Task 2 Initiating and Inspecting a V90 Test Call

Before you let users dial in to the NAS, initiate and inspect a V.90 test call. V.90 call performance is heavily dependent upon the telco's network topology. There are many variables.

Most modem manufactures have unique AT command sets. The AT commands used in the following procedure might not be supported by your modem. For more information, see the following URLs:



Step 1 Locate a client PC, client modem, and an analog line. The following figure shows the network environment for this test.

Step 2 Test your RS-232 connection to the client modem:

Step 3 Verify that the modem is running the recommended firmware version. The following example shows a U.S. Robotics 56K fax external modem running V.4.11.2. Compare the firmware version with the version that is posted on the modem vendor's web site.

The Ati3 and ati7 modem firmware commands are commonly used and are shown below: ati3

U.S. Robotics 56K FAX EXT V4.11.2 OK


Configuration Profile.

Product type Product ID: Options Fax Options Line Options Clock Freq EPROM RAM

FLASH date FLASH rev

DSP date

DSP rev

US/Canada External 00568602

Class 1/Class 2.0

Caller ID, Distinctive Ring



Step 4 Verify that the modem is configured correctly. Enter the ati4 (USR) or at&v (Conexant) command. To reset the modem to the factory defaults, enter the at&f, at&fl, or at&f2 command.


U.S. Robotics 56K FAX EXT Settings...


&A1 &B1 &C1 &D2 &G0 &H0 &I0 &K0 &M4 &N0 &P0 &R1 &S0 &T5 &U0 &Y1

S00=000 S07=060 S15=0 0 0 S25=005 S33=000 S41=000

S01=000 S08=002 S16=000 S27=000 S34=000 S42=000

S02=043 S09=006 S18=000 S28=008 S35=000

S03=013 S10=014 S19=000 S29=020 S36=014

S04=010 S11=070 S21=010 S30=000 8=000

S05=008 S12=050 S22=017 S31=128 9=000

S06=002 S13=000 S23=019 S32=002 0=001

LAST DIALED #: T14085551234

Step 5 Dial the access server's telephone number, log in, and access the EXEC shell. The client modem is connected at 48000 bps in this example.

atdt14085551234 CONNECT 48000/ARQ

This is a secured device. Unauthorized use is prohibited by law.

User Access Verification



Step 6 Inspect your call on the access server. In the example, the call landed on TTY line 1. The call has been up for 36 seconds.

5300-NAS>show caller

Line tty 1

vty 0

User dude admin





Idle Time


00:02:29 00:02:16

5300-NAS>show caller

Note The show caller command is supported in Cisco IOS Release 11.3 AA and 12.0 T. Use the show user command if your software does not support the show caller command.

Step 7 Inspect the physical terminal line that received the call. In the example, the call landed on modem 1/0.

53 0 0-NAS>show terminal

Line 50, Location: "", Type: ""

Length: 24 lines, Width: 8 0 columns

Status: PSI Enabled, Ready, Active, No Exit Banner Capabilities: Hardware Flowcontrol In, Hardware Flowcontrol Out Modem Callout, Modem RI is CD, Line usable as async interface Integrated Modem Modem state: Ready modem(slot/port)=1/0, state=CONNECTED

dsx1(slot/unit/channel)=0/0/0, status=VDEV_STATUS_ACTIVE_CALL.VDEV_STATUS_ALLO CATED.

Modem hardware state: CTS DSR DTR RTS

Special Chars: Escape Hold Stop Start Disconnect Activation ^x none - - none

Timeouts: Idle EXEC Idle Session Modem Answer Session

00:10:00 never none

Idle Session Disconnect Warning never

Login-sequence User Response

00:00:30 Autoselect Initial Wait not set

Modem type is unknown. Session limit is not set. Time since activation: 00:00:36 Editing is enabled.

History is enabled, history size is 10. DNS resolution in show commands is enabled

Dispatch not set

Full user help is disabled

Allowed transports are pad telnet rlogin udptn v120 lapb-ta. Preferred is pad t elnet rlogin udptn v12 0 lapb-ta. No output characters are padded No special data dispatching characters

Step 8 Program the display window so it does not pause in the middle of a screen display:

53 0 0-NAS>terminal length 0

Step 9 Generate traffic across the modem link. Perform a light-weight stress test between the modems to generate meaningful modem-performance statistics.

53 0 0-NAS>show modem log

Modem 1/0 Events Log:

3w4d :Startup event:MICA Hex modem (Managed)

Modem firmware = 3w4d :RS232 event: noRTS, noDTR, CTS, noDCD 3w4d :RS232 event: noRTS, DTR, CTS, noDCD


The output generated by the show modem log command sends a sizeable data stream across the modem link—about 1 MB of data. The data should scroll freely for one or two minutes.

