T1 CAS VoIP for Cisco Access Platforms

This feature adds support for T1 Channel Associated Signaling (CAS) and limited support for E1 R2 signaling to the Cisco AS5300 universal access server with the Voice Feature Card (VFC).

CAS is the transmission of signaling information within the voice channel. Various types of CAS signaling are available in the T1 world. The most common forms of CAS signaling are loop-start, ground-start, and E&M. The biggest disadvantage of CAS signaling is its use of user bandwidth to perform signaling functions. CAS signaling is often referred to as robbed-bit-signaling because user bandwidth is being "robbed" by the network for other purposes. In addition to receiving and placing calls, CAS signaling also processes the receipt of DNIS and ANI information, which is used to support authentication and other functions.

The service provider application for T1 CAS includes connectivity to the public network using T1 CAS from the Cisco AS5300 to the end office switch. In this configuration, the Cisco AS5300 captures the dialed-number or called-party number information and passes it along to the upper level applications for IVR script selection, modem pooling, and other applications. Service providers also require access to calling party number, ANI, for user identification, for 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 their VoIP connectivity to the PSTN; others will use tandem-type service provider connections.

Benefits

The T1 CAS interface is used for both connection to private PBX's, and to the PSTN. This feature is required by both Enterprise customers and Service Providers in North America. For most enterprise customers, T1 CAS is the only kind of line they use from the PSTN, and for connecting to their PBX's, E&M may be the only option.

List of Terms

E&M—Ear and mouth. A signaling technique for two and four wire telephone and trunk interfaces.

FXS—Foreign Exchange Subscriber (as in FXS-loop-start and FXS-ground-start). FXS loop and ground start protocols are a type of signaling used to indicate the beginning of a call. The FXS interface is used on the line-side access to CO (for example, communication between CO and key system).

MF—Multiple Frequency, an interoffice address signaling method in which 10 decimal digits and five auxiliary signals are each represented by a pair of the following frequencies: 700, 900, 1100, 1300, 1500 and 1700 Hz.

Session Application—Application in the VoIP system responsible for providing the telephony user interface.

SAS—Special Exchange Subscriber (as in SAS loop-start and ground-start). Identical to FXS loop and ground start in functionality, but use of the A and B bits are different. (SAS transmitted B Bits are complementary to FXS transmitted B bits. SAS received A bits are complementary to FXS received A bits).

SGCP Application—The application in the VoIP via SGCP system responsible for SGCP call management.

VFC—Voice feature card. The voice processing card which resides in one of the slots in the Cisco AS5300 platform. Up to five DSP modules (DSPM) can be installed onto the VFC to perform voice processing for up to 30 B channels and potentially 60 B channels. The VFC is a multi-DSP coprocessing card and software package that adds VoIP capabilities to the Cisco AS5300.

VoIP—Voice over IP. The ability to carry normal telephony-style voice over an IP-based internet with POTS-like functionality, reliability, and voice quality. VoIP is a blanket term which generally refers to Cisco's standards-based (for example, H.323) approach to IP voice traffic.

Platforms

Cisco IOS software is packaged in feature sets that support specific platforms. To get updated information regarding platform support for this feature, access Cisco Feature Navigator. Cisco Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature.

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Functional Description

The new functionality of T1 CAS for VoIP includes all the T1 CAS and E1/R2 signaling already supported for the Cisco AS5300 in data applications, with the addition of dialed-number and calling-party number capture whenever available.

The implementation of this feature supports the following T1 CAS signaling systems for VoIP applications:

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

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 tells the originating side that the terminating side is ready to receive addressing digits. After receiving addressing digits, the terminating side then goes off-hook for the duration of the call. The originating endpoint maintains off-hook for the duration of the call.

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 (transition from on-hook to off-hook and back again) just as in the original Wink Start. This wink tells the originating side that the terminating side is ready to receive addressing digits. After receiving addressing digits, the terminating side then provides another wink (called an Acknowledgment Wink) that tells the originating side that the terminating side has received the dialed digits. The terminating side then goes off-hook to indicate connection when the ultimate called endpoint has answered. The originating endpoint maintains off-hook for the duration of the call.

