ISDN Voice Configuration Guide, Cisco IOS Release 15M&T
Implementing T1 CAS for VoIP
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Implementing T1 CAS for VoIP

Implementing T1 CAS for VoIP

Last Updated: December 4, 2012

This chapter describes how to implement the T1 Channel-Associated Signaling (CAS) for VoIP feature. This feature adds support for T1 CAS and E1 R2 signaling with the voice feature card (VFC).

The T1 CAS interface is used for connection to both a private PBX and the PSTN. This feature is required by North American enterprise customers and service providers. For most enterprise customers, T1 CAS is the only type of line they use from the PSTN; E&M may be the only option for connecting to their PBX.

Feature History for T1 CAS for VoIP

Release

Modification

12.1(5)XM

This feature was introduced on the Cisco AS5800.

12.2(2)XB1

This feature was implemented on the Cisco AS5850.

12.2(11)T

This feature was integrated into this release.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Prerequisites for Configuring T1 CAS

  • Perform the prerequisites that are listed in the "Prerequisites for Configuring ISDN Voice Interfaces" section.

Restrictions for Configuring T1 CAS

Restrictions are described in "Restrictions for Configuring ISDN Voice Interfaces". In addition, the following applies.

Internet service providers can provide switched 56-kbps access to their customers with this feature. The subset of T1 CAS (robbed-bit) supported features is as follows:

  • Supervisory: line side
    • fxs-ground-start
    • fxs-loop-start
    • sas-ground-start
    • sas-loop-start
    • Modified R1
  • Supervisory: trunk side
    • e&m-fgb
    • e&m-fgd

Note


e&m-fgd can receive calling-party number (ANI) and send called-party number (dialed-number identification service or DNIS) but cannot send ANI.
    • e&m immediate start
    • fgd-eana

Note


fgd-eana can send both ANI and DNIS but cannot receive ANI.
  • Informational: line side
    • DTMF
  • Informational: trunk side

Information About T1 CAS for VoIP


Note


General information about ISDN voice interfaces is presented in the "Information About ISDN Voice Interfaces" section.

CAS Basics

CAS is the transmission of signaling information within the voice channel. In addition to receiving and placing calls, CAS also processes the receipt of DNIS and ANI information, which is used to support authentication and other functions.

Various types of CAS are available in the T1 world. The most common forms are loop-start, ground-start, Equal Access North American (EANA), and E&M.

The biggest disadvantage of CAS is its use of user bandwidth to perform signaling functions. CAS is often referred to as robbed-bit-signaling because user bandwidth is "robbed" by the network for other purposes.

Service-provider application for T1 CAS includes connectivity to the public network using T1 CAS from the Cisco router to the end-office switch. In this configuration, the router captures dialed-number or called-party-number information and passes it to the upper-level applications for IVR script selection, modem pooling, and other applications. Service providers also require access to ANI for user identification, billing account number, and, in the future, more complicated call routing.

Service providers who implement VoIP include traditional voice carriers, new voice and data carriers, and existing internet service providers. Some of these service providers might use subscriber-side lines for VoIP connectivity to the PSTN; others use tandem-type service-provider connections.

New CAS functionality for VoIP includes all CAS and E1/R2 signaling already supported for supported Cisco platforms in data applications, with the addition of dialed-number and calling-party-number capture whenever available.

EandM and Ground Start Protocols

This feature supports the following T1 CAS systems for VoIP applications:

  • E&M--E&M robbed-bit signaling is typically used for trunks. It is generally the only way that a CO switch can provide two-way dialing with direct inward dialing. In all E&M protocols, off-hook is indicated by A=B=1 and on-hook is indicated by A=B=0. For dial-pulse dialing, the A and B bits are pulsed to indicate the addressing digits. There are several further important subclasses of E&M robbed-bit signaling:
    • EandM Wink Start--Feature Group B

In the original Wink Start protocol, the terminating side responds to an off-hook from the originating side with a short wink (transition from on-hook to off-hook and back again). This wink indicates that the terminating side is ready to receive addressing digits. After receiving digits, the terminating side goes off-hook for the duration of the call. The originating side maintains off-hook for the duration of the call.

