstream rate set by the CO, the maximum upstream rate at which the subscriber can train.

Provisioned Down

Displays the downstream rate set by the CO, the maximum downstream rate at which the subscriber can train.

Provisioned Down Margin

Displays the downstream noise margin that the operator provisions.

Provisioned Up Margin

Displays the upstream noise margin that the operator provisions.

Actual Down Margin

Displays the downstream noise margin that is actually occurring within the margin that you have provisioned for the subscriber.

Actual Up Margin

Displays the upstream noise margin that is actually occurring within the margin that you have provisioned for the subscriber.

The Active Connections dialog box includes fields for provisioned upstream and downstream bit rates, actual trained upstream and downstream bit rates, and the received signal-to-noise ratio.


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Posted: Wed Feb 23 15:00:54 PST 2000
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