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This feature module describes enhancements to call admission control using Resource Reservation Protocol (RSVP) in Cisco H.323 Voice over IP (VoIP) networks. This feature synchronizes RSVP procedures with H.323 Version 2 (Fast Connect) setup procedures to ensure that the required Quality of Service (QoS) for a call is maintained across the IP network.
This document includes the following sections:
RSVP is the IP service that allows applications to request end-to-end QoS guarantees from the network. Cisco VoIP applications use RSVP for call admission control, limiting the accepted voice load on the IP network to guarantee the QoS levels of calls. The VoIP Call Admission Control using RSVP feature synchronizes RSVP signaling with H.323 Version 2 signaling to ensure that the bandwidth reservation is established in both directions before a call moves to the alerting phase (ringing). This 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.
Prior to Cisco IOS Release 12.1(3)XI, VoIP gateways used H.323 Version 1 (Slow Connect) procedures when initiating calls requiring bandwidth reservation. This feature, which is enabled by default, allows gateways to use H.323 Version 2 (Fast Connect) for all calls, including those requiring RSVP. To enable backward compatibility, commands are available to force the originating gateway to initiate calls using Slow Connect procedures if the terminating gateway is running Cisco IOS Release 12.1(1)T or later. You can configure Slow Connect globally for all VoIP calls by using the h323 call start voice-service command, or configure Slow Connect per the individual VoIP dial-peer by using the call start voice-class command.
A timer can be set by using the call rsvp-sync resv-timer command to limit the number of seconds that the terminating gateway waits for bandwidth reservation setup before proceeding with the call setup or releasing the call, depending on the configured QoS level in the dial peers.
Synchronized RSVP is attempted for a VoIP call as long as the desired (requested) QoS for the associated dial peer is set to controlled-load or guaranteed-delay. If the desired QoS level is set to the default of best-effort, bandwidth reservation is not attempted. If RSVP reservation is attempted but fails, the acceptable QoS for the dial peer determines the outcome of the call. When the acceptable QoS is configured for best effort, the call setup proceeds but without any bandwidth reservation in place. When the acceptable QoS on either gateway is configured for other than best effort, and the RSVP reservation fails, the call is released. The desired QoS and acceptable QoS are configured through Cisco IOS software by using the req-qos and acc-qos dial-peer configuration commands, respectively.
Table 1 summarizes the results of nine call setup scenarios based on the QoS levels configured in the dial peers at the originating and terminating gateways.
| Originating Gateway | Terminating Gateway | ||||
|---|---|---|---|---|---|
| Desired QoS | Acceptable Qos | Desired QoS | Acceptable QoS | Results | |
1 | controlled-load or guaranteed-delay | best-effort | controlled-load or guaranteed-delay | best-effort | RSVP is attempted but if RSVP fails, the call proceeds. |
2 | controlled-load or guaranteed-delay | best-effort | controlled-load or guaranteed-delay | controlled-load or guaranteed-delay | RSVP is attempted and if RSVP fails, the call is released. |
3 | best-effort | best-effort | controlled-load or guaranteed-delay | controlled-load or guaranteed-delay | RSVP is not attempted and the call is released. |
4 | controlled-load or guaranteed-delay | controlled-load or guaranteed-delay | controlled-load or guaranteed-delay | best-effort | RSVP is attempted and if RSVP fails, the call is released. |
5 | controlled-load or guaranteed-delay | best-effort | best-effort | best-effort | RSVP is not attempted and the call proceeds. |
6 | controlled-load or guaranteed-delay | controlled-load or guaranteed-delay | best-effort | best-effort | RSVP is not attempted and the call is released. |
7 | best-effort | best-effort | controlled-load or guaranteed-delay | best-effort | RSVP is not attempted and the call is released. |
8 | best-effort | best-effort | controlled-load or guaranteed-delay | best-effort | RSVP is not attempted and the call proceeds. |
9 | controlled-load or guaranteed-delay | controlled-load or guaranteed-delay | controlled-load or guaranteed-delay | controlled-load or guaranteed-delay | RSVP is attempted and if RSVP fails, the call is released. |
For detailed descriptions and instructions on configuring the desired and acceptable QoS levels, see the Cisco IOS Multiservice Applications Command Reference , Cisco IOS Release 12.1.
RSVP-based resource admission control is related to the existing RSVP feature, which is documented in the Cisco IOS Quality of Service Solutions Configuration Guide , Cisco IOS Release 12.1.
The VoIP Call Admission Control Using RSVP feature runs on all platforms that support Cisco IOS Release 12.1(3)XI and H.323-based VoIP.
Standards
No new or modified standards are supported by this feature.
MIBs
For descriptions of supported MIBs and how to use MIBs, see the Cisco MIB web site on CCO at http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml.
RFCs
No new or modified RFCs are supported by this feature.
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Note An inbound dial peer is not required if the originating and terminating gateways have outbound dial peers configured to reach the calling number at the far-end and if the dial peers use the same QoS parameters. Configure an inbound dial peer if the corresponding outbound dial peers at the originating and terminating gateways do not have matching QoS configurations, or if calls can be established in one direction only (e.g., calls can be made from gateway A to gateway B, but not from gateway B to gateway A). |
The following sections describe optional configuration tasks for the VoIP Call Admission Control Using RSVP feature. The tasks in the first section are for configuring synchronization:
Use the following tasks only if you require backward compatibility with Version 2 gateways running a release earlier than Cisco IOS Release 12.1(3)XI (must be Cisco IOS Release 12.1(1)T or later):
Synchronization between RSVP and the H.323 voice signaling protocol is enabled by default; no configuration tasks are required to enable this feature. To reenable the feature if it has been disabled, perform the following steps in global configuration mode:
| Command | Purpose | |
|---|---|---|
Step 1 | | Enters global configuration mode. |
Step 2 | Router(config)# call rsvp sync | Enables synchronization between RSVP and the H.323 voice signaling protocol. |
Step 3 | Router(config)# | Sets the timer for reservation requests. The default is 10 seconds. |
To enable an H.323 gateway to be backward compatible with a destination gateway that is running Cisco IOS Release 12.1(1)T or later (up to Cisco IOS Release 12.1(3)XI), perform the following steps beginning in global configuration mode. This procedure is optional and selects Slow Connect globally for all VoIP services.
| Command | Purpose | |||
|---|---|---|---|---|
Step 1 | | Enters global configuration mode. | ||
Step 2 | Router(config)# voice service voip | Enters voice-service configuration mode for VoIP services. | ||
Step 3 | Router(conf-voi-se)# | Forces the H.323 gateway to use Slow Connect procedures.
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Note The previous procedure selects Slow Connect globally for all VoIP calls. To change the type of connect procedures for calls associated with a specific dial peer, use the following procedure, "Configuring Slow Connect for the Dial Peer". |
To enable an H.323 gateway to be backward compatible with a destination gateway that is running Cisco IOS Release 12.1(1)T or later (up to Cisco IOS Release 12.1(3)XI), perform the following steps beginning in global configuration mode. This procedure is optional and selects Slow Connect for a specific VoIP dial peer.
| Command | Purpose | |||
|---|---|---|---|---|
Step 1 | | Enters global configuration mode. | ||
Step 2 | Router(config)# | Enters voice-class configuration mode and creates a voice class for H.323 attributes. | ||
Router(config-clas)# | Forces the H.323 gateway to use Slow Connect procedures. The default is system, which causes the H.323 gateway to use the connect procedure that is configured by using the h323 call start voice-service configuration command (see "Configuring Slow Connect for VoIP Services").
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Step 4 | Router(config-clas)# | Exits voice-class configuration mode and returns to global configuration mode. | ||
Step 5 | Router(config)# dial-peer voice number voip | Enters dial-peer configuration mode for the VoIP dial peer. | ||
Step 6 | Router(config-dial)# | Assigns the voice class attributes to the dial peer, including the H.323 connect procedure that was selected in Step 3. |
To verify that RSVP-based call admission control is configured correctly, enter the show running-config command to display the command settings for the router, as shown in "Configuration Examples".
The following examples display the screen output using the show running-config command:
The following examples show that calls can be made in either direction between gateway A and
gateway B, which are connected to POTS phones, with phone numbers 711 and 712 respectively. The requested QoS indicates that RSVP setup must be completed before the destination phone rings. The acceptable QoS indicates that the call will be released if the RSVP setup fails or does not complete within the allotted time.
Gateway A
call rsvp-sync call rsvp-sync resv-timer 15 ! interface Ethernet0/0 ip address 10.10.107.107 10.255.255.255 fair-queue 64 256 31 ip rsvp bandwidth 1000 1000 ! voice-port 3/0/0 ! dial-peer voice 712 voip destination-pattern 712 session target ipv4:10.10.107.108 req-qos controlled-load acc-qos controlled-load ! dial-peer voice 711 pots destination-pattern 711 port 3/0/0
Gateway B
call rsvp-sync ! interface Ethernet0/0 ip address 10.10.107.108 10.255.255.255 fair-queue 64 256 31 ip rsvp bandwidth 1000 1000 ! ! voice-port 2/0/0 ! dial-peer voice 711 voip destination-pattern 711 session target ipv4:10.10.107.107 req-qos controlled-load acc-qos controlled-load ! dial-peer voice 712 pots destination-pattern 712 port 2/0/0
The following example shows that Slow Connect is configured globally for all VoIP calls because the h323 call start slow command is used in the voice service configuration:
! dial-peer voice 712 voip destination-pattern 712 session target ipv4:10.10.107.108 req-qos controlled-load acc-qos controlled-load ! voice service voip h323 call start slow !