    • E&M Wink Start--Feature Group D

In Feature Group D Wink Start with Wink Acknowledge Protocol, the terminating side responds to an off-hook from the originating side with a short wink just as in the original Wink Start. After receiving digits, the terminating side provides another wink (called an acknowledgment wink) to indicate that the terminating side has received the digits. The terminating side goes off-hook to indicate connection when the ultimate called endpoint has answered. The originating side maintains off-hook for the duration of the call.

    • E&M Immediate Start

In the Immediate Start Protocol, the originating side does not wait for a wink before sending addressing digits. After receiving digits, the terminating side goes off-hook for the duration of the call. The originating side maintains off-hook for the duration of the call.

  • Ground Start/FXS--Ground Start Signaling was developed to help resolve glare when two sides of the connection tried to go off-hook at the same time. This is a problem with loop start because the only way to indicate an incoming call from the network to the customer premises equipment (CPE) using loop start was to ring the phone. The six-second ring cycle left a lot of time for glare to occur. Ground Start Signaling eliminates this problem by providing an immediate-seizure indication from the network to the CPE. This indication tells the CPE that a particular channel has an incoming call on it. Ground Start Signaling differs from E&M because the A and B bits do not track each other (that is, A is not necessarily equal to B). When the CO delivers a call, it seizes a channel (goes off-hook) by setting A to 0. The CO equipment also simulates ringing by toggling the B bit. The terminating equipment goes off-hook when it is ready to answer the call. Digits are usually not delivered for incoming calls.

How to Configure T1 CAS for VoIP

Configuring T1 CAS for Use with VoIP

To configure T1 CAS for use with VoIP, perform the following steps.


Note


The following shows how to configure the voice ports as ds0-group for channelized T1 lines.
SUMMARY STEPS

1.    enable

2.    configure terminal

3.    controller {t1| e1} slot / port

4.    framing type

5.    linecode type

6.    ds0-group group-number timeslots range type type {dtmf| mf} {ani| dnis| ani-dnis}

7.    Repeat steps 4 to 6 for each additional controller (there are 12). Be sure to increment the controller number and ds0-group number.

8.    dial-peer voice tag type

9.    dial-peer voice tag type

10.    Repeat steps 8 and 9 for each dial peer.

11.    exit


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Router> enable

 

Enters privileged EXEC mode. Enter your password when prompted.

 
Step 2
configure terminal


Example:

Router# configure terminal

 

Enters global configuration mode.

 
Step 3
controller {t1| e1} slot / port


Example:

Router(config)# controller t1 1/0/0

 

Enters controller configuration mode for the specified slot/port. The controller ports are labeled RI and E1/PRI cards.

 
Step 4
framing type


Example:

Router(config-control)# framing esf

 

Enters your telco framing type.

 
Step 5
linecode type


Example:

Router(config-control)# linecode b8zs

 

Enters your telco line code type.

 
Step 6
ds0-group group-number timeslots range type type {dtmf| mf} {ani| dnis| ani-dnis}


Example:

Router(config-control)# ds0-group 1 timeslots 1-24 type e&m-fgb

 

Configures all channels for E&M, FXS, and SAS analog signaling. T1 range: 1 to 24. E1 range: 1to 31.

Some of the valid signaling types and keyword combinations are as follows:

  • Type: e&m-fgb
    • dtmf and dnis
    • mf and dnis
  • Type: e&m-fgd
    • dtmf and dnis
    • mf and ani-dnis or dnis
  • Type: fgd-eana
    • mf and ani-dnis
Note    Use the same type of signaling that your central office uses. For E1 using the Anadigicom converter, use e&m-fgb. See restrictions applicable to e&m-fgb and e&m-fgd in the Restrictions for Configuring T1 CAS.
 
