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Cisco IOS Software Releases 12.3 T

Trunk-Management Features

Table Of Contents

Trunk-Management Features

Contents

Information About Trunk Management

Simulated Lines and Trunks

Trunk Conditioning

Congestion Monitoring and Management Features

T1/E1 Alarm Conditioning Feature

PSTN Fallback Feature

Busyout Features

Call Admission Control Features

Analog DID Feature

Analog Centralized Automatic Message Accounting E911 Trunk Feature

How to Configure Trunk Conditioning and Connections

Prerequisites for Configuring Trunk Conditioning and Connections

Configuring Trunk Conditioning

Configuring Trunk-Conditioning Signaling Attributes

Assigning Trunk-Conditioning Attributes to Network Dial Peers

Assigning Voice Classes to Voice Ports

Verifying Signaling Attributes and Trunk Conditioning

Configuring T1/E1 Alarm Conditioning

Assigning Alarm-Generation Parameters

Verifying Alarm-Generation Parameters

Configuring Trunk Connections

Configuring PLAR (Switched) Connections

Configuring Trunk and Tie-Line Connections

Configuring PLAR-OPX Connections

Configuration Examples for Trunk Conditioning and Connections

Trunk-Conditioning: Example

PLAR (Switched Calls) Configuration: Example

Permanent Trunks Configuration: Example

How to Configure Trunk Monitoring and Management

Configuring Analog Centralized Automatic Message Accounting E911 Trunk

Configuring CAMA Card for CAMA Signaling

Configuring ANI Mapping

Verifying CAMA Signaling

Troubleshooting Tips

Monitoring and Maintaining Analog CAMA-E911

Configuring Analog DID

Configuring Voice Ports to Support DID

Verifying DID Voice-Port Configuration

Configuring Call Admission Control

Configuring Call Admission Control for H.323 VoIP Gateways

Configuring MGCP VoIP Call Admission Control

Configuring Local and Advanced Voice Busyout

Configuring the Busyout Trigger Event

Configuring a Voice Port to Busy Out

Configuring a Voice Port to Monitor the Link to a Remote Interface

Configuring a Busyout-Monitoring Voice Class

Configuring a Graceful Busyout

Configuring Busyout Monitor

Configuring Busyout Monitor Gatekeeper

Verifying Busyout Status

Configuring PSTN Fallback

Configuring Fallback to Alternate Dial Peers

Configuring Destination Monitoring without Fallback to Alternate Dial Peers

Configuring Call-Fallback Cache Parameters

Configuring Call-Fallback Jitter-Probe Parameters

Configuring Call-Fallback Probe-Timeout and Weight Parameters

Configuring Call-Fallback Threshold Parameters

Configuring Call-Fallback Wait-Timeout

Configuring VoIP Alternate Path Fallback SNMP Trap

DETAILED STEPS

What to Do Next

Configuring Call-Fallback Map Parameters

Verifying PSTN Fallback Configuration

Monitoring and Maintaining PSTN Fallback

Configuration Examples for Trunk Monitoring and Management

Analog Centralized Automatic Message Accounting E911 Trunk: Examples

Busyout: Examples

Local Voice Busyout Configuration: Examples

Alarm Trigger for Busyout of Voice Ports Configuration: Example

Call Admission Control: Examples

Call Admission Control for H.323 VoIP Gateways: Examples

MGCP VoIP Call Admission Control: Examples

PSTN Fallback: Examples

Additional References

Related Documents

MIBs

Technical Assistance


Trunk-Management Features


This document describes how to condition and connect trunks and how to configure the following trunk-management features:

Analog Centralized Automatic Message Accounting E911 Trunk

Analog DID (Direct Inward Dial)

Busyout features:

Busyout Monitor

Local and Advanced Voice Busyout

Call admission control (CAC) features:

Call Admission Control for H.323 VoIP Gateways

MGCP VoIP Call Admission Control

PSTN Fallback

T1/E1 Alarm Conditioning

Trunk Conditioning

Feature History for Analog Centralized Automatic Message Accounting E911 Trunk

Release
Modification

12.2(11)T

This feature was introduced on the Cisco 2600 series, Cisco 3600 series, and Cisco 3700 series.


Feature History for Analog DID (Direct Inward Dial)

Release
Modification

12.1(5)XM

This feature was introduced on the Cisco 2600 series and Cisco 3600 series.

12.2(2)T

This feature was integrated into this release.


Feature History for Busyout Monitor

Release
Modification

12.0(3)T

This feature was introduced on the Cisco MC3810.

12.0(5)XK

This feature was implemented on the Cisco 2600 series and Cisco 3600 series.

12.0(7)T

This feature was integrated into this release.


Feature History for CAC Features (Call Admission Control for H.323 VoIP Gateways and MGCP VoIP Call Admission Control

Release
Modification

12.1(5)XM

This feature was introduced on the Cisco AS5300, Cisco AS5400, and Cisco AS5800.

12.2(2)T

This feature was integrated into this release.


Feature History for Local and Advanced Voice Busyout

Release
Modification

12.2(13)T

This feature was introduced on the Cisco 200, Cisco 2600 series, Cisco 3600 series, and Cisco 3725.

12.4(2)XA

This feature was enhanced on the Cisco 2600 series and Cisco 3600 series to include support for the busyout monitor gatekeeper command under the voice class busyout mode.

12.4(6)T

The busyout monitor gatekeeper command feature was integrated into this release.


