This document describes the steps to configure H.323 gateway.
The function of a gateway is to allow connectivity between dissimilar systems. Basically, the job of the gateway is to allow your phone system to make calls to other phone systems.In most cases, the first system to which you should connect your system is the Public Switched Telephone Network (PSTN). This allows callers on your system to call nearly any other phone in the world. In addition to connecting to the PSTN, you may also want to connect your system to other systems in your company and bypass the PSTN. In either case the steps are very similar.
There are four types of gateways. The main difference in these gateways is the protocol they use to communicate with the CallManager. Their functions are the same to provide connectivity to another system.
H.323 — Typically used to connect to the PSTN and requires its own dial plan configuration. Requires a significant amount of configuration on the gateway.
MGCP — Typically used to connect to the PSTN and does not require its own dial plan configuration. Requires minimal configuration on the gateway.
Non-IOS MCGP — Typically used to connect to the PSTN and does not require its own dial plan configuration. Requires almost no configuration on the gateway itself.
Inter-cluster Trunk — Connects CallManager clusters together. Runs on the CallManager server and does not require additional hardware.
Adding H.323 Gateways
H.323 is best described as a suite of protocols. It is also often referred to as an umbrella under which a number of other protocols exist. The configuration steps required for an H.323 gateway are somewhat more advanced than those of other types of gateways. This is because much of the configuration has to be done using the command-line interface (CLI) of the gateway itself. For example, when configuring a Media Gateway Control Protocol (MGCP) gateway, only a few commands must be entered in the CLI, and CallManager handles all the call routing. An H.323 gateway does not depend on the CallManager for call routing; it contains a dial plan of its own. This means that the dial plan must be entered using the CLI, which increases the difficulty of configuring an H.323 gateway. In order to properly configure an H.323 gateway, you must have a high level of experience in configuring IOS devices for VoIP deployments.
After the entire CLI configuration of the gateway is completed, it can be configured in CallManager. There are a number of Cisco devices that can be configured as H.323 gateways.
The following steps are required to configure a Cisco 3620 as an H.323 gateway:-
Step 1:- From within CCMAdmin select Device>Gateway.
Step 2:- Click on Add New.Select Gateway from the Gateway type drop-down list and click Next.
Step 3:- Select the H.323 Gateway from the Gateway type drop-down list.
Step 4:- Click next.
Step 5:- In The Gateway Configuration screen, Enter the DNS Name or IP address of the gateway in the Device Name field.
Step 6:- In the Description field, enter a description that will help make this device easily identifiable.
Step 7:- From the Device Pool drop-down list, select the desired CallManager group for this gateway.
Step 8:- The next field is Media Resource Group List. This determines to which media resources this phone will have access. Configuring CallManager Features and Services. From the Media Resource Group List drop-down list, select the desired group. If no Media Resource Group List is chosen, the one defined in the device pool is used.
Step 9:- Information entered in the Location field is used to prevent WAN links from becoming oversubscribed in centralized deployments. If you have defined locations, select the appropriate one for this phone from the drop-down list.
Step 10. The AAR Group field determines the AAR group with which this device is associated. An AAR group provides the prefix that is assigned when a call fails due to insufficient bandwidth. Select an AAR group if AAR is being used. If this field is set to None, AAR is, in effect, disabled on this device.
Step 11. The Signaling Port field defines the H.225 signaling the gateway uses. The default of 1720 can be used in most cases.
Step 12:- The Media Termination Point Required check box needs to be checked if the H.323 device does not support features such as hold and transfers. This is the case with H.323 version 1 gateways. These gateways cannot support such features because H.323v1 does not have the ability to modify a channel, which means it cannot transfer a call or place a call on hold, because this would require modifying the channel.
Step 13:- If the Retry Video Calls as Audio box is checked, CallManager sets up a voice call if a video calls fails to set up.
