© 2008 Cisco Systems, Inc. All rights reserved. CVOICE v6.0—1-1

Introducing Voice over IP

Introducing Voice Gateways

© 2008 Cisco Systems, Inc. All rights reserved. CVOICE v6.0—1-2

Understanding Gateways

A gateway connects IP communication networks to analog devices, to the PSTN, or to a PBX

Specifically, its role is the following:

– Convert IP telephony packets into analog or digital signals

– Connect an IP telephony network to analog or digital trunks or to individual analog stations

Two gateway signaling types:

– Analog

– Digital

© 2008 Cisco Systems, Inc. All rights reserved. CVOICE v6.0—1-3

Gateways

Support these gateway protocols:

– H.323

– MGCP

– SIP

– SCCP

Provide advanced gateway functionality

– DTMF relay

– Supplementary services

Work with redundant Cisco Unified Communication Manager

Enable call survivability

Provide QSIG support.

Provide fax or modem services, or both

© 2008 Cisco Systems, Inc. All rights reserved. CVOICE v6.0—1-4

IP WAN

PSTN

San Jose Chicago

MGCPSJ-GW

Denver

Unified Communications Manager Cluster

Unified Communications Manager Express H.323

CHI-GW

SIPDNV-GW

SIP Proxy Server

Deploying Gateways

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Gateway Hardware Platforms

Modern enterprise models:

Cisco 2800 Series Routers Cisco 3800 Series Routers Cisco Catalyst 6500 Series

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Gateway Hardware Platforms (Cont.)

Well-known and widely used older enterprise models:

Cisco 1751-V RouterEOS: 03/2007EOL: 03/2012

Cisco 3600 Series PlatformsEOS: 12/2004EOL: 12/2008

Cisco 1760-V RouterEOS: 03/2007EOL: 03/2012

Cisco 2600XM Series RoutersEOS: 03/2007EOL: 03/2012

Cisco 3700 Series RoutersEOS: 03/2007EOL: 03/2012

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Gateway Hardware Platforms (Cont.)

Special voice gateways:

Cisco VG224 and VG248 Gateways

Cisco AS5300 and AS5400 Series Gateways

Cisco 7200 Series RoutersCisco ATA 186

Cisco 827-4V RouterEOS: 05/2005EOL: 05/2010

Cisco AS5850 Gateway

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Gateway Hardware Platforms (Cont.)

H.323Cisco Unified

Communications Manager MGCP

SIP SCCP

Cisco 827-4V Router Yes No No No

Cisco 2800 Series Routers Yes Yes Yes Yes

Cisco 3800 Series Routers Yes Yes Yes Yes

Cisco 1751-V and 1760-V Routers Yes Yes No Yes1

Cisco 2600XM Series Router Yes Yes No No3

Cisco 3600 Series Platforms Yes Yes No No3

Cisco 3700 Series Routers Yes Yes No No3

Cisco VG224 Gateway Yes2 Yes2 No Yes

Cisco VG248 Gateway No No No Yes

Cisco AS53XX and AS5400 and AS5850 Cisco Gateways Yes No No No

Communication Media Module Yes Yes Yes Yes

GW Module WS-X6608-x1 and FXS Module WS-X6624 No Yes No Yes

Cisco ATA 180 Series Yes2 Yes2 No Yes2

Cisco 7200 Series Routers Yes No No No1 Conferencing and transcoding only2 FXS only3 DSP farm

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IP WAN

Supported IP telephony deployment models: Single-site deployment

Multisite WAN with centralized call processing

Multisite WAN with distributed call processing

Clustering over the IP WAN

Headquarters

Branch

Applications

Cisco Unified Communications Manager Cluster

Applications

Cisco Unified Communications

ManagerCluster

PSTN

IP Telephony Deployment Models

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Single-Site Deployment

SIP or SCCP

Cisco Unified Communications Manager Cluster

PSTN

Cisco Unified Communications Manager servers, applications, and DSP resources at same physical location

IP WAN (if one) used for data traffic only

PSTN used for all external calls

Supports approximately 30,000 IP phones per cluster

WAN

Data

Only

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Design Guidelines

Provide a highly available, fault-tolerant infrastructure. Understand the current calling patterns within the enterprise. Use the G.711 codec for all endpoints; DSP resources can be

allocated to other functions, such as conferencing and MTP. Use H.323, SIP, SRST, and MGCP gateways for the PSTN. Implement the recommended network infrastructure for high

availability, connectivity options for phones, QoS mechanisms, and security.

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Multisite WAN with Centralized Call Processing

Cisco Unified Communications Manager Cluster

SIP or SCCP

SIP or SCCP SIP or SCCP

PSTNIP

WAN

Cisco Unified Communications Manager at central site; applications and DSP resources centralized or distributed

IP WAN carries voice traffic and call control signaling

Supports approximately 30,000 IP phones per cluster

Call admission control(limit number of calls per site)

SRST for remote branches

AAR used if WAN bandwidth is exceeded

SRST-capable

SRST-capable

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Design Guidelines

Minimize delay between Cisco Unified Communications Manager and remote locations to reduce voice cut-through delays.

Use the locations mechanism in Cisco Unified Communications Manager to provide call admission control into and out of remote branches.

The number of IP phones and line appearances supported in SRST mode at each remote site depends on the branch router platform.

At the remote sites, use SRST, Cisco Unified Communications Manager Express in SRST mode, SIP SRST, and MGCP gateway fallback to ensure call-processing survivability in the event of a WAN failure.

Use HSRP to provide backup gateways and gatekeepers.

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Multisite WAN with Distributed Call Processing

Gatekeeper

Cisco Unified Communications Manager and applications located at each site

IP WAN carries intercluster call control signaling

Scales to hundreds ofsites

Transparent use of the PSTN if the IP WAN is unavailable

SIP or SCCP

SIP or SCCP

SIP or SCCP

PSTN IPWAN

GK

Cisco Unified Call Manager

Cluster

Cisco Unified Call Manager

Cluster

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Design Guidelines

Use a Cisco IOS gatekeeper to provide CAC into and out of each site.

Use HSRP gatekeeper pairs, gatekeeper clustering, and alternate gatekeeper support for resiliency.

Size the gateway and gatekeeper platforms appropriately per the SRND.

Deploy a single WAN codec. Gatekeeper networks scale to hundreds of sites. Provide adequate redundancy for the SIP proxies. Ensure that the SIP proxies have the capacity for the call rate and

number of calls required in the network.

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Clustering over the IP WAN

Publisher or TFTP server

QoS-Enabled Bandwidth

IP WANIP WAN

<40 ms Round-Trip Delay

SIP or SCCP

SIP or SCCP

Applications and Cisco Unified Communications Managers of the same cluster distributed over the IP WAN

IP WAN carries intracluster server communication and signaling Limited number of sites

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WAN Considerations

40-ms maximum RTT between any two Cisco Unified Communications Manager servers in the cluster

Use QoS to minimize jitter for the IP Precedence 3 ICCS traffic.

Design network to provide sufficient prioritized bandwidth for all ICCS traffic, especially the priority ICCS traffic.

The general rule of thumb for bandwidth is to over-provision and undersubscribe.

QoS-enabled bandwidth must be engineered into the network infrastructure.

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Gateways connect IP communications networks to traditional telephony networks.

There are several types of voice gateways that can be used to meet all kinds of customer needs, from small enterprises to large service provider networks.

Supported Cisco IP telephony deployment models are single-site, multisite with centralized call processing, multisite with distributed call processing, and clustering over the IP WAN.

In the single-site deployment model, the Cisco Unified Communications Manager applications and the DSP resources are at the same physical location; the PSTN handles all external calls.

Summary

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The multisite centralized model has a single call-processing agent, applications and DSP resources are centralized or distributed, and the IP WAN carries voice traffic and call control signaling between sites.

The multisite distributed model has multiple independent sites, each with a call-processing agent, and the IP WAN carries voice traffic but not call control signaling between sites.

Clustering over an IP WAN provides central administration, a unified dial plan, feature extension to all offices, and support for more remote phones during failover, but places strict delay and bandwidth requirements on the WAN.

Summary (Cont.)

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