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

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Ground Start / FXS—Ground Start Signaling was developed to aid in resolving 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 CPE using loop start was to ring the phone. The 6-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 is different than E&M in that 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 the A bit to 0. The Central Office 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.

Channelized T1 Robbed Bit Features

Internet service providers can provide switched 56-kbps access to their customers using the Cisco AS5300. The subset of T1 CAS (robbed bit) supported features are as follows:

Supervisory: Line Side

Supervisory: Trunk Side

Informational: Line Side

Informational: Trunk Side

Configuration Tasks

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.

Note For additional software configuration examples using T1 signaling, see Configuring Channelized T1 or E1. To access the document on Cisco Connection Online (CCO), go the following URL: http://www.cisco.com/univercd/cc/td/doc/product/access/acs_serv/5300/5300swbk/5300bas.htm#xtocid1968913

Configuring Service Provider T1 CAS

The following sample configuration is an example of how to configure the voice ports as a cas-group for the channelized T1 lines.


Step	Command	Purpose
1	`5300> enable` `Password: <password>` `5300#`	Enter enable mode. Enter the password. You have entered enable mode when the prompt changes to `5300#`.
2	`5300# config term` `Enter configuration commands, one per line. End` `with CNTL/Z.` `5300(config)#`	Enter global configuration mode. You have entered global configuration mode when the `5300#` prompt changes to `5300(config)#.`
3	`5300(config)# controller t1 0`	Enter controller configuration mode to configure your controller port. The controller ports are labeled 0 through 3 on the Quad T1/PRI and E1/PRI cards.
4	`5300(config-controller)# framing esf`	Enter your telco's framing type.
5	`5300(config-controller)# clock source line primary`	Enter the clock source for the line. Configure other lines as clock source secondary or internal. Note that only one PRI can be clock source primary and one PRI can be clock source secondary.
6	`5300(config-controller)# linecode b8zs`	Enter your telco's line code type.
7	`5300(config-controller)# cas-group 1 timeslots 1-24 type e&m-fgb dtmf dnis`	Configure all channels for E&M, FXS, and SAS analog signaling. Enter 1-24 for T1. If E1, enter 1-31. Signaling types include e&m-fgb, e&m-fgd, e&m-immediate-start, fxs-ground-start, fxs-loop-start, sas-ground-start, and sas-loop-start. You must use the same type of signaling that your central office uses. For E1 using the Anadigicom converter, use cas e&m-fgb signaling.
8	`5300(config-controller)# controller t1 1` `5300(config-controller)# framing esf` `5300(config-controller)# linecode b8Zs` `5300(config-controller)# clock source line secondary` `5300(config-controller)# cas-group 2 timeslots 1-24 type e&m-fgb`	Repeat steps 3 to 7 to configure each additional controller (there are four). In this example, note that the controller number is 1, instead of 0. The clock source is secondary, instead of primary. The cas-group is 2, instead of 1.
9	`5300(config-controller)# controller T1 2` `5300(config-controller)# clock source internal` `5300(config-controller)# cas-group 0 timeslots 1-24 type e&m-fgd mf ani-dnis`	Repeat steps 3 to 7 to configure each additional controller (there are four).
10	`5300(config-controller)# controller T1 3` `5300(config-controller)# clock source internal`	Repeat steps 3 to 7 to configure each additional controller (there are four).
11	`5300(config-controller)# dial-peer voice 3070 pots` `destination-pattern +30...` `port 0:1` `prefix 30`	Enter the dial peer configuration mode to configure a POTS peer. Specify destination pattern for this POTS peer.
12	`5300(config-controller)# dial-peer voice 4080 pots` `destination-pattern +40...` `direct-inward-dial` `port 1:2` `prefix 40`	Specify destination pattern, and direct inward dial for each POTS peer.
13	`5300(config-controller)# dial-peer voice 1050 pots` `destination-pattern +10...` `direct-inward-dial` `prefix 50`	Specify the destination pattern and the direct inward dial for the dial peer.
14	`5300(config-controller)# dial-peer voice 2060 pots` `destination-pattern +20...` `direct-inward-dial` `prefix 60`	Specify the destination pattern and the direct inward dial for the dial peer.
15	`5300(config-controller)# dial-peer voice 5050 voip` `answer-address 10...` `destination-pattern +50...`
16	`5300(config-if)# Ctrl-Z` `5300#` `%SYS-5-CONFIG_I: Configured from console by console`	Return to enable mode. This message is normal and does not indicate an error.