Step 10 Inspect the NAS modem that answered the call, and verify that it has acceptable connect speed, throughput, and line shape. This example examines MICA modem 1/0. If you have Microcom modems, enter the modem at-mode slot/port command followed by the [email protected] command.

53 0 0-NAS>show modem operational-status 1/0

Modem(1/0) Operational-Status:

Parameter #0 Type ( = Class (= Reason (= Parameter #1 Parameter #2 Parameter #3 Parameter #4 Parameter #5 Parameter #6 Parameter #7 Parameter #8 Parameter #9 Parameter #11 Parameter #13 Parameter #15 Parameter #16 Parameter #17 Parameter #18 Parameter #19 Parameter #20 Parameter #21 Parameter #22 Parameter #23 Parameter #24 Parameter #25 Parameter #26 Parameter #27 Parameter #28 Parameter #30 Parameter #32

Disconnect Reason Info: (0x0) )

<unknown> Other no disconnect has yet occurred Connect Protocol: LAP-M Compression: None EC Retransmission Count: 2 Self Test Error Count: 0 Call Timer: 118 secs Total Retrains: 0 Sq Value: 3

Connected Standard: V.90 TX,RX Bit Rate: 48000, 28800

TX,RX Symbol Rate: 8000, 3200

TX,RX Carrier Frequency: 0, 1920

TX,RX Trellis Coding: 0, 16

TX,RX Preemphasis Index: 0, 6

TX,RX Constellation Shaping: Off, Off

TX,RX Nonlinear Encoding: Off, Off

TX,RX Precoding: Off, Off

TX,RX Xmit Level Reduction: 0, 0 dBm

Signal Noise Ratio: 36 dB

Receive Level: -19 dBm

Frequency Offset: 0 Hz

Phase Jitter Frequency: 0 Hz

Phase Jitter Level: 0 degrees

Far End Echo Level: -37 dBm

Phase Roll: 0 degrees

Round Trip Delay: 23 msecs

Characters transmitted, received: 67109, 43

Characters received BAD: 0

Parameter #33 PPP/SLIP packets transmitted, received: 0, 0 Parameter #35 PPP/SLIP packets received (BAD/ABORTED): 0 Parameter #36 EC packets transmitted, received OK: 565, 43 Parameter #38 EC packets (Received BAD/ABORTED): 2 Parameter #39 Robbed Bit Signalling (RBS) pattern: 0

Parameter #4 0 Digital Pad: 6.0 dB, Digital Pad Compensation:None

Line Shape:

Table 4-5 describes the significant output fields (bold font) in the previous example:

Table 4-5 Show Modem Operational-Status Field Descriptions



Parameter #6 Total Retrains: 0

Total retrains and speed shifts for the current connection. There are no retrains.

Parameter #8

Connected Standard: V.90

V.90 modulation is negotiated.

Standard connect protocol which can be V.21, Bell03, V.22, V.22bis, Bell212, V.23, V.32, V.32bis, V.32terbo, V.34, V.34+, K56Flex, or V.90.

Parameter #9

TX, RX Bit Rate: 48000, 28800

The transmit speed (TX) is 48000 bps. The receive speed (RX) is 28800 bps.

TX is the bit rate from the local DCE (NAS modem) to the remote DCE (client modem). RX is the bit rate from the remote DCE to the local DCE. V.90 uplink speed tends to be lower than V.34 uplink speed.

Table 4-5 Show Modem Operational-Status Field Descriptions (continued)



Parameter #21

Signal Noise Ratio: 36 dB

The signal to noise ratio (SNR) is 36 dB. (40 dB is a perfect SNR.

MICA measures the SNR in the signal band. The SNR value ranges from 0 to 70 dB, and it changes in 1 dB steps.

A 28.8 kbps connection requires a SNR of about 37 dB. SNRs lower than 37 dB reduce the quality of the connection.

A 33.6 kbps connection requires a SNR of about 38 to 39 dB.

Parameter 3 0

Characters transmitted, received: 67109, 43

67109 characters are transmitted by the NAS modem to the client modem over the synchronous/asynchronous connection.

Line shape:

* * * * * * *

A line shape is the frequency-response graph of the channel.

A flat vertical line shape is an ideal V.90 line shape. ISDN uses a 64-kb clear channel. No statistical roll off should exist at the low end or the high end of the spectrum. The spectrum has a Y and X axis.

• The Y axis (vertical) represents frequencies from 150 Hz (top of chart) to 3750 Hz (bottom of chart) in 150 Hz steps. A flat spectrum plot is best, it is available for V.34, V.90, and K56Flex.

