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This document describes the Redundant H.323 Zone Support that was introduced in Cisco IOS Release 12.1(1)T. This document contains the following sections:
The Redundant H.323 Zone Support feature allows users to configure multiple gatekeepers to service the same zone or technology prefix. This feature can be used with the Gateway Support for Alternate Gatekeepers feature, which allows a user to configure a gateway to point to two gatekeepers (one as the primary and the other as the alternate). Together, these features allow a user to configure a Cisco gateway to send location requests (LRQs) to two or more Cisco gatekeepers---one as a primary and the others as back up gatekeepers. All gatekeepers are active. The gateway can choose to register with any one (but not all) at a given time.
The zone prefixes (typically area codes) serve the same purpose as the domain names in the H.323-ID address space.
For example, the local gatekeeper can be configured with the knowledge that zone prefix "212......" (that is, any address beginning "212" and followed by 7 arbitrary digits) is handled by the gatekeeper gatekeeper_2. Then, when the local gatekeeper is asked to admit a call to destination address 2125551111, it knows to send the Location Request to gatekeeper_2.
When gatekeeper_2 receives the request, the gatekeeper must resolve the address so that the call can be sent to its final destination. There may be an H.323 endpoint with that E.164 address that has registered with gatekeeper_2, in which case gatekeeper_2 returns the IP address for that endpoint. However, it is possible that the E.164 address belongs to a non-H.323 device (for example, a telephone or an H.320 terminal). Because non-H.323 devices do not register with gatekeepers, gatekeeper_2 cannot resolve the address. The gatekeeper must be able to select a gateway that can be used to reach the non-H.323 device. This is where the technology prefixes (or "gateway-type") becomes useful.
The network administrator selects technology prefixes (tech-prefixes) to denote different types or classes of gateways. The gateways are then configured to register with their gatekeepers with these prefixes. For example, voice gateways can register with tech-prefix "1#," H.320-gateways with tech-prefix "2#," voicemail-gateways with "3#," and so on. More than one gateway can register with the same type prefix. When this happens, the gatekeeper makes a random selection among gateways of the same type.
If the caller knows the type of device they are trying to reach, they can include the technology prefix in the destination address to indicate the type of gateway to use to get to the destination. For example, if the caller knows that address 2125551111 belongs to a regular telephone, then they can use the destination address of 1#2125551111, where 1# indicates that the address should be resolved by a voice gateway. When the voice gateway receives the call for 1#2125551111, it strips off the technology prefix and bridges the next leg of the call to the telephone at 2125551111.
The Redundant H.323 Zone Support feature provides gatekeeper redundancy by allowing multiple gatekeepers to service the same zone or technology prefix. Gatekeeper redundancy is achieved through the use of multiple LRQs. The gateway registers with one of the gatekeepers and, if that gatekeeper becomes unavailable, it registers with another. The LRQ messages are sent simultaneously to all gatekeepers in a given prefix or technology zone.
The Redundant H.323 Zone Support feature has the following restrictions and limitations:
The Redundant H.323 Zone Support feature is related to the H.323 VoIP Gatekeeper for Cisco Access Platforms feature and the Gateway Support for Alternate Gatekeepers feature.
The Redundant H.323 Zone Support feature is supported on any existing IOS gatekeeper platforms, including the following:
Standards
No new or modified standards are supported by this feature.
MIBs
No new or modified MIBs are supported by this feature.
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Note Although the Redundant H.323 Zone Support allows multiple gatekeepers to service a specific prefix or technology zone, the MIB can query only the first gatekeeper that is configured to handle a particular E.164 address. Likewise, the MIB is allowed to configure only one gatekeeper for a specific E.164 address. |
For descriptions of supported MIBs and how to use MIBs, see the Cisco MIB web site on CCO.
RFCs
No new or modified RFCs are supported by this feature.
The Redundant H.323 Zone Support feature requires the Cisco H.323 VoIP Gatekeeper for Cisco Access Platforms feature.
See the following sections for configuration tasks for the Redundant H.323 Zone Support feature. Each task in the list indicates if the task is optional or required.
The order in which zone and technology prefixes are configured determines the order in which the local Gatekeeper sends LRQs. Using zone prefixes as an example, the local Gatekeeper routes the call to the first zone that responds with an LCF. If the local Gatekeeper is configured for a zone prefix that already has remote Gatekeepers configured, the local Gatekeeper will automatically put that zone prefix at the top of the list.