Feature History for PSTN Fallback

Release
Modification

12.1(3)T

This feature was introduced on the Cisco 2600 series, Cisco 3600 series, and Cisco MC3810.

12.2(2)XA

The call fallback and call fallback reject-cause-code commands were introduced.

12.2(4)T

This feature was implemented on the Cisco 7200 series and Cisco 7500 series.

12.3(14)T

The VoIP Alternate Path Fallback SNMP Trap feature was added to the PSTN Fallback feature.


Feature History for T1/E1 Alarm Conditioning

Release
Modification

12.1(3)T

This feature was introduced on the Cisco 2600 series, Cisco 3600 series, and Cisco MC3810.


Feature History for Trunk Conditioning

Release
Modification

12.0(3)XG

This feature was introduced on the Cisco MC3810.

12.0(4)T

This feature was integrated into this release.


Finding Support Information for Platforms and Cisco IOS Software Images

Use Cisco Feature Navigator to find information about platform support and Cisco IOS and CatOS software image support. Access Cisco Feature Navigator at http://www.cisco.com/go/fn.


Note For more information about this and related Cisco IOS voice features, see the entire Cisco IOS Voice Configuration Library—including library preface and glossary, other feature documents, and troubleshooting documentation—at http://www.cisco.com/en/US/products/ps6441/prod_configuration_guide09186a0080565f8a.html.


Contents

Information About Trunk Management

How to Configure Trunk Conditioning and Connections

Configuration Examples for Trunk Conditioning and Connections

How to Configure Trunk Monitoring and Management

Configuration Examples for Trunk Monitoring and Management

Additional References

Information About Trunk Management

A trunk is a communication line between two switching systems—in this case, the switching equipment in a central office (CO) and a PBX. It is a physical and logical point-to-point connection with a permanent wire over which network traffic travels. A backbone is composed of a number of trunks.

VoIP simulates trunk connections between PBXs that are connected to Cisco routers or access servers on each side of the network.

In Figure 1, two PBXs connect to a router using a simulated trunk and a recEive and transMit (E&M) voice port. In this case, a permanent, nonswitched connection transparently connects the two PBXs.

Figure 1 Simulated Trunk Connection

Simulated Lines and Trunks

Simulated lines and trunks enable a telephone user at one location to dial an access code to access a PBX at another location. The user hears a second dial tone from the remote PBX. You can configure two types of simulated connection—switched and permanent—for both analog and digital systems. The connection command creates these connections.

The connection trunk command creates a permanent call that is connected as soon as the routers on each end are booted (see Figure 2). Permanent calls pass limited telephony signaling and operate without collecting digits or requiring changes to the overall dial plan.

Figure 2 Connection Trunk Configuration

The calls simulate a permanent tie line between two PBXs. Both ends must be configured and have compatible voice-port signaling that is either E&M to E&M or foreign exchange office (FXO) to foreign exchange station (FXS). The signaling cannot be FXO to ground-start.

When a switched call is configured (see Figure 3), the user can make a call without dialing any digits. Telephony signaling, such as hookflash, is not passed. If the remote telephone does not answer and digits from an attached telephony device are not collected, the call does not roll over to voice mail.

Figure 3 Connection Private-Line Auto Ringback (PLAR) Configuration

The switched-call configuration works with any type of voice port (E&M, FXO, or FXS) and without any effect on an existing dial plan. It is commonly used to connect PBXs in which the remote devices appear to be physical extensions. The PBX, rather than the router, provides dial tone to the extensions.

The connection tie-line command creates a switched call between two stations or PBXs, and this call bypasses the switch. The connection plar-opx command creates a call that is similar to a switched call. The connection does not take place between the PBX and the local router until the far-end FXS device answers. This enables the PBX to provide centralized voice mail or attendant services when the remote device does not answer.

Trunk Conditioning

The Trunk Conditioning feature enables you to create a voice class, configure specific signaling attributes to the voice class, and then map the attributes in the voice class to either a Voice over Frame Relay, Voice over ATM, or a Voice over HDLC dial peer. Using the voice class, you can define the keepalive-signaling packet interval and the signal pattern (ABCD) bit pattern for Cisco-trunk (private-line) calls.

Trunk-conditioning signaling attributes apply to permanent point-to-point voice connections (private lines and tie lines) that you create using the connection trunk command.

Trunk conditioning enables control over Cisco private-line calls that are sent over Frame Relay or ATM networks. When private-line or tie-line calls are sent between two PBXs, fault indications are sent to the sending PBX. If the call fails, the PBX can select an alternate path to route the calls. Selecting an alternate path applies to analog connections or digital T1/E1 using channel-associated signaling (CAS) ABCD signaling. It does not apply to common-channel signaling (CCS).

When T1/E1 CAS is carried in transparent pass-through mode for arbitrary, unknown, or unsupported CAS protocols, you must define on-hook/idle patterns so that the digital signal processor (DSP) code can sense the idle call state and shut off the flow of voice packets when no active call is in progress. This mode provides an additional idle bandwidth-saving mechanism for those cases when Voice Activity Detection (VAD) is not desired.


Note Cisco MC3810 series concentrators support additional trunk-conditioning features that specify timing, signaling, and transmission options. The features provide enhanced control over call rerouting in cases of trunk failure and increased bandwidth availability due to suppression of voice packets on out-of-service (OOS) trunks.