The following example shows the same basic configuration but demonstrates that when the call start system command is used in the voice class configuration, the gateway defaults to the connect procedure that is configured in the voice service; otherwise the dial peer configuration takes precedence (see the H.323 Slow Connect by Dial Peer Example).
!
dial-peer voice 712 voip
voice-class h323 2
destination-pattern 712
session target ipv4:10.10.107.108
req-qos controlled-load
acc-qos controlled-load
!
voice class h323 2
call start system
!
voice service voip
h323 call start slow
!
The following example shows that calls from VoIP dial peer 712 use Slow Connect procedures because the call start slow command is configured in the voice class assigned to the dial peer:
!
dial-peer voice 712 voip
voice-class h323 2
destination-pattern 712
session target ipv4:10.10.107.108
req-qos controlled-load
acc-qos controlled-load
!
voice class h323 2
call start slow
!
voice service voip
h323 call start fast
!
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Note The h323 call start fast voice-service command is ignored because the voice class configuration takes precedence, unless the call start system voice-class command is used (see the H.323 Slow Connect by Voice Service Example). |
This section documents new commands. All other commands used with this feature are documented in the Cisco IOS Release 12.1 command reference publications.
To enable synchronization between Resource Reservation Protocol (RSVP) signaling and the voice signaling protocol, use the call rsvp-sync global configuration command. To disable synchronization, use the no form of this command.
call rsvp-syncSyntax Description
This command has no keywords or arguments.
Defaults
Synchronization is enabled between RSVP and the voice signaling protocol (for example, H.323).
Command Modes
Global configuration
Command History
12.1(3)XI This command was introduced.
Release
Modification
Usage Guidelines
The call rsvp-sync command is enabled by default.
Examples
The following example enables synchronization between RSVP and the voice signaling protocol:
call rsvp-sync
Related Commands
Sets the timer for reservation requests. Forces an H.323 Version 2 gateway to use Fast Connect or Slow Connect procedures for the specific VoIP dial peer. Forces an H.323 Version 2 gateway to use Fast Connect or Slow Connect procedures for all VoIP services. ip rsvp bandwidth Enables the use of RSVP on an interface.
Command
Description
To set the timer on the terminating VoIP gateway for completing RSVP reservation setups, use the call rsvp-sync resv-timer global configuration command. To restore the default value, use the no form of this command.
call rsvp-sync resv-timer seconds
Syntax Description
seconds Number of seconds in which the reservation setup must be completed, in both directions. Value range is 1 through 60 seconds.
Defaults
The timer default is 10 seconds.
Command Modes
Global configuration
Command History
12.1(3)XI This command was introduced.
Release
Modification
Usage Guidelines
The reservation timer is started on the terminating gateway when the session protocol receives an indication of the incoming call. This timer is not set on the originating gateway because the resource reservation is confirmed at the terminating gateway. If the reservation timer expires before the RSVP setup is complete, the outcome of the call depends on the acceptable QoS level configured in the dial peer; the call either proceeds without any bandwidth reservation or it is released. The timer must be set long enough to allow calls to complete but short enough to free up resources. The optimum number of seconds depends on the number of hops between the participating gateways and the delay characteristics of the network.
Examples
The following example sets the reservation timer to 30 seconds:
call rsvp-sync resv-timer 30
Related Commands
Enables synchronization of RSVP and the H.323 voice signaling protocol.
Command
Description
To force the H.323 Version 2 gateway to use Fast Connect or Slow Connect procedures for a dial peer, use the call start voice-class configuration command. To restore the default condition, use the no form of this command.
call start {fast | slow | system}
Syntax Description
fast Gateway uses H.323 Version 2 (Fast Connect) procedures. slow Gateway uses H.323 Version 1 (Slow Connect) procedures. system Gateway defaults to the voice service configuration that is defined using the h323 call start command in voice-service configuration mode.
Defaults
The default is system.
Command Modes
Voice-class configuration
Command History
12.1(3)XI This command was introduced.
Release
Modification
Usage Guidelines
In Cisco IOS Release 12.1(3)XI and later, H.323 VoIP gateways by default use H.323 Version 2 (Fast Connect) for all calls including those initiating RSVP. Previously, gateways used only Slow Connect procedures for RSVP calls. To enable Cisco IOS Release 12.1(3)XI gateways to be backward compatible with earlier releases of Cisco IOS Release 12.1 T, the call start command allows the originating gateway to initiate calls using Slow Connect.