Step 7
Repeat steps 4 to 6 for each additional controller (there are 12). Be sure to increment the controller number and ds0-group number. 
--
 
Step 8
dial-peer voice tag type


Example:

destination-pattern



Example:

port



Example:

prefix



Example:

Router(config-control)# dial-peer voice 3070 pots



Example:

destination-pattern 30...



Example:

port 1/0/0:D



Example:

prefix 30

 

Enters dial-peer configuration mode and configures a POTS peer destination pattern.

 
Step 9
dial-peer voice tag type


Example:

incoming called-number



Example:

destination-pattern



Example:

direct-inward-dial



Example:

port



Example:

prefix



Example:

Router(config-control)# dial-peer voice 21 pots



Example:

incoming called-number 11...



Example:

destination-pattern 40...



Example:

direct-inward-dial



Example:

port 12/0:2:0



Example:

prefix 21

 

Specifies, for each POTS peer, the following: incoming called number, destination pattern, and direct inward dial.

 
Step 10
Repeat steps 8 and 9 for each dial peer. 

--

 
Step 11
exit


Example:

Router(config-control)# exit

 

Exits the current mode.

Note    The message "%SYS-5-CONFIG_I: Configured from console by console" is normal and does not indicate an error.
 

Verifying and Troubleshooting a T1 CAS Configuration

To verify and troubleshoot a T1 CAS configuration, perform the following steps (listed alphabetically).

SUMMARY STEPS

1.    debug cas

2.    show controllers t1 | e1 dial-shelf / slot / port

3.    show isdn status

4.    show running-config

5.    show voice port


DETAILED STEPS
Step 1   debug cas

Use the debug cascommand to identify and troubleshoot call connection problems on a T1/E1 interface. With this command, you can trace the complete sequence of incoming and outgoing calls.

Examples

The following shows an example session to enable debugging CAS and generate troubleshooting output:



Example:
Router# show debug 
Router# debug cas slot 1 port 0 
CAS debugging is on 
Router# 
debug-cas is on at slot(1) dsx1(0) 
Router# show debug 
CAS debugging is on

The following example shows output for the first outgoing call:



Example:
Router# p 1.1.1.2
Type escape sequence to abort. 
Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds:
*Mar 2 00:17:45: dsx1_alloc_cas_channel: channel 0 dsx1_timeslot 
1(0/0): TX SEIZURE (ABCD=0001)(0/0): RX SEIZURE_ACK (ABCD=1101)(0/1): 
RX_IDLE (ABCD=1001)(0/2): RX_IDLE (ABCD=1001)(0/3): RX_IDLE 
(ABCD=1001)(0/4): RX_IDLE (ABCD=1001)(0/5): RX_IDLE (ABCD=1001)(0/6): 
RX_IDLE (ABCD=1001)(0/7): RX_IDLE (ABCD=1001)(0/8): RX_IDLE 
(ABCD=1001)(0/9): RX_IDLE (ABCD=1001)(0/10): RX_IDLE (ABCD=1001)(0/11): 
RX_IDLE (ABCD=1001)(0/12): RX_IDLE (ABCD=1001)(0/13): RX_IDLE 
(ABCD=1001)(0/14): RX_IDLE (ABCD=1001)(0/16): RX_IDLE (ABCD=1001)(0/17): 
RX_IDLE (ABCD=1001)(0/18): RX_IDLE (ABCD=1001)(0/19): RX_IDLE 
(ABCD=1001)(0/20): RX_IDLE (ABCD=1001)(0/21): RX_IDLE 
(ABCD=1001).(0/22): RX_IDLE (ABCD=1001)(0/23): RX_IDLE 
(ABCD=1001)(0/24): RX_IDLE (ABCD=1001)(0/25): RX_IDLE (ABCD=1001)(0/26): 
RX_IDLE (ABCD=1001)(0/27): RX_IDLE (ABCD=1001)(0/28): RX_IDLE 
(ABCD=1001)(0/29): RX_IDLE (ABCD=1001)(0/30): RX_IDLE 
(ABCD=1001)...(0/0): RX ANSWERED (ABCD=0101). 
Success rate is 0 percent (0/5) 
Router# 
*Mar 2 00:18:13.333: %LINK-3-UPDOWN: Interface Async94, changed state to up 
*Mar 2 00:18:13.333: %DIALER-6-BIND: Interface As94 bound to profile Di1 
*Mar 2 00:18:14.577: %LINEPROTO-5-UPDOWN: Line protocol on Interface Async94, changed 
state to up 
Router# p 1.1.1.2 
Type escape sequence to abort. 
Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: 
!!!!! 
Success rate is 100 percent (5/5), round-trip min/avg/max = 160/180/236 ms

