Cisco Unified Customer Voice Portal (CVP) 4.x Solution Reference Network Design (SRND)
Gateway Options
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Gateway Options

Table Of Contents

Gateway Options

PSTN Gateway

VoiceXML Gateway with DTMF or ASR/TTS

VoiceXML and PSTN Gateway with DTMF or ASR/TTS

TDM Interfaces

Gateway Choices

Gateway Sizing

Using MGCP Gateways


Gateway Options


Cisco offers a large range of voice gateway models to cover a large range of requirements. Many, but not all, of these gateways have been qualified for use with Unified CVP. For the list of currently supported gateway models, always check the latest version of the Hardware and System Software Specification for Cisco Unified CVP (formerly called the Bill of Materials), available at

http://www.cisco.com/en/US/products/sw/custcosw/ps1006/prod_technical_reference_list.html

Gateways are used in Unified CVP for conversion of TDM to IP and for executing VoiceXML instructions. The following sections help you determine which gateways to incorporate into your design:

PSTN Gateway

VoiceXML Gateway with DTMF or ASR/TTS

VoiceXML and PSTN Gateway with DTMF or ASR/TTS

TDM Interfaces

Gateway Choices

Gateway Sizing

Using MGCP Gateways

PSTN Gateway

In this type of deployment, the voice gateway is used as the PSTN voice gateway. The voice gateway is responsible for converting TDM speech to IP and for recognizing DTMF digits and converting them to H.245 or RFC2833 events. Unified CVP does not currently support passing SIP-Notify or KPML DTMF events.

In a centralized Unified CVP deployment, you can separate the VoiceXML functionality from the ingress gateway to provide a separate PSTN ingress layer. The separate PSTN layer and VoiceXML farm enables the deployment to support a large number of VoiceXML sessions and PSTN interfaces. For example, the Cisco AS5400XM can accept a DS3 connection, providing support for up to 648 DSOs. However, a gateway that is handling that many ingress calls cannot also support as many VoiceXML sessions. In such cases, the VoiceXML sessions should be off-loaded to a separate farm of VoiceXML-only gateways.


Note Any TDM interface can be used as long as it is supported by the Cisco IOS gateway and by the Cisco IOS version compatible with CVP.


In a distributed Unified CVP deployment, gateways that reside at the branch office must be dual-use gateways. When the Unified CVP Call Server receives a call from a branch-based ingress gateway and is asked by the ICM to transfer that call to a VoiceXML gateway, it must be careful to return the call to the same branch office in order to avoid establishing a media stream from one branch to another. It does this by always forcing the VRU leg to go back to the same gateway from which it received the call initially.


Note The Cisco AS5850eRSC and the Catalyst 6500 Communication Media Module (CMM) are recommended only for PSTN gateway use. They are not designed to process VoiceXML.


VoiceXML Gateway with DTMF or ASR/TTS

A standalone VoiceXML gateway is a voice gateway with no PSTN interfaces. The VoiceXML gateway enables customers to interact with the Cisco IOS VoiceXML Browser via DTMF tones or ASR/TTS. Because the gateway does not have PSTN interfaces, voice traffic is sent via Real-Time Transport Protocol (RTP) to the gateway, and DTMF tones are sent via out-of-band H.245 or RFC2833 events.

A voice gateway deployment using VoiceXML with DTMF or ASR/TTS, but no PSTN, enables you to increase the scale of the deployment and support hundreds of VoiceXML sessions per voice gateway.

In a centralized Unified CVP deployment, you could use a VoiceXML farm. For example, if you want to support 300 to 10,000 or more VoiceXML sessions, the recommended voice gateway is the Cisco AS5350XM. The standalone AS5350XM can support many DTMF or ASR/TTS VoiceXML sessions per voice gateway. In addition, Cisco recommends that you stack the AS5350XM gateways to support large VoiceXML IVR farms.

In a distributed Unified CVP deployment, consider providing an extra layer of redundancy at the branch office. You can deploy a separate PSTN gateway and a VoiceXML gateway to provide an extra layer of redundancy. In addition, for a centralized Cisco Unified Communications Manager deployment, you must provide support for Survivable Remote Site Telephony (SRST). The Cisco 3800, 3700, and 2800 Series routers are the best choice for the voice gateway because they support SRST.

VoiceXML and PSTN Gateway with DTMF or ASR/TTS

The most popular voice gateway is the combination VoiceXML and PSTN Interface Gateway. In addition, for a centralized Cisco Unified Communications Manager deployment, you must provide support for Survivable Remote Site Telephony (SRST). The Cisco 3800, 3700, and 2800 Series routers are the best choice for the voice gateway because they support SRST.

TDM Interfaces

Cisco AS5400 Series Universal Gateways offer unparalleled capacity in only two rack units (2 RUs) and provide universal port data, voice, and fax services on any port at any time. High density (up to one CT3), low power consumption (7.2 A at 48 VDC per CT3), and universal port digital signal processors (DSPs) make the Cisco AS5400 Series Universal Gateways ideal for many network deployment architectures, especially co-location environments and many points of presence (POPs).