Verify

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Enter the show controller t1 or show controller e1 command and specify the port number.

Tips

Command Reference

This section documents new or modified commands. All other commands used with this feature are documented in the Cisco IOS Release 11.3 command references.

cas-group - (controller t1)

To configure a channel group using CAS signaling, the cas-group command is used to specify the channels/timeslots to be allocated for the CAS group and the CAS signaling type.

cas-group channel timeslots range type signal [[tone] [service]]
no cas-group channel timeslots range type signal [[tone] [service]

Use the no form of this command to disable channel associated signaling for one or more timeslots. The service type are:

For these two CAS signaling types the tone type is always set to mf and dnis is always required. They can be used for both voice and data calls.


channel	Specifies a single channel group number, which can be between 0 and 23.
timeslots range	Specifies a timeslot range of values from 1 to 24.
type signal	Specifies the type of robbed bit signaling. Choose one of the following signal types to configure: •e&m-fgb dtmf [dnis] or e&m-fgb mf [dnis]—Specifies ear and mouth channel signaling with feature group B support, which includes the wink start protocol. You can further customize this feature by specifying dtmf [dnis] or mf [dinis]. •e&m-fgd dtmf [dnis] or e&m-fgd mf [ani-dnis]—Specifies ear and mouth channel signaling with feature group D support, which includes the wink start protocol. ani-dnis means the CAS group is provisioned to collect ANI (answer number identification) and DNIS (dialed number identification). •e&m-immediate-start—Specifies ear and mouth channel signaling with immediate start support. •fxs-loop-start— Specifies Foreign Exchange Station loopstart signaling support. •fxs-ground-start—Specifies Foreign Exchange Station ground start signaling support. •sas-loop-start—Specifies Special Access Station loopstart signaling support. •sas-ground-start—Specifies Special Access Station ground start signaling support.
tone	specify dtmf or mf
service	specify voice or data

Default

Command Mode

Usage Guidelines

This command was implemented on the Cisco AS5850 platform in Cisco IOS Release 12.2(2)XB1.

Use this command to enable an integrated modem to receive and transmit incoming and outgoing call signaling (such as on-hook and off-hook) through each T1 controller.

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If you want to collect DNIS information on a T1 controller, you must manually configure it on the access server.

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To collect DTMF DNIS for E&M-fgb under a controller T1 configuration, issue the cas-group 0 timeslots 1-24 type e&m-fgb dtmf dnis command.

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To collect MF DNIS for E&M-fgb, issue the cas-group 0 timeslots 1-24 type e&m-fgb mf dnis command.

By configuring DNIS as part of the cas-group command, the system can collect DNIS digits for incoming calls which can be directed as VoIP calls, or alternately can be redirected to specific modem pools setup for different customers or uses. To support modems you must be running MICA modems in the system and have at least 10% of your total modems in the default modem pool.

The following example configures the required signaling to support modem pooling and the digital number identification service (DNIS) over channelized T1 lines on a Cisco AS5300.

Example Configuration

Note T1 CAS fgd is asymmetric. When calling the switch, we only generate DNIS. When receiving form the CO, we get both ANI and DNIS.

Table Of Contents

Configuring T1 CAS for VoIP on Cisco Access Platforms

Feature Summary