The following example shows that the call is cleared on the router:



Example:
Router# clear int dialer 1 
Router#
(0/0): TX IDLE (ABCD=1001)(0/0): RX IDLE (ABCD=1001) 
*Mar 2 00:18:28.617: %LINK-5-CHANGED: Interface Async94, changed state to reset 
*Mar 2 00:18:28.617: %DIALER-6-UNBIND: Interface As94 unbound from profile Di1 
*Mar 2 00:18:29.617: %LINEPROTO-5-UPDOWN: Line protocol on Interface Async94, changed 
state to down 
et2-c3745-1# 
*Mar 2 00:18:33.617: %LINK-3-UPDOWN: Interface Async94, changed state to down

The following example shows a subsequent outbound CAS call:



Example:
Router# p 1.1.1.2
 
Type escape sequence to abort. 
Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds:
*Mar 2 00:18:40: dsx1_alloc_cas_channel: channel 5 dsx1_timeslot 
6(0/5): TX SEIZURE (ABCD=0001)(0/5): RX SEIZURE_ACK 
(ABCD=1101)....(0/5): RX ANSWERED (ABCD=0101). 
Success rate is 0 percent (0/5) 
Router# 
*Mar 2 00:19:08.841: %LINK-3-UPDOWN: Interface Async93, changed state to up 
*Mar 2 00:19:08.841: %DIALER-6-BIND: Interface As93 bound to profile Di1 
*Mar 2 00:19:10.033: %LINEPROTO-5-UPDOWN: Line protocol on Interface Async93, changed 
state to up 
Router# p 1.1.1.2 
Type escape sequence to abort. 
Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: 
!!!!! 
Success rate is 100 percent (5/5), round-trip min/avg/max = 160/167/176 
ms

The following example shows the call cleared by the switch:



Example:
Router# 
(0/5): TX IDLE (ABCD=1001)(0/5): RX IDLE (ABCD=1001) 
*Mar 2 00:19:26.249: %LINK-5-CHANGED: Interface Async93, changed state to reset 
*Mar 2 00:19:26.249: %DIALER-6-UNBIND: Interface As93 unbound from profile Di1 
*Mar 2 00:19:27.249: %LINEPROTO-5-UPDOWN: Line protocol on Interface Async93, changed 
state to down 
Router# 
*Mar 2 00:19:31.249: %LINK-3-UPDOWN: Interface Async93, changed state to down

The following example shows an incoming CAS call:



Example:
Router# 
(0/0): RX SEIZURE (ABCD=0001) 
*Mar 2 00:22:40: dsx1_alloc_cas_channel: channel 0 dsx1_timeslot 
1(0/0): TX SEIZURE_ACK (ABCD=1101)(0/0): TX ANSWERED (ABCD=0101) 
Router# 
*Mar 2 00:23:06.249: %LINK-3-UPDOWN: Interface Async83, changed state to up 
*Mar 2 00:23:06.249: %DIALER-6-BIND: Interface As83 bound to profile Di1 
*Mar 2 00:23:07.653: %LINEPROTO-5-UPDOWN: Line protocol on Interface Async83, changed 
state to up
Step 2   show controllers t1 | e1 dial-shelf / slot / port

Use this command to display the controller and alarm status for the specified dial shelf/slot/port. Configuration is successful if the controller reports being up and no error are reported.