Congestion Monitoring and Management Features

Congestion monitoring of permanent and switched calls is performed with the following features:

T1/E1 alarm conditioning

PSTN fallback

Busyout functionality including busyout monitoring, CAC, Analog DID, and analog centralized automatic message accounting E911 trunk.

These features provides the following capabilities:

Signaling and suppression of voice traffic for idle or OOS network trunks

Busyout of the ports interfacing with a local PBX

Graceful refusal of calls by gateways when resources are unavailable

Direct dialing to an extension on a PBX without the assistance of an operator or automated call attendant

Sending of the calling number to each switching point via Centralized Automatic Message Accounting (CAMA)

An OOS condition can be signaled using an ABCD bit pattern that is different from the busy or seized state. The difference enables the PBX to differentiate between OOS and congestion.

T1/E1 Alarm Conditioning Feature

The T1/E1 Alarm Conditioning feature provides status monitoring on T1/E1 PBX voice interfaces for simulated lines and trunks that you create using the connection command. It supports operation with CAS but not with CCS.

A T1/E1 alarm can be triggered by events detected through the monitoring of a specified set of voice ports within a T1/E1 trunk. A monitored set includes a defined voice port that has a specified DS0 group or groups and configured for one of the following:

End-to-end connection of permanent virtual circuits (PVCs)

Busyout of switched virtual circuits (SVCs), where busyout is initiated by means of the busyout monitor command

When all monitored voice ports on a T1/E1 trunk are OOS (PVCs are OOS and SVCs are busied out), a T1/E1 alarm indication signal (AIS) is generated on the T1/E1 trunk that connects to the PBX or PSTN.


Note Voice ports that are busied out by the busyout forced command do not trigger a T1/E1 alarm.


PSTN Fallback Feature

The PSTN Fallback feature monitors congestion in the IP network and redirects calls to the PSTN or rejects calls based on network congestion. You define congestion thresholds based on your configured network. This feature can reroute calls to an alternate IP destination or, if the IP network is found unsuitable for voice traffic during periods of network congestion, to the PSTN. This enables a service provider to give a reasonable guarantee about conversation quality to its VoIP users at the time of call admission.


Note For information on VoIP, ATM, Calculated Planning Impairment Factor (ICPIF), and Service Assurance Agent (SAA), see the "Related Documents" section.



Note PSTN fallback does not ensure that a VoIP call is protected from the effects of congestion. This is the function of other quality-of-service (QoS) mechanisms such as IP Real-Time Transport Protocol (RTP) priority and low-latency queueing (LLQ).


PSTN fallback includes the following capabilities:

Offers flexibility to define the congestion thresholds based on the network by defining the following thresholds:

A threshold based on ICPIF, which is derived as part of ITU G.113, including the following: G.729, G.711, G.723, G.726, GSM, and G.728

A threshold based solely on packet delay and loss measurements

Uses SAA probes to provide packet delay, jitter, and loss information for the relevant IP addresses. Based on the packet loss, delay, and jitter encountered by these probes, an ICPIF or delay/loss value is calculated. For more information, see the "Service Assurance Agent" section.

Supports calls of any codec specified in G.113, including the following: G.729, G.711, G.723, G.726, GSM, and G.728.

The fallback subsystem has a network-traffic cache that maintains the ICPIF or delay/loss values for various destinations. The subsystem helps performance, because new calls to a well-known destination do not have to wait on a probe. The value is usually cached from a previous call.

Once the ICPIF or delay/loss values are calculated and stored, they remain until the cache ages out or overflows. Until a value ages out, probes are sent periodically for that destination. The time interval is user configurable.

The following is an example of the PSTN fallback sequence. In the example, call fallback active is enabled and an ICPIF threshold is defined. Call control would be similar if loss and delay thresholds were defined.

1. A call comes into the router. The IP address of the destination is checked against the configured maps to see if it should be sent to another router, such as a backhaul router, or to an alternate dial peer. If it should be sent to another router, the IP address for the fallback subsystem is replaced with the target router. If it should be sent to an alternate dial peer, the router matches that dial peer and obtains the destination information (codec, IP address, and so on).


Note The change is made in the destination address of the probing address. The destination for the actual call is not changed.


2. The router calls the fallback subsystem to look up the specified destination in its network traffic cache. If the ICPIF value exists and is current, then the router uses that value to decide whether to permit the call into the VoIP network. If the router determines that the network congestion is below the configured threshold (by looking at the value from the probe or a cached value), then the call is connected. Otherwise, the router checks the next dial-peer match again in the same way. Eventually, if all the VoIP dial peers are deemed unsuitable, then the call is hairpinned to the PSTN by virtue of a configured POTS dial peer (for analog or digital interfaces). If no PSTN dial peer is present, a fast-busy is sent to the PBX (in case of digital interfaces).


Note It is not possible to signal a fast-busy to some interfaces.


3. The fallback subsystem continues probing in the background periodically (period time is configured by the call fallback probe-timeout command), so that the network congestion information is available when there is a call request. The first call for a particular dial peer may be delayed while the router calculates the congestion information for that destination.

If the timeout threshold is set and the router has not received calls for a particular destination after the threshold expires, the router removes that destination's traffic information from the cache.


Caution Configuring call fallback active in a gateway creates an SAA jitter probe against other (target) gateways to which the calls are sent. In order for the call fallback active to work properly, the target gateways must have the rtr responder command (in Cisco IOS releases prior to 12.3(14)T) or the ip sla monitor responder command (in Cisco IOS Release 12.3(14)T or later) in their configurations. If one of these commands is not included in the configuration of each target gateway, calls to the target gateway will fail.

Calculated Impairment Planning Factor

ICPIF calculates an impairment factor for every piece of equipment along the voice path and adds the values to get the total impairment. The ITU assigns the different types of impairments, such as noise, delay, and echo. The threshold is based on ICPIF, which is derived as part of ITU G.113 including the following: G.729, G.711, G.723, G.726, GSM, and G.728.

The ICPIF handling has been introduced for compatibility with H.323. Part of ICPIF includes a concept of Total Impairment Value that is a function of loss of packets, delay of packets, and codecs used based on the round-trip reports from SAA.

Service Assurance Agent

SAA is a network-congestion analysis mechanism. SAA provides delay, jitter, and packet-loss information for configured IP addresses. SAA is based on a client-server protocol defined on UDP. It has an Message Digest 5 (MD5), which is a message authentication algorithm in SNMP v.2. MD5 verifies the integrity of the communication, authenticates the origin, and checks for timeliness.

SAA uses the UDP port (port 1976) for sending the SAA control message to the terminating gateway. SAA probe packets go out on randomly selected ports from the top end of the audio UDP port range (16384 to 32767).

The port pair (RTP and Real-Time Transport Control Protocol [RTCP] port) is selected, and by default SAA for call fallback uses the RTCP port (odd number) to avoid going into the priority queue, if enabled. If fallback is configured to use the priority queue, the RTP port (even number) is selected. The audio UDP port range must be included in the priority queue for fallback priority queueing to work.

Busyout Features

This section describes the following busyout features:

Local Voice Busyout Feature

Advanced Voice Busyout Feature

Busyout Monitor Feature

Local Voice Busyout Feature

The Local Voice Busyout feature busies out trunks that are assigned to PVCs so that the PBX does not seize the circuit. It enables the PBX to route a call based on the actual availability of trunks. Local voice busyout enables the following:

A group of voice ports to be marked busy if a link is broken.

Specific voice ports in a PVC application to be marked busy under specified conditions.

When ports are marked busy, a call is forced back to the originating equipment (typically a PBX) that reroutes the call over an alternate path. This action ensures that a caller does not experience "dead air" resulting from a connection that never terminates.

The feature provides a way to busy out a voice port if a monitored network interface changes state. When a monitored interface changes to a specified state—to OOS or in-service—the voice port presents a seized/busyout condition to the attached PBX or other customer premises equipment (CPE). The PBX or other CPE can then attempt to select an alternate route.

This feature differs from busy-back. Busy-back refers to the signal sent from within the network to the calling party that indicates a busy (or congested) state anywhere along the route, up to and including the condition of the called party.


Note The Local Voice Busyout feature is supported on analog and digital voice ports using CAS, but not on Cisco MC3810 BRI voice modules.


Advanced Voice Busyout Feature

The Advanced Voice Busyout feature adds the following functionality to the local voice busyout feature:

For VoIP, monitoring of links to remote, IP-addressable interfaces by use of service assurance agent (SAA)

Configuration by voice class to simplify and speed up the configuration of voice busyout on multiple voice ports (or n DS-0/PRI groups on universal gateway platforms).

This feature enables you to do the following:

Configure individual voice ports to enter the busyout state if an SAA probe signal returned from a remote, IP-addressable interface detects loss of IP connectivity by crossing a specified delay or loss threshold.

Define voice classes with specified busyout conditions, and assign a particular voice class to any number of voice ports.

SAA-probe monitoring of remote interfaces is intended for use with VoIP networks, although it can also be used with Voice over Frame Relay (VoFR) and Voice over ATM (VoATM) networks.

Busyout Monitor Feature

The Busyout Monitor feature is one aspect of call admission control that uses a data network and the PSTN to provide the best possible quality and cost savings for VoIP calls. It also provides the following:

Logical connections between LAN/WAN interfaces of routers in a VoIP gateway with directly connected voice ports

Port-by-port definition

Tracking of any directly connected main interface, subinterface, or virtual interface without monitoring the status of remote devices

Call Admission Control Features

This section describes the following CAC features:

Call Admission Control for H.323 VoIP Gateways Feature

MGCP VoIP Call Admission Control Feature

Call Admission Control for H.323 VoIP Gateways Feature

This feature provides the ability to support resource-based CAC processes. These resources include system resources such as CPU, memory, and call volume, and interface resources such as call volume.

If system resources are not available to admit the call, the result is either a system denial (which busies out all T1 or E1) or per-call denial (which disconnects, hairpins, or plays, a message or tone). If the interface-based resource is not available to admit the call, the call is dropped from the session protocol (such as H.323).

PSTN Fallback offers CAC based on congestion thresholds in H.323 networks.


Note For information on H.323, see the"Related Documents" section.


User-Selected CAC Commands

The feature allows you to configure thresholds for local resources and memory and CPU resources.


Note For a list of local resources that are configured by the call threshold poll-interval command for call admission, see the command-reference document listed in the "Related Documents" section.


With the call threshold command, you can configure two thresholds, high and low, for each resource. Call treatment is triggered when the current value of a resource exceeds the configured high. The call treatment remains in effect until the current resource value falls below the configured low. Having high and low thresholds prevents call admission flapping and provides hysteresis in call admission decision making.