• The X axis (horizontal) represents a normal amplitude. The graph identifies nulls, bandwidth, and distortion (irregular shape).

Step 11 Enter the +++ command to jump back to the client modem and examine client-side performance statistics. The modem connection to the NAS is not dropped.

In the example, the client modem reports both "OK" messages. The +++ modem-escape sequence is similar to a router's telnet-escape mode (Shift + Ctrl + 6 + x). See Figure 4-8.

Figure 4-8 Using Modem-Escape Mode to View Client-Side Modem Statistics

+++ enables the client PC to communicate directly to the client modem

The connection to the NAS is still up

Step 12 Enter the ati6 command to display, among other things, the receive and transmit-carrier speeds.

Compare the displayed information with the output from the show modem operational-status command.

If ati6 is not supported by your modem, try at&vl. For additional client report statistics, enable Window's modemlog.txt or ppplog.txt files.


U.S. Robotics 56K FAX

EXT Link Diagnostics...

Chars sent


Chars Received


Chars lost


Octets sent


Octets Received


Blocks sent


Blocks Received


Blocks resent


Retrains Requested


Retrains Granted


Line Reversals




Link Timeouts


Link Naks


Data Compression










V.90 Peak Speed


Current Call



Tech Tip For a detailed explanation of this command, refer to the following URL: http://808hi.com/56k/diag3com.htm

Step 13 Inspect frequency levels (dB) and other diagnostic functions. The following AT commands display the client modem's view of the frequency response. The display is a companion to the output of the show modem operational-status command (see Step 9).


Freq Level (dB)

150 24

300 23

450 22

600 22

750 22

900 22

1050 22

1200 22

1350 22

1500 22

1650 22

1800 23

1950 23

2100 23

2250 23

2400 23

2550 23

2700 23

2850 23

3000 23

3150 23

3300 24

3450 25

3600 27

3750 31


U.S. Robotics 56K FAX EXT Link Diagnostics...


Carrier Freq (Hz)

Symbol Rate

Trellis Code Nonlinear Encoding Precoding Shaping

Preemphasis (-dB)

Recv/Xmit Level (-dBm) Near Echo Loss (dB) Far Echo Loss (dB) Carrier Offset (Hz) Round Trip Delay (msec) Timing Offset (ppm)

Speed Shifts Up/Down Status : OK


None/1920 8000/3200

None/64S-4D None/ON None/ON ON/ON 6/2 19/10 7 0


Step 14 (Optional) To return to online mode and the router prompt, enter the ato command. After your enter this command, however, the +++ escape sequence is still in the EXEC session's input buffer. If you press the carriage return (<CR>), you will receive an error about +++ being an unknown command. To clear the input buffer, type Ctrl U after the ato command.

% Unknown command or computer name, or unable to find computer address 53 0 0-NAS>


Configuring PPP and Authentication

In this Section

This section describes how to configure the Cisco AS5300 and AS5800 for PPP and local authentication.

The following sections are provided:

• Task 1. Configuring PPP Authentication for Local AAA

• Task 2. Configuring IPCP Options

• Task 3. Configuring LCP Options

• Task 4. Enabling PPP Autoselect

• Task 5. Testing Asynchronous PPP Connections

• Task 6. Inspecting Active Call States

• Task 7. Confirming the Final Running-Config

In this case study, Maui Onions and THEnet perform these same tasks to configure their network access servers (NAS). Maui Onions uses a Cisco AS5300; THEnet uses a Cisco AS5800. After local authentication if verified, Maui Onions expects to use TACACS+ and a remote authentication server. THEnet expects to use RADIUS.

Task 1. Configuring PPP Authentication for Local AAA

Configure AAA to perform login authentication by using the local username database. The login keyword authenticates EXEC terminal shell users. Additionally, configure PPP authentication to use the local database if the session was not already authenticated by login.

Step 1

Create a local login username database in global configuration mode. In this example, admin is used for the administrator. In this case study, the remote client's login password is dude.

username admin password adminpasshere username dude password dudepasshere


This step also prevents you from getting locked out of the NAS. If you get locked out, you must reboot the device and perform password recovery.

Step 2 Configure local AAA security in global configuration mode. You must enter the aaa new-model command before the other two authentication commands.

aaa new-model aaa authentication login default local aaa authentication ppp default if-needed local

Step 3 Log in with your username and password:


This is a secured device. Unauthorized use is prohibited by law.

User Access Verification Username:dude Password:

Warning Successfully logging in means that your local username will work on any TTY or VTY line. Do not disconnect your session until you can log in. (If you get locked out, you will need to perform password recovery by rebooting the device.)

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