The Cisco AS5350 Universal Gateway is the only one-rack-unit (1 RU) gateway that supports 2-, 4-, or 8-port T1/7-port E1 configurations and provides universal port data, voice, and fax services on any port at any time. The Cisco AS5350 Universal Gateway offers high performance and high reliability in a compact, modular design. This cost-effective platform is ideally suited for internet service providers (ISPs) and enterprise companies that require innovative universal services.

The Cisco 2600, 2800, 3700, and 3800 Series Routers support the widest range of packet telephony-based voice interfaces and signaling protocols within the industry, providing connectivity support for more than 90 percent of the world's private branch exchanges (PBXs) and public switched telephone network (PSTN) connection points. Signaling support includes T1/E1 Primary Rate Interface (PRI), T1 channel associated signaling (CAS), E1-R2, T1/E1 QSIG Protocol, T1 Feature Group D (FGD), Basic Rate Interface (BRI), foreign exchange office (FXO), E&M, and foreign exchange station (FXS). The Cisco 2600, 2800, 3700 and 3800 Series Routers can be configured to support from two to 540 voice channels.

For the most current information about the various digital (T1/E1) and analog interfaces supported by the various voice gateways, refer to the latest product documentation available at the following sites:

Cisco 2800 Series

http://www.cisco.com/en/US/products/ps5854/tsd_products_support_series_home.html

Cisco 3700Series

http://www.cisco.com/en/US/products/hw/routers/ps282/tsd_products_support_series_home.html

Cisco 3800 Series

http://www.cisco.com/en/US/products/ps5855/tsd_products_support_series_home.html

Cisco AS5300

http://www.cisco.com/en/US/products/hw/univgate/ps501/tsd_products_support_series_home.html

Cisco AS5400HPX

http://www.cisco.com/en/US/products/hw/univgate/ps505/tsd_products_support_series_home.html

Gateway Choices

Unified CVP uses gateways for two purposes: TDM ingress and VoiceXML rendering. Any Cisco gateway that is supported by Unified CVP can usually be used for either purpose or both. However, depending on your deployment model, you might need only one of the functions:

Model #1: Standalone Self-Service

All calls use both ingress and VoiceXML.

Model #2: Call Director

All calls use ingress only.

Model #3a: Comprehensive Using ICM Micro-Apps

All calls use ingress, and some calls use VoiceXML.

Model #3b: Comprehensive Using CVP VoiceXML Server

All calls use ingress, and some calls use VoiceXML.

Model #4: VRU Only with NIC Controlled Routing

All calls use VoiceXML only.

In cases where both ingress and VoiceXML are required, you can choose to run both functions on the same gateways or you can choose to designate some gateways for ingress and others for VoiceXML. Use the following guidelines to determine whether the functions should be combined or split:

In classical branch office deployments, where the call needs to be queued at the branch where it arrived, ingress and VoiceXML functions must always be combined.

In cases where a large number of non-CVP PSTN connections will share the gateways, it is recommended to dedicated Ingress for that purpose, and use separate VXML gateways.

The Cisco AS5850eRSC or Cisco Catalyst 6500 Communication Media Module (CMM) can be used for ingress only; they cannot be used for VoiceXML.

VoiceXML-only gateways are less costly because they do not require DSP farms or TDM cards. Use a spreadsheet to determine which way you obtain the best price.

With relatively low call volume, it is usually better to combine the functions for redundancy purposes. Two combined gateways are better than one of each because the loss of one gateway still allows calls to be processed, though at a lower capacity.

The next decision is whether to use Cisco Integrated Service Router (ISR) gateways (Cisco 2800 or 3800 Series) or the Cisco AS5x00 Series Gateways. Guidelines state that ISR gateways should be used only in branch office sites, whereas AS5x00 Series gateways should be used in centralized data center sites.

Sometimes it is difficult to determine what constitutes a branch office, and therefore which gateway should be used. The following guidelines can help with that determination:

The classical definition of branch offices, for which you should use ISR gateways, includes:

Multiple sites where TDM calls will be arriving from the PSTN.

Those sites are separated from the data centers where most of the Unified CVP equipment resides.

You will be placing only one gateway at each site.

If you have sites where you will be stacking multiple gateways for any reason, then those sites are data center sites and should use Cisco AS5x00 Series gateways.

For more information on the Cisco AS5x00 Series Gateways, refer to the technical specifications available at

http://www.cisco.com/en/US/products/hw/iad/index.html

For more information on the Cisco Integrated Service Routers (ISRs), refer to the documentation available at

http://www.cisco.com/en/US/products/hw/routers/index.html

Gateway Sizing

Individual Cisco gateways can handle various call capacities depending on whether they are doing ingress only, VoiceXML only, or a combination of the two. Gateways doing VoiceXML activities also have different call capacities depending on whether or not they are supporting ASR or TTS activities.

In general, gateways performing ingress-only can be sized according to the number of TDM cables that can be connected to them. For gateways that are combined or VoiceXML-only, it is important to ensure that the overall CPU usage will be less than 70% on average. The numbers in Table 7-1 are based on Unified CVP VoiceXML documents; other applications that generate more complex VoiceXML documents will have a higher impact on performance. The following factors affect CPU usage:

Calls per second (cps)

Maximum concurrent calls

Maximum concurrent VoiceXML sessions

Before sizing the voice gateways, use the IPCC Resource Calculator to determine the maximum number of trunks (DS0s) and VoiceXML IVR ports needed to support the entire solution.

For almost all Unified CVP deployment models, sizing is based on the maximum number of concurrent VoiceXML sessions and VoIP calls, as listed in Table 7-1 and Table 7-2.

Table 7-1 Maximum Number of VoiceXML Sessions Supported by Cisco Voice Gateways 

Cisco Voice Gateway Platform
Dedicated VoiceXML Sever
Voice Gateway and VoiceXML
Memory Recommended
VoiceXML and DTMF
VoiceXML and ASR/TTS
VoiceXML and DTMF
VoiceXML and ASR/TTS

2801

7

6

6

4

256 MB

2811

30

24

24

20

256 MB

2821

48

36

36

30

256 MB

2851

60

56

56

48

512 MB

3725

68

50

50

38

512 MB

3745

100

80

77

60

512 MB

3825

120

96

96

72

512 MB

3845

150

144

144

96

512 MB

AS5400HPX

96

90

90

72

512 MB

AS5350XM

240

192

192

192

512 MB (default)

AS5400XM

240

192

192

192

512 MB (default)


The numbers in Table 7-1 assume that the only activities running on these gateways are VoiceXML with basic routing and connectivity. If you intend to run additional applications, such as fax, security, normal business calls, and so forth, then the capacity numbers presented here should be prorated accordingly. These figures apply to Cisco IOS Release 12.4 (Mainline).


Note These performance numbers are accurate when used with either the Cisco Call Server or Cisco VoiceXML Server. Performance can, and often does, vary with different applications. Performance from external VoiceXML applications (such as Nuance OSDMs) might not be representative of the performance when interoperating with non-Cisco applications. You must ensure that the CPU usage is less than 70% on average and that adequate memory is available on Cisco gateways at full load when running external VoiceXML applications. Users should contact the application provider of the desired VoiceXML application for performance and availability information. Be aware that external VoiceXML applications are not provided by Cisco, and Cisco makes no claims or warranties regarding the performance, stability, or feature capabilities of the application when interoperating in a Cisco environment.



Note If you run VoiceXML on one of the Cisco 2800, 3700, or 3800 gateways, additional licenses (FL-VXML-1 or FL-VXML-12) are required.


Also consult Table 7-2 to ensure that the concurrent call load and call arrival rates do not exceed the listed capacities.

Table 7-2 Maximum Number of Calls Supported per Gateway Platform 

Cisco Voice Gateway Platform
Maximum Calls per Second
Maximum VoIP Calls

2801

1

32

2811

1

80

2821

1.2

128

2851

2

192

3725

2

192

3745

4

384

3825

4

384

3845

8

540

AS5400HPX

7

384

AS5350XM

20

192

AS5400XM

20

648


In addition to these capacities, also consider how much DRAM and flash memory to order. The capacity that comes with the machine by default is usually sufficient for most purposes. However, if your application requires large numbers of distinct .wav files (as with complex self-service applications) or if your application has unusually large .wav files (as with extended voice messages or music files), you might want to increase the amount of DRAM in order to accommodate more cache space. The .wav files are recorded at 8 kbps. Additionally, if you plan to use the flash memory itself rather than a media server to house media files, you might want to expand your flash memory order. The use of DRAM for prompt caching is discussed in detail in the chapter on Media File Options, page 12-1.

Using MGCP Gateways

Cisco Unified CVP requires the deployment of H.323 or SIP gateways. However, customers might require the use of MGCP 0.1 voice gateways with Cisco Unified Communications Manager deployments for purposes of call survivability, overlap sending, or simplified deployment. The following design considerations apply to deploying Cisco Unified CVP in this environment:

Design and plan a phased migration of each MGCP voice gateway to H.323 or SIP.

Implement both MGCP 0.1 and H.323 or SIP.

Deploy a second H.323 or SIP voice gateway at each Unified CVP location.

Because of the way MGCP works, a PSTN interface using MGCP can be used for MGCP only. Therefore, if you want to use MGCP for regular Cisco Unified Communications Manager calls and H.323 or SIP for Unified CVP calls, you will need two PSTN circuits.