With the call spike command, you can configure the limit for incoming calls during a specified time period. A call spike is the term for when a large number of incoming calls arrive from the PSTN in a very short period of time (for example, 100 incoming calls in 10 ms).

With the call treatment command, you can select how the call should be treated when local resources are not available to handle the call. For example, when the current resource value for any one of the configured triggers for call threshold has exceeded the configured threshold, the call treatment choices are as follows:

Time-division multiplexing (TDM) hairpinning—Hairpins the calls through the POTS dial peer.

Reject—Disconnects the call.

Play message or tone—Plays a configured message or tone to the user.

Resource-Unavailable Signaling

The Resource Unavailable Signaling feature supports the autobusyout feature where channels are busied out when local resources are not available to handle the call. Autobusyout is supported on both CAS and PRI channels:

CAS—Uses busyout to signal that local resources are unavailable.

PRI—Uses either service messages or a cause code to signal that resources are unavailable.

MGCP VoIP Call Admission Control Feature

The MGCP VoIP Call Admission Control feature enables certain Cisco CAC capabilities on VoIP networks that are managed by Media Gateway Control Protocol (MGCP) call agents. These capabilities permit the gateway to identify and gracefully refuse calls that are susceptible to poor voice quality.

Poor voice quality on an MGCP voice network can result from transmission artifacts such as echo, from the use of low quality codecs, from network congestion and delay, or from overloaded gateways. The first two causes can be overcome by using echo cancellation and better codec selection. The last two causes are addressed by MGCP VoIP CAC.

Before the release of MGCP VoIP CAC, MGCP voice calls were often established regardless of the availability of resources for those calls in the gateway and the network. MGCP VoIP CAC ensures resource availability by disallowing calls when gateway and network resources are below configured thresholds and by reserving guaranteed bandwidth throughout the network for each completed call.

MGCP VoIP CAC has three components for improving voice quality and reliability (see Table 48).

Table 48 MGCP VoIP CAC Components

Component
Purpose
Supported Platforms

System Resource Check (SRC) CAC

Evaluates memory and call resources local to the gateway

MGCP 1.0

MGCP 0.1

Resource Reservation Protocol (RSVP) CAC

Surveys bandwidth availability on the network

MGCP 1.0

MGCP 0.1

Cisco Service Assurance Agent (SA Agent)1 CAC

Appraises network congestion conditions on the network

MGCP 1.0

1 SA Agent was called Response Time Reporter (RTR) in earlier Cisco IOS software releases.


If all three CAC types are configured on a gateway, the gateway checks resources in this order: SRC CAC, then RSVP CAC, then SA Agent CAC. If any resource check fails, the call fails and no further checks are performed. When the call fails, the gateway refuses to accept it.

MGCP VoIP CAC supports several types of calls, depending on platform (Table 49).

Table 49 MGCP VoIP CAC Call Types by Platform 

Call Type
Cisco Platform
IAD2420
2600 series
3620
3640
3660
MC3810

911 calls

Yes

Call-waiting calls

Yes

Yes

Yes

Yes

Yes

CAS PBX calls, both immediate-start and wink-start

Yes

Yes

Yes

Yes

Yes

Yes

Named Signaling Event (NSE)-based audible ringback calls

Yes

Yes

Yes

Yes

Yes

Yes

One-direction voice-path calls

Yes

Yes

Yes

Yes

Yes

Yes

Regular two-way calls

Yes

Yes

Yes

Yes

Yes

Yes

Signaling System 7/ISDN User Part (SS7/ISUP) calls

Yes

Three-way calls

Yes

Yes

Yes

Yes

Yes


Fax/modem pass-through and fax/modem relay are not supported.


NoteMGCP VoIP CAC is not supported on the following profiles of MGCP 1.0: PacketCableTM Network-based Call Signaling (NCS) 1.0 and PacketCableTM Trunking Gateway Control Protocol (TGCP) 1.0.

For information on MGCP, SRC, RSVP, and SA Agent, see the "Related Documents" section.


SRC CAC

When a call agent attempts to set up or modify a call, MGCP SRC CAC measures available local resources on the gateway and compares them to the configured thresholds for those resources. If one or more resources are beyond their thresholds, SRC CAC notifies the call agent of the results and refuses the call. If resources are within bounds and a call is subsequently established, local resources are guaranteed for the duration of the call.

SRC CAC checks these gateway thresholds, as configured by the user:

CPU usage: both finest CPU utilization and average CPU utilization

Memory usage, including I/O memory, process memory, and total memory

Total calls allowed on the gateway

If several types of thresholds are configured on the gateway, the gateway checks them in sequence to determine if sufficient resources are available to continue setting up the call.


Note Network access server data calls are not counted by SRC in the total call calculations.


When the gateway sends an unavailable condition to the call agent, the call agent takes responsibility for the type of treatment to attach to the call attempt. The call agent may choose to handle such situations by rerouting the call, playing an announcement that the call cannot be completed, playing special tones, or sending the call back to take a different path. Once resources become available again, the gateway resumes the acceptance of new calls.

RSVP CAC

MGCP RSVP CAC determines if sufficient bandwidth exists across the IP network to accept a call and refuses the call if end-to-end bandwidth is not available.

To accept a call, MGCP RSVP CAC checks for and reserves the network bandwidth between the originating gateway and the terminating gateway before attempting to complete the call. If sufficient bandwidth is not available or cannot be reserved, the gateway alerts the call agent to this condition and the call agent applies a previously configured treatment to the refused call (plays an announcement or special tones, or sends the call back to take a different path).

