This Release Notes document describes the features of Cisco Unified Survivable Remote Site Telephony, Release 15.0. The Cisco Unified Survivable Remote Site Telephony, Release 15.0 is included in Cisco IOS XE 17.18.1a and later releases.

To ensure that you have the latest version of this Release Notes, go to https://www.cisco.com/c/en/us/products/unified-communications/unified-survivable-remote-site-telephony/index.html. Choose Release and General Information > Release Notes, and locate the latest release notes pertaining to your release.

Hardware Platforms Supported

Unified SRST supports the following Cisco 4000 Series Integrated Services Router platforms:

• Cisco 4321 Integrated Services Router

• Cisco 4331 Integrated Services Router

• Cisco 4351 Integrated Services Router

• Cisco 4431 Integrated Services Router

• Cisco 4451 Integrated Services Router

• Cisco 4461 Integrated Services Router

Unified SRST supports the following Cisco 8300 Catalyst Edge Series platforms:

• C8300-1N1S-6T

• C8300-1N1S-4T2X

• C8300-2N2S-6T

• C8300-2N2S-4T2X

Unified SRST supports the following Cisco 8200 Catalyst Edge Series platform:

• C8200-1N-4T

• C8200L-1N-4T

Unified SRST also supports the following Router platforms:

• Cisco 1100 Series Integrated Services Router (ISR1100 running IOS XE)

• Catalyst 8000V

Software Compatibility

For more information on supported images and minimum software version requirement for Unified SRST features, see Cisco Unified SCCP and SIP SRST System Administrator Guide.

To determine the correct Cisco IOS release to support a specific Unified SRST version, see the Cisco Unified CME, Unified SRST, and Cisco IOS Software Version Compatibility Matrix.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. You do not need an account on Cisco.com for access.

Determine the Software Version

To determine the release of Cisco IOS software currently running on your Cisco router, log in to the router and enter the show version command. The following sample output from the show version command indicates the Cisco IOS release on the first output line:

Device# show version
Cisco IOS XE Software, Version Cisco IOS XE 17.18.1a 
Cisco IOS Software, ISR Software (X86_64_LINUX_IOSD-UNIVERSALK9-M), 
Copyright (c) 1986-2025 by Cisco Systems, Inc.
Compiled Thu 31-July-25 17:49

Upgrade to a New Software Release

To determine which Cisco IOS software release supports the recommended Unified SRST version, see Unified SRST and Cisco IOS Software Compatibility Matrix. To install the new software release, see the “Install Cisco IOS Software” section of the Cisco Unified Communications Manager Express Administrator Guide.

Feature Set Tables

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn.

New Features in Unified SRST, Release 15.0 (Cisco IOS XE 17.18.1a)

• From Unified SRST Release 15.0, smart licensing reports flex subscription entitlement tag. To maintain the continued support and entitlements to the future application versions, purchase a Collaboration Flex subscription. For more information, see Cisco Unified SCCP and SIP SRST System Administrator Guide (All Versions).

• From Unified SRST Release 15.0, support is added for Cisco Desk Phone 9861 (DP-9861) and Cisco Desk Phone 9871 (DP-9871) devices. For more information, see Compatibility Information for Unified SRST/E-SRST 15.0 Supported Firmware, Platforms, Memory, and Voice Products.

Open Caveats—Unified SRST, Release 15.0

There are no open or unresolved caveats for Unified SRST, 15.0 Release.

Software Documents

Administrator Guides

• Cisco Unified Communications Manager Express System Administrator Guide

• Cisco Unified SCCP and SIP SRST System Administrator Guide (All Versions)

• Phone Feature Support Guide for Unified CME, Unified SRST, Unified E-SRST, and Unified Secure SRST

Command References

• Cisco Unified Communications Manager Express Command Reference

• Cisco Unified SRST and Cisco Unified SIP SRST Command Reference (All Versions)

Release Notes

• Release Notes for Cisco Unified Communications Manager Express

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This document is to be used in conjunction with the documents listed in the “Related Documentation” section.

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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.