This call start command is configured as part of the voice class assigned to an individual VoIP dial peer. It takes precedence over the h323 call start voice-service configuration command, which applies globally to all VoIP calls, unless the system keyword is selected. If the system keyword is used for the call start voice-class command, the gateway defaults to the voice-service configuration.
Examples
The following example selects Slow Connect for voice class 1000:
voice class h323 1000 call start slow ! dial-peer voice 210 voip voice-class h323 1000
Related Commands
acc-qos Selects the acceptable quality of service for a dial peer. Enables synchronization between RSVP and the H.323 voice signaling protocol. Sets the timer for RSVP reservation setup. Selects whether the H.323 gateway uses Fast Connect or Slow Connect procedures for all VoIP services. req-qos Selects the desired quality of service to use in reaching a dial peer. voice class h323 Enters voice-class configuration mode and creates a voice class for H.323 attributes. voice-class h323 Assigns a voice class to the dial peer.
Command
Description
To force the H.323 Version 2 gateway to use Fast Connect or Slow Connect procedures for all H.323 calls, use the h323 call start voice-service configuration command. To restore the default condition, use the no form of this command.
h323 call start {fast | slow}
Syntax Description
fast Gateway uses H.323 Version 2 (Fast Connect) procedures. slow Gateway uses H.323 Version 1 (Slow Connect) procedures.
Defaults
The default is fast.
Command Modes
Voice-service configuration
Command History
12.1(3)XI This command was introduced.
Release
Modification
Usage Guidelines
In Cisco IOS Release 12.1(3)XI and later, H.323 VoIP gateways by default use H.323 Version 2 (Fast Connect) for all calls including those initiating RSVP. Previously, gateways used only Slow Connect procedures for RSVP calls. To enable Cisco IOS Release 12.1(3)XI gateways to be backward compatible with earlier releases of Cisco IOS Release 12.1 T, the h323 call start command forces the originating gateway to initiate calls using Slow Connect.
This h323 call start command is configured as part of the global voice-service configuration for VoIP services. It does not take effect unless the call start system voice-class configuration command is configured in the VoIP dial peer.
Examples
The following example selects Slow Connect procedures for the gateway:
voice service voip h323 call start slow
Related Commands
Enables synchronization between RSVP and the H.323 voice signaling protocol. Sets the timer for RSVP reservation setup. Selects whether the H.323 gateway uses Fast Connect or Slow Connect procedures for the specific VoIP dial peer. voice service Enters voice-service configuration mode and specifies the voice encapsulation type.
Command
Description
acceptable QoS--Minimum level of QoS that is required for a call, or the call is released.
Call Admission Control--Procedures that determine whether to admit a VoIP call based on the available bandwidth in the IP network. There must be sufficient bandwidth to support the new VoIP call with the required QoS, while also maintaining the required QoS of already established VoIP calls.
desired QoS--Requested level of QoS that is preferred for a call. The desired QoS is typically equal to or higher than the acceptable QoS for the call.
Fast Connect--Allows H.323 endpoints to establish media channels without waiting for a separate H.245 connection to be opened. This streamlines the number of messages that are exchanged and the amount of processing that must be done before endpoint connections can be established.
gateway--An H.323 endpoint on the LAN that provides real-time, two-way communication between H.323 terminals on the LAN, other ITU-T terminals in the WAN, or to another H.323 gateway. A gateway allows H.323 terminals to communicate with non-H.323 terminals by converting protocols. A gateway is the point where a circuit-switched call is encoded and repackaged into IP packets.
H.323--An International Telecommunication Union (ITU-T) standard that describes packet-based video, audio, and data conferencing. H.323 is an umbrella standard that describes the architecture of the conferencing system and refers to a set of other standards (H.245, H.225.0, and Q.931) to describe its actual protocol.
QoS--Quality of Service. The performance of a transmission across a network. To ensure that receivers get the quality they expect, for example a video image that is smooth rather than choppy, various strategies have been developed that enable routers to give preference to one set of packets over others that arrive at the routers at the same moment. These strategies are known as Quality of Service features.
RSVP--Resource reSerVation Protocol. An IETF protocol used for signalling requests (setting up reservations) for Internet services by a customer, before that customer is permitted to transmit data over that portion of the network.
VoIP--Voice over IP. The ability to carry normal telephone-style voice over an IP-based Internet with POTS-like functionality, reliability, and voice quality. VoIP is a blanket term, that generally refers to the Cisco standards-based (for example H.323) approach to IP voice traffic.
VoIP dial peer--Dial peer connected by a packet network; in the case of Voice over IP, this is an IP network. VoIP peers point to specific VoIP devices.
Posted: Tue Aug 15 10:15:39 PDT 2000
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