Verifying Modem Performance

In this Section

Background on Asynchronous Data Communications

Async DataComm Model

Logical Packet and Circuit Components of a NAS

RS-232 in Cisco IOS

Cisco IOS Line-Side Inspection

Understanding Modem Modulation Standards

V.34 Basic Rules

V.90 Basic Rules

Task 1. Initiating a Modem Loopback Test Call

Task 2. Initiating and Inspecting a V.90 Test Call

What to do Next

Verifying Modem Performance

In this Section

This section describes how to verify and test modem performance on a Cisco AS5300 and AS5800 by using an EXEC terminal shell service.

The following sections are provided:

An EXEC terminal shell service tests modem performance (lower layers) independently of PPP (and higher layers). A terminal-shell service test gets quick test results in a simple environment.

In this case study, Maui Onions and THEnet perform the same tasks to verify modem performance and set up V.90. Maui Onions uses a Cisco AS5300; THEnet uses a Cisco AS5800.

For information on how to manage modem pools and collect call statistics, see the section "Modem Management Operations."

Background on Asynchronous Data Communications

Understanding how RS-232 states function with the Cisco IOS software helps you test and troubleshoot modem connections:

Async DataComm Model

Figure 4-1 shows how traditional DTE-to-DCE relationships map to a Cisco network access server (NAS). Data terminal equipment (DTE) uses data communication equipment (DCE) to send data over the PSTN.

In the context of RS-232 and Cisco IOS:

The DTE is the client PC and the Cisco IOS TTY lines.
The DCE is the client modem and the modem inside the NAS.
The dashed line between the DCEs is the modem carrier running on top of the voiceband circuit through the PSTN. RS-232 (whether physical or logical) is used on the DTE lines, not on the DCE link.
The PSTN circuit runs through the circuit-switched half of the NAS.

Figure 4-1: A Standard Dial-Up Connection

Logical Packet and Circuit Components of a NAS

The NAS functions as a gateway between two different networks:

A circuit-switched network (for example, the PSTN)
A packet-switched network (for example, the Internet)

The NAS is half a circuit switch and half a packet switch (router). RS-232 signaling on the line is displayed by the show line command and debug modem command. Figure 4-2 shows the modem access connectivity path.

Figure 4-2: Modem Access Connectivity Path

To understand the general call-processing sequence, match the following numbered list with the numbers shown in Figure 4-2:

1. 64K DS0 circuits extend from the NAS modems, through the internal TDM CSM bus, and through the circuit network (PSTN).

2. The NAS modems demodulate digital streams into analog-voiceband modulation. The virtual RS-232 interface connects the modems (DCE) to the TTY lines.

3. The TTY lines are mapped into asynchronous interfaces. Interfaces are Cisco IOS objects that move packets. TTY lines function at Layer 1. Interfaces function at Layer 2 and Layer 3.

4. The packets are delivered into the IP network.

RS-232 in Cisco IOS

The Cisco IOS variation of asynchronous RS-232 is shown in Figure 4-3. The variation exists between the Cisco IOS line (DTE) and the NAS modem (DCE).

Six RS-232 pins exist between each NAS modem and Cisco IOS line. One or more grounding wires also exist on physical RS-232 lines; however, these wires do not convey signaling.
Each pin controls a different RS-232 signal.
The arrows in Figure 4-3 indicate the signal transmission direction.

Figure 4-3: Cisco IOS RS-232

Tips In Figure 4-3, notice that the DSR signal is the DCD signal for the modem. In the scheme of Cisco IOS, the DCD pin on the DCE is strapped to the DSR pin on the Cisco IOS DTE side. What the Cisco IOS calls DSR is not DSR; it is DCD. The DCE's actual DSR pin and ring ignore (RI) pin are ignored by the Cisco IOS.

Table 4-1 describes how Cisco uses it's RS-232 pins. The signal direction in the table is from the perspective of the DTE (IOS line):

Data signals (TxD, RxD)
Hardware flow control signals (RTS, CTS)
Modem signals (DTR, DSR, DCD, RI)

Table 4-1: RS-232 Signal State Behavior

Signal Signal Direction Purpose

Transmit Data (TxD)

------>
(Output)

DTE transmits data to DCE.

Receive Data (RxD)

<------
(Input)

DCE transmits received data to DTE.

Request To Send (RTS)

------>
(Output)

DTE uses the RTS output signal to indicate if it can receive characters into the Rx input buffer¹.

The DCE should not send data to the DTE when DTR input is low (no RTS).

Clear To Send (CTS)

<------
(Input)

DCE signals to DTE that it can continue to accept data into its buffers.

DCE asserts CTS only if the DCE is able to accept data.

Data Terminal Ready (DTR)

------>
(Output)

DTE signals to DCE that it can continue to accept data into its buffers.

DTE asserts RTS only if the DTE is able to accept data.

