Unified Communications:Infrastructure:Analog Connectivity

From WWJCDOWiki

Contents 1 Description of Solution 2 Technical Requirements of Solution 3 External References

Description of Solution

This solution is for the need to utilize analog devices such as fax and credit card processing machines, modems, or any device that will attempt a data connection over an analog signal in a Voice Over IP (VoIP) environment. Since there is multiple signal conversions going on (analog to IP then back to analog) this configuration is an end to end (per hop) configuration that must match on every relevant device in the UC network. If this configuration is followed end to end and issues exist 90% of the time it is due to a mismatch in configuration.

There are multiple methods of fax and modem protocols in a Cisco UC environment.

• Modem Passthrough
• Cisco Modem Relay
• Fax Pass-Through
• Cisco Fax Relay
• T.38 Fax Relay
• T.37 Store-and-Forward Fax

Technical Requirements of Solution

This solution provides the following due to simplicity and ease of support and troubleshooting:

• Global Configuration (not at the dial peer level)
• Modem Passthrough utilizing Named Signaling Events (NSE) and the G711ulaw codec
• Fax Passthrough utilizing the H.323 or SIP protocol stacks and the G711ulaw codec
• Engaging DSPs for POTS to POTS calls vs. dynamic allocation
• Disabling Fax Relay for POTS to POTS calls (Fax Relay is on by default for POTS to POTS calls)

NOTE: After reviewing the configuration guides I have some belief that there is possibly redundant or conflicting configuration in the solution outlined below. At this time I am publishing as is due to it works but will research complete relevance.

For SCCP Gateways the following configuration needs to be completed:

voice service voip
 fax protocol none
 modem passthrough nse codec g711ulaw

For MGCP Gateways the following configuration needs to be completed on the gateway:

mgcp modem passthrough voip mode nse
no ccm-manager fax protocol Cisco

Note: If the MGCP Gateway is configured to download its XML configuration from Cisco Unified Communications Manager do not forget to configure these settings within the MGCP Gateway configuration under Device - Gateway.

For H323 Gateways the following configuration needs to be completed on the gateway:

voice service voip
 modem passthrough nse codec g711ulaw

For POTS to POTS Gateways the following configuration needs to be completed on the gateway:

voice-card 0
 no local-bypass
!
voice service pots
 fax rate disable

Common Issues:

1. Reports of 'dirty' faxes or incomplete faxes occurring:

Check to ensure you have clocking set up correctly for your PRIs. This is the number one common issue with faxing. The following two commands are examples of setting up clocking assuming your PSTN interface is WIC slot 0 port 1 (0/0/1). Remember clocking is required for voice interfaces.

network-clock-participate wic 0
network-clock-select 1 T1 0/0/1

External References

Cisco IOS Fax, Modem, and Text Support over IP Configuration Guide

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