Q. What is Cisco® Unified Survivable Remote Site Telephony (SRST)?
A. In a centralized Cisco Unified Communications Manager environment, when IP phones lose connectivity to Cisco Unified Communications Manager because the WAN is down or Cisco Unified Communication Manager is unreachable, IP phones in remote branch offices lose call-processing capabilities. The SRST feature provides basic IP telephony backup services so that IP phones can fall back to the router in a local branch office when losing the connectivity to the Cisco Unified Communications Manager. The SRST feature takes advantage of existing Cisco IOS® Software features to provide basic telephony services such as off-net calls to 911, calls within a branch office, or calls between branch offices through the public switched telephone network (PSTN). The application is ideal for enterprise organizations looking to cost-effectively deploy IP telephony in their branch office location.
Q. What is the latest version of Cisco Unified SRST? What is the latest reliable SRST release?
A. For latest features, use Cisco Unified SRST 4.1 (Cisco IOS Software Release 12.4(15)T).
Cisco tests all software extensively to ensure highest levels of reliable operations. As an extra precaution for customers, Cisco generally recommends a version that also has been well-proven in the field. Version 3.3 (Cisco IOS Software Release 12.4(3)T) is the current recommended release for Cisco Unified SRST unless you need newer features.
Q. Where can I get the SRST files and SRST and Cisco IOS Software versions and supported features?
A. The SRST functionality is part of the Cisco IOS Software itself. Multiple Cisco IOS Software packages that support SRST are available. Go to the Cisco IOS Software feature navigator to choose the right Cisco IOS Software image for your router and the functionality you require. The Cisco IOS Software feature navigator is available at: http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp.
Cisco Unified SRST routers do not need phone software files because all the phones load their software directly from the Cisco Unified Communications Manager.
You need extra files on your SRST router only if you want to use the Music on Hold (MOH) file that Cisco provides and the H.450 call transfer application. These files are available (look for srst-3.3.zip) at: http://www.cisco.com/cgi-bin/tablebuild.pl/ip-key.
Q. Which Cisco IOS Software feature set is required to run SRST?
A. SRST requires a minimum of a Cisco IOS IP VOICE image on the Cisco 2600XM, 3700, and Cisco 2800/3800 Integrated Services Routers, and an IP/ADSL VOX PLUS image on the Cisco 1751-V and 1760 Modular Access Routers. If you are using the AIM-ATM-VOICE-30 image on the Cisco 2600XM or Cisco 3600 and 3700 Series, you must also have the SP SERVICES image. In addition, you must purchase an SRST feature license.
Q. What new features does Cisco Unified SRST 4.1 support?
A. With Release 4.1 the following are added to the SRST feature set:
• Support for Enhanced 911 (E-911) services
• Cisco Unified IP Phone 7921G
• SIP line-side enhancements including
– Support for Cisco Unified IP Phone 7971G-GE, 7970G, 7941G, 7961G, 7911G, and 7906G models
– Dial-plan pattern and Key Press Markup Language (KPML) for faster dialing for SIP phones
– Music on Hold for SIP phones
– SIP caller ID update
– Status line update
– SRST status prompt with customizable message
Q. What is difference between SRST and Cisco Unified Communications Manager Express (CME) in SRST fallback mode?
A. You can choose either Cisco Unified SRST or Cisco Unified CME in SRST fallback mode to provide survivability at remote sites when the WAN link between the central site and the remote site fails. Table 1 compares the two.
Table 1. Comparison of Cisco Unified SRST and Cisco Unified CME in SRST Fallback Mode
Q. Where can I find information about router platforms, the maximum number of phones or virtual ports, and recommended memory requirements for SRST?
A. In addition to the information in Table 2, please also refer to the SRST product documentation and specification list posted at: http://cco/en/US/products/sw/voicesw/ps2169/tsd_products_support_series_home.html.
Table 2. Supported Platforms, Maximum Phones and Directory Numbers, and Memory Requirements
Note:
1. The Cisco 7200 was supported up to Cisco Unified SRST 2.1 (Cisco IOS Software Release 12.3(4)T).
2. The Cisco Catalyst 6500 CMM supports Cisco Unified SRST 3.2 in Cisco IOS Software Release 12.3(8)XY and Cisco Unified SRST 2.1 with Cisco IOS Software Release 12.2(13)ZC.
3. Memory recommendations and maximum numbers of IP phones are for common Cisco Unified SRST configurations only. Systems with large numbers of phones and complex configurations may not work on all platforms and may require additional memory or a higher performance platform.
Q. Do I need to buy a license in order to use Cisco Unified SRST?
A. Yes, you need to buy a separate feature license to run SRST in a production network. You can either individually buy the SRST feature license and a supported router to run the SRST feature or buy the integrated services router SRST bundles that come with the SRST feature license included.
Table 3 gives the feature license part number you should order based on the number of IP phones you need. Note that the SRST license can be converted to a Cisco Unified CME license with the same number of phones supported for investment protection.