Data Carrier Detect (DCD)

<------
(Input)

DCE indicates to DTE that a call is established with a remote modem. Dropping DCD terminates the session.

DCD will be up on the DCE only if the DCE has achieved data mode with its peer DCE (client modem).

¹The name RTS is illogical with the function (able to receive) due to historical reasons.

Signal	Signal Direction	Purpose
Transmit Data (TxD)	------> (Output)	DTE transmits data to DCE.
Receive Data (RxD)	<------ (Input)	DCE transmits received data to DTE.
Request To Send (RTS)	------> (Output)	DTE uses the RTS output signal to indicate if it can receive characters into the Rx input buffer¹. The DCE should not send data to the DTE when DTR input is low (no RTS).
Clear To Send (CTS)	<------ (Input)	DCE signals to DTE that it can continue to accept data into its buffers. DCE asserts CTS only if the DCE is able to accept data.
Data Terminal Ready (DTR)	------> (Output)	DTE signals to DCE that it can continue to accept data into its buffers. DTE asserts RTS only if the DTE is able to accept data.
Data Carrier Detect (DCD)	<------ (Input)	DCE indicates to DTE that a call is established with a remote modem. Dropping DCD terminates the session. DCD will be up on the DCE only if the DCE has achieved data mode with its peer DCE (client modem).

Cisco IOS Line-Side Inspection

To display the current modem-hardware states applied to a specific Cisco IOS line, enter the show line tty number command. The states of each logical RS-232 pin change according to line conditions and modem events.

The following shows a line-side inspection of the idle state for TTY line 1:

5300-NAS#show line tty 1
   Tty Typ     Tx/Rx    A Modem  Roty AccO AccI   Uses   Noise  Overruns   Int
I    1 TTY              - inout     -    -    -      2       0     0/0       -
 
Line 1, Location:"", Type:""
Length:24 lines, Width:80 columns
Status: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:Idle
  modem(slot/port)=1/0, state=IDLE
  dsx1(slot/unit/channel)=NONE, status=VDEV_STATUS_UNLOCKED
Modem hardware state:CTS noDSR  DTR RTS
Special Chars:Escape  Hold  Stop  Start  Disconnect  Activation
                ^^x    none   -     -       none         
Timeouts:     Idle EXEC    Idle Session   Modem Answer  Session   Dispatch
               00:10:00        never                        none     not set
                            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:never
Editing is enabled.
History is enabled, history size is 10.
DNS resolution in show commands is enabled
Full user help is disabled
Allowed transports are pad telnet rlogin v120 lapb-ta.  Preferred is telnet.
No output characters are padded
No special data dispatching characters

Table 4-2 describes some of the significant fields shown in the previous example:

Table 4-2: Show TTY Line Field Descriptions

Field Description

Capabilities

Describes different aspects of the line:

The flowcontrol hardware command displays as "Hardware Flowcontrol In, Hardware Flowcontrol Out."

The modem inout command displays as "modem callout."

The text "Line usable as async interface" means that there is an "interface async N" that corresponds to "line N."

The text "Modem RI is CD" displays for historical reasons.

Modem state

Displays the current status of the modem.

Possible values include:

Idle---Modem is ready for incoming and outgoing calls.

Conn---Modem is connected to a remote host.

Busy---Modem is out of service and not available for calls.

D/L---Modem is downloading firmware.

Bad---Modem is in an inoperable state, which is manually configured by the modem bad command.

Bad*---During initial power-up testing, the modem startup-test command automatically put the modem in an inoperable state.

Reset---Modem is in reset mode.

Bad FW---The downloaded modem firmware is not usable.

Modem Hardware state

Displays the RS-232 signal state status.

CTS and noDSR are incoming signals. DTR and RTS are outgoing signals. NoDSR means that no call is currently connected.

Field	Description
`Capabilities`	Describes different aspects of the line: The flowcontrol hardware command displays as "Hardware Flowcontrol In, Hardware Flowcontrol Out." The modem inout command displays as "modem callout." The text "Line usable as async interface" means that there is an "interface async N" that corresponds to "line N." The text "Modem RI is CD" displays for historical reasons.
`Modem state`	Displays the current status of the modem. Possible values include: `Idle`---Modem is ready for incoming and outgoing calls. `Conn`---Modem is connected to a remote host. `Busy`---Modem is out of service and not available for calls. `D/L`---Modem is downloading firmware. `Bad`---Modem is in an inoperable state, which is manually configured by the modem bad command. `Bad`---During initial power-up testing, the modem startup-test* command automatically put the modem in an inoperable state. `Reset`---Modem is in reset mode. `Bad FW`---The downloaded modem firmware is not usable.
`Modem Hardware state`	Displays the RS-232 signal state status. CTS and noDSR are incoming signals. DTR and RTS are outgoing signals. NoDSR means that no call is currently connected.

