First Published: December 20, 2025

Last Updated: April 25, 2026

Release Notes for Cisco Unified Survivable Remote Site Telephony

Introduction

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 the following releases:

  • Cisco IOS XE 17.18.1a

  • Cisco IOS XE 17.18.2

  • Cisco IOS XE 26.1.1

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.

System Requirements

Hardware Platforms Supported

Unified SRST supports the following Cisco 8300 Series Secure Router platform:

  • C8375-E-G2 Secure Router with vDSP enabled

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 26.1.1
Cisco IOS Software [IOSXE], Virtual XE Software (X86_64_LINUX_IOSD-UNIVERSALK9-M),
Copyright (c) 1986-2026 by Cisco Systems, Inc.
Compiled Mon 02-Mar-26 20:04

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 and Changed Information

New Features in Unified SRST, Release 15.0 (Cisco IOS XE 26.1.1)

  • Insecure TLS versions (v1.0, v 1.1) and ciphers are not supported in default configurations. However, these insecure configurations are supported in "system mode insecure" mode. Support for the following non-compliant ciphers has been discontinued:

    • DHE_RSA_WITH_AES_256_CBC_SHA

    • CHACHA20_POLY1305_SHA256

    See Configure Secure SRST for SCCP and SIP.

New Features in Unified SRST, Release 15.0 (Cisco IOS XE 17.18.2)

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

Caveats

Bug Search Tool

The Bug Search Tool contains information about open and resolved issues for the release, including descriptions of the problems and available workarounds. The identifiers listed in this release notes takes you directly to a description of each issue.

To look for information about a specific issue:

  1. Using a web browser, go to the Bug Search Tool.

  2. Sign in with a cisco.com username and password.

  3. Enter the bug identifier in the Search field and click Search.

To look for information when you do not know the identifier:

  1. Type the product name in the Search field and click Search.

  2. From the list of bugs that appear, use the Filter drop-down list to filter on Keyword, Modified Date, Severity, Status, or Bug Type.

Use Advanced Search on the Bug Search Tool home page for a specific software version. The help pages have further information on using the Bug Search Tool.

Open and Resolved Issues

Follow the links to read the most recent information about open and resolved issues in SRST release.

Service and Support

The Cisco Support and Documentation website provide online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies.

Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

To access the website, go to: http://www.cisco.com/cisco/web/support/index.html.