RSVP is an out-of-band, end-to-end signaling protocol that requests a certain amount of bandwidth and latency with each network hop that supports RSVP. If a network node (router) does not support RSVP, RSVP moves on to the next hop. A network node has the option to approve or deny the reservation on the basis of the load of the interface to which the service is requested.

A voice call triggers two RSVP reservations because the reservation and admission control mechanisms provided by RSVP are unidirectional. Each voice gateway is responsible for initiating and maintaining one reservation toward the other voice gateway. RSVP CAC for a VoIP call fails if at least one of the reservations fails.

Cisco VoIP CAC applications use RSVP to limit the accepted voice load on the IP network and guarantee the QoS levels of calls. RSVP CAC synchronizes RSVP signaling with the call setup signaling protocol (MGCP, in this case) to ensure that the bandwidth reservation is established in both directions before a call moves to the alerting phase (ringing). This synchronization ensures that the called-party phone rings only after the resources for the call have been reserved. Using RSVP-based admission control, VoIP applications can reserve network bandwidth and react appropriately if bandwidth reservation fails.

SA Agent CAC

Cisco SAA is a Cisco IOS feature that allows users to monitor network performance and congestion between a Cisco router and a remote device, which can be another Cisco router, an IP host, or a multiple virtual storage (MVS) host. Performance can be measured for real-world scenarios through the configuration of SA Agent operations that are executed periodically. Performance metrics include round-trip response time, connect time, packet loss, application performance, and interpacket delay variance (jitter). The SA Agent feature allows users to receive notifications and perform troubleshooting and problem analysis on the basis of the statistics collected by the SA Agent.

SA Agent probes traverse the network to a given IP destination and measure the loss and delay characteristics of the network along the path traveled. These values are returned to the outgoing gateway to use in making a decision on the condition of the network and its ability to carry a voice call. SA Agent probes do not provide any bandwidth information, either configured or available. However, if bandwidth across a link anywhere in the path that the voice call will follow is oversubscribed, it is reasonable to assume that the packet delay and loss values returned by the probe will indeed reflect this condition, even if indirectly. The SA Agent protocol is a client/server protocol defined in User Datagram Protocol (UDP). The client builds and sends the probe, and the server (previously the RTR Responder) returns the probe to the sender.

SA Agent probe delay and loss information is used in calculating a single value that can be used as a gauge of network impairment and as a threshold for CAC decisions.

Analog DID Feature

The Analog Direct Inward Dialing (DID) feature is a service offered by telephone companies that enables callers to dial directly to an extension on a PBX without the assistance of an operator or automated call attendant. It makes use of DID trunks, which forward only the last three to five digits of a phone number to the PBX. If, for example, a company has a PBX with extensions 555-1000 to 555-1999, and a caller dials 555-1234, the local CO would forward 234 to the PBX. The PBX would then ring extension 234. This entire process is transparent to the caller.

When this feature is configured, a voice-enabled router equipped with an analog DID interface can receive calls from a DID trunk and connect them to the appropriate extensions. The DID state machine is identical to the E&M state machine and uses one of the following signaling types:

Immediate-start—The originating end seizes the line by going off hook and, without waiting for a response, it begins to outpulse digits. The address signaling used with immediate-start signaling consists only of dial-pulsing.

Wink-start—The originating end seizes the line by going off-hook. It waits for acknowledgment from the other end before outpulsing digits. This serves as an integrity check that identifies a malfunctioning trunk and allow the network to send a re-order tone to the calling party.

Delay dial—The originating end seizes the line and waits 200 ms to determine if the far end is on-hook. If so, the originating end then outpulses digits. If the far end is off-hook, the originating end waits until the far end is on-hook before outpulsing digits.

Figure 4 shows a hypothetical topology where a user connected to the PSTN (Caller A) dials various numbers and is connected to the appropriate extensions on a PBX.

Figure 4 DID Support

Number Dialed by User A
Number Received by Router
Extension Receiving Call

555-1234

234

User C

555-1345

345

User D

555-1456

456

User B

555-1678

678

No dial-peer match found; fast busy tone is played.



Note For information on installing and configuring Cisco 2600 series and Cisco 3600 series, on voice configuration, and on IP, Frame Relay, and ATM, see the "Related Documents" section.


Analog Centralized Automatic Message Accounting E911 Trunk Feature

Because E911 calls require special routing, the North American emergency E911 phone system is built largely outside of the normal PSTN on which common voice traffic rides. Calls to emergency services are routed based on the calling number, not the called number. The calling number is checked against a database of emergency service providers that cross-references the providers for the caller's particular location. The call is then routed to the proper public-service answering point (PSAP), which, in turn, dispatches those services for the caller's location.

During setup of a call to E911, before the audio channel is connected, the calling number is sent to each switching point (known as a Selective Router [SR]) via an old telephony protocol known as CAMA. CAMA was originally designed as a protocol for long-distance billing, because it provides for carrying both calling and called number using in-band signaling. CAMA allows the telephone system to send a station identification number to the PSAP via multifrequency (MF) signaling through the telephone company's E911 equipment. CAMA trunks are used in 80 percent of E911 networks.

The calling number is needed at the PSAP for two reasons:

To use the calling number to reference the Automatic Location Identification (ALI) database to find the caller's exact location and any other information about the caller that may have been stored in the database.

To have the callback number in case the call is disconnected.

Figure 5 illustrates the topography in existing E911 networks. Figure 6 illustrates an E911 network using the VIC-2CAMA card with Cisco 2600 series or Cisco 3600 series routers.

Figure 5 Existing E911 Networks

Figure 6 Analog CAMA E911 Networks

How to Configure Trunk Conditioning and Connections

This section contains the following procedures:

Prerequisites for Configuring Trunk Conditioning and Connections

Configuring Trunk Conditioning

Configuring T1/E1 Alarm Conditioning

Configuring Trunk Connections

Prerequisites for Configuring Trunk Conditioning and Connections


Note For information on the following configuration tasks, see the "Related Documents" section.


Configure the following as appropriate:

VoFR using FRF.11

VoATM

VoIP

Voice ports

Configuring Trunk Conditioning

This section contains the following procedures:

Configuring Trunk-Conditioning Signaling Attributes

Assigning Trunk-Conditioning Attributes to Network Dial Peers

Assigning Voice Classes to Voice Ports

Verifying Signaling Attributes and Trunk Conditioning

Configuring Trunk-Conditioning Signaling Attributes

Different trunk-conditioning signaling attributes may be required to match the characteristics of the different PBXs to which the router connects. For this reason, you configure these attributes by creating a voice class for each set of attributes required. You then configure trunk-conditioning attributes for each voice class and assign the voice class to one or more dial peers. You must configure a voice class and assign it to at least one dial peer before trunk-conditioning signaling attributes take effect.


Note This configuration supports the North America CAS protocol and applies only to Cisco private-line or FRF.11 trunk calls. It does not apply to digital T1/E1 trunks using CCS.


To configure trunk-conditioning signaling attributes, use the following commands.

SUMMARY STEPS

1. voice class permanent tag

2. signal keepalive seconds

3. signal sequence oos {both | idle-only | no-action | oos-only}

4. signal pattern {idle receive | idle transmit | oos receive | oos transmit} bit-pattern

5. signal timing oos timeout {seconds | disabled}

6. signal timing oos restart seconds

7. signal timing oos slave-standby seconds

8. signal timing oos {suppress-all | suppress-voice} seconds

9. signal timing idle suppress-voice seconds

10. exit

DETAILED STEPS

 
Command
Purpose

Step 1 

Router(config)# voice class permanent tag

Enters voice-class configuration mode and creates a voice class. Range: 1 to 10000 (must be unique on the router).

Note This command differs from the voice-class command in dial-peer voice configuration mode, which contains a hyphen.

Step 2 

Router(config-class)# signal keepalive seconds

(Optional) Defines the keepalive signaling packet interval, in seconds. Range: 1 to 65535. Default: 5.

Step 3 

Router(config-class)# signal sequence oos {both 
| idle-only | no-action | oos-only}

(Optional) Sets the signaling pattern (when the far-end keepalive message is lost or when AIS is received from the far end). Keywords are as follows:

both—Restores the default (both signaling patterns are sent). The no form of the command restores the default also.

idle-only or oos-only—Sends only one signaling pattern.

no-action—Sends no signaling pattern.

Step 4 

Router(config-class)# signal pattern 
{idle receive | idle transmit | oos receive | 
oos transmit} bit-pattern

(Optional) Overrides the default values for the idle and receive OOS patterns or configures OOS transmit signaling patterns.

Repeat the command entry for each signal pattern required.

Step 5 

Router(config-class)# signal timing oos timeout 
{seconds | disabled}

(Optional) Changes the timeout period for asserting a receive OOS pattern to the PBX when signaling packets are lost. This action changes the delay time before a busyout is sent to the PBX.

Step 6 

Router(config-class)# signal timing oos restart 
seconds

(Optional) Configures permanent voice connections to be restarted after the trunk has been OOS for a specified time. Default: no signal timing OOS pattern parameters are configured.

Note This command has no effect if the signal timing oos timeout command is set to disabled.

Step 7 

Router(config-class)# signal timing oos 
slave-standby seconds

(Optional) Configures a slave port to return to its initial standby state after the trunk has been OOS for a specified time. Default: no signal timing OOS pattern parameters are configured.

Note This command has no effect if the signal timing oos timeout command is set to disabled.

Step 8 

Router(config-class)# signal timing oos 
{suppress-all | suppress-voice} seconds

(Optional) Configures the router or concentrator to stop sending voice packets or voice and signaling packets to the network if it detects a transmit OOS signaling pattern from the PBX for a specified time. Default: no signal timing OOS pattern parameters are configured.

Note An OOS transmit signaling pattern must be configured with the signal pattern oos transmit command (see Step 4).

Step 9 

Router(config-class)# signal timing idle 
suppress-voice seconds

(Optional) Configures the router or concentrator to stop sending voice packets after the trunk has been idle for a specified time. Default: no signal timing OOS pattern parameters are configured.

Step 10 

Router(config-class)# exit

Exits the current mode.

Assigning Trunk-Conditioning Attributes to Network Dial Peers

After you create a voice class, you must apply it to the dial-peer configuration. You can assign trunk-conditioning attributes to VoIP, VoFR, or VoATM dial peers, but not to POTS dial peers.


Note This feature applies only to Cisco trunk (private-line) or FRF.11 trunk calls and does not apply to digital T1/E1 trunks using CCS.


To apply trunk-conditioning signaling attributes to a network dial peer, use the following commands.

SUMMARY STEPS

1. dial-peer voice tag {pots | vofr | voip}

2. voice-class permanent tag

3. exit

DETAILED STEPS

 
Command
Purpose
 

Router(config)# dial-peer voice tag {pots | vofr | voip}

Enters dial-peer configuration mode for a particular peer.

 

Router(config-dial-peer)# voice-class permanent tag

Assigns the voice class to the dial peer. Range: 1 to 10000 (must be unique on the router).

Note This command differs from the voice class command in global configuration mode, which does not contain a hyphen.

 

Router(config-dial-peer)# exit

Exits the current mode.

Assigning Voice Classes to Voice Ports

To assign a voice class to a voice port, use the following commands.

SUMMARY STEPS

1. voice-port slot/subunit/port

2. voice-class permanent tag

3. exit

DETAILED STEPS

 
Command
Purpose

Step 1 

Router(config)# voice-port slot/subunit/port

Enters voice-port configuration mode for a specified voice port.

Step 2 

Router(config-voiceport)# voice-class permanent 
tag

Assigns the voice class to a voice port. Range: 1 to 10000 (must be unique on the router).

Note This command differs from the voice class command in global configuration mode, which does not contain a hyphen.

Step 3 

Router(config-voiceport)# exit

Exits the current mode.

Verifying Signaling Attributes and Trunk Conditioning


Step 1 show voice trunk-conditioning signaling

Use this command to verify signaling attributes (timing parameters).

The following is sample output for voice-port 1/5 on a Cisco MC3810.

Router# show voice trunk-conditioning signaling 1/5

1/5 :
TX INFO :slow-mode seq#= 25, sig pkt cnt= 42, last-ABCD=0000
hardware-state ACTIVE signal type is NorthamericanCAS
signal path is OPEN
 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000
 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000
 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000
RX INFO :slow-mode, sig pkt cnt= 37
missing = 0, out of seq = 0, very late = 0
playout depth = 0 (ms), refill count = 1
prev-seq#= 25, last-ABCD=0000
trunk_down_timer = 4212 (ms), idle timer = 0 (sec),
tx_oos_timer = 0 (sec), rx_ais_duration = 0 (ms)
forced playout signal pattern = NONE
signaling playout history
0000 0000 0000 0000 0000 0000 0000 0000 0000 0000
0000 0000 0000 0000 0000 0000 0000 0000 0000 0000
0000 0000 0000 0000 0000 0000 0000 0000 0000 0000

The following is sample summary output for voice ports on a Cisco MC3810:

Router# show voice trunk-conditioning signaling summary

1/1 is shutdown
1/4 is shutdown
1/5 :
TX INFO :slow-mode seq#= 25, sig pkt cnt= 40, last-ABCD=0000
hardware-state ACTIVE signal type is NorthamericanCAS signal path is OPEN
RX INFO :slow-mode, sig pkt cnt= 36, prev-seq#= 25, last-ABCD=0000

Step 2 show voice trunk-conditioning supervisory

Use this command to determine the status of trunk supervision and configuration parameters.

The following is sample output for a Cisco MC3810 multiservice concentrator.

Router# show voice trunk-conditioning supervisory 1/5

1/5 : state : TRUNK_SC_CONNECT, voice : on, signal : on, slave
status: trunk connected
sequence oos : idle and oos
pattern :rx_idle = 0x0 rx_oos = 0xF tx_oos =  0xF
timing : idle = 0, restart = 0, standby = 0, timeout = 40
supp_all = 50, supp_voice = 0, keep_alive = 5
timer: oos_ais_timer = 0, timer = 0

Step 3 show voice call summary

Use this command to show summary call data.

The following is sample output sample is for voice port 1/5 on a Cisco MC3810:

Router# show voice call summary

PORT      CODEC    VAD VTSP STATE            VPM STATE
========= ======== === ===================== ========================
1/1                                          *shutdown*
1/2       -         -  -                     FXSLS_ONHOOK
1/3       -         -  -                     FXSLS_ONHOOK
1/4                                          *shutdown*
1/5       g729r8    n  S_CONNECT             S_TRUNKED
1/6       -         -  -                     EM_ONHOOK

Step 4 show running-configuration

Use this command to verify signaling and timing parameters. The trunks do not have to be connected and active.

The following is sample output for voice-ports 0:0, 0:1, and 0:2 on a Cisco MC3810.

Router# show running-configuration

Building configuration...

Current configuration:
.
.
.
voice class permanent 100
signal timing idle suppress-voice 2000
signal timing oos restart 1000
.
.
.
voice-port 0:0
 voice-class permanent 100
 compand-type a-law
!
voice-port 0:1
 voice-class permanent 100
 compand-type a-law
!
voice-port 0:2
 voice-class permanent 100
 compand-type a-law
.
.
.


Configuring T1/E1 Alarm Conditioning

This section contains the following procedures:

Assigning Alarm-Generation Parameters

Verifying Alarm-Generation Parameters

You can configure a network to monitor any combination of DS0 groups on a T1 or E1 trunk. An alarm is triggered only if all of the monitored DS0 groups on a T1 or E1 trunk are OOS. If one monitored DS0 group is in service, no alarm is triggered. DS0 groups can be either of the following types:

DS0 groups configured as voice ports for permanent point-to-point voice connections created using the connection command (for private lines and tie lines). These DS0 groups can go OOS due to a trunk-conditioning event or busyout e