Understanding Modem Modulation Standards

To optimize modem connect speeds, you must understand the basic modem modulation standards. This section provides the basic rules for achieving maximum V.34 and V.90 modulation speeds:

V.34 Basic Rules

V.34 modulation should work on any land-line voiceband circuit. V.34 supports speeds ranging from 2400 to 33600 bps.

Speed is a function of:

The amount of usable spectrum across the channel (for example, 2400 to 3429 Hz)
The signal to noise ratio (SNR)

To achieve 33600 bps, the channel must deliver:

A response from 244 to 3674 Hz
A SNR of 38 dB or better

In practice, toll-quality voiceband circuits support V.34 at speeds of 21600 to 33600 bps.

The following six items reduce the achieved V.34 speed:

1. Robbed-bit signaling links in the circuit, which reduce SNR.

2. Extra analog-to-digital conversions. For example, non-integrated or universal Subscriber Line Concentrators (SLCs) reduce bandwidth and SNR.

3. Load coils on the local loop, which reduce bandwidth.

4. Long local loops, which reduce bandwidth and SNR.

5. The following electrical disturbances in the house wiring, which reduce SNR:

Cross talk from two lines in the same quad cable
Corroded connectors
Bridge-tapped lines running parallel to fluorescent lights
Flat silver-satin cables running parallel to power cables
Extra electrical equipment sharing the same power jack as the modem

6. Voiceband circuits that pass through sub-64k coding, such as a cellular or 32k ADPCM link. With 32k ADMCM, the speed is typically 9600 to 16800 bps.

V.90 Basic Rules

Many circuit components work together to deliver V.90 modulation. See Figure 4-4.

Figure 4-4: V.90 Network Components

Here are the V.90 basic rules:

Select recommended modem code. The following are reliable V.90 releases at the time of this publication:
- MICA portware version 2.6.2.0
- Microcom firmware version 5.2.1.0

: The latest modem code is posted on CCO at the following URL. You must be a registered CCO user to view the link:
: http://www.cisco.com/kobayashi/sw-center/sw-access.shtml

Run a Cisco IOS release that is compatible with V.90. Table 4-3 shows the V.90 supported Cisco IOS Releases at the time of this publication.

Table 4-3: V.90 Supported Cisco IOS Releases

Chassis Modem Type Cisco IOS

Cisco AS5800

MICA

11.3(6+)AA

12.0(1+)T

Cisco AS5300

MICA

Microcom

12.0(1+)

11.3(5+) {T, AA, NA}

11.2(16+)P

Cisco AS5200

MICA

Microcom

11.3(5+) {T and AA}

12.0(1+)

11.2(14+)P (Microcom only)

Cisco 3600

MICA

12.0(1+)

11.3(5+) {T, AA, NA}

11.2(16+)P

Chassis	Modem Type	Cisco IOS
Cisco AS5800	MICA	11.3(6+)AA 12.0(1+)T
Cisco AS5300	MICA Microcom	12.0(1+) 11.3(5+) {T, AA, NA} 11.2(16+)P
Cisco AS5200	MICA Microcom	11.3(5+) {T and AA} 12.0(1+) 11.2(14+)P (Microcom only)
Cisco 3600	MICA	12.0(1+) 11.3(5+) {T, AA, NA} 11.2(16+)P

Exactly one digital to analog conversion must exist in the circuit. The digital line must connect into a digital switch, not a channel bank. V.90 requires PRI (64k clear-channel DS0s). Channel banks destroy V.90 by adding additional analog-to-digital conversions. Telcos occasionally refer to channel banks as line-side services. Digital switches are sometimes referred to as trunk-side services. Figure 4-5 shows this.

Figure 4-5: No Channel Banks for V.90

In the local loop, less than three miles of twisted-pair copper line with no load coils is ideal. Load coils limit frequencies (passband). V.90 requires a 3000 Hz passband. A circuit that does not deliver a 3200 Hz passband will most likely not deliver V.90. Load coils are common in long loops in North America (at the 3.5 mile mark).

Sometimes the PSTN switch fabric is extended by a digital carrier. It is then converted to analog by a SLC. This setup complies with V.90. The digital-to-analog conversion is moved closer to the subscriber. However, non-integrated or universal SLCs do not comply to V.90.

Use a recommended V.90 client modem.

Electrical house wiring sometimes causes V.90 trainup to fail. For details, see the section "V.34 Basic Rules."

Task 1. Initiating a Modem Loopback Test Call

Test the access server's ability to initiate and terminate a modem call. Similar to sending a ping to the next-hop router, this test verifies basic connectivity for modem operations. Successfully performing this test gives you a strong indication that remote clients should be able to dial into the NAS. Figure 4-6 shows this test.

After completing this test, dial into the EXEC from a client PC and a client modem (no PPP).

Figure 4-6: Initiating and Terminating a Modem Call on the Same NAS

Note When calling between two digital modems, you will not achieve V.90. V.90 requires one digital and one analog modem.

Step 1 From a workstation, open two telnet sessions into the NAS. One telnet session is used to simulate the client. The other session is used to administer and run the debugs. In this way, the debug messages will not be scrambled into the loopback screen display. Figure 4-7 shows an example of this.

Figure 4-7: Opening Two Telnet Sessions

Step 2 Configure the lines to support dial in, dial out, and outbound telnet connections:

!
line 1 96
 modem inout
 transport input telnet
!

Step 3 From the administrative telnet session, turn on the appropriate debug commands. Older software might require the debug modem csm command.

5300-NAS#debug isdn q931
ISDN Q931 packets debugging is on
5300-NAS#debug csm modem
Modem Management Call Switching Module debugging is on
5300-NAS#debug modem
Modem control/process activation debugging is on
5300-NAS#show debug
General OS:
  Modem control/process activation debugging is on
ISDN:
  ISDN Q931 packets debugging is on
  ISDN Q931 packets debug DSLs. (On/Off/No DSL:1/0/-)
  DSL  0 --> 7
  1 1 1 - - - - -  
 
Modem Management:
  Modem Management Call Switching Module debugging is on
5300-NAS#

Tips For channel associated signaling (CAS), robbed bit signaling (RBS), and R2, use the debug cas command. If this command is not included in your software, use the modem-mgmt csm debug-rbs command; however, the service internal command is required.

5300-NAS(config)#service internal
5300-NAS(config)#end
5300-NAS#modem-mgmt csm debug-rbs

At the time of this publication, the Cisco AS5800 does not support the debug cas command or modem-mgmt csm debug-rbs command. As a work-around, complete the following steps:

1. Determine the slot positions of each card. Enter the show dial-shelf command.
2. Access the trunk card's console port. Enter the dsip console slave X command where X is the slot of the card that you want to perform debugging on.
3. Enter the command debug trunk cas port port-number timeslots range.

Step 4 Ensure that your EXEC session receives logging and debug output from the NAS:

5300-NAS#terminal monitor

Step 5 From the client telnet session, telnet into one of the idle modems (not in use). To do this, telnet to an IP address on the NAS (Ethernet or Loopback) followed by 2000 plus a TTY line number. This example telnets to TTY line 1 (2001).

5300-NAS#telnet 172.22.66.23 2001
Trying 172.22.66.23, 2001 ... Open

Note This step is also known as a reverse telnet.

For a Cisco AS5800, create an arbitrary IP host followed by a reverse telnet. Use the show modem shelf/slot/port command to determine which modem is associated with which TTY line. The following example telnets to TTY 500, which maps to modem 1/2/68.

5800-NAS#show modem 1/2/68
     Mdm  Typ     Status     Tx/Rx     G  Duration  RTS   CTS   DCD   DTR
     ---  ---     ------     -----     -  --------  ---   ---   ---   ---
   1/2/68 V.90    Idle    37333/31200  1  00:01:05  RTS   CTS   noDCD DTR
 
Modem 1/2/68, Cisco MICA modem (Managed), Async1/2/68, TTY500
Firmware Rev: 2.6.2.0

Note

5800-NAS(config)#ip host mod500 2500 172.22.66.23
5800-NAS(config)#^Z
5800-NAS#telnet mod500
Trying mod500 (172.22.66.23, 2500)... Open

Step 6 Log in from the client telnet session. The Cisco IOS sends out a username-password prompt.

This is a secured device. 
Unauthorized use is prohibited by law.
 
 
User Access Verification
 
Username:admin
Password:
 
Sep 23 05:04:58.047: TTY0: pause timer type 1 (OK)
Sep 23 05:04:58.051: TTY1: asserting DTR
Sep 23 05:04:58.051: TTY1: set timer type 10, 30 seconds
Sep 23 05:05:03.583: TTY1: set timer type 10, 30 seconds

Step 7 Enter the at command to test connectivity to the NAS modem. The modem reports an "OK" return message.

at
OK

Step 8 Dial the PRI phone number assigned to the NAS (in this example, 5551234). A connect string appears when the modem connects.

atdt5551234
CONNECT 33600 /V.42/V.42bis

In this example:

Modulation connect speed = 33600 bps. Expect to get a maximum of 33600 bps if you use a PRI line. If you use RBS, expect to get a maximum of 31200 bps.
Error correction = V.42
Data compression = V.42bis

Step 9 From the administrative telnet session, inspect the debug output:

*Jan  1 00:34:47.863:ISDN Se0:23:RX <-  SETUP pd = 8  callref = 0x0053
*Jan  1 00:34:47.863:        Bearer Capability i = 0x8090A2
*Jan  1 00:34:47.863:        Channel ID i = 0xA98381
*Jan  1 00:34:47.863:        Calling Party Number i = 0x0083, '408'
*Jan  1 00:34:47.863:        Called Party Number i = 0xC1, '5551234'
*Jan  1 00:34:47.867:ISDN Se0:23:TX ->  CALL_PROC pd = 8  callref = 0x8053
*Jan  1 00:34:47.867:        Channel ID i = 0xA98381
*Jan  1 00:34:47.867:ISDN Se0:23:TX ->  ALERTING pd = 8  callref = 0x8053
*Jan  1 00:34:47.867:EVENT_FROM_ISDN::dchan_idb=0x6149A144, call_id=0x1A,ces=0x1
   bchan=0x0, event=0x1, cause=0x0

The bearer capability 0x8090A2 indicates an analog voice call. Alternative bearer services include 64K data calls, which are indicated by 0x8890. The calling party number is 408 (also known as ANI). The called party number is 5551234 (also known as DNIS). The debug q931 command shows the call coming into the NAS over ISDN.

*Jan  1 00:34:47.867:VDEV_ALLOCATE:1/2 is allocated from pool System-def-Mpool
*Jan  1 00:34:47.867:csm_get_vdev_for_isdn_call:fax_call=0
*Jan  1 00:34:47.867:EVENT_FROM_ISDN:(001A):DEV_INCALL at slot 1 and port 2
*Jan  1 00:34:47.867:CSM_PROC_IDLE:CSM_EVENT_ISDN_CALL at slot 1, port 2
*Jan  1 00:34:47.867:Mica Modem(1/2):Configure(0x1 = 0x0) 
*Jan  1 00:34:47.867:Mica Modem(1/2):Configure(0x23 = 0x0) 
*Jan  1 00:34:47.867:Mica Modem(1/2):Call Setup
*Jan  1 00:34:47.867: Enter csm_connect_pri_vdev function
*Jan  1 00:34:47.867:csm_connect_pri_vdev:tdm_allocate_bp_ts() call. BP TS allocated at bp_stream0, bp_Ch5,vdev_common 0x610378B0
*Jan  1 00:34:47.883:ISDN Se0:23:RX <-  ALERTING pd = 8  callref = 0x8004
*Jan  1 00:34:47.883:        Progress Ind i = 0x8288 - In-band info or appropriate now available 
*Jan  1 00:34:48.019:Mica Modem(1/2):State Transition to Call Setup
*Jan  1 00:34:48.019:Mica Modem(1/2):Went offhook
*Jan  1 00:34:48.019:CSM_PROC_IC2_RING:CSM_EVENT_MODEM_OFFHOOK at slot 1, port 2
*Jan  1 00:34:48.019:ISDN Se0:23:TX ->  CONNECT pd = 8  callref = 0x8053
*Jan  1 00:34:48.047:ISDN Se0:23:RX <-  CONNECT_ACK pd = 8  callref = 0x0053
*Jan  1 00:34:48.047:EVENT_FROM_ISDN::dchan_idb=0x6149A144, call_id=0x1A, ces=0x1 bchan=0x0, event=0x4, cause=0x0
*Jan  1 00:34:48.047:EVENT_FROM_ISDN:(001A):DEV_CONNECTED at slot 1 and port 2
*Jan  1 00:34:48.047:CSM_PROC_IC4_WAIT_FOR_CARRIER:CSM_EVENT_ISDN_CONNECTED at slot 1, port 2
*Jan  1 00:34:48.047:Mica Modem(1/2):Link Initiate
*Jan  1 00:34:48.047:ISDN Se0:23:RX <-  CONNECT pd = 8  callref = 0x8004
*Jan  1 00:34:48.047:EVENT_FROM_ISDN::dchan_idb=0x6149A144, call_id=0x8005, ces=0x1 bchan=0x16, event=0x4, cause=0x0
*Jan  1 00:34:48.047:EVENT_FROM_ISDN:(8005):DEV_CONNECTED at slot 1 and port 0
*Jan  1 00:34:48.047:CSM_PROC_OC5_WAIT_FOR_CARRIER:CSM_EVENT_ISDN_CONNECTED at slot 1, port 0
*Jan  1 00:34:48.051:ISDN Se0:23:TX ->  CONNECT_ACK pd = 8  callref = 0x0004

MICA modem 1/2 goes offhook and receives the call. The debug modem csm command shows the call getting switched over to a modem.

*Jan  1 00:34:49.159:Mica Modem(1/2):State Transition to Connect
*Jan  1 00:34:53.903:Mica Modem(1/2):State Transition to Link
*Jan  1 00:35:02.851:Mica Modem(1/2):State Transition to Trainup
*Jan  1 00:35:04.531:Mica Modem(1/2):State Transition to EC Negotiating
*Jan  1 00:35:04.711:Mica Modem(1/2):State Transition to Steady State
*Jan  1 00:35:04.755:TTY3:DSR came up
*Jan  1 00:35:04.755:tty3:Modem:IDLE->(unknown)

Inspect the different modem trainup phases. The modem goes from Connect to Steady State in 15 seconds. The debug modem csm command displays the trainup phases. The debug modem command displays the logical RS-232 transition message "DSR came up."