Step 14:- When the Wait for Far End H.245 Terminal Capability Set box is checked, CallManager expects to receive the far ends capabilities
before sending its own.
Step 15:- The only MLPP setting that can be configured is the MLPP Domain. Enter the domain in this field. If left blank the settings found in enterprise parameters are used.
Call Routing Information—Inbound Calls
Step 16:- The next set of fields deals with inbound calls. The Significant Digits field determines the number of digits of an incoming dialed number that CallManager uses. CallManager counts from right to left, so if the number entered in this field is 4 and the digits received are 8105559090, 810555 would be removed and only 9090 would be used to determine the destination of this call.
Step 17:- A Calling Search Space (CSS) determines what destination inbound calls to this gateway will be able to reach.Choose a CSS from the Calling Search Space drop-down list. If this field is left at None, the dial privileges of this device could be limited.
Step 18:- The Automated Alternate Routing (AAR) is used to provide an alternate route if a call fails due to insufficient bandwidth. The AAR
CSS can be used to limit the paths a call may use when it is rerouted. Select an AAR CSS from the AAR Calling Search Space drop-down list.
Step 19:- The Prefix DN field defines what digits will be added to the front of the incoming destination number. This is applied to the number, after CallManager truncates the number based on the Significant Digits setting.
Step 20:- If your voicemail system supports Redirecting Number IE, check the Redirecting Number IE Delivery-Inbound box. Otherwise, leave this box unchecked.
Step 21:- Check the Enable Inbound Faststart box if you wish to support H.323 FastStart. H.323 FastStart requires only two message exchanges
to open logical channels, whereas normal setup requires 12. However, if FastStart is selected, both ends must support and be configured for
Call Routing Information—Outbound Calls
Step 22:- The next set of fields deals with outbound calls. The Calling Party Selection field determines what number is sent to outbound
calls. The choices are:
Originator — the directory number of the device that placed the call
First Redirect Number — the directory number of the first device to forward the call
Last Redirect Number — the directory number of the last device to forward the call
First Redirect Number (External) — the external directory number of the first device to forward the call
Last Redirect Number (External) — the external directory number of the last device to forward the call
Select the desired value for this field.
Step 23:- The Calling Party Presentation field determines if CallManager sends Caller ID information. To send caller ID information, select Allowed from the drop-down list. To block caller ID, select Restricted from the drop-down list.
Step 24:- Cisco recommends that the next four fields remain set to the default of Cisco CallManager:
- Called party IE number type unknown
- Calling party IE number type unknown
- Called Numbering Plan
- Calling Numbering Plan
These fields deal with dial plan issues and should be changed only when advised to do so by Cisco or an experienced dial plan expert. The
need to change these usually occurs when installing CallManager internationally.
Step 25:- The Caller ID DN field is used to determine what caller ID is sent out this gateway. A mask or a complete number can be entered in
this field. For example, if the mask 55536XX is entered in this field, CallManager sends 55536 and the last two digits of the directory number (DN) that is placing the call.
Step 26:- If the Display IE Delivery check box is checked, then the calling and called party name information is included in messages.
Step 27:- The Redirecting Number IE Delivery-Outbound check box should be checked when integrating with a voicemail system that supports
Redirecting Number IE. Otherwise, leave it unchecked.
H.323 Gateways and SRST
On H.323 gateways, when the WAN link fails, active calls from Cisco Unified IP Phones to the PSTN are not maintained by default. Call preservation may work with the no h225 timeout keepalive command, but call preservation using the no h225 timeout keepalive command is not officially supported by Cisco Technical Support.
Under default configuration, the H.323 gateway maintains a keepalive signal with Cisco Unified CallManager and terminates H.323-to-PSTN calls if the keepalive signal fails, for example if the WAN link fails. To disable this behavior and help preserve existing calls from local IP phones, you can use the no h225 timeout keepalive command. Disabling the keepalive mechanism only affects calls that will be torn down as a result of the loss of the H.225 keepalive signal.