For example:
gatekeeper zone local gnet-2503-2-gk cisco.com zone remote gnet-2600-1-gk cisco.com 172.18.194.131 1719 zone remote gnet-2503-3-gk cisco.com 172.18.194.134 1719 zone prefix gnet-2600-1-gk 919....... zone prefix gnet-2503-6-gk 919.......
With this configuration, LRQs are first sent to gnet-2600-1-gk (which is the first zone prefix because it has a remote Gatekeeper configured for it) and then to gnet-2503-6-gk (which is the second zone prefix). If you add the local gatekeeper to that zone prefix, it automatically goes to the top of the list, as shown below:
gatekeeper zone local gnet-2503-2-gk cisco.com zone remote gnet-2600-1-gk cisco.com 172.18.194.131 1719 zone remote gnet-2503-3-gk cisco.com 172.18.194.134 1719 zone prefix gnet-2503-2-gk 919....... zone prefix gnet-2600-1-gk 919....... zone prefix gnet-2503-6-gk 919.......
As you can see, the zone prefix for the local Gatekeeper (gnet-2600-2-gk) has been inserted at the top of the zone prefix list. If the local gatekeeper can resolve the address it will not send LRQs to the remote zones.
This also applies to the configuration of technology prefixes.
| Command | Purpose | |
|---|---|---|
Step 1 | Router# config term | Enter configuration mode. |
Step 2 | Router(config)# gatekeeper | Enter gatekeeper configuration mode. |
Step 3 | Router(config-gk)# zone local gatekeeper-name domain-name [rasIPaddress] | Configure the local gatekeeper. |
Step 4 | Router(config-gk)# zone remote other-gatekeeper-name other-domain-name other-gatekeeper-ip-address [port-number] | Configure the remote gatekeeper. |
| Command | Purpose | |
|---|---|---|
Step 1 | Router# config term | Enter configuration mode. |
Step 2 | Router(config)# gatekeeper | Enter gatekeeper configuration mode. |
Step 3 | Router(config-gk)# zone prefix gatekeeper-name e164-prefix | Configure the local gatekeeper to service the prefix zone. |
Step 4 | Router(config-gk)# zone prefix gatekeeper-name e164-prefix | Configure the remote gatekeeper to service the prefix zone. |
You can configure multiple remote gatekeepers for the same zone, but only one of the gatekeepers defined for any given zone prefix can be local. We recommend that you limit the number of remote gatekeepers that service the same zone prefix to two.
| Command | Purpose | |
|---|---|---|
Step 1 | Router# config term | Enter configuration mode. |
Step 2 | Router(config)# gatekeeper | Enter gatekeeper configuration mode. |
Step 3 | Router(config-gk)# gw-type-prefix type-prefix hopoff gkid1 hopoff gkid2 ... hopoff gkidn | Configure the gatekeepers to service a technology zone. |
You can enter the hopoff keyword and gkid argument multiple times in the same command to define a group of gatekeepers that will service a given technology prefix. Only one of the gatekeepers in the hopoff list can be local. We recommend that you limit the number of remote gatekeepers that service the same technology prefix to two.
To verify that multiple gatekeepers are defined for a zone prefix, enter the show gatekeeper zone prefix command. The output lists all the gatekeepers and the zone prefixes serviced by each.
router# show gatekeeper zone prefix
ZONE PREFIX TABLE
=================
GK-NAME E164-PREFIX
------- -----------
c3620-1-gk 917300....
c2514-2-gk 917300....
c2600-1-gk 919.......
c2514-1-gk 919.......
To verify that multiple gatekeepers are defined for a zone prefix, enter the show gatekeeper gw-type-prefix command. The output lists all the gatekeepers and the zone prefixes serviced by each.
router# show gatekeeper gw-type-prefix (GATEWAYS-TYPE PREFIX TABLE ================================ Prefix:3#* (Hopoff zone c2600-1-gk c2514-1-gk)
This section provides the following configuration examples:
In the following example, two remote gatekeepers are configured to service the same zone prefix:
gatekeeper zone remote c2600-1-gk cisco.com 172.18.194.70 1719 zone remote c2514-1-gk cisco.com 172.18.194.71 1719 zone prefix c2600-1-gk 919....... zone prefix c2514-1-gk 919.......
In the following example, two remote gatekeepers are configured to service the same technology prefix:
gatekeeper zone remote c2600-1-gk cisco.com 172.18.194.70 1719 zone remote c2514-1-gk cisco.com 172.18.194.71 1719 gw-type-prefix 3#* hopoff c2600-1-gk hopoff c2514-1-gk
This section documents new or modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.1 command reference publications.