*Jan  1 00:35:04.759:TTY3:EXEC creation
*Jan  1 00:35:04.759:TTY3:set timer type 10, 30 seconds
*Jan  1 00:35:08.915:TTY3:Autoselect(2) sample 61 <------------------- a
*Jan  1 00:35:09.187:TTY3:Autoselect(2) sample 6164 <----------------- d
*Jan  1 00:35:09.459:TTY3:Autoselect(2) sample 61646D <--------------- m
*Jan  1 00:35:09.459:TTY3:Autoselect(2) sample 61646D69 <------------- i
*Jan  1 00:35:09.715:TTY3:Autoselect(2) sample 646D696E <------------- n
*Jan  1 00:35:09.715:TTY3:Autoselect(2) sample 6D696E0D <------------- <cr>

Decode the incoming character-byte stream for an EXEC shell login (no PPP). In this example, match the username "admin" to the character stream: 616D696E0D = admin carriage return.

The Cisco IOS samples four packets at a time. It searches for a header that matches one of your autoselect styles. The debug modem command generates the autoselect debug output.

*Jan  1 00:35:09.715:TTY3:set timer type 10, 30 seconds
*Jan  1 00:35:11.331:TTY3:Autoselect(2) sample [suppressed--line is not echoing]
*Jan  1 00:35:11.667:TTY3:Autoselect(2) sample [suppressed--line is not echoing]
*Jan  1 00:35:11.987:TTY3:Autoselect(2) sample [suppressed--line is not echoing]
*Jan  1 00:35:11.987:TTY3:Autoselect(2) sample [suppressed--line is not echoing]
*Jan  1 00:35:11.987:TTY3:Autoselect(2) sample [suppressed--line is not echoing]
*Jan  1 00:35:12.339:TTY3:Autoselect(2) sample [suppressed--line is not echoing]
*Jan  1 00:35:12.391:TTY3:create timer type 1, 600 seconds
5300-NAS>

Type 10 is the login timer. The timeout is 30 seconds. The user's EXEC-shell login password is suppressed.

Step 10 Identify who is logged in. TTY line 3 corresponds to modem 1/2. Use the show terminal command to see which modem is assigned to the TTY line.

5300-NAS>show user
    Line     User      Host(s)                  Idle Location
   3 tty 3   admin     idle                     0 
* 98 vty 0   joe       172.22.66.1              0 leftfield.mauionions.com
 
  Interface  User      Mode                     Idle Peer Address

Step 11 Program the terminal window not to pause in the middle of a screen display. To adjust the display output on a Cisco AS5800, enter the terminal length 2000 command instead.

5300-NAS>terminal length 0

Step 12 Generate traffic across the modem link. Force the answering modem (in the NAS) to send a data steam to the client modem. The data stream generated by the show modem log command is about 1 MB. The data should scroll freely for one or two minutes.

5300-NAS>show modem log
Modem 1/0 Events Log:
  2d09h   :Startup event:MICA Hex modem (Managed)
           Modem firmware = 2.7.1.0
  2d09h   :RS232 event:  noRTS, noDTR, CTS, noDCD
  2d09h   :RS232 event:  noRTS, DTR, CTS, noDCD
  2d09h   :RS232 event:  RTS, DTR, CTS, noDCD
  2d09h   :RS232 event:  noRTS, DTR, CTS, noDCD
  2d09h   :RS232 event:  noRTS, noDTR, CTS, noDCD
  2d09h   :RS232 event:  noRTS, DTR, CTS, noDCD
  2d09h   :RS232 event:  RTS, DTR, CTS, noDCD

Note

Step 13 Look at the modem's operational statistics and verify that you have acceptable speed, line shape, and throughput. In this example, modem 1/2 accepts the call.

If you do not have a scroll bar in your telnet application, limit terminal length to 24 lines to see all the command output.

If you are using Microcom modems, enter the modem at-mode slot/port command followed by the at@e1 command.

5300-NAS>show modem operational-status 1/2
Modem(1/2) Operational-Status:
 