Example:
Router# show controllers t1 1/0/0
T1 1/0/0 is up.
  Applique type is Channelized T1
  Cablelength is long gain36 0db
  No alarms detected.
  alarm-trigger is not set
  Framing is ESF, Line Code is B8ZS, Clock Source is Line.
  Data in current interval (180 seconds elapsed):
     0 Line Code Violations, 0 Path Code Violations
     0 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins
     0 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs
Step 3   show isdn status

Use this command to display the status of all ISDN interfaces, including active layers, timer information, and switch-type settings.

Step 4   show running-config

Use this command to display the basic router configuration.

Step 5   show voice port

To display configuration information about a specific voice port, use the show voice port command in privileged EXEC mode. Command syntax and options vary according to platform and configuration.


Configuration Example for T1 CAS for VoIP

The sample configuration is only intended as an example of how to use the commands to configure T1 CAS. It is not an example of a complete configuration for setting up the entire signaling for a telco network.

Figure 1 T1 CAS for VoIP: Network Topology


Router# show running-config
version 12.1
service timestamps debug datetime msec localtime show-timezone
service timestamps log datetime msec localtime show-timezone
service password-encryption
!
hostname travis-nas-01
!
aaa new-model
aaa authentication login default local
aaa authentication login NO_AUTHENT none
aaa authorization exec default local if-authenticated
aaa authorization exec NO_AUTHOR none
aaa authorization commands 15 default local if-authenticated
aaa authorization commands 15 NO_AUTHOR none
aaa accounting exec default start-stop group tacacs+
aaa accounting exec NO_ACCOUNT none
aaa accounting commands 15 default stop-only group tacacs+
aaa accounting commands 15 NO_ACCOUNT none
enable secret 5 $1$LsoW$K/qBH9Ih2WstUxvazDgmY/
!
username admin privilege 15 password 7 06455E365E471D1C17
username gmcmilla password 7 071824404D06140044
username krist privilege 15 password 7 0832454D01181118
!
call rsvp-sync
shelf-id 0 router-shelf
shelf-id 1 dial-shelf
!
resource-pool disable
!
modem-pool Default
 pool-range 1/2/0-1/2/143,1/3/0-1/3/143
!
modem-pool accounts
!
modem-pool accounts1
!
modem-pool accounts2
!
clock timezone CST -6
clock summer-time CST recurring
!
ip subnet-zero
ip domain-name cisco.com
ip name-server 172.22.53.210
ip name-server 171.69.2.133
ip name-server 171.69.2.132
ip name-server 171.69.11.48
!
isdn switch-type primary-5ess
!
controller T1 1/0/0
 framing esf
 linecode b8zs
ds0-group 1 timeslots 1-24 type e&m-fgb
!
controller T1 1/0/1
 framing esf
 linecode b8zs
 ds0-group 1 timeslots 1-24 type e&m-fgb
!
controller T1 1/0/2
 framing esf
 linecode b8zs
 ds0-group 1 timeslots 1-24 type e&m-fgb
!
controller T1 1/0/3
 framing esf
 linecode b8zs
 ds0-group 0 timeslots 1-24 type e&m-fgb dtmf dnis
!
controller T1 1/0/4

Additional References

General ISDN References

  • "Overview of ISDN Voice Interfaces" --Describes relevant underlying technology; lists related documents, standards, MIBs, and RFCs; and describes how to obtain technical assistance
  • "Additional References" section --Lists additional ISDN references

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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

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