To configure a technology prefix in the gatekeeper, use the gw-type-prefix command. To remove the technology prefix, use the no form of the command.
gw-type-prefix type-prefix [hopoff gkid1] [hopoff gkid2] [hopoff gkidn] [default-technology] [[gw ipaddr ipaddr [port ]] ...]
Syntax Description
type-prefix A technology prefix is recognized and is stripped before checking for the zone prefix. It is strongly recommended that you select technology prefixes that do not lead to ambiguity with zone prefixes. Do this by using the # character to terminate technology prefixes, for example, 3#. hopoff gkid (Optional) Use this option to specify the gatekeeper where the call is to hop off, regardless of the zone prefix in the destination address. The gkid argument refers to a gatekeeper previously configured using the zone local or zone remote comment. You can enter this keyword and argument multiple times to configure redundant gatekeepers for a given technology prefix. default-technology (Optional) Gateways registering with this prefix option are used as the default for routing any addresses that are otherwise unresolved. gw ipaddr ipaddr [port] (Optional) Use this option to indicate that the gateway is incapable of registering technology prefixes. When it registers, it adds the gateway to the group for this type-prefix, just as if it had sent the technology prefix in its registration. This parameter can be repeated to associate more than one gateway with a technology prefix.
Defaults
None.
Command Modes
Gatekeeper configuration
Command History
11.3(6) NA2 This command was introduced. 12.1(1)T This command was modified to allow the user to specify multiple hop offs.
Release
Modification
Usage Guidelines
You do not have to define a technology prefix to a gatekeeper if there are gateways configured to register with that prefix, and if there are no special flags (such as hopoff gkid or default-technology) that you want to associate with that prefix.
Examples
The following example defines two gatekeepers for technology zone 3:
gw-type-prefix 3#* hopoff c2600-1-gk hopoff c2514-1-gk
Related Commands
show gatekeeper gw-type-prefix Displays the list of currently defined technology zones and the gatekeepers responsible for each.
Command
Description
gatekeeper---A gatekeeper maintains a registry of devices in the multimedia network. The devices register with the gatekeeper at startup, and request admission to a call from the gatekeeper.
The gatekeeper is an H.323 entity on the LAN that provides address translation and control access to the LAN for H.323 terminals and gateways. The gatekeeper may provide other services to the H.323 terminals and gateways, such as bandwidth management and locating gateways.
gateway---A gateway allows H.323 terminals to communicate with non-H.323 terminals by converting protocols. A gateway is the point at which a circuit-switched call is encoded and repackaged into IP packets.
A H.323 gateway is an endpoint on the LAN that provides real-time, two-way communications between H.323 terminals on the LAN and other ITU-T terminals in the WAN, or to another H.323 gateway.
E.164---ITU-T recommendation for international telecommunication numbering, especially in ISDN, BISDN, and SMDS. An evolution of standard telephone numbers.
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.
hop off---The point at which a call transitions from H.323 to non-H.323, typically at a gateway.
LRQ---A RAS message sent as a location request.
POTS---Plain old telephone service. Basic telephone service supplying standard single line telephones, telephone lines, and access to the PSTN.
PSTN---Public switched telephone network. PSTN refers to the local telephone company.
RAS---Registration, admission, and status protocol. This is the protocol that is used between endpoints and the gatekeeper to perform management functions. The RAS signaling function performs registration, admissions, bandwidth changes, status, and disengage procedures between the VoIP gateway and the gatekeeper.
technology prefix---Discriminators used to distinguish between gateways having specific capabilities within a given zone. In the exchange between the gateway and the gatekeeper, the technology prefix is used to select a gateway after the zone has been selected. Technology prefixes can be used to tell the gatekeeper that a certain technology is associated with a particular call (for example, 15# could mean a fax transmission), or it can be used like an area code for more generic routing. No standard defines what the numbers in a technology prefix mean; by convention, technology prefixes are designated by a pound (#) symbol as the last character.
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 which generally refers to Cisco's standards-based (H.323, etc.) approach to IP voice traffic.
zone prefix---A prefix that identifies the addresses to be serviced by a given gatekeeper. Zone prefixes are typically area codes and serve the same purpose as the domain names in the H.323-ID address space.
Posted: Wed Mar 22 13:14:47 PST 2000
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