 Parameter #0  Disconnect Reason Info: (0x0)
       Type (=0 ): <unknown>
      Class (=0 ): Other
     Reason (=0 ): no disconnect has yet occurred 
 Parameter #1  Connect Protocol: LAP-M 
 Parameter #2  Compression: V.42bis both 
 Parameter #3  EC Retransmission Count: 0 
 Parameter #4  Self Test Error Count: 0 
 Parameter #5  Call Timer: 597 secs 
 Parameter #6  Total Retrains: 0 
 Parameter #7  Sq Value: 4 
 Parameter #8  Connected Standard: V.34+ 
 Parameter #9  TX,RX Bit Rate: 33600, 33600 
 Parameter #11 TX,RX Symbol Rate: 3429, 3429 
 Parameter #13 TX,RX Carrier Frequency: 1959, 1959 
 Parameter #15 TX,RX Trellis Coding: 16, 16 
 Parameter #16 TX,RX Preemphasis Index: 0, 0 
 Parameter #17 TX,RX Constellation Shaping: Off, Off 
 Parameter #18 TX,RX Nonlinear Encoding: Off, Off 
 Parameter #19 TX,RX Precoding: Off, Off 
 Parameter #20 TX,RX Xmit Level Reduction: 0, 0 dBm 
 Parameter #21 Signal Noise Ratio: 41 dB 
 Parameter #22 Receive Level: -12 dBm 
 Parameter #23 Frequency Offset: 0 Hz 
 Parameter #24 Phase Jitter Frequency: 0 Hz 
 Parameter #25 Phase Jitter Level: 0 degrees 
 Parameter #26 Far End Echo Level: -52 dBm 
 Parameter #27 Phase Roll: 31 degrees 
 Parameter #28 Round Trip Delay: 1 msecs 
 Parameter #30 Characters transmitted, received: 70966, 80 
 Parameter #32 Characters received BAD: 2 
 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: 269, 61 
 Parameter #38 EC packets (Received BAD/ABORTED): 0 
 Parameter #39 Robbed Bit Signalling (RBS) pattern: 0 
 Parameter #40 Digital Pad: None,  Digital Pad Compensation:None
Line Shape:
..............................*
................................*
.................................*
................................*
................................*
.................................*
.................................*
.................................*
................................*
.................................*
.................................*
................................*
................................*
................................*
................................*
................................*
................................*
................................*
.................................*
.................................*
................................*
................................*
.................................*
.................................*
...............................*

Table 4-4 describes the significant parameters in the previous example. For a complete command reference description, refer to the following URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/dial_r/drdshom.htm

Parameter	Description
`Parameter #1 Connect Protocol: LAP-M`	LapM is the connection protocol.
`Parameter #6 Total Retrains: 0`	The modem has no retrain counts.
`Parameter #8 Connected Standard: V.34+`	The modem connects at V.34.
`Parameter #9 TX,RX Bit Rate: 33600, 33600`	The receive and transmit bit rate is 33600 bps, which is the fastest possible V.34 speed. You will never attain V.90 with this test. MICA-to-MICA calls default to V.34 modulation. V.90 requires one analog modem.
`Parameter #11 TX,RX Symbol Rate: 3429, 3429`	The transmit and receive symbol rate is 3429. To achieve 33600 bps, you must have a 3429 Hz passband.
`Parameter #21 Signal Noise Ratio: 41 dB`	The signal to noise ratio is 41 dB.
`Parameter #26 Far End Echo Level: -52 dBm`	Use this field to detect a near-end digital-to-analog conversion. For this test, an acceptable value is less than -55 dB. If you see a high level of far end echo (-55 or higher), a digital-to-analog conversion most likely exists between the NAS and the switch. This conversion severely impairs modem performance.
`Parameter #30 Characters transmitted, received: 70966, 80`	The number of characters transmitted and received by the modem.
`Line shape:` `..............................` `................................` `.................................` `................................` `................................` `.................................` `.................................` `.................................` `................................` `.................................`	A line shape is the frequency-response graph of the channel. For this modem loopback test call, there should be no rolloff (even at the highest frequency). High-end rolloff is characteristic of an analog-to-digital conversion (not good). 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 14 Turn off all debug commands:

5300-NAS#undebug all
All possible debugging has been turned off

Task 2. Initiating and Inspecting a V.90 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.

Figure 4-8:
Test Environment

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

at
OK

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
 
ati7
Configuration Profile...
 
Product type           US/Canada External
Product ID:            00568602
Options                V32bis,V.34+,x2,V.90
Fax Options            Class 1/Class 2.0
Line Options           Caller ID, Distinctive Ring
Clock Freq             92.0Mhz
EPROM                  256k
RAM                    32k
 
FLASH date             6/3/98
FLASH rev              4.11.2
 
DSP date               6/3/98
DSP rev                4.11.2
 
OK

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&f1, or at&f2 command.

ati4
U.S. Robotics 56K FAX EXT Settings...
 
   B0  E1  F1  M1  Q0  V1  X1  Y0
   BAUD=38400  PARITY=N  WORDLEN=8
   DIAL=TONE    ON HOOK   CID=0
 
   &A1  &B1  &C1  &D2  &G0  &H0  &I0  &K0
   &M4  &N0  &P0  &R1  &S0  &T5  &U0  &Y1  
 
   S00=000  S01=000  S02=043  S03=013  S04=010  S05=008  S06=002
   S07=060  S08=002  S09=006  S10=014  S11=070  S12=050  S13=000
   S15=000  S16=000  S18=000  S19=000  S21=010  S22=017  S23=019
   S25=005  S27=000  S28=008  S29=020  S30=000  S31=128  S32=002
   S33=000  S34=000  S35=000  S36=014S38=000  S39=000  S40=001
   S41=000  S42=000
 
   LAST DIALED #: T14085551234
 
OK

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
 
Username:dude
Password: 
 
5300-NAS>

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
                                                Active    Idle
  Line         User               Service       Time      Time
  tty 1        dude               TTY           00:00:36  00:00:00      
  vty 0        admin              VTY           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.