Table 3. Part Numbers for Ordering
Q. Is there any way to save money when ordering routers and the SRST license together?
A. Yes, ordering a Cisco SRST router bundle gives you the base components and a cost savings.
Table 4 summarizes currently shipping SRST bundles.
Table 4. SRST Bundles
If you want security along with SRST functions, choose one of the bundles listed in Table 5.
Table 5. SRST Bundles with Security
Note: These bundles are available as of August 2007, but availability can change over time. Visit http://www.cisco.com/go/isr for information about the latest available bundles.
Q. What version of Cisco Unified Communications Manager does Cisco Unified SRST support?
A. All versions of Cisco Unified SRST work with all versions of Cisco Unified Communications Manager (3.0, 3.1, 3.2, 3.3, 4.0, 4.1, 5.0, 5.1, and 6.0). It is not the Cisco Unified Communications Manager version that affects the support, but the phone load or firmware version (associated with the Cisco Unified Communications Manager release).
Q. Which IP phones or phone loads are supported and tested with Cisco Unified SRST 4.1?
A. Cisco Unified SRST supports all versions of Cisco Unified Communications Manager phone loads. Table 6 lists all the Cisco IP phone models supported.
Table 6. Cisco Unified IP Phone Compatibility for Cisco Unified SRST Software Versions Through Cisco Unified SRST 4.1
For the list of phone loads for Cisco Unified SRST 4.1, refer to Cisco Unified SRST 4.1 Supported Firmware, Platforms, Memory, and Voice Products at http://cco/en/US/products/sw/voicesw/ps2169/prod_installation_guide09186a00808770c4.html.
Cisco Unified SRST 4.1 Features
Q. Can you explain the E-911 feature support in Cisco Unified SRST?
A. With Enhanced 911, the location of a caller is identified by the emergency workers at the Public Safety Answering Point (PSAP) using a database called the Automatic Location Identifier (ALI) database. Businesses generally have a few special numbers called Emergency Line Identification Numbers (ELINs) registered with the ALI database. The total number of registered numbers is determined by local laws, depending upon the geographic area of the business.
With the E-911 for SRST feature, the calling number sent in outgoing emergency calls is replaced by an ELIN so that emergency workers can identify the caller's location. The E-911 feature also allows emergency operators to call back to get connected to the last caller who called the emergency services.
Q. How much does E-911 for SRST feature support cost?
A. There is no charge for E-911 for SRST feature support on the Cisco Unified SRST router, but the local telco could charge for the PSTN trunks to connect to the E-911 network.
To deploy E-911 for SRST feature support, you only need to buy the right Cisco IOS Software image and SRST feature licenses for the number of phones you have along with the right modules for the PSTN trunk for E-911 connectivity.
Q. What PSTN trunks are needed for E-911 for SRST support?
A. E-911 for SRST is supported for Centralized Automated Message Accounting (CAMA) and ISDN Primary Rate Interface (PRI) trunks.
Q. With the support for the E-911 feature in SRST, do I still need Cisco Emergency Responder?
A. Yes. E-911 for SRST works only in the fallback mode. During normal operation, when the WAN link is up, you need to use Cisco Emergency Responder, which works with Cisco Unified Communications Manager.
Q. With the E-911 for SRST feature, can I support all the Cisco Emergency Responder features in the fallback mode?
A. Both Cisco Emergency Responder and the E-911 for SRST feature support location tracking of a phone based on the IP address subnet that is assigned to each phone.
The Cisco Emergency Responder using the Cisco Discovery Protocol also provides automatic location tracking for phones based n the switch port that the phone is plugged into. The E-911 for SRST feature does not support per-phone emergency response location (ERL) assignment to an individual Skinny Client Control Protocol (SCCP) or Session Initiation Protocol (SIP) phone.
Note: Per-phone ERL assignment for SCCP phones is supported in the Cisco Unified CME in SRST fallback mode (for details refer to the Cisco Unified CME 4.1 system administrator guide).
Q. What types of phones and fallback modes are supported with the E-911 for SRST feature?
A. E-911 is supported for SCCP, SIP, and analog phones. It is supported in the SIP, MGCP and H.323 fallback modes.
Q. What is dial-plan pattern and Key Press Markup Language (KPML) for SIP phones?
A. Dial-plan pattern and KPML support is introduced in SRST 4.1 to speed up the dialing with SIP phones. Previously, SIP phones in a Cisco Unified SRST system required users to press the DIAL soft key or number(#) key, or wait for the interdigit-timeout to trigger call processing, which slowed down the dialing out from SIP phones.
KPML uses SIP SUBSCRIBE and NOTIFY methods to report user input digit by digit. Each digit dialed by the phone user generates its own signaling message to Cisco Unified SRST, which performs pattern recognition by matching a destination pattern to a dial peer as it collects the dialed digits.
A dial plan is a set of dial patterns that SIP phones use to determine when digit collection is complete after a user goes off-hook and dials a destination number. Dial plans enable SIP phones to perform local digit collection on the phone itself and recognize dial patterns as user input is collected. After a pattern is recognized, the SIP phone sends an INVITE message to Cisco Unified SRST to initiate the call to the number matching the user's input.