Guest

Cisco Unified Communications Manager (CallManager)

CallManager 5.x: Ring Back not Received for PSTN Transferred Calls with SIP

Document ID: 99341

Updated: Oct 15, 2007

   Print

Introduction

This document describes how to resolve the absence of a ring back tone when a Session Initiation Protocol (SIP) call is transferred over the Public Switched Telephony Network (PSTN) through a Cisco IOS® gateway to a Skinny Client Control Protocol (SCCP) IP phone.

Prerequisites

Requirements

Cisco recommends that you have knowledge of these topics:

  • Cisco Unified Communication Manager (Cisco CallManager) 5.x

Components Used

The information in this document is based on Cisco Unified Communication Manager 5.x.

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Conventions

Refer to Cisco Technical Tips Conventions for more information on document conventions.

Background Information

For SCCP initiated blind transfers, Cisco CallManager needs to generate tones or a ring back after a call is already connected. In other words, Cisco CallManager provides a media announcement for blind transfers. Blind transfers initiated from an SCCP IP phone allow ring back to the original, connected SIP device user. In order to accomplish ring back, Cisco CallManager uses an annunciator software device that is often located with an Media Transfer Protocol (MTP) device.

Problem

A ring back tone is not heard for a call from PSTN through a SIP trunk to the SCCP IP phone when it transfers to another destination.

Solution

In order to resolve this problem, complete these steps:

  1. Add an annunciator to the Media Resource Group List (MRGL) of the particular SIP trunk through which the call originates.

  2. Reset the MRGL.

An annunciator is used for SIP ring back. The SIP trunk needs to have an MRGL that contains the annunciator, or the annunciator needs to be in the default list.

Cisco CallManager uses SCCP messages in order to establish a Real-time Transport Protocol (RTP) stream connection between the annunciator and the device. The annunciator plays the announcement or tone to support these conditions:

  • Ring back tone—When you transfer a call over the PSTN through a Cisco IOS gateway. The annunciator plays the tone because the gateway cannot play the tone when the call is active.

  • Ring back tone—When you transfer calls over an H.323 intercluster trunk

  • Ring back tone—When you transfer calls to the SIP client from a SCCP phone

  • Announcement—Devices configured for Cisco Multilevel Precedence Preemption

  • Barge tone—Before a participant joins an ad hoc conference

Refer to Annunciator for more more information about annunciators.

Related Information

Updated: Oct 15, 2007
Document ID: 99341