5300-NAS>show terminal
Line 50, Location: "", Type: ""
Length: 24 lines, Width: 80 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   Dispatch
               00:10:00        never                        none     not set
                            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
Full user help is disabled
Allowed transports are pad telnet rlogin udptn v120 lapb-ta.  Preferred is pad t
elnet rlogin udptn v120 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:

5300-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.

5300-NAS>show modem log
Modem 1/0 Events Log:
  3w4d    :Startup event:MICA Hex modem (Managed)
           Modem firmware = 2.7.1.0
  3w4d    :RS232 event:  noRTS, noDTR, CTS, noDCD
  3w4d    :RS232 event:  noRTS, DTR, CTS, noDCD

Note

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 at@e1 command.

5300-NAS>show modem operational-status 1/0
Modem(1/0) Operational-Status:
 
 Parameter #0  Disconnect Reason Info: (0x0)
       Type (=0 ): <unknown>
      Class (=0 ): Other
     Reason (=0 ): no disconnect has yet occurred 
 Parameter #1  Connect Protocol: LAP-M 
 Parameter #2  Compression: None 
 Parameter #3  EC Retransmission Count: 2 
 Parameter #4  Self Test Error Count: 0 
 Parameter #5  Call Timer: 118 secs 
 Parameter #6  Total Retrains: 0 
 Parameter #7  Sq Value: 3 
 Parameter #8  Connected Standard: V.90 
 Parameter #9  TX,RX Bit Rate: 48000, 28800 
 Parameter #11 TX,RX Symbol Rate: 8000, 3200 
 Parameter #13 TX,RX Carrier Frequency: 0, 1920 
 Parameter #15 TX,RX Trellis Coding: 0, 16 
 Parameter #16 TX,RX Preemphasis Index: 0, 6 
 Parameter #17 TX,RX Constellation Shaping: Off, Off 
 Parameter #18 TX,RX Nonlinear Encoding: Off, Off 
 Parameter #19 TX,RX Precoding: Off, Off 
 Parameter #20 TX,RX Xmit Level Reduction: 0, 0 dBm 
 Parameter #21 Signal Noise Ratio: 36 dB 
 Parameter #22 Receive Level: -19 dBm 
 Parameter #23 Frequency Offset: 0 Hz 
 Parameter #24 Phase Jitter Frequency: 0 Hz 
 Parameter #25 Phase Jitter Level: 0 degrees 
 Parameter #26 Far End Echo Level: -37 dBm 
 Parameter #27 Phase Roll: 0 degrees 
 Parameter #28 Round Trip Delay: 23 msecs 
 Parameter #30 Characters transmitted, received: 67109, 43 
 Parameter #32 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 #40 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:

Parameter	Description
`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.
`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 30 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.

5300-NAS>+++
OK
at
OK
 
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 4-9.

Figure 4-9: Using Modem-Escape Mode to View Client-Side Modem Statistics

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&v1. For additional client report statistics, enable Window's modemlog.txt or ppplog.txt files.

ati6
U.S. Robotics 56K FAX EXT Link Diagnostics...
 
Chars sent                   98      Chars Received           104701
Chars lost                    0
Octets sent                 354      Octets Received          104701
Blocks sent                  95      Blocks Received             914
Blocks resent                 4
 
Retrains Requested            0      Retrains Granted              0
Line Reversals                0      Blers                         0
Link Timeouts                 0      Link Naks                     1
 
Data Compression       NONE
Equalization           Long
Fallback               Enabled
Protocol               LAPM
Speed                  48000/28800 
V.90 Peak Speed        48000
Current Call           00:04:46
 
Online
 
OK

Tips 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).

aty11
 
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
 
ati11
U.S. Robotics 56K FAX EXT Link Diagnostics...
 
 
Modulation                  V.90
Carrier Freq     (Hz)       None/1920
Symbol Rate                 8000/3200
Trellis Code                None/64S-4D
Nonlinear Encoding          None/ON
Precoding                   None/ON
Shaping                     ON/ON
Preemphasis      (-dB)      6/2
Recv/Xmit Level  (-dBm)     19/10
Near Echo Loss   (dB)       7
Far Echo Loss    (dB)       0
Carrier Offset   (Hz)       NONE
Round Trip Delay (msec)     24
Timing Offset    (ppm)      1638
SNR              (dB)       48.1
Speed Shifts Up/Down        0/0
Status :                    uu,5,13Y,19.4,-15,1N,0,51.1,7.3
OK

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.

ato
% Unknown command or computer name, or unable to find computer address
5300-NAS>

What to do Next

Perform the tasks in the section "Configuring PPP and Authentication."

Table of Contents

Verifying Modem Performance