一旦ICPIF或延误或损失value is calculated, it is stored in a fallback cache where it remains until the cache ages out or overflows. Until an entry ages out, probes are sent periodically for that particular destination. This time interval is configurable.
To configure PSTN Fallback, use the following global configuration mode command:
call fallback active
This command enables a call request to fallback to alternate dial peers in case of network congestion. Theactivekeyword enables a call request to fall back to alternate dial peers in case of network congestion.
Configuring Resource Availability Check
User-selected thresholds allow you to configure call admission thresholds for local resources and end-to-end memory and CPU resources. You can configure two thresholds, high and low, for each global or interface-related resource. The specified call treatment is triggered when the current value of a resource goes beyond the configured high and remains in effect until the current resource value falls below the configured low.
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 exceeds the configured threshold, you have the following call treatment choices:
TDM hairpinning—Hairpins (that is, redirects) the calls through the POTS dial peer
Reject—Disconnects the call
Play message or tone—Plays a configured message or tone to the user
To configure resource availability checking, use the following global configuration mode command:
call threshold globaltrigger-namelowvaluehighvalue[busyout][treatment]
This command enables a trigger and defines associated parameters to allow or disallow new calls on the router. Action is enabled when the trigger value exceeds the value specified by thehighkeyword and is disabled when the trigger value drops below the value specified by thelowkeyword.
Table 7-8 shows thecall thresholdcommand options.
Table 7-8 call thresholdCommands
Command |
Description |
trigger-name |
Can be one of the following:
|
lowvalue |
Value of low threshold; range is from 1 to 100 percent for utilization triggers and from 1 to 10,000 for total calls |
highvalue |
Value of high threshold; range is from 1 to 100 percent for utilization triggers and from 1 to 10,000 for total calls |
busyout |
(Optional) Busies out the T1 or E1 channels if the resource is not available |
treatment |
(Optional) Applies call treatment from the session application if the resource is not available |
To configure call treatment, use the following global configuration mode command:
call treatment{on|actionaction[value]|cause-codecause-code|isdn-reject
value}
This command configures how calls should be processed when local resources are unavailable.
Table 7-9 shows thecall treatmentcommand options.
To configure resource availability checking for interface resources, enter the following global configuration mode command:
call threshold interfaceinterface-name interface numberint-callslowvaluehighvalue
This command allows threshold values to be configured for total numbers of voice calls placed through a particular interface. This command is used to allow or disallow admission for new calls on the router.
Table 7-10 shows thecall threshold interfacecommand options.
Table 7-9 call treatmentCommands
Command |
Description |
on |
Enables call treatment from the default session application. |
actionaction |
Specifies the action to be taken when call treatment is triggered. The action argument can be one of the following:
|
cause-codecause-code |
Specifies the reason for disconnection to the caller. The cause-code argument can be one of the following:
|
isdn-rejectvalue |
Applies to ISDN interfaces only and specifies the ISDN reject cause code. Thevalueargument ranges from 34 through 47 (ISDN cause code for rejection). |
Table 7-10 call thresholdinterfaceCommands
Command |
Description |
interface-name |
Specifies the interface used in making call admission decisions. Types of interfaces and their numbers depend on the configured interfaces. |
interface-number |
Specifies the number of calls through the interface that triggers a call admission decision. |
int-calls |
Configures the gateway to use the number of calls through the interface as a threshold. |
lowvalue |
Enables the specified call treatment until the number of calls through the interface drops below the configured low value.Thevalueargument specifies the number of calls used to make call admission decisions.The range is from 1 to 10,000 calls. |
highvalue |
Enables the specified call treatment until the number of calls through the interface exceeds the configured high value.Thevalueargument specifies the number of calls used to make call admission decisions.The range is from 1 to 10,000 calls. |
Consider the following examples of the SIP CAC commands:
SAA RTR Responder:
Router(config)#rtr responder
PSTN Fallback
Router(config)#call fallback active
Resource availability checking
Router(config)#call threshold global total-calls low 5 high 1000 busyoutRouter(config)#call treatment action cause-code 17Router(config)#call threshold interface ethernet 0 int-calls low 5 high 2500
MGCP CAC
The MGCP VoIP CAC feature enables certain Cisco CAC capabilities on VoIP networks that are managed by MGCP call agents. These capabilities permit a 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. You can overcome the first two causes of echo by using echo cancellation and better CODEC selection. You can address network congestion, delay, and overloaded gateways by using 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:
System Resource Check (SRC) CAC evaluates memory and call resources local to the gateway. It is supported in MGCP 1.0 and MGCP 0.1.
RSVP CAC allocates bandwidth on the network. RSVP is supported in MGCP 1.0 and MGCP 0.1.
Cisco SAA CAC appraises network congestion conditions on the network. It is supported only in MGCP 1.0.
To set thresholds and enable MGCP SRC CAC, use the following command in global configuration mode:
call threshold globaltrigger-namelowvaluehighvaluetreatment
This command enables a resource and defines its parameters. Treatment of attempted calls is enabled when the resource cost goes beyond the high value. Treatment is not disabled until the resource cost drops below the low value. The arguments and keywords are shown in Table 7-11.
Table 7-11 call threshold globalCommands
Command |
Description |
trigger-name |
Can be one of the following:
|
lowvalue |
Value of low threshold; range is from 1 to 100 percent for utilization triggers and from 1 to 10,000 for total calls |
highvalue |
Value of high threshold; range is from 1 to 100 percent for utilization triggers and from 1 to 10,000 for total calls |
treatment |
(Optional) Applies call treatment from the session application if the resource is not available |
If network conditions rise above the high threshold value, SRC rejects the call by sending the call agent an MGCP error message with the return code 403. The call agent applies a treatment to the rejected call.
The following sections illustrate the configuration of CAC for an MGCP environment. Specifically, configurations for the following CAC mechanisms are addressed: RSVP CAC, Cisco SAA CAC, and Cisco Unified CallManager CAC.
Configuring RSVP CAC
To configure MGCP RSVP CAC on a media gateway, use the following command in global configuration mode:
ip rsvp bandwidth(interface-kbps[single-flow-kbps])
This command enables RSVP for IP on an interface. RSVP is disabled by default. It should be noted that, in order for RSVP to operate correctly end to end, it must be configured on all routers in the network. The arguments are shown in Table 7-12.
Table 7-12 ip rsvpBandwidth Commands
Command |
Description |
interface-kbps |
(Optional) Maximum amount of bandwidth, in kilobits per second, that might be allocated by RSVP flows. The range is from 1 to 10,000,000. This parameter should be configured for the maximum amount of voice bandwidth that this interface is limited to for all calls. |
single-flow-kbps |
(Optional) Maximum amount of bandwidth, in kilobits per second, that might be allocated to a single flow. The range is from 1 to 10,000,000. This parameter should be configured for the amount of bandwidth for one call. |
Configuring Cisco SAA CAC
Cisco SAA is an application-aware synthetic operation agent that monitors network performance by measuring response time, network resource availability, application performance, jitter (interpacket delay variance), connect time, throughput, and packet loss. Performance can be measured between any Cisco device that supports this feature and any remote IP host (server), Cisco routing device, or mainframe host. Performance measurement statistics provided by this feature can be used for troubleshooting, problem analysis, and designing network topologies.
The SAA Responder, enabled using thertr respondercommand, is a component embedded in the target Cisco routing device that allows the system to anticipate and respond to SAA request packets. The SAA Responder can listen on any user-defined port for UDP and TCP protocol messages. In client/server terminology, the SAA Responder is aconcurrent multiservice server.
The global configuration mode commands to configure Cisco SAA CAC are as follows:
call fallback active—Enables a call request to fall back to alternate dial peers in case of network congestion
mgcp rtrcac—Enables MGCP SAA CAC
rtr responder—Enables the SAA Responder functionality on a Cisco device
The configuration shown in Example 7-6 enables all three types of MGCP VoIP CAC: SRC, RSVP, and SAA. Notice that CAC configuration commands are highlighted in the output. Comments are provided in the example in the lines preceding the CAC commands to help you identify the commands needed for a particular CAC type.
Example 7-6MGCP CAC Configuration
version 12.2 ! ! Output omitted for brevity !!以下命令中使用MGCP SA剂CAC. call fallback active ! The following command is used in MGCP RSVP CAC. call rsvp-sync ! The following six commands are used in MGCP SRC CAC. call threshold global cpu-5sec low 55 high 70 treatment call threshold global cpu-avg low 70 high 80 treatment call threshold global total-mem low 70 high 80 treatment call threshold global io-mem low 70 high 80 treatment call threshold global proc-mem low 70 high 80 treatment call threshold global total-calls low 10 high 12 treatment!!Output omitted for brevity ! interface FastEthernet0/0 ip address 192.168.1.61 255.255.255.0 duplex auto speed auto!The following command is used in MGCP RSVP CAC to configure the bandwidth allocated. ! for VoIP calls through the interface. ip rsvp bandwidth 512 512!!Output omitted for brevity ! mgcp mgcp call-agent 10.13.57.88 service-type mgcp version 1.0 mgcp modem passthrough voip mode nse mgcp modem passthrough voaal2 mode mgcp package-capability trunk-package!The following command is used for MGCP SA Agent CAC. mgcp rtrcac ! The following command is used in MGCP SRC CAC. mgcp src-cacno mgcp timer receive-rtcp ! mgcp profile default ! dial-peer voice 1 pots application mgcpapp port 3/0:1 ! dial-peer voice 2 pots application mgcpapp port 3/0:2 ! dial-peer voice 3 pots application mgcpapp port 3/1:1 ! dial-peer voice 4 pots application mgcpapp port 3/1:2 !!以下命令中使用MGCP SA剂CAC. rtr responder ! ! Output omitted for brevity ! end
Cisco Unified CallManager CAC
While Cisco supports a variety of CAC mechanisms, most of these mechanisms are router-centric. However, in environments containing multiple Cisco Unified CallManager (CCM) clusters, other CAC approaches might be more appropriate. With CCMs